Characterization of Overtopping Waves on Sea Dikes with Gentle and Shallow Foreshores

Tomohiro Suzuki,Corrado Altomare,Tomohiro Yasuda,Toon Verwaest

doi:10.3390/jmse8100752

Abstract

Due to ongoing climate change, overtopping risk is increasing. In order to have effective countermeasures, it is useful to understand overtopping processes in details. In this study overtopping flow on a dike with gentle and shallow foreshores are investigated using a non-hydrostatic wave-flow model, SWASH (an acronym of Simulating WAves till SHore). The SWASH model in 2DV (i.e., flume like configuration) is first validated using the data of long crested wave cases with second order wave generation in the physical model test conducted. After that it is used to produce overtopping flow in different wave conditions and bathymetries. The results indicated that the overtopping risk is better characterized by the time dependent h (overtopping flow depth) and u (overtopping flow velocity) instead of hmax (maximum overtopping flow depth) and umax (maximum overtopping flow velocity), which led to overestimation of the risk. The time dependent u and h are strongly influenced by the dike configuration, namely by the promenade width and the existence of a vertical wall on the promenade: the simulation shows that the vertical wall induces seaward velocity on the dike which might be an extra risk during extreme events.

Highlights

Global climate change has manifold impacts on the ocean and its behavior, which directly translates to the coastal/nearshore region as well as the governing processes
There is some literature related to the stability of people on the dikes/promenade (e.g., [3,4,5]), which deals with the relationship between human’s stability and flow parameters
The model has been validated in different studies applied for shallow foreshores but it is further validated in terms of maximum individual volume based on a physical model

Summary

Introduction

Global climate change has manifold impacts on the ocean and its behavior, which directly translates to the coastal/nearshore region as well as the governing processes One such climate-induced response is the augmented frequency and intensity of extreme waves, leading to increased overtopping risk for people living in coastal area [1,2]. Other works focused on the characterization of overtopping flow depths and/or velocities, see [9,10,11,12] These are important works to understand the basic risk exposed to the flows on dikes, the present knowledge cannot cover all the risks due to different layouts and hydraulic conditions. The return flow or reflected wave in front of a vertical wall can influence the human’s stability, a detailed discussion on such different flow directions has not been made explicitly so far

Objectives

Methods

Conclusion