Initial formation of channel–shoal patterns in double–inlet systems

Abstract

Channel-shoal patterns are often observed in the back-barrier basins of inlet system and are important from both an economical and ecological point of view. Focussing on double-inlet systems, the initial formation of these patterns is investigated using an idealized model. The model is governed by the depth-averaged shallow water equations, a depth-integrated concentration equation and a tidallyaveraged bottom evolution equation. Focussing on rectangular basins and neglecting the effects of earth rotation, it is found that laterally uniform morphodynamic equilibria can become linearly unstable, resulting in initial patterns that resemble channels and shoals. Initial formation of channel-shoal patterns in double-inlet systems diffusive instabilities are found anymore for the parameters considered in this paper. This implies that all instabilities are migrating in time.In all cases considered, the bed perturbations have only an appreciable amplitude at locations where the underlying laterally uniform equilibrium has a local minimum in water depth. This is consistent with observations from numerical models and laboratory experiments.