Modelling spatial patterns of overbank sedimentation on embanked floodplains

This paper presents a GIS-based mathematical model for the simulation of fl oodplain sedimentation. The model comprises two components: (1) the existin g hydrodynamic WAQUA model that calculates two-dimensional water flow patte rns; and (2) the SEDIFLUX model that calculates deposition of sediment base d on a simple mass balance concept with a limited number of model parameter s. The models were applied to simulate floodplain sediment deposition over river reaches of several kilometres in length. The SEDIFLUX model has been calibrated and validated using interpolated raster maps of sediment deposit ion observed after the large magnitude December 1993 flood on the embanked floodplain of the lower river Rhine in the Netherlands. The model appeared to be an adequate tool to predict patterns of sediment deposition as the pr oduct of the complex interaction among river discharge and sediment concent ration, floodplain topography, and the resulting water flow patterns during various discharge levels. In the investigated areas, the resulting annual average sedimentation rates varied between 0.5 mm/year and 4.0 mm/year. The role of the most important mechanisms governing the spatial patterns of ov erbank deposition, i.e. inundation frequency, sediment load, floodplain top ography and its influence on the flow patterns over the floodplain, are dis cussed.