Deposition of sediment mixture due to jet effluent into a rectangular shallow reservoir

Shallow reservoirs are threatened by fast filling up with sediments, even if the entering sediments are only suspended loads. The sedimentation process is strongly influenced by the geometry of such shallow reservoirs. In the framework of a research project, the influence of the geometry of the reservoir on sediment transport and deposition is studied by experimental approach. The experimental tests have been conducted in a 6 m long, and 4 m wide and 0.3 m deep a rectangular shallow basin. Two test procedures were examined. Crushed walnut shells with a median grain size, d50, of 50 μm, and a density of 1500 kg/m3 were used to simulate the suspended sediments. The flow and sediment conditions used during the tests grantee fully developed turbulent flow. During the tests several parameters were measured, as 2D surface velocities, 3D velocity profiles, thickness of deposited sediments, and sediment concentration at the inflow and outflow. The results help to understand the mechanism of the flow and the sediment exchange process. First, the results of a series of experimental tests with clear water and with sediments are depicted. They reveal that, under clearly identified hydraulic and geometrical conditions, the flow pattern is found to become asymmetric, in spite of the symmetrical inflow conditions, outflow conditions and geometry of the basin. But after changing the condition by adding suspended sediment to water in the mixing tank the flow pattern changed and bed forms emerged. They indicate that the flow pattern can easily switch to different directions, depending on the boundary and initial conditions. Moreover, bed forms affect the flow structure. It confirms the important role of boundary conditions in sedimentation and flow field patterns. Furthermore, these first results allow assessing the time evolution of deposition patterns.

Published in:
Alexandria Engineering Journal, 47, 5, 451-462

 Record created 2010-01-19, last modified 2018-03-17

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