Input for a 1D sand-gravel morphodynamic computation including a bedload layer

Abstract

In the mass balance of a riverbed, some terms are usually assumed constant for reasons of simplicity. One of the terms assumed to be constant is the change in bedload layer, which is defined as the sediment transport divided by the particle velocity. To study the effect of this assumption, a numerical morphodynamic model has to be computed. For such a morphodynamic model to work, some input parameters and models have to be determined. The most important input models are those of the predicted sediment transport and particle velocity, which are studied in this research. The Dutch upper Rhine is used as basis for this study, with particle diameters and sediment composition as stated in earlier studies. To compare the predicted sediment transport by sediment transport models, sediment transport data of three measurement campaigns is used. Before the sediment transport models are compared with the measured data, a small literature study is used to determine which sediment transport models might be applicable for predicting the sediment transport. With the available specifications of the sediment transport models, two fractional transport models were chosen as applicable: the model of Wu et al. (2000) and the model of Wilcock & Crowe (2003). Both original models approximate the measured data quite well, so no calibration of the models is required. The model of Wu however, shows some unusual behavior for increasing sand/gravel ratios and is more sensitive for changes in its calibration parameter. Therefore, the model of Wilcock & Crowe is chosen as most applicable for this part of the Rhine. To determine the propagation velocity of the particles, two models of Van Rijn (1984) and one model of Engelund-Fredsoe (1976) were used. One of the Van Rijn models predicted unrealistic particle velocities, but the remaining models approximated the particle velocity in a similar way, approaching measurements from Francis (1973) and Luque (1974). Due to the similar behavior of both models, no choice was made between them. Eventually, the thickness of the bedload layer was determined, providing a realistic input for a 1D sand/gravel morphodynamic model.