Development of a reach scale two-dimensional finite element model for floodplain sediment deposition

Abstract

This paper discusses the development of a two-dimensional finite element coupled hydraulic–sediment transport scheme for application to lowland floodplain environments. Recent developments in numerical algorithms have led to the development of two- and three-dimensional hydraulic models which are capable of simulating open channel and floodplain hydraulics at river reach scales of 1–60 km. However, these hydraulics schemes have not been linked with suitable sediment dynamics schemes. This paper describes the numerical developments necessary to extend an existing two-dimensional finite element solution of coupled hydraulic and sediment transport to fluvial floodplains. These include correct choice of numerical solvers to prevent artificial build-up of tracer mass in dry areas, control of artificial diffusion and implementation of an equation base appropriate to moving-boundary problems. Four experiments of increasing complexity were undertaken in order to ascertain the predictive ability of the model to produce realistic simulations of floodplain sediment deposition. Results showed that a two-dimensional-depth averaged flow field representation captures much of the gross behaviour of suspended sediment transport for reach scale fluvial applications.