Floodplain and channel dynamics in a meandering river bend

Abstract:

A migrating river bend is able to maintain a stable channel width when bank processes of erosion and deposition occur at nearly equal rates. This requires an active communication between river banks influenced by both in-channel flow and floodplain characteristics. In an earlier model that attempted to capture channel bank dynamics, erosion and deposition processes were tied to a specified bank configuration i.e. banks were assumed to have a fixed height and to be primarily cohesion-less with the exception of a thin cohesive top layer. By adopting this configuration, the model implicitly acknowledges the role of floodplain processes but does not incorporate the feedback between floodplain and channel geometry. An expanded framework that accounts for the influence of floodplain dynamics in channel width selection is proposed here. In this new framework, flood plain geometry is taken into consideration in two ways: (1) a floodplain width is imposed within which a channel is allowed to meander and (2) floodplain thickness (and thus channel bank height) is allowed to vary spatially and temporarily through the processes of overbank deposition and floodplain shaving. By tracking the transport of sand and mud, the model is able to explicitly describe changes in floodplain characteristics over time and how these changes reflect on bank migration rates and channel geometry.