Coastal erosion Hoi An

Transcription

1 Coastal erosion Hoi An Multidisciplinary project Delft University of Technology Authors: Joep Fila Maurits Kampen Kees Knulst Richard Marijnissen Roel van Noort January 2016

2 Multidisciplinaryproject CoastalerosionalongHoiAnbeach Authors StudyTrack Studentno. JoepFila HydraulicStructures&FloodRisk MauritsKampen WaterManagement&Engineering MScannotationIntegralDesign&Management(IDM) KeesKnulst HydraulicStructures&FloodRisk RichardMarijnissen CoastalEngineering RoelvanNoort River,Ports,Waterways&DredgingWorks SupervisorsTUDelft MarcelStive ChairmanoftheDepartmentHydraulicEngineering HenkJanVerhagen AssociateProfessorinHydraulicEngineering SupervisorsThuyLoiUniversity(WRU) HaiTrungLe TranThanhTung NguyenTrungViet LecturerWRU ViceDeanMarineandCoastalEngineeringinHanoi RectorCentralRegionCollegeinHoiAn FacultyofCivilEngineeringandGeosciences Building23 Stevinweg1/PObox CNDelft/2600GADelft i CoastalerosionHoiAn

3 ii CoastalerosionHoiAn Table of Contents TableofContents...ii Acknowledgements...iv Summary...v 1. Introduction Problemdefinition Problemdescription Projectgoal Systemboundaries HoiAncoastalsystem Evolutionofthecoast Riverinfluence Shorelinemovements Stakeholderanalysis Problemsandgoals Powerinterestdiagram Reasonsforshorelineretreat Humanimpacts Naturalcauses Naturalvariation Hypotheses Solutions Strategytodealwithcoastalerosion Solutionrequirements Resultsofanalysisofpossiblemeasures Threealternatives Nourishmentstrategy Quicksolutions Beachpolicy Conclusionandrecommendations Conclusion Recommendations...29 References...31 Listoffigures...37 A. Area...40 A.1VietnamandHoiAn...40 A.2Studyarea...42 A.3ChamIslandprotectedarea...43

4 A.4CoastalerosionproblemsinVietnam...44 A.5Legalaspects...45 B. Stakeholders...47 B.1Interviews...47 B.2Interviewsconclusion...63 B.3Stakeholderproblemstatementsandgoaltrees...64 B.4Estimationofhotelvalues...73 C. Coastalsystem...74 C.1BruunRule...74 C.2CERCformula...75 C.3Bathymetry...76 C.4Waveclimate...77 C.5Tide...78 C.6SandBalance...79 C.7Erosionrateestimates...80 D. Estimatesofriversedimentsupply...81 E. Researchintoreasonsforshorelineretreat...86 E.1Humanimpacts...86 E.2Naturalcauses...92 E.3Naturalvariation...95 F. Currentlyappliedsolutions F.1Appliedsolutions F.2Failureofseawallsandrevetments G. Erosionpreventionpossibilities G.1Systematiccriteriaandoptionfinding G.2Hardversussoftmeasures G.3Possiblemeasures G.4Multicriteriaanalysis H. Mainalternatives+nourishmentstrategy H.1Largesandnourishment H.2Mediumnourishment+groynes H.3Smallnourishment+revetment H.4Nourishmentstrategy H.5Beachpolicy I. Measurements I.1Measurementstick I.2ThuBonriverobservations I.3Sedimentsamplesanalysis iii CoastalerosionHoiAn

5 Acknowledgements Conductingthisprojectissomethingwecouldnothavedoneonourown. Firstofall,wewouldliketothankoursupervisorsfromtheTUDelft:HenkJanVerhagenandMarcel Stive. Several meetings showed us their involvement in the subject and contributed to steer the projectintherightdirection.also,beingavailableduringourstayinvietnamhashelpedusoutof someurgentmatters. NextwewouldliketoshowourgratitudetooursupervisorsinVietnam.ToHaiTrungLeandTran Thanh Tung for inviting us at the Thuy Loi University and for their contribution in the project by reachingdataandideas.andalsotonguyentrungviet,rectorofthecentralregioncollegeinhoi An,forshowingusaroundandarrangingallthatwecouldnothavedoneourselves.Weadmirehis commitmenttomakethebestoutofcuadaibeach.furthermore,wewouldliketothankallthose workingorstudyingatthethuyloiuniversitywhohasgivenusdataorhelpedusinanotherwayin conductingourresearch. AnotherthankstoKoninklijkeBoskalisWestminsterN.V.forthinkingalongwithourprojectandtheir financialcontributiontotheproject. Lastbutnotleast,wewouldliketothankallthepeoplethatmadeusfeelathomeinVietnam.Those thatinvitedustotheirhomestotalkaboutvietnamandthenetherlands.aspecialthankstocao DucHaiforwelcomingusonourfirstdayinanewcountry,showingusaroundandtranslatingour Vietnamesequestionnaires. Hanoi,January2016 JoepFila MauritsKampen KeesKnulst RichardMarijnissen RoelvanNoort iv CoastalerosionHoiAn

6 Summary SevereerosionofCuaDaiBeach,withitsmanyresorts,hotelsandrestaurants,hasbecomea hugeissueforhoian.theshorelinevariationbecameproblematicsincetheconstructionofthefirst buildingsalongthebeachandcurrentlyitiscostlytoadapttotheretreatingcoastline.toovercome the current problems, the goal of this project is to present three economic and technical durable optionswhicharesupportedbythecommunityandwillrecreatecuadaibeach. ThecoastalsystemaroundCuaDaiBeachextendsfromTamKyuntilDanangandincludes Cham Island. Cham increases the complexity by blocking certain wave directions and influencing sedimentmovements.satelliteshaverecordedlargechangesinthecoastlineinthepastdecades, fromanonshoremigratingsandbanktotheformationofaspitanditserosion.twodominantwave climatesareidentifiedcausinganetnorthwarddirectedsedimenttransport. There are several contributors to the recent erosion rate: sea level rise (5%), increasing storms(525%),sandmining (4080%),damconstruction (5%)andnaturalvariation(1050%). The following were excluded as significant reasons for the current erosion: changes in watershed, deforestation,landsubsidenceduetogroundwaterextraction,tectonicsubsidence,changesinnear shoreunderwaterconditionsandsedimentblockagebyhydropowerdams,althoughthelattercould beofinfluenceinthefuture.toexplainthecurrenterosionratethreehypothesesarepresented. Thefirsthypothesisfocusesontheincreasingamountofstormsincombinationwithareducedriver supply,thesecondhypothesishasthedecreaseofthesedimentsupplyfromtheriverassolemain cause and the third hypothesis considers natural variation in combination with a reduced river supply.allhypothesesaccountforerosionduetosealevelrise.thehypothesesdifferinpredictions ofthefutureerosion.withthefirsthypothesisitisuncertainifthecurrenterosionwillincreaseor decrease,withthesecondthereiscontinuederosionatthecurrentratewhilethethirdislikelyto seeacontinuederosionatareducedrate. To halt structural erosion without shifting the drawbacks only combinations with sand nourishments followed from the multi criteria analysis as feasible options. Therefore three nourishmentalternativesaresuggestedtorestorecuadaibeach,wherebyahighattractivenessofa certainalternativeisconsideredhighlyimportant.thecostsofthesolutionsarebetweenyearlycosts of 1.3and 2.1millionwhenaveragedoveratwentyyearperiod.Thefirstalternative,alargebeach nourishmentwithoutextrastructures,hastheadvantageofcombiningwellwithcurrentmeasures andhavinganattractivewidebeach.thedisadvantagesarethatitneedsalargeinitialinvestment andthesolutionisfeelslesssafe.assecondalternativeamediumsandnourishmentwithgroynesas sedimentretainingstructuresissuggested.theadvantagesofthisalternativearethatthebeachin frontoftheresortsiseasilymaintainedandasmallerbeachwidthisneededbetweenthegroynesto dealwiththestructuralerosion.thedisadvantagesarethatconstructingmultiplestonegroynesin combination with a sand nourishment is costly. A small sand nourishment combined with a revetmentissuggestedasthirdalternative.ithastheadvantageofgivingagoodprotectionagainst incidentalstormerosion.inaddition,itcreatesasaferfeelingforthelocalpeopleandalsoapartof such a revetment is already present. However, some disadvantages are that the beach might not alwaysbepresentafterastormandthatthemovementoftouristsandotherpeopleontothebeach islessfluent. To execute any of the current solutions the most financially attractive source location for sandwithpropertiescomparabletothecurrentbeachsandhastobefound.possiblelocationsarein frontofthemouthandfurtheroffshore.furthermore,moredataaboutthelocalcurrentsandwaves ispreferredformakingareliablemodelthatpredictstheeffectsofsandnourishments.untilthat moment,smallnourishmentsshouldbeusedasmaintenancesolutionstopreventfurtherproblems. All options and maintenance solutions should be combined with a proper beach management to maketheimplementationoffuturesolutionspossibleandtopreventfutureexpenseforprotecting buildingsthatarebuilttoclosetotheshore. v CoastalerosionHoiAn

7 1.Introduction Almost all coasts in the world are retreating. Causes are amongst others the rising sea level and increasing storms. However, the erosion rates at Hoi An, Vietnam over the last few years are alarmingandarenotlikelytobeexplainedbytheabovephenomenaalone.hoianisacoastalcity lyingatthemouthofthethubonriverandhasaround120,000inhabitants.inthelasttwentyyears large resorts were built along the famous Cua Dai Beach to provide luxury accommodations for tourists.andnowthisbeachexperiencessevereerosion. Althougherosionitselfdoesnothavetobeproblematic,itbecomessowhenmoneyisinvestedclose totheseaanditisdifficulttoadapttotheretreatingshoreline.furthermore,thebeachhaschanged tosuchanextentthattourismratesaredecreasing.beingoneofthemostimportantsectorsforhoi An,theerosionhasfarreachingconsequences.Inordertodealwiththisissue,thetotalsystemhas to be understood. What is causing the erosion? What problems are created by it? What is the preferredfuturesituation?thisstudyisconductedtoanswerthesequestionsandtopresentoptions todealwiththisurgentmatter. Thecoastalsystemanditsdisturbancesthatarecausingtheerosionneedtobeanalysedtofindthe problem.severalcausesexistforalandwardmovingshoreline,whicharealsoapplicabletohoian. In this study the possible reasons are investigated and quantified in order of magnitudes on their contributiontotheerosionrate.thisishoweveronesideofthestory.ifactionsneedstobetaken,it isimportanttoknowwhattheactionsarerequiredtoachieve.interviewswithresortmanagersand questionnaires for the local community will provide a good understanding of the effects of the shorelineretreatonhoian.thisinterviewresultsinsocalledsocialproblems.combinedwiththe technical problems, these translates into requirements for solutions. Three alternatives will be reachedthatfittheboundariesandwishesoftheregionandareabletobringbackhoianonthe mapaspopularholidaydestination. Themainreportconsistsofanconciseoverviewofthetotalworkthatisdoneintheeightweeksof thisstudy.itstartswithamoreelaborateproblemdefinitionthanisgivenhereandthegoalthatis set for this project in Chapter 2. After that, the social problems, dilemmas and influences of the different stakeholders engaged in the current erosion issue are presented in Chapter 3. The next chapter,chapter4,describesthecoastalsystemofhoian.amongstothers,itshowshowthecoast has evolved over the past 40 years and how the current shape can be explained by coastal engineeringtheory.chapter5followsbyshowingthereasonsforshorelineretreat.althoughdatais limited,itispossibletoestimatetheinfluenceofdifferentmechanismsontherateoferosion.here arealsothreehypothesesgiventhatcanexplainthecurrentshorelinemovements.futuremeasures havetocounterthesehypothesesandfittherequirementsthatarepresentedinchapter6.chapter 6alsoelaboratesonthethreealternativesandgivesadvicefortheimplementationofthesolutionin togetherwithacoastalmanagementstrategytopreventsimilarproblemsinthefuture.themain reportendswithaconclusionandrecommendationsforfurtherresearch. 1 CoastalerosionHoiAn

8 2.Problem definition Thischapterdescribeswhythecurrentsituationisproblematicandwhatgoalissetfortheproject.It includes the future perspectives of the Hoi An area and how these affect the problem definition. Furthermore, the research is focussed between certain boundaries, which are also given in this chapter. 2.1 Problem description Figure2.1ErosionproblemsinHoiAn OverthelastdecadeCuaDaiBeachatHoiAnhasbeenerodingtoanextentthatCuaDaiBeachisno longerpresentandnowshoreadjacentbuildingsarethreatened.thesouthernendofcuadaibeach has changed substantially and the northern stretch is eroding at an average of 12 m/year (see Chapter3fortheexactevolutionofthecoast).Theproblemoferosionistwofaced.Onesideisthe threatening of the buildings. Figure 2.2 shows Cua Dai Beach and the large number of hotels and resortsalongit.theamountofinvestmentsalongthebeachandtheirproximitytotheseamakesthe erosion a large problem. The other side is the loss of an attractive landmark for tourism which reducestheincomeofthecity. Figure2.2HotelsandresortsatCuaDaiBeach(Booking.com,2015) HoiAnlivesontourism.With64%ofthetotalmunicipalrevenueitistheirmainsourceofincome andwithouttourismthereisnotmuchleftofthecityinitscurrentform(hoiantourism.com,2013). In2013tourismintheQuangNamprovinceaccountedfor3.6trillionVNDor 170million,whichwas equal to 10% of the gross provincial product (Vietnam News, 2013). In 2007 Hoi An itself earned revenuefromtourismworthvnd950millionor 40million(UNESCO,2008).Mosttourisminthe provinceisbasedin,ororiginatesfrom,hoian.thenewsoftheerodingcoastisspreadingaround theworldandtheamountoftouriststhatisvisitinghoianisalreadydecreasing.thisaffectsthe resorts,butalsothelocalinhabitantswhosebusinesshasshiftedtotourismaswell.thehighamount oftailors,restaurantsandhomestayscannotsurvivewithadecliningrateoftourists(vietnamnews, 2013). 2 CoastalerosionHoiAn

9 InthefuturetheproblemcanalsooccurinotherHoiAnareas;in2012abridgeisconstructedfrom HoiAntowardsthelandsouthoftheriver.Withthebeachonthesouthernsideoftherivermouth stillpresent,itcanbeexpectedthatresortsandtourismwillsettletothispartoftheareaaswell. Althoughtherearenoproblemswiththisprospectyet,similarmistakesasforCuaDaiBeachmight bemade:toomuchinvestmentstooclosetothesea.anotherperspectivehoianhastodealwithin thefutureisthechangingclimate.inthenextdecadesthesealevelwillriseduetoclimatechange, according to ASEC Consultants sea level rise nearby Hoi An will be 5 mm/year (ASEC Consultants, 2014).IntheirpredictionaquarteroftheareaofHoiAnwillberegularlyfloodedbytheyear2020. Furthermore, typhoons are shifting south and the number arriving at the coast of Vietnam is increasing (DiGregorio, 2015). The increasing amount of typhoons or tropical storms is leading to moreextremewaveconditionsthatcanleadtomoreerosion. 2.2 Project goal Thefollowingprojectgoalisdefined: PresentingatleastthreeeconomicandtechnicaldurableoptionswhicharesupportedbytheHoiAn communitytorecreatethefamouscuadaibeach. TherecreationofCuaDaiBeachisnecessarytokeeptheamountoftouristshighandtomaintainthe economyofthehoiancommunityandresorts.importantpartsofthisgoalarethattheoptionsthat willbeprovidedintheendarebotheconomicandtechnicaldurable.thisimpliesthatonlyrealistic alternatives will be designed which have the possibility of being implemented in Hoi An. Furthermore, the options should be carried by the whole community: local beach users, resorts, fishermen, et cetera. This will set certain boundaries, but will eventually provide better options. Furthermore,avoidanceofshiftingtheproblemstoadjacentareasisimportant.Theproblemisnot solvedwhenitisshiftedtoanotherplace. Toachievetheprojectgoalthefollowingquestionshavetobeansweredduringtheproject: WhatdoesthecoastalsysteminHoiAnlooklike? Whatarethereasonsforshorelineretreat? Whatproblemsistheerosioncausing? Whatarethestakeholdersneedsandwishesforthefuture? Whataretherequirementsforsolutions? Howtomaketheoptionsdurable? 2.3 System boundaries Theboundariesofthesysteminwhichthestudyisconductedareheredefinedintwostages.First followingthesizeofaprovinceandthenfollowingthesizelevelofatown Provinciallevel Atthesizeofaprovince,thecoastalstretchnorthofHoiAnhasanaturalboundaryatthepeninsula neardanang.inthesouth,thesystemissimilarlybounded.theboundingoftheinfluenceisbased on the expectancy that those particular points will act as a barrier for sediment. Seawards, the sphereofinfluenceincludesthechamislandfortworeasons.first,theislandhasinfluenceonthe wave directions and wave refraction at Hoi An. Second, tourism to the island is likely to rise and declinewiththetourismathoian.anotherimportantfactoristhethubonriver,whichflowsinto theareaofinterestandcarriessediment.therivercoursehaschangedinhistory,butcurrentlythe maincatchmentareaforrainfallandsedimentofthethubonriverisdepictedontheleftsideof Figure CoastalerosionHoiAn

10 Sincefundsforprojectsareallocatedbytheprovinces,itisquiteimportantthatashy12kilometres north of Hoi An lies the bordering town of Danang, which is a municipality with the status of a province.aprovincemostlysolvesitsownproblemsinvietnamandthusprojectswillbecheckedto bebeneficialwithinitsownborders.anyfixforhoianordanangwouldbetakenonindependently and a local fix which shifts the problem outside its own area is sometimes accepted. This current projectdoesnotfollowtheprovincialboundarystrictly.iftherewouldbeexpectedeffectsonthe Danangcoastalstretch,thosewillbequalitativelycheckedaswell. Figure2.3Systemboundariesatprovinciallevel (left)andcitylevel(right) TosummarizetheleftsideofFigure2.3:inthesphereofinfluenceisthetownofHoiAn,theCham Island, the mouth of the Thu Bon river and the coastal stretch to the points where alongshore sedimenttransportisexpectedtobebounded Citylevel Thisreportfocusesontwosmallerareaswhichtogethercomprisethesystem,seerightsideofFigure 2.3.ThenorthpartofthesystemhasitsinlandboundaryattheinlandriverthatdividestheCuaDai Beach strip from the city. The south part has its boundary 400 meters inward from the 2015 coastline. Seawardsthesystemstretchesonaveragearound3kilometres.Itisboundedbythewaterdepthof 18meters.Thiswaterlevelistheboundary,becausefromhereontheseabottomishorizontalfora significantstretch(seeappendixc.3bathymetrymaphoian).twopartsinthissystemhavebeen chosen, because the north part will be treated differently than the south part.this affects what coastal changes are acceptable and is the result from the fact that less invested money has been investedin thesouthpartofthesystem.thecity itselforsandbarslandwardsofthemouth,fall outside of the system boundaries. At this level of scope, the river will be seen as a supply input parameterforanyestimationsinthesystemarea. 4 CoastalerosionHoiAn

11 3.Hoi An coastal system ThischapterelaboratesonthecoastalsystemaroundHoiAn.Itstartswithadescriptionofhowthe coasthasevolvedsince1975,usinglandsatimagestoshowthemovementsoftheshoreline.after this,theinfluenceofthethubonriveronthecoastalsystemisgiven,togetherwithanestimateof the sediment discharge. Furthermore, some theory about erosion is given. This chapter concludes withasandbalanceoftheareainfrontofthecoast. 3.1 Evolution of the coast TherivermouthofHoiAnhasseenmuchmorphologicalactivityinthepast.Landsatimageswere analysed by Hoang, Tanaka, Viet & Duy (2015) to study this activity. Starting from 1975 several changescanbeobserved.thespitonwhichcuadaibeachissituatedwasrelativelysmallin1975.it begantowidenduetoalargesandbankthatmigratedtotheshoreandmergedwithitbetween 1979and1991(seeFigure3.1A).Between1991and2007thecoastfeaturedtwospits(seeFigure 3.1B).SpitBwastheremainderofthesandbankandcontinuedtomergewiththecoast.Meanwhile ontherightsideoftheriver,thesandbankmigratestotheright.anoutcropformedonthisside between 1995 and From 2003 to now this outcrop has been eroding quite fast while still migratingtotheright(seefigure3.1c).inthesameperioderosioncanbeobservedalongthewhole lengthofthespitleftoftheriver.intheobservedperiodthecumulativechangesare:aspitthathas firstaccretedafter1975andthenerodedbackby2015toaboutthesamesizeasitwasin1975; erosionalongtheleftpartofthespit;arivermigratingright(southward)andachangingshaperight (south)oftheriver. (A) Approachingandmergingsandbank (B) Doublespitformation Figure3.1EvolutionoftheHoiAncoastbasedonLandsatimages(Hoang,Tanaka,Viet,&Duy,2015) 5 CoastalerosionHoiAn

12 (C) Overallerosion (D) Overview Figure3.1EvolutionoftheHoiAncoastbasedonLandsatimages(Hoang,Tanaka,Viet,&Duy,2015) Coastsformthetransitionbetweentheseaandland.Theirappearancecanvarywidelydependingon thecircumstances.howevertheycanbeclassifiedbycomparingtheinfluenceofwaves,tidesand river supply, see Figure 3.3 (Boyd, Dalrymple, & Zaitlin, 1992). This classification helps to link the appearanceofthecoasttothedominantprocesses.forexampleadeltastretchinginalldirections indicates a large river supply and relatively low wave and tidal power. In the case of Hoi An, the wedge shape south of the river is typical of a wavedominated coast (Boyd, Dalrymple, & Zaitlin, 1992),seeFigure3.3.Thesandridgesshowthissectionofthecoasthasbeenprograding,meaning thattheshorelinehasmovedseawards.basedontheappearanceofthecoastthehoianestuarycan beexpectedtohavelargeinfluencefromwavesandriversupplyandtobeaffectedlessbytides. Figure 3.1 shows net erosion in the last 10 years rather than accretion. Clearly the coast is not progradinganylonger.fromthethreecomponentsthatshapethedelta,onemusthavechangedto cause a shift from prograding to transgression, meaning a landward moving shore. It is estimated thattheyearlyerosionis12m/year,leadingtoayearlyerosionofcuadaibeachof240,000m 3.This isbasedonappendixc.7. Figure3.2Coastalfeaturesofthebeachat> HoiAn(EditedmapfromGooglemaps) Figure3.3Coastclassification(Boyd,Dalrymple,& Zaitlin,1992) 6 CoastalerosionHoiAn

13 3.2 River influence TheVuGia ThuBonriversystemisoneofthelargestriver systems in central Vietnam and covers a large part of the Quang Nam Province. Both rivers originate in the high mountainsonthewestsideofvietnamandflowintotheeast Seathrough Dai(HoiAn) andhan (Danang),see Figure3.4. The average annual discharge of Thu Bon River is about 327m 3 /s. However, the flow regime in the river has a large seasonallyfluctuation.theflowduringthefloodseasonis62 69%oftheannualvolume,with2631%occurringinthepeak month November (Long, Tung, & Huy, 2013). These flash floodscarryenormousamountsofsedimentdowntheriver, whichistransportedtotherivermoutharea.thesediment supply from the river basin to the river mouth area is a sediment source for the advancement of the river delta shoreline.todetermineifadecreaseofthesedimentsupplyofthethubonrivertotheshoreline mightinfluencethecoastalerosionofcuadaibeachtheamountofthissedimenttransporttothe river mouth is estimated with three different methods. For the complete calculation with these methods,seeappendixd.allsedimentestimatesaregivenintable3.1below. Table3.1Thethreedifferentsedimentestimates Figure3.4RivernetworkoftheVuGia ThuBonbasins(Long,Tung,&Huy,2013) Estimatebasedon: Catchmentarea Bedslope Sedimentconcentration EstimatedSedimentTransport(m 3 /y) 600, , ,000 Theordersofmagnitudeofthethreedifferentmethodsarecomparableandtheresultsgiverealistic values.however,theresultsdifferquitealotfromeachotherandallhaveitsownremarks.thefirst method, based on the relationship between specific sediment yield and catchment area gives a comparable river in Japan. However, the climate in Japan differs from the climate in Vietnam. In additiontheamountofextremerainfalleventsoccurringatthecatchmentareasofbothriversmight differandtheremightbedifferentwaysoferosionoccurringinthewatershedsoftherivers.these situations probably cause different amounts of particles flushing into the river. For the second method,thebedslopeanddominantdischargeareusedandusuallysuchaformulacanbeusedfor approximations.themethodisusuallyappliedatriversectionswithuniformcrosssectionalongthe wholelengthofthesectionandthesystemisdefinedasaclosedsystemwithoutlateralinflow.the sectionsusedforthismethodarenonuniformandthereprobablyislateralinflowineachsection. Also because there is a lack of discharge data, the same discharge value is used for each section. Withthethirdmethod,thedischargeandsedimentconcentrationforeachmontharedefinedand multiplied with each other. This means the discharge and sediment concentration per month are averagedoverthewholeriverstretch. Inconclusion,nocomparisonbetweenthereliabilityofeachmethodisneeded.Eachmethodcanbe seen as a reliable approximation of the sediment supply with its own remarks. For further calculationsinthisreportthemostextremevalueisconsideredtodeterminehowbigtheinfluence ofthereductionofthesedimentsupplyofthethubonriveris. 7 CoastalerosionHoiAn

14 3.3 Shoreline movements In paragraph 3.1, the evolution of the coast over the recent decades is described. This paragraph zoomsinontheerosionandaccretiontheory.afterthis,itisexplainedwhythecoastlinelooksasit doesnow.furthermore,itshowsthewayofsedimenttransportalongthecoastandthisparagraph finisheswithafindingaboutanincreasedamountofsandoffshore Erosionandaccretiontheory Inthesection3.1Evolutionofthecoast,itwasexplainedthatthetides,wavesandriversupplyare majorinfluencesofthecoast.however,themechanismsbehinditwerenotdiscussed.inthissection the erosion and accretion patterns will be assessed by looking at the wave driven sediment transport. The capacity for wave driven sediment transport can be approximated by the CERC formula,whichisshowedindetailinappendixc.2. Thealongshoresedimenttransportisdependentonbothwaveheightandangleofincidencewith thecoast.transportofsedimentitselfdoesnotcauseerosionoraccretion,butgradientsintransport do.ifmoresedimentistransportedintoasectionofthecoastthanistransportedoutofit,accretion hastakenplaceandthecoastgrowsinoffshoredirection.ifmoresedimentistransportedoutofa sectionofthecoastthanistransportedintoiterosionhasoccurredandthecoastretreats.changes in the coastline occur when the alongshore sediment transport is not constant. This transport changes when waves break at different angles along the shore or when the wave heights are different, assuming there is no difference in sediment characteristics alongshore. If wave heights decreaseinalongshoredirectionaccretionisexpected,whileifwaveheightsincreaseinalongshore direction erosion can be expected. Another consequence of these relations is that an alongshore uniformwaveclimatewithalowangleofincidencewillstrivetocreateastraightcoastsmoothing outanyhumpscreatedbyforexamplerivers CoastlineformationHoiAn TheshapeofthecoastlineofHoiAncanpartiallybeexplainedbylookingatthelongshoresediment transportbythewaves.figure3.5showsschematicallytheinfluenceofnormallyincidentwavesona rivermouth.eventhoughthewaveclimateathoianisnotnormallyincidentthecombinationofthe mildersouthernsummerwavesandthehighnothernwinterwavescanadduptoasimilareffect.as sedimentssettleattherivermouththeycreateanoutcrop.thewavesatthisoutcropwillbreakat anangleandhenceinduceasedimenttransportawayfromtheoutcrop.theresultisawedgeshape. ThisshapecanbeobservedsouthoftherivermouthofHoiAn,seeFigure3.2.Therateatwhichthe deltacangrowdependsonthesedimentsupply.ifthesupplybecomesinsufficient,asmighthave becomethecaseinhoian,thewaveswilltransportsedimentawayfromtherivermouthtothesides andflattenoutthecoastlineandthustherewillbeerosionaroundtherivermouthandaccretionon thesides. Thenorthpartdoesnotformawedgeshapebutfeaturesaspitinstead.Wavesbreakinginfrontof the coast at an angle generate a longshore current that is interupted by the river outflow. This reduces the sediment transport rate and thus accretion occurs at the updrift side. Downdrift the wavesregaintheirstrengthandthetransportrateincreasesleadingtoerosiondowndrift.theresult isaspitslowlymigratinginthedirectionofthelongshorecurrent.thespitathoianhaslikelybeen formedbythesamemechanism.theappearanceofbothaspitandwedgeatthecoastisquiterare andindicatesthatthedominantwaveclimatemightbevaryingspatially.thereasonforthevariation inwaveclimateislikelytobechamisland. 8 CoastalerosionHoiAn

15 Figure3.5Developmentsofadeltaiccoastlinewithnormally incidentwaves(bosboom&stive,2015) Figure3.6Spitformationatarivermouth (Bosboom&Stive,2015) 3.3.3NetsedimenttransportdirectionsaccordingtoProfessorStive Itisknownthatthetransporthasseasonalcomponentsashighwinterwavescomefromthenorth whiletherestoftheyearwavestendtocomefromthesouth(seeappendixc.4).firstcalculations neglectingtheinfluenceofchamislandsuggestasouthwardtransportof20,000m 3 /year,northward transportof340,000m 3 /yearandnetnorthwardtransportintheorderof320,000m 3 /yearwitha gradienttothenorthofapproximately100m 2 /yearalongcuadaibeach(ponsioen,2015). Professor Stive estimated the directions of the sediment transport based on the geographic characteristicsofthehoiandelta.sedimentsuppliedbytheriverisdumpedintheouterdeltaand forms a source for sediment. This river supply, in terms of discharge and suspended sediment, is highlyvariable.mostsedimentissuppliedinthewetperiod(augusttodecember)whenriverrunoff ishigher.fromfigure3.7,bothanetnorthwardsandnetsouthwardsdirectedsedimenttransport canbenoted.intheareanorthoftheriver,acertaindivergencepointisassumedwherethenet sedimenttransportiszero.fromthispoint,thenetsedimenttransportisdirectedtothenorthand tothesouth.themultiplesedimenttransportdirectionssuggestthatchamislandisaffectingthe dominantwaveclimate(forinstancebyshoaling,refractionanddiffractionofwaves)differentlyfor differentsectionsofcuadaibeach.southofthedivergencepoint,thenetsedimenttransportis directedsouthwards.a bypassofsedimentaroundtheouterdeltaisassumedwhereit continues alongthebeachsouthoftheriver.theareaswhereerosionandaccretionhavebeenobservedare markedwithdifferentcolours. Figure3.7 Estimatedsedimenttransportdirections byprofessorstive(stive,2015) 9 CoastalerosionHoiAn

16 3.3.4Seasonalerosionandaccretion The crossshore profile of the beach responds differently during calm periods with normal wave conditions(dryseason)andduringstormeventswithstrongerwaveconditions(wetseasons),which resultsinaseasonalbehaviouroftheprofileasshowninfigure3.8.inthestrongerwaveconditions, the storm surge level is high and the waves can reach the upper shoreface and impacts it. Consequently, an avalanching process takes place where sand is eroded from the dunes and falls downtothelowershoreface.thesesandbarsarethentransportedoffshorebyastrongundertow.in themilderwaveconditions,thewiderbermofthebeachisrebuildagainsincetheseoffshorebars moveonshoreandfinallyattachtotheshore(list&farris,1999). This principle shows that the material which has been eroded from the beach is not lost permanently.afterthewetseason,thebeachis(partly)restoredbythismechanism.similarly,the highwinterwavesinhoianwillcausetemporaryerosionofthebeachanddunefrontthatwouldbe restoredbythecalmersummerwavesiftherewerenostructuralerosionpresent. Figure3.8Left:profileduringdry(calm)season.Right:duringwet(rough)season(Bosboom&Stive,2015) 3.3.5Sandbalance Fromthreeyears,1965,2001and2014,thebathymetryisshowninFigure3.9.Inthefigurethereare depthcontourlinesfor5,10and15meters.basedonthispicturethevolumeofsandabovethe15 mdepthlinecanbecalculatedforeachyear,whichisshowedinappendixc.6. Normally when erosion takes place, there is sand transported along the shore to a place where accretiontakesplaceorintoasinklocatedinadelta.however,asiscalculatedfromthebathymetry from(tanaka,hoang,&viet,2016)depictedinfigure3.9,thismightnothavebeenthecaseathoi An.Thesandintheassumedouterdeltahasincreasedwith25.3millioncubicmetersintheyears from2001to2004.thiswouldnormallycoincidewithaccretionattheshoreandagoodexplanation whythisisnotthecaseisstillpending.inrecenthistory,30yearsago,itisseenthatasandbank emergedin thisouterdelta.theaccretionin theouterdelta mightleaduptoanothersandbank emergingandthecurrenterosionmightbepartofnaturalvariation.oranothermechanismmightbe present.inbothcasesthedatashouldbecheckedandconfirmedsinceariseof25.3millioncubic metersdwarfsthepresenterosioninsize(240,000m 3 /yearlossversusa2,000,000m 3 /yeargain). Figure3.9Contouredareas,basedon(Tanaka,Hoang,&Viet,2016) 10 CoastalerosionHoiAn

17 4.Stakeholder analysis In Hoi An the coastal erosion at the Cua Dai beach has a multitude of stakeholders. For example resortowners,localsandgovernmentbodies.thestakeholdersthatareinvolvedinthisproblemare presentedinthischapterwiththeirgoals,dilemmasandtheirinfluenceonasolution. 4.1 Problems and goals Thestakeholdersareanalysedusingproblemstatementsandgoaltrees.Thesearederivedfromthe results of interviews and questionnaires or common sense when this was not possible. The full analysis can be found in Appendix B. Stakeholders. In this chapter a concise overview of the stakeholders problems,dilemmasandgoalsrelatedtothebeacherosionathoianisgiven.itshows howeverystakeholderisinvolvedintheproblemandwhyitisdifficulttofindeasysolutions. Nationalgovernment TheNationalgovernmentisthehighestadministrativebodyoftheVietnamesestateandiscalledthe National Assembly. They control the local governments of the provinces and give orders to those provincialgovernments(ronaldj.cima,1987).thegoalofanationalgovernmentistostriveforthe bestfortheircountry sinhabitants.however,thereisthedilemmaofthenationalgovernmentnot tofavouroneprovinceaboveothers,otherwiseitwouldbeeasytogetenoughresourcesavailable forthecoastalerosionproblem. LocalgovernmentoftheQuangNamProvince The city of Hoi An is of economic importance for the Quang Nam Province.The economy of the whole province has financial benefits of the touristic city of Hoi An. Due to that the provincial government also wants Hoi An to have an attractive beach. However, recreating the beach is not easy. The sand mining and hydropower dams in the rivers might be (partly) responsible for the coastalerosion,butthosearealsoimportantsourcesofincomefortheprovinceandindustriesthat shouldnotbehamperedtoomuch.theprovincehasalsoalargeinfluenceonthesolutionsinceany large coastal intervention in Vietnam is normally paid for by the province. The province of Quang Nam already disbursed VND 54 billion or 2.3 million in 2012 for a dike at Cua Dai Beach. (ThanhNienNews,2014) LocalgovernmentofHoiAn ThecityofHoiAnisaprovincialcityaccordingtothepoliticalstructureofVietnamandisunderthe directauthorityoftheprovincialgovernment.oneofthemajorproblemsthelocalgovernmentof HoiAnhastodealwithnowadaysisthecoastalerosionoftheCuaDaiBeach.Extremeerosioncan damagethecity,bothstructuralandeconomicwise.thedilemmathatexistshereistheamountof moneyavailabletosolvethis.thecoastalerosionisnottheonlyissuethatneedstobefinancedand the budget is finite. The expected income from the beach is estimated on 3.6 million a year, as explainedinb.4estimationofhotelvalues.aninvestmentwhichislowerthanthisamountwillbe profitableforthecity. CitizenslivingfromthebeachinHoiAn Awidebeachispartoftheprotectionofthecity.Nexttothat,thetouristswhovisitthecitywill createincomesforthecitizensofhoian,whenthebeachesdisappeartherewillbelesstouristsand soonlessincomeforthecitizens.thesecitizensareforexamplerestaurantandbarowners,bicycle keepers,fishermenandlifeguards.thewishofthecitizensforkeepingtheirjobsisclear,butthe problem is that these people do not have a lot of power to urge the government to implement effective solutions for their future and are therefore dependent on how the beach tourism is evolvingnow. 11 CoastalerosionHoiAn

18 Resortmanagers Nowadays the resorts at Cua Dai Beach are very important to attract tourists to the city and the beachesofhoian.wideandbeautifulbeacheshaveadirectvalueforthehotelsandresortslocated at the beaches, but it is noticed that the amount of tourists is already decreasing. The resort managerscanbeclassifiedintwoparts:thoseatcuadaibeachandaffectedbytheerosionorthose atnorthofwheretheerosioniscurrentlytakingplace.thecurrentproblemsfitsthelatterinthe futuretoo.thewishoftheresortsatcuadaibeachistogettheoriginalbeachbacktocounteract the reducing amount of beach tourists. The dilemma here is that a government program and cooperationbetweentheresortsonthewholestretchisneededtobeeffective.thisisnotthecase yetandseenasahurdlebyseveralresorts. Financialcontribution Beachhotelownerscouldbefinancialcontributorstoasolutionaswell.Itisintheirbestinterestto protecttheirinvestmentbyinvestingalittlemore.forexampletworesortswereinvesting"several hundred billion dong" (Tre, 2014) which is equivalent to tens of millions in Euros. If such an investment can be more profitable by paying (partly) for the coastal defences this is a smart investment.howevercoastalmeasuresaremostlyonlyusefulwhenitisdoneforanareaaswhole andthiswouldaskforararecooperationofdifferentinvestorswithdifferentideas.alsotheprison dilemmaisineffectaseverysolutionhelpseveryone,alsotheoneswhowerenotpayingtheirpart. Soitisforanindividualhotelownerthemostprofitabletonotpay,butforthewholegroupofhotel ownersitwouldbebestifeveryonepays. Buildingindustry One of the main industries of Vietnam is their building industry. The Vietnamese infrastructure development triggers a great demand for sand and concrete. This demand has been increasing significantlyoverthepastyears(stoxresearch,2015).thebuildingindustryinvietnamusesalotof sandminedatseveralriversinthecountry.awishfromthebuildingindustryistoacquireenough materialstobuildwith,butthedilemmaisthattheywanttobuyitatlowcosts,otherwiseother sourcesthantheriverswerepossibilitiestogettherightmaterials. Sandminers ThebuildingindustrymentionedaboveusessandthatisminedfromtheVietnameseriversasthe Thu Bon river, which might have negative effects on the rate of coastal erosion Sand miners operatingforthebuildingindustrywanttominethesandfromsourceswhereitiseasyandcheapto extract.althoughthisisalreadyprohibitedwithoutlicense,itstilloccurs.however,whenitcanbe provedthatthissandminingisaffectingtheerosion,thismightleadtoextracontrolinthefuture. Thisisthedilemmathatsandminershavetodealwithtomaintainaprofitablebusinessintheyears tocome. Tourists Touristshavethewishforanicebeach,butnotonlyforthemselves,alsofortheenvironmentand localcommunity.touristsareflexibleandcanthereforealwaysshifttoaplacethatmatchestheir interestsmore.however,ifthewiderbeachcanbeachieved,theywouldliketoseemorecheapand public space instead of resort owned beaches. This is the dilemma here, because a public beach wouldimplythatthegovernmenthastoinvestinit.currently,itisunclearwhetherthisfundingwill evercomeandwhen. 12 CoastalerosionHoiAn

19 4.2 Power interest diagram Inthefollowingpowerversusinterestdiagramthestakeholdersarerankedontheirinterestand possibleinfluenceintheissue,seefigure4.1.themostimportantstakeholdersarethosewithhigh interestandhighpowertomakechangesandthereforerequirethemostattentionwhen implementingapossiblesolution. Figure4.1Powerversusinterestdiagram 13 CoastalerosionHoiAn

