Comment on “Quasi-theoretical end-depth–discharge relationship for trapezoidal channels”

Recently, it is proposed a direct equation for discharge in terms of end depth in subcritical flows by simulation of the free overfall in trapezoidal channels with a sharp-crested weir. According to this discussion, the theoretical end-depth ratio (EDR) is almost constant with an average value of 0.809 over the practical range of 0.01 < XC < 1 and is constant with an average value of 0.832 over the practical range of 1 < XC < 10. These results are questionable compared to available experimental data. Moreover, this discussion shows that the proposed equation by the authors for theoretical discharge in subcritical flow regime is not accurate (the errors increase up to 50%), thus it is derived an accurate equation (with maximum error less than 0.6%) for prediction of theoretical discharge in trapezoidal channels with a single measurement of end flow depth. This accurate solution is also questionable compared to available experimental data.