Optimising flow–sediment transport parameters for rivers

Abstract

The unsteady flow–sediment transport equations for a real river–reservoir system contain unknown hydraulic, sediment and geometric parameters. Knowledge of these parameters and input data comprising initial and boundary conditions is required to simulate flow–sediment transport, water surface and river bed profiles. The sensitivity analysis and optimisation procedure, which involves determining these parameters by fitting a model with real river field data, is an important tool for finding the best-fit values of each parameter in a river–reservoir sediment transport model. Sensitivity analysis and optimisation methods have been found to be very useful when applied to sediment routeing problems in river–reservoir systems. This technique was employed for optimisation of some of the important parameters involved in graded sediment routeing and bed armouring processes using a non-linear coupled model (NCMG). The particular parameters studied in this investigation are degradation, bed armouring and grain size distribution of bed material in a river bed downstream of a dam. The effects of bed roughness, sediment parameters and thickness of the active layer on bed level changes are studied. A combined Gauss–Newton and modified Newton method are employed to calculate optimised parameters.