Characteristics of Free Hydraulic Jump Downstream Silled Sluice Gates

This study presents the results of an experimental ivestigation on the effect of the under-gate sill on the hydraulic jump characteristics. Under-gate sills of trapezoidal shape with different heights are tested under wide range of flow conditions. The downstream slopes varied between 1:1 to 9:1 while the upstream one is kept constant at 1:1. A wide variation of the height ratio of the sill is considered. The sequent depth, the length and the energy loss ratios of the jump are analyzed. Also, nondimensional prediction equations for the considered jump characteristics in terms of the initial Froude number, the downstream slope and the sill height ratios are developed. The analysis and discussions of the obtained results have shown that the under-gate sill increases both the sequent depth and the length of jump ratios and decreases the energy loss ratio compared to the case of no-sill. The increase in both the sequent depth and length ratio depends on the downstream slope and the relative height of sill as well as the initial Froude number. The study proved that the sill having a downstream slope of 5:1 provides the minimum increase in the jump length compared to the other downstream slopes. The prediction based on the developed equations are found to agree reasonably with the experimental results. Also, theoretical equation for computing the sequent depth ratio is developed, calibrated and verified using the experiemental data.