20 5.Reasons for shoreline retreat ThesevereerosionatCuaDaiBeachmightnotbecausedbyonefactor,butbyacombinationof factors.inthischapter,thepossiblecausesaredescribedandquantifiedwithanorderofmagnitude. HowthesenumberarederivedisgiveninAppendixResearchintoreasonsforshorelineretreat.This chapterfacilitatesingivinganoverviewofthepossiblecausesandconcludeswiththreehypotheses thatwouldexplaintheerosion. 5.1 Human impacts Changesinthecoastalandriversystemcanbeinducedbyhumansandtheirpossibleactionswhich givecauseforerosionaregiveninthisparagraph.twofactorshaveinfluenceontheerosionaresand mininganddamconstructionupstreamonthethubonriver.threefactorscanbeexcludedasbeing areasonfortheerosion.thesearehumanchangesinthewatershed,landsubsidenceduetowater extractionandlandreclamationforthebridgeconstruction Sandmining Orderofmagnitude:5m/year OneofthesedimentsourcesforthecoastalareainthesystemareaistheThuBonRiver,thisriver takessedimentfrominlandareastotransportittotheebbtidaldeltainfrontofthecuadaiinlet andafterthatitwillbedistributedalongthecoast.theimpactofsandminingintheupperpartof theriverdiffersfromtheimpactofsandmininginthelowerpartoftheriver.whensandisminedin the upper part of the river it does not change the total sediment transport in the river to the shorelinebecausethelossinsedimentduetotheextractioniscompensatedbythedegradationof theriverbed. Inthelowerpartoftherivertheeffectofsandminingchangesthesedimenttransporttothecoast. When sediment is extracted, the river bed at the same location will erode to compensate for the sedimentloss.thiswillcausealoweringreductionoftheflowvelocity(waterlevelstaysthesame) andthusaloweringofthesedimentdischargetotheshoreline.basedononedaytimeobservation, the amount of sand mining is roughly estimated on 100,000 m 3 sand per year. With a sediment transport rate of 400,000 to 600,000 m 3 per year this is a reduction of 25%. Using an order of magnitudefortheerosionthiswouldbearound5m/yearshorelineretreat Damconstruction Orderofmagnitude:0.5m/year Possible coastal erosion by sediment blockage by hydropower dams requires the blocking of a sedimentrichpartoftheriverscatchmentsareaandwillinfluencetheareadownstreamofthedam first.itisunlikelythatthesedimentblockagebythedamsisinfluencingtheerosionatthemouthof HoiAn,becausetheerosionstartedbeforethecurrenthydropowerdamintheThuBonriverwas constructed.itisalsoconstructedfarupstreaminthewatershed,relativelylimitingtheamountof sedimentthatwillbetrapped. However,adifferentflowregimewillchangetheyearlytransportcapacityoftheriverandthiswill influence the amount of sediment arriving at the mouth of the river. Using an assumption of the reservoir capacity, the yearly transport would have declined for approximately 3% since the placementofthedam.thisreductionindominantflowhasaninfluenceontheerosionrateofabout 0.5mperyear. 14 CoastalerosionHoiAn

21 5.1.3Excludedpossibilities Forthechangesinthewatershed,anewriverconnectionbetweentheThuBonandVuGiariversand deforestationarethemainfactorsthathaveahighinfluenceontheamountofsedimenttransported bytheriver.however,itturnedoutthattheriverconnectionanddeforestationwouldincreasethe sedimentsupplyinsteadofdecreaseit.relativesealevelriseduetowaterextractionrelatedtoland subsidence could be another cause for erosion, but groundwater extraction in Central Vietnam is very low (WEPA, 2015). It is however a problem for, for example, the Mekong Delta in South Vietnam.ThelastexcludedreasonfortheerosionisanareaofreclaimedlandintheThuBonriver. Thisareawasmadetobuildthebridgecrossingtheriverandcouldhavechangedtheriveroutflow direction. However, the erosion was already taking place before this land was reclaimed and thereforedonotmatchtogether. 5.2 Natural causes Alsopossiblenaturalcausesfortheerosionexist.Onenaturalcausethatisaffectingtheerosionis climate change. Sea level rise and the increasing rate of storms are contributing to the erosion. Naturalcausesthatareexcludedaretectonicsubsidenceandchangesinnearshoreconditions Sealevelrise Orderofmagnitude:0.5m/year Sealevelriseisawellknowndriverforcoastalretreat.ThesealevelriseatHoiAnhasbeenaround 4mm/yearforthelast50years(ISPonreVietnam,2009)andexpectedtorise6mm/year(Ministryof NaturalResourcesandEnvironment,2009).FollowingtheBruunRule(seeAppendixC.1BruunRule) theshorelineretreatsduetotheanadaptionofthebed.sandfromtheshoreistransportedtothe near shore to form the same bed slope as before the sea level rise. Erosion or more precise, shorelineretreat,isexpectedtobetakingplaceatarateofhalfameterperyearwhennottaking riversupplyintoaccount Increasingamountofstorms Orderofmagnitude:2.5m/year Anothereffectofachangingclimatethatcanimpactthecoastalbalanceandcauseerosionisthe increasingamountofstorms.asexplainedinchapter3.3.4seasonalerosionandaccretion,during storm conditions sediment is transported seawards. Normally this in balance with the return of sedimentduringcalmerconditions.howeverwhenthereisanincreasingfrequencyand/orintensity ofthestormthelossofsedimentcanbepartlypermanent.duetothewarmerairattheequatorand thereforelargertemperaturedifferencesbetweenequatorandpoles,heavierstormswillformwith more extreme wave conditions (ISPonre Vietnam, 2009). This process is already going on, when looking at the increasing rate of typhoons hitting Vietnam. Using the amount of sediment displacementbyalargestormandtheincreaseinstorms,thisleadstoanroughestimationof2.5m peryearoferosion Excludedpossibilities Excludednaturalcausesaretectonicsubsidenceandchangesinnearshoreconditions.Sinceerosion isoccurringalongalmostthetotalcoastofvietnam,youmightsuspectacommoncause. Oneofthereasonsfortheerosioncouldbetectonicmovements,whichcanleadtorelativesealevel risecomparedtovietnam sshoreandthereforeerodethecoasthowever,hoianisnotlocatednear a colliding edge of earth plates and also the vertical movements are relatively slow compared to othercontributorsofcoastalerosion. Near shore underwater conditions like morphology and water depth influence the local wave climate.iflargerwavescanmeettheshore,moreerosioncomparedtothepastwillhappen.some changes are seen for in the near shore conditions, for example the increased amount of sand offshore,asgiveninchapter3.3.5sandbalance.however,possibleeffectsofthischangewouldbe infavourofaccretioninsteadoferosion. 15 CoastalerosionHoiAn

22 5.3 Natural variation Theshapeofmostcoastlinesisdynamic.Thecoastcanmovelandwardsinonedecadeandmove seawardsinthenext.alsothenaturalyearlyamountandintensityofstormsvaries.thisparagraph givesthreepossibleformsofvariationthatcouldexplaintheerosionwithoutinfluenceofhumansor changingexternalfactors Stormvariation Orderofmagnitude:35mfor 1 / 5 yearstorm 120mfor 1 / 50 yearstorm Averaged over one or several years a constant crossshore profile can be expected as extreme conditionsandmildconditionsaverageoutoverlongperiod.dependingonthewaveconditionsthe profile shifts over the year due to heavier wave attack during storms. This is the cause of the variationintheprofileandmakesforatemporarylossofsandofthebeach.withmodellingofthe HoiAncrossshoreprofileandwavedata,erosionratescanbefoundforcertainreturnperiodsof storms. The effect of typhoons on the beach can be devastating over a large width of the beach movingalotofsandtotheforeshore.theempiricalcalculationsuggests120mofbeachimpactedby itand79.5m 3 /mofsanddisplaced.lesserstormswithareturnperiodoffourtofiveyearsorlonger cancausesandtomovetotheforeshore.thecalculationsuggests35mofbeachisaffectedand10.6 m 3 /msanddisplaced.forthesestormstheproblemisratherlimitedifthereissufficientbeachto compensate the temporary loss, which is currently not the case due to the construction of the resorts Sandbarmovingonshore Orderofmagnitude:60mintotal In 1989 a sandbar was observed approaching the coast of Hoi An, which is already described at Chapter3.1Evolutionofthecoast.Thevolumeofsandcarriedbythesandbartothecoastcanbe approximated from the Landsat images. With this calculation the volume of sand amounts to 1,370,000m 3 or1.37millioncubicmeters.theassumptionisthat90%ofthisvolume,1,230,000m 3, wasaddedtocuadaibeach.cuadaibeachhasalengthofabout3kmandwithanassumedactive depthof5mitiscalculatedthatthebeachwidenedbysuchanourishmentwithabout60m.last yearsthenaturalequilibriumisrecoveringandthatcouldbethereasonswhythereisalotoferosion theseyears SedimentstreamingduetoriveroutflowvariationOrderofmagnitude:5m/year AnothernaturalcausefortheerosionmightbethemovementsoftheThuBonrivermouthandin whichdirectionmostofthesedimentisflowingwhenitreachesthesea.thiswouldexplainthesand barthatisvisiblein1989inadifferentway.namely,aspartoftheebbtidaldeltaabovesealevel, formedbysedimentfromtheriver.thehypothesishereisthatthemajoroutflowdirectionofthe ThuBonriverhasshiftedfromnorthwardstosouthwardsinabout30years,whiletheamountof accretionatthespitwasinfluencedbythesandbankinfrontofit. Atsomepointintime,probablyaround1990,theshapeofthespithaschangedsomuchthatthe easiestoutflowdirectionbeganturningsouthwards.theerosionbywavesonthesandbankstarted overrulingtheaccretionbysedimentsupplyandthesandbankandspitweregettingsmaller. Muchslowerratesoferosioncomparedtothoseattheendofthedynamicspitareoccurringnowat Cua Dai Beach. To quantify the influence of the change in river outflow direction is difficult. The alongshoretransportofsedimentthatdistributesthesedimentalongthecoastisforalargepart basedonwavesandwinds.usingtheoutflowdirectionoftheriveritisestimatedthatthesediment supplytothenorthsideoftherivermouthhasdecreasedintheorderof100000m 3.Similartothe effectofsandminingthisagainleadstoanorderofmagnitudeforerosionof5mperyear. 16 CoastalerosionHoiAn

23 5.4 Hypotheses Inthisparagraphthreehypothesesarepresentedwhichareabletocausethewitnessedshoreline retreatatcuadaibeach.eachhypothesisfocusesaroundamaindriveroftheerosionandseveral secondarydrivers.thehypothesesshouldbeabletopartlyexplainthefollowingobservations: Shorelineretreatof12m/yearfrom Overastretchof4000m(resultingin~240,000m 3 /year) Anincreaseofforeshoresandamountof25,000,000m 3 between Hypothesis1:Relativelylargeincreaseintheroughwaveconditions The increasing amount of storms approaching or impacting the coast of Central Vietnam have, accordingtothishypothesis,thelargestimpactonthecoastalerosion.thesestormsareformeddue tothechangingclimateandtheamountofitisincreasing.stormwavestransportsandoffshoreand duetothefactthatwhentherearenoortoofewmildwavestobringthewavesbackitwillnotorin toolittleamountsbetransportedbacktothebeach.themaindriverofthisfirsthypothesisisthe increasing amount of storms. Secondary drivers are the reduction of sediment supply, which is relativelylargecomparedtotheothersecondarydrivers.thesearethesealevelriseandthenatural variationoftheshorelinemovement.thisisshowninfigure5.1. Thefactthattheamountofsandlyingintheforeshoreisincreasingsupportsthishypothesisand thatwouldsuggestthishypothesismightbetrue.inadditionitisproventhattheamountofstorms hasbeenincreasinginthepastseveralyears.oneofthethingsthatiscontradictingthishypothesisis thattheerosionalongthecoastisnotuniform,closetothemouththeerosionismoreseverethan furtherawayfromthemouth. Continuederosiontakesplaceonlywhenthestormconditionscontinuetorise,itisunsurehowthe rough conditions will continue to developand therefore future predictions are unsure for this hypothesis 5.4.2Hypothesis2:Relativelylargesedimentsupplyreductionoftheriver Several factors like sand mining, the dam in the river and changes in the watershed of the river influence the sediment transport of the Thu Bon River to the shoreline. The sand mining has the largestimpactontheamountofsedimenttransportedtotheshoreline.thedamintheriveralso reducesthesedimenttransport,howeverwithasmalleramount.furthermore,thechangesinthe watershed do not give a reduction of the sediment transport in the river. According to this hypothesis the river sediment supply is experiencing a higher decrease than with the other two hypotheses, causing more coastal erosion compared to the other two. This hypothesis involves a riversedimentreductionasmaindriverfortheerosionproblem.thesecondarydriversarethesea levelrise,increasingstormsandthenaturalvariationasshowninfigure5.1. AsmentionedbeforeinthisreporttheerosionclosetotheThuBonriverestuaryisalotmorethan theerosionfurtherawayfromthisinlet.thiswouldsuggestthatthereductionoftheriversediment supplyisdroppingandcausingtheerosionatthisrivermouth.howevertheincreasingamountof sediment at the foreshore is contradicting the suggestion that the sediment supply reduction is influencingtheerosion.thissuggeststhattheriverissupplyingenoughsedimenttonotcauseany erosion. Thishypothesiswillseecontinuederosioninthefuture,evenwhensandminingisreducedinthe firstyearstofirstdecadesnochangeisgoingtooccurinthesedimentdischargeoftheriver.the riverfirsthastorestoretoitsformerbedlevels. 17 CoastalerosionHoiAn

24 5.4.3Hypothesis3:Relativelylargenaturalcyclicshorelinemovement Thebiggestfactorofthecoastalerosioninthishypothesisisthenaturalvariation,whichcontainsthe natural variation of the river mouth in the southward direction and the moving sandbars in the foreshore.accordingtothishypothesis,thedirectionofthesedimentflowfromtherivermouthhas been moving southward in the past several years due to natural processes and the situation of nowadaysisalmostthesameasseveralyearsagowhentherewasasandbaraspartofthecoast, causingalotofsandlossatthebeach.alsothemultipleyearlystormvariationiscausinganatural cyclicshorelinemovement. Thisthirdhypothesisinvolvesthenaturalvariationoftheshorelinemovementasthemaindriverfor coastalerosion.thesecondarydriversarethereductionofsedimentsupplywhichhasarelatively largeorderofmagnitudecomparedtotheothersecondarydriverswhicharesealevelriseandthe increasing amount of storms. Figure 5.1 shows the orders of magnitude of all the drivers of this hypothesis. Acontradictingpointofthishypothesisisthattherearenodatathatshowthatthereisacyclicsand baranditmightalsobeanoncyclicsandbar,indicatingthatitmightnotbeanaturalcyclicshoreline movement.however,whatissupportingthishypothesisisagaintheincreasingamountofsandin theforeshore. Thishypothesisislikelytoseeareducederosioninthefuturesincethesandfromtheforeshorewill notcontinuetoaccreteintheforeshorebutwillbemovedtothecoast. Hypothesis1 Sealevelrise Reductionofsediment supply Hypothesis2 Increasingstorms Naturalvariation Hypothesis3 Figure5.1Orderofmagnitudeoftheinfluenceofmainandsecondarydriversofthethreehypotheses 18 CoastalerosionHoiAn

25 6. Solutions Withtheproblemsknown,thischapterlooksintosolutions.Thischapterstartswiththreepossible strategiesfromwhichoneischosen.afterthat,therequirementsforalternativesaregiven,which arebasedonansystematicapproachofstakeholderanalysis.afteranalysisofpossiblemeasures,the threemostpromisingarefurtherworkedout.thischapterconcludeswithsomequicksolutions,that canbeusedtoovercometheproblemsuntilapermanentsolutionwillbeimplemented. 6.1 Strategy to deal with coastal erosion Three options are available when confronted with an erosion problem: take no action, relocate endangered structures, or take positive action to halt the erosion. All are described below, after whichoneischosenasbeststrategy. Possiblestrategies Option1:Noaction.Itisanoptiontoundertakenoactionwhenconfrontedwithcoastalerosion.If onlyundevelopedlandorinexpensivestructuresarethreateneditismoreprofitabletoacceptthe losses than to invest in measures. It is also a good reference point from which to evaluate other measures. Option 2: Relocation. To prevent damages by coastal erosion, the relocation of endangered structures can be considered. This can be done either by moving them to a different location or furtherawayfromthewater.movingabuildingisacostlyoperationandwillbeineffectiveifitisnot movedbackfarenough.therefore,itisrequiredtoknowthecurrenterosionrate(m/year)andthe likelihoodthatthiserosionratewillcontinueoralterinthefuture. Option 3: Positive action to halt erosion. If the invested money along the shoreline is large and if relocationofthispropertyisdifficult,itisoftenpreferredtotakeactiontopreventfurthererosion. Protectionmeasurescanbeinstalledbothasatemporaryandasalongtermsolution.Thisoptionis oftencheaperandmuchmoreconvenientthanrelocation. Chosenstrategy At Cua Dai beach the money invested at the location makes the no action or relocation option unwanted.alsoconsideringtheamountoflocalpeoplelivingfromthebeach,makesthefirsttwo optionsnotasocialandeconomicfeasibleoption.thereforethischaptercontinueswithfindingthe rightpositiveactiontoundertaketopreventunwantedcoastalerosion. 6.2 Solution requirements Numerousoptionsarepossibletostoptheerosion.TheHoiAnsituationmakescertainoptionsmore advantageousthanothers.asystematicapproachisusedtotranslatethegoalsofthestakeholders into requirements, which is described in Appendix G.1 Systematic criteria and option finding. Two importantloopsinthesystemarefoundhere. The first loop shows the vicious circle between the declining tourism due to the reducing beach attractiveness, this leads to economic damage to the resorts, which results in a lower budget for measuresandalowerrateoftheimplementationofmeasures.theimplementationofmeasuresis positivelyrelatedtobeachrecovery,soifnomeasureswillbeimplementedthebeachwillfurther deteriorate, reducing the beach width and attractiveness of the beach even further, leading to a furtherdeclineintourism.tomitigateeffectsofeconomicdamagethiscircleneedstobebrokenby asuitablealternative. Thesecondloopissmallerandstartswithstructuraldamageduetotheerosion,leadingagainto economicdamagetoresorts,areducingbudgetformeasuresandadeclineintheimplementationof 19 CoastalerosionHoiAn

26 measures, reducing the coastal flood protection even further, leading to more structural and economicdamage.thisisanotherviciouscirclethatwillgoonuntiltheresortsrunoutofresources torepairitself,ifitisnotbrokenbyanalternative.thecurrentparagraphelaboratesonthefinal requirementswhicharegivenbelow. 1. Highprotectionofbuildings The protection of buildings against the erosion is a requirement that is shared by several stakeholdersandthereforeimportant.furthermore,analternativethatcanlimitortakeawaythe structuraldamagetobuildingswillbreaktheviciouscircle. 2. Highattractiveness Theattractivenessofthecoastisveryimportanttomakesurethetouristskeepcoming(back)to HoiAn.Ifthegivenalternativescanmakethebeachattractiveagainandmaintainitlikethat,the otherviciouscirclewillbebroken.attractivenessisherenotonlythebeachwidth,butalsothe distancetothebeach,thecostsofbeachvisitandthesafetyoftheswimmingwater. 3. Lowcosts Thecostsofmeasuresisalwaysimportant.Somebodyhastopayforitandlikestoachievethe highestvalueforthelowestprice.ifthetouristsarenotwillingtopayforabeachvisit,thecosts ofmeasureshavetobedividedamongstotherparties.measureswillbeimplementedsoonerif thecostsarelowandthetwodescribedloopscanbebrokenbeforeitistoolate. 4. Longlifetime Currently,mostlytemporarymeasuresareusedthathardlysurviveonestormseason,duetothe lackoffunding.measureswithalonglifetimecanformamorepermanentprotection.itturned out that cooperation to one single solution is difficult. When measures have a long lifetime, it saves the effort of consult that would be needed every several years with more temporary measures. 5. Highspeedofeffectiveness The current state of erosion is severe and at some locations not much of the beach is left. Furthermore, some buildings have already collapsed due to the erosion. A solution that shows resultsfastisimportanthere.itreassuresfloodprotection,butwouldalsomaintainorperhaps increasetherateoftourismagain. 6. Noshiftingofproblemstoadjacentareas Animportantcriterionisthatmeasuresmaynotshifttheproblemstoothersintheareathanthe local users and resorts in Hoi An. Currently the resorts are protecting their own property with hardstructures,thatkeepshiftingtheerosionnorthwards.todealwiththeproblemeffectively, thismaynotbethecaseforthepermanentsolution. 7. Highsafety Partoftheattractivenessisthesafetyofstayingatthebeachandswimmingthereaswellasthe safetyoftheresorts.solutionsthatdonotpayattentiontooneofthesekindsofsafetyshouldbe avoided,sincethiswouldfurtherreducethereputationofhoian. 8. Combineswellwithcurrentmeasures Action needs to be taken fast, to break the loop of declining tourism and structural damage beforeitistoolate.thepossibilityforalternativestocombinewiththecurrentmeasureswilllead toimplementationofthisnewmeasuresmoreeasy. 9. Nobadinfluenceonotherindustries Thefinalrequirementforalternativesisthattheyshouldnotaffectotherindustriesthantourism in a bad way. Industries like sand mining and hydropower generation are important money makersfortheprovinceandvietnamasnationandcannotbehampered. 20 CoastalerosionHoiAn

27 6.3 Results of analysis of possible measures This paragraph concludes into the three most promising measures. Those three measures will be consideredandelaboratedinmoredetailedinthenextparagraph.allcurrentappliedmeasuresand otherpossiblemeasuresarerankedinamulticriteriaanalysis,allofwhichisgiveninwhicharegiven inappendixfandg.3.theresultsarethefollowing: The highest ranked measure was sand nourishment. It scores very well on all requirements thatweregiveninthepreviousparagraph.furthermore,itisveryflexibletocopewithfuture changes.itsdrawbacksarethatthereisnoreductionintheyearlyvariationandpeoplemight stillfeelunsafe.itisalsoaperiodicmeasure,withalifetimeofaround5years. Themeasurethatwastiedinsecondplacewasasubmergedbreakwater.Thisonescoresquite average on all measures and in such a way has no large drawbacks. It can recreate some beach,butitwillstillshifttheproblemtotheareawithoutbreakwaters. Theothermeasuretiedinsecondplacewastheconcreterevetmentmeasure.Itscoredvery well on almost every criteria, except for two criteria of which the attractiveness has a very largeinfluenceontheoverallresult.aconcreterevetmentdoesnothaveagreatappealfor mosttourist.whenabeachisexpected,concreteisabitdisappointing.themeasuredoesnot bringthebeachbackatall.italsoshiftstheproblemtodowndriftareassinceitdoesnotsolve theerosion,butonlydivertsit.therevetmentonlyprotectsagainstincidentalerosioncaused bystorms.intheenditwillfailbyunderminingoftheconstruction. Sandnourishmentscoreda91/100pointsandtheconcreterevetmentandbreakwateronly66/100. Further designing the latter two would be needless, since they would never outscore the sand nourishment.theydohoweverhavesomebenefitscomparedtonourishmentalone.therefore,the following three most promising alternatives are all based on sand nourishment, whether or not combinedwithothermeasures. ThefirstalternativeasseeninFigure6.1isonlytheuseofsandnourishment.Thisisverypromising, butneedsalotofsandtoretainthebeachandgiveadequatestormsafety.thesecondalternative makes use of sand nourishment in combination with sand retaining structures like (submerged) breakwatersorgroynes.thiswaythesandnourishmenthasanincreasedlifespanandthereissome reducedwaveactionforpossibleswimmingbenefits.italsoneedswaylessnourishmentthanthe firstalternativethirdthealternativefocusesonstormsafety.thebasisisagainsandnourishmentto battle the structural erosion, but this option needs a relative small amount of sand since storm protectioncomesfromaconcreterevetment.thereisstillanadequatebeachinthecalmseasonbut afteraheavystormthebeachneedsasmallnourishmenttoreturn. Largenourishment Mediumnourishment+ soilretainingstructures Smallnourishment+ revetment Figure6.1Threealternatives 21 CoastalerosionHoiAn

28 6.4 Three alternatives Thischapterdescribestheideabehindthethreechosenalternativesandshowstheir(dis)advantages relativetoeachother.amoredetailedexplanationaboutthealternativessuchassketchdesigns, costsandeffectsonthecoastlinearegiveninappendixh.1toh.3.furthermore,severalbenefitsand downsidesexistforusingnourishment.thesearegiveninappendixg.2hardversussoftmeasures Largesandnourishment The first alternative is a wide sand nourishment along the entire beach. Takingintoaccounttheincidentalerosion caused by storms and the structural erosion, the sand nourishment has to createa180mwidecuadaibeach.thisis similartoasitwasseveralyearsago.to keep the width sufficient at all times a nourishment interval of 5 years is Figure6.2 Coastlineimpressionwithlargenourishment needed.atthesouthernpartofthestretchmoresandhaserodedthanfurthernorth,meaningthat moresandhastobenourishedmoreclosetotherivermouth.however,mostresortsalreadyhavea hardstructureprotectingtheirproperty.duetothis,thebeachinfronttheresortscanbelessthan 180m.Onaveragetheresortsarelocated40mmoreseawardthanthecurrentshoreline,meaning that140mofextrabeachwillbecreatedhere.relativetotheotherthreealternatives,alargesand nourishmenthasthefollowingadvantages: Itcombineswellwithcurrentmeasures. Thebeachwidthislargerduetotheprotectivefunctionofit. Itshowsalsosomedisadvantagescomparedtotheotheralternatives: Arelativelylargeinitialinvestmentisneededduetomuchlargerbeachwidthtonourish. Suchasolutionisalessvisibledecisivesolutionandcreatesalesssaferfeelingtothelocal peoplecomparedtohardstructures. Thelargenaturalvariationofthecoastlinewillcontinue. Thenetpresentvalueofthecostforthecomingtwentyyearsofthisoptionis 37.8millionorVND 950billion Mediumsandnourishmentwithretainingstructures As soil retaining structures, groynes are chosen over breakwaters. Although breakwaters as single measure score better, groynes are a good combination with a nourishment. In this alternative a setof145mlonggroyneswillbeplacedto protect the Cua Dai beach and several Figure6.3Coastlineimpressionwithmediumnourishment+ groynes hotels from further erosion. Once protected the beaches between the groynescanberestoredtoawidthof60mbyasandnourishment.besidestherecreationofabeach, nourishment would accomplish to other issues: mitigate the erosion induced by the groynes on adjacentareasandcompensateforthestructuralerosioninthefuture. The beaches in between the groynes can be restored with a single large nourishment that would requirelittlemaintenance,asonlystormsarestrongenoughtomovesomesandoutofthesystem andinduceerosionofthesebeaches.thesebeacheswouldadapttothedominantwavedirections, leadingtoasawtoothshapeshoreline. 22 CoastalerosionHoiAn

29 Thecombinationwithgroyneshasthefollowingadvantages: Thebeachinfrontoftheresortsiseasilyrestoredbyalargeinitialnourishment,withsand partlytrappedbetweenthegroynes. Groynesreducethelongshoremovementofthesand,meaningthatasmallerbeachwidthis neededbetweenthegroynestodealwiththestructuralerosion. Comparedtotheotheralternatives,isalsohasitsdisadvantages: Constructingmultiplestonegroynesiscostly,especiallywhencombiningthemwithasand nourishmentofalargevolume. Arowofgroynesonlyprotectsthatparticularareawheretheyareplaced.Anerosionpattern willdevelopintheunprotectedareabeyondtheoutergroyne,duetothepartialreductionin alongshoresedimenttransport.thispatternwillalwaysdevelop,nomatterhowmanygroynes willbeconstructed.asuitablelocationhastobefoundtoallowforthiserosion. Nearthegroynesisanlesssafelocationforswimmers Thenetpresentvalueofthecostforthecomingtwentyyearsofthisoptionis 41.0millionorVND 1025billion Smallsandnourishmentwithrevetment Thethirdalternativeisacombinationofa revetment and sand nourishment. The revetments deal with the task of storm protection of present buildings by preventing incidental erosion. The nourishment creates a beach for tourists and prevents the structural erosion and underminingofthetoeoftherevetments. Currently, two revetments are already in placealongcuadaibeach.forthisoption, Figure6.4Coastlineimpressionwithsmallnourishment+ revetment only another revetment has to be placed along the part that is now temporary protected by sandbagsandotherprovisionalmethods.thereis alsononeedforrevetmentsalongthebeaches betweentwobeachresorts.theprotectingstructuresoftheresortsactasgroynesandpreventthe shorelinefrommovingtoofarinland. Atthelocationwherenormallynowaveactionispresenttherevetmentcanbeconstructedasastair structure,tomakeiteasierforpeopletogettothebeach.forthelandsideofthenewrevetment therearetwooptions:keepitmostlyasitisnow,orchangeitintoaboulevard. There are several advantages, but also disadvantages to this alternative. Both will be described below.theadvantagesarethefollowing: Duetothecombinationofnourishmentandarevetment,thisalternativeoffersagood protectionagainsttheincidentalerosioncausedbythehighwavesduringstorms.andsinceit isaconcretestructure,italsofeelssafer. Comparedtotheothertwoalternatives,lessinitialnourishmentisneededhere.Thestorm protectioniscoveredbytherevetment,notbyextranourishment. ArevetmentisalreadypresentalongalargestretchofCuaDaiBeach. 23 CoastalerosionHoiAn

30 Aswithalloptions,therearesomedisadvantagestothisalternative.Whichare: Thebeachmightnotalwaysbepresent.Afterthestormseason,thesandcanmoveoffshoreto suchanextentthatthesandlevelliesbeneaththewatersurface,untilthesandisbrought backonshorebycalmerwavesoranextnourishmentiscarriedout.thiscanhamperthe tourism. Comparedtofullbeachnourishmentortheuseofgroynes,themovementtothebeachisless fluentduetotherevetment. Thenetpresentvalueofthecostforthecomingtwentyyearsofthisoptionsis 23.9millionorVND 595billion. 6.5 Nourishment strategy There are several possibilities to choose from, when the decision for nourishment is made. This paragraphisasummaryofappendixh.5andshowsadvisesforthesourceofsand,thecrossshore locationofnourishmentandtheintervalbetweennourishments Sourceofsand Since the shortest distance makes it the cheapest adequate supply the river deposit before the mouth is advised as source. Furthermore, the sand has the same properties as the beach sand (following from the sand sample analysis in Appendix I.3) The distance to the nearest sediment reservoirisoneofthelargestfactorsdeterminingthepricepercubicmeterofsand(m.marchand, 2012)Thissourceishowevernotyetconfirmedtobeavailablewithsufficientbathymetrycharts. Thesecondbestsourceisfurtheroffshoredredging.Itisnotyetcertainwheretofindsuitablemining locations. However it is known that the depth at those locations is around 80 meters and the distanceislargerandsubsequentlythecostsrise Crossshorelocationofnourishment The use of shoreface nourishment is advised, since the costs are lower than the costs of a direct beach nourishment. When a limited amountofcubicmetersfromanearbysource is available, a combination with a beach nourishment should be considered since this nourishment type requires a reduced amount ofsand. Figure6.5 Crossshorelocationofnourishment 6.5.3Intervaltimeofbeachnourishment Following from Figure 6.6 the most cost efficient maintenance strategy is nourishing every 2 years. Although nourishing every 5 yearsisaroundthesamecostsandthisoption hassomeadvantages,itisnotadvisedtostart with an large initial nourishment as first nourishment in an area without experience with previous nourishments. For the first nourishment an interval of 2 years is advised andwhenadditionalresearchisdonea5year intervalcanbeused. Figure6.6Nourishmentintervalstrategy 24 CoastalerosionHoiAn

31 6.5.4Longshorelocationofnourishment Duetothecostsitisadvisedtonourishthecoastatnourishmentpointsevery200metersanduse naturalspreadingbywaves.notdistributingitbylandbasedmovingequipmentreducesthecosts. The coastline will smoothen itself when the distance between the nourishment points is not too large. 6.6 Quick solutions Whileenoughdataandinfluenceisbeingcompiledtosupportandimplementafinalsolution,the problem continues. This paragraphs shows two quick solutions that could be used to limit the problemsuntilanalternativeisconstructed.followingfromthemulticriteriaanalysisinappendix G.4incombinationwiththeirabsolutecosts,thefollowingoptionsarepracticalsolutionstoreduce theerosiontemporarily Topreventtheerosionfrommovingnorthwards Asexplainedintheprevioussectionsstructuralerosioncanonlybestoppedbyanourishmentofthe beach. Currently all measures move the erosion northwards and the beach that is marked red in Figure6.7iserodingheavily,basedonobservationofJanuary2016.Topreventthedamagemoving northwards the not used dunes, depicted with yellow, could be gradually flattened and used for nourishment to maintain the coast line and thus prevent further erosion north of this side. The amount of 160,000 m3 is only adequate for 2/3 yearofnourishment.itdoeshalttheerosionfully and is well combined with any future nourishment. Moreover, since the location is directly adjacent to the beach the cost are very low. Although dunes are normally used as sea defenceagainststorms,thisisnotthecasehere. The dunes next to this stretch are already removedforresorts.however,futurepossibilities forcoastalprotectionarediminishedifthisoption Figure6.7Dunefix ischosen Topreventerosionlocally Quick(temporary)protectionshouldonlybeappliedat locationswherebuildingsarethreatenedbytheerosion. Otherstretchesshouldbeleftunprotectedtonotmove the erosion northwards. To prevent the erosion locally geotextilesandbagsaremosteffective,whichallowfor a steeper slope. Long geotextile bags can be used for retaining sand locally, by placing them as breakwaters orshortgroynes.thesandbagsandgroynevariantwith alengthoftwolonggeotextilebagsisdepictedinfigure 6.8. Figure6.8 Quicklocalfix 6.7 Beach policy Aneffective policyandmanagementofthecoastal zonewillmitigateorpreventsimilarproblems inducedbyerosioninthefuture.coastalzonemanagementisabroadsubjectthatcanbeappliedon alargescale,buthereitwillbeusedonafewkilometrestosetupastrategyforthepreservationof thecuadaiarea(firstpart)andthestretchofbeachsouthofthethubonriver(secondpart).citing fromthiaeng(2015),chairmanoftheeastasianseaspartnershipcouncil,coastalzonemanagement canbeused toreachthe followingfourgoals:maintainingthecoastalresourcesystems,reducing resourceuseconflicts,maintainingtheenvironmentandfacilitatinginmultisectoraldevelopment. 25 CoastalerosionHoiAn

32 WhichresourcesareavailableandpossibleconflictsthatcanariseoverthisaregiveninAppendix H.4.Thisparagraphgivesaconciseoverviewofthedesignedstrategies CuaDaiBeach AtthetimethelocationforthefirsthotelorresortalongCuaDaiBeachwasdefined,thedesigners were not aware of the future coastline variations at the defined location. For years most resorts, hotelsandrestaurantswerebuilttooclosetothecoastline,ifyoutakethenaturalcoastlinevariation in mind. One of the most important suggestions to facilitate the progress of multisectoral developmentistoconstructanyfuturebuildingorstructurefarenoughfromthecoastline.thisway therewillbenoerosionissuesthreateningtheresorts,hotelsorrestaurantalongthebeach. Duetoclimatechangethereiserosionfollowingfromsealevelriseandnexttothat,moretropical stormsarehittingcuadaibeach.thereforeitisadvisedtobuildbehindtheduneswhenpresent,to have the possibility for extra nourishments in the future and to have enough palm trees and vegetationinfrontofthebuildings.dunesprotectagainsthighstormsurges,palmtreesandother vegetation might protect against damage due to the wind and the extra nourishment protects againststructuralerosiondamage. Whentranslatingtheabovestrategyintoapolicy,thefollowingzoningmapcanbeused.Itshowsa nourishedcuadaibeacharea,dividedintoaredandagreenzone.theredzonestretchesfromthe startofthenourishedbeachtowards300meterintothesea.thiscanbeseenasa nobuild zone,to createspaceforthenaturalmovementsofthebeachzone,preventerosionrelatedproblemsinthe futureandadapttoclimatechange.itstretchesintotheseatoalsoforbidtheconstructionofprivate structuresthatmightlimitthelongshoretransport.alsothesandypartoftheendofthespitisa prohibitedzonetobuildon,sincethisisstilladynamicpartofthebeach.thegreenzoneisfreeto build.althoughthiszoneincludesthedunezone,mostoftheduneshavealreadybeenremovedfor the construction of buildings and cannot contribute anymore to the natural nourishment of the beachsystem. Figure6.9ZoningCuaDaiBeach Another important issue these days is that a large amount of licenses are provided to allow the construction of hotels, resorts and restaurants. According to the interviews with resort managers, the amount of tourists has been decreasing last years while more hotels and restaurants have openedtheirdoors.whileindividualpeoplecouldmakemoremoney,hoianasawholegainsmore withfullyusedhotelsandopenbeachpartsinsteadofhalffullhotelswithoutanypublicbeach.this wouldreducethetotalamountoftourists.thereforetheamountofhotels,resortsandrestaurants shoulddependontheamountoftouristscomingtoandstayinginhoian.thiswayallparticipantsin thesectorlivingfromtourismcandurablesustainthemselves.onthelongrunthiswillcreateamore attractivehoian,withoutemptycateringfacilities. 26 CoastalerosionHoiAn

33 Furthermore, a balance between the beach use by fishermen, resorts, restaurants and nature will arise to give everybody and everything enough space to flourish. It is advised not to provide any extralicensesforthisstretchofcoasttopreventpossibleconflicts Southernstretch The following advice of the development of the area south of the Thu Bon river followsfrom the preferencesthatcoastalerosionshouldnotrequireanyadaptionmeasures.thesuggestedcoastal zonemanagementforeseesfuturechangesandadaptitslandusepolicytoit. Figure6.10ZoningsouthofThuBonriver ThezoningmapdepictedinFigure6.10shouldbefollowed.Alargepartofthebulgenexttotheriver mouthisaprohibitedzonetobuildin.lookingattherecenthistory(seechapter3.1)itisclearthat thisisahighlydynamicpartofthecoast.buildinghereandclosetotherestofthebeachgivesahigh chanceoflostvalueinthefuture,ascancurrentlybeseenatcuadaibeach. Betweentheredzonesurroundingthebeachandthegreenzone,ayellowzoneispresentatthis sideoftherivermouth.mostofthenaturalbeachanddunesystemisstillintactanditisadvisedto keep it that way. Dunes are an effective soft structure to prevent flooding. Following this policy, building in the yellow zone is only allowed if it is the only possible location for a structure that contributestotheregionaldevelopment.inthiszoneagricultureorsimilarusageshouldbeapplied with the knowledge that is not a permanent usage. The green zone is a zone where building is allowedwithnorestrictionsincenoproblemsareexpectedinthecomingdecades. InFigure6.11thecurrentcrosssectionsituationisdepictedatthetopandapossiblefuturesituation placedunderit.iferosionwouldtakeplace,allstructuresthatarebuiltinthegreenzonewouldstill besafe. Figure6.11Crosssectionwithadaptionprofile 27 CoastalerosionHoiAn

34 7.Conclusion and recommendations Thislastchapterfinalisesthereportbypresentingthemainconclusionsandrecommendationsfor furtherresearch.thelatterprovidesoptionsthatwouldfurtherdevelopstrategiesandpredictthe effectsofsandnourishment. 7.1 Conclusion Theprojectstartedwiththefollowinggoal: PresentingatleastthreeeconomicandtechnicaldurableoptionswhicharesupportedbytheHoiAn communitytorecreatethefamouscuadaibeach. Before being able to present durable options, it was necessary to know what the reasons for the erosionare,whatproblemstheyarecausingandfindingoutwhatneedstobesolvedorwhateffects needtobemitigated. Itbecameclearthatseveralfactorsarecausingtheshorelineretreatof12m/yearatCuaDaiBeach. Although not enough data is present yet to proof their precise quantitative influence, order of magnitudesaregiventotheimpactofthesefactorsonthecurrenterosionrateandtranslatedhere intopercentagesofcontribution.asteadyfactorissealevelrise,whichaccountsfor5%ofthetotal erosion rate. Another consequence of the global changing climate is the increased amount and intensity of storms reaching Hoi An, which contributes to 525%. Human contributions are the reduction of sediment supply caused by the construction of the hydropower dam in the Thu Bon river amounts to 5% and sand mining in this river to 4080%. As can be seen, sand mining has a relativelargeinfluence.thereisalsosomenaturalvariationpresent,accountingfor1050%ofthe erosionrate.otherfactorsareafterresearchexcludedaspossiblereasonsforerosionathoian. Thewiderangesinpossiblecontributionsaretranslatedintothreehypothesesthatwouldexplain the current shoreline movements. The first hypothesis is based on the increasing storms as main contributor.thesecondhypothesisexplainstheerosionbythereductioninsedimentsupplyfrom the river. The last hypothesis interprets the shoreline retreat with natural variation as the main reason. The other factors are secondary contributors in these hypotheses. Robust solutions were neededthatwouldbeabletodealwitheachofthehypotheses. Threealternativesaredesignedwhilekeepingthewiderangeoffactorsthatcausetheerosionand therequirementsforsolutionsbasedoninterviewsinmind.themostimportantrequirementsare that the options may not shift the problems to adjacent areas and that they have a high attractiveness. Hoi An has to remain an attractive destination for tourists, since this is the main source of income for the local community. This implies that doing nothing or relocation of the existing buildings are not the right way, social and economic wise, to deal with the problem. Furthermore,basedonthefirstrequirement,theuseofsolelyhardstructuresalongthecoastwas notanoption.hardstructuresdonotstopthestructuralerosionandkeepsshiftingtheerosionin downdriftdirection.restoringthesedimentsupplyturnedouttobeadifficultsolutionandwhich takeseffectonlyafterseveraldecades.thisleadtotheconclusionthatsandnourishment,whether ornotincombinationwithotherstructures,istheonlysuitableoptioninhoian. Thealternativesdonottakeawaythecausesoferosion.Theexternalcausesofclimatechangeand naturalvariationcannotbediminished,atmostbesteeredinawaythatwouldreducetheireffects. Increasingthesedimentsupplyseemsaviableoption,butwouldcreateothernegativeeffects. 28 CoastalerosionHoiAn

