Estimation of Hydrodynamic Infiltration Coefficients Using Optimization of SCS & Horton Equations

Determination of infiltration equations coefficients with proper accuracy is one of the important issues in irrigation planning. For determination of these coefficients, double-ring test method is usually used which only involves the point and hydrostatic dimension of infiltration. In this research, a parabolic shape furrow was used for simulation of an irrigation furrow with 50 m length, 12 cm depth, and 0.20 m/m bed slope. Three experiments were performed with lengths of 4.7, 20 and 40 m, and inflow of 0.6±0.02 lit/s with three replicates. For each length, a test with the minimum measurement error was selected. To determine the infiltration equations coefficients, input and output hydrographs were measured using flow measurement flume and the output hydrographs were routed by Muskingum-Cunje, Zero-inertia and kinematic wave methods. Finally, the infiltration discharge values were obtained by considering the SCS and Horton infiltration equations and the average flow area in the proposed furrows. Computational hydrographs were obtained from the difference between routed output hydrographs and infiltration discharges. Finally, the objective function was derived using the least square method (LSM) for observational and computational output hydrographs. The results indicated that the mean value of the relative error between the observed and optimized output hydrographs of the proposed method is less than 5 percent. By increasing the length interval, the amounts of infiltration discharges decrease due to the reduction of  static head water. The efficiency of the model for all lengths was more than 90 percent based on the Nash-Sutcliff criterion which indicates that the simultaneous use of the Horton equation and the zero-inertia method provides the best results.