Wave overtopping in harbour areas

Abstract

Wave overtopping in harbour areas is a fairly untreated topic in the context of flood risk analyses. Pragmatic approaches were undertaken to evaluate the possible influence of wave overtopping on the frequency of flooding. However no consensus was reached on how wave overtopping in a harbour area could be quantified. Therefore it is also difficult to determine whether wave overtopping should be accounted for in a flood risk assessment or not. This master thesis seeks to find an answer on the question which method is best suitable to quantify wave overtopping in harbour areas. Along the way it is studied which wave processes play a role and how available models take into account these processes. Subsequently a choice for a certain method or model can be made. Using this approach the question whether the effect wave overtopping might be significant in a flood risk analysis is answered. At first a theory study is undertaken which consists of two parts. The first part examines the theory on the wave processes which play a role in the nearshore and inside harbours. The second part explores the capabilities and limitations of empirical and numerical modelling of wave heights and wave overtopping in harbour areas. It was chosen to develop a non-numerical model within the scope of this thesis. The available numerical models are either not capable of modelling all relevant wave processes or model an entire harbour area in a sufficiently efficient way. These considerations might change by future updates of the discussed numerical models or the development of a new and suitable numerical model. Furthermore the computational speed is expected to keep growing, such that the problem of a lack of computational efficiency might decrease in the future. The developed non-numerical WGPO model considers the most relevant processes, namely: wave generation, wave penetration and wave overtopping. Wave generation is estimated using the empirical Bretschneider formula. Wave diffraction and wave transmission and the interaction between the two are the considered components to determine the contribution of penetrated waves. The wave diffraction pattern is determined using the analytically derived Goda diffraction diagrams. Finally the expected amount of wave overtopping over the quay walls of the harbour is estimated using the empirical EurOtop formulas. Using the case of the Vlissingen Buitenhaven the performance of the WGPO model was verified with respect to earlier researches. Due to the assumptions which lie at the basis of the model it is not (yet) possible to model complex harbour geometries. This would require improvements to the WGPO model or the application of a numerical wave model. By applying the model to the case of the Brittaniëhaven in the Botlek area of the harbour of Rotterdam the influence of wave overtopping on the probability of flooding was estimated. It appears that the frequency of flooding of the harbour areas may double. In conclusion, this case study of the Brittaniëhaven thus shows the importance of taking into account wave overtopping in a flood risk analysis of a harbour case.