Simplified Formula for Calculating Contracted Water Depth of Channel with Cubical-Parabola Cross Section

The current formula to calculate the contracted water depth of the channels with the cubical-parabola cross section is complex.This paper introduces the optimal fitting method to deform the basic equation for calculating the contracted water depth.The new method is based on the objective function of the minimum residual standard deviation,and it uses the successive approximation approach to generate an approximate formula to calculate the contracted water depth of the channels with the cubical-parabola cross section,which has a simplified form of expression and is easy to remember,quick for calculation,and convenient for the engineering staff.Compared the results from the new method with those from the original equation,the maximum error of the calculated contracted water depth is about 0.46%,which suggests that the new method is applicable for the practical engineering calculations.