Inlet equilibrium morphological modelling: Comparison of a laboratory study and an entropy based model

The management of coastal environments such as groyne fields, offshore breakwaters, jetties and tidal inlets requires the accurate prediction of equilibrium morphologies. Currently, the evolution of coastal morphologies is modelled using traditional process-based methods, where wave, current, sediment transport and sediment balance modules are linked together in a time-stepping process. These modules are reapplied and assessed until a stable morphology is formed. These types of models may have a number of limitations. Small errors may be amplified over the time-stepping process and starting conditions impart a large influence on the predicted morphology. Most importantly, these models must be run for a length of time equivalent to the time taken for a stable morphology to develop. In this paper a new way of modelling equilibrium morphologies of tidal inlets is detailed. It involves the use of entropy-based objective functions, where energy dissipation rates calculated from averaged conditions are minimised in order to find equilibrium morphologies, without the need to step through time. The equilibrium morphology is predicted immediately, without the modelling of intermediate steps. The results of the model are compared to a laboratory study of flow entering and exiting an inlet. This entropy-based method represents a different approach to traditional equilibrium morphological modelling, overcoming some of the associated limitations. It is able to predict stable morphologies without the intermediate steps that the system may pass through to reach its desired bed profile. The predicted morphologies compare favourably to those obtained in a laboratory study