Risk Analysis of Coastal Protections at Tidal Coasts

Transcription

1 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 Abtact Rik Analyi of Coatal Potection at Tidal Coat Stephan Mai Fanziu-Intitut fo Hydaulic, Wateway and Coatal Engineeing, Univeity of Hannove, Hannove, Geany Clau Zieann Fanziu-Intitut fo Hydaulic, Wateway and Coatal Engineeing, Univeity of Hannove, Hannove, Geany A pobabilitic deign concept fo coatal potection uppleenting the taditional deteinitic deign appoach wa woked out and applied nea Wilhelhaven and Beehaven at the Gean Noth Sea coat. Uing thi oden deign concept the pobability of failue of the coatal potection yte wa calculated taking into account wave ovetopping at the ain dike being the ot ipotant failue echani. Today ecuence inteval i appoxiately 1000 yea. In the event of cliate change aiing wate-level and inceaing peed the ecuence inteval i ignificantly educed. An inceae of the wate-level of 0.50 will educed the ecuence inteval to 40 %, while an inceae in -peed of 10 % lead to a 20 % eduction of the ecuence inteval. All eult wee analyed with epect to uncetaintie caued by the extapolation of and wate-level tatitic to extee event evealing the difficultie of a pobabilitic deign. Intoduction At the Gean Noth Sea Coat the hinteland i potected fo flooding by a eie of coatal potection eleent. The deign of the atificial coatal potection eleent, like buh wood fence, ue dike and ain dike, i taditionally deteinitic. Thi deteinitic deign appoach i today copleented with pobabilitic deign ethod in ode to deive the ecuence inteval of failue of the coatal potection yte [1]. Taking into account the daage due to failue, e.g. inundation of coatal aea in conequence of a dike beach, the pobabilitic deign concept ay be extended to a ik analyi [2, 3]. Beide the calculation of today afety tandad the pobabilitic ethod povide a ean to etiate the effect of aiing wate-level and intenifying, e.g. caued by cliate change [4]. In thi pape pecial ephai i put on the quantification of the uncetainty of the calculated failue pobabilitie due to the extapolation of the tatitic of wate-level and deived fo long-te data-et [5, 6]. The analyi of failue pobabilitie i woked out fo the potection yte of the coatal zone between the pot of Wilhelhaven and Beehaven. A detailed deciption of the potection yte and the potected hinteland can be found in [7]. Theoetical Backgound Rik analyi ue the idea of a failue function, Z, decibing the diffeence between the eitance of the coatal potection eleent, R, and the te acting on the eleent, S:

2 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 Z(u, v = R(u S(v whee u, v ae the paaete vecto decibing the eitance and te. Failue i denoted to all cobination of vaiable u and v leading to negative value of the failue function, i.e. Z (u, v < 0 The paaete u and v ae geneally pobability ditibuted and ae decibed by uing the joint pobability denity function p u, v (u, v. The pobability of failue p Z < i 0 deteined by integating the joint pobability denity function ove the failue egion: p L < = Z< 0 Z 0 p u, v (u, v du dv Fo the ea dike, the ot ipotant coatal potection eleent at the Gean Noth Sea Coat, wave ovetopping i conideed to be the ot ipotant failue ode (Fig. 1 [2]. The failue function i defined uing two diffeent citeia, one calculating the unup level [8] and the othe calculating the ovetopping ate [5]: (1 (2 (3 Z = h Thw R (4a Z Q Q tol with h : height of the dike Thw: tidal high wate-level R: wave un-up Q tol : toleable ovetopping ate [9] Q: ovetopping ate (4b Fig. 1 Failue echani wave ovetopping The wave un-up i given by [10]: 1 R = 0.75 γ g H T (5 n whee H, T ae the ignificant wave height and ean wave peiod, 1/n the lope of the dike, g the acceleation of gavity and γ a eduction facto decibing the effect of lope oughne, hallow foe hoe, be and oblique wave attack.

