Simplified Calculation Method for Contracted Water Depth of Rectangular Cross-section

According to the complicated calculation and low accuracy of fruits in the contracted water depth calculation of rectangular cross-section,and after sorting out the basic equations for the calculation,the power series is introduced and simplified to get the relatively simple iteration early-value function.Then after the first iteration,the approximate calculation formula is deduced by the mathematical method,which is simple,easy to remember and compute,convenient for practical application,and reliable in the result's accuracy.The analysis and application results show that in the range of practical engineering(ie,0α≤0.4,α as dimensionless water depth),the relative error of the calculation is less than 0.54%,which has a good application value.