Prediction of discharge coefficients for sluice gates equipped with different geometric sills under the gate using multiple non-linear regression (MNLR)

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 (C-d) must be quantified. This study investigates the effect of sill shape under a vertical sluice gate on C-d. 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 C-d values and the results show that circular sills under the gate can increase C-d by 23-31%. A circular sill with a 3 cm diameter has the highest C-d and trapezoidal sills have the lowest C-d. On the other hand, semicircular sills have moderate values of C-d. The most influential parameters affecting C-d are H-1/p and Z/G where H-1 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 C-d in free flow conditions with and without a sill is presented. The equation agrees with previously published results and can be implemented for predicting C-d in sluice gates with and without sills to within 6% accuracy.