Development of an equilibrium bay: A long-term morphodynamic modeling study

Bay-shapes, which are 'supported' by either natural or artificial headlands, are omnipresent. These bays tend towards a certain state, regarded more or less as a dynamic or static equilibrium. To know beforehand what is the (dynamic) equilibrium position of a bay behind headlands is important for the shoreline defense strategy. Powerful coastal area morphological models, which are able to simulate the relevant processes, such as wave refraction, long- and cross shore currents and the corresponding sediment transport should in principle be able to model such an equilibrium state for a shoreline, starting from an arbitrary (non-equilibrium) initial situation. Long-term simulations of the development of a dynamic equilibrium bay at a coastal stretch of the southern Baltic Sea is carried out with a A Q3D-coastal area model, applying two different forcing scenarios. Starting from the actual shoreline as initial model topography, the main features of the 2 modelled bay topographies are similar. A further model study takes a static equilibrium bay shape based on an empirical formulation (Hsu, 1987) as initial topography. The assumption of the static bay shape can be regarded as the maximum possible shoreline indentation. Here the model predicts a shoreline situation with less indentation and similar features like those of the long-term simulations. Thus the latter study confirms the rightness of the final results of the long-term model study. The Q3D-coastal area model is able to find a dynamic equilibrium solution for the given situation from two oppositional non-equilibrium situations, even in a long-term application.