Prediction models for discharge estimation in rectangular compound broad-crested weirs

• Geometry effect on the discharge and approach velocity coefficients was investigated.
• The discharge and approach velocity coefficients were generalized.
• Discharge can be predicted with high accuracy.

Experimental results of the flow of water over 9 different rectangular compound broad-crested weirs with varying lower weir crest width and step height were analyzed to develop prediction models for discharge estimation. The compound cross sections were formed by a combination of three sets of step heights and three sets of lower weir crest widths in a horizontal laboratory flume of 11.0 m length, 0.29 m width and 0.70 m depth. Flow depths at the approach channels were measured for a wide range of discharges. The dependence of the discharge coefficient (Cd) and approach velocity coefficient (Cv) on different parameters of the model was investigated. Multiple regression equations based on three dimensionless ratios R2, R3 and R4 for Cd and three dimensionless ratios R1, R2, and R4 for Cv were developed. Two derived prediction models can be used for the prediction of discharge over rectangular compound broad-crested weirs for free flow regime. The predictive capabilities of these models were evaluated using the experimental data obtained. By using the general equations of Cd and Cv, one can estimate the flow discharge in rectangular compound broad-crested weirs when the head at the upstream head measurement section, h1, is given with an absolute mean error of less than 5%.