35 The three alternatives counteract the effects of the mechanisms that contribute to the coastal retreatbynourishingthebeach.whichalternativesuitsthesituationandbudgetthebestisupto thehoian sandquangnampolicymakers.allalternativesareexpectedtogiveanetprofittothe citywiththeaveragedcost/yearbeingbelowincome/year. Afterthebeachhasreturned,witha widthdependingonthe alternativethatwillbe chosen,itis importanttohaveastrategytomanagethebeachuse.ifnot,thesameproblemsoflosingproperties thatwerebuilttoclosetotheseacanariseagaininthefuture.azoningpolicycanbeusedtokeep structuresoutofcertainareasthatarepronetoerosionafter,forexample,astorm.asimilarpolicy should be made for the stretch south of the Thu Bon river mouth. Although this area is not used intensively,duetotherecentlyconstructedbridgethelandhasbecomeeasieraccessiblefortourism andrelatedconstructionactivities.alsoextracarehastobetakenfortheamountoflicensesthatwill beprovidedfortheconstructionandopeningofhotels,resortsandrestaurants.thetourismsector hastogrowinthesamepaceastheamountofvisitorscomingtohoian.thiswayallparticipantsin the sector living from tourism can sustain themselves. On the long run this will create a more attractivehoian,withoutemptyresortsandrestaurants.furthermore,abalancebetweenthebeach usebyfishermen,resorts,restaurantsandnaturewillarisetogiveeverybodyandeverythingenough spacetoflourish. 7.2 Recommendations This project does not yet result in a solution for Cua Dai Beach that can be implemented straight away.toachievethisstatus,thereisoneissuethatshoulddefinitelyberesearchedandthreeothers that are preferably researched. Of the three preferred research options all are advised to be conductedevenaftertheinitialnourishmenthasbeenplaced.thisresearchcanbeusedtofurther developandenhancefuturemaintenancestrategiesandbetterpredictandmitigateadverseeffects Fieldworknearthesourcelocationofsediment More detailed bathymetry data and analysis should be made for the foreshore sand balance. A confirmationofthesandbalancedescribedinsection4.3.5wouldmeanthatacheaprecyclingofthe sandcouldtakeplacerightaway.thedataishoweverinconsistentwithwhatwasexpected.ifthis dataisprovedtobeincorrect,othersourcesintheareashouldbecheckedforavailability.onlythe area relatively close to the shore is expected to be feasible as a source location, based on the sedimentanalysisundertakeninthisproject,whichisgiveninappendixi.3.anewfieldworkshould focusonfindingsandwithsimilarpropertiesasthebeachsandatcuadai Researchintowaveshielding(localwavedata) ResearchofthewaveclimateclosetoHoiAnshouldbedonetotaketheinfluenceofshieldingby thechamislandsintoaccount.atleasttwo,yearlong,wavemeasurementslocatedhalfwaybetween ChamandHoiAnareneededtomeasurewaveheight,periodanddirection.OneinfrontofCuaDai Beachandonemoretothesouth.Itismorepreferredtocollectsuchdataatmultiplelocationsto determinethecomplexwavemovementsbehindtheislands.alsopreferredisthedataofalonger time period to take multiyear variation into account, but one year is the bare minimum to make morereliablequantitativemodelsorpredictions.thisresearchwouldfocusonlongshoresediment transport for different coastal stretches and on how Cham shields different beach stretches from differentwaves Researchintothecurrentandfutureriversedimentsupply A more detailed analysis of the Thu Bon River is recommended to make a more reliable approximationofthesedimenttransporttothecuadaiinlet,sincethedecreaseinsedimentsupply fromtheriverisoneofthemainfactorscontributingtothepresentcoastalerosion.theestimation methodsusedasdescribedinsection3.2coulduseimprovement. 29 CoastalerosionHoiAn

36 Togetherwiththeacquirementofmoredata,softwarelikeSOBEKREorDelft3Daresuggestedto makeamoredetailedmodelofthethubonriver. Thewaterlevelanddischargeatmultiplelocationswouldbeneededforsucha model. Especially dataofjustupstreamanddownstreamoftheconnectionsbetweenthevugiaandthubonriverare needed.whenmodellingthethubonriverinmoredetail(withenoughdatapointsandattheright locations)the effects of sand extraction in the middle and lower stretch of the river could be determined. Also its effect on the sediment output into the coastal system could be found. A researchintothistopiccouldresult,nexttoabettersedimentinputestimateforcoastalmodels,into abetterunderstandingoftheriversystemanditsproblemslikefloodsandbankerosion Delft3Dmodelforthecoastalzone WithaDelft3Dmodelthecurrentsandsedimenttransportpatternscanbesimulatedinmoredetail. While more simplified models can give good estimates, Delft 3D can simulate in more detail the complicatedinteractionsinandaroundtherivermouth,whichisacrucialpartinunderstandingthe dynamicsofthiscoastalsystem.anotherpartoftheproblemisthecomplicatedbathymetrythatcan influencethewaveclimatetoagreatextent.moresimplifiedprogramsusuallyassumealongshore uniform profile which is not present in Hoi An, due to shallow areas south of Cham Island. The calibrated model can be used to better assess the impact and effectiveness of structures and nourishmentsneartherivermouth. ForaDelft3Dmodelamultitudeofdataisneededandthereforecanonlybeundertakenifsomeof theotherresearchsuggestionsareconductedaswell: Wavedataandcurrents:thisfollowsfromsection Bathymetry:adequatedataispresent,buthastobeconfirmedorimprovedifpossible. Morereliablesedimentsupply:couldfollowfromsection Bedtypedata:thisprojectprovidesadequateroughdata,howevermorelocationswitheacha reliableanalysisofthebedsoilispreferred. 30 CoastalerosionHoiAn

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42 Tre,T.(2014,July11).Vietnam shoiancitylosingbeachtoalarmingcoastalerosion.retrieved November24,2015,fromtuoitrenews.vn: hoianoldtownlosingbeachtoalarmingcoastalerosion Tung,B.N.,&Hien,N.T.(2014,December).Vietnam'sNewLawonHousing.RetrievedNovember24, 2015,fromVietnamInternationalLawFirm: updates/news/391vietnamsnewlawonhousing.html U.S.ArmyCorpsofEngineers.(2008).FeasibilitystudyandenvironmentaassessmentsCanonsnurg Lakeecoystemrestorationproject.PittsburgDistrict. U.S.ArmyMapService.(1984).HoiAnsheet:66401series:L7014edition:3DMA. UNESCO.(2008).TheeffectsoftourismofcultureandtheenvironmentinAsiaandthepacific. Thailand:UNESCOBANGKOK. UNESCO.(2009).CuLaoChamHoiAn.RetrievedDecember23,2015,fromUENSCOMABBiosphere ReserveDirectory: UNESCO.(n.d.).BiosphereReserves.RetrievedDecember23,2015,fromEcologicalSciencesfor SustainableDevelopment: sciences/environment/ecologicalsciences/biospherereserves/ USarmycorpsofengineers.(2007).ShoreProtectionAssessment. Viet,&Tanaka.(2015).PossiblemechanismofsevereerosiononCuaDaiBeach.VietnamJapan WorkshoponEstuaries,CoastsandRIvers(p.28).HoiAnCity:CentralRegionCollegeof TechnologyEconomicsandWaterResources. Viet,N.T.(2015,December8).personalcommunication. VietnamNews.(2013,June25).HoiAnpromotesheritagetourism.RetrievedNovember24,2015, fromvietnamnews.vn: tourism.html VisitHoiAn.(2015).RetrievedNovember23,2015,fromVisithoian.com: VuThiThuThuy.(2003).StormSurgeModellingforVietnam'sCoast.Delft:InternationalInstitutefor Infrastructural,HydraulicandEnvironmentalEngineering. Wang,Z.,Hoekstra,P.,Burchard,H.,Ridderinkhof,H.,DeSwart,H.,&Stive,M.(2012). MorphodynamicsoftheWaddenseaanditsbarierislandsystem.Ocean&Coastal Management68,pp WEPA.(2015).Stateofwaterenvironment,waterrelatedissuesandpoliciesinVietnam.Retrieved fromhttp:// Xie,S.L.(1981).Scouringpatternsinfrontofverticalbreakwatersandtheirinfluencesonthestability ofthefoundationsofbreakwaters.delft:delftuniversityoftechnology. 36 CoastalerosionHoiAn

43 37 CoastalerosionHoiAn List of figures Figures Figure2.1ErosionproblemsinHoiAn2 Figure2.2HotelsandresortsatCuaDaiBeach(Booking.com,2015)2 Figure2.3Systemboundariesatprovinciallevel(left)andcitylevel(right)4 Figure3.1EvolutionoftheHoiAncoastbasedonLandsatimages(Hoang,Tanaka,Viet,&Duy,2015)6 Figure3.2Coastalfeaturesofthebeachat>HoiAn(EditedmapfromGooglemaps)6 Figure3.3Coastclassification(Boyd,Dalrymple,&Zaitlin,1992)6 Figure3.4RivernetworkoftheVuGia ThuBonbasins(Long,Tung,&Huy,2013)7 Figure3.5Developmentsofadeltaiccoastlinewithnormallyincidentwaves(Bosboom&Stive,2015)9 Figure3.6Spitformationatarivermouth(Bosboom&Stive,2015)9 Figure3.7EstimatedsedimenttransportdirectionsbyProfessorStive(Stive,2015)9 Figure3.8Left:profileduringdry(calm)season.Right:duringwet(rough)season(Bosboom&Stive,2015)10 Figure3.9Contouredareas,basedon(Tanaka,Hoang,&Viet,2016)10 Figure4.1Powerversusinterestdiagram13 Figure5.1Orderofmagnitudeoftheinfluenceofmainandsecondarydriversofthethreehypotheses18 Figure6.1Threealternatives21 Figure6.2Coastlineimpressionwithlargenourishment22 Figure6.3Coastlineimpressionwithmediumnourishment+groynes22 Figure6.4Coastlineimpressionwithsmallnourishment+revetment23 Figure6.5Crossshorelocationofnourishment24 Figure6.6Nourishmentintervalstrategy24 Figure6.7Dunefix25 Figure6.8Quicklocalfix25 Figure6.9ZoningCuaDaiBeach26 Figure6.10ZoningsouthofThuBonriver27 Figure6.11Crosssectionwithadaptionprofile27 FigureA.1Vietnamoverview(JohoMaps,2015)40 FigureA.2MapofHoiAn40 FigureA.3CuaDaiBeach(Vietnamheritagetours,2015)41 FigureA.4CuaDaiBeachresorts(Vietnamdiscovery,2015)41 FigureA.5Studyareaprovince42 FigureA.6HoiAnBiospherezones(Thao,2015)43 FigureA.7ChamIslandMarineprotectedarea44 FigureB.1Goaltreenationalgovernment65 FigureB.2Goaltreeprovincialgovernment66 FigureB.3Goaltreecitygovernment67 FigureB.4GoaltreecitizensofHoiAnlivingfromthebeach68 FigureB.5Goaltreeresortmanagers69 FigureB.6Goaltreebuildingindustry70 FigureB.7Goaltreesandminers71 FigureB.8Goaltreetourists72 FigureC.1TheBruunruleexplainedvisually(Bosboom&Stive,2015)75 FigureC.2MapbathymetryEastSea/SouthChinaSeanearHoiAn(U.S.ArmyMapService,1984)76 FigureC.3WavecompassoftheoffshorewaveclimateofHoiAn(ARGOSS,2015)77 FigureC.4HistogramoftheoffshorewaveclimateofHoiAn(ARGOSS,2015)77 FigureC.5TidechartHoiAn(Tideforecast,2016)78 FigureC.6Bathymetryandcrossshoresandbalance79 FigureC.7Erosionschematisation80 FigureD.1Estimationofsedimentsupplybycomparablecatchmentarea(Viet&Tanaka,2015)81 FigureD.2Riversectionusedforthecalculations84 FigureE.1RiverconnectionsbetweentheVuGiaRiverandThuBonRiverdistributingdischarge87 FigureE.2ExploitablegroundwaterinBillionm 3 /year(nationalwatersectorprofile,2002)88 FigureE.3Sedimentbalanceofariversegment(Mangor,2008)88

44 38 CoastalerosionHoiAn FigureE.4Initialdeformationandpropagationofatrenchtowardsthedownstreamendoftheriver89 FigureE.5SandminingonThuBonriver90 FigureE.6HydropowerdamsintheThuBonriver(ADB,MONRE,EVN,MOIT,QuangNamDONRE,2008)91 FigureE.7NarrowingbyreclamationforthebuildingoftheCuaDaiBridge92 FigureE.8Earthplates(JohoMaps,2015)93 FigureE.9Shorelinechangeduetoincreasedroughconditions94 FigureE.10Consideredcrossshoreprofile.(Chang,2015)96 FigureE.11DatafittedtotheBruunprofilefromFigureE.1096 FigureE.12DUROS+resultfor1/50yeartyphoonconditions97 FigureE.13HssandTpfittings99 FigureE.14DUROS+resultfor1/5yearconditions100 FigureE.15Observedsandbarinin1989.Adaptedondatafrom(Hoang,Tanaka,Viet,&Duy,2015)100 FigureE.16Coastlinevariationbetween1975and1991(Hoang,Tanaka,Viet,&Duy,2015)101 FigureE.17Coastlinevariationbetween1975and2015(Hoang,Tanaka,Viet,&Duy,2015)102 FigureE.18Directionofsedimentoutflowfromtheriver103 FigureF.1LocationsofcoastalprotectionmeasuresalongCuaDaiBeach104 FigureF.2Manlookingdownatfailureoftheimprovisedsandbags104 FigureF.3Geotextilesandbagsalonga105 FigureF.4Schematiccrosssectionofsandbagrevetment105 FigureF.5BreakwaterinfrontofVictoriaresort106 FigureF.6Longgeotextilebagsascoreofapermanentbreakwater(TenCate,2015)106 FigureF.7LshapedbreakwateratGoldenSandsresort106 FigureF.8Concreterevetment107 FigureF.9Schematiccrosssectionofconcreterevetment.107 FigureF.10CollapsedHoiAnHideawayresort108 FigureF.11Schematiccrosssectionofseawall.108 FigureF.12Casuarinaequisetifolialocatedonspit109 FigureF.13Staggeredpatterninplantingvegetation109 FigureF.14CurrentfailedseawallinHoiAn109 FigureF.15Failuremechanisms.Seawardoverturning(left)toescourandrotation(right)110 FigureF.16Typicalbottomscourprofilesforfine(left)andcoarsematerial(right)111 FigureF.17Groundwaterflowthroughtoecylinder(Hoop,2006)111 FigureF.18Downwardprofilechangeswithaninfinitelylongrevetment112 FigureF.19Landwardmigratingprofilewhenafiniterevetmentisconsidered112 FigureG.1Causaldiagram116 FigureH.1Nourishmentwidthofdifferentcoastalsections127 FigureH.2Basicdesignofalternative128 FigureH.3Expectederosionandaccretionnexttoagroyne.129 FigureH.4Currentrockrevetments131 FigureH.5Effectofthegroynefieldwithoutnourishments132 FigureH.6Dimensionsandstackingofthelonggeotextilebagsforthetrialgroynes133 FigureH.7Locationofrevetments134 FigureH.8Beachwidth136 FigureH.9Shiftingoferosion136 FigureH.10Visualoverviewofdifferentbeach/bedlevels137 FigureH.11Revetmentsurface137 FigureH.12Stairsexample137 FigureH.13Topviewwithnewbeachwithrevetment138 FigureH.14Topviewandimpressionofboulevard(Verkeersbureausinfo.nl,2014)138 FigureH.15Landclassification139 FigureH.16Sandsources140 FigureH.17Crossshorelocationofnourishment141 FigureH.18Nourishmentintervalstrategy142 FigureH.19Longshorenourishmentlocations142 FigureH.20Focuspointsofnourishments143 FigureH.21Differenceinresources(GoogleEarth,2015)145 FigureI.1Photoseriesofmeasurementstick147

45 FigureI.2Graphindicatingthelengthofthestickasfunctionoftime148 FigureI.3Graphindicatingtherelativeverticalbeachchangeasfunctionoftime148 FigureI.4Observationsmap149 FigureI.5Fieldworkriverobservation149 FigureI.6Sandminingexample149 FigureI.7Locationsofthesedimentsamples150 FigureI.8Sieves150 FigureI.9Gradationofsoilbydrysievingmethod151 FigureI.10Grainsizedistributioncurve(Verruijt,2012)151 FigureI.11Grainsizedistributionsofbeachsamples153 FigureI.12Grainsizedistributionsofseasamplescomparedtobeachsand153 FigureI.13ResearchlocationsseabedEastSea/SouthChinaSea154 Tables Table3.1Thethreedifferentsedimentestimates7 TableB.1TaxincomeHoiAnfromhotelsCuaDaiBeach73 TableC.1Sandbalancecalculation79 TableC.2Tablesummaryofuseddataforerosion80 TableD.1Sedimentdischargeriversections83 TableD.2SedimentdischargecalculationwithformulaofGrayandSimoes85 TableE.1Sedimentreductionduetodam91 TableE.2Waveheightcalculation98 TableE.3Waveperiodcalculation98 TableE.4ExtrapolationofHssandTpforlongerreturnperiodsbasedonmeasureddatafrom(hi,2010)99 TableG.1Weightofdifferentcriteria123 TableG.2Currentlyusedmeasures124 TableG.3Otherpossiblemeasures124 TableH.1Totalneededbeachwidth126 TableH.2TotalnourishmentwidthsofdifferentpartsofCuaDaiBeach127 TableH.3Requiredstonesizes(D n50 )forthegroynesindicatedfordifferentreturnperiods131 TableH.4MeasuredstonesizesatVictoriaandGoldenSandresort,categorized131 TableH.5Referenceprojects134 TableH.6Sandsourcesoverview140 TableI.1WeeklymeasurementsofthesticklengthatCuaDaibeach,HoiAn.147 TableI.2Classificationofsoils(Verruijt,2012)151 TableI.3GrainSizeDistributionCurveResults CoastalerosionHoiAn

46 A.Area Inthisappendixsomeextrainformationabouttheareaisgiven.Itstartswithashortintroduction aboutvietnamanditsrecenthistory.afterthis,theareaaroundhoianwillbedescribedinmore detailtogivesomebackgroundinformationofthehoianarea.inparagrapha.2thereiselaborated on the study area, after which the regulations related to the Cham Islands are given. In the next paragraphanoverviewofcoastalerosionproblemsinvietnamisgiven.thischapterendswithsome legalaspectsrelevantforthisproject. A.1 Vietnam and Hoi An Vietnam is a Southeast Asian country with a relatively long coastline.asareference:itscoastlinestretchesasfarasthe coastfromdenmarktoportugalwithanareacomparableto Germany(ThiaEng,2015).Withapopulationofmorethan90 million people Vietnam is in the top 15 of the world's most populated countries with a GDP of 1,902 dollar per capita (Landenwijzer Vietnam, 2014). The GDP is fairly low at the moment, but with a sustained 6% expected growth for the coming years it is expected to improve in the future. While having multiple religions, in the recent centuries there have been no religious tensions in the country. Most practiced religionsarebuddhismandcatholicism. InthewholeofVietnamthereisacommunistsystemwitha onepartystatesincethecountrywasunifiedin1975.while still having a communist party system, more and more capitalistic ideas are allowed to support economicgrowthinthecountry.thereare58provincesinvietnamandfivemunicipalitieswiththe samestatusasaprovince.whilethereisasubdivisioninsmaller,morelocalpartitions,theprovinces haveanimportantpartinthedecisionmakingandfundsallocation(provincesofvietnam,2015). HoiAnisacoastalcitylyingatthemouthoftheThuBonRiver.ItispartoftheprovinceofQuang Namandhasaround120,000inhabitants.It usedto beanimportant portin the middle of Vietnam and with it came wealth to the city.thismightbepartlyduetothefactthat Hoi An is translated in English as "peaceful meeting place". When the French got the exclusivetradingrightstodanang,acity50 km to the north of Hoi An, and when siltation of the harbour of Hoi An started, thetownstoppedtobeimportant.thiswas aroundtheendofthe18thcentury(visithoi An,2015).Duetothisdeclineinimportance the city stayed quite the same until now. Even during the Vietnam war the town survived quite well. Partly because both sideswanteditso(unesco,2008). FigureA.2MapofHoiAn FigureA.1Vietnamoverview(JohoMaps, 2015) 40 CoastalerosionHoiAn

47 In1999UNESCOdeclaredtheoldtownofHoiAntobea'WorldHeritageSite'(UNESCO,2008).This increased the amount of tourism to Hoi An substantially while also the amount of tourism in the wholeofvietnamrose.theamountofinternationalvisitorstovietnamincreasedfrom1.8millionin 1999to7.9millionin2014(MinistryofCulture,Sports&Tourism,2014).HoiAnanditsinhabitants wealthincreasedwithit.inthelasttwentyyearsbeachhotelswerebuiltnearthefamouscuadai beach to provide luxury resorts for tourists. In both pictures below the new touristic situation is depicted, but it is showing the difference in beach use. More small investment based, flexible vendersusethebeach,whereasbeachresortsrequirealargeinvestmenttostartwithbybuilding permanentstructures. FigureA.3CuaDaiBeach(Vietnamheritagetours,2015) FigureA.4CuaDaiBeachresorts(Vietnamdiscovery, 2015) 41 CoastalerosionHoiAn

48 A.2 Study area LandwardsofHoiAnalargeriversystem(theVuGiaandThuBonrivers)ispresent,whichoriginates inthehighmountainsontheeastsideofthetruongsonmountainrangeandflowsoutintothesea throughthehoiananddanangrivermouths.thethubonriveristheoneimportantforthehoian coastwithrespecttosedimentanddischarge.theaverageannualdischargeofthethubonriveris 327m 3 /s(viet&al.,2014).inthewetseason,thewavedirectionisfromthesouthandthedischarge oftheriverishigh,whichcausesthesedimentintherivertobewashedseawards.asaresult,alarge amountofsedimentisdepositedattheoutsideoftheestuary.theriveractsasasedimentsourcein the wet season, which increases the volume of the ebb tidal delta. In the dry season, the wave directionisfromthenorthandthedischargeoftheriverisverylimited.duringthistime,themore severewaveclimatehasalargeeffectonthedevelopmentofthecoastalstretch. FigureA.5Studyareaprovince If we zoom in at Hoi An, we find a more detailed overview of our study area. It consists of the beachesnorthofthethubonrivermouthwhichhavealengthofapproximately4km.presently,this coastalstretchisrapidlydevelopingintoahighclasstouristresortarea.theshapeofthedeltamight giveussomeinformationaboutthesedimentflowpatternsinthestudyarea.aspitisformedjust northofthethubonriverestuary,whichindicatestheflowshouldbetowardstheriverinlet.onthe southsideoftheriver,awavedominatedcoastisobserved,whichhasarathersmoothshoreline withwelldevelopedbeachesanddunes.ingeneral,theshapeissymmetricallycuspate.basedonthe studyofviet&al.(2014),itcanbeseenthatthetipofthissandycoasthasbeenmigratedfurtherto thesouth. InfrontofHoiAnliesChamIsland,whichinfactisagroupofonelargeislandandsevensmaller ones. The distance to the coast is 16km and 19km to the town of Hoi An. Probably due to Cham Island,theflowpatterninfrontofthewholecoastalstretchchangesinsuchawaythatadifferent shapeisobservedateithersideoftheriverestuary. 42 CoastalerosionHoiAn

49 A.3 Cham Island protected area TheoldtownofHoiAnhascarriedthenameofWorldHeritagesitesince1999.Andduetothecities relationshipwiththeestuaryandharmonywithnaturetheareaofhoianisdesignatedasworld BiosphereReservein2009(UNESCO,CuLaoChamHoiAn,2009).BiosphereReservesaredivided intothreezones:acorezone,bufferzoneandtransitionzone.thecorezoneisastrictlyprotected ecosystem.thebufferzonesurroundsthecoreareaandisusedforactivitiesthatbenefitscientific research, education and monitoring. The transition zone of the reserve allows the most activities withsustainableeconomicandhumandevelopment(unesco,biospherereserves,n.d.).howthe zonesaredistributedinthehoianbiospherereserveisgiveninthepicturebelow.thechamislands formthecoreareaofthereserve.theoldtownofhoiantogetherwiththesurroundingseaforms thebufferzone.thetransitionzonesliesnorthofhoian. FigureA.6HoiAnBiospherezones(Thao,2015) Thecorezone,formedbytheChamIslands,isalsoaMarineProtectionArea.Thiszonewascreated for the conservation of its marine resources and biodiversity and improvement of the local livelihood (Management of Cham Islands, 2014). The area is again divided into different zones, depicted in the following map. There are several strictly protected core zones, given with the red areas. The conservation of the coral reef ecosystem makes any kinds of visiting prohibited. This impliesthecollectingofcoralandsamples,butalsoexcursions,swimmingorotherformsoftourism. A large part of the island s coast forms tourism development zones. Touristic activities are concentrated in this area to provide income for the local people. Other important zones are the rehabilitation zones. The activities in these zones focus on the recovering of ecosystems. It might thereforebepossiblethatpartoftheseareasbecomeprotectedcorezonesinthefuture(nhung, 2010). 43 CoastalerosionHoiAn

50 FigureA.7ChamIslandMarineprotectedarea A.4 Coastal erosion problems in Vietnam Vietnam has a 3,260km long coast, with on average every 20km a river mouth (Cat & al., n.d.). Coastal erosion is not a problem unique for Hoi An. On multiple locations along the Vietnamese coast,erosionoccurs,differinginintensityandcauses.inthispart,anoverviewofsimilarproblems tothehoianerosionisgiven. NorthVietnam MostnorthinVietnamliestheQuangNinhregion.Duetothetopography,erosionisonlyoccurring onshortsections.furthermorethisregionisshelteredagainstwavesbythemainlandofchinaand thechineseislandofhainan.however,theotherlargepartofthenorthernregionisdominatedby theredriverdelta,ofwhichlongcoastalsectionsinthesouthernpartareeroding. Theproblemsinthisregionarecausedbyacomplexplayoferosionandsedimentationnearriver mouths.neartherivermouth,sedimentcansettlewithahighrate,whilefurtherfromthemouth severeerosionoccurs.typhoons,causinghighwaveaction,aredestroyingthebeachesafterwhich the longshore currents can redistribute the sediment over a long stretch of coasts. This causes erosion in on region and sedimentation in another. The construction of dams further limits the sedimentsupplyandincreasingtheerosionrate.forthedinhvuregion,thecauseoferosionisthe subsidenceoftheestuaryincombinationwithsealevelriseduetoclimatechange.theactionsof wavesandtidearenotinequilibriumwiththecurrentbeachprofileandarethereforereshapingit. CentralVietnam All coastal provinces in the Central region of Vietnam are dealing with coastal erosion (Cat & al., n.d.).theriversinthisregionareshortandcarryalowsedimentcontent,whiletheseahasrelatively the highest wave energy. In the Quang Nam province alone, in which Hoi An is located, eighteen coastalsectionsareeroding.onthetotal1765kmlongstretchfromthanhhoaregionsouthofhanoi tobinhthuanregionalittlenorthofhochiminhcity,392kmofthecoastiseroding.theratesat whicherosionoccursdiffers.themoreirregularshapedcoastswithbaysandpeninsulasareeroding atalowerrate.moststrongerosionoccursonconvexsandycoasts,whofacemorewindandwave directionsthanconcavecoasts.43%ofthecentralvietnamesecoasterodeswitharateof1530m peryear,ofwhichsomeregionsaredealingwithover100mperyear(cat&al.,n.d.). 44 CoastalerosionHoiAn

51 Althoughtheprocessoferosionisdifferentperlocation,itcanbesaidthattheoverallrateoferosion isstillincreasing,especiallysince1990. QuangNgaiprovince,locatedsouthoftheQuangNamprovince,iserodingwiththehighestintensity ofallregionsalongthe centralcoast. Atotallengthof60kmiserodinganddespiteofreinforcing measures, erosion still continues. Revetments, piling, protective walls and tree plants are unsuccessfulinstoppingit.untilthecauseoferosionisnotfound,thepreventivemeasuresarenot efficient.differentcausesforerosioninthispartofvietnamincludinghoiancanexist,whichare furtherspecifiedinchapter5orappendixe. SouthVietnam Basedonsurveysandmaps,noerosiontookplacebefore1940inthesoutherncoastalareas.Since 1960erosionbecameacommonproblemhereandsince1995ithasbeencausingseriousproblems. Not only a disappearing beach is problematic, also the threatening of residential areas, increased floodsandsalineintrusionareaffectinghumanlivesandeconomicdevelopment(thao,2014). Alsointhispartofthecountry,therateandintensityoftheerosiondiffersperlocation.Oneofthe provinceswithsevereerosionistheprovinceofhochiminhcity.theconstructionofadamisoneof thereasonsforasedimentdeficitandincreasingerosionrate.theprovincelocatedmoresouthis alsodealingwithareducedsedimentsupply,thistimecausedbytheconstructionofirrigationand flood channels. Also the destruction of mangrove forests, which used to protect the coast from extremewaveactions,isalocalreasonforerosion. A.5 Legal aspects A.5.1Landownership AccordingtotheVietnameseLawonLand,anindividualcannotownapieceofland.Article5.1from the Law on Land No QH11 about ownership of land states: Land belongs to the entire peoplewiththestateastherepresentativeowner,meaningthatlandisacollectivegoodinvietnam andthevietnamesestateistheadministrativeowneronbehalfofthepeople.however,thestate canallocateorleaseapieceoflandtoanindividualorentity.thedurationofthisrighttousethe landandthepurposeforwhichthelandhastobeusedisdeterminedbythestate,followingfrom thelandzoningandplanning. After being allocated a piece of land, the land user receives a so called land use right (LUR) certificate.thislurisgrantedbythepeople scommitteeonprovincialordistrictlevel,depending onthetypeoflanduseanduser.thedistrictpeople scommitteeisallowedtograntlurcertificates to domestic or overseas Vietnamese and for residential use only. The provincial level has the authoritytoalsoallocatelandtoreligiousandforeignentities.(binh,2011) Althoughyoucannotownland,withaLURcertificateyouhaveseveralrightstohavecontrolover yourland.besidesusingit,therearerightstogetamortgageandleaseorsubleaseittoanother party.thepieceoflandcanalsobetransferredtogetherwiththecertificateforthespecificduration andpurpose.however,eachtypeoflanduserhasdifferentrights.vietnamesecitizenshavemore landuserightsthanoverseasvietnameseorforeignersanddifferencesexistbetweenforeignerswith diplomaticfunctionsorwithout. ComparedtoVietnamese,therightstoleasealandasforeignerareverylimited.Untilrecentlythe samewasthecasefortheabilitytobuyahouseinvietnamasforeigner.injuly2015thelawon HousingNo.65/2014/QH13wastakenintoaction,whichincreasedthepossibilities.Withthisnew law, foreign organisations and individuals have the same right to own houses as domestic Vietnamesecitizens.However,theamountislimitedto250separatehousesinthesameareaand 30%oftheapartmentsinanapartmentbuilding.(Tung&Hien,2014) 45 CoastalerosionHoiAn

52 A.5.2.Coastalmanagement Bylaw CoastalmanagementinVietnamisapproachedthroughseverallevelsofgovernmentalagencies.On the highest level, ministries are responsible for making policies for their sector and implementing them. The most relevant ministries for coastal related issues are the Ministry of Resources and Environment and the Ministry of Agriculture, Rural Development and Planning. The first one is responsible for environmental monitoring and maintaining the quality of water resources. The second ministry s tasks are water quantity management, flood protection and coastal defence. Furthermore, the Ministry of Planning and Investment is responsible for the financing and spatial planningofinfrastructureatthecoast(thang,n.d.).thepoliciesoftheministriesareimplemented perprovincebythepeople scommittee,whoareinturnresponsibleforthedevelopmentoftheir ownprovince. The Law on Environmental Protection No. 55/2014/QH13 is important for developments in the coastal zone. This law provides the rights, duties and obligations of governmental bodies, organizationsorindividualswhoareengagedinthetaskofenvironmentalprotection.itisimportant that all protection measures are in line with the planning for land use, which is made at national level.thisplanningisbasedonanassessmentofthecurrentenvironmentalstatusandthezoningof the environment and land use. The actions on provincial level must be aligned with this national planning. This provincial planning should also be made in consult with district level People s Committeeandrelevantagenciesandorganisations. Inpractice Althoughalotofregulationexistsforcoastalmanagement,inpracticeitdoesnotalwaysworkout well.accordingtoresearchbydenniseucker,integratedcoastalapproachesareoftenunsuccessful in Vietnam due to incomplete communication and favouring of certain sectoral interests (Eucker, 2008).Alsocertainaspectsofcoastalmanagementaredifficulttounderstand,makingitevenharder to get an integrated approach. Furthermore, the distribution of power can be uneven and the decisionmakingisoftentopdownratherthanbypartnershiponlocallevels.accordingtothesame research,localcommunitiesinvietnamoftenfeelunderminedbyauthoritieswithlimitedinterests. StatedintheLawonLand,thecoastalzoneismanagedbythestateandtheuseofitshouldfitthe nationalplanning.inpracticeitcantranslateintopeoplebeingabletoexploitresourceswherever theylike. As said before, several ministries are responsible for the coastal zone. All of them have to be consulted for major changes in the coastal zone, making it a resource consuming process. Unfortunately,asinglepartyforcoastalcoordinationdoesnotexistandthecooperationbetween thedifferentministriesisnotalwaysthatwell.theabovemakesitdifficultforcitizenstoparticipate incoastalmattersandresultsinagapbetweenpoliticalandsocialinterests. 46 CoastalerosionHoiAn

53 B.Stakeholders Thisappendixgivestheextensivestakeholderanalysis.Itstartswithalltheanswerstotheinterviews and questionnaires, which is summarized in the second paragraph. After this, each stakeholder is analysedusingproblemstatementsandgoaltrees.oneothercomponentisaddedtothisappendix, whichisanestimationofthevalueofthehotelsalongcuadaibeach. B.1 Interviews InHoiAn,severalresortmanagers,touristsandlocalsareinterviewedtogaininsightsinthecurrent problemandhowtheyfeelaboutit.thispartoftheappendixshowstherawdatathatisrequired withit. B.1.1.Resorts VictoriaHoiAnBeachResortandSpa Interviewee GeneralManager,Frenchmanwhohaslivedherefor20years Resortlocation AtCuaDaiBeach,dealingwithheavyerosion Date 2December2015 Onrequestoftheintervieweethisinterviewisleftoutofthereport. Itisareputationissue,whenyouhavehadabeachbefore,butnotanymore.15yearsagothesea wall was built 45m from the highest tide, now all that beach is gone, since the erosion started in 2008.Theamountofguestshasdeclined,buttherearealsomanycompetitorsinHoiAn,duetoHoi An spolicy.wehavenodiscountontheroomsbecauseofthebeach. 2.Do/didyouorganiseactivitiesonthebeach,ifyes,whichone? Before,yes.Therewereparties,coconuttrees,abar,lyingatthebeach,massages. 3.Last30yearstherehasbeenalotofsanddisappearingfromthebeach.Whohavetriedtosolveit andweretheysuccessful? Vietnamisacommunistcountry,sothegovernmentshouldtakecareofit,butthisisnotalwaysthe case.thepeople scommitteegiveswrongadvice,becausetheyarenoexperts. We have had a big investment this year. There is also no cooperation with other resorts, which is stupid.wehavehadmeetingswithotherresorts,butintheendeverybodymakestheirowndecision. Themanagersworktogether,buttheownersdonotcooperate. Also,RoyalHaskoningDHVcomeshereregularlytoinvestigate. 4.Haveyoutriedsomethingtoprotectthebeach?Whatkind,whenandaloneorincollaboration? Thisyearweplacedthesandbagprotectionaroundtheproperty.TheconstructionstartedinJune andfinishedinseptember.itisasystemfromjapanandfrance,calledgeotubes.thesandbagsare placedintwolinesoffshore. 47 CoastalerosionHoiAn

54 Thepurposeisthattheybreakthewavesinthestormyseasonstoprotecttheproperty.Thissystem worksverywell.lastyear,whentherewerenosandbags,therewaserosionatthewall.butnotall peopleunderstandthisconceptandstillbuiltconcretewalls. 5.Whydidyouchoosethislocationfortheresort? Whenwecameherein1999,wehadoneofthebestlocations,placedbetweentheriverandthesea. Itwaswonderful.Weevenbuilttheroadtotheresortourselves,becausetherewasnoneyet. 6.Whatisyourexpectationofthefutureoftheresortandthebeach? Iamnotscaredaboutthebeach.WehavesomebeachleftbetweenthisresortandGoldenSands. However,toomanylicensesaregiventohotelsandrestaurant.Noweverybodycanopenwhatthey like. Danang is better. The prices in Hoi An are crazy. Danang has more activities, so Vietnamese touristscometohoianinthedayandsleepandpartyindanang. There is also a large resort being built 3km from here, with 800 rooms. That will likely affect the VictoriaResort. 7.Doyouthinkthebeachwillbedifferentin10years? Thesandmightcomeback,maybeitisacycle.SandneedstocollectbetweenthetwoGeotubessand baglines. Theerosionstartedbyworkatthebeachandintheriver. 8.Whichsolutiondoyouthinkisthebestsolution? Idon tmakesolutions.wehireprofessionalsbasedonreferencesofsuccessfulprojects.likeadoctor, whereyougotowhenyouaresickandyouexpecttheywillhelpyouintherightway. The Cua Dai Beach is disappearing and now the government starts thinking about copying the solutionofvictory,butitistoolate. Weneedacommonprojectforthewholebeach.Alltheresortsaredoingtheirownstuff.Wehave had4to5meetingssofarsince2008,butnobodywantstoworktogether.thereisalsolittlehelp fromthepeople scommittee. 9.Isthecurrentsituationgoodenoughorisabeachnecessary? Ofcourseweneedabeachasbefore.Itwasauniquelocation,withdirectaccessfromyourroomto the beach. But we cannot control nature. The same system of Geotubes is used somewhere else, wherethebeachcamebackinacoupleofweeks,butnotatthisresort.thereisacurvatureinthe CuaDaiBeach,aconclavebeachwouldcomebackmoreeasily. Thereshouldbemorecooperation.LikeacommonbeacherosionprobleminWestFrance,wherea 20kmprojectisimplemented. BoutiqueHotel Interviewee Resortlocation Date FrontOfficeManager,Vietnamese northofcuadaibeach/anbangbeach,wherethereisabeachleft 2December CoastalerosionHoiAn

55 1.Howdidthecoastalerosionimpactthehotelintermsofpriceoftheroomandtheamountof guests? Currently we have no worries about beach erosion. We have had no erosion since the opening in Do/didyouorganiseactivitiesonthebeach,ifyes,whichone? Notmuch,onlysunbathing.Noactivitieslikewatersports. 3.Doyouthinkthebeachwillbedifferentin10years? In10years,Idon tknow.butiexpectthatin5yearsthebeachwillstillbethesame.wearenot alongtheerodingcuadaibeach,butanotherone.maybetherewillbeerosion,butwedon tknow. 4.Whydidyouchoosethislocationfortheresort? Thislocationwaschosenbecausetherestwasalreadyoccupied. 5.TheresortsalongCuaDaiBeachallhavetheirownsolution.Howdoyoufeelaboutthat? Thelocalsnorthegovernmenthastherightsolutionyet.Thegovernmentisworkingonaprojectand ifneededwemightfollowthat. Thebestwayistoinvolvethegovernmenttocarryontheproject.Iunderstandthatotherswantedto protecttheirownpropertyfirst.butthebestwayisviathegovernment. 6.Isthecurrentsituationgoodenoughorismorebeachnecessary? TherearelesstouristsatCuaDaiBeach,Ithinksomewillcometousthen.Sowehaveabitofan advantagefromtheerosion. MuongThanhHoiAnHotel Interviewee EntertainmentManager,borninHoiAn(difficulttocommunicatewith) Resortlocation atcuadaibeach,butonlandsideoftheaucoroad Date 2December Whenhasthishotelbeenbuilt? Lastyear.Itisopenforelevenmonthsnow. 2.Doyouorganiseactivitiesonthebeach? Yes,foodbars,watersports.Everyonewantactivitiesatthebeach.Butnowtherearenoactivities, becausetheweatherisnotgood:highwater,wavesandwind. 3.Last30yearstherehasbeenalotofsanddisappearingfromthebeach.Whohavetriedtosolveit andweretheysuccessful? Due to high water and wind, the sand is disappearing. But the government comes around for a projectnow. 49 CoastalerosionHoiAn

