A Fuzzy Model for Simulation of Water Infiltration into the Soil

Infiltration modeling in unsaturated zone is usually based on the numerical solution of Richards equation. Complexity in numerical solution, disregard of parameter’s uncertainties, and difficulty in application of this model at large scale attracted the attention of researchers to other approaches. In this research, a rule-based fuzzy model for infiltration in the soil matrix is presented. The rules were derived from a large generated training sets obtained by numerical solution of Richards equation by using Hydrus model. Forty-nine fuzzy rules based on 7 moisture classes were applied in fuzzy model. Fuzzy rule based model could simulate flux in any time step, and by using continuity equation could calculate moisture in any depth in soil profile. Results showed good accuracy for both flux and moisture predictions for loam, sand, and silt soil textures in any time steps (average NRMSE =3.84). Model performance had the best result in saturated zone and a poor result for wetting front. Because of duplicate process of calculating moisture in any time step and replacing it as an initial moisture for t+∆t time step, mass balance could prevent cumulative error for the large time steps.