Effect of downstream apron elevation and downstream submergence in discharge coefficient of ogee weir

Discharge coefficient in ogee spillways is essential factor for producing discharge–head relationship. Discharge coefficient is relevant to the downstream water level submergence and downstream apron elevation. In this study, both submergence and apron effect are investigated using experimental data. To mathematical expression for discharge coefficient, the gene expression programming (GEP) and multiple regression technique were applied using dimensionless parameters. Results showed that GEP is superior to the regression analysis in predicting of discharge coefficient (C s). Performance criteria of GEP are R 2 = 0.967, RMSE = 0.041 and MAE = 0.035. For facility, some design examples are presented that show application of the proposed GEP equation and eliminates linear interpolation using existing graphs. The threshold value for submergence (S = h d/h) is 0.8 in this study. That is for S < 0.8, the discharge coefficient is approximately independent from the tail water elevation. But for S > 0.8, the discharge coefficient is dependent to tail water elevation and reduces rapidly with increasing of submergence. With increasing of submergence from 0.32 to 1, relative discharge coefficient (C s/C0) decreases from 1 to 0.47. Moreover, C s is dependent on P d (vertical distance between spillway crest and downstream apron invert) and P (ogee spillway height). © 2018 Indian Society for Hydraulics.