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Comparison of Reliability Methods for Flood Defence Systems

Author: De Boer, E.
Mentor: Vrijling, J.K. · Van Gelder, P.H.A.J.M. · Ter Horst, W.L.A. · Veenhuijsen, A.G.P. · Vrouwenvelder, A.C.W.M.
Faculty:Civil Engineering and Geosciences
Type:Master thesis
Date:2007-06
Publisher: TU Delft, Civil Engineering and Geosciences, Hydraulic Engineering
Keywords: pc-ring · prodeich
Rights: (c) 2007 E. de Boer

Abstract

Floods are a threat to millions of people who are living in lowlands. A lot of research is done about flood risk analysis. A general expression of flood risk is the probability of flooding times the consequences. This graduation research focuses on the probabilities of failure and leaves the consequences out of the comparison. The objective is to find the most interesting parts for a flexible and widely applicable reliability method. By describing existing reliability methods and applying those to a model dike and a dike ring in the German Bight area (Germany) more insight will be gained into the advantages and disadvantages of these methods. The reliability methods PC-Ring and ProDeich are described and compared with each other. PC-Ring is developed in the Netherlands and used in the VNK-project to test the Dutch dike rings. ProDeich is developed in Germany as a model to assess the overall failure probabilities for sea dikes. Both methods are designed to analyse the separate flood defences and systems of flood defences. Furthermore the approach of determining the failure probability is in general the same. The dike ring is divided in equal sections. A limit state function describes the strength and loading for the failure mechanisms and the failure probabilities are calculated using probabilistic level II or level III calculations. Differences can be found in the general background of the methods, the application area, the available fault trees and failure mechanisms. The use of stochastic and hydraulic input is rather different in PC-Ring and ProDeich. PC-Ring considers correlations and dependencies, while this is neglected in ProDeich. The amount of hydraulic input in PC-Ring is very extensive compared to ProDeich. Differences in the output are caused by the following aspects: The calculation methods lead to differences for all failure mechanisms. Piping is in PC-Ring preceded by heave. Differences in the limit state functions. Different use of model factors (which account for uncertainties in the used models). Different wave heights and periods, these are provided in a different way in each program and therefore lead to different results. The comparison of both methods leads to many differences and similarities and a new software tool should comprise aspects from both programs.

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