56 4.Haveyoualreadytriedsomethingtoprotectthebeach? Wehavenoprojectyet,andalsonoplansfordoingaproject.Wehavetwopublicbeachesnearby: CuaDaiBeachandinfrontofthehotel.Also,ourhotelisfarawayfromthebeach,sothereisnoneed forprotectionlikearockwall. 5.Willthehotelbedoingbetterinthefuture? Yes,whynot?Itisanewhotel. 6.Isthecurrentbeachenough? Everybodywantsmorebeach.Toplayfootball,watersports,andotheractivities. HoiAnBeachResort Interviewee GeneralManager,Vietnamese Resortlocation AtCuaDaiBeach,butonlandsideoftheAuCoroad Date 3December Howdidthecoastalerosionimpactthehotelintermsofpriceoftheroomandtheamountof guests? Both reduced due to the erosion. The major erosion occurred around October 2014 and scared touriststocometocuadaibeach.lessguestsarecomingtohoianbeachresortandtheguestswho arecomingtotheresortwantabeautifulbeachwhichisn tthere,sotheresorthastocompensatefor that.wegiveadiscountofapproximately10%or20%foraroomattheseasideandalsothetourists whoarevisitingtheresorttrytogetadiscountwhentheyseethebeachisalmostgone.thebeachin frontoftheresortattheothersideoftheroadbelongstohoianbeachresort. 2.Do/didyouorganiseactivitiesonthebeach,ifyes,whichone? Beforetheerosionwhenitwasawidebeachalotofsportactivitieswereorganised.Sportactivities likevolleyball,jetskiing,kayakingandalsootherwatersports.nowthebeachisalmostgoneand thereisnearlynoareatoorganisetheseactivities.theresortorganisesonlythekayakingandhasa barwithdrinksandfoodstillleftandaddedsomeromanticactivities. 3.Last30yearstherehasbeenalotofsanddisappearingfromthebeach.Whohavetriedtosolveit andweretheysuccessful? Thepast30yearsthebeachwaswideandbeautiful.Lastyear,2014,therewassevereerosionand thebeachhasretreatedalot.theprovincialgovernmentorganisedseveralmeetingsandconferences aboutthebeacherosionlastyear,butitwastoolate. 4.Haveyoutriedsomethingtoprotectthebeach?Whatkind,whenandaloneorincollaboration? Before the storm season this year a lot of sandbags were placed on a talud to protect the beach againstmoreerosion.theplantoplacethosesandbagsisfromthegovernment,howeveritisnotso successful.thestorm,windandwavesstillaffectthesandbagsandthesandbeneathit,somesand bags are sinking. Manypeople andresortsincludingthelocal peoplearerequesting thecitiesand provincialgovernmenttodosomethingandrescuethebeach.thereasonforthetaludwithsandbags isthatpeoplewhowanttoswimstillcangodownwhenthewaterissavetoswim. 50 CoastalerosionHoiAn

57 5.Whydidyouchoosethislocationfortheresort? TheHoiAnBeachResortisopenedatthe15 th ofaugust2000.thelocationofthisresortisatapoint wheretherivermeetstheoceanandthatisthemainreasonofchoosingthislocation.thesloganof theresorthastodowiththat: Anoasisofthepeacewheretherivermeetstheocean. 6.Whatisyourexpectationofthefutureoftheresortandthebeach? The waves created by the storm are still a threat for the beach and the resorts located along the beach. We are scared for the storm which takes sand away from the beach and damages the protectionofsandbags.wehopetheerosionwillnolongeraffectthebeachsotheresortwillhavea beautifulandwidebeachwherewecanorganisemanyactivities. 7.Doyouthinkthebeachwillbedifferentin10years? Ifthecitiesandprovincialgovernmenthasnogoodsolutionwithin10yearsthebeachwillattackthe resortandtheerosionwillbeathreatfortheresort.theroadinbetweentheresortandthebeach willnotholdtheerosion,itwillthenalsodisappearduetothebeacherosion. 8.Whichsolutiondoyouthinkisthebestsolution? Thebeachhastobeaswideaspossible,becauseguestswantawidebeachtodoactivitiesonthe beachandtowalkslowlyintothesea. The offshore breakwater is the best solution because it breaks the waves and makes the waves smaller and less strong. In addition the local people could also use the beach behind an offshore breakwater.howeverthegapsinbetweenthosebreakwatersshouldbeasnarrowaspossible. Agroynehasanegativeeffectonthelandscapeandduetothefactthatitisbuildoutofrocksitis notsafetoswimnearbyagroyne. When a revetment is applied as beach protection there is no beach anymore so that is also no workingsolution. Thesandnourishmentcouldwork,butsinceitonlybringssandbacktothebeachanddoesnotgive anyprotectiontothebeachitmightnotbeaworkingsolution.furthermore,theextractionofsandat theseabottomisn tsafefortheenvironment. 9.Isthecurrentsituationgoodenoughorisabeachnecessary? Itisveryvaluabletohaveabeachandthesituationwhenthebeachwaswideandbeautifulshould comeback. WetoldabouttheinterviewwiththegeneralmanagerofVictoriaBeachResortandaccordingtothe generalmanagerofhoianbeachresorttheopiniontocollaborateasmuchaspossibleistheright opinion. Everyoneshouldcollaborateasmuchaspossibleandthegovernmentshouldlistentotheopinionof thehotelandresortownersandofthelocalpeople,thesupportofthecommunityisveryimportant. Localpeoplecancollaborate,howevertheirbudgetislimitedandsoontheirinfluenceonaworking solutionisalsolimited.thegovernmentshouldinvitecoastalexpertsfromabroadwhoknowwhatto do. Therearemanyreasonsofthecoastalerosionlikethedecreaseofsandandmudfromupstream.Too many people and resorts are extracting too large amounts of sand and mud from the river. Local peopletakesandfromtheriverwhichisactuallyforbiddenandthelocalpeopledonotprotectthe environmentwiththeiractions. 51 CoastalerosionHoiAn

58 52 CoastalerosionHoiAn Sunrisehotel Interviewee GeneralManager,German Resortlocation AtCuaDaiBeach,dealingwithheavyerosion Date 14December2015 Onrequestoftheintervieweethisinterviewisleftoutofthereport. TherearemasterplansmadebyAustraliaandtheNetherlands,readytouseandthegovernmentjust needstocreateafund.sunriseinvestedalotofmoneyintheprotectionoftheresortandmeanwhile thetouristbusinessisdecreasing.therealbeachbusinessisshiftingtodanang,leavinghoianfora fewhoursexcursiondestination.thebeachshouldbeimportant,theoldtownisnotthemoney makerhere.thenewsoferosionisnowwidespreadovervietnamandtherestofasia,andhoianis notpromotedasabeachdestinationanymore. 1.Howdidthecoastalerosionimpactthehotelintermsofpriceoftheroomandtheamountof guests? Negatively.Thepriceshavetodropinordertofilltherooms.Therearealsoincrementallossesfrom i.e.thespa.withthelowerroomprices,thetypeofcustomersischangingtoo. 2.Do/didyouorganiseactivitiesonthebeach,ifyes,whichone? Yes,wedosomesportandgamesonthefrontbeach.Thegovernmentalsoaskedforhelptoorganise someactivitiesforhoian;bigeventsthathavetoputcuadaiinapositivelightagain. 3.Lastyearstherehasbeenalotofsanddisappearingfromthebeach.Whohavetriedtosolveitand weretheysuccessful? Theerosionstartedin2011/12,whensomemajortyphoonshittheland.In2011westartedwith Geotubes,butdebrisfromtheriverslicesthemopen.Thesecondinvestmentwastoplace1000 sandbags,weighing2tonseach,ontheoutsideofthecurrentwall.thereweresevenlayersofbags placedontopofeachother.itwasamassiveinvestment.nowthewallonpilesisbuilt,costing around$700,000( 640,000).Thenextstepistoplaceabreakwater,butwehavenofundingyet.In totalwespentaround$2million( 1.8million)onprotection. 4.Whydidyouchoosethislocationfortheresort? Theconstructionstartedin2006/7andweopenedin2012.Itusedtobeawonderfulbeach,complete withcoconuttrees.itarenotonlythestormsthataffectedit,alsothehydropowerdamsupstreamin theriverandthesandmining,soseveralcontributingfactors.thereisalotofnewlandfilling,and thissandcomesfromtheriver. 5.Whatisyourexpectationofthefutureoftheresortandthebeach? In2016thegovernmenthastocreateafundandagreeonaninternationalproject.Allisalready submitted,theplansarethere.whykeepspendingmoneyonsandbags?itwasalreadyclearthat ourlargesandbagsdidnothold,nowtheyarestillusingsandbagsandevenmuchsmallerones.

59 6.Doyouthinkthebeachwillbedifferentin10years? Ifwecannotfindasolutionforthebeach,HoiAnwillfurtherdeteriorate.Thisisnottheonlyproblem. Therearealsotoomanyhomestays.Thedifferencebetweenhomestaysandmultistarhotelswastoo largeandthesehotelshadtodroptheirprices.hoianisbeingdestroyedwithoutanyonenoticingit. NowadaysHoiAnisnotmuchmorethana1000tailorsandrestaurants. 7.Whichsolutiondoyouthinkisthebestsolution? Breakwatersarethebest.Groinsdonotwork;duetotheverystrongcurrenttheyaresinking.Also thesandcomingfromtherivercannotdistributeevenlyalongthecoastwhengroinsareused.and breakwaterscanbebuiltrelativelyinexpensive.however,fishermendonotlikethisbecausetheyfeel likeitis their water.resortsareseenasthebadguyshere. Andsandnourishment? Ithinkthegovernmentdoesnotallowthis.Wealsohadsomedifficultiesfillingupourfrontbeach. No,breakwatersareneededwhenyouhavetodealwith8mhighwaves.Ourfrontvillashadtobe rebuildandtheswimmingpoolhasalreadysunkintotheseaonce.alsothegeotubesystemwillnot last. Shouldtherebecollaborationwithotherresorts? Itshouldbemanagedongovernmentlevel.Resortsalltrytoshowoffwiththeirownsolutions, showingtheyknowbest.however,alsotherocksfromgoldensandswereoncethrownaround duringastorm.meetingsbetweenmanagersarealsonoteffective.thegovernmentneedstofixit onceandforall.forexample,inthesummerthewateriskeptinthedams,releasingitinthewinter andcausingfloods.iftheydon ttrytofixithoianwilldie.butdanangalso,theerosionisalready movingnorthwards. Somesayclimatechangeisthecausefortheerosion. Climatechangeisnotthecausehere.Theproblemismismanagement.Thereissomanyinternational support,allfreeofcharge.itistimetouseit. Dubaihasanicesystemtoo,withhollowconcreteblocksthatreducethewaveactionontheislands. Normally,duringChristmasandNewYearwehave7080%occupancyandpeakingthewholeyear roundexceptforseptember.currentlywehave30%occupancy.itallwentwelluntiloctober2015. TherehasbeenalotofnegativitywhattheAsiansseeonthenews.Travelagentswillnottakethe risktosendinternationalstohoian,notknowingthatwestillhaveourfrontbeachandbeachatthe sideofourresort.promotionisverydifficult.butthereforewealsohavetheseeventsnextyear. Otherresorts Other resorts that could not be interviewed, but are sometimes referred to in this report are the following: AgriBankResort PalmGardenResort 53 CoastalerosionHoiAn

60 IndochineHotel GoldenSandResortsandSpa B.1.2.Tourists Interviewedduringthethreesunnydaysof9,10and11December2015. #1 Gender Age Nationality Male 30 German 1.HowlongareyoustayinginHoiAn?4days 2.DidyouchoosetostayinHoiAnforitsbeach?No,fortheoldtown 3.Whydoyougotothebeach?Relax,toswim 4.HowoftendoyougotothebeachinHoiAn?23daysduringmystay 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Afewhours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?No,becauseIdidn tknowaboutituntil now 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Iftheseawaseasieraccessible;ifthe wholebeachwasaccessibletothepublicandnotownedbyhotelsand/orresorts #2 Gender Age Nationality Male 30 Ireland 1.HowlongareyoustayinginHoiAn?3days 2.DidyouchoosetostayinHoiAnforitsbeach?No 3.Whydoyougotothebeach?Relax,dosports 4.HowoftendoyougotothebeachinHoiAn?Lessthaneveryweek 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Afewhours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?N/A,onlyoneday 7.DidyouknowCuaDaiBeachwaseroding?No 8. Do you care about the beach erosion at Cua Dai Beach? Yes, because we need to sustain our naturalresourcesandcounteractmasstourism. 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthewholebeachwasaccessibletothe publicandnotownedbyhotelsand/orresorts;whenthereisthepossibilityforkitesurfing 54 CoastalerosionHoiAn

61 55 CoastalerosionHoiAn #3 Gender Male Age 73 Nationality Sweed 1.HowlongareyoustayinginHoiAn?5nights 2.DidyouchoosetostayinHoiAnforitsbeach?Yes,mostly 3.Whydoyougotothebeach?Relax,running 4.HowoftendoyougotothebeachinHoiAn?Everydaythesunshines 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?4hours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach,Ithinkitis partofourhotel. 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,itmighteffectthisplacetoo. 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifitwaslesscrowded #4 Gender Male Age 40 Nationality German 1.HowlongareyoustayinginHoiAn?3days 2.DidyouchoosetostayinHoiAnforitsbeach?Yes,butalsofortheoldcityofHoiAn 3.Whydoyougotothebeach?Relax 4.HowoftendoyougotothebeachinHoiAn?Once 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Afewhours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach 7.DidyouknowCuaDaiBeachwaseroding?Yes 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseIgenerallycareaboutthe environment.butionlystayhereforashortholiday. 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthebeachwaswiderandlarger;ifthe seawaseasieraccessible #5 Gender Male Age 24 Nationality Australian 1.HowlongareyoustayinginHoiAn?2days 2.DidyouchoosetostayinHoiAnforitsbeach?Yes,butalsoforoldtown 3.Whydoyougotothebeach?Relax,toswim 4.HowoftendoyougotothebeachinHoiAn?EverydaythatIamhere

62 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Halfaday 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach 7.DidyouknowCuaDaiBeachwaseroding?Yes 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseitaffectsalotofpeople 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthewholebeachwasaccessibletothe publicandnotownedbyhotelsand/orresorts #6 Gender Age Nationality Male 19 German 1.HowlongareyoustayinginHoiAn? 2.DidyouchoosetostayinHoiAnforitsbeach?Yes,butalsoforthetown 3.Whydoyougotothebeach?Meetpeople,relax,dosports,toswim 4.HowoftendoyougotothebeachinHoiAn?Almosteveryday 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Halfaday 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,butI veneverheardaboutit 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthebeachwaswiderandlarger;ifthe seawaseasieraccessible;ifthewholebeachwasaccessibletothepublicandnotownedbyhotels and/orresorts;ifthereweremoreactivities #7 Gender Age Nationality Male 24 Australian 1.HowlongareyoustayinginHoiAn?6days 2. Did you choose to stay in Hoi An for its beach? Yes, but also for motorbike riding and tailored clothes 3.Whydoyougotothebeach?Relax 4.HowoftendoyougotothebeachinHoiAn?Everydayitisn training 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Afewhours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,ifthebeachiserodeditisdifficultfor peopletoenjoythebeach 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthebeachwaswiderandlarger;ifthe seawaseasieraccessible;ifthewholebeachwasaccessibletothepublicandnotownedbyhotels and/orresorts 56 CoastalerosionHoiAn

63 57 CoastalerosionHoiAn #8 Gender Male Age 60 Nationality UK 1.HowlongareyoustayinginHoiAn?2days 2.DidyouchoosetostayinHoiAnforitsbeach?No,fortheoldtown 3.Whydoyougotothebeach?Relax 4.HowoftendoyougotothebeachinHoiAn?AlmosteverydayIamhere 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Lessthananhour 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseIamanenvironmentalist 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthewholebeachwasaccessibletothe publicandnotownedbyhotelsand/orresorts #9 Gender Female Age 59 Nationality Canadian 1.HowlongareyoustayinginHoiAn?4days 2.DidyouchoosetostayinHoiAnforitsbeach?Yes,butalsoforsightseeing 3.Whydoyougotothebeach?Relax 4.HowoftendoyougotothebeachinHoiAn?Lessthaneveryweek 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Lessthananhour 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?Nofavouriteyet 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthebeachwaswiderandlarger #10 Gender Female Age 30 Nationality USA 1.HowlongareyoustayinginHoiAn?2days 2.DidyouchoosetostayinHoiAnforitsbeach?No,touristlocations 3.Whydoyougotothebeach?Meetpeople,relax,dosports 4.HowoftendoyougotothebeachinHoiAn?AlmosteverydayIamhere

64 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Afewhours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?CuaDaiBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becausethebeachesarebeautiful 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthebeachwaswiderandlarger;ifthe wholebeachwasaccessibletothepublicandnotownedbyhotelsand/orresorts #11 Gender Age Nationality Female 35 USA 1.HowlongareyoustayinginHoiAn?3days 2.DidyouchoosetostayinHoiAnforitsbeach?Yes,butalsoforitslocationonourtravelsgoing south 3.Whydoyougotothebeach?Meetpeople,relax,dosports 4.HowoftendoyougotothebeachinHoiAn?Onceinthreedays 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Afewhours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?CuaDaiBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?No,becauseIwasunaware 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthereweremoreactivities #12 Gender Age Nationality Male 38 German 1.HowlongareyoustayinginHoiAn?5days 2.DidyouchoosetostayinHoiAnforitsbeach?Yes,butalsoforourhotel(MngThanhResort), surroundingsanditisquiet 3.Whydoyougotothebeach?Relax 4.HowoftendoyougotothebeachinHoiAn?Everydayitisnotraining 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Halfaday 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?CuaDaiBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseiftheerosionisleadingto failure,somethinghastobedone. 9.WhatwouldmakeyougotoCuaDaibeachmoreoften? Ialreadygothereeveryday 58 CoastalerosionHoiAn

65 #13 Gender Age Nationality Female 28 Belgian 1.HowlongareyoustayinginHoiAn?3days 2.DidyouchoosetostayinHoiAnforitsbeach?No,forthecityanditsculture 3.Whydoyougotothebeach?Relax,nature 4.HowoftendoyougotothebeachinHoiAn?Almosteverydaywearehere 5.Howmuchtimedoyouspendonthebeach,onaverage,whenyouarethere?Afewhours 6.IfyougotothebeachinHoiAn,towhichbeachdoyougomoreoften?AnBangBeach 7.DidyouknowCuaDaiBeachwaseroding?No 8.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becausethesituationisproblematic andthereisneedforapermanentsolution 9.WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthebeachwaswiderandlarger;ifthe wholebeachwasaccessibletothepublicandnotownedbyhotelsand/orresorts;iftherewereno extracostsfori.e.parkingofbicycles. B.1.3.Restaurant/barsinterviews #1 Restaurant/barname Gender Age Nationality QunchinRestaurant Male 50 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoianfor50years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?Yes 3.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseIsellfoodatthebeach 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthebeachwaswiderandlarger 5.HaveyoutakenanyactiontodealwiththebeacherosionatCuaDaiBeach?Yes,buildingthesea dike,piling #2 Restaurant/barname Gender Age Nationality Donutstall Male 41 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoianfor41years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales? 3. Do you care about the beach erosion at Cua Dai Beach? Yes, because it affects the economic activitiesoflocalpeople.andthelandscapeandcivilizationoftheancientcity. 59 CoastalerosionHoiAn

66 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthebeachwaswiderandlarger;ifthere weremoreactivities;ifthewholebeachwasaccessibletothepublicandnotownedbyhotelsand/or resorts 5. Have you taken any action to deal with the beach erosion at Cua Dai Beach? I gave a hand to contributetoabettercommunity. #3 Restaurant/barname Gender Age Nationality Hidden Female 32 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoianfor32years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?No 3.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,Iwouldliketokeepthecoastlineso thatmoretouristswilltraveltohoian.itisaplacethattouristscanvisittorelaxandsunbathe 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthewholebeachwasaccessibletothe publicandnotownedbyhotelsand/orresorts 5.HaveyoutakenanyactiontodealwiththebeacherosionatCuaDaiBeach?Yes MyfamilyhaslivedinHoiAnformorethan100years.Theerosionandtheamountofresortsare reducingtheamountoftouriststhatcometohoian. #4 Restaurant/barname Gender Age Nationality RestaurantFamily Male 30 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor30years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?Yes 3.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseitreduceoureconomy.The touristsectorwillnolongerbe. 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthebeachwaswiderandlarger;ifthere weremoreactivities. Thereshouldbeinvestmentsfromdifferentclients,aswellasgovernmentallevelorganizations. 5.HaveyoutakenanyactiontodealwiththebeacherosionatCuaDaiBeach?Yes I have joined activities as building the sea dike, helping everyone carrying soil to the beach and protectingtheseaenvironment(waterresource,keepthebeachclean) Iwouldliketoseethatmoreforeignerswillcome,likeyou,andtalktous,fishermenandotherpeople alongthebeachtohelp,together. 60 CoastalerosionHoiAn

67 #5 Restaurant/barname Gender Age Nationality HoaHung Female 18 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor18years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?Yes,touristsdon twantto visitusbecausethereisnobeach.asaresult,wearehitinoureconomicactivities. 3.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,itimpactsourjobandwemightlose ourjob. 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthebeachwaswiderandlarger;Ifthere weremoreactivities 5.HaveyoutakenanyactiontodealwiththebeacherosionatCuaDaiBeach?Yes,Imadesandbags topreservethebeachinfrontofmyrestaurant.ihopethegovernmenthaspoliciestoovercomethe processoferosioninaneffectiveway. #6 Streetsaleswoman Restaurant/barname Gender Age Nationality Female 64 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor50years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?Yes 3.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becausetheerosionisimpactingour job.wemightloseourjob. 4.WhatwouldmaketheCuaDaiBeachmoreattractive? 5.HaveyoutakenanyactiontodealwiththebeacherosionatCuaDaiBeach?Ihelpedmakingsand bags,buttheywillbreakafteralongtime.ireallyhopethatthegovernmentwillpayattentionand helpuswithoureconomicactivities. #7 Restaurant/barname Gender Age Nationality RestaurantMinhVinh Male 62 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor62years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?Yes,lesstouristscome because the Cua Dai Beach is eroding. As a result, the economic activities of my restaurant are declining. 61 CoastalerosionHoiAn

68 3.DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,inthiserodingsituationIworryabout thesalesofmyrestaurant. 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthebeachwaswiderandlarger;ifthere weremoreactivities 5.HaveyoutakenanyactiontodealwiththebeacherosionatCuaDaiBeach?Yes,makingsand bags,plantingtrees.ialsobuiltatemporaryembankmenttokeepthebeachattractivetotourists. #8 Restaurant/barname Gender Age Nationality RestaurantVyQuynh Female 36 Vietnamese 1.DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor36years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?Yes 3. Do you care about the beach erosion at Cua Dai Beach? Yes, because the erosion of the beach affectsalotofpeoplefromhoianorpeoplethatworkhere. 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthebeachwaswiderandlarger 5.HaveyoutakenanyactiontodealwiththebeacherosionatCuaDaiBeach?Yes,Iencouragelocal peopleto help restaurants near the beach to prevent erosion, with hopefully a reducing rate of erosion. I hope Cua Dai Beach will no longer erode and I wish that all governmental level organisationshaveasolutiontoimprovethestateofthebeach. B.1.4.Otherlocals Fishermen Hobbyfisherman Gender Nationality Age Male Vietnamese DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor6years 2. Howoftendoyougotothebeach?Onceperweek 3. Howmuchtimedoyouspendonthebeachwhenyouarethere?Afewhours 4. IfyouusethebeachinHoiAn,whichbeachdoyouusemoreoften?CuaDaiBeach 5. DidyouknowCuaDaiBeachwaseroding?Yes 6. DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseCuaDaiBeachiseroding 7. Do you think the disappearing of the beach has an impact on your job? It will influence the ancientcityofhoian. 8. WhatwouldmakeyougotoCuaDaibeachmoreoften?Ifthebeachismadelargerandbigger, itwillbemoreattractivefortouriststocometohoian. 62 CoastalerosionHoiAn

69 Lifeguard Gender Nationality Age Male Vietnamese DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor50years 2. Howoftendoyougotothebeach?Almosteveryday 3. Howmuchtimedoyouspendonthebeachwhenyouarethere?Almostthewholeday 4. IfyouusethebeachinHoiAn,whichbeachdoyouusemoreoften?AnBangBeach 5. DidyouknowCuaDaiBeachwaseroding?Yes 6. DoyoucareaboutthebeacherosionatCuaDaiBeach?Yes,becauseitattacksourlife. 7. Doyouthinkthedisappearingofthebeachhasanimpactonyourjob? 8. WhatwouldmakeyougotoCuaDaibeachmoreoften?Wewouldliketokeepabeachthatis largeandbeautiful. BicyclekeeperCuaDaiBeach Gender Male Nationality Vietnamese Age 30 1.DoyouliveinHoiAn?Yes,IhavelivedinHoiAnfor30years 2.DidtheerosionatCuaDaiBeachaffectyourbusinessintermsofsales?Yes 3.DoyoucareaboutthebeacherosionatCuaDaiBeach?Thenumberoftouristsgoingtothebeach hasdecreasedsignificantly.iworryeverydayaboutmycountryandthatitwillnotbeagainasitwas beforetheerosionofthebeachstarted. 4.WhatwouldmaketheCuaDaiBeachmoreattractive?Ifthewholebeachwasaccessibletothe publicandnotownedbyhotelsand/orresorts 5. Have you taken any action to deal with the beach erosion at Cua Dai Beach? Yes, urging the governmenttoinvestmoneyinbuildinganembankment. B.2 Interviews conclusion Usingtheinterviews,thefollowinglinecanbedrawnfortheopinionsoftouristsandlocalpeople. Thediversityamongresortmanagersmakesithardtoconcludeitinonecommonstory. B.2.1.Tourists SincethetouristsareresponsibleforalargepartoftheincomeofHoiAn,itisimportanttoknow what they expect from the beach. Tourists on both Cua Dai as An Bang Beach were given a questionnairetogettoknowthis.itisremarkablethatmostofthetouristsatanbangbeachdidnot knowabouttheerosionatcuadaibeach.mostofthemareonlystayingforacoupleofdaysinhoi An.Itcouldbethatthisisawinterseasonphenomenon,wheremosttouristsaretravellingthrough VietnamorothercountriesinAsiaandnotstayingatthesamespotfortoolong.WhentheyvisitHoi An,itwasoftennotonlyforthebeach,butalsoforitsoldtown.Reasonstogotothebeachare mostlyrelaxingandswimming. 63 CoastalerosionHoiAn

70 Mostofthemwouldthereforeliketoseeawiderbeachwithaseathatiseasyaccessibleandalso morepublicbeach.alsomoreactivitiesisoftenmentionedasawishforabetterbeach. However,despitenotknowingabouttheerosionbyalotoftourists,mostofthemdocareaboutit, forvariousreasons.thetouristsatanbangbeachdidnotcareaboutthemselves,sincetheyfounda proper beach, but worried about the environment or the local people.beaches are seen as a beautifulthingthatneedtobepreserved.touriststhatareinterviewedatcuadaibeachworrymore abouttheeffectsoffailure.inshort,thetouristsdonotworryaboutthebeachforindividualreasons; theycanalwaysmovesomewhereelse.however,theydocareabouttheeffectontheenvironment andthelocalcommunityandthereforewishforalargeandsustainablebeach. B.2.2.Locals Different kinds of local people from Hoi An are making a benefit out of the beach and its related tourism. For the purpose of this project the restaurant and bars along or near the beach, sales(wo)men,bicyclekeepers,lifeguardsandfishermenaregivenaquestionnaire.thishelpedto understandthevalueofthebeachandhowtheerosionisaffectingthoselivingfromthebeach.both thestakeholdersontheseverelyerodedcuadaibeachastheanbangbeach,wherethereisstilla beachleft,werevisited.itcanbenoticedfromthequestionnairesthatbothareasworryaboutthe erosion,eventhoughtheerosionhasnotreachedallofthemyet. TherestaurantandbarsalongAnBangBeachworryaboutthefutureoftourisminHoiAn,because of the erosion at Cua Dai. Tourism is one of their most important sources of income. A reducing amountofvisitorswouldseriouslyaffecttheirbusinesses.theyalsocareaboutthosesituatedalong Cua Dai Beach. They care much about the whole community and therefore most of them have helpedinawaytoinfluencethebeacherosion.thiscouldbebymanuallabour,asfillingsandbags and making the temporary embankments at CuaDai, but also by urging the government to do somethingaboutit. Therestaurantandbarsandotherslivingfromthebeachin thecuadaiareaareaffectedbythe beach erosion. It has reduced the amount of tourists, which is their main source of income. This makes them worry about the future of their current jobs. Therefore almost all of them helped in constructingtheprimitivebeachprotections.theywishthatthegovernmentwillsooncomeupwith effectivecountermeasuresandtohelpthemsustaintheircurrentfinancialactivities. ThestakeholdersonbothAnBangasCuaDaiBeachagreeontherequirementforawiderandlarger beach.eventhosewhostillhaveadecentbeachleft.anotheropinionthatisoftensharedisthewish formorepublicspaceonthebeachinsteadofstretchesownedbybeachresorts. B.3 Stakeholder problem statements and goal trees Stakeholders are analysed in this appendix using problem statements and goal trees. These are derived from the results of interviews and questionnaires or common sense when this was not possible.eachstakeholderchapterexistsinacurrentstateandhasadesiretochangeits(future) situation. This is called the gap. The gap makes up the first clause of an actor specific problem statement.thereasonanactorisnotalreadyinitsdesiredstateisthedilemma.thedilemmamakes up the second clause of the problem statement. It can also be viewed a tradeoff between the desiredstateandanegativedrawback.together,thegapanddilemmamakeacompleteproblem statementthatdescribestheissuesthestakeholderisdealingwith.theseissuescanbemadevisible insocalledgoaltrees.goaltreesareusedtoidentifythemaingoalsofdifferentactorsandtolist theirdesiresanddilemmas(drawnfromtheproblemstatements)assubgoals.lowerlevelsofgoal treesrepresenttheabstractconceptsofthesubgoalswithseveralcriteria.thisbottomrowofthe goaltreeservestomakeallthegoalsmoreconcreteandmeasurableandthereforeincludeunits. Both methods of analysis are described by (Haan & Heer, 2012) in their book Solving Complex Problems andusedforthefollowingstakeholders. 64 CoastalerosionHoiAn

71 Nationalgovernment TheNationalgovernmentisthehighestadministrativebodyoftheVietnamesestateandiscalledthe National Assembly. They control the local governments of the provinces and give orders to those provincialgovernments(cima,1987).thereisabudgetlawinvietnam,howeverthedistributionof revenuesbetweendifferentlevelsofgovernmentsarenotfixedbythatlaw.thenationalassembly setsthesharingratesforthedistributionofthebudgetoverthedifferentlevelsofgovernmentsfor eachperiodofthreetofiveyears(hien,2005).thereisnodirectinfluenceofthenationalassembly on the coastal erosion of Cua Dai Beach however the Ministry of Resources and Environment is responsibleforthecoastalaffairsandtheministryofagriculture,ruraldevelopmentandplanningis responsibleforthecoastalprotection. Thegoalofanationalgovernmentistostriveforthebestfortheircountry sinhabitants.vietnamis currentlydevelopingfastandithasthepossibilitytoimprovethelivingstandardsofthevietnamese people. To make the goal more specific, the focus is on the people along the coast and their problemswithcoastalerosion.however,provincesplayalargeroleinthepolicyimplementation.it isthedilemmaofthe nationalgovernmentnotto favouroneprovinceaboveothers,otherwiseit would be easy to get enough resources available for the coastal erosion problem. The problem statementofthenationalgovernmentisthereforethefollowing: HowtoimprovelivingstandardsalongthecoastfortheVietnamesepeople,withoutfavouringone province? The wish and dilemma of the national government are put in the goal tree, see Figure B.1. Good livingstandardswithrespecttolivingalongthecoastarefurtherspecifiedinahighincomeanda highsafetyagainstwater.thelattercanbefurtherbrokendowninalowamountoferosionandlow amountofflooding,whichcanbemeasuredinunits. Thedilemmathatmakesithardtofulfilthewishisthenecessityforequaltreatmentofprovinces. Breakingthisgoaldownintomeasurablegoalsfollowsinthegoalofsimilarallocationoffundsand fewtononelegislationexemptions.allthesegoalsfollowfromthetopgoalofahighwelfareofthe nation. FigureB.1Goaltreenationalgovernment 65 CoastalerosionHoiAn

72 LocalgovernmentoftheQuangNamProvince The city of Hoi An is of economic importance for the Quang Nam Province.The economy of the whole province has financial benefits of the touristic city of Hoi An, due to that the provincial governmentalsowantshoiantohaveaniceandwidebeach.accordingtoarticle26.3oflawon LandNo QH11,theProvincialPeople scommitteeshouldapprovethelandusezoningand planningofthepeople scommitteeofthecityhoian.inaddition,theprovincialpeople scouncilhas to decide at which rates the revenues will be distributed over the lower levels (Hien, 2005). The incomeforthelocalgovernmentisgeneratedwithrevenuesfromseveraltaxesandfees. Assaidbefore,provincesandtheirPeople scommitteeplayalargeroleinthedailymanagementof the country and they are greatly responsible for what happens in their province. The provincial People scouncilcandecidetheamountofbudgettheygivetotheprovincialcityofhoian.acurrent probleminthequangnamprovinceisthe coastalerosion.however,solvingthisis not easy.the sandminingandhydropowerdamsintheriversmightbe(partly)responsibleforthecoastalerosion, butthoseareimportantsourcesofincomefortheprovinceandindustriesthatcannotbehampered toomuch.theproblemforquangnamprovinceisthereforethefollowing: HowtopreventdamageduetoerosionattheQuangNamProvince,withouthamperingindustries? The damage due to erosion can be broken down into structural and economical damage to hotels/resortsandhomes,ascanbeseeninthegoaltree,seefigureb.2.furthermore,economic damage due to erosion to the Cham Islands and to the rest of the province, should be low. The preventionofhamperingindustriesistranslatedintothegoalofbloomingindustries.themeasure forthisistheincomeduetoindustriesandthegrowthrateofthissector. Similar to the national government, this goals should be achieved to benefit the welfare of the region,inthiscasethequangnamprovince. FigureB.2Goaltreeprovincialgovernment 66 CoastalerosionHoiAn

73 LocalgovernmentofHoiAn ThecityofHoiAnisaprovincialcityaccordingtothepoliticalstructureofVietnamandisunderthe directauthorityoftheprovincialgovernment.ithasapeople scouncilasthedailygovernmentof the city and a People s Committee as its executive hand. The People s Council is a democratically elected council and is defined as the local representative organ of state power. The People s Committeeistheadministrativelocalorganofthestateandisresponsiblefortheresolutionsofthe People scouncilandaswellasimplementingstatedocumentsfromhigherauthorities.thepeople s Council consists of people who are nominated by the Communist Party or selfnominated. So not onlypartymembershaveaseatintheprovincialcitycouncil. Provincialcities,likeHoiAn,mayusecontributionsfromorganizationsandindividualsforinvestment in infrastructure and other constructions in its own city. The revenues which are in its totality assignedtothelocalgovernmentsincludethelandandhousingtaxesandthetouristtaxes(hien, 2005).According to Article 25.3 of Law On Land No QH11, the People s committee of provincesandcitiesundercentralauthorityisresponsibleforthelandusezoning. OneofthemajorproblemsthelocalgovernmentofHoiAnhastodealwithnowadaysisthecoastal erosionofthecuadaibeach.extremeerosioncandamagethecity,bothstructuralandeconomic wise. The dilemma that exists here is the amount of money available to solve this. The coastal erosion is not the only issue that needs to be financed and the budget is finite. This leads to the followingproblemstatement: HowtopreventdamageduetocoastalerosionatCuaDaiBeach,withoutlosingbudgetforother matters? Thelowerosiondamagecanagainbesplitupinstructuralandeconomicdamagetohotels/resorts andhomes,comparabletotheprovince,butnowonlyapplicabletodamageinhoian.thedilemma oflimitedbudgetistranslatedintothegoalofefficientspending.thismeansthatasufficientpart shouldgotodealwiththeerosionproblems,butleavesenoughbudgetforothercitymatters.allin all,thisshouldleadtoanincreasedwelfareofthecity. FigureB.3Goaltreecitygovernment 67 CoastalerosionHoiAn

74 CitizenslivingfromthebeachinHoiAn Awidebeachispartoftheprotectionofthecity.Whenthereissevereerosionofthecoastandthe erosion continues until it reaches the borders of the city, the erosion will deteriorate the historic valuablebuildingsandhouses.nexttothat,thetouristswhovisitthecitywillcreateincomesforthe citizensofhoian,whenthebeachesdisappeartherewillbelesstouristsandsoonlessincomefor thecitizens. SeveralcitizensofHoiAngaintheirincomesfromthebeachanditsrelatedtourism.Thesecitizens areforexamplerestaurantandbarowners,bicyclekeepers,fishermenandlifeguards.especiallythe restaurants owners along the beach are attached to their location. It will not be easy to let the locationgoandsearchforanewsourceofincome,whenthebeachiseroding.itiscrucialforthem thatthebeachtourismkeepsexisting,asfollowedfromtheinterviews.however,theproblemisthat thesepeopledonothavealotofpowertourgethegovernmenttoimplementeffectivesolutionsfor theirfutureandarethereforedependentonhowthebeachtourismisevolvingnow.thecitizensare thereforedealingwiththefollowingissue: Howtokeepjobsonthebeach,withoutanypowertostoptheerosion? Thevaguegoalofenoughjobsonthebeachcanbebrokendowninthesubgoalsofhavingahigh densityofrestaurant,barsandotherbeachrelatedjobopportunitiesalongthecoast.thegoalof havingthepowertostoptheerosionistranslatedintothepowertoadapttotheproblem.together theycontributetothegoalofselfreliance. Theadaptationpowerisbrokendownintotheflexibilitytomove,financialpowerandgovernment support.theflexibilitytomovedependsontheamountofowninvestmentsinafixedlocationover the income the citizens make. The less investment in a fixed location, the easier it is to move to anotherplacetoexploitthebusiness.anotherimportantgoalforpoweristhefinancialpossibilityto controltheerosion.againthisisrelatedtotheyearlyincome.whenthepercentageofthecostof mitigationmeasuresoveryearlyincomeislow,thecitizenshavemorefinancialpowertodealwithit. A last factor of power is the support of the government. With funding from the government and sharedwisheswiththegovernment,morecanbedonetocontrolthesituation. FigureB.4GoaltreecitizensofHoiAnlivingfromthebeach 68 CoastalerosionHoiAn

75 Resortmanagers Nowadays the resorts at Cua Dai Beach are very important to attract tourists to the city and the beachesofhoian.wideandbeautifulbeacheshaveadirectvalueforthehotelsandresortslocated atthebeaches.nexttothat,suchbeacheshavealsoanindirectvalueforthehotelsinthecentreof thecityofhoianbecausealsothosehotelvisitorswanttousethebeaches.thismeansthebeaches areofgreatimportancefortheresortmanagers. The resort managers can be classified in two parts: those at Cua Dai Beach and affected by the erosionorthoseatanbangbeach.theproblemstatementfitsthelatterinthefuturetoo.thoseat AnBangBeachareeithernotawareoftheproblemyetoralsofeartheerosion.However,without actiontheerosionwilleventuallyreachtheirresortaswell. ThewishoftheresortsatCuaDaiBeachistogettheoriginalbeachbacktocounteractthereducing amountofbeachtourists.thedilemmahereisthatagovernmentprogramandcooperationbetween the resorts on the whole stretch is needed to be effective. This is not the case yet andseen as a hurdle by several resorts, as followed from the interviews. The problem can therefore be summarizedinthefollowingstatement: Howtogettheoriginalbeachback,whilecooperationisdifficult? Alargegoaltreeisneededtospecifythesewishanddilemma.Theoriginal,nicebeachmeansthata certainwidthofbeachisrequired.alsothesmalldistancetotheseafromtheroomsoftheresortis an important measurement for this goal. Also the presence of coconut trees was seen as an importantcontributortotheappearanceofthebeach.togetherwithaffordableroomsthismakesan attractiveresort.theothersideofthetreefocusesonthedilemma:thecooperation.cooperation heremeanscooperationwiththegovernment,butalsowithotherresortsinhoian.sharedwishesis a measure for cooperation, and also the funding from the government and meetings with other resorts are benchmarks for cooperation. Eventually, the fulfilment of these goal should lead to lastingtourism. FigureB.5Goaltreeresortmanagers 69 CoastalerosionHoiAn

76 Buildingindustry One of the main industries of Vietnam is their building industry. The Vietnamese infrastructure development triggers a great demand for sand and concrete. This demand has been increasing significantlyoverthepastyears(stoxresearch,2015).thebuildingindustryinvietnamusesalotof sandminedatseveralriversinthecountry. Mining sand from rivers for selling it to other countries or domestic use like the elevation of a highwayisdonerepeatedlyandthisisfinanciallyattractiveforthecountry.thequangnamprovince isoneofthedominantregionsinvietnamfortheextractionofsand(lynch,2014).oneofthemain sourcesforthisusefulsandistheestuarynearbyhoian,thethubonbasin.theminingofthissand mighthaveanegativeeffectonthecuadaibeach.itcouldbethecasethatduetothisextraction thereislesssandsuppliedtothecoastandthismightcausemoreerosionofthebeaches. Awishfromthebuildingindustryistoacquireenoughmaterialstobuildwith,butthedilemmais thattheywanttobuyitatlowcosts,otherwiseothersourcesthantheriverswerepossibilitiestoget therightmaterials.theproblemisclearfromthefollowingsentence: Howtogetenoughbuildingsmaterialsforconstruction,atlowcosts? Themaingoalofthebuildingindustryforhavingahighavailabilityofbuildingmaterialsatlowcosts istheprofitthatcanbemadewithrespecttothepurchasingofthematerials.ahighavailabilityof materials means a high amount of sand available, but also the availability of other materials, like steel and gravel. The wish for low costs can also be broken down in these two types of material classes. FigureB.6Goaltreebuildingindustry 70 CoastalerosionHoiAn

