اثر باز بستر بر مشخصات جهش هيدروليكي در حوضچه آرامش مستطيلي

Effect of Bed Load Transport on Hydraulic Jump in a Rectangular Stilling Basin

An experimental investigation was made to study the effects of bedload transport on hydraulic jump characteristics in a rectangular stilling basin. Experiments were performed in a channel of glass sides and smooth bed, and of rectangular cross-section 500 mm wide and 9 m long. The uniform sand of 4.05 mm with different concentration was used in the experiments for a wide range of hydraulic jump by Froude number ranging from 3 to 9. The results show that the sediment laden inflow has no effect on the main characteristics of the jump namely sequent depth, energy loss and length of jump. However, the incoming sediments are deposited in the sub critical zone (end of jump) and move downstream as bed load. The motion of the sediment is wave-like with a mild slope at the front followed by a raised bed of nearly uniform thickness terminating into a step. The position of the front of this dune-wise sand wave is almost unvarying in a certain flow and sediment conditions but the ending step moves downstream making a growing sand wave with a constant speed which is related to the inflow sediment rate. This sand wave performs a control section similar to an end sill in a stilling basin and keeps the hydraulic jump position at the beginning of the basin. The thickness of the front of this sand wave is expressed as a function of upstream Froude number. The results presented in this paper are expected to be useful in designing the stilling basins length and bed elevation in the presence of sediment laden inflow.