The rectangular piano key side weirs (RPKSW) usually use and install in the outer arch of the channels, which is a convenient location for side weirs. As well, the calculation of the discharge coefficient (Cd) in the weirs is of particular importance in their proper design. Accordingly, in the present study, first, the number of 239 experiments were performed on C-Type RPKSW at two arc angles of 30 and 120 degrees. First, two data-mining models of GPR and LSTM were utilized for modelling. Then, the data-mining models were developed using the Pelican Optimization Algorithm (POA) to enhance the discharge coefficient predictions of basic models. By evaluating these models, it was found that the optimization (POA) performed on GPR was effective and caused a reduction in the prediction error of the weir discharge coefficient. In this study, the best model was the GPR-POA model with RMSE = 0.0486, R2 = 0.9388, and KGE = 0.9533. The GPR and LSTM models were ranked after the GPR-POA model. By evaluating the results of different combinations in modeling, it was determined that P/h1 and pd/B ratios had a greater effect in providing correct results.
