SCOURING DOWNSTREAM OF SLUICE GATE

Abstract

This paper presents the results of an extensive experimental study on local scour caused by high velocity jets issuing from submerged sluice gates of 2-D jet outlets. 84 sets of experiments have been conducted, out of which 63 sets were under deeply submerged jet conditions. Dimensional analysis is used to delineate the characteristic parameters affecting the maximum scour depth downstream of the structure. Under certain hydraulic conditions, the study discovered a cyclical jet-flipping phenomenon whereby the jet action would flip from the bed to the water surface and vice versa. The erosion at the interface between the solid apron and the sand bed, i.e., at the brink of the apron was measured. The maximum brink scour depth immediately at the downstream end of the apron was found to be about 0.44 times the maximum scour depth. For the prediction of the maximum scour depth, an empirical formula has been proposed, based on a database of 163 experiments from the present study and various other researchers. The formula takes into account the jet size and velocity, median sediment size, sediment density and gradation and the length of the protective apron. The formulation directly takes into account the effect of the apron length, which is a key parameter in the design of scour countermeasure for this type of problem. The range of applicability of the formula, and its uses and limitations has been discussed. The formula was used to estimate the scour caused by the high jet velocity issuing from the sluice gate of the Shimen Arch Dam in China and the prediction was close to the measured scour in the field.