12 th Polish German Seminar on Coastal Research The Baltic Sea at the middle of 21 th century

Transcription

1 Risk Analyis for Coastal Areas 12 th Polish German Seminar on Coastal Research The Baltic Sea at the middle of 21 th century M.Sc. Angelika Gruhn, Dipl.-Ing. Dörte Salecker, Prof. Dr.-Ing. Peter Fröhle Hamburg University of Technology October

2 Content What is Flood Risk Projects HoRisK Methodology of Risk Assessment Loads on Flood Defences Flood Defences and their Failure Consequences of Failure Coastal Flooding Damages and Damage Assessment Summary

3 What is Flood Risk

4 Project HoRisK - Partners November 1st, 2009 to December 31st, 2013 HoRisK-A Failure of Coast Protection Constructions and Damages Lehrstuhl und Institut für Wasserbau und Wasserwirtschaft, RWTH Aachen HoRisK-B Loads on Coast Protection Constructions and Consequences of Failure Hamburg University of Technology, Institute of River and Coastal Engineering HoRisK-C Consequences of Failure of Coast Protection Constructions and Minimization of Damages Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz Betriebsstelle Norden-Norderney

5 Project HoRisK - Partners Other Partners Landesbetrieb für Küstenschutz, Nationalpark und Meeresschutz Schleswig-Holstein, Husum Staatliches Amt für Landwirtschaft und Umwelt Mittleres Mecklenburg, Rostock Landwirtschaftskammer Niedersachsen, Oldenburg HKV Hydrokontor GmbH, Aachen Main Goal of Reseach Additional information: http//:

6 Project HoRisK Risk Analysis & Work Packages I. Definitions and available methods Hazard Analysis II. Hazards and loads Reliability Analysis III. IV. Reliability and failure of constructions Consequences Coastal Flooding Hydrodynamic Analysis V. Consequences Damages Analysis of Consequences VI. VII. Integration Risk-Analysis Damage and Risk Minimization

7 Project HoRisK Project Areas

8 Loads on Flood Defences Hazards and forces that act on coastal structures and might cause their failure high water levels the sea state currents ice Data collection (Waterways and Shipping Administration of the Federal Government, local authorities, own measurements, numerical simulation) Statistical analyses of single forces and assignment of probabilities of occurrence Statistical analyses of combinations of two forces and assignment of probabilities of occurrence Derivation of storm surge hydrographs for all focus areas Results are used as boundary conditions for further investigations in the following work packages

9 Loads on Flood Defences - Input data Samples of annual peak water levels are derived from the water level time series For all annual maximum water levels the corresponding fullness is calculated Fullness is the area between a threshold water level of 60 cm NHN and the water level progression over the time Erläutern des generellen Vorgehens bei der Festlegung von Bemessungsgrößen am Beispiel von Sturmflutganglinien für die Ostsee 1: Eingangsdaten Data: WSA

10 Loads on Flood Defences - Statistical analyses Univariate distribution functions are fitted to annual peak water level samples and fullness samples

11 Loads on Flood Defences - Statistical analyses Pairs of annual maximum water levels and corresponding fullness are plotted together to analyse the dependence of both measures A cumulative distribution function has to be found that is able to describe the bivariate sample A way to write a cumulative distribution of a bivariate sample is in terms of the marginal distribution functions and a copula

12 Loads on Flood Defences - Statistical analyses The marginal distribution functions describe the water level and the fullness, the copula describes the dependence structure between the components A probability of occurrence can be assign to two characteristics of storm surge hydrographs in tideless seas (water level and duration)

13 Loads on Flood Defences - Storm surge hydrograph shapes To generate random shapes both parameters (a und b) are generated randomly The time of the peak water level varies within the limits of actually measured times for each location Assuming that the shape of a storm surge is random, no probability of occurrence has to be assigned r θ = r θ = a cos θ + b 2 a sin θ + b 2 a cos θ b 2 a sin θ b 2 a) b)

14 Loads on Flood Defences - Storm surge hydrographs Shapes of storm surge hydrographs are being scaled in height and width using random combinations of water levels and fullness of a desired probability of occurrence

15 Flood Defences and their Failure Investigations of failure mechanisms and probability of failure for different flood defences Identification of the decisive failure mechanisms for flood defences and their corresponding probability of failure damage based and / or risk based approaches and methods for the determination of flood risk Dike Flood protection walls Dune Sluice 2. Dike line

16 Flood Defences and their Failure Flood Defence Dunes Possible failure mechanisms for flood protection dunes: (i) erosion due to wave attack, (ii) overflow & (iii) overtopping Focus on failure due to wave attack: applying different dune erosion models for assessment of probability of failure Dune

17 Flood Defences and their Failure Dune Erosion Models Applying semi-empirical models as well as numerical models Semi-empirical dune erosion model Van Gent et.al. (2008) Based on the assumption of an equilibrium profile Input parameter direct H 0s, T p, w; indirect storm surge water level Calculation of the equilibrium profile (numerical integration Simpson rule) 7,6 y=0,4714* 7,6 H os H 0S 1,28 * 12 Tp 0,45 * w 0,0268 0,56 0,5 *x+18-2,0 x R =250* H 0S 7,6 1,28 * 0,0268 w 0,56 y R = H 0S 7,6 * 0,4714* 250* 12 T p 0, ,

18 Flood Defences and their Failure Dune Erosion Models Applying semi-empirical models as well as numerical models Numerical dune erosion model Xbeach (open source) Calibration at coastal area at the German Baltic Sea Coast Markgrafenheide

19 Flood Defences and their Failure Dune Erosion Models Numerical dune erosion model Xbeach (open source) Calibration at coastal area at the German Baltic Sea Coast Markgrafenheide

