Abstract
Gates in dams and irrigation canals are used for controlling discharge and for water regulation. To determine the discharge under a gate, the discharge coefficient (Cd) must be quantified. This study investigates the effect of sill shape under a vertical sluice gate on Cd. The study also includes the influence of height. The investigated shapes are comprised of polyhedral and non-polyhedral sills. Multiple nonlinear regression (MNLR) is applied to predict Cd values and the results show that circular sills under the gate can increase Cd by 23–31%. A circular sill with a 3 cm diameter has the highest Cd and trapezoidal sills have the lowest Cd. On the other hand, semicircular sills have moderate values of Cd. The most influential parameters affecting Cd are H1/p and Z/G where H1 is the upstream head over the sill crest, p is the sill wetted perimeter, Z is the height of sill, and G is the gate opening. Using dimensionless parameters and regression analysis, an equation for predicting Cd in free flow conditions with and without a sill is presented. The equation agrees with previously published results and can be implemented for predicting Cd in sluice gates with and without sills to within 6% accuracy.
•The effect of sill shape on discharge is studied.•Circular sills under the gate can increase Cd between 23 and 31%.•Hydraulic radius, gate opening and upstream head are most influential.•Predictive equations for discharge coefficients are provided.