Modeling of Surface Flow and Infiltration During Surface Irrigation Advance Based on Numerical Solution of Saint-Venant Equations Using Preissmann's Scheme

In this research, a full hydrodynamic model based on the numerical solution of Saint-Venant equations is described to simulate the advance phase of surface irrigation. The full hydrodynamic model is the complete form of Saint-Venant equations. This model is the most complex and accurate among all models and can be applied for analyzing the flow hydraulics and managing surface irrigation. The Preissmann finite difference scheme was used for implicit discretizing terms of the equations. The model presented herein is able to give cumulative infiltration and hydraulic properties including discharge, velocity and depth of flow for any time and distance which can be introduced as an upper boundary condition in water transport models in soil. The model was used to evaluate different situations and soil textures, and the results were compared with results of SIRMOD software, which indicated that relative error was less than 4%. The accuracy of the model was also evaluated in comparison with observed data, and the result showed that the model is able to estimate advance time with normalized root-mean-square error (NRMSE) of less than 8%. Conventional relationships of surface and subsurface shape factor overestimate them by as much as 4.7 and 17.2%, respectively, based on the inflow rate.