3 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 Two diffeent appoache decibing the ovetopping ate intoduced in equation (4b can be ditinguihed one uing the peak ovetopping ate [5] the othe uing the ean ovetopping ate[10]: Q peak = γ p,1 g H T e γ 1 (h Thw p,2 T g H (6 Q ean = γ,1 g H 3 e γ 1 (h Thw,2 H (7 with the dienionle paaete γ p,1, γ p,2, γ,1 and γ,2. The wave paaete H and T at the coatal defence tuctue can be etiated uing nueical wave odel, e.g. SHALLOW WAVES NEARSHORE SWAN [11]. In atheatical te the wave paaete ae a function of wate-level Thw and condition ( u, α : Wind Wind H T = H = T (Thw, u (Thw, u, α, α (8 (9 Fo the failue echani of wave ovetopping the paaete vecto v decibing the te i given by v = (Thw, u, α (10 while the paaete vecto u decibing the eitance i given by u = (h u = (Q tol (11a (11b depending on the choen citeia (equation 4a/b. Within thi tudy the height of the dike epectively the toleable ovetopping ate at a cetain poition i aued to be exactly deteined, i.e. not pobability ditibuted. The load vecto v i epeented by a joint pobability function of wate-level and, deived fo a 50 yea data et. Pobability of ike Failue in the Event of Cliate Change An exaple of the pobability ditibution of the tidal high wate-level i given in figue 2 (left uing data of a gauge at Wilhelhaven. The olid black line epeent today pobability ditibution while the coloued line ae cenaio of inceaed tidal high wate-level in cae of cliate change. The cenaio coepond to etiate of ea-level ie at the Gean Noth Sea coat within the next 50 epectively 100 yea deived by downcaling global cliate change etiate to egional cale [11].

4 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 Pobability denity function p (Thw [ -1 pe tide] ata bae: (Gauge: Feddewadeiel Thw Thw +0.2 Thw +0.5 Thw +0.8 Thw Tidal high wate level THW [NN] Pobability denity function p (Thw [ -1 pe yea] Pobability denity function p [ -1-1 ] E-005 1E-006 1E-007 1E-008 1E-009 Wind diection 300 1E-010 Statu quo Wind velocity % W ind velocity + 10 % 1E Wind peed [/] Fig. 2 Scenaio of pobability denity function of wate-level and The peed u i Weibull ditibuted [12]: k 1 k k u u p (u = exp (12 A A A with caling paaete A and k. An exaple of a pobability ditibution of peed fo fo 300 i given in figue 2 (ight. Again the olid black line give today ituation and the coloued line give cenaio of inceaed peed Vaele Schleue Schweibuge Siel Wate-level: MSL + 6, Wind: 24 /, Wave height H [] Vaele Schleue Schweibuge Siel Wate-level: MSL + 6, Wind: 24 /, 0 Beehaven Wilhelhaven Feddewade Siel Nodenha Beehaven Wilhelhaven Feddewade Siel Nodenha Wavepeiod T [] Fig. 3 Nueical iulation of wave popagation within an etuay

5 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 Fo vaiou et of the paaete vecto v the wave cliate i calculated uing the wave odel SHALLOW WAVE NEARSHORE (SWAN in ode to deive the tanfe function tated in equation (8 and (9. An exaple of the wave popagation calculated with SWAN i given in figue 3. The calibation of the odel i decibed in [13]. Both wave paaete ignificant wave height and ean wave peiod educe ignificantly fo wave popagating towad the coat becaue of the eduction in wate depth. Extacting the wave paaete at diffeent location of the nueical odel (fig. 3 fo all et of the paaete vecto v give the ecuence tie of wave paaete. An exaple of the ecuence tie of the ignificant wave height within the odel aea i given in figue 4. At the odel bounday the 100-yea ignificant wave height i 3.5 deceaing to ove the tidal flat and to ove the foeland in font of the ain dike Model bounday Tidal flat (-1,0 NN Tidal flat (-0,3 NN Recuence tie [yea] Tidal flat (0 NN op of the foeland Toe of the dike Significant wave height H [] Fig. 4 Recuence inteval of ignificant wave height at diffeent location within the coatal potection yte With thee wave paaete the ecuence inteval of wave ovetopping at the ain dike i calculated fo vaiou cenaio of cliate change applying equation 3, 4a and 5. Figue 5 peent the influence of wate-level ie on the ecuence inteval of wave ovetopping fo the dike nea the citie Wilhelhaven and Beehaven. Today ecuence inteval of wave ovetopping i appoxiately 1000 yea. It deceae to about 350 yea in cae of a wate-level ie of 0.50 and to 100 yea in cae of a wate-level ie of 1.00.

