NATURAL STREAMS UNSTEADY SEDIMENT MOTION PREDICTED BY COMPLETE FULLY COUPLED NON-LINEAR NUMERICAL SOLUTIONS

The aims and objectives of the present work are unsteady flow-sediment transport and flood prediction in the natural streams, analysis of exisiting problems involved within the natural real rivers situations imposed by man, and looking at the effects of flooding on flow-sediment characteristics change within a certain period of time and at different locations along the reach. This study is particulary dealing with merits and disadvantage of several numerical solution techniques applied to real rivers flow – sediment transport regimes at upstream and downstream of a dam (river-reservoir system). The basic physical principles of conservation of mass and moment are used to describe the flow-sediment transport and flooding flow. A new approach for governing sediment particle movement is adopted to establish the interaction between the highly non – linear unsteady flow-sediment motion including , rapidly varying flooding flow transporting different sediment particles. Since the resulting mathematical formulation is highly non-linear and complex, it is impractical , if not impossible , to solve them analytical. Therefore the governing equations for flow-sediment continuity, momentum. Equations were solved numerically. To see the importance of non-linear terms in the governing equations, a comparison was made between different solutions when they were solved in linear coupled or uncoupled , and or in the most complete non-linear and fully coupled or uncoupled forms. This means that two phase of flow and sediment movements may or may not be considered together at a time step, i.e., by ignoring certain terms, the sediment continuity equation may be uncoupled from the other governing flow and hydraulic equations. Algorithms were developed for linear or non-linear and coupled or uncoupled solutions. Solutions were also obtained with the grain sorthing / armouring included or excluded.

Keywords:

Sediment transport four different approaches (Linear , Non-linear , fully coupled , uncoupled numerical techniques)