Transient bottom topography changes in alluvial streams

Abstract

The development of a quasi two-dimensional computational model for simulating the transient variations of bed topography profiles in alluvial river channels is reported. The formulation of the model is based on combining the longitudinal flow momentum with the continuity principle of the sediment bed load. The Engelund-Hansen formula is employed in estimating the total sediment bed load along the reach of a river channel. The lateral bed load contribution from the total load is calculated in the same way as in calculating the lateral secondary currents from the main flow velocities. The numerical scheme and the computational procedure used in the study are described in detail. The simulated bed level profiles are verified through comparisons with experimental and field measurements taken from case studies in the literature for different flow conditions, channel characteristics, and sediment properties. The correlation between flow discharge, bed load, boundary friction, and channel slope is discussed. On the basis of the reasonably good comparisons with field data, it may be deduced that the model can be used for predicting the bottom topography variations in river channels.Key words: meandering rivers, bottom topography, sediment transport, bed load, boundary roughness, field measurements, experimental data, computational modelling, finite difference method.