6 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 The effect of an enhanceent of the peed on the ecuence inteval i ino, a hown in figue 6. An inceae of peed of 10% educe the ecuence inteval only fo appoxiately 1000 yea to 900 yea. An inceae of peed of 3.8 %, begin a oe pobable etiate of poible cliate change within the next 100 yea, only lead to a eduction of 20 yea in ecuence inteval. Latitudinal coodinate [] Wange Land P3 P4P5 P2 Butjadingen Stadland P Invetigated Longitudinal coodinate [] pofile Height [NN] Recuence inteval [yea] Scenaio of wate-level ie MThw MThw MThw MThw MThw P 1 P 2 P 3 P 4 P ike - k Fig. 5 Recuence inteval of wave ovetopping at the ain dike in cae of ea-level ie Latitudinal coodinate [] Wange Land P3 P4P5 P2 Butjadingen Height [NN] Recuence inteval [yea] 1000 Scenaio of enhancing Statu quo Wind peed % Wind ped + 10 % Stadland P Invetigated Longitudinal coodinate [] pofile P 1 P 2 P 3 P 4 P ike - k Fig. 6 Recuence inteval of wave ovetopping at the ain dike in cae of inceaing Uncetainty of Calculated Failue Pobabilitie Beide the intinic uncetainty, which i a conequence of tidal high wate-level and being tochatic pocee [6], tatitical uncetaintie and odel uncetaintie hould be taken into account calculating the pobability of ovetopping, e.g. [14] tate that thee additional uncetaintie ight change the pobability by a facto of 10. In the following tatitical uncetaintie epectively ditibution type uncetaintie and thei effect on the pobability of wave ovetopping ae analyed exeplay fo tidal high

7 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 wate-level. Figue 2 exeplifie the poble of ditibution type uncetaintie giving fou diffeent extapolation of the pobability denity function of the tidal high watelevel at the coat nea Wilhelhaven ata bae: (Gauge: Wilhelhaven pobability denity function p (Thw [ -1 pe tide] pobability denity function p (Thw [ -1 pe yea] Type of ditibution exponential ²= Weibull ²= Gubel ²= Gau ²= tidal high wate level THW [NN] Fig. 7 Pobability denity function of wate-level The extapolation ae calculated uing non-linea leat-quae ethod auing diffeent type of pobability ditibution: Noal ditibution (Gau Gubel ditibution Weibull ditibution Exponential ditibution The fit of exponential and Gubel ditibution lead to appoxiately the ae pobability denity fo extee wate-level while epecially the noal ditibution eult in lowe value of the pobability denity function. The tidal high wate-level with a ecuence inteval of 100 yea epectively 1000 yea i lited fo the diffeent type of pobability ditibution in table 1. ecuence type of pobability ditibution of tidal high wate-level intevall noal Gubel Weibull exponential Tab yea / 1000-yea tidal high wate-level at the gauge Wilhelhaven

