A framework for the analysis of noncohesive bank erosion algorithms in morphodynamic modeling

In this paper, we analyze the performance of several noncohesive bank erosion algorithms to be embedded into two-dimensional models for river hydromorphodynamics on nonmoving meshes. To avoid the complexity of analyzing two-dimensional model results arising from the nonlinear interaction between flow, fluvial transport, and bank erosion, we develop a simplified framework. In detail, we reduce the two-dimensional morphodynamic model to a cross-sectional model under the assumption of longitudinal morphodynamic equilibrium, and apply bank erosion algorithms therein. To build candidate bank erosion models, we break down bank erosion algorithms into three modeling steps: identification of the bank, computation of sediment fluxes due to bank erosion, and bank updating. Different potential models are created by choosing different options for each step. We assess model performance against surveyed bank erosion over a flood event in the transitional Selwyn River, New Zealand. This study is preliminary to implementation of bank erosion in a fully two-dimensional setting, to model braided planform dynamics.