An Idealised Morphodynamic Model of a Double Inlet System

Abstract

Due to their ecological significance and their role in providing grounds for a variety of human activities, understanding how tidal inlet systems evolve is of interest to scientists, engineers, and managers. The seabed profile in such systems evolves due to the erosion and deposition of sediment particles from and onto the seabed. Equivalently, this can be described by the tidally averaged convergences and divergences of sediment transport, which takes place due to diffusive and advective processes. The aim of this thesis is to systematically investigate the importance of the different sediment transport mechanisms in double-inlet systems, in which the back-barrier basin is connected to the open sea by two inlets. The geometry under consideration is that of a shallow tidal inlet with a prescribed length and arbitrary width. Starting from an idealised process-based model, in which all sediment transport mechanisms are included, the model is reduced to a formulation, in which only the dominant transport mechanisms are retained. The results obtained suggest that the transport mechanisms, which must be retained in order to obtain equilibrium bed profiles, comparable to those obtained with the original process-based model, are advection, erosion, and deposition. Modelling the transport of sediment using these terms results in reproducing the equilibrium bed profiles found with the original model in the case when the inlet system is modelled as a rectangular channel. When the width of the channel in non-constant, the equilibrium bed profiles obtained with the two approaches have similar shapes, with slight variations in their exact values.