8 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, 2000 The intoduction of the diffeent ditibution into equation (3 give the ecuence inteval. Figue 8 how the ecuence inteval of wave ovetopping at the dike pofile P2 located at the Jade etuay fo the diffeent type of pobability ditibution and the cenaio of ea-level ie. Fo today ituation the ecuence inteval ange fo 500 yea (Weibull to 4000 yea (Gau. The influence of ditibution type uncetainty on the ecuence inteval deceae with deceaing ecuence inteval. In the event of a ea-level ie of 1 the ecuence inteval vaie fo 60 yea (Weibull to 90 yea (Gau. Latitudinal coodinate [] Wange Land P Invetigated Longitudinal coodinate pofile Butjadingen Stadland [] Height [NN] Recuence inteval [yea] Type of ditibution exponential Weibull Guble Gau Thw-level ie [] Fig. 8 Recuence inteval of wave ovetopping at the ain dike uing diffeent extapolation of the tatitic of tidal high wate-level Concluion A pobabilitic analyi of the afety of dike i woked out within thi pape. Today ecuence inteval of wave ovetopping will educe to 10 % in cae of a ie in tidal high wate-level of The pobabilitie of ovetopping ae not identical with the pobability of inundation but can be tanfeed by ultiplication with a o-called tanition pobability decibing the pobability that a dike fail unde the condition of wave ovetopping. Beyond intinic uncetaintie tatitical uncetaintie have a lage influence on the calculated ecuence inteval leading to vaiation of an ode of agnitude. Refeence 1. Mai, S., Schwaze, H., Zieann, C., Safety of Coatal efene Syte - An Aeent of the Reliability of Coatal Syte in the Event of Riing Wate Level due to Cliate Change, Poceeding of the 1-t Int. Conf. PORT COAST ENVIRONMENT, Vana, Bulgaia, Mai, S., v. Liebean, N., Intenet-baed Tool fo Rik Aeent fo Coatal Aea, Poc. of the 4th Int. Conf. on Hydoinfoatic, IAHR/AIRH , Iowa, USA (accepted

9 Auzug au: Poc. of the 2nd Int. Conf. Pot evelopent & Coatal Envionent, Vana, Bulgaia, Mai, S., v. Liebean, N., Rik Aeent of Coatal efence - An Application at Gean Tidal Inlet - Poc. of the Intenational Sypoiu on Flood efence, , Kael, Geany (accepted 4. Mai, S., Schwaze, H., Zieann, C., Safety Vaiation of Coatal efene Syte, Poceeding of the 2-nd Indian National Confeence on Habou and Ocean Engineeing (INCHOE, Tivandu, India, Reeve,.E., Coatal Flood Rik Aeent, Jounal of Wateway, Pot, Coatal, and Ocean Engineeing, No. 5, van Gelde, P.H.A.J.M.: Statitical Method fo the Rik-Baed eign of Civil Stuctue, Counication on Hydaulic and Geotechnical Engineeing, elft, Netheland, No. 00-1, v. Liebean, N.,Mai, S., Flood Potection of the Coatal Zone between the Jadeetuay and Wee-etuay (oiginal in Gean: Stuflutchutz de Natu- und Witchaftaue zwichen Jade und Wee, Bee Beitäge zu Geogaphie und Rauplanung, Been, Geany, Cente fo Civil Engineeing Reeach and Code CUR Technical Advioy Coittee on Wate efence TAW, Pobabilitic eign of Flood efence, epot 141, Gouda, Netheland, Fanco, L., de Geloni, M., van de Mee, J.W., Wave ovetopping on vetical and copoite beakwate, Coatal Engineeing, Van de Mee, J.W., Janen, J.P.F.M., Wave un-up and wave ovetopping at dike and evetent, elft Hydaulic Publication, no. 485, elft, Netheland, V. Stoch, H., Reichadt, B.-H., A cenaio of to uge tatitic fo the Gean bight at the expected tie of double atopheic cabon dioxide concentation, Jounal of Cliate, Vol. 10, Toen, I., Peteen, E. L., Euopean atla, Rokilde, enak, Mai, S., Zieann, C., Feaibility Studie on a Planned eep Wate Pot in Geany, Poceeding of the 2-nd Int. Conf. PORT COAST ENVIRONMENT, Vana, Bulgaia, Vijling, J.K., van Gelde, P.H.A.J.M., Uncetainty analyi of wate level on Lake Ijel in the Netheland, XXVIII IAHR conge, Gaz, Autia, 1999