A regularization strategy for the two-dimensional active layer model : development and implementation in Delft3D-FM

The active layer model used to account for mixed-size sediment morphodynamic processes may be ill-posed under certain circumstances. Well-posedness guarantees the existence of a unique solution continuously depending on the problem data. When a model becomes ill- posed, infinitesimal perturbations to a solution grow infinitely fast. Apart from the fact that this behaviour cannot represent a physical process, numerical simulations of an ill-posed model continue to change as the grid is refined. For this reason, ill-posed models cannot be used as predictive tools. There exists a regularization strategy that guarantees that the one- dimensional active layer model is well-posed. Here we show that the extension of this strategy to two dimensions does not regularize the model. We propose a different regularization strat- egy that guarantees that the two-dimensional active layer model is well-posed. We implement the two-dimensional regularization strategy in Delft30-FM and apply it to an idealized case and a field case.