77 Sandminers ThebuildingindustrymentionedaboveusessandthatisminedfromtheVietnameserivers,which mighthavenegativeeffectsontherateofcoastalerosion.severalsandminingactivitiestakeplacein the rivers. Sand miners operating for the building industry want to mine the sand from sources whereitiseasyandcheaptoextract.oneofthosesourcesisthethubonriverbasinnearbyhoian. Thiswaythesandminerscouldselltheextractedsandforalowpriceandthesandandconcrete industrystaysfinanciallyattractivefordomesticuseandforexporttoothercountries.thiswillbea goodincomefortheseindustriesandthecountry. Althoughthisisalreadyprohibitedwithoutlicense,itstilloccurs.However,whenitcanbeproven thatthissandminingisaffectingtheerosion,thismightleadtoextracontrolinthefuture.thisisthe dilemmathatsandminershavetodealwithtomaintainaprofitablebusinessintheyearstocome: Howtomaintainaprofitablesandminingbusiness,whensandminingintheriverisprohibitedinthe future? A profitable sand mining business, means that the costs for mining are low and the sales of the materialishigh.theprohibitionismoredifficulttobreakdownintosubgoals.itistranslatedinto thegoalofsmalllegaldrawbacksforsandmining.thismeansthattherearelittlerestrictions,low changeofconviction,butalsoalowlevelofpenaltywhencaught.althoughitseemsstrangetoput thisasgoalsinagoaltree,itfitsthefactthatpeoplearestillwillingtominesandintheriver,despite being a prohibited business. This would imply that the business continuation is the main goal for sandminers. FigureB.7Goaltreesandminers 71 CoastalerosionHoiAn

78 Tourists Theproblemofthetouristsisofadifferentkindthanoftheotherstakeholders.Theyhavethewish foranicebeach,butnotonlyforthemselves,alsofortheenvironmentandlocalcommunity.tourists areflexibleandcanthereforealwaysshifttoaplacethatmatchestheirinterestsmore.however,if the wider beach can be achieved, they would like to see more cheap and public space instead of resort owned beaches. This is the dilemma here, because a public beach would imply that the governmenthastoinvestinit.currently,itisunclearwhetherthisfundingwillevercomeandwhen. Thiscanbesummarizedinthefollowingproblemstatement: Howtogetanicebeach,withoutpayingtoomuchforthebeachuse? Thesubgoalsofhavinganicebeacharetakenalmostthesameashowtheresortmanagersseea nicebeach:largewidth,smalldistancetothebeachandpresenceofcoconuttrees.lowcostsfora chair and umbrella, parking and cheap restaurants at the beach all contribute to a cheap beach visit.thenicebeachtogetherwiththepricethatisspendforvisitingitleadstothemaingoalofan enjoyablebeachvisit. FigureB.8Goaltreetourists 72 CoastalerosionHoiAn

79 B.4 Estimation of hotel values TableB.1TaxincomeHoiAnfromhotelsCuaDaiBeach Rooms Priceperroom[/day] Occupancy Income[/year] Income[ /jaar] CuaDaiBeachHotel* 60 VND450,000 20% VND1,972* ,000 SunriseHoiAnResort 222 VND3,500,000 60% VND170,275*10 6 6,888,000 Golden Sands Resort andspa 212 VND5,681,818 60% VND263,970* ,679,000 MuongThanh* 159 VND1,483,084 60% VND51,676*10 6 2,090,000 VictoriaResortandSpa 109 VND4,000,000 60% VND95,547*10 6 3,865,000 HoiAnbeachresort 121 VND2,150,000 60% VND57,010*10 6 2,306,000 PalmGardenResort 214 VND3,000,000 60% VND140,691*10 6 5,691,000 AgribankResort 166 VND1,750,000 60% VND63,661*10 6 2,575,000 BoutiqueHoiAnResort 82 VND3,000,000 60% VND53,909,*10 6 2,180,000 *notlocateddirectlyatthesea Total VND898,716* ,359,000 VAT(10%) VND89,871,*10 6 3,636,000 Thevaluegeneratedby thepresence ofthe hotelsatthe beachwasestimated bytheamountof roomsandpriceofeachofthehotels.withanaverage60%occupancyaroundtheyeartheincome ofeachhoteliscalculated.theexceptioniscuadaibeachhotelwhichlookedabandonedduringthe timeofourvisitbutstilloffersroomsonline. Thecurrent valueaddedtax(vat)is10%meaningthispercentageoftheincomegeneratedisan incomeforthestate.iftheoccupancyofthehotelsdropsorhotelsandresortsareabandoneddueto thecontinuederosion,thestatelosesasignificantportionofitsincome.eventhoughthebenefitsof anattractivebeachexceedtheeconomicvaluethisanalysishighlightstheimportanceofmaintaining thecoastline. 73 CoastalerosionHoiAn

80 C.Coastal system This appendix supplements Chapter 4 about the coastal system around Hoi An. A principle that is usedseveraltimesthroughoutthereportisthatofbruun,whichisfirstdescribedhere.afterthatthe CERCformula,bathymetry,wavedata,tidedata,thesandbalancecalculationandtheestimationfor theerosionratearegiven. C.1 Bruun Rule Thecrossshoreprofileofabeachisdynamicduringtheyear.Dependingonthewaveconditionsthe profile shifts. However, averaged over one or several years a constant equilibrium profile can be expectedasextremeconditionsandmildconditionsaverageoutoveralongperiod.bruunfounda waytodescribesuchabeachprofilewithasimpleexpression: Eq.C1 (Bruun,Coasterosionand thedevelopmentofbeach profiles,1954) With: Theassumptionofanequilibriumprofilecanbeappliedforthecaseofsealevelrise(seeFigureC.1). Asthesealevelrisestheoriginalprofile[1]nolonger fits thenewequilibriumprofile[2].sincethe volumeofsandinthecrosssectionremainsconstanttheprofileneedstoshiftsuchthattheerosion attheupperpartoftheprofileisequaltotheaccretionatthelowerpart.thisresultsinthefinal profile[3]thatbothsatisfiestheshapeoftheequilibriumprofileandcontinuity.thismethodcanbe expressedwiththefollowingformulaknownasthebruunrule: Eq.C2 (Bruun,1962) Inwhich: 74 CoastalerosionHoiAn

81 FigureC.1TheBruunruleexplainedvisually(Bosboom&Stive,2015) C.2 CERC formula In this section erosion and accretion will be assessed by looking at the wave driven sediment transport. The capacity for wave driven sediment transport can be approximated by the CERC formula(rewrittenforwavesatthebreakerzone): Eq.C3 (Bosboom&Stive,2015) With: Asexpressedintheformula,thealongshoresedimenttransportisdependentonbothwaveheight and angle of incidence. Transport of sediment itself does not cause erosion or accretion, but gradients in transport do. If more sediment is transported into a section of the coast than is transportedoutofit,accretionhastakenplaceandthecoastgrowsinoffshoredirection.ifmore sedimentistransportedoutofasectionofthecoastthanistransportedintoiterosionhasoccurred andthecoastretreats.thissinglelineapproachcanbeexpressedas: Eq.C4 (Bosboom&Stive,2015) Inwhich: Eq.C4expressesthatchangesinthecoastlineoccurwhenthealongshoresedimenttransport(S x )is not constant while Eq.C3 expresses that this transport changes when waves break at different anglesalongtheshoreorthewaveheightsaredifferent(assumingthereisnodifferenceinsediment characteristics alongshore). If wave heights decrease in alongshore direction accretion is expected while if wave heights increase in alongshore direction erosion can be expected. Another consequence of these relations is that an alongshore uniform wave climate with a low angle of incidence (which is true for all waves close to the shore due to refraction) will strive to create a straightcoastsmoothingoutanyhumpscreatedby,forexample,rivers. 75 CoastalerosionHoiAn

82 C.3 Bathymetry Figure C.2 Ͳ Map bathymetry East Sea / South China Sea near Hoi An (U.S. Army Map Service, 1984) 76 Coastal erosion Hoi An

83 C.4 Wave climate Figure C.3 Wave compass of the offshore wave climateofhoian(argoss,2015) Figure C.4Histogram of the offshore wave climate of Hoi An (ARGOSS,2015) Wave height and angle of incidence are important for sediment transport and consequently for structuralerosionofthecoast,aswasexplainedinparagraphc.2withthecercformula.itisknown thatduetothemonsoonstrongwindsfromthenorthcanbeexpectedwhileinthesummercalmer windsfromthesouthareexpected.asaresultthehighestwavesarefromthenorthwhilemilder waves are from the south, see Figure C.3. Important to note is that the dominant wave direction (ENE)cannotdirectlyreachHoiAnduetheChamIsland. Figure3.7EstimatedsedimenttransportdirectionsbyProfessorStiveillustratesthatwhenwaves areincomingfromthenortheastalargepartisblockedbychamisland.duetorefractionaroundthe islandanddiffractionbehindit,thewaveclimateathoiancanbealteredsignificantly.however,a lot of research has still to be done concerning the influence of this island, since it is not exactly known how or if it is related to the coastal erosion along the Cua Dai Beach in Hoi An. For the purposeofthisstudyitisassumedtheislandcreatesawindowinwhichonlywavesfromthenorth andfromthesouthtosoutheastcanreachhoian. The average wave climate as a whole is assumed to be composed of high winter waves from the northeastwithwaveheightsaround2to3meterandmildsummerwavesfromthesouthofabout1 to 2 meter. For a better understanding of the wave climate just offshore of Hoi An, yearly wave statisticswouldberequiredwhicharenotavailableyet. 77 CoastalerosionHoiAn

84 C.5 Tide AlongthecoastalstretchofQuangNamprovinceamixedsemidiurnaltideoccurs(VuThiThuThuy, 2003).Mixedsemidiurnaltidecontainstwolowtidesandtwohightidesofdifferentheights.Thiscan alsobeseeninfigurec.5,wherewithinmostofthetidalcycleslowwaterandhighwatertakeplace twice. The major tidal constituents having influence on this tidal system are O 1 (Diurnal lunar delination tide), K 1 (Diurnal lunarsolar declination), M 2 (Semidiurnal principle lunar) and S 2 (Principle solar semidiurnal)(vuthithuthuy,2003). FigureC.5TidechartHoiAn(Tideforecast,2016) 78 CoastalerosionHoiAn

85 C.6 Sand Balance Fromthreeyears,1965,2001and2014,thebathymetryisshowninFigureC.6.Inthefigurethereare depthcontourlinesfor5,10and15meters.basedonthispicturethevolumeofsandabovethe15 mdepthlinecanbecalculatedforeachyear.firsttheareabetweenthecontourlinesismeasured andconvertedtotherealareawiththedrawingscale.secondlytheareabetweencontourlinesis assumedtobeconstantindepthandequaltotheaverageofthedepthcontoursitliesbetween.this givesawaterdepthof2.5,7.5and12.5foreacharea.sinceonlytheareaabove15misconsidered thesewaterdepthscanbeexpressedastheheightofsandabove15mandisreferredtoas sand depth.fromlightbluetodarkbluethisgivessanddepthsof12.5m,7.5mand2.5m.multiplyingthe sanddepthwiththemeasuredareaofeachsectionandaddingupthesesectionsonearrivesatan estimateforthesandvolumeabove15m.thisvolumehasincreasedovertheyears,withwhichit lookslikethateithermoresandhadmovedtowardsthecoastortheforeshorehasextended. FigureC.6Bathymetryand crossshoresandbalance TableC.1 Sandbalancecalculation 79 CoastalerosionHoiAn

86 C.7 Erosion rate estimates BasedonmeasurementswithGoogleEarthviewsfrom ,whicharesupportedbyLandsat images,theyearlyerosionis12metersayearforastretchof3.5kilometresafterwhichitgradually reduces.toaccountforthisgraduallyreducederosionoutsidethe3.5kilometresstretchan500m stretchof12metererosionisadded.thereforeabeachlengthof4kmisconsidered. Theactivedepthwasestimatedwith2similarformulas: Eq.C5 (Hallermeier,1981) Eq.C6 (Birkemeier,1985) Inwhich: Using the extrapolated yearly wave height and period data from appendix E3.1 (H s =2.62m and T p =11.1s) the closure depth is estimated to be between 5.58m and 4.25m. Taking the average of thesevaluestheclosuredepthisestimatedtobe5m. Theamountofsquaremetersoferosionfollowfromthelogicalassumptionthatthebedprofilestays stableanderosionmeansalandwardsmovementoftheactivezone.seefigurec.7. Eq.C7 with Whenmultipliedwiththebeachlengthanaverageyearlyerosionof240,000m 3 isestimated,as shownin TableC.2. FigureC.7Erosionschematisation TableC.2Tablesummaryofuseddataforerosion Activedepth(m) Beachlength(m) Yearlyretreat Areaerodedfrom Erodedvolumeper (m/year) profile(m 2 /year) year(m 3 /year) 5 4, , CoastalerosionHoiAn

87 D.Estimates of river sediment supply This appendix shows the different calculation methods for the estimation of the Thu Bon river sedimentsupply. Onsomeplaces,datafromownThuBonriverobservationsareused,whichare describedinappendixi.2. D.1Estimationbasedoncomparablerivercatchmentarea ThismethodusedbyVietandTanaka(2015)isbasedonthecomparisonbetweentheThuBonriver andseveralotherriversystemsintheworld.first,thespecificsedimentyieldofseveralriversystems around the world in [m3/km2/y] and the catchment area in [km 2 ] of these river systems are determined. These relationships between the specific sediment yield and catchment area can be shown in a diagram, see Figure D.1. After that, trends between the same type of rivers can be observedandthisisusedfordeterminingthespecificsedimentyieldofthethubonriver.therefore thecatchmentareaofthethubonriversystemhastobeknownandariversystemwithasimilar catchment area (in this case the Tenryu River in Japan) can be used to determine the sediment dischargeofthethubonriversystem(viet&tanaka,2015). ThismethodgivesayearlyamountofsedimentsupplyofthisriverofQ s =600,000m 3 /year. FigureD.1Estimationofsedimentsupplybycomparablecatchmentarea(Viet&Tanaka,2015) 81 CoastalerosionHoiAn

88 D.2Estimationwithacalculationwiththeriverbedslopeanddominantdischarge For this estimation of the river sediment supply the Engelund and Hansen formula is applied. To definetheannualsedimenttransportthedominantdischargeisneeded,whichiscalculatedwiththe formulafordominantdischargeshownbelow.valuesforthebase,peak1andpeak2dischargeare obtained from a report of the (Department of Natural Resources and Environment, 2011) of the Quang Nam Province. The month November has the highest peak discharge and the months September, October and December have less high peak discharge. The remaining months have a basedischargeascanbeseenintabled.2. Eq.D1 With: (devriend,h.j.etall., 2011) Finally this formula gives a dominant discharge of Qdom m s. The Engelund and Hansen methodcanbeusedtocalculatethetotalsedimenttransportinthecrosssectionoftheriver.several parameterslikethewidth,frictionfactor,gravitationalconstant,riverbedslopeandthecoefficient m havetobedeterminedbeforecalculatingthesedimentdischargeinthethubonriver.thewidth is defined with Google Earth and the friction factor by checking the river bed during fieldwork. Furthermore, the bed slope is also determined with Google Earth by measuring the height at the beginandendpointofthesectiontakenanddividingbythetotallengthoftheriver.thecoefficient m isdefinedinliterature. Eq.D2 n n cb f ES ibed gqdom m (devriend,h.j.etall.,2011) With: 82 CoastalerosionHoiAn

89 Eq.D3 ibed ES m (devriend,h.j.etall.,2011) cb n f gqdom With: Forthecalculationfivedifferentsectionsaredefinedbasedondifferentwidthsandsidechannels pouringintotheriver.thesectionsarebetweentananandhoianandshowninfigured.2.the sedimenttransportcalculationwiththeformulasgivenaboveandthebedslopeandwidtharegiven intabled.1. TableD.1Sedimentdischargeriversections Location TanAn Thon5 HiepHoa DaiHoa DienPuong Mouth Wetwidth[m] Drywidth[m] Height[m] Distancefrommouth[m] 90,000 82,000 70,000 37,000 15,000 0 Bedslope 5.00E E E E E04 B[m] c f *B^0.4/(9.81*386) E E E05 2.2E E05 E(S)[m 3 /s] E(S)[m 3 /year] 1,295, , ,431 65,726 30,146 Accordingtothecalculationsshownabove,theyearlysedimentdischargeflowingthroughtheCua DaiInletisonlyQ s =30,150m3/yearsediment.Thisisaverylowamountcomparedtotheother calculation methods. The reason for that could be that with this method several sections are consideredfromupstreamtothedownstreamendandwiththeothermethodsonlyonesectionfor thewholeriveristaken.whentheaveragebedslopeandtheaveragewidthforthewholeriveris used for the calculation the resulting average sediment transport is higher compared to the calculationwithineachriversection.thelastsectionclosetothemouthhasthelowestbedslope andlargestwidthcausingamuchlowersedimenttransportthroughthatsection.thisleadstoalarge amount of sediment that will be deposited in the downstream sections. Note that this deposited sediment finally also might be transported to the sea, however that is not due to normal flow conditions. This deposited sediment might be eroded again and transported to the sea by a flush flowthroughtheriverinthemonthswithpeakdischarge.thispeakdischargeisactuallytakeninto account with the calculation of the dominant discharge. Nevertheless the highest peak discharge mighthavemoreimpactonthesedimentflushoftheriverandthatiswhyanapproximationofthe sedimentdischargeisdonebyaveragingitoverthefivesections:qs=441513m3/year. 83 CoastalerosionHoiAn

90 FigureD.2Riversectionusedforthecalculations D.3Estimationbycalculationwithsedimentconcentration This method (Gray & Simoes, 2008) follows from the possibility to make sediment concentration measurementsatlocationsintheriverandthenmultiplythosewiththedischarge.accuracydepends ontheamountofmeasurementsofsedimentconcentration,andcorrectchoosingofthelocationsin theriver.furthermore,theknowledgeaboutthedischargeoftheriverandthechangeofsediment concentrationwithhighorlowdischargewouldinfluencetheaccuracy.theformulaforthismethod isshownbelow. Eq.D4 Qs QwCsk (Gray&Simoes,2008) With: *Acoefficientbasedontheunitoftimemeasuredandtheunitofweightusedandincluding thedensityofthematerial(60*60*24*30*1/10^6*1000*1/2650)= WhentheThuBonriverwasobservedoneofthepurposesofthisfieldtripwastoobtainsediment concentrationdata.however,measurementscouldnotbedoneatthemomentofthefieldtrip.so sediment concentration data from other measurements done before are used for this calculation, followingfrom(ledinhmaum.sc.,2006).thedischargebeingaroundtheyearlyaveragedischarge of327m 3 /s(huyen,2009).theresultsofthecalculationwiththeformulaofgrayandsimoesare shownintabled CoastalerosionHoiAn

91 TableD.2SedimentdischargecalculationwithformulaofGrayandSimoes Dischargedistribution (%) Discharge[m 3 /s] Sediment concentration[mg/l] Sediment transport [m 3 /year] Jan ,245 Feb ,245 Mar ,245 Apr ,245 May ,245 Jun ,245 Jul ,245 Aug ,245 Sep ,086 Oct ,086 Nov ,200 Dec ,086 Total 100 Average= ,421 As can be seen in Table D.2 the total amount of annual sediment transport obtained with this method is Q s =390,000 m 3 /year. Hold in mind that actually this is only the suspended sediment transport.adistinctionhastobemadebetweenthesuspendedandbedloadsedimenttransport. Thetotalsedimenttransportisthetotalofthesuspendedandbedloadtransport.Thisiswhythis valuemightbelowerthanthevalueobtainedwiththefirsttwomethods. 85 CoastalerosionHoiAn

92 E.Research into reasons for shoreline retreat Inthisappendixawiderangeofpossiblereasonsforshorelineerosionwillbediscussedandtheir impactquantifiedwithintheboundariesofuncertainty.firstthehumanimpactwillbediscussed:a changeinthewatershedoftheriver,landsubsidenceduetowaterextraction,lesssedimentsupply duetosandmining,waterandsedimentdischargechangesfollowingdamconstructionandchanges intherivermouthflowpatterns.secondlythenatureimpactwillbeaddressed:tectonicsubsidence, climatechange(sealevelriseandincreasedstormsurges),andachangeinforeshoremorphology.as athirdpartthenaturalyearlyandmultiyearlyvariationoftheshorelineisresearched. E.1 Human impacts E.1.1Changeinwatershed Orderofmagnitude:None The amount of sediment transport in the Thu Bon River might change if there are changes in the watershedoftheriverandthiscancontributetothecoastalerosion.anewriverconnectionwith anothermainriveranddeforestationarethemainfactorsthathaveahighinfluenceontheamount of sediment transported by the river. In addition the removing of vegetation on the beaches and duneshasanegativeimpactonthepreventionagainstcoastalerosion. The Vu Gia River and Thu Bon River have two connections between each other relatively far downstreamtomanagethefloods.theexchangeofflowbetweenthetworiversinthewetseason from the Vu Gia to the Thu Bon River flows through the Quang Hue crossconnection. Further downstreamtheexchangeofwaterfromthethubonrivertothevugiaflowsthroughthevinh DienRiverasshowninFigureE.1. Due to the construction of upstream reservoirs the difference in water level between the Vu Gia RiverandThuBonRiverhasincreased.Thisisanincreaseofabout30cm.Duetothisincreaseabout 20%to40%morewaterisflowingfromtheVuGiaRivertotheThuBonRivernowadays(NgoLe Long,TranThanhTung,&DuongQuocHuy,2014).FurtherdownstreamoftheThuBonRiveralittle part of the discharge flows back through the Vinh Dien River to the Vu Gia River during the wet season(ministryofagricultureandruraldevelopment,2012),noexactamountsareknownhowever itcanbesaidthatthisamountwillnotbehigherthantheamountofdischargeflowingintothethu BonRiverfromtheVuGiathroughtheQuangHue. AftertheconstructionoftheQuangHueRivertherehasbeenalotofsanderodingfromtheriver banksinthispartandalsodownstreamofthisconnectionbetweenthevugiariverandthethubon River (Tran Tan Van, 2002) indicating that the sediment concentration in the flowing water is increasing.duetothefactthatboththewaterdischargeandsoonalsothesedimentdischargeare increasing in the Thu Bon River in the wet season it is unlikely that there will be less sediment transportedtotheshorelinenearbycuadaiinlet. 86 CoastalerosionHoiAn

93 FigureE.1RiverconnectionsbetweentheVuGiaRiverandThuBonRiverdistributingdischarge Other factors like deforestation within the watershed of the Thu Bon River Basin are unlikely to contributetothecoastalerosionbecausedeforestationwouldprobablyleadtoamoreloosesoilon theriverbanksandmountainareasandsoonleadtohigheramountofsoilflushedawaytotheriver. Thatiswhyitislikelythatdeforestationwillleadtoahighersedimentdischargeintheriverandthus causeaccretioninsteadoferosion. Coastal forests and trees function as coastal protection against erosion and the removal of trees, coastalforestsandothervegetationincreasedthevulnerabilityofthecoastlinetoerosion.human interventions like deforestation of the coastline at Central Vietnam are mostly to build resorts, residentsandrestaurantsforthetourists. Asdescribedabove,theriverconnectionbetweentheVuGiaandThuBonRiverhasnoimpacton theshorelineretreatofcuadaibeach.whatmighthavehadsomeimpactontheshorelineretreat afteralotoferosionalreadyoccurredisthecoastaldeforestation.duetothefactthatnormally(in thehistoryofcuadaibeach,severalyearsago)coastaltreesandvegetationarelocatedseveraltens ofmeterfromtheshoreline,thedeforestationhasonlyaninfluenceontheshorelineretreatwhen thebeachisalreadygone.soinconclusiontheorderofmagnitudeofshorelineretreatisnone. E.1.2Landsubsidence Orderofmagnitude:None Arelativesealevelrisecancontributetothecoastalerosionproblem.Landsubsidenceoccurswhen large amounts of groundwater are withdrawn from the soil. Ground water is pumped from pore spacesbetweenthesoilgrains,causingthesoilparticlestogetclosertogether.landsubsidencemay causemanyproblems,suchaschangesinriverbedslopes,damagetobridges,roadsandbuildings.in somecoastalareas,subsidencehasresultedintidesmovingintolowlyingareasthatwerepreviously abovehightidelevels. 87 CoastalerosionHoiAn

94 GroundwaterexploitationismainlyexecutedinHanoiandinthelowerregionsoftheMekongDelta. Due to socioeconomic growth in Hanoi, the groundwater extraction system has been broadened, whichhasledtolandsubsidence.insomeplaces,thegroundsurfacehasdeclinedupto1.0min somepartsofhanoi(phi&strokova,2015).thelowerregionsofthemekongdelta,mostofwhich lies<2mabovesealevel,isalsosubjectedtolandsubsidence.ifpumpingcontinuesatpresentrates, approximately 0.88 m ( m) of land subsidence is expected by 2050 (Erban, Gorelick, & Zebker,2014). FigureE.2ExploitablegroundwaterinBillionm 3 /year(nationalwatersectorprofile,2002) AccordingtotheWaterEnvironmentPartnershipinAsia(WEPA),groundwaterextractionincentral Vietnam is very low. The distribution of the exploitable groundwater over the whole country is showninfiguree.2(wepa,2015).basedonthisinformation,itisconcludedthatthecityofhoian, located in the central part of Vietnam is not subjected to significant land subsidence caused by groundwaterexploitation.veryminor(<1mmayear)averagesubsidencecanstillbepresentbutthis isconsideredas(near)zeroinfluenceandthusexcludedasreasonforshorelineretreat. E.1.3Sandmining Orderofmagnitude:5m/year(100,000m 3 /year) IntheQuangNamprovinceitisonlyallowedtominesandfromtheriverorfromtheriverbankswith alicense.oneofthesedimentsourcesforthecoastalareainthesystemareaisthethubonriver, thisrivertakessedimentfrominlandareastotransportittotheebbtidaldeltainfrontofthecua Daiinletandafterthatitwillbedistributedalongthecoast.Theamountofthesedimenttransported bytherivertothecoastalareaisapproximatedin3.2riverinfluence.thisamountisinfluencedby differentfactorsnexttosandmininglikeriverregulationworks. If the sediment balance of a general river section is considered as shown in Figure E.3sediment extractionfromtheriverbedorriverbankcanbeconsideredasasedimentsink.sandmininginthe ThuBonRivercauseslesssupplyofsedimenttotheshorelineandmightcontributetothecoastal erosionofcuadaibeach. FigureE.3Sedimentbalanceofariversegment(Mangor,2008) 88 CoastalerosionHoiAn

95 Inthissedimentbalanceextractionofsedimentandsedimentdischargetothecoastaresinksand thebankerosion,beddegradationandsupplyfromthecatchmentareaoftheriveraresourcesof thesedimentintheriversegment.ofcourse,thesourcesandthesinkshavetobalanceeachother asformulatedineq.e1(mangor,2008). Eq.E1 (Mangor,2008) Theimpactofsandminingintheupperpartoftheriverdiffersfromtheimpactofsandmininginthe lowerpartoftheriver.theupperpartoftheriveristhesteepandlesswidthriversegmentupinthe mountainsandthelowerpartisthegentlyslopingriversegmentnearthecoast. When sand is mined in the upper part of the river it does not directly change the total sediment transportintherivertotheshorelinebecausethelossinsedimentduetotheextractionisinitially compensatedbythedegradationoftheriverbed. Whenclosetothemouthatrenchintheriverbedatthelocationoftheextractionexiststhistrench willgraduallytraveltowardsthecoast,asshowninfiguree.4.thisissimilartosandminingupstream butthemovementhastocoverlessdistancesoiteffectstheshorelinefaster. FigureE.4Initialdeformationandpropagationofatrenchtowardsthedownstreamendoftheriver The amount of sand extraction in the Thu Bon River is not known. There have been observations doneinthelowerpartoftheriveratdaytimeandthereareseveralformsofsandextractioninthis lowerpartoftheriverlikeextractionfromriverbanks,alsoinnerbanksofriverbendsandfromthe riverbed.about25sandminerswereactiveinthelowerstretchofthethubonriverduringdaytime thedaytheobservationsweredoneandeachsandmineroperatesapproximately300daysayear and can produce a daily amount of approximately 10 m 3. Including the sand extraction at night, approximately10sandminers,thismightleadtoatotalamountofsandminingofapproximately m 3 sandperyear.thisisanveryroughapproximationbasedonlimitedobservations,theexact amountofsandminersdiffersperdayandthesandminersactiveatnight couldnotbecounted. Takingthisamountofsandextractioninmind,thismightleadtoapproximatelyasedimentreduction of100000m 3 /yearbecausethisistheextractioninthelowerpartoftheriver. AssumethataccordingtotheobservationsattheThuBonRiverthesedimenttransportisreduced with 25%. Namely the total amount of sediment transport in the river (without sand mining and dams)isapproximatelyintheorderof400,000to600,000m 3 (calculationisshowninappendixd). Withareductionofthesedimentsupplytothecoastofapproximately25%therewillbeashoreline retreatoftheorderofmagnitudeof5mperyear.thisiscalculatedbytakenanactivewaterdepthof 5mandashorelinelengthof4000m,whentheactivedepthismultipliedbytheshorelineretreat andtheshorelinelengththisgives100,000m 3 /year. 89 CoastalerosionHoiAn

96 FigureE.5SandminingonThuBonriver E.1.4DamconstructionupstreaminThuBonRiver Orderofmagnitude:0.5m/year(20,000m 3 /year) Possible coastal erosion by sediment blockage by hydropower dams requires the blocking of a sedimentrichpartoftheriverscatchmentsareaandwillinfluencetheareadownstreamofthedam first.fornowitisunlikelythatthesedimentblockagebythedamsisinfluencingtheerosionatthe mouthofhoianbecauseofthefollowingthreereasons: Thesedimentblockageoftheriverissomethingoftherecentyears.ThefirstdamintheThu Bonwasfinishedin2011,theseconddamisfinishedinthisyear.Whilethethirddamthat wouldblockasignificantpartiscancelled. The upstream reach of the river has a relatively small impact at the amount of sediment comparedwiththemiddlereachofariver.therealisedhydropowerdamsarelocatedinthe upstreamreach. Whensedimentgetsblockedbyadamfirstthelocationdownstreamofthedamthiswillresult in erosion of the river bed. Since the transport capacity of the river has not changed the amountofsedimentblockedwillbebalancedbybeddegradationandthereisnodirectimpact ofthesupplyofsandtothecoast. However,adifferentflowregimewillchangetheyearlytransportcapacityoftheriverandthiswill influencetheamountofsedimentarrivingatthemouthoftheriver.inthefuturealsothechangeof bedlevelduetothe(slightly)reducedamountofsedimentwilldecreasethetransportcapacityof the river. With an over assumption of reservoir capacity the reduced flow near Hoi An leads to a reductionintheorderofmagnitudeof3%oftheyearlysedimentdischargeoftheriver.basedona reductionofthedominantflowfrom386m 3 /sto378m 3 /s. 90 CoastalerosionHoiAn

97 TableE.1Sedimentreductionduetodam Dakmi4Cisinusefrom 2011(greendotin FigureE.6 (OperationNews,2012) TheproposedSong Tranh5(reddotinFigure E.6)washaltedalong withotherprojects (News,2012) ThebuildingofSong Tranh4(yellowdotin FigureE.6)hasstarted in2011 (QNDN,2011) FigureE.6HydropowerdamsintheThuBonriver(ADB,MONRE,EVN,MOIT, QuangNamDONRE,2008) E.1.5Landreclamationinfluencingflowpattern Orderofmagnitude:None Apossiblecauseforlocalerosionisthechangeofconditionsjustbeforethemouth.Anychangesin dynamicsinsuchlocationwouldhaveanquickimpactonthecoastalzone. In2009(CuaDaibridgeground breakingceremony,2010)thebuildingofthecuadaibridgestarted with the temporary reclamation of land to build bridge parts. In December 2015 this land is still reclaimed after finishing the bridge two years ago. The width of the river is reduced by this reclamationbyonethirdfromthenorthsideasseeninfiguree CoastalerosionHoiAn

98 Suchchangewoulddefinitelychangetheriverdynamicsandflowconditionsandthuscanbeseenas areasontocauseerosionatcuadaibeach.howevertherearealsovalidreasonswhytheerosionis notsignificantlycausedbythislandreclamation.herefollowsalistofreasonwhynot: Theerosionstartedseveralyearsbeforethestartoftheconstructionofthebridge. Anarrowingoftheriverwillcauseaccretionaroundthereclaimedlandbutalsoerosioninthe narrowedbed. Theflowoftheriverisatthelocationofthebridgestill700meterswidecomparedtoawidth ofonly400metersinthemouth. Thenorthsideoftheriverthatisblockedseemstobethesidethatcarriesaverysmallamount of(sediment)dischargecomparedtothesouthsidewhichisstillunblocked. Tosupport/confirmthishypothesisthatthistemporaryreclamationisnotasignificantfactorforthe erosionatcuadaibeachtherewouldbeaneedfordata.severalaerialphotographsormapsfrom the last ten years for the river area could be used. Also a model can be set up to simulate the situationwithandwithout.thiswouldrequiretimeandresourcesandtheresultwouldbeasreliable asthedata.withthelistedreasonsitisnotadvisedtoresearchfurtherintothisdirection.toregain as much as the original conditions to prevent a possible negative influence, it is however highly advisedtoremovethelandreclamationinthenearfuture. FigureE.7NarrowingbyreclamationforthebuildingoftheCuaDaiBridge E.2 Natural causes E.2.1Tectonicsubsidence Orderofmagnitude:None SinceerosionisoccurringalongalmosttheentirecoastofVietnam,youmightsuspectacommon cause.oneofthereasonsfortheerosioncouldbetectonicmovements,whichcanleadtorelative sealevelrisecomparedtovietnam sshoreandthereforeerodethecoast.theearth scrustisbroken upinseveralearthplates,whichcanconvergetoanddivergefromeachother.inthefollowingmap, themajorearthplatesaredepicted. 92 CoastalerosionHoiAn

99 FigureE.8Earthplates(JohoMaps,2015) Theedgesofearthplatesaremostactiveinshapingthelandscape.Convergingearthplates(depicted bytheblacklinesinfiguree.8)canshiftovereachother,divergingearthplates(depictedbythered lines) can create rifts. Besides the occurrence of earthquakes in those regions, the converging movementofplatescanalsopushlanduporpulllanddownbeneathanotherplate,calledtectonic subsidence. Vietnam, part on the Eurasian plate, is not located on the edge of a plate. However, the Austral IndianPlateissubsidingundertheendoftheEurasianPlate.Thisendisaminorearthplate,called thesundashelfofsundaplate,onwhichthesouthernhalfofvietnamislocated.thiscollidingzones, asdepictedinthemap,arethemostactiveintheworldandcausedamongstotherthedisastrous December2004tsunami(EarthScope,2014). Thecomplexplayofearthplatescancauseedgestosinkandwouldgeneratearelativesealevelrise thaterodesthecoast.measurementsofverticalmovements,byforexamplegps,arenotavailable forhoianoranyotherpartofvietnam.othertectonicsubsidencemechanismsthantheearthplates collisionarenotknownandcouldalsonotbeverifiedwithmovementdata.adefinitiveexclusionof tectonicinfluencesisthereforedifficult.however,hoianisnotlocatedalongacollidingedgeand due to the elasticity of the plates, the influence of collision between the AustralIndian Plate and SundaPlatewouldbeminor.Furthermore,theverticalmovementsarerelativelyslowcomparedto othercontributorsofcoastalerosion(thao,2014).theassumedinfluenceisthereforenearzero. E.2.2Climatechange TherearetwooptionswhyclimatechangeisapossiblecontributingfactorintheerosionatHoiAn. The first being sea level rise and the second being changing weather conditions. The changing weatherconditionsmostlyfocusonanincreasingfrequencyandintensityofstormsortyphoonsdue toglobalwarming(fengcaia,2009). Sealevelrise Orderofmagnitude:0.5m/year Sea level rise is a wellknown driver for coastal retreat. The sea level rise at Hoi An is around 4mm/yearforthelast50years(ISPonreVietnam,2009)andexpectedtorise6mm/year(Ministryof NaturalResourcesandEnvironment,2009). FollowingtheBruunRule,asexplainedinAppendixC.1theshorelineretreatsduetotheanadaption of the bed. Sand from the shore is transported to the near shore to form the same bed slope as before the sea level rise. Although sea level rise valid for Hoi An, the extreme amount of erosion cannotbesolelyexplainedbyaminorchangeinsealevel(son,2016). 93 CoastalerosionHoiAn

100 Eq.E2 (Bruun,1962) Inwhich: TheBruunRulehassomecriticsandthereforealsotheLeathermananalysisisused.Followingthe Leathermananalysisthiswouldcauseanretreatof0.480m/yearwhennottakingintoaccountthe accretionduetotheriversupply(bosboom&stive,2015). Erosionormoreprecise,shorelineretreat,duetosealevelriseisexpectedtobetakingplaceata rateofhalfameterperyear. Increasingstorms Orderofmagnitude:2.5m/year Anothereffectofachangingclimatethatcanimpactthecoastalbalanceandcauseerosionisthe increasing amount of storms. As explained in chapter four, during storm conditions sediment is transportedseawards.normallythisinbalancewiththereturnofsedimentduringcalmerconditions. Howeverwhenthereisanincreasingfrequencyand/orintensityofthestormthelossofsediment canbepartlypermanent. Duetothewarmerairattheequatorandthereforelargertemperaturedifferencesbetweenequator andpoles,heavierstormswillformwithmoreextremewaveconditions(isponrevietnam,2009)( PrimeMinisterNguyenTanDung,2011)(NASA,n.d.).Thiscanalreadybeseenwhenlookingatthe rateoftyphoonshittingthecentralcoastinvietnamoverthelastcentury(cat&al.,n.d.): :117typhoons :134typhoons :171typhoons Itcanbenoticedthattheamountoftyphoonsisincreasing.Again,higherwavesthatariseduring typhoonscancausemoreerosion,andwithmorestormsthiserosionwilloccurmoreoften. FigureE.9Shorelinechangeduetoincreasedroughconditions 94 CoastalerosionHoiAn

101 Arelativerougherwaveclimate(duetoincreasingstorms)couldchangetheoffshorebathymetryas showninfiguree.9.themildconditionroughconditionvariationofsedimentispresent.however nexttothisthereisalsoamovementofsedimentoffshoretomakealongerrelativelyflatstretchof seabed.thesandforthisincreasedstretchislikelytocomefromthecoast. Thefollowingisaveryroughestimationofthesedimentlossduetoincreasedstormconditions.A newbedisexpectedtoforminaperiodofadecadeafterwhichastablesituationshouldappearin respect to increased storm conditions. In this decade it is assumed that the sediment that is lost temporary to the foreshore during the extra storms will not return. The amount of storms is expectedtoriseanalogueandareexpectedtorisesimilartothetyphoons.alargestormdisplaces cubic meters of sand over a four kilometre stretch of beach, see the section E.3.1 Storm variation.theamountofstormsincreasedwith171134=37peryear~1.2storms.thisresultsina slight overestimation with 1.2 times 40,000 ~ 50,000 m 3 /year or 2.5m/year. The overestimation comesfromtakingaoneinfiveyearstorm. E.2.3Nearshoreconditions Orderofmagnitude:None Near shore underwater conditions like morphology and water depth influence the local wave climate.duetochangingunderwaterconditions,likeshiftingsandbarsoraccretionwaveclimateis likelytochange.iflargerwavescanmeettheshore,moreerosioncomparedtothepastwillhappen. The change in near shore bathymetry as depicted in Chapter might change the stream directions. Thechangeinstreamdirectionsmightchangethelocalsedimentbalanceandsuchresultinaccretion and erosion at locations as explained in the paragraph about river streaming. If this change in bathymetryalsochangesthewavesconditionsnegativelyisunsure. Reasonswhyitislikelythattheerosioniscausedbyachangeinwaveclimateduetothebathymetry change: Thereisalargechangeinthenearshorebathymetry,thiswilldefinitelyinsomewayinfluence thenearbybeach. Wavescomingfromthesoutharepartlyblockedbythereduceddepth.Thismightreducethe accretioninthemildseasonsinceerosiontakesplaceonthelocationofbreaking. Stormsurgelevelscanslightlyincreaseduetoanincreasedfunneleffect. Reasonsagainsterosioncausedbyachangeinflowduetothebathymetrychange: Normallyareductioninwaterdepthwillresultinareductionofthesignificantwaveheight andthereforeresultsinreducederosion,notincreasederosion. Itisnotlikelytocauseasedimentlossoveralongerstretchofcoast.Theeffectwould expectedtobemorelocal. Following this reasoning the expected effect, if any, would be in favour of accretion instead of erosion. In both causes the effect is limited in time and therefore the order of magnitude will be expectedtobezero. E.3 Natural variation The shape of most coastlines is dynamic. In Hoi An the coastline has a seasonal character due to typhoonsandstormsinthestormseasonandmilderconditionstherestoftheyear.furthermorean onshoremovingsandbarhasbeenobservedbetween1989and1995.itcannotbedeterminedyet whether such a sand bar is a cyclical occurrence or that it was a single instance, since long term recordsarenotavailable. 95 CoastalerosionHoiAn

102 Whereas storm appear yearly the amount and intensity varies. Even without climate change this influencestheyearlyandmultiyearlyvariationoftheshoreline.thecoastcanmovelandwardsin onedecadeandmoveseawardsinthenext.withthestormvariationthisisaprovenconceptforthis location,howeverifthesandbarmovementonshoreortheriverstreamdirectionarecycliceventsit islesssure.inthissectionitisthereforechosentogivetheorderofmagnitudeofdifferenterosion driversinmetersinsteadofmetersperyear. E.3.1Stormvariation FigureE.10Consideredcrossshoreprofile.(Chang, 2015) Orderofmagnitude: 1 / 5 yearstorm:35m 1 / 50 yeartyphoon:120m TheBruunprofilewasusedtofittheprofileofthe erosional beach in Hai Hau in northern Vietnam. FortheparametersAandthevalues0.136m 1 and were found respectively (Nguyen, Zheng, & Zhang, 2012). Although this erosional beachisatadifferentlocationinvietnamitcanbe usedasareferenceforthecuadaibeachprofileas thisbeachisalsoinastateoferosion. Fittingbathymetricdataofthecrossshoreprofile ofcuadaibeachfromtheyear2010resultedina similar value for A of m 1.There was howeveralargervalueforof0.629thatiscloser tothevaluesuggestedbybruun.bruunsuggestsa value forof 2/3. This gives confidence in the assumption that the profile from the data is trustworthy.sinceitisinlinewithobservationsof othercoastsandthereforereliabletobeusedfor further analysis. This check is done since the source of the data and the method of measurementsarenotknown. FigureE.11DatafittedtotheBruunprofilefromFigure E.10 The crossshore profile shifts due to a heavier waveattackduringstorms.thisisthecauseofthe variationintheprofileandmakesforatemporary lossofsandofthebeach.theextentofthistemporaryerosionisimportantasstructuresclosethe beachcanbethreatened. ToquantifytheretreatofthecoastlineduethestormstheDUROS+methodwillbeused.Theinputis formedbytheprofilefoundinthedata,thesediment,thecharacteristicsofthestormwavesandthe surgelevel.theedgeatthedunewillerodewithanangleof1:1whiletheangleunderwateratthe toewillstabiliseat1:12.5(denheijer,2013).inbetweenaprofileisfittedsuchthatthetotalvolume depositedatthetoeisequaltothevolumeofsanderodedatthecoast.theprofilehastheformula: Eq.E3 (DenHeijer, 2013) With: 96 CoastalerosionHoiAn

103 The formula can be used for both storms and typhoons. Between 1945 and 2003 roughly 1.2 typhoons reached Hoi An each year. For Hoi An the largest typhoon was named Fritz. It had an offshoresignificantwaveheightof10.5mandpeakperiodof13.4sbutduetotheshallowdepthin frontofhoianwavebreakingreducedthewaveheightto6m(mau,2006).sincethisstormwasthe largestinabout50yearstostrikehoianitisassumedthesearethe1in50yearconditions.thelocal stormsurgeconditionswitha1/50returnperiodisasurgeof2.86m(thuy,2003).basedonthis inputtheeffectofasuchatyphooncanbecalculated.basedonthiscalculation79.5m 3 /mofbeach wouldbetemporarilyerodedanditextends120mlandinward.thisishoweveranextremesituation. Overwashandsubsequentfloodingareignoredinthisempiricalcalculation. FigureE.12DUROS+resultfor1/50yeartyphoonconditions Themorecommonstormscanalsomovesandfromthebeachoffshore.Dataaboutmoreaverage stormswaslimited.onlybetween and wavedatawascollected.dividingthis datafrom(thy,2010)into12hourblocksandaveragingthewaveheightsandperiodswithinthese blocksgivesrepresentative storm waveconditionswhenassumingeachstormlasts12hours.asthe dataisfromoctober,whichisamonthinthestormseasonthatlastfromseptembertodecember,it isassumedthemeasuredclimateisaboutthesameasfortheothermonthsinthestormseason.if largerstormsareexpectedlaterinthestormseasonthisanalysiswillunderestimatewaveconditions onlargerreturnperiods.howeversincenobetterdataisavailablethisassumptionhastobetaken. The yearly storm conditions are derived by calculating the once in four months wave conditions based on the measured data. Since the other months outside the storm season are assumed to containnostormsthisalsotranslatesintoaonceperyearstorm.alsoimportanttonoteisthatno typhoonsweremeasuredinthedatasothesearenotincluded. 97 CoastalerosionHoiAn

104 TableE.2Waveheightcalculation Hss_bin[m] Observations Cumulative observations P Q HigherHss expected permonth LN(Q) Totalof12h measurements TableE.3Waveperiodcalculation 31 Tp_bin[m] Observations Cumulative observations P Q HigherTp expected permonth LN(Q) Totalof12h measurements CoastalerosionHoiAn

105 FigureE.13HssandTpfittings Thefittothedatagivesstormconditionsthatarenotrelatedtotyphoons.Byusingthesevaluesthe storm profiles for lesser storms can be computed. Monthly and yearly storms turn out to be not strongenoughtobesuitableforacalculationwithduros+.howeverthestormwithareturnperiod onceper5yearsdoes.thecorrespondingsurgelevelis0.86m(thuy,2003).damagetothebeach extends35minlandas10.6m 3 /mismovedfromthebeachtotheforeshore. TableE.4ExtrapolationofHssandTpforlongerreturnperiodsbasedonmeasureddatafrom(hi,2010) Q(prob.of exceedance) Hss Tp permonth peryear* per5years per25years per50years per100years *assuming4monthsofstormseasonwithnostormstherestoftheyear 99 CoastalerosionHoiAn

106 FigureE.14DUROS+resultfor1/5yearconditions Inconclusiontheeffectoftyphoonsonthebeachcanbetemporarydevastatingoveralargewidthof thebeachmovingalotofsandtotheforeshore.theempiricalcalculationsuggests120mofbeach impactedbyitand79.5m 3 /mofsanddisplaced.lesserstormswithareturnperiodof4to5yearsor longercancausesandtomovetotheforeshore.thecalculationsuggests35mofbeachisaffected and 10.6 m 3 /m sand displaced. For these storms the problem is rather limited if there sufficient beach to compensate the temporary loss. Under normal conditions sand that is moved to the foreshorecanreturnprovidedthereissufficienttimebetweenconsecutivestorms. E.3.2Sandbarmovingonshore Orderofmagnitude:averaged60m(1,230,000m 3 ) FigureE.15Observedsandbarinin1989.Adaptedondatafrom(Hoang,Tanaka,Viet,&Duy,2015) In 1989 a sandbar was observed approaching the coast of Hoi An. As stated earlier in section3.1 Evolutionofthecoast,thissandbareventuallymergedwiththecoastbetween1991and2000and widenedthebeaches.thevolumeofsandcarriedbythesandbartothecoastcanbeapproximated fromthelandsatimages.assuminganaveragewaterdeptharoundthebarof3m,aslopeof1:20(3 degrees)andthatanadditional20%ofthevolumeofthebarispresentunderwaterthevolumecan becalculatedasfollows: 100 CoastalerosionHoiAn

107 Eq.E4 With: [] Withthiscalculationthevolumeofsandamountsto1,370,000m 3 or1.37millioncubicmeters.the assumptionisthat90%ofthisvolume,1,230,000m 3,wasaddedtoCuaDaibeach.CuaDaibeachhas a length of about 3 km and with an assumed active depth of 5 m it is calculated that the beach widenedbysuchanourishmentwithabout80m.indeedalargeadvancementofthecoasthasbeen observedinsubsequentyearswiththemostadvancementclosetotherivermouthandlessatthe endofcuadai.althoughtheseareveryroughcalculations,itillustratesthescaleofsuchanatural sandbaranditseffectonthecoast.lastyearsthenaturalequilibriumisrecoveringandthatiswhy thereisalotoferosiontheseyears. E.3.3Sedimentstreamingduetoriverflowdirectionvariation Orderofmagnitude:5m/year AnothernaturalcausefortheerosionmightbethemovementsoftheThuBonrivermouthandin whichdirectionmostofthesedimentisflowingwhenitreachesthesea.thiswouldexplainthesand barthatisvisiblein1989inadifferentway. Namely, as part of the ebb tidal delta above sea level, formed by sediment from the river. The hypothesisisthatthemajoroutflowdirectionofthethubonriverhasshiftedfromnorthwardsto southwards in about 30 years, while the amount of accretion at the spit was influenced by the sandbankinfrontofit.howthismighthavehappenedisdescribedinthetextbelow. FigureE.16Coastlinevariationbetween1975and1991(Hoang,Tanaka,Viet,&Duy,2015) It is presumed that 40 years ago the main outflow direction was directed to the north. This preferenceforacertainoutflowistheresultofhowtheriverbankisshapedbeforetheriverflows intothesea.thesandbankmightbeexplainedbyseveralyearsofexcesssedimentsupplyfromthe river.withagrowingheightofthebank,moresedimentwastrappedandaccretedonthebankuntil itwaspushedupabovethesealevelbywavesandwindfromtheseaandriverflowfromtheother direction. LookingatFigureE.16,thewidthofthespithasincreasedbetween1975and1989andwasdeclining againwhenthesandbankwasgettingsmaller.thesandbankmightbethecauseforthis. 101 CoastalerosionHoiAn

108 Sedimentcanbetrappedbetweenthecoastandthebank,leadingtoaccretionattheendofthespit andareducingamountofsedimentthatisdistributedoverthetotalstretchofcoastnorthofthe river mouth. The erosion that would arise at this northern stretch is also visible on the Landsat image:between1975and1989thebeachisretreating. Atsomepointintime,probablyaround1990,theshapeofthespithaschangedsomuchthatthe easiestoutflowdirectionbeganturningsouthwards.theerosionbywavesonthesandbankstarts overrulingtheaccretionbysedimentsupplyandthesandbankisgettingsmaller.thesandbankis alsoshiftingtothecoastduetothereducedwateroutflowagainstthesandbank,whilewavespush thesandtowardsthecoast.whenthebankreachedthecoast,itleadtoaninitialincreaseinbeach widthofabout80m,ascalculatedintheprevioussection.thatthedominantoutflowdirectionhas turnedsouthwardsisalsovisiblefromlandsatimageinfiguree.17.from1975to2015,theland southoftherivermouthisfollowingtheexpectedoutflowdirection. FigureE.17Coastlinevariationbetween1975and2015(Hoang,Tanaka,Viet,&Duy,2015) With the sediment supply moving southwards, the spit started changing fast. Figure E.17 shows a major retreat between 2000 and 2015, which is explained purely by natural processes in this hypothesis.theshapeofthespitisadaptingtothereducedsedimentsupplyfromtheriver,which wasdirectedtowardsthespitbythesandbank.usingthesatelliteimagesofgoogleearth,thewidth ofthetipofthespithasdecreased60mfrom2004to2012andanother100muntil2015.without anyfixationfromtreesorbuildings,thisendofthespitischangingfromyeartoyear.meanwhile,the ebbtidaldeltaisshiftingsouthwardsaswell,sincethisdeltaisformedbyriversedimentsupply.this isshowedinfiguree.18.itisalsoclearlyvisibleherehowtheshapeofthelandjustsouthoftheriver mouthhaschangedovertheyears. Muchslowerratesoferosioncomparedtothoseattheendofthedynamicspitareoccurringnowat Cua Dai Beach. This can also be explained by the reduced sediment supply due to the southward shifting outflow of the river. To quantify the influence of the change in river outflow direction is difficult.thealongshoretransportofsedimentthatdistributesthesedimentalongthecoastisfora largepartbasedonwavesandwinds.thecontributionofthedirectionoftheoutflowdirectionis thereforehardtomeasure.fromtheshapeofthetidaldelta,themajoroutflowdirectionoftheriver canbeseen.infiguree.18,theblacklineshowsisplacedperpendiculartothecoast. Ifoutflowoftheriver,depictedwiththeredline, coincideswiththeblackline,equalamountsof sedimentaredeliveredtobothsidesoftherivermouth(nottakingintoaccounttheactionofwaves andwind).itisassumedthatthedeltashapein1965iscomparabletothatin1975,becauseitis similar to the 1975 shape in the Landsat images. The outflow direction is slightly directed to the north, and based on eye comparison it is sending about 55% of the sediment north and 45% southwards.in2014thedirectionismoresouthwards.thedistributionisaround35%tothenorth and65%tothesouth.thesedimentsupplytothenorthhasthereforedecreasedby20%.usingan annualriversedimentsupplyof500,000m 3,thesedimentdeclineis100,000m 3.Thisiscomparable tothesedimentreductioncausedbysandminingandthereforetheorderofmagnitudeoferosion duetochangesintheriveroutflowdirectionisalso5m/year. 102 CoastalerosionHoiAn

109 FigureE.18Directionofsedimentoutflowfromthe river Followingthishypothesis,itmightwellbepossiblethattheoutflowdirectionwillturnnorthwards againinthefuture.however,whenthespitisgettingmoreandmorefixedbytheconstructionof buildings,thisnaturalprocessmightbedisturbedtosuchextentthatmuchvariationisnotpossible anymore. 103 CoastalerosionHoiAn

110 F.Currently applied solutions InHoiAn,severalcoastalprotectionmeasureshavebeeninstalledalongtheCuaDaiBeach,which canbefoundatlocation1to7,asshowninfiguref.1.inthissection,ananalysisofthesemeasures isgiven.itstartswithanoverviewofthecurrentmeasures,thesecondpartdescribeshowcurrent seawallsandrevetmentscanfail. FigureF.1LocationsofcoastalprotectionmeasuresalongCuaDaiBeach F.1 Applied solutions F.1.1Smallsandbags Starting on the left at location 1, a simple shore protection has been built which consists of small sandbagsinordertoprotectthebeachfromwave impact. These bags should fulfil the same function as the geotextile bags, but due to their smaller dimensions and weight, they are more susceptible to displacement, as can be seen in Figure F.2.To increase the resistance against sliding, dozens of small bags are put into one large bag of approximately2x2x3m.onastormyday,itcan beseenthattheseimprovisedsandbagstructures donotworkproperly,becausethebagsaremoving duetothewaveimpact. FigureF.2Manlookingdownatfailureofthe improvisedsandbags F.1.2Geotextilesandbags Atlocation2,afivehundredmeterlongrevetmentofgeotextilesandbagsisinstalledtolimitthe coastal erosion. According to (Viet N. T., 2015)the bags cost approximately 140 each and are imported from the Netherlands. This is a governmental investment, which only protects a certain stretchofthebeach. Function The geotextile sand bags need to protect the beach from strong wave impact. The sandy beach behind the bags is kept in place. As a result, the sand cannot wash out and the beach width is maintained. 104 CoastalerosionHoiAn

111 Methodofplacement The bags placed on Cua Dai Beach are measured and have dimensions of 230 x 130 x 45 cm, containingabout3tonsofsand.thefillingandplacingisdoneonsitewithsandfromthebeach. First,ageotextilesheetisplacedonthesandybeachslope. A relatively steep slope can be built with a maximum of 1:1.5, as shown in Figure F.4 (Scottish NationalHeritage,2015).Adoublerowofbagscouldpreventwavesfrompenetratingintothegaps betweenthebagsandthuspreventawashoutofsediment.inhoianhowever,onlyasinglerowof bagsisinstalled.thesandbagsarestackedagainstthepreparedslopewiththeirlongaxesparallelto theshorelineandfixedatthetoewithwoodenpiles. (Dis)advantages Thebagscanbeplacedwithoutcostlyequipmentorskilledlabourandcanfollowanyshorelineform, but they have a short life expectancy due to a low resistance to physical damage (debris and vandalism) or UV sunlight. Generally, the bags have an unattractive appearance, which could be solvedbyburyingthebagswithanadditionalsandlayertoputthecompleterevetmentunderthe duneface.thisishowevernotdoneinhoian. FigureF.3Geotextilesandbagsalonga sectionofcuadaibeach FigureF.4 Schematiccrosssectionofsandbagrevetment F.1.3Breakwaterwithlonggeotextilebags Thelonggeotextilebagismadeoutofawovenpolypropylenegeotextile.Itrangesinsizefrom1.5to 5mintheoreticaldiameter(TenCate,2015). Function Thelonggeotextilebagscanbeseenasanemergedorsubmergedbreakwater,whichreducesthe waveimpactonthesandybeach.consequently,soilisretainedandthereforeerosionisprevented. As such it can be used in revetments and breakwaters. At location 3 (see Figure F.1) an entire breakwaterhasbeenconstructedusingthesesandbagunits.itfulfilsthesamefunctionasanormal breakwater. Methodofplacement Firsttheareaispreparedandclearedofdebris.Thenalayerofgeotextilesheetisappliedonwhich the unfilled bags will be placed. Finally a mix of sand and water is pumped into the bag to fill it (TenCate,2015).Theinstallationusuallytakesplacearoundlowwatertomakeinstallationofallthe bagseasier.thisentireprocesscanbecompletedquitequickly. (Dis)advantages Advantagesofthelonggeotextilebagsaretherelativelowcostandsimpleinstallation.Becauseof thistheycaneasilybeapplied.however,thereareseveraldisadvantages.geotextilesareproneto creepovertimewhensubjectedtorepeatedstrain.polypropyleneinparticularisvulnerableasithas a high elasticity modulus. As a result the tensile strength is reduced by 75% for designs with this application of a polypropylene geotextile (Schiereck & Verhagen, 2012). Additionally, the creep causesthebagstosagandshiftovertimecausingpartsofthestructuretobecomeunstable. 105 CoastalerosionHoiAn

112 Thismakestheapplicationofgeotextilesandbagslesssuitableasalongtermsolution.Anouterrock layerandarockunderlayerassuggestedbythemanufacturercanmitigatethisproblemasthebags willnolongerbeexposedtotherepeatedwaveforcing.thiscouldhaveturnedthestructureintoa moreconventionalrubblemoundbreakwater,buttheyarenotappliedinhoianthisway. FigureF.5BreakwaterinfrontofVictoriaresort F.1.4Rubblemoundbreakwater FigureF.6Longgeotextilebagsascoreofapermanent breakwater(tencate,2015) Function Thebreakwaterblocksincomingwavesandprovidesacalmerwaveclimatebehindit.Inturnthis prevents erosion by waves behind the breakwater. At location 4 (see Figure F1) an Lshaped breakwaterhasbeenbuilttoprotecttheresortatthatlocation.withinthelshapesomesandhas accumulatedandformsasmallbeach. Methodofplacement Usually a breakwater consists of a core, one or several filter layers, an under layer and an outer armourlayer.inthiscaseonlyonelayerofrockshasbeenappliedasbreakwater.thestonesrangein sizebetweenadiameterof500mmto1250mm.assumingadensityof2000kg/m 3 theweightofthe stonesrangesbetween250kgand3750kg.nofilterlayerseemstohavebeenappliedbeneaththese stones.thestoneshavesimplybeendumpedintheappropriateshapeasprotection. (Dis)advantages The advantage of a welldesigned breakwater is that it can block longshore transport over some distance and stop the structural erosion over a particular area. Furthermore it can easily be maintainedduetoitssimpleconstructionelements.howevertheconstructioncanbeexpensiveasit requirestheuseoflargerocksthatoftenneedtobetransportedforsomedistancetotheintended site. Breakwaters also do not solve the erosion on a larger scale. The breakwater enhances the erosiondowndriftofthebreakwaterwhichusuallyresultsinthebuildingofmorebreakwatersuntil anareaisreachedthatisallowedtoerode. Finally, in this particular case no bed protection seems to be applied under the rocks. This allows sandtobetransportedoutofthegapsbetweentherocksofthebreakwaterandscourdevelops.this canleadtodamageandevenfailureofthestructureovertime. FigureF.7LshapedbreakwateratGoldenSandsresort 106 CoastalerosionHoiAn

113 F.1.5Impermeableconcreterevetment The750mlongimpermeableconcreterevetmentcanbefoundatlocation5,wheretheroadisvery closetothesea.thestructureispaidbygovernmentalinvestment. Function The main function of the hard revetment structure is to prevent seasonal erosion by creating a impervioussurface.roughnesselementsareplacedontopoftheslopetoreducethewaverunup. Fromvisualobservations,ithastobenotedthatthestairsintherevetmentweremoreeffectiveat reducingtherunopthantheroughnesselementsthemselves. Theslopeandheightoftherevetmentwerecalculatedbymeasuringthedimensionsofthestairs, whichisbuiltintherevetmentandthereforehasanidenticalslope.atlowwater,21stairsof0.55m longand0.16mhighwerecounted.sinceitisnotpossibletolookbelowthewaterline,itisassumed thattherevetmenthasfouradditionalstairsuntilitreachestheconcretecylinderfoundation;theso called Vietnamesetoes (Hoop,2006). FigureF.8Concreterevetment FigureF.9Schematiccrosssectionofconcreterevetment. Methodofplacement The height of the dike consists of the design water level, the wave runup and the extra height needed for the relative sea level rise during the plan period. The slope of the revetment should extendwellbelowthenormalbeachleveltoallowsomeforeshoreerosion. InVietnam,verticallyplacedconcretecylinderswithalengthofabouttwometersandadiameterof aboutonemeter,areplacedatthetoeoftherevetmentstructure.rockarmourplacedinfrontof thetoestructurewillprovideadditionalsupportandreducetheintensityoftheforeshoreerosion. Thecrestlevelfortheconcreterevetmentwillbehigherthanarockrevetmentsincethestructure willsuffergreaterwaverunupoverthesmoothandimpermeablesurface. (Dis)advantages Theadvantagesarethattheyarestrongandprovidegoodprotectionbyabsorbingthewaveenergy. The continuous and impermeable concrete revetment presents neat appearance and allows easy accesstothewater.theyhavehighinitialinvestmentcosts,butalowmaintenancecosts(scottish National Heritage (2015). Another advantage is that buildings can be placed close to the sea. The disadvantage is that the concrete appearance is not attracting tourists compared to the sandy beachestheyexpected.also,thesmoothsurfaceoftherevetmentdiscourageshabitationbywildlife ormarineorganisms. F.1.6Seawall Location6indicatesthepositionoftheverticalseawallatCuaDaiBeach.Thishardstructureinthe formofaverticalconcretewallisoftenappliedinareaswheregoodprotectionisneededandwhere space is scarce. The exposed beach fronts of the resorts are a good example. At location 8, the verticalseawallhascollapsed,whichhascausedtremendousdamagetothehoianhideawayresort. 107 CoastalerosionHoiAn

114 Function Theprimaryfunctionofaseawallistopreventdamagetostructuresclosetotheshoreline.Theyare builtparalleltotheshoreandaimtoholdorpreventslidingofthesoil,whileprovidingprotection from wave action. Hard engineered structures such as the seawall have a secondary function as coastalflooddefences. Methodofplacement Duetothereflectingwaves,thescourcanbecometoolarge,whichmayleadtototalfailureofthe structure. The seawall at the collapsed Hoi An Hideaway resort seemed to be built on a pile foundation.thiswasvisibleatthebottomsideofthecollapsedwallsection.approximatelythree metersinfrontoftheseawall(attheseaside),arowofcylindricalconcretetubeswasvisibleduring lowwater.possiblytheywereimplementedtoinducewavebreakingawayfromthewallandthus reducingthewaveimpactorforgeotechnicalstabilityofthewall.horizontalanchorrodsareplaced inthesoilforhorizontalequilibrium.ascanbeseeninfiguref.10,theseanchorrodsarebrokendue tothefailureofthewall. (Dis)advantages An advantage of seawalls is that they can be constructed at locations where there is less space available.thatisjustinfrontofthehotelsalongthebeachstrip.seawallsarestrongdefencesthat aredurableeveninincreasedenergyenvironments. Ontheotherhand,theconstructionofseawallsisexpensiveandmakesthebeachnonfunctionalfor recreation.thestructureisnotapleasingsightandmayruinthelandscapeofthesea,whichisan importantfactorforthetourisminhoian. FigureF.10CollapsedHoiAnHideawayresort FigureF.11Schematiccrosssectionofseawall. F.1.7.Vegetation At the tip of the spit (location 7), young vegetation has been planted in the dune area. It takes a coupleofyearsforittobecomeafullydevelopedvegetationzone.nevertheless,effortisdoneto installaprotectionmeasureinanaturalway.inotherwords:buildingwithnature. Function Plantingvegetationhelpsinstabilizing dunesbyreducingtheimpactofwindandwater. Thevery young vegetation at Cua Dai Beach (plant name: Casuarina equisetifolia. In Dutch: Australische pijnboom)canbefoundintheduneareaatthefullwidthofthespit. Method Toprovidemaximumwinderosioncontrol,vegetationisplantedonthedunesofthespit,whichhold toloosesoilinplace. 108 CoastalerosionHoiAn

115 (Dis)advantages Foraminimuminvestment,vegetationplantingswillhelpbindthesoilagainsterosionandextend thelifetimeoftheprotectedsandbody.theplantsneedtobearhighsalinityconditions,directsun, extremeheat,lackoffertilesoilandafluctuatingwatersupply.especiallyveryyoungvegetationis notabletoprotectagainsttoughstormconditions.vegetationwillalsoneedoccasionalfertilization. FigureF.12Casuarinaequisetifolialocatedonspit FigureF.13Staggeredpatterninplantingvegetation F.2 Failure of seawalls and revetments TheHoiAnHideawayresortisanabandonedestablishmentalongCuaDaiBeach.Duetothesevere coastal erosion, the beach has disappeared and the buildings are very close to the water. For protectionagainstfurtherdegradation,averticalseawallhasbeenbuiltatthewaterline.ascanbe seen from the pictures below, the vertical wall has failed and the property has been destructed heavily. Consequently, the resort has been closed. The failure mechanism behind this collapse is analysedhere.furthermoreothersimilarstructureslikerevetmentsfacethesameriskandassuch makethisanalysismorevaluable. FigureF.14CurrentfailedseawallinHoiAn 109 CoastalerosionHoiAn

116 F.2.1Calculationforscourinfrontofaverticalwall Based on visual observations, two scour failure mechanisms can be identified (compare F.14 with F.15):seawardoverturningandsettlementofagravitywall(left)andtoescourundercutandrotation ofaverticalwall(right).bothfailuresarecausedbyscourinfrontofthestructure,whichleadsto geotechnical instability. A quantitative estimation for the scour profile in front of the wall can be calculatedwiththeformulas: Eq.F1 (Xie,1981) With: Forfinesediment: Forcoarsesediment: Thescouratanymomentcanbecalculatedwith: Eq.F2 (Xie,1981) With: FigureF.15Failuremechanisms.Seawardoverturning(left)toescourandrotation(right) The wave height and wave period is taken as the highest measured wave in October 2010 (Thy, 2010)andthewaterdepthinfrontofthestructureisassumedtobe2meter.Thebreakerindexis theratiobetweenthebreakingwaveheightandthewaterdepthatbreaking(h b =h b ).Innature, wavesareirregularandrandom.thetimeaveragedvalueofthebreakerindexisthenintheorderof Here,theupperlimitof=0.5istaken. Anothermodelstudyfoundthatthescouringpatternsofasandbedinfrontofaverticalwallunder theactionofstandingwaveswasdifferentwiththesandgrainsizes.finematerial(d 50 =130m)is transportedlargelyinsuspension,whichscoursatthenodesanddepositsneartheantinodesofthe standingwave. 110 CoastalerosionHoiAn

117 Thecoarsematerial(D 50 =220m)movesmainlyasbedloadandisscouredhalfwaybetweenthe nodes and the antinodes and deposited at the nodes (Best, Bijker, & Wichers, 1971). Figure F.16 showsthetypicalbottomprofilesforfineandcoarsematerialsmentionedabove. FigureF.16Typicalbottomscourprofilesforfine(left)andcoarsematerial(right) Using formula F1, the maximum local scour depth is calculated at a certain distance from the structure.thecalculationindicatesthatascourholeofy max =1.13moccursatat3.50mfromthe verticalwallatl/8sincethesandonthebeachiscoarse(d 50 >220m),seeAppendixI.3.Although 1.13misasignificantscourhole,giventhe3.5mdistanceitisunlikelytohavebeenthesolecauseof thefailure.structuralerosionmusthaveplayedapartaswell,increasingthedepthinfrontofthe structureleadingtoitseventualfailure. F.2.2Scourinfrontofarevetment AstudyconductedonVietnamesedikesfoundthatatypicalconcreterevetmentcanexpect1.5mof scour(hoop,2006).sincethetoesgenerallyareonly2mdeepinsteadoftherequired4mthishas causedseveraldikefailures(hoop,2006).similarscourcanbeexpectedattherevetmentscurrently implemented in Hoi An.Over the last few years, displacement of these cylinders is observed at severallocationsinvietnam.severalmechanismscanleadtothisfailure: Scour.Failureoccurswhenthescourholegetsdeepenoughtounderminethetoe. Geotechnicalinstability.Failureoccursiftheloadonthetoeexceedsthestrengthofthesoil thatsupportsit. Outwash of the foundation due to flow through the cylinder. Failure occurs in the situation wherethereisahighwaterlevelinsidethedikeandalowerwaterlevelinfront.asaresult, ground water flows through the dike to the toe. Water flowing through the cylinder might washawaythesedimentunderneath.theproblemcaneasilybeavoidedbyapplyingafilter layerorclosingoffthetopofthecylinder(seefiguref.17). HowevertherevetmentinHoiAnshowsnosignsofdamage,althoughthetoesunderwatercould notbeobservedfordamage.sincetherevetmentwasbuiltin2012itispossiblesomeminordamage hasoccurred(especiallyatthetoes)thatisnotvisibleyet. FigureF.17Groundwaterflowthroughtoecylinder(Hoop,2006) 111 CoastalerosionHoiAn

118 F.2.3Structuralerosion A final aspect to cover is the fact that along Cua Dai Beach structural erosion is present. Under normalconditionsitisassumedthatasthewaveconditionsandsandcharacteristicsremainsimilar, theprofileshouldremainsimilaraswell.theerosionwillthereforeonlyleadtoalandwardmigration of the coastline. However, in the case of the revetment sand is taken out of the system by the revetments.thismeansthattheprofilecannolongermigratelandward.althoughthereislimited research into how the profile continues to develop in the presence of a revetment or seawall, observations in California show no significant differences between the beach profiles fronting the wallandthosefromtheadjacentbeach(griggs,etal.,1997). Ifassumedthattheprofilemovesdownwardtocompensatefortheerosionanestimatecanbegiven as to how fast it would be. This situation would resemble an infinitely long revetment where no erosionispossiblefromthebeach.atcuadaibeach60m 3 /m/yearislost(seesectionc.7).at300m from the coast the active depth of 5m is reached. Dividing the 60 m 3 /m/year by 300 m of active length the conclusion is that the seabed would erode by 0.2m/year. This is however a rough estimationbasedontheassumptionthattherevetmentisinfinitelylong.itisalsopossibletoassume that the profile continues to migrate landward and is cut off by the revetment. The revetment prevents erosion on the upper part of the profile and leads to a greater shortage of sediment downdrift.thisassumptionalsofitswithobservationsfrom(griggs,etal.,1997).the0.2m/yearwill beusedasanapproximationwiththeknowledgethattheactualdepthchangemightbedifferent. FigureF.18Downwardprofilechangeswithaninfinitelylongrevetment FigureF.19Landwardmigratingprofilewhenafiniterevetmentisconsidered F.2.4Consequencesforthecurrentstructures AtypicalVietnamesedikeisnotexpectedtosurviveastormwithsurgelevelsof3m(Hoop,2006). Luckilythesestormsurgesonlyhaveareturnperiodof50years(Thuy,2003).Ifaftertwoyearsof erosionthebedlevelhasdropped0.4mthereturnperiodhasreducedtoonly33years(thuy,2003). Iferosioncontinuesatthesamerateafter8yearsoncein10yearstormswillcausetherevetmentto fail.consequentlythelifeexpectancyoftheserevetmentsisreducedsignificantlybythecontinued erosion. 112 CoastalerosionHoiAn

119 G.Erosion prevention possibilities ThisappendixsupplementsChapter6aboutsolutionstothecurrentproblems.Itstartsbyshowing thesystematicapproachthatisusedtotranslatethestakeholder swishesintocriteria.afterthat,an overview of the total problem field is given. This diagram will be used to determine the concrete requirementsfordesigningalternatives.italsofacilitatesinfindingmeasuresforthecurrentissues. Thepossiblemeasuresarestartedwithacomparisonbetweenhardandsoftmeasures.Afterthis, severalpossiblemeasuresaregivenandrankedwiththehelpofamulticriteriaanalysis. G.1 Systematic criteria and option finding Before designing alternatives, it is necessary to know how the alternatives should perform. It is important to know beforehand what the criteria and requirements are for a good solution. The requirementscanbetakenfromthestakeholderanalysisandanoverviewofthetotalsystem. G.1.1Criteria Thestakeholdergoaltrees,asgiveninChapter4.1,canbeusedtoselectcriteria.Whendesigning alternatives for dealing with the problems along the beach of Hoi An, the criteria will be used to checkwhetherthealternativesmeetthecriteria.potentialcriteriaareallitemsinthelowestlevelof thegoaltrees.theseitemscouldallbeusedtoanalysethecoastalerosionproblem.manyofthe stakeholdershaveoverlappinggoals.itemsthatappeartobeimportanttomultipleactorsbecome the most important criteria. These criteria describe the wishes for the whole system on which alternativescanbetested. Potentialcriteria Takingallthelowestlevelsfromthegoaltrees,thefollowingpotentialcriteriaariseforthedifferent stakeholders: Nationalgovernment Lowamountoferosion Lowamountofflooding Highpersonalincome Similarallocationoffunds Fewlegislationexemptions LocalgovernmentoftheQuangNamProvince Lowstructuraldamagetohotels Lowstructuraldamagetohomes Loweconomicdamagetohotelowners Loweconomicdamagetocityinhabitants LoweconomicdamagetoChamIsland Loweconomicdamagetorestoftheprovince Highindustrialincome Highindustrialgrowth LocalgovernmentofHoiAn Lowstructuraldamagetohotels Lowstructuraldamagetohomes Loweconomicdamagetohotelowners Loweconomicdamagetocityinhabitants Partofbudgettoerosionproblems Partofbudgettoothermatters Buildingindustry Highamountofsandavailable Highamountofalternativematerialsavailable Lowcostsofsand Lowcostsofalternativematerials Resortmanagers Largebeachwidth Smalldistancetotheseafromroom Highdensityofcoconuttrees Highgovernmentalfunding Highamountofsharedwishedwithgovernment Highamountofsharedwishedwithotherresorts Frequentmeetingswithotherresorts Tourists Largebeachwidth Smalldistancetothebeach Highdensityofcoconuttrees Lowcostsofchair Lowcostsofentrance Lowcostsofbeverages 113 CoastalerosionHoiAn

120 CitizenslivingfromthebeachinHoiAn Highnumberofrestaurants Highnumberofbars Highnumberofotherjobpossibilities Highflexibilitytomove Highfinancialpower Highgovernmentalfunding Highamountofsharedwishedwithgovernment Sandminers Highsalesofsand Lowminingcostsofsand Lowexportrestrictions Lowminingrestrictions Lowchanceofconviction Lowfine Shortprisonterm Selectedcriteria Inordertodescribethewishesforallthestakeholdersinthesystem,itiswisetoselectcriteriafrom different stakeholders and especially those criteria that are found most important for several stakeholders.thispreventsdisagreementsaboutthesolutioninthefutureandmakeseverybodyfeel engaged. The following list of eight criteria cover the most important wishes. They are generated fromthelistabovebytakingsomegoalstogetherorrewritingtheminordertomakethemfitseveral stakeholders.allstakeholdershavesomeoftheirwishesincorporatedinthesecriteria. 1. Lowstructuraldamagealongthecoast Theerosionrateatsomeplacesissoseverethatitleadstostructuraldamage.Untilnow, tworesortshavebeendamagedandabandoned.inthefuture,moreresortsandalsolocal residences might be structurally damaged. A suitable alternative should prevent more damage. 2. Loweconomicdamagetolocalbeachusers Thestructuraldamageleadstoeconomicdamage,butthisisnottheonlykindofeconomic damage.forexample,adeclineintouristswilldamagethosewholivefromthebeachtoo. Otherfactorsthatleadtoeconomicdamagetolocalbeachusers(restaurant/barowners,life guards, salesmen, et cetera) are defined later on. The beach users are economically dependentofactivitiesonthebeachandthereforeapreventionofmoreeconomicdamage isanimportantcriterionforasuitablealternative. 3. Loweconomicdamagetoresorts Thedistinctionbetweeneconomicdamagebetweenlocalbeachusersandresortsismadeon purpose. Both stakeholders have different ideas about what should happen to the beach. Themostimportantoneisthatthelocaluserswouldliketoseemorepublicbeach.Since resortsareanimportantstakeholderintheproblemandperhapsalsofinancialcontributors to a solution, a low rate of economic damage to resorts is an important criterion for an alternative. 4. Loweconomicdamagetoothersinthearea SomethinglesscommoninVietnam,butacriterionthatwouldfitthegovernmentalbodies, isthattheproblemmaynotbeshiftedtoadjacentareas.currentmeasuresarenotstopping the erosion, but moving the process northwards. An efficient and long lasting solution reducestheproblemsonalargespatialscaleandshouldnotbringdisadvantagestoother regions. The goal of low economic damage to other people in the area than resorts and citizensinhoianisthereforeanimportantcriterionforafuturealternative. 5. Largebeachwidth Thismorephysicalgoalissupportedbybothresortsandlocalbeachusersastourists.Amore attractive, large beach would lead to more tourism, which is advantageous for the local residentsandresorts.sincealargepartofthestakeholdersfindthisgoalimportant,itisa criterionthatshouldbetakenintoaccountwhendesigninganalternative.thedefinitionof beach is here the area of sand between the waterline and the first trees, dune or other obstacles. 114 CoastalerosionHoiAn

121 6. Smalldistancetothebeach Thedistancetothebeachisanimportantfactorforresortsandtourists.Touristswouldnot like to travel too far for a public beach and resort visitors like to walk out of their room straight onto the beach. The tourism affects the resorts and local citizens and therefore anothercriterionthatisimportantforalargepartofthestakeholdersinthesystem. 7. Highindustrialincome Untilnow,mostcriteriafittedthetourists,resortsandlocal beachusers. However,future alternativesmaynothampertheindustrialsectorinthearea.besidestourism,thisisanother important source of income for Vietnam. The industries, for example sand mining or hydropowergenerationintheriver,andbeacherosionmightturnouttobeinterrelated.an alternativefortheproblemmaydisadvantageonofthesectorstoomuch. 8. Lowcostsofbeachvisit If there were to be enough financial resources available for the implementation of an alternative, the situation would not be so difficult to solve. This money might come from resortsorentrancefeestothebeach.however,thebeachbecomeslessattractivetotourists whenthecostsofabeachvisitbecometoohighandwhenthereislesspublicspace.less tourists would again affect the local beach users and resorts. Therefore, this criterion is importanttokeepinmindwhendesigningalternativesanditindirectlykeepsthecostsofa solutionlow. G.1.2Systemoverview Theeightcriteriadescribedabovearesupportedbytheallofthestakeholders.Allthefactorsthat influencethesecriteriaarefactorsthatcanbechangedwithalternativestopushthecriteriainthe requireddirection.combinethiswiththepossiblecausesforerosionasderivedinchapter5anda totalsystemoverviewcanbemade,asgiveninfigureg.1.thediagramthatarosehereiscalleda causaldiagram.itshowsallthecausalrelationsbetweenthedifferentfactors. Thecausalrelationcanpositiveornegative,givenwithaplusorminussignrespectively.Apositive relation means that when a factor is increasing, the factor it is influencing will also increase. For example,anincreaseinglobaltemperaturewillleadtoanincreaseinsealevelrise,indicatedwitha plussignnearthearrow.anexampleofanegativerelationistheonebetweenroughwavesandthe safetyofswimmingwater.iftheamountofroughwavesisincreasing,thesafetyforswimmingis decreasing. Thecausaldiagramissplitintotwomainparts:thecausesforerosionanditseffects.Thecausesare given above the dashed grey line. These causes are climate change (light blue factors), natural variation(greenfactors)andsediment reductionfromtherivertocuadaibeach(brownfactors). Theyallleadeventuallytothefactorofbeacherosion,madeboldtoshowthecentreofthediagram. Belowthegreylinearetheeffectsofbeacherosion.Theseeffectsaredividedintobeachtourism (yellow factors), income and damage (red factors) and how the implementation of measures influencesthetourismandincomeanddamage(darkblue). 115 CoastalerosionHoiAn

122 FigureG.1Causaldiagram Goingthroughthediagram,mostlinkswillspeakforitself.Itisasummaryofthesystemasderivedin Chapter 3 to Chapter 5and therefore follows from technical analysis and the interviews with the stakeholders.itshowsthetotalsystemandwhatfactorscanbeinfluencedbyalternativestochange somethingintheproblem. Twoimportantloopsariseinthisdiagramthatwillprobablynotbeseenimmediately.Thefirstloop showstheviciouscirclebetweenthedecliningtourismduetothereducingbeachattractiveness,this leadstoeconomicdamagetotheresorts,whichresultsinalowerbudgetformeasuresandalower rate of the implementation of measures. The implementation of measures is positively related to beachrecovery,soifnomeasureswillbeimplementedthebeachwillfurtherdeteriorate,reducing thebeachwidthandattractivenessofthebeachevenfurther,leadingtoafurtherdeclineintourism. Tomitigateeffectsofeconomicdamagethiscircleneedstobebrokenbyasuitablealternative. Thesecondloopissmallerandstartswithstructuraldamageduetotheerosion,leadingagainto economicdamagetoresorts,areducingbudgetformeasuresandadeclineintheimplementationof measures, reducing the coastal flood protection even further, leading to more structural and economicdamage.thisisanotherviciouscirclethatwillgoonuntiltheresortsrunoutofresources torepairitself,ifitisnotbrokenbyanalternative.therequirementsthatultimatelyflowedoutof thisdiagramaregiveninchapter CoastalerosionHoiAn

123 G.2 Hard versus soft measures Therearetwopossibilitiesforcoastalprotectionwhenerosionoccurs:hardorsoftsolutions.Hard solutionsaremanmadestructuresthatprotecttheshorefromfurthererosionand/orcreatewave climates where sand can accrete. Soft solutions are used to restore the beach with sand from elsewhere or by steering the natural process of sediment supply. Below, both coastal engineering techniquesarefurtherexplainedandassessed. G.2.1Softmethods Softengineeringisanappropriatemeasurewhenthecauseoftheerosioncannotbetakenaway. This can be the case for sea level rise, for example, or a situation in which solving the problem creates more disadvantages than maintaining the current situation and nourishing the beach to counteract the erosion. This also implies that, when the cause of erosion is not taken away, the beach will continue to erode with the use of soft methods. However, when the erosion becomes problematicagain,anewnourishmentcanbecarriedout. Soft methods are given extra benefits when the motto building with nature instead of building againstnature isused(devriend&vankoningsveld,2012).examplesofbuildingwithnaturearethe socalledsandenginealongthedutchcoastandtheuseofmangroveforestsintropicalareas.also the Dutch coast is eroding, due to climate change, reduced river sediment supply and the still ongoingadaptationofthewaddenseatotheclosureoftheijselmeer(elias,vanderspek,wang,& deronde,2012)(wang,etal.,2012).thesandengineisalargestockofsandplacednearthecoast, thatwillbedistributedalongthecoastbylittoralandaeoliantransport.mangroveforestsalongthe shore restore and/or preserve the ecosystem. The forest dissipates the wave energy and traps sedimentthatwouldotherwiseflowbackintothesea.thebenefitsofthesesolutionsarethatthey alsocreateextravaluebystimulatingtheopportunitiesforrecreationandnaturepreservation. Nourishingofsandhasmanyadvantages,howeveralsodisadvantages.Thesewillbediscussedinthe followingpart.firstsomeadvantagesofabeachnourishmentingeneral. Oneofthemainadvantagesofabeachnourishmentcomparedwithsolutionsofonlyjusta hardstructureisthatitprovidesadditionalsandtocompensateforthebeacherosion.when onlyahardstructureisappliedascoastalerosionprotectionittakesawaytheerosionatthe locationofplacementbuttherewillbemoresevereerosionatadjacentupdriftlocations.the beacherosionwillcontinuewiththisalternative.howeverthewidenedbeachhasaprotective functionforthecoastalstructures,infrastructureandotherassetsfortheeffectsoferosion andstormdamage. Due to the fact the erosion continues it provides sediment to the longshore sediment flow which transport the sediment to adjacent areas and redistributes it along the coastline. So beachnourishmentmighthaveapositiveeffectonthoseadjacentareaswhichdidnothavea nourishment. The amount of sediment can be assumed constant within one coastal cell, a coastalcellisastretchofcoastlinewherenosedimentistransportedinoroutof(e.gdueto rockyoutcrops). Naturalappearanceofthebeachnourishmentisalsobeneficialforthelandscapeandnatural valuesofthecoastline.byasandnourishmentthenaturallandscapeofthebeachisretained orevenincreased. ThetourismofacitylikeHoiAndependsmainlyonthewidebeachesandthesea.Itattracts touristsandispositivefortherecreationatthebeach.theattractionofmoretouristsleadsto abetterdevelopmentofthecity. Everybeachnourishmenthasalsoitsdisadvantages.Thesedisadvantagesforageneralnourishment aredescribedbelow. 117 CoastalerosionHoiAn

124 Adisadvantageofthisalternativeisthatitdoesnotgivethesamefeelingofsafetyaswitha hardstructure.ahardstructurelikearevetmentgivestheintentionitprotectsthehinterland betteragainststormsurgelevelsandsogivesasaferfeelingforthepeoplelivingbeyondthe beach and dunes and the people who have properties over there. Anyway this intention is right, because a wide beach cannot give protection against high storm surge levels and typhoonsandwillremainexposedtonaturaldisasterswithlongreturnperiods. Alsothebeachnourishmentisnopermanentsolution.Itdoesnotgiveanyprotectionagainst further erosion and the erosion will continue. Due to that periodic renourishments are neededtokeepthewidebeachasaprotectionforthestructuresandpropertiesbeyondthe beach.howeverthesetopupsorrenourishmentscanbeseenasmaintenancecosts. Placingnew sandinfrontofthebeachorontopofthecurrentbeachmighthavenegative effectsonthebeachandoceanhabitatsofbirdsandotherspecieslivingonthebeachwhen theirlivingandnestingpatternisunknown.thatiswhythepropertiesofthenourishedsand havetobe(nearly)equalthepropertiesofthecurrentsandonthebeachotherwiseitmight havenegativeeffects(ioc,2009). Dredgingsedimentandnourishingitonthebeachcanhavenegativeenvironmentaleffects. Whendepositedonthebeachitcanburyanimals,vegetationandorganismsonthebeach.It might cause more water turbidity and the different sediment compositions can affect the faunawhichinhabitthearea(dean,2002). G.2.2Hardmethods Hardengineeringcanfulfilafixedprotectionforalongperiod,ifconstructedwell.Optionsforhard methodsaretheconstructionofseawalls,groinsandbreakwaters.seawallsareusedtoprotectthe hinterlandfromfurthererosion,butdonotmaintainthebeach.groinsareplacedperpendicularto thebeachandtrapthelongshoreflowoftransportbyinterruptingtheflow. However, sand is trapped on one side of the groin at the expense of erosion on the other side. Breakwaterscanhavevariousshapesandareusedtoprovidecalmwater,byblockingthewaves.In thiscalmerwater,erosionwillbelesssevereandthesandmayevenaccrete.advantagesofhard structuresarethefollowing: Lowcostcomparedtolifetime Thelifetimeofthesolutionislong Themaindisadvantageisthatwiththeconstructionofhardstructurestheproblemoferosionshifts toanotherplace,whenthecauseoferosionisnottakenaway.thesandinfrontofseawallsmay continuetoerode,influencingitsstability,orthebeachnexttotheseawallwillerode.groinscan trapsedimentattheexpenseofotherplacesnexttoitandbreakwaterscanactinthesameway.as longastheequilibriuminthesandbudgetisnotrestored,hardstructuresmaysolvetheproblemon location,butworsenitsomewhereelse.otherdisadvantagesare: Largeinitialinvestment Difficultforecastingofeffectsonlocationandonsurroundingbeaches G.3 Possible measures InAppendixF,thecurrentmeasuresaregivenandevaluatedontheireffectiveness.Ifuseful,those measures or elements from it can be applied as a solution for the total stretch of coast. All the applied measures are hard measures, but looking at the previous paragraph of this appendix soft measuresmightalsobeanoption.thereareotherpossibilitiesthantheonescurrentlyused,bothas hardandsoftmeasure.whenlookingatthecausaldiagram,thereareseveralfactorsthatcanbe dealtwithtotakethecauseofcoastalerosionawayormitigateitseffects. 118 CoastalerosionHoiAn

125 Someconventionalmeasuresaregiveninthefirstsixalternatives.Thelastthreearelesscommon, more creative and probably unfeasible solutions. Whether or not they will exceed the other possibilitiesbecomesclearinthecomparinganalysisinparagraphg.4,whereamulticriteriaanalysis isconducted. G.3.1Restoresedimentsupplyfromtheriver Function Totakeawaythepossiblecauseoferosion,theriversedimentsupplycanberestored.Thisfocusses on the brown part of the causal diagram. The supply has reduced due to sand mining and hydropowerdams.hydropowerdamsnotonlytrapsediment,theyalsoreducetheflowvelocityof theriver.thisreducesthesedimentcarrycapacityofthewaterandsedimentwillsettleontheriver bed before it has reached the sea. By restoring the original sediment supply from the river, it is expectedthattheerosionwillstoporaccretingmightevenoccur. Methodofplacement Althoughnothinghastobeplaced,certainthingshavetobedonetorestorethesedimentsupply. Settingstricterrulesonsandminingisonepartofthisalternative.Itisalreadyprohibitedwithout license,butitstilloccurs.whencertaintypesofsandminingarepossiblewithouterodingthebeach, these should be regulated and stimulated above other types with more control on the river. The otherpartofthealternativeisbetterhydropowerdammanagement.withregularflushingofthe reservoir,thesedimentcanbereleased.alsotheriverflowcanbemoreregulated,tokeeptheflow velocityhighduringmoreperiodsovertheyear. (Dis)advantages The advantage of restoring the original sediment supply to the situation before sand mining and hydropowergenerationstartedtotakeplaceisclear:ittakesawayapossiblecausefortheerosion. Increasingthesedimentsupplyagainwouldstoptheerosion.IfthecoastofHoiAnwasaccreting beforedistortionsintheriverstarted,thecoastmightevenadvanceagain. Thedisadvantageisthatitwilltakeyearstobeaneffectivesolution.Furthermore,sandminingand hydropower generation are taking place for economic reasons. If they are limited, it will result in financiallosses. G.3.2Divertriverstreamdirection Function Oneofthenaturalcausesforsedimentreductionisthediversionoftheriveroutflowtowardsthe south instead of Cua Dai Beach, lying north of the river mouth. This is given by one of the green factorsinthecausaldiagram.withthehelpofhardstructurestherivermouthcanbemodifiedsuch thattheriverwillflowoutintherightdirectionagain.thiswouldstoptheerosionandmighteven leadtoaccretion. Methodofplacement The river has to be controlled to flow out in the northern direction. For example, groynes can be placedalongthesouthernriverbank,restoringahigherflowvelocityalongthenorthernbank.this constructed from the land, so no pontoons are needed for this. The size of the groynes and the stoneswithwhichtheycanbebuiltdependontheflowconditions.morecalculationsareneededto designgroynesthere. (Dis)advantages Theadvantageofthissolutionisthatitwouldtakeawayanotherpossiblecausefortheerosion.The onlychangestakeplaceintheriver,soalongcuadaibeachnofurtherstructureshavetobebuilt. Therearehowevertwomaindisadvantages. 119 CoastalerosionHoiAn

126 First,bydivertingtheriveroutflowtowardsthenorth,erosionatthebeachsouthoftheriveroutlet canoccur.second,howtheriverwillbehaveaftertheplacementofgroynesisdifficulttopredictand detailedmodelsareneededforthis. G.3.3Submergedbreakwateroffshore Function Anotherpossiblecausefortheerosionwastheincreasedstormconditions,givenaslightbluefactors inthecausaldiagram.itisimpossibletoreversetheclimatechange,atleastonshortnotice,sothis cause cannot be taken away. It is however a possibility to adapt to the higher waves. Emerged breakwatersarealreadyinuseatsomeplacesatcuadaibeach.submergedbreakwatersareanother typeofdetachedbreakwaters.thistypealsoliesoffshoreinfrontofthebeach,butissubmerges underwater.theyhavethesamefunction,namelyreducingthewaveenergy.itreducesthewave impactontheshoreandcanalsotrapsediment. Methodofplacement Submergedbreakwatersusuallyconsistofacore,whichcanbesand,andanarmourlayerontop. Filter layers between the core and armour are used to prevent the core from washing away. However,othermethodsexistforplacingansubmergedbreakwater.Forexampleoldtrainsorships canbesunkdowntocreateastructurethatbreaksthewaves.althoughthisseemsenvironmentally dangerous, when the polluting parts are stripped it does not have to be. Furthermore, new ecosystemscanariseintheopenspacesoftheimprovisedstructures. (Dis)advantages Thesame(dis)advantagesexistforsubmergedbreakwatersastheiremergedrelatives.Theycanstop the structural erosion over a certain stretch and can stimulate accretion in the calmer water. Submerged breakwaters can be a little less effective in reducing the wave energy than emerged breakwatersandtheireffectisdifficulttopredict,butitdoesnotspoilthesightonthehorizon.a largedisadvantageisthatisdoesnotsolvetheerosion,butshifttheproblemtodowndriftstretches ofcoast. G.3.4Mangroveforests Function Thewaveenergyofroughwaves,againthelightbluefactorinthediagram,canalsobereducedby theuseofmangroveforestsinfrontofthecoast.mangroveforestsdidnotoccurnaturallyathoian in the recent period, but they are present in the south of Vietnam. Unfortunately the mangrove forestsareremovedthere,whichisoneofthereasonsforanerodingcoasttherenow.plantingtrees infrontofthebeachofhoianwouldworktheotherwayaroundandcancounteracttheerosion. Thenetworkoftreesandbranchesbreakthewavesbeforetheycanreachthecoast.Furthermore, they are effective in trapping the sediment. The high stability of the mangrove forests helps to prevent shoreline erosion, shielding inland areas from severe damage during typhoons and tidal waves. Methodofplacement Mangrovescouldbeplacedonthebeachitselforintheseainfrontofthebeach.Itisveryimportant the roots of the mangroves are penetrated deep enough into the sand so their functionality is optimized. Also when planting these mangrove trees it is of great value that the trees are well developedandfullgrownwhenexposedto(storm)waves. (Dis)advantages Theeffectivenessofthesandtrappingofthemangrovesisveryhigh.However,whenplacedonthe beachithasanegativeeffectontherecreationonthebeach. 120 CoastalerosionHoiAn

127 Itblocksthewaytotheoceanandthepeoplewhowanttoswiminthewaterinfrontofthebeach cannotreachthatwater.oneoftheadvantagesisthatithasahighenvironmentalvalue. G.3.5Groynesalongthebeach Function Ifthecauseoferosioncannotbetakenaway,thereisalwaysthepossibilitytomitigatetheeffects.If an attractive beach can be restored, given in yellow in the causal diagram, the loop between declining tourismandeconomicdamagecan bebroken.onepossibilityforthisistheuseofhard shorelineprotectionstructureslikegroynes.groynespartlyblockthelongshoretransport.itreduces thegradientinlongshoretransportandthereforetheerosionreduces.awelldesignedgroyneblocks exactlyenoughsedimenttobringtheincreasedtransporttoahaltandkeepitconstant.theresultis a saw tooth shape coast, since sand is trapped between the groynes and adapts to the wave conditions.noextrasandisaddedtothesystemhere. Methodofplacement Groynes normally are placed perpendicular or slight obliquely to the shoreline depending on the dominantwavedirectionandtheshapeofthecoastline.differenttypesofgroynescanbeapplied, somefunctionbetterbyblockinglongshoresedimenttransportandsomearesemipermeableand do not entirely block sediment transport in longshore direction. Different groyne types are the woodengroynes,steelgroynes,groynesofconcreteelements,rubblemoundgroynesorsandfilled baggroynes.becauseofthedisadvantagesofagroynetypestructure(whichareshownbelow)the best system is to combine the groynes with soft shore protection measures like artificial beach nourishmentorshorenourishment. (Dis)advantages Mosttimestheconstructionofgroynesischosenbecausesandistrappedinbetweenthegroynes anditpreventserosion.erosionwilloccurattheleesideofthegroyneasthelongshoretransport increasesagainsinceitisnolongerblockedbygroynes.thiscausesawashingoutofthebeachat thatside. G.3.6Sandnourishment Function Anotherpossibilitytoregainanattractivebeachwithouttakingawaythecauseissandnourishment. Sand from elsewhere is placed on the current beach. When this has eroded too much, the next nourishmentwilltakeplace.thefunctionofasandnourishmentistorecreateawidebeachwhich canbeusedformainlyrecreationalvalues.ifthenourishmentsaredoneontherightmomentsit preventstheerosionwillreachthedunesandprobablyendangersthebuildings,landandstructures behindthedunes. Methodofplacement Thereexistseveralpossibilitiesforsandnourishments.Thesandcanbedirectlyplacedonthebeach, bypipelinesorspraying.afterthat,bulldozerscandistribute thenewbeachevenlyoverthetotal stretch. Sand can be also be placed offshore, while waiting for the calm waves to bring it to the beach. Another possibility is the placement of a large stock of sand somewhere along the coast. Longshoretransportandwindwilldistributethissandalongthecoastoverseveralyears.Allofthe possible measures above do not restore the beach immediately. The combination with sand nourishmentisapossibilitytorestorethebeachbeforetheactionhastakeneffect. 121 CoastalerosionHoiAn

128 (Dis)advantages One of the advantages of a sand nourishment is that it has a high natural, environmental and recreationalvalue.therearenoconcretestructuresusedandthereisawidebeachwhichcanbe usedforrecreation.oneofthedisadvantagesisthattheerosionstillcontinuesandthatisstillas severeasbeforeduetothisrelativelyalotofmaintenanceisneeded.furthermore,dependingon thenourishmethodused,itmighttakesometimebeforethenourishmentisfinishedlikewiththe foreshorenourishment. Thelastthreealternativesfollowfromabrainstormsessionandarewiththecurrentresourcesnot feasible or effective solutions. The brainstorm session was used to come up with more creative optionsthatmighthaveledtomoreoutoftheboxideas. G.3.7Enclosedsea Function Theideaofthisveryunconventionalmeasureisthatthetouristicbeachandfirstfewhundredmeters of sea will be enclosed by a structure with a cross section comparable to a regular emerged breakwater.thismeasurewouldnottakeanycauseoferosionaway,butfacilitatesinconstructing anattractivebeach,todrawtouristsbacktohoian.similartoadetachedbreakwater,itreducesthe waveenergythatreachestheshore.furthermore,onceabeachisrecreatedsedimentcannotleave thisenclosedsea,soawidebeachwillalwaysbepresent. Methodofplacement Theenclosingstructurecanbeconstructedsimilartoabreakwater,withsandycore,armourcover andfilterlayers.afterwardsthebeachhastobereconstructedtotheoriginalwidth,asitwasbefore theerosionstarted. (Dis)advantages Themainadvantageisthatanattractivebeachwillberecreatedthatishardlyaffectedbyinfluences fromoutside.therearemoredownsidestothismeasure.itisverycostly,thestructurespoilsthe horizon,thewatermaybecomedirtyduetothereducedconnectionwiththeseaandalargeamount of labour and materials is needed for the construction. With the current resources this is not a feasibleidea. G.3.8Barrierislands Function ChamIslandworksasawaveblockeragainstwavesfromtheopensea.Duetotherelativelylarge distancebetweenthisbarrierislandandthecoastofmainlandvietnamcomparedtoitswidth,thisis not protecting the beach at Hoi An. However, more barrier islands more close to the coast is a theoreticaloptiontoassurethatlargestormwavescannotreachthecoast.thereforethismeasureis basedonthelightbluepartofthecausaldiagram.thebarrierislandscanblockorbreakthewave energyfromopenseaandthereforereducetheerosioncausedbylargewaves. Methodofplacement Theseartificialbarrierislandscanbeconstructedfromrocksandsand.Withlargebouldersthebase oftheislandscanbeconstructed,afterwhichalargeamountofsandcanturnitintoanaturalisland onwhichfloracangrowandfaunacanthrive. (Dis)advantages Thisotherunconventionalmeasurehasmoredisadvantagesthanadvantages.Themainadvantages arethatitblockswavefromopenseaandcanthereforereducethewaveenergythatreachesthe coast.thisshouldreducetheerosioncausedbywaves. 122 CoastalerosionHoiAn

129 Anotherbenefitcanbethesightofbarrierislandsoffshore,whichcanalsobevisitedforrecreation. Of course, this measure is too expensive to carry out. It is an ineffective measure in terms of resourcesandeffects. G.3.9Temporary(inflatable)winterprotection Function Apossiblesolutiontoreducethewaveheightorevenblockthewavesapproachingthebeachisan inflatableprotectionthatoperatesduringthestormseason(thewinterseason)betweenseptember anddecember.thiswaytherewillbenowaveshittingthebeachorthewhentheprotectionisnot ashighasthewaveheightthewaveshittingthebeachhavelessenergy.duetothattheerosionof the beach will be less severe than it is nowadays. During the summer the air and water in the protectionisreleasedanditislayingonthebottomofthesea.areferenceprojectofthisprotection istheramspolbarrierinthenetherlands. Methodofplacement BecauseofthelargelengthofCuaDaiBeachthisinflatablewinterprotectionhastobeaslongasthis beach.theconstructionisplacedatthebottomoftheseaandshouldbelocatedaboutseveraltens ofmetersinfrontofthecoastline.aboutevery80metersofbarrieritshouldhaveasmallpumping stationwhichisabletopumpairandwaterintothebarriersoitcanriseabovethewaterlevelofthe sea. In the summer months this construction is laying on the seabed and there is no air or water insideandinthewintermonthsitisfullyinflatedandrisesabovethewaterlevelofthesea. (Dis)advantages Duringthestormseasoniteffectivelyblocksthewavesandreducesthewaveenergyandduringthe summer it is invisible so no one can see the construction. Some disadvantages are that it has difficultieswiththedeflationofthebarrieranditisverycostly. G.4 Multi criteria analysis A multi criteria analysis is conducted in this section to rank the different measures. The currently used and possible measures are rated respectively in Table G.1 and Table G.2. The following paragraphswillprovideanexplanationaboutthecriteriaitself,howtheywereratedintheanalysis andontheirweighingfactorsintheoverallresult. The criteria follow from the goal trees of the different stakeholders and are then translated into comparablecriteria.thecriteriaareexplainedinmoredetailearlierinthisappendix.theratingof thedifferentmeasuresisbasedonarelativerankingona1to5scale.thehighestscoreinthetable isafiveandisdepictedbygreen,anaveragescoreisdepictedbyyellowandaredcolourmeansit scoresnotthatwellonthatcriteria.itisanbroadcomparisonandamoredetailedcomparisonwill beusedlaterintheprocess. Theweightofthedifferentcriteriaintheoverallresult isnotequalsinceitfollowedfromtheinterviewsthat were conducted that certain criteria were considered more important by the stakeholders. The different weighing factors are shown in Table G.1. Most weighingisselfexplanatory,buttheextraweighingof the attractiveness and speed of effectiveness will be explained. The attractiveness strongly influences the amountoftourismwhichisthemainsourceofincome andisthusofverylargeinfluenceonthebenefitside. TableG.1 Weightofdifferentcriteria Criteria Protectsbuildings Attractiveness Costs Lifetime Speedofeffectiveness Problemshiftingtoadjacentareas Safetyandreliability Combineswellwithcurrentmeasures Badinfluenceonotherindustries x CoastalerosionHoiAn

130 Thespeedofeffectivenessisalsoofmorethanexpectedimportancebecauseoftworeasons:whena measureisimplementeditispreferredtoshowquickresultfortheinvestmentdoneanditdecreases theneedfortemporarymeasures. G.4.1Ranking Inthefollowingtwotablesthecurrentlyusedmeasuresandtheotherpossiblemeasuresareranked, usingtheaboveexplainedcriteriaandweightfactors. TableG.2Currentlyusedmeasures TableG.3Otherpossiblemeasures Someinterestingpartsoftheanalysis: Thecostsofthesandbagsarehigherperyearthanofmostothersolutions,sincetheyneed tobereplacedmoreoften. Safetyandreliabilityisformostmeasuresnotperfectexceptforaconcreterevetment. Anaturalsolutionisnotanpreferredoption. Groynesscorelessthanexpected,thisfollowsfromarelativelylowscoreonattractiveness. Thethreehighestscoringmeasuresare: 1. Sandnourishment 2. Submergedbreakwater 3. Concreterevetment 124 CoastalerosionHoiAn

131 Quiteclosetothosesolutionsare:Restoresedimentsupplyandanemergedbreakwater.Therestore ofsedimentsupplyhassomemajorpositivepoints,howeveritisstillnotthatinterestingasasole measure,sincetheothersoftmeasureslikesandnourishmenthasthesamepositivepointswithout the large drawbacks. The emerged breakwater is quite similar to the submerged and the positive pointsoftheemergedonewillbeusedinthedesignofthesubmergedbreakwater. Togetabetterresultssomeofthemeasurescanbecombinedwithothermeasures.Especiallyalow amount of sand nourishment can be very well combined with other measures to improve or the effectivesofthenourishment,ortomitigatenegativeeffectsofotheroptions.howeveroftensucha combinationleadstoanunwantedincreaseofthecosts.howthisconcludesisshowninchapter6.3 Resultsofanalysisofpossiblemeasures. 125 CoastalerosionHoiAn

132 H.Main alternatives + nourishment strategy This appendix provides additional information about the three main alternatives that are given in Chapter6.4.Itelaboratesontheamountofsandthatneedstobenourished,thecostsandsketch designs of the used structures. The same order is used as in the main chapter: first large sand nourishment,afterthatthemediumnourishmentwithgroynesassedimentretainingstructureand finallyasmallnourishmentcombinedwitharevetment.theappendixconcludeswithanadvicefor beachpolicyandanourishmentstrategytouseforthethreealternatives. H.1 Large sand nourishment Thefirstalternativeisasandnourishmentalongtheentirebeachwithoutanyfurtherprotectionofa hardstructure. H.1.1Design Thenourishedbeachhastowithstandthe1in5yearstormsandthe1in50yeartyphoonswhich give 35m and 120m erosion respectively, as calculated in E.3.1 Storm variation. In addition the erosion rate of 12m per year has to be taken into account and also the prevention against this erosionisimportant.furthermore,therehastobeabufferinfrontoftherestaurantsandresorts whenthemostextremeerosionoccurs.themostextremesituationisdefinedastheerosionatthe endofthefiveyearsjustafteratyphoon,assumingthatatyphoonandastormdonotoccurboth withinfiveyears. Duetothesefactorsthebeachhastohaveawidthof180meterwhenconstructed.Witheveryfive yearamaintenancenourishingof60mpluserosiondamageduetostormsortyphoonsisneeded. Thiswidthofthebeachgivesareliableprotectionforrestaurants,resortsandotherstructuresand properties beyond the beach. It should protect against a possible storm and typhoon occurring in thesefiveyearsandtheerosionratewithintheseyears. TableH.1Totalneededbeachwidth Structuralerosion Typhoonerosion Totalbeachwidth 60m 120m 180m Theamountofsandneededforthenourishmentcanbedeterminedwiththeformulabelow. Eq.H1 With: 126 CoastalerosionHoiAn

133 Nevertheless,mostresortshavealreadyahardstructureprotectingtheirproperty.Duetothisthe beach in front of the resorts may be less wide than the beaches without any hard structure as protection.theresortsarelocatedapproximately40mmoreseawardthanthecurrentshorelineat thesouthpartofcuadaibeach.thisleadstoaninitialbeachwidthof140minfrontoftheresorts. AtthenorthpartofCuaDaiBeachthereisstillbeachleft,solessnourishmentisneeded.Theresorts atthenorthernparthavenohardstructureasprotectionagainststormsandtyphoons,soinfrontof theseresortsthereshouldalsobe180mofbeach.thereisalreadyarevetmentplacedatthesouth partofcuadaibeach,whichcanbetakenintoaccountfortheprotection.becauseofthisrevetment alesswidebeachispossibletomeettherequirementsforprotectionagainststorms,typhoonsand erosion.nevertheless,thebeachadjacenttothispartinfrontoftherevetmenthastobe180mwide, becauseatthatpartnorevetmentisplaced.thereforethebeachinfrontoftherevetmentstillhas tobe180minwidth.nearbytherivermouththeshorelinehastobegraduallybendedsothatithas noplaceswheretheerosionismoreextremethanotherlocations.thisresultsinaverywidebeach atthislocation,butwhencoastalmanagementisappliedatthispartitcanturnintoausefulbeach. Inshort,thebeachwidthofCuaDaiBeachjustafternourishingwilllookthefollowing: TableH.2TotalnourishmentwidthsofdifferentpartsofCuaDaiBeach Resorts Beach Resorts Beach Already placed Spit NorthPart NorthPart SouthPart SouthPart Revetment 180m 180m 140m 180m 180m 180m Duetopresenceofa relativelywidebeach already,lessinitial nourishmentisneeded 200mbeachwidth 160mbeachwidth 200mbeachwidth howeverrevetment alreadypresent Anoptionforextra beachnourishment, also200mwidth Widebeachatthespitis suggestedasanextra optionsothaterosionmore updriftislessandfor recreationandtourism FigureH.1Nourishmentwidthofdifferentcoastalsections H.1.2Costsestimation Thecostsforthebeachnourishmentaremainlyinitialcostsfortheconstructionofthewidebeach. Compared to the other two alternatives the initial sand costs are more expensive. The costs are basedonreferenceprojects,asisdescribedinappendixh.4.3. Totalinitialcosts VND640billion 25.5million NPVincludingmaintenancefor20year VND950billion 37.8million 127 CoastalerosionHoiAn

134 H.2 Medium nourishment + groynes Inthisalternativeasetof145mlonggroyneswillbeplacedtoprotecttheCuaDaiBeachandseveral resortsfromfurthererosion.onceprotectedthebeachesbetweenthegroynescanberestoredtoa width of 60m by a sand nourishment. On average the beach will be 50m over the four kilometre stretch. However, the groynes will worsen the erosion on the unprotected areas, hence a yearly nourishmentschemewillbeusedtomitigatetheseeffects.alargebenefitofthisapproachisthat thevaluablebeachesofcuadaiarestabilisedandwillonlyoccasionallyrequiremaintenanceafter largestormevents. FigureH.2Basicdesignofalternative Atnourishmentlocation1theareawillbenourishedfor1kmandincreasethewidthuntilthetipof thefirstgroyneisreached.thisallowsbypassingofthelongshoresedimentandpreventserosionat thedowndrift.theregularnourishmentsarefocusedonlyonnourishmentlocation2whichmakes thenourishmentoperationmucheasier.herethestructuralerosionisamplifiedbythepresenceof thegroynessuchthat240,000m 3 ofsandmustbenourishedtomitigateiteachyear(seeappendix C.7).Thedownsidesaretherelativelyhighconstructioncostsofthegroynes,theuncertaintyinthe designaspectsofthegroynesandintensifiederosionoftheareaadjacenttothegroynes. H.2.1Effects Asexplainedbefore,groynesworkbyinterruptingthelongshoretransportandthusreducingoreven inhibitingitscapacitytoerodethebeach.thebeachesbetweenthegroynesarethusprotectedfrom thestructuralerosioninducedbylongshoretransportgradients.thesebeachescanberestoredwith asinglelargenourishmentthatwouldrequirelittlemaintenance,asonlystormsarestrongenough tomovesandoutofthesystemandinduceerosionofthesebeaches. However updrift of the groyne system sand will accumulate whereas downdrift additional erosion willbeinduced.theextentofwhichisdeterminedbytheireffectonthelongshoretransport(see section3.3shorelinemovements).usingtheanalyticalsolutionofthepelnardconsidereequation foragroyne(derivedfromeqc3andc4)(roelvink&reniers,2012)andmakingafewassumptions regardingwavedirection aroughapproximationoftheexpectedretreatattheendofthegroyne fieldcanbegiven.theretreatinthefirstyearwouldbearound55m,thesecondyear80mandafter fiveyears125m.after10yearstheerosionwouldbe180m.attheothersidethesameamountof accretionisexpected.thiserosionwillcontinueuntilthesandonthesouthernendhasreachedthe tipofthegroyneafterwhichthesandwillbypassthegroynes.mitigationofthiserosioncanbedone by placing additional nourishments at this location. This will be discussed in more detail in the followingsectionaboutthedesignofthenourishment. 128 CoastalerosionHoiAn

135 Calculatedby superimposing thesolutionsfor S=20,000m 3 /year withwaveangle of20degreesand S=340,000 m 3 /yearwith waveangleof10 degreesassuming theactive depth=5m. FigureH.3Expectederosionandaccretionnexttoagroyne. H.2.2Design Spacingofthegroynes Basedonthe100m 2 /yeargradientalongcuadaibeach(ponsioen,2015)thegroynesystemwould needtoblock200,000m 3 /yearofnorthwardsedimenttransporttostabilisethe2kmlongstretchof beach protected in this alternative. The northward sediment transport is around 340,000 m 3 /year (Ponsioen, 2015) meaning 58% of transport needs to be blocked. Estimating from satellite images that the surf zone is about 150m wide and the longshore transport is equally distributed in this region the length of the groyne would be about 145mlong (60m nourished beach +85m to block transport). The spacing of groynes is another design aspect. Although there is no easy way to compute the optimal spacing without modelling there is good experience for which amount of spacing works. (Kraus,Hanson,&Blomgren,1994)suggestedthat groynesonsandybeachesperformbestiftheir spacingistwotofourtimesthegroynelength.the(spm,1984)recommendedaspacingratiooftwo tothree,whilethecem(usace,2006)suggestedagroynespacingtolengthratiooftwotofour. (Silvester,1992)presentedagraphicalprocedureforestimatingtheratioofgroynespacingtolength. Theratioisafunctionoftheincidentwaveangleandvariesfromtwotofourteen.However,nofield orlaboratorydatawascitedtosupportthismethod.basedonallthesefindingsthespacingshould be between two to four times the groyne length which results in a spacing between 170 m and 340m. Notethattherearemanyassumptions,simplificationsanduncertaintiesindeterminingthesedesign aspectsandtheyshouldbeverifiedbyalargemodelstudytoobtaintheoptimalgroynedimensions. These models would require more input data on the bathymetry, wave climate, currents and sedimenttomakeviablepredictions.sinceonlylimiteddataisavailabletheseshouldbemeasuredin advance.suchresearchisimportant,butalsotranslatesinamuchlongerdesignphaseoftheproject forcollectingdata. Locationofthegroynes Groynesarecostlysotheamountofgroynesshouldbelimitedasmuchaspossible.Thismeansthat onlyalimitedlengthofbeachcanbeprotected.southofthesunrisehoianbeachresortthereis onlylimitedvalueleft.itconsistsofarevetmentandastretchofabandonedresorts.thereforethese willnotbeprotectedasthecostsforadditionalgroyneswouldnotoutweighthevalueitprotects. Between the Sunrise Hoi An Beach resort and the Victoria Beach resort north there is one other active resort and two beaches. Further north of Victoria there is a beach currently protected by sandbagswithafewrestaurantsevenfurthernorth. 129 CoastalerosionHoiAn

136 Since this section does have economic activity it is considered valuable enough to protect with groynes.nexttotheserestaurantsthereissectionofabout500mthatiscurrentlyunprotectedand undeveloped.thegroynefieldwillendatthelastrestaurantandthisundevelopedsectioncanbe usedtofocusthenourishmentandmitigatethemostoftheerosioninducedbythegroynes.northof thisareaisthepalmgardenresortwhichhasnotsufferedlargeerosion.bymonitoringtheerosion anddoingregularnourishmentsatthenourishmentlocationthepropagationoftheerosiontothe northcanbestopped. Withthestretchthatneedstobeprotecteddefined,thelocationofthegroynescanbedetermined. Theeasiestandprobablymostconvenientwayistoplacethemattheedgesofthecurrentresorts andhotelsastheirwidthsdonotexceedthe340mspacinglimit.thebeachcurrentlyprotectedby sandbagsbetweentherestaurantsandvictoriawillbedividedintwosectionsofabout300m.the spacingisalsopresentedinfigureh.2. Determinationstonesizeforgroynes There are many empirical methods to estimate the size of the armour stone for a groyne or breakwater,whichisrequiredforstabilityorrocksunderwaveattack.eachstabilityformula,derived byiribarren(1938),hudson(1953,1959),hedar(1960,1986)andvandermeer(1988)hasitsown rangeofvalidityandaspecificfieldofapplication.(ciria,therockmanual,2007). TheHudsonformulaiswellknownforitssimplicity,butithasbeenfoundbymanyuserstohavealot ofshortcomings.forexample,itusesregularwavesonly,itdoesnotincludetheinfluenceofwave periodandstormduration,thereisnodescriptionofthedamagelevelanditcanonlybeusedat nonovertoppedandpermeablestructures. Amoreadvancedequationformultiplelayersofrubbleunderwaveattackcanbecalculatedwiththe VanderMeerformula.Onthebasisofhisexperiments,VanderMeerfoundthatadistinctionshould bemadebetweenplungingandsurgingbreakers,whichresultedinthefollowingsetofequations. Eq.H2 Forplungingwaves (VanderMeer,1988) Eq.H3 Forsurgingwaves With: P=0.1inanimpermeablefoundation (sandclaybody) P=0.5inapermeablefoundation (e.g.withmultiplelayersofrubble) P=0.6inaverypermeablefoundation Thenumberofloststonespertransversecrosssection [ ] 130 CoastalerosionHoiAn

137 The breaker parameter (also known as the Iribarren number) is computed to determine which formula to use; for plunging or for surging waves. For computation, an assumption for several parametershastobegiven.assumingthevolumetricweightofthestonestobe2650kg/m 3 leadsto arelativedensityof1.59.thepermeabilityfactorisassumedtobe0.5,thebedslopeis1:50andthe maximumwaterdepthatthetoeofthestructureistakenas5meters.thevalueofthedamagelevel istakentobe2,whichmeansthatonlyaminoramountofdamageisallowedforthedesign.table H.3indicatestherequiredstonesizes(D n50 )fordifferentreturnperiods. Eq.H4 Iribarrennumber Eq.H5 With TableH.3Requiredstonesizes(D n50 )forthegroynesindicatedfordifferentreturnperiods (Iribarren,1988) CriticalvalueIribarrennumber Prob.of exceedance Hs[m] T[s] Required stone size, D n50 [m] Permonth m Peryear m Per5years m Per25years m Per50years m Per100years m ComparedtothestonesizesthatwereusedfortheprotectionoftheVictoriaHoiAnresortandthe GoldenSandresort,thecalculatedD n50 ismuchlowerthantheactualstonespresent,evenforhigh return periods. The required stone sizes are comparable to the smallest stone size measured at Victoriaresort.TherelativelylowvalueD n50 mightmeanthattherubblemoundrevetmentsatthese resortsareoverengineeredorthewaveconditionshavebeenunderestimated. TableH.4MeasuredstonesizesatVictoriaandGoldenSandresort,categorized Stonesize[incm] VictoriaHoiAnresort GoldenSandresort Small LxBxH 55x35x30 60x50x45 Medium LxBxH 75x95x40 75x70x50 Large LxBxH 130x85x x100x75 FigureH.4Currentrockrevetments 131 CoastalerosionHoiAn

138 Nourishment The nourishment must accomplish three things: restoration of the beach to an acceptable width, mitigatetheerosioninducedbythegroynesandcompensateforthestructuralerosioninthefuture. Eachrequiresadifferentapproachinthisalternative. The restoration of the beach should return the entire beach from the Sunrise resort to the Palm Garden resort to a sufficient width. Out of cost considerations it cannot be made too large, as nourishmentcostsincreasesaswellasthetotallengthofthegroyne.basedontheeconomicvalue ofthebeachfromappendixb.4aneconomicallyviablebeachwidthis60m.thiswillbethestatethe beach will be restored to. Additionally as Appendix E.3.1 Storm variation demonstrated such a beachwidthislargeenoughtodealwithtemporarystormerosionfromminorstorms. Figure H.3 shows the effect of a groyne (field) on the beach with downdrift erosion and updrift accretion.sincethegroynesneedtoextendanestimated85mbeyondtheshoreand60mofbeach will be nourished the total length amounts 145m. Based on the calculation it would take an estimatedsixyearsbeforeenoughsandhasaccretedforbypassing.insteadthisamountofsandwill be nourished directly after construction of the groynes so no downdrift erosion will occur. This meansthataninitialnourishmentisrequiredthatmovesthecoastlineonaverage40mseawardin the1.5kmupdriftofthefirstgroyne.theshapehoweverwillneedtolooklikethepinklineinfigure H.3. The final nourishment is of structural nature to counteract the structural erosion. The retreat measured in the last several years is 12m per year over the 3.5km of Cua Dai. As calculated in AppendixC.7theamountofsandlostis240,000m 3 /year.sincethissandcannolongerbeeroded from the beaches protected by the groynes, additional structural erosion is expected. A rough approximationforthiseffectiscalculatedwithanumericalmodelcombiningthecercformulawith the oneline coastline model (model explained in Appendix C.2 CERC formula ). Adding a 12m per yearerosionandfixingthecoastlinefor2kilometrestosimulatethegroynefieldgivesinsightinto the consequences. Most notably the downdrift erosion has significantly increased to almost 80m/yearsuchthatregularnourishmentsbecomeinevitable.Onaveragetheerosionis32minthe first1.5kmdowndrift.theyearlynourishmentnorthofthegroynesshouldmirrortheshapeofthe bluecoastlineoffigureh.5. FigureH.5Effectofthegroynefieldwithoutnourishments Intotalthenourishmentamountstoanaverageof40mfor1.5kmupdriftofthegroynes,60mfor the2kmofbeachwithinthegroynesandeveryyear32mthefirst500mdowndriftofthegroynes. 132 CoastalerosionHoiAn

139 Withanactivedepthof5mthisamountsto400,000m 3 updriftofthegroynes,600,000m 3 withinthe groynesandeveryyearand240,000m 3 downdriftofthegroynes. Trialgroyne Beforethestonegroynesareadopted,itisrecommendedthatatrialstructureisbuilttoassessthe effectiveness of a groyne field. A trialanderror approach is followed whereby the effects of the groynesarecloselymonitored.thetrialgroynecouldbeprogressivelybuiltoutfromtheshoreline until 145m. The shoreline changes are measured at each trial configuration. Data retrieved from actualprocessesalongthebeachcanenhancethemodellingpredictionssignificantly.thesemodels canthenbeusedtoassessthelongtermsolutions.theobtaineddataisnecessarytounderstandthe uncertaintiesconcerningtheerosionproblematcuadaibeach,suchas: Localwaveclimate.Alackoflocaldirectionalwavedatalimitstheunderstandingofsediment transportprocessesandtheinfluenceofimportantfeaturessuchaschamisland. Informationonsedimentbudget.Thevolumeofsedimentmovingintoandoutofthecoastal cell. TemporarygroynescanbeconstructedfromgeotextilefabriccontainerslikeGeotube,whichisa relativelycheapshorttermprotectionmeasure.accordingtothebathymetrymapinappendixc.3, thewaterdepthatthetipofthe145mlonggroyneisfivemeters.atotalof13longgeotextilebags, with dimension shown in Figure H.6, should be stacked according to the indicated geometry. Multipliedwithaunitcostpricepervolumeof 18perm 3 (U.S.ArmyCorpsofEngineers,2008)leads to a costs of 32,000, per bag. The total construction costs for seventeen long geotextile bags is estimatedtobe 544,000,. FigureH.6Dimensionsandstackingofthelonggeotextilebagsforthetrialgroynes H.2.4Costsestimation Costsgroynes Costsofgroynesdifferconsiderablyduetodifferentwaveconditions,bathymetryandinvestment budgets.thereforedifferentdesignsareappliedwhichmakeseachprojectunique.toestimatethe costsofrubblemoundgroynesalongcuadaibeach,aconstructioncostestimationpermetergroyne lengthismadebasedonseveralreferenceprojects.averagingthecostsofthesereferenceprojects givesacostof 1,550,000(or38VND)pergroyne.Thisdesignalternativeconsistsofsevengroynes, leadingtoatotalcostforgroynesof 10million. 133 CoastalerosionHoiAn

140 TableH.5Referenceprojects Details Length[m] Costsfor1groyne EUR VND x1,000,000 GroyneextensionLakeViewPark,Ohio 252,296 6,183 LakeCathiegroyne 180 2,060,426 50,492 Rockgroynes 2,117,508 51,891 Swanagefrontage ,723 24,082 Rockgroynesseries ,512 12,045 Coastalprotectionmeasures 270,332 6,625 Kingscliffbeach 150 1,111,059 27,227 Kingscliffbeach 150 1,880,255 46,077 KirraPointgroyne 180 4,615, ,098 BangKhunthiancoast 200 1,714,286 42,010 Averagecostforastonegroyne: 1,550,000 38,000 Groynes are costeffective coastal defence measures, which require little maintenance. Once installed, it is relatively simple and inexpensive to replace damaged or dislodged stones. Costs associatedwithmaintenanceworksforgroynesarenotwidelyrecordedandthereforenotreadily available.inspectionofthegroynesareanimportantelementinthecoastalmaintenancestrategy andcanbedoneinvariouswayssuchasvisualinspectionsatlowtide,aerialsurveys,beachprofile surveysanddiversurveys. Totalcosts The costs for the nourishment with groynes are partly initial costs for the construction of the groynes( 10million)andpartlyinitialnourishment( 11.1million).Duringthemaintenancethecosts arealittlehigherthanwiththeotheralternatives,becauseofthefactayearlynourishmentstrategy hastobeapplied. Totalinitialcosts VND530billion 21.2million NPVincludingmaintenancefor20year VND1025billion 41.0million H.3 Small nourishment + revetment Thisalternativeisacombinationofarevetmentandsandnourishment.Therevetmentsdealwith thetaskofstormprotectionofpresentbuildingbypreventingincidentalerosion.thenourishment createsabeachandpreventsthestructuralerosionandunderminingofthetoeoftherevetments. FigureH.7Locationofrevetments Currently,tworevetmentsarealreadyinplacealongCuaDaiBeach,consistingofasmallstretchand longerstretch.lookingfromthesouth(fromtherightsideofthemapinh.7),thefirsttwosolidlines areshowingtheserevetments.theyarebuiltasconcreterevetments,asdescribedinappendixf CoastalerosionHoiAn

141 Forthisoption,anotherrevetmenthastobeplacedalongthepartthatisnowtemporaryprotected bysandbagsandotherprovisionalmethods.startingatthevictoriabeachresortthisrevetmentwill stretch900mnorthwards. Thedashedlinesinthemapareoptional.Itshowslocationsinfrontofresortsthatcurrentlyhave their own protection. If this is a sufficient measure, there is no need for replacement. It is the responsibilityoftheresortstoprotecttheirownproperty.twodashedlinesmostsouthshowthe two abandoned resorts. Dependent on if these projects will be continued if there is sufficient protectionagain,revetmentsorotherformsofprotectioncanalsobeappliedhere.iftheyremain abandoned,thereisnoneedforarevetment;thesandnourishmentwillpreventfurtherlandloss and stabilise the situation. There is also no need for revetments along the beaches between the Victoria, Golden Sand and Sunrise beach resorts. The protecting structures of the resorts act as groynesandshelterthebeachesforfurthererosion.especiallywithsandnourishmentthewidthof thisbeachisalsosufficienttodealwithincidentalerosionduetostorms. Thesecondpartofthisoptionissandnourishment.Thenourishmentcreatesabeach,whichisan importantattractionfortourists.italsomaintainsthefoundationandprotectionoftherevetments. Without taking away the cause of erosion, it will still continue. The sand is there to prevent underminingoftherevetmentsthatultimatelyleadstofailure.thebeachisnourishedregularly,to keeptheamountofsandsufficientoveralongerperiodoftime. Therevetmentdoesnothavetolooklikeasolidblockofconcrete,butcanbeturnedintoamodern lookingprotection.furthermore,therevetmentcannotonlybeusedforprotectionorwalkingdown tothebeach,italsoprovidesextraspaceforrecreation.however,thefriendlyandeasyappearance willreducewiththeplacementofarevetment.thenaturallookdisappears,comparedtotheoption ofafullbeachnourishment. Onthelandsideoftherevetment,severaloptionsarepossible.Itcanbekeptasitisnow,butthe revetmentalsocreatespossibilitiesforaboulevard.thismightstimulatethewholecuadaibeach area,makingitapopularattractionagain.bothpossibleoptionsarefurtherdescribedinparagraph Landwardoptions. H.3.2Design Thecombinationoftheconcreterevetmentwithabeachinfrontsustainedbynourishmentwillbe designedintwoparts.firstthebeachcreation(nourishment)willbelookeduponandsecondlythe revetment. Nourishment To retain the beach a maintenance nourishment to prevent the structural erosion is needed. This means a 240,000 m 3 /year, see Appendix C.7. A minimum width of 1 meter at high tide is wanted when the beach is at its smallest width in the year. In combination with the most effective maintenanceintervaloftwoyears,theneededinitialnourishmentcanbecalculated.infigureh.8 thebeachwidthisshownatitslargestwidthduringayearandatitsmallest. Eq.H6 With: 135 CoastalerosionHoiAn

142 FigureH.8Beachwidth Fortheinitialnourishmentitishereadvisedtoaddtenmeterbeachforunforeseenconsequences andshowanincreasevisibilityofthesolution.tenmetersofbeachwillmeana m 3 extra, 22%extra.Itcanalsobechosentonotdothisandscheduleanourishmentinthestartofyeartwo instead(sizeinaccordancewithinspectionoftheinitialnourishmentseffect),andstartwiththetwo yearintervalafterthis.asstatedbefore,sincethebeach/nourishmentisonlyforstructuralerosion, incidental erosion margins are not included in the calculation above. The revetment is preventing damagetothebuildingsandpalmtreesalongthecoast. Revetment Theotherpartofthecoastaldefence isasolidrevetment.asolidrevetmentinthisalternativeis neededsincethelocationalsohasrecreationaluses.arockrevetmentislesssuitedforrecreational use.therevetmenthastwomajorfunctions.thereisaheightdifferencebetweentheheightofthe roadandtherestaurantsalongitandtheheightoftherecreatedbeach.thisheightdifferencecanbe overcomewithoutusingalotofsandandwidthbyarevetment,sinceitallowsforasteeperslope. The second function is a fixing of the shoreline against incidental erosion during, for example, a typhoon.itdoesnotpreventstructuralerosion;however,theshiftingoferosioncanpreventdamage tobuildings.theerosiontakesplaceinfrontoftherevetmentwhereitdoesnotcausedamageto buildings.thestripedyellowinfigureh.9iswheretheerosionwouldoccurwithoutarevetment,the lightstripedyellowiswhereitoccurswitharevetment. FigureH.9Shiftingoferosion Thedepthoftherevetmentfollowsfromthemaximumexpectedincidentalerosionwithanadded extralengthforsafety.theincidentalerosioncomesfromstormsastyphoons.theareaonwhere thisscourtakesplaceisquiteconcentratednearsuchrevetment. Eq.H7 136 CoastalerosionHoiAn

143 With: TheestimatewithE1.H7ofscourof1.33meterisalsoinlinewiththereferenceresourceofscourat seadikesinvietnam,withacalculationscourof1.5meter(hoop,2006).thevalueof1.5isused fromhereon. FigureH.10Visualoverviewofdifferentbeach/bedlevels Thesolidrevetmentshouldbelessreflectiveatthelocationbelowthewaterlinelevelofthenormal situation. Since this part is not visibleand normally covered by sand, it is less important that it is useful for recreation. More scour reducing measures can be applied which will result in a less reflectivesurface. At the location where normally no wave action is present a stairs is constructed to facilitate easy reachingofthebech,seefigureh.12,withnowavereducingmeasures.atthelocationcloserthe bottom,depictedbythestripedgreyinfigureh.11,therewillbewavereducingmeasurestoreduce thewaveactionwhenincidentalerosionstartstocreateascourhole. FigureH.11Revetmentsurface FigureH.12 Stairsexample 137 CoastalerosionHoiAn

144 Landwardoptions Forthelandsideofthenewrevetmenttherearetwooptions:keepitmostlyasitisnow,orchangeit intoaboulevard.bothoptionsareelaboratedinthisparagraph. Maintaincurrentlanduse Currently,thelandusenearCuaDaiBeachiscomposedofsand,palmtreesandsomeundeveloped plots of land. It gives a natural and relaxing appearance, which can still be maintained with the constructionoftherevetment.anexampleofhowitcanlooklikeisshowninthepicturebelow.it showsthestretchofcoastthatiscurrentlyprotectedwiththegeotextilesandbags. FigureH.13Topviewwithnewbeachwithrevetment Therevetmentcanbeconstructedonthecurrentcoastline.Bykeepingtheroombetweentheroad andtherevetmentsandy,itmaintainsthebeachfeeling,completewithpalmtreesandbeachchairs. Theonlydisturbancebetweenthesandonthelandsideofthelineofprotectionandtheseawould betherevetment. Boulevard Anotheroptionisexpandingthealternativebyaddingaboulevardonthelandsideoftherevetment. Thislongstreetalongtheseacanbeusedforcycling,walkingorrelaxing.Itchangesthesandylook toamoremodernlook.afterconstructionoftheinfrastructure,theadjacentplotsoflandcanbe furtherdevelopedintomoreshops,combiningwiththecurrentresortsandrestaurants.againamap ofthemodifiedbeachisshowedinfigureh.14,accompaniedbyanimpressionofhowitmightlook like. FigureH.14Topviewandimpressionofboulevard(Verkeersbureausinfo.nl,2014) Thisexampleofareadevelopmentshowsapavementareaalongtherevetmentandopensquares towards the main road. The keep the tropical feeling, enough green area can be maintained. The map depicted in paragraph H.2.1 that showed the location of revetments and nourishment is expanded in Figure H.15with the current location of resorts and hotels, current green areas and currentroad.theareahighlightedinrediscurrentlyundevelopedandabletochangeintoboulevard areaandsurroundingsquares. 138 CoastalerosionHoiAn

145 FigureH.15Landclassification H.3.4Costsestimation The costs for the nourishment with revetment are partly initial costs for the construction of the revetment( 1million)andpartlyinitialnourishment( 6.3million).Thisvariantischeaper,buthasa verysmallbeach.permanentlyadding10meterbeachincreasesthecostwithonemillion. Totalinitialcosts VND210billion 7.3million NPVincludingmaintenancefor20year VND630billion 23.9million H.4 Nourishment strategy Theelaborationonwhichnourishmentstrategyismost(cost)effectiveaddressesthefollowingparts: Source/locationthesandcomesfrom Crossshorelocationofthenourishment Intervaltimeofthenourishment. Longshorelocationofthenourishment The yearly amount of sand that needs to be applied is 240,000 cubic meters, as followed from AppendixC.7. H.4.1Source Thedistancetothenearestsedimentreservoirisoneofthelargestfactorsdeterminingthepriceper cubicmeterofsand(m.marchand,2012).thecostsandavailabilityofdifferentsourcesareshowed infigureh.16andtableh.6.theriverdepositinfrontofthemouthispreferredassource,sincethe distance makes it the cheapest adequate supply. This source is however not yet confirmed with sufficientbathymetrychartstobeavailable.thedunescouldbeusedasaquickfixorasemergency reserve.thequantityistoosmallforanythingmore. Thesecondbestsourceisfurtheroffshoredredging.Itisnotyetcertainwheretofindsuitablemining locations. However, it is known that the depth at those locations is around 80 meters and the distanceislarger.subsequentlythecostsrise. Thelandwardsoptionofgettingsandisnotpreferred,becauseofitsnegativesideeffects.Sucha largedemandwillleadtorisingprices.alsothesandminingintheriver,whichcreatespartofthe erosion,willlikelyrisewhensuchademandisintroducedtothemarket. ThecoastsouthofHoiAnislessdevelopedandminingatsuchalocationwillshifttheproblemtoa location with less value present. It is an option that will likely be too costly for just moving the shorelineretreatinsteadofhaltingit. 139 CoastalerosionHoiAn

146 TableH.6Sandsourcesoverview Availabilitym 3 DepictedinFigureH.17,by Locationofthesource /m 3 orderof magnitude Landwards 10 Adequate Lightblue Adjacentdune <1 4*200*200=160,000 Arrowandpurple Riverdepositbefore 36 Possibly Green,amountuncertain mouth 10,000,00025,000,000 Furtheroffshore >6 Adequate Orange,locationuncertain CoastsouthofHoiAn 5 Shiftsproblem Notdepicted FigureH.16Sandsources H.4.2Crossshorelocationofnourishment The main options for nourishment at Cua Dai beach are shoreface or beach nourishment. With a shorefacenourishmentlargernourishmentvolumesarerequiredasonly30%to50%ofnourishment volumewillreachthebeach.withbeachnourishmentsthesandisdirectlyplacedonthedrybeach and no sand volume is lost, whereas with a shoreface nourishment part of the sand is lost in the transportprocessfromshorefacetowardsthedunes.however,shorenourishmentsare50%to70% cheaperperm 3 becauseofthefactthatthesedimentcanbeplacedoffshoreataplacewherethe shipshavesufficientnavigationaldepth(bosboom&stive,2015). 140 CoastalerosionHoiAn

147 FigureH.17Crossshorelocationofnourishment The shoreface nourishment provides a more stable coastal profile compared to the beach nourishment,becauseitispartofthebarzonewithintheshorezoneandthereforethenourishment quicklybecomesanintegratedpartofthebarsysteminsteadofbeingerodedaway(usarmycorps ofengineers,2007).furthermore,whentheoptimalsituationisconsidered(whichishowevernot verylikely)where50%oftheshorefacenourishmentvolumewillreachthebeachandthecostsare 70%cheaperperm 3 comparedtothebeachnourishment,shorefacenourishmentwillbemorecost effective. However, it also increases the longshore transport according to a research project of a combinednourishmentategmondaanzee(nipius,2002).whenalimitedamountofcubicmetersof nearby nourishment material is present, beach nourishment might be cheaper than a shoreface nourishment. For the current erosion problem of Cua Dai Beach it is best to use the combination of both nourishmentoptionsbecausethereisasquicksolutionneeded.thebeachoptionactsquickandis highlyvisiblewhiletheshorefacenourishmentisslightlycheaperandgivesamorestablecoast. H.4.3Intervaltimeofnourishment Thebestintervaltimeofnourishmentisinthisparagraphcalculatedonafewbasisrules: Itismorecostefficienttodepositlargeramountsofsandatthesametime Futurecostsaretranslatedtotoday scostswithadiscountrate Thecostefficiencyofdepositinglargeamountsatthesametimeiscalculatedwithafixedcostsanda unitcostwhichdecreaseswithanincreasingnourishmentamount.theusednumbersineqh9are fittedwithamultitudeofreferenceprojects(20)frommultiplecountries(11)androughestimate numbers from dredging companies (2). The referenced projects are using different kind of cross shorenourishments. Eq.H9 For till~ m 3 Eq.H10 For With: The discount rate used in the calculation is 8%, following from an average of the government discountrateinnewzealand(thetreasury,2015)andthecentralbankrateinvietnam(ciaworld factbook,2015). 141 CoastalerosionHoiAn

148 Following from Figure H.18 the most cost efficient maintenance strategy is nourishing every two years. However, the costs of nourishing every five years is around the same and this option has advantages with less disturbance for the beach users. Since coastal nourishment can have unforeseensideeffectsitisnotadvisedtostartwithalargeinitialnourishmentoffiveyearsasfirst nourishmentinanarea.ameganourishmentinthenetherlands,thesocalled sandengine,was onlyplacedafteramultitudeofdecadesofexperiencewithcoastalnourishmentsandresearch.for thefirstnourishmentanintervaloftwoyearsisadvisedandwhenadditionalresearchisdoneafive yearintervalisadvised. FigureH.18Nourishmentintervalstrategy H.4.4Longshorelocationofnourishment There are some options concerning the longshore location of the nourishment. The basic three optionsaredepictedinfigureh.19.theoptionsareanevenlyspreadoutnourishment, (multiple) spotnourishmentsfromwherethesandspreadsbywavesorbyfocusingthenourishmentonthe locationwheretheerosionfocuses. FigureH.19Longshorenourishmentlocations 142 CoastalerosionHoiAn

149 Option2isthecheapest,howeveroption1ispreferredfortheview, option 3 is only possible in combination with groynes or similar structureswhichfocusestheerosion.acombinationofoption2and 1 is advised. Focus point of nourishment at locations ~200 meters apart(furtherresearchneeded)whichwouldresultinthesituationas depictedinfigureh.20.thedistanceinbetweenischoseninsucha waythatinafewmonthsafterthenourishmentthecoastisalmosta fluent line without a need to move it with onshore land moving equipment.tosummarize:nourishmentatfocuspointsat~200meter withanaturalspreadingduetowavesisadvised. H.5 Beach policy Effective management of the coastal zone will mitigate or prevent similar problems in the future. Afteranintroductiontocoastalzonemanagement(CZM),inthisparagraphageneralstrategywillbe givenonhowtoretaincoastalresourcesandpreventconflicts.inthefirstpartastrategyisgivenfor CuaDaiBeach,inthesecondpartitisgivenforthestretchofcoastsouthoftheThuBonRiver.Ifthat beach will be further developed in the near future, a strategy is needed to prevent the current problemsofcuadaifromhappeningthere. H.5.1IntroductiontoCZM Coastal zones are the most exploited areas throughout the world and are also the areas that are likelytoundergothemostchangeinthefuture(post&lundin,1996).thiscombinationwillleadto future dilemmas between different usages of the area as a so called resource. Present nature should not be forgotten in this equation, partly for tourist attractiveness and partly for intrinsic value. If these resources need to be maintained, utilised and protected for socioeconomic development,anintegratedmanagementapproachisneeded. Coastalzonemanagementisabroadsubjectthatcanbeappliedonalargescale,buthereitwillbe usedonafewkilometrestosetupastrategyforthepreservationofthecuadaiareaandthestretch ofbeachsouthofthethubonriver.thefocuswillbeontheuse,anddevelopment,ofthebeach andnearbyseainsteadofthewholecoastalzonewhichcanreachseveralkilometresinland.already on this small area of the coast, policy is needed to exploit the limited resources without large drawbacks and to anticipate on changes in the environment. One of the current problems is that buildingsareconstructedtooclosetothesea,whichleavesnoroomforadaptationtotheerosion. Bettermanagementinthefuturecanpreventsimilarproblemsfromhappeningagainafterthebeach isrecreated. Citing from (ThiaEng, 2015), chairman of the East Asian Seas Partnership Council, coastal zone managementcanbeusedtoreachthefollowingfourgoals: Maintainingthefunctionalintegrityofthecoastalresourcesystems Reducingresourceuseconflicts Maintainingthehealthoftheenvironment Facilitatingtheprogressofmultisectoraldevelopment FigureH.20Focuspointsof nourishments GuidedbythesefourgoalsstrategiesaredesignedforthetwobeachesaroundHoiAn.Thegoalsare translatedintothreestepstocreatethestrategy.thefollowingsectionseachgothroughthestepsof elaboratingonthepresentcoastalresourcesandpossibleconflictsfirst,afterwhichthisistranslated intoastrategyforpreservationanddevelopmentofthearea. 143 CoastalerosionHoiAn

150 H.5.2CuaDai Coastalresources Thethreemajorresourcesinthestudyareaare:thebeach,theduneswithitsvegetationandthe sea.allareelaboratedbelow. Thebeachisanimportantresourceandintermsofareaitislimited.TouristscometoHoiAnpartly forthebeachanduseittorelaxordosports.resortsandfamilyrestaurants/barsknowthatabeach isanimportantattraction,thesetwokindofexploitershavetosharethebeach.resortsoftenhave theirownprivatepartofthebeach,thesmallerrestaurantsandbarshavetousethepublicareasto dobusiness.besidesthetourismsector,fishermenalsousethebeach.thelittleboatsdonotlieina harbour,butareparkedonthebeachovernightuntilitistimetosailoutagain.morelandward,the beachchangesintodunes. Inthepast,duneshavebeenflattenedtoconstructresortbuildingsonit.Thestillexistingdunesare notdirectlyusedbytourists,butsomehomesandrestaurantsarebuiltonit.thevegetationthat growsonthedunesandthedunesitselfareanotherresourcesinthisarea.thesceneryofpalmtrees isimportantfortouristsandthereforeagainalsoforthetourismsector.furthermore,thevegetation onthedunesisimportanttokeepthecattlealive. Nexttothebeachanddunesliesthesea,whichisagainimportantforthetourismsector.Aseathat iseasilyaccessibleandsafetoswiminisimportantfortouristsandthereforeneededforthosewho livefromthisbusiness.again,thesearenottheonlyusers.theseaisusedbythefishermentocatch theirfishandsubsequentlysellittomakealiving.importantforthemaretheconditionsofthesea andthelimitedamountoffishthatispresent.disturbancesintheseacanchangetheecosystemand thereforealsothefishingstrategies. Possibleconflicts Abovethethreemajorlimitedresourcesarementioned.Theyhavetobesharedbyseveralusersand everyonepreferstogettheopportunitytoexploittheirpart.conflictscanarisewhenresourcesare notequallydistributedandbusinessesarehamperedbyothers.thefollowingconflictofinterests canarise: Resortsversuslocalrestaurants/bars.Themajorissuehereisthatsomeresortsclaimapartof thepublicbeachandmakeitprivateproperty.iftoomuchbeachbecomesprivate,thereisno placeforthelocalfamilyrestaurantstodotheirbusinessanymore. Resortsversusfishermen.Thepossiblecauseforthisconflictofinterestindivisionofbeach areaisagaintheprivatisationbyresorts.fishermenneedspacetostoretheirmaterial,which canonlytakeplaceonpublicparts.furthermore,themodificationofthecoastasitiscurrently donebyresortscanaffectthefishery. Resortsversushomesandfarmers.Thefinalconflictinvolvingresortsiswithhomesand farmersonthedunes.assaid,dunesarechangedoroccupiedbyresortstoconstructtheir property.thiscantakeawaylandforfarmingandliving. Touristsversusfishermen.Althoughnotonpurpose,conflictsinvolvingtouristscanariseifthe beachandseausebecomestooextensive.ifthepublicbeachesbecometoocrowded,it becomesharderforthefishermentoosailoutandtofishalittledistanceoffshore.alsotourist activitiesaswatersportscandisturbthefishery. Natureversuspeople.Conflictofinterestsdonotarisesolelybetweenpeople,alsobetween peopleandnatureconflictofinterestsarepossible.ifallhumanactivitiesbecometoo extensive,itishardertomaintainorevenfurtherdevelopthenaturalsystems.thisisfurther explainedinthenextparagraph. 144 CoastalerosionHoiAn

151 CZMStrategy Environmentpreservation Theecosystemsintheseaandonthebeachesandduneshavetobemaintainedforanattractive environmentfortourists.thisisalsoimportantforthefishery,the(eco)tourismandthefloraand faunainandaroundtheregion.howeverwiththecurrentmeasuresthisisnotthecase. Several years ago there was much more vegetation at the dunes and at the beach than at this moment.inadditiontheecosystemsinthesea,mainlyattheforeshore,andatthebeachwerenot damaged by concrete revetments, and geotextile and plactic bags. When continuing the way of handlingtheenvironmentatthismomentthehealthofitwilldrop.theplasticsandbags,geotextile sandbagsandothererosionpreventionmeasuresusedincombinationwiththeerosionitselfwill damagetheecosystemsandthevegetationonthebeachandthedunes.inadditiontherearealotof unmanagedduneandbeachzoneswithgarbageandunusedstructuresorbuildingsonit. Whenapplyingthealternativeofonlysandnourishmenttheuseofplasticandgeotextilesandbags becomesunnecessaryandthereforeispreferredfortheenvironment.atthenourishedbeachazone can be created for beach vegetation and palm trees conforming the current ecosystems at the location.furthermore,byusingsandforthenourishmentthathasthesameproperties,organisms living on the beach can maintain their habitat. And by using the same type of vegetation the ecosystemsaredisturbedaslittleaspossible. Development It is important to have a strategy to facilitate the progress of multisectoral development. When therewasnotourism,resortsandrestaurantsoncuadaibeachyet,itwasawidebeachwithpalm trees. At the time the location for the first hotel or resort along Cua Dai Beach was defined, the designerswerenotawareofthefuturecoastlinevariationsatthedefinedlocation.thisholdsfor most of the hotels, resorts and restaurants at the south part of Cua Dai Beach. For years most resorts,hotelsandrestaurantswerebuilttooclosetothecoastline,ifyoukeepthenaturalcoastline variationinmind.oneofthemostimportantsuggestionstofacilitatetheprogressofmultisectoral developmentistoconstructanyfuturebuildingorstructurefarenoughfromthecoastline.thisway therewillbenoerosionissuesthreateningtheresorts,hotelsorrestaurantalongthebeach. HowthistranslatedintoazoningmapisgiveninChapter H.5.3Southernstretch Coastalresources ThecoastalresourcesinthestretchofbeachsouthoftheThuBonrivermoutharemostlysimilarto thoseontheotherside.oneofthedifferencesisthesizeofthebeachanddunearea.whenlooking atthemapbelowandcomparingthelanduse,thelargerbeachwidthonthesouthisclearlyvisible. EvenifthebeachatCuaDaiwillberecreated,thedunewidthatthesouthisstillalotlarger.The distancefromthebulgeonthesouthernstretchtotheclosestroadisaround700meter.theareain betweeniscoveredbytreesandsmallsanddunesandsparselyinhabited.someagriculturetakes placeinthearea. FigureH.21Differenceinresources(GoogleEarth,2015) 145 CoastalerosionHoiAn

152 Possibleconflicts Currently,thesouthernbeachisnotintensivelyused.Fishermenarethemostimportantbeachusers andnolargeamountoftouristshavefoundtheareayet.theonlyconflictsthatcanariseatthistime arethosebetweennatureandfisherman.fishermendonothavemuchreasonstodisturbtheinland resources.thetourismisfornowlimitedinthisareahoweverthebeachonthesouthernpartisstill largelypresent,andbecauseofthisitispossiblethattourismwillincreaseatthislocationinthenear future.especiallyduetothebridgethatisrecentlyconstructedovertheriver.togetherwithtourists theconstructionofresortsandrestaurantsmightbeexpected,resultinginthesamepossibleconflict ofinterestsasdescribedforcuadaibeach. CZMStrategy It should not be thought that with the currently low tourism it is less important to have a good coastalplanningthanatcuadaibeach.toavoidfutureproblemsagoodcoastalzonemanagement strategy is important. Adaption to shoreline variation or erosion is preferred over taking positive actionsinceitrequiresnoinvestment.adaptionisbestdonewhenadequateforesightisdisplayed withthedevelopmentofthearea.adaptationmeansnouseofcertainzones,orusagesthatcanbe movedwithoutanycosts. Environmentpreservation ThecurrentenvironmentatthebeachofSouthHoiAnhasnotmuchchangedthepastseveralyears. This beach is widely used by fishermen and there are no structures or measures for erosion preventionlikeatcuadaibeach.thisiswhytheecosystemsatandaroundthisbeacharesufficiently maintained. Itisadvisedtomanagethefisheryaroundthecoastsothattheexistingecosystemscanbeconserved and there will be no overfishing. Next to that the suggestion for Cua Dai Beach should also be followedforthisbeachofsouthhoian;itisimportanttoreplantvegetationwhencutorremovedso thatecosystemisconserved. Development ThispartisgiveninChapter CoastalerosionHoiAn

153 I. Measurements I.1 Measurement stick LocatedonthelowershorefaceofthebeachsectionbetweenGoldenSandsandSunriseresort,there isaplasticmeasurementstickfixedintotheground,withwhichtheverticalshorelinechangecould bemonitored.accordingtothelifeguardswhomanagethisprivatebeachsection,theresortowners installed the stick to obtain some data by themselves. The length of the stick is measured on a weeklybasisforatotaloffiveweeksinordertogetinformationabouttheverticalshorelinechange ofthisbeach. TableI.1showstheweeklymeasurementsofthelengthofthestick,whichcorrespondstothegraph infigurei.2.whenmeasurement#1istakenasareferencepoint(heightofbeach=0),thegraphof Figure I.3 can be drawn. Some interesting, yet adverse results were observed. Between measurementnumber1and2,calmweatherwaspresent.however,thebeacherodedsignificantly and a very gently beach slope was observed. Stormy weather had prevailed in the days between measurementnumber2and3andyet,thebeachaccretedtoabovethereferencelevelagain.onlya smallpartofthestickwasvisibleandamuchsteeperbeachslopewasobserved,ascanbeseenin picture#2infigurei.1.theweatherintheremainingtwoweekswasquite normal,butthesteep beachsloperemained. FigureI.1Photoseriesofmeasurementstick TableI.1WeeklymeasurementsofthesticklengthatCuaDaibeach,HoiAn. Measurement Date Lengthstick[cm] Verticalbeachchange*[cm] #1 4dec #2 11dec #3 18dec #4 25dec #5 1jan *Takemeasurement#1asareferencelevel.Thestartpointistakenaszero. 147 CoastalerosionHoiAn

154 Lengthofmeasurementstickasfunctionoftime Lengthofstick[cm] /nov/yy 4/dec/yy 11/dec/yy 18/dec/yy 25/dec/yy 1/jan/yy 8/jan/yy Time[days] FigureI.2Graphindicatingthelengthofthestickasfunctionoftime Changeinverticalbeachlevelasfunctionoftime Verticalchangeinbeachlevel[cm] /nov/yy 4/dec/yy 11/dec/yy 18/dec/yy 25/dec/yy 1/jan/yy 8/jan/yy Time[days] FigureI.3Graphindicatingtherelativeverticalbeachchangeasfunctionoftime 148 CoastalerosionHoiAn

155 I.2 Thu Bon river observations ObservationsweremadefortheriverpartfromTanAn totheupstreamendofhoian,anaround82kmstretch of the river. This has taken place in the beginning of december after the peak floods but still above average discharges.seenfromtheplastichanginginthetreesthe water level with peak discharge present will rise two metersintheupperreachandlessthanonemeterclose tohoian Upperreach Intheupperreachpartnormalerosionandaccretionis seenintherespectiveouterandinnerbendoftheriver. Not that much activity on the river and flow velocities areintheorderof2m/s Middlereach Inthemiddlereachtherewasmoreactivityontheriver, a few occasions of smallamount sand extractions from theplentifulpresentsandybanks.theflowvelocitywas present but smaller. Just between the middle and the bottom reach a high water channel is present between the Thu Bon and the Vu Gia. The direction of the inlet suggeststheflowgoesmostlyfromthegiatothubon. Bottomreach Inthisparttherewerearound1020sandminingships, but only in three occasions they were active. The ships were small in size and mostly active at the river banks. The river in this part was very wide and flow velocities wereverylow.somesignsofsandminingwerepresent, likedeeppitsinunexpectedpartsoftheriver.alsosome banks seemed to be excavated (Actually one sand excavationactivityonthebankwasspotted). ClosetoHoiAntherewerenosignsoferosionandthe river area appeared to be reduced compared to maps. Theflowvelocitywasverysmall<1m/s. Interpretations Erosion due to sediment blockage of the dam does not seem apparent. A very sandy bed still so depletion of sediment supply in the area is also not likely to reduce the sediment concentration. Sand mining is present (quantitiesunsure)butseemsnottobecausingerosion downstream in the river so it is not likely to be a very largeinfluence.sedimentationintheriversbottomreach mightbeanreasonforreducedsedimentoutflowatthe mouthsincethenotpeakflowvelocityisverysmallin thebottomreach. FigureI.4 Observationsmap FigureI.5 Fieldworkriverobservation FigureI.6 Sandminingexample 149 CoastalerosionHoiAn

156 I.3 Sediment samples analysis Onthe24 th ofdecembersedimentsamplesfromtheseabottomseveralkilometresoffshoreatthe EastSea/SouthChinaSeaweretakenforananalysistofindasuitablesandextractionlocation.For theproposedbeachnourishmentasandsourceisneededandfromaneconomicpointofview,itis preferredtogetitfromanearbylocation.thelocationofeachsedimentsampletakenisindicatedin Figure I.7. For every sediment sample the grain size distribution and the type of sediment is determined,whichisgiveninthedatasheetsattheendofthisparagraph.thesameisdoneforthe nativebeachsandatseverallocationsalongcuadaibeachandtheshorelinemorenorthwards.with this information it is possible to determine if the sediment at that specific location in the sea is suitablefornourishingcuadaibeach. FigureI.7Locationsofthesedimentsamples In total fourteen samples are taken, nine from the beach and five fromtheseabed.allthebeachsamples(1until7,13and14)and the ebb tidal delta samples (8 and 9) are sand samples. The locationsofthesamplesfromthe beachstartatthespit nearthe rivermouthandendsathamy.twooftheseasamplesweretaken infrontoftherivermouthattheebbtidaldeltaandthethreeother samplesnorthofchamisland.nexttothesefourteensamplesmud was observed south and north of Cham Island (indicated with the reddotsinfigurei.7withoutanumber). I.3.1Method First the sand samples were analysed by the dry and wet sieving method.forthegrainsizedistributionasieveanalysisisusedwith sievesoftheastmstandard,seefigurei.8.itshowsthesievesused atdry(2.00mm1.00mm0.500mm0.250mm)andwetsieving method(0.100mm0.075mm0.063mm). FigureI.8Sieves 150 CoastalerosionHoiAn

157 Notethatthe0.100mmsieveisnotanASTMstandard,butduetoalackofASTMsieves,0.100mm sievewasincludedforabetterfitofthegrainsizedistribution.fromtheresultsofthisgrainsize distributionthepercentagesoffines,sandandgravelaredeterminedandalsothegradationofthe soil.afterthatthemudsampleswereanalysedbyusingahydrometertest.withthefallvelocityof the fines in water the particle diameter is calculated and this way the grain size distribution is determined. FigureI.9Gradationofsoilbydrysievingmethod Awayofrepresentinggrainsizesinasoilisbyanalysingthecorrespondinggrainsizedistribution curve.itisamathematicalfunctionthatdefinestherelativemasspercentagesofparticlesinasoil mixture,accordingtosize.threesoilparameterscanbedeterminedfromthecurve: Effectivesize(D 10 ).Ameasureofparticlesizerange(D 10 =thegraindiameter,forwhich10%of thesamplewillbefiner). Uniformity coefficient (C u ). A measure in variation in particle sizes, given by the ratio: Coefficientofcurvature(C c ).Ameasureoftheshapeoftheparticlesizecurve,givenby: Certaincoefficientsleadto different kind of grain distribution curves. This is showninfigurei.10.how the coefficientsdetermine the type of soil can furthermore be seen in thetablei.2below. FigureI.10 Grainsizedistributioncurve(Verruijt,2012) TableI.2Classificationofsoils(Verruijt,2012) Soilgradation Shapeofgradingcurve C u C c Schematisation Very uniform, poorly <5 <1 graded Medium uniform, gap graded Nonuniform, graded well 5 >5 <1 1<C c <3 151 CoastalerosionHoiAn

158 I.3.2Resultsoverview TheresultsfromthegrainsizedistributionsofallthesamplesaregiveninTableI.2. TableI.3GrainSizeDistributionCurveResults D10 D30 D50 D60 D90 Gravel Sand Fines C u C c [mm] [mm] [mm] [mm] [mm] [%] [%] [%] Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample FromtheresultsshowninTableI.3itcanbeconcludedthatallsamplesarepoorlygradedandhavea veryuniformgradingcurve.usingthegrainsizedistributiondiagramsandtable,thefollowing observationscanbemade: Sample4containsmorefines.Thisisbecausethissampleistakenfromthedunesbehindthe smallgeotextilesandbags.dunesnormallycontainmorefinesorfinersand. Sample5istheleastuniformgradedsoilasithasthehighestuniformitycoefficientC u. Sample3hashighercontentofcoarsegrainscomparedtotheothersamples. Sample9isthemostuniformgradedsoilasithasthelowestuniformitycoefficientC u. Allthebeachsamples(Sample1until7,13and14),exceptforsample4,haveallquitesimilar properties.allhaveaveryhighcontentofsandparticlesandaverylowcontentoffinesand gravel. Next to that these samples have quite similar uniformity coefficients and curvature coefficients. This can be explained by the fact that the samples are taken from the beach withinasmallrangeoftenkilometres,sopropertiesareexpectedtobethesame. Sample8andSample9showalittledifferenceinproperties.Bothsamplesaretakencloseto each other in the ebb tidal delta. Sample 9 contains coarser sand particles than sample 8, howeverthepercentagesofsand,gravelandfinescontentaresimilar.alsotheuniformityand curvature coefficients are quite similar. The difference in size of the sand particles can be explainedbythefactthatsample8istakenseveraltensofmetersfurtherawayfromtheriver mouthandsmallerparticlescantravelfurtherbeforedepositingontheseabed. FigureI.11showsthegrainsizedistributionsofallsoilsamplesinonesinglegraph.Sample19,13 and14areallintherangeofmediumsandandshowmoreorlessthesamecurve.samples10,11 and12aretakenfromtheseabedandindicateveryfinesandandfines.thesesampleshaveasteep curvewhichindicatesaverypoorsoilgradation.infigurei.12therangeofbeachsamplesisdepicted togetherwiththeseasamples.itcanbeseenthatsamples8and9,whicharetakenfromtheriver delta, match with all the beach samples. Samples 10, 11 and 12 are taken several kilometres offshore.theycontainalotoffines,whichdoesnotmatchthenativebeachsand. 152 CoastalerosionHoiAn

159 FigureI.11Grainsizedistributionsofbeachsamples FigureI.12Grainsizedistributionsofseasamplescomparedtobeachsand 153 CoastalerosionHoiAn

160 I.3.3Conclusion Inconclusionitcanbesaid,followingtheobservationsdoneduringtheobtainingofthesediment samples and the results of the sediment sample analysis, that the sand in the ebb tidal delta has similarpropertiesasthesandfromthebeach.grainsizesofthesandfurtherawayfromtheriver mouth(location8)ismoresimilartothegrainsizesofthesandfromthebeachthanthegrainsizeof thesandclosertotherivermouth(location9). Atthelocationsnorth(locations10,11and12)andsouthofChamIsland(atadistanceofatleast6 kmfromthebeach)thereisonlymudandthatiswhythoselocationsarenotsuitableassourcefor the nourishment. Due to this information the entire area around Cham Island and beyond Cham Islandarenotsuitableforsandextraction. Furtherinvestigationispossiblecloserthan6kmtothebeachandfurthernorthwardstothecityof DanangandfurthersouthfromChamIsland.However,furtherawayfromthenourishmentlocation the costs will rise. That is why further investigation to a suitable sand extraction location is only advisedifsandextractioncloserthan6kmtothebeachisdesirable,thisisshowninfigurei.13. Nevertheless,atthelocationofsample8(infrontoftherivermouth)theremightbeasuitablesand extractionlocationifthereisenoughsandavailableatthatlocationintheebbtidaldelta.according tothecalculationofthesandbalancethereshouldbealargeamountofsandattheforeshore. Legend: Sedimentsamplelocation Protectedarea Toodeeptoextractsand Muddyseabedexpected Possiblesandextractionlocation Furtherresearchsuggested(closeto thebeach) Furtherresearchsuggested(further offshore) FigureI.13ResearchlocationsseabedEastSea/SouthChinaSea 154 CoastalerosionHoiAn