Nearshore waves and related wave overtopping in complex estuaries

Abstract

This dissertation focuses on the Eems-Dollard estuary in the north of the Netherlands and contributes to the MVED (’Meerjarige Veldmetingen Eems-Dollard’) field measurement project in the area. The Eems-Dollard estuary is part of the Wadden Sea, a shallow shelf sea with barrier islands, deep tidal channels, shallow tidal flats and wetlands. The Eems-Dollard estuary is even more complex than theWadden Sea, because of the deep channels, which run close to the dikes, and the very shallow flats, as well as the funnel shape, which can lead to very high water levels during storms. A particular aspect for this area is that the dike design conditions consist of an offshore-directed wind and very obliquely incident waves, up to 80° relative to the dike normal. Almost no studies have been performed on the estuary and almost no measurements were available inside the estuary.
This dissertation considers two main knowledge gaps, related to the modelling of wave propagation effects and measuring of (very) oblique wave run-up and overtopping, in a complex estuary. First, the performance of the SWAN wave model in predicting the wave conditions in a highly complex area, such as the Eems-Dollard estuary, has not been assessed before. Second, knowledge on and (field) measurements of the extra parameters (such as front velocities) necessary for the cumulative overload method are still scarce. This method considers the overtopping and erosion of the dike cover explicitly. Added to this, the few available (lab) investigations on wave run-up and overtopping during (very) oblique wave attack have not yet led to clear conclusions or guidelines. Therefore, the aim of this dissertation is to gain more insight into the uncertainties related to wave propagation processes and (very) oblique wave run-up and overtopping, which are important for the extreme wave loads on the dikes around the Eems-Dollard estuary.