Coastal protection in future climate

Transcription

1 Coastal protection in future climate Per Sørensen, Head of coastal research, Coauthors Holger Toxvig Madsen, Søren B. Knudsen, Matthew Earnshaw, Radu Ciocan, Thorsten Piontkowitz, Marianne Skov and Peter F. Klagenberg

2 Outline Introduction Flood protection and erosion protection Erosion protection, focus Erosion atlas Erosion protection Flood protection Guidelines for climate adaptation Dessimination COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 2

3 Main threath s Erosion Flooding COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 3

4 Passive erosion protection COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 4

5 Active erosion protection, nourishment methods Fællesaftale mio. m³ pr. år COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 5

6 Erosion atlas and 10 analyzed sand nourishments COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 6

7 Beach nourishments COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 7

8 Fjaltring Beach nourishment 1992

9 Nourtec 1, beach nourishment m 3 9

10 15 Morphodynamics, the bar system

11 16 The design parameters

12 17 The nourished section design parameters

13 18 The upstream section design parameters

14 19 The downstream section design parameters

15 Conclusions After ¾ year the nourishment has been moved probaly migrated downstream A stronger bar system has developed For the whole monitored area: 1 m 3 nourishment sand substitutes 1 m 3 eroded sand COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 20

16 Julebæk Beach nourishment 2010

17 Julebæk beach nourishment COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 22

18 Surveys and nourishments COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 23

19 Decay of beach nourishment COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 25

20 Sediment transport pattern Sediment redistributes mainly crosshore A minor downstream sedimentransport COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 26

21 Blåvand Beach nourishment 2010

22 Blåvand Location: northern part of the Danish Wadden Sea, Blåvandshuk Skallingen. Sandy beach ( m wide) Dune up to 6 m elevation Exposed to north sea waves Coastal protection in form present in the form of groynes Nourishment type: Beach Quantity: m 3 Monitored using bathymetric surveys COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 28

23 Volume changes COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 29

24 Krogen Beach nourishment 2012

25 Krogen, beach nourishment Location: West Coast of Jutland. Exposed sandy beach (67 m) Narrow dune (<40 m) Continuous sandbar Nourishment type: Beach Quantity: m 3 Monitored using bathymetric surveys and LiDAR scans over 20 months Exposed to two seasons of severe weather COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 31

26 Monitoring programme Segment Width [m] Total [m 3 ] Per length [m 3 /m] North Middle South Total COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 32

27 Volume changes m Measured development Natural erosion Dean / / / / /2014 COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 33

28 Duneface: Change in design parametres advances 30 m due to the nourishment retreats every year after nourishment one can see the tendency of nature to straighten out artificial undulations Duneface position Shoreline: moves outwards due to nourishment retreats in periods with rough weather advances again in mild weather Shoreline position Profile: most notable changes in and Profile position COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 34

29 Shoreface nourishments COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 35

30 Fjaltring Shoreface nourishment 1992

31 37 Nourtec 1, shoreface nourishment

32 42 Morphodynamics, the bar system

33 43 The design parameters

34 44 The nourished section design parameters

35 45 The upstream section design parameters

36 46 The downstream section design parameters

37 Conclusions The volume in the nourishment box increases to 1.5 times the nourished volume and stays at this level Positive effect on the coastline and the dune face inside Accretion upstream on the beach and in the bar zone. The effect could be influenzed by the beach nourishment upstream The volume increases downstream in the beach and bar zone For the 3.5 km section around the shoreface nourishment the volume has increased by 490,000 m 3 from the start to the end of the monitoring period. It means that the shoreface nourishment has more than counteracted the autonomous erosion The outer bar has become continuous downstream. The inner bar has not become continuous but the segments have become longer COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 47

38 Fjaltring Shoreface nourishment

39 49 Nourtec 2 shoreface noursihment

40 57 The bar system,

41 59 The bar index

42 60 The design parameters

43 61 The nourished section

44 62 The upstream section

45 63 The downstream section

46 65 The average effect on the profile after 4 years

47 Nourtec 2/shoreface summary/conclusion The volume in the nourishment box increases to 86 % of the nourishment volume. After 4 years 58 % is still there The bar trough inside becomes deeper and the coastline advances In the boxes upstream the volume decreases except for the box at the bar where there is accretion Downstream the volume decreases on the beach and in the bar trough. On the bar and just outside the bar there is a small volume increase The average number of bars in the measured profiles has been doubled and both bars become more coherent Compared to the autonomous retreat the coastline advances 58 m behind the nourishment. Advance is also seen downstream Outside the +1 m contour the average profile advances with m compared to the autonomous retreat 66

48 Husby Shoreface nourishment 2007

49 Husby, 3 shoreface nourishments The aim of the study is to analyze the effects of dividing one long massive bar nourishment into three smaller spaced Am harum nourishments unt dolor sum, tectem delestio eos arunt ut volorem Necerio moloratur Di omnim aut prorum Bus dellicae ea cupis quis dignam susci reptatem re plibus sequi il COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 68

