Improving the Stability of a Morphodynamic Modeling System

Abstract

Coastal area morphodynamic modeling systems couple modules for tidal hydrodynamics, wave propagation, sediment transport and bottom update. The non-linear coupling between these modules generates spurious oscillations and stability problems that are still poorly understood. This paper assesses and compares various methods to avoid the oscillations and improve the stability of a coastal area morphodynamic modeling system (MORSYS2D). The model is assessed with a simple case, the propagation of a sinusoidal bedform, and a complex natural system (Óbidos Lagoon, Portugal), whose exceptional dynamics enhances numerical problems in the morphodynamic models. The best results are obtained with a combination of methods: a predictorcorrector method to improve the implicitness of the solution, along-flux diffusion in the Exner equation to control oscillations, and a morphological factor below unity to reduce the Courant number. With these methods, the modeling system can be used with Courant numbers well above unity.