Validity of the WEPP model for predicting infiltration on irrigated lands

Abstract

The objective of this research was to establish the validity of the hydrologic component of the YVEPP erosion model for predicting infiltration on irrigated lands. WEPP uