HYDRAULIC BEHAVIOR OF AN ALLUVIAL RIVER FLOWING INTO A RESERVOIR

Abstract

River flows are usually laden with a considerable amount of sediment. When a river enters a reservoir, the water depth increases and the flow velocity decreases. Due to the decrease of velocity, the flow looses its turbulence and ability to carry sediment. The coarser sediment deposits at the reservoir upstream zone, forming a delta topset, and the deposition of finer particles forms a delta foreset. The finer sediment moves towards the reservoir downstream zone by the density current, which starts when the flow begins to• • plunge under the reservoir clear water, due to its larger density.

In the present study, the hydraulic behavior of an alluvial river flowing into a reservoir is studied in the first region upstream the plunging point. The divergence of the flow and the corresponding vertical and horizontal velocity distributions are investigated. Studying the variations of the concerned hydraulic parameters longitudinally along the reservoir length, the vertical and horizontal velocity distributions are investigated. Consequently, the partial percentage of discharge passing through each vertical segment of the cross section could be determined. Each segmental discharge will determine how much sediment is going to be deposited or scoured from the river bed of each segment. This means that each river cross section will be subjected to a nonuniform variation due to uneven deposition and scour.

The hydraulic procedure is conducted assummg a hypothetical reservoir. When the reached results were found to be satisfactory, the procedure was then extended and applied to a natural reservoir as a case study, namely, the Aswan High Dam Reservoir (AHDR). The results of the case study agreed with the field measured data.