SENSITIVITY OF SEDIMENT PREDICTION TO SIZE GRADATION

Varied unsteady flow-sediment equations for a graded river bed contain a variety of unknown sediment characteristics, hydraulic, and geometric parameters. These parameters, together with input data comprising initial and boundary conditions, would be required to simulate flow-sediment variations. Sensitivity analysis and optimisation procedure involves determining these parameters by fitting the model to either field or simulated data. Prior to optimisation a sensitivity analysis of existing flow-sediment parameters was found useful in highlighting the role of each parameter and reduced the time and number of iterations in the solution process. In this paper an optimization technique is employed for finding best fitted value of some important parameters involved in graded sediment routing and bed armouring processes using Advanced non-linear coupled model (ANCMG). The particular case study used for this investigation is degradation, bed armouring and grain size distribution of bed material in a river bed downstream a dam. For a graded river bed, the effects of bed roughness, sediment parameters and thickness of the active layer on sediment sizes, and bed level changes were studied. A combined Gauss-Newton and modified Newton method [9] was employed to calculate the optimised parameters.

Keywords:

Graded sediments , NCMG model , sensitivity analysis , optimization