Hydraulic model study of bed level changes of alluvial river

Abstract

The Saint-Venant equations describing unsteady flow in open channels and the continuity equation for the conservation of sediment mass are numerically solved to determine the aggradation-degradation of channel bottom due to an imbalance between water flow and sediment discharge. For this purpose the MacCormack explicit finite difference scheme is used. The scheme is second order accurate, handles shocks and discontinuities in the solution without any special treatment, and allows simultaneous solution of the water and sediment equations, thereby obviating the need for iterations. The sediment transport relationship in any form may be included in the computations. The mathematical model presented here is applied to predict the bed level changes of alluvial channel due to sediment over loading. To verify this model, the laboratory experiment is carried out at the Hydraulics and River Engineering Laboratory of Department of Water Resources Engineering, Bangladesh University of Engineering and Technology, Dhaka. The sediment transport equation qs = aub is calibrated through experimental rnns and the value of the coefficient 'a' and 'b' is detemiined, which are used in the mathematical model. Fifteen experimental runs were carried out for different water discharge (q), different bed slope (So) and different sediment over loading ratio. For each rnn, four transient bed profiles are plotted at onehour interval of flow. The computed results are compared with the experimental data. The agreement between the computed and experimental results is satisfactory.