Surface Runoff Prediction of Catchments Hillslopes Based on Kinematic Wave Method and Subsurface Runoff Based on Solving Richard Equations in Hydrus Model

Prediction of surface and subsurface runoff as elements of direct runoff of catchment is very important for designing hydraulic structures. In many of the catchments with high permeability and suitable vegetation, subsurface flow is also highly important. In this research, Hortonian mechanism has been used for predicting surface runoff of catchment overland using Kinematic wave method. For prediction of subsurface runoff of catchments hillslopes, Richard equation in an unsaturated zone by means of Hydrus software was used. Runoff hydrograph of subsurface runoff was calculated. For verification, experimental data from rainfall simulator with length of 2 meters, width of 1 meter and depth of 0.35 with loamy sand was used. The experiments were conducted under three angles of 0.1, 6.3 and 9 degrees and under rainfall intensity of 31.73, 47.6 and 63.46 millimeter per hour (mm / h), respectively. The subsurface and surface flow of the system were compared with the results of the kinematic wave in the surface flow and the results of the Hydrus model in the subsurface flow. The peak runoff mean error predicted by the kinematic wave method in the 12 events calculated is 3.5% and the mean prediction error of the subsurface runoff peak in 9 events is 10%, which is an acceptable value. The results of the Hydrus model for predicting the slope of zero tilt angle had 40% error in calculating the subsurface runoff peak that has not been acceptable.