20 Flood Defences and their Failure Fragility Curves & their Calculation Assessment of reliability of flood defence Show the probability of failure and non-failure as function of stresses acting on the structure Shape depends on flood defence related parameters after Bachmann et.al Calculation of the fragility curve on the basis of reliability analysis for discrete points of the applied stress Determination of a limit state equation compares the strength of the flood defence with the stresses acting on this structure Z = R - S Applying Monte Carlo simulations for the calculation of the limit state equation flood defence failure occurs in the case of a negative result of the limit state equation

21 Flood Defences and their Failure Fragility Curves & their Calculation Needed limit state equation: Z = m*d Krobr_akt d KroBr_kr with: d Krobr_akt : determined by dune erosion model, d KroBr_kr : 5 m (width of the safety part), m: Model factor; m = 0,6 Calculation of failure probability by using using Monte Carlo analyses based on the limit state equation and the derived input paramters P f n fai n Carrying out a multitude of simulations for fixed values of water levels in combination with possible sea state conditions and durations of storm events of the same return period

22 Flood Defences and their Failure Resulting Fragility Curves Van Gent et.al. (2008) Xbeach (Roelvink et.al., 2009)

23 Consequences of Failure Coastal Flooding Assessment of different protection systems concerning: Protective effect Effect on inundation propagation Analyses of relevant processes and decisive parameters Breach development of dikes and dunes Influence of coastal protection systems Influence of topography within protected area Influence on polder dimension and 2. dike line Sensitivity of applied methodology

24 Consequences of Failure Coastal Flooding Systematic sensitivity analyses derivation of dependencies concerning conditions of a specific coastal area and parameters necessary for damage assessment Investigated parameters Breach width Breach location Duration of failure Return period of storm surges Storm surge fullness Influence of tides Derived inundation parameters Inundation height Flow velocity Retention time of maximum inundation Statistical analyses of potential inundation areas at the German Baltic Sea derivation of typical dimension of potential inundation areas and ground levels Baltic Sea coast => areas: 20 km² with a ground level of 0,375 m & 50 km² with a ground level of 0,875 m

25 Consequences of Failure Coastal Flooding Storm surge hydrographs Derivation of the storm surges by means of bivariate statistical models Return periods of 50 years, 100 years, 150 years & 200 years, 3 forms of the hydrographs each

26 Consequences of Failure Coastal Flooding Influence of the Breach Width Failure duration : 1hour Beginning of failure: 1 hour before storm surge water level Return period: 200 years Polder dimension [km²] Breach Width [m] , ,8 16,8 7 3, ,3 39,3 12,6 6, ,1 65,6 21, ,7 34, ,3 15, ,7 18, ,3 20,

27 Consequences of Failure Coastal Flooding Influence of the Return period Failure duration : 1hour Beginning of failure: 1 hour before storm surge water level Breach width: 50m Polder dimension [km²] Return period [years] , ,9 31,8 18,6 7, ,9 27,4 17,2 6, ,7 21,9 14 5,

28 Consequences of Failure Coastal Flooding Influence of the Storm surge fullness Failure duration : 1hour Beginning of failure: 1 hour before storm surge water level Breach width: 50m, Polder area: 5 km² Return period [years] Fullness ,3 18, ,5 24,4 27,2 3 2,4 2,8 3,

29 Consequences of Failure Coastal Flooding Influence of time of beginning of failure max. area = m² max. area = m²

30 Consequences of Failure Coastal Flooding Influence of breach width: 100m (left), 50m (right) max. area = m² max. area = m²

31 Consequences of Failure Coastal Flooding Influence of storm surge water level: design storm surge (left), T = 200a (right) max. area = m²

32 Project XtremRisk German Joint Research Project XtremRisK (Extreme storm surges at open coasts and estuarine areas: Risk assessment and mitigation under climate change aspects) overall aim of the project: improvement of knowledge of the influences of morphological changes (uncertainties of storm surge predictions) the joint effect of extreme water level and sea waves and the quantification of the overall flood risk for two pilot areas

33 Damages and Damage Assessment Vulnerability assessment Spatial delineation of pilot area Definiton of damage categories Identification of elements at risk Typification of elements Value assessment & generation of damage functions Scenarios of extreme storm surges Flood propagation Direct damages Indirect damages Residential Infrastructure Commercial Agriculture Value added loss per Sektor Time for Reconstruction

34 Damages and Damage Assessment Outer wall Inner wall Floor Ceiling Windows & doors Rooms Cleaning Residential Damage functions [ /m²], [%] Classes: Building (geometry, construction), Inventory (configuration/furniture) Type: Absolute and Relative Intervall: 10cm steps for both inventory and building. In sections defined as linear functions

35 Damages and Damage Assessment Storm surge scenarios (1) (2) (3) * Exceeding the bearable capacity of the Hinterland (~120 Mio. m³)

36 Damages and Damage Assessment Transfer of results into GIS

37 Damages and Damage Assessment Transfer of results into GIS Transfer into grid structure Intersection with risk elements Calculation of direct damages based on damage functions Damage [ ]

38 Damages and Damage Assessment (1) (2) (3) 10% 32-78% 61% 99% 52%

39 Summary Estimation of the flood risk of coastal areas by means of risk analysis Succession of different analyses results are used as input for subsequent analyses Results of statistical analysis of hydraulic loads are used as input parameters for reliability analysis & simulation of flood propagation Reliability analysis allow us to assess the probability of failure of a certain structure in case of an occurrence of a certain storm surge event Simulation flood propagation determine the flooded area and the inundation height Damage calculation combines the results of hydrodynamic simulations with an analysis of the risk element and its values Combination of results of the reliability analysis and the damage analysis defines the flood risk

40 Thank you A. Voelker