9. Estimation of Coefficient of Discharge for Side Compound Weir Using the GMDH Technique

A sharp-crested side compound weir is a flow diversion structure provided in one or both sidewalls of a channel to spill/divert water from the main channel. It is widely used in irrigation, hydraulic and environmental engineering. The mechanism of flow through the compound side weir is complicated, and it is difficult to establish a model to accurately predict the coefficient of discharge. In this study, the group method of data handling network with quadratic polynomial, ratio and linear two-variable functions was used to predict the coefficient of discharge for side compound sharp-crested weir. The discharge coefficient of compound side weir has a high correlation with three dimensionless parameters including upstream Froude number (F₁), ratio of weighted crest height of side weir to crest length of side weir (\(P\)/L) and the ratio of upstream flow depth to crest length of side weir (y₁/L). Therefore, a new model for the determination of coefficient of discharge of side rectangular sharp-crested compound weir was developed. Results of the GMDH model were also compared with the available regression model, and it was found that GMDH results were better than that of the regression model. The performance of the present model is based on the coefficient of correlation (R = 0.8489), mean absolute percentage error (MAPE = 17.62) and average root means square error (RMSE = 16.10). On the basis of sensitivity analysis, it was found that (\(P\)/L) was the most effective parameter for the prediction of coefficient of discharge.