Developing a New Method for Estimating Discharge Coefficient of Sluice Gates under Free and Submerged Flow Conditions

Discharge measurement by sluice gates is one of the classical issues in hydraulic engineering. Based on the energy conservation relation, this study presents a novel method for estimating the discharge coefficient of sluice gates under free and submerged flow conditions. This method gives the discharge coefficient of sluice gates only as a function of upstream depth and bottom pressure measured by manometers located under the gate lip and is independent of flow conditions (free and submerged), gate opening and tailwater depth. For evaluating the applicability of the proposed equation in this research for estimating the flow discharge, the experimental results (418 runs) of two sluice gates with 25 and 40 cm widths are used in the conditions of presence and absence of end baffle blocks for both free and submerged flows. Independency of discharge coefficient from the tailwater depth has important advantages such as: continuous estimation of discharge coefficient under free and submerged flow conditions using a unified equation and higher accuracy at the lower submergence. Also being independent of tailwater depth makes easy flow estimation even at the presence of baffle blocks on the stilling basins. The results show that, applying the energy loss coefficient in the proposed equation decreases the mean absolute relative errors to 0.4% and 2.6% for free and submerged flow conditions respectively. Also the proposed equation has a relative error less than 5% under submerged flow conditions. The proposed method is very sensitive to bottom pressure head especially under higher submergence levels.