MODELING HYDROLOGY OF AGRICULTURAL CATCHMENTS USING PARAMETERS DERIVED FROM RAINFALL SIMULATOR DATA

The ANSWERS model was modified to include a multi-layer, transient conductivity infiltration equation, based on the Green and Ampt equation, capable of simulating infiltration into soils which develop a surface seal under rain. Prediction of runoff hydrographs with the modified model was tested for 88-m2 rainulator plots and cultivated catchments of 0.07 and 3.2 ha, using infiltration parameter values derived from data from 1-m2 rainfall simulator plots. All other parameters were either measured (e.g. catchment topography, cover) or estimated from published values (e.g. Manning's n) based on conditions observed in the field. No calibration or fitting of the model to runoff data were used. Preliminary results of the study are presented. Prediction of the runoff hydrograph for rainulator plots was excellent. Good prediction of hydrographs was obtained for the catchments. Infiltration parameters from 1-m2 rainfall simulator plots appear to be appropriate for modelling runoff for these "simple" catchments when the infiltration method used in the model is physically realistic, and the model takes into account the spatial and temporal nature of the ensuing overland and channel flow. The results are sufficiently encouraging that validation for further events and more complex catchments will be undertaken.