An experimental study of plunge depth in the case of clear water movement

Abstract

ABSTRACTThe condition in which ambient clear water moves opposite to a density current usually happens in river estuaries during the tide of the sea. The examination of this condition can improve our understanding of plunging phenomenon, which can result in a better estimation of river morphology. In this experimental study, it has been tried to examine the effects of bed slope and clear water discharge on plunge depth in moving clear water condition and to compare these effects with those of stagnant clear water. Fifty four experiments were conducted in a flume with adjustable bed slope. Its length, width, and depth were 9, 0.35, and 0.66 m, respectively. By adjusting the rate of discharge valves, the first 18 experiments were performed under the condition of static clear water, while the others were conducted as clear water was moving opposite to a density current. Results show that, in both static and moving clear water conditions, plunge depth increases as bed becomes steeper. In addition, the discharge of clear water has a direct relationship with plunge depth and moving clear water condition results in higher plunge depths than the static condition. At the plunge point, the dense underflow is critical or subcritical and there is an inverse correlation between densimetric Froude number and bed slope. Finally, empirical equations have been developed to estimate plunge depth.