The effect of erosion resistant layers on the morphological evolution of a schematized tidal inlet system using Delft3D

Abstract

The Northern part of the Dutch coast is characterized by several connected tidal inlet systems. These systems are important features as they provide coastal safety, are unique in their natural assets and are known for their recreational function. Numerical modelling is used to predict the long-term evolution of these systems. These models do not include erosion resistant layers. These layers might play an important role in the evolution of these systems and should therefore be properly incorporated. The aim of this study is to evaluate the effect of these erosion resistant layers on tidal inlet systems. In addition, the representation of these layers in a model can be done by altering the two parameters (1) Critical shear stress for erosion and (2) Erosion rate. This lead to the question; What is the effect of different erodibility parameterizations of erosion resistant layers (ERL) on tidal inlet systems? A literature study is conducted to derive a representative range of values for the erodibility of the ERL. These values can be determined by using formulations that are related to soil properties. This resulted in representative values for the critical shear stress for erosion ranging from 1.4 to 4.4. A model study, using a process-based model proposed by Dissanayake et al. (2009), is used to evaluate the different effects of varying critical shear stress for erosion and erosion rate. There are two sets of models containing erosion resistant layer at a depth of -23 meters NAP (set 1) and -10 meters NAP (set 2). This model study covers the long-term evolution of tidal inlet systems for 80 years. Model performance analyses are used to discriminate between a phase of model adjustment and a phase of system dynamics. Subsequently, the different implemented erosion resistant layers are analysed for their erosion behaviour. The eventual morphological analyses aims a quantifying the effect of erosion resistant layers on both large scale system development as small scale morphology effects. Several characteristic features are more thoroughly examined providing an insight into tidal inlet system evolution. Especially the presence of the erosion resistant layer at a depth of - 10 meters NAP has significant morphodynamical effects. Mainly effects on channel activity and channel geometry are observed. This is caused by differences in incision due to varying erodibility of the erosion resistant layer. Effects on the long-term evolution of tidal inlet systems are not observed. The modelled erosion resistant layers have predominantly a local effect. Furthermore, this thesis provides a clear overview of the effect of erosion resistant layers, the corresponding erosion processes and the long-term evolution of tidal inlet systems in general.