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

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.