50 Central nourishment COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 69

51 Nourishment north COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 70

52 Space North COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 71

53 Space South COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 72

54 Summary and conclusion Short bar nourishments ~ 750 m with 400 m 3 /m gathers sand the first 3 years. Short bar nourishments cause lee side erosion. Short bar nourishments advance the dune foot, the coastline and the profile. It is assumed, that short bar nourishments reduce erosion along the entire section the first years, because the strong bars disturb the long shore transport It is recommended that the gap between the bar nourishments is increased to 3000 m at future nourishments COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 73

55 Sdr. Holmland tange Shoreface nourishment 2012

56 Sdr Holmsland tange shoreface nourishment COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 75

57 Volume change in 1000 m3 Northern nourishment Entier profile Shoreline zone Inner bar zone Outer bar zone Nourishment Nourishment Date COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 76

58 Volume changes in 1000 m3 South of the northern nourishment Entire profile Shoreline zone Inner sand bar Outer sand bar Nourishment 2011 Nourishment date COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 77

59 Deposit in 1000m3 Southern nourishment Entire profile Shoreline zone Inner sand bar Outer sand bar Nourishment 2011 Nourishment Date COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 78

60 Deposition in 1000 m3 South of the southern nourishment Entire profile Shoreline zone Outer sand bar Inner sand bar Nourishment 2010 Nourishment Date COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 79

61 Sand bar movement Sand bar movment offshore =positive 0,5 0,4 0,3 0,2 0, , , , , , , ,01-0,1-0,2-0,3-0,4-0,5 Survey COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 80

62 Numbers of sandbars Total number of sand bars , , , , , , ,01 Survey COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 81

63 Conclusions Coastal retreat is on average reduced after the nourishment. The number of sand bars increases after the nourishment then continues a declining trend again. The outer sand bar moves in towards the coast as the nourishment sand redistributes itself. There remains is a traceable coastline undulation in the southern part of the study area throughout the nourishment period, however this is the only visible pattern that is carried over from the pre nourishment phase. The nourishment to the north caused an increased in volume in the inner bar zone, which met the design aim. The effect last longer than the last survey i.e. longer than 3 years. An increase in shoreline volumes south of the nourishment is also apparent. The nourishment to the south shows a rapid distribution of half of the nourishment volume to south again fulfilling the design aim. The effect of the nourishment is again longer than 3 years. COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 82

64 Design recommendations for sandnourishment Knowledge on variability of the coast are crucial Nourishment volume = profile erosion Shoreface nourishment when in due time (cheapest) Beach nourishment when not in due time (disaster management) Shoreface nourishment can disturb coastal system Beach nourishment distribution slower than Dean More R&D is needed COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 83

65 Adapting coastal flood protection in Denmark

66 Coastal flood protection in a changing climate Denmark has about 1,100 km of dike line; the reliability of the defences is often unknown Function of sea dikes is essential, as they are protecting high values Hydrodynamic forces on sea dikes will change due to climate change This implies: an improvement of reliability assessments of flood defences to avoid dikes breaches a broader understanding of the importance of sea defence maintenance new thinking of flood protection in the coastal zone COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 85

67 Reliability assessment of sea dikes Understanding of changing hydrodynamic forces due to climate change Time-dependent aspects such as the frequency and the retention period of hydraulic loading conditions on dikes Consideration of other dike failure modes than wave overtopping Consideration of active wave energy disipatation COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 86

68 Maintenance of sea dikes Erosion of grass cover layers has been investigated in EroGRASS Aggregate erosion and block erosion is dependent on the frequency of wave loading events Erosion develops sooner at weak locations such as dead plants or bare spots At well rooted locations mostly no erosion, however weak spots in the vicinity have negative effect EroGRASS showed high erosion resistance of wellmaintained grass cover layers Conclusion: Performance of a grass cover layer depends on its management COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 87

69 Adapting coastal flood protection Degree and pattern of land use and activity are important when designing coastal flood protection Hinterland comprising e.g.: settled towns and villages industrial facilities and sites for hazardous substances e.g. chemical plants conservation areas, biotopes or catchment areas for drinking water abstraction high cultural values Vulnerability of the hinterland defines adaptation of coastal flood protection Not only considerations of a defence line, but more than a defence zone COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 88

70 Urban areas COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 89

71 The Danish Dike Manual Guidance on the design and reliability assessment of coastal flood defences, including climate adaptation Focus on sea dikes and vertical seawalls Guidance to good practice in design, construction, maintenance and management Target towards engineers and planners who are familiar with coastal processes and coastal engineering Provides information to support decision making COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 90

72 When to adapt coastal protection to climate change Guidelines Use of planning lines Use of action lines COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 91

73 Overall conclusions Coastal protection can be adapted to futures climate Requires more sustainable thinking i Denmark Planning and understanding of coastal processen and their variability is crucial. Multifunctional coastal protection proposed. Socioeconomical approach suggested. COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 92

74 Højbovej Lemvig Tlf: kdi@kyst.dk COADAPT, WP2 Coastal protection, Dancore seminar december 3rd 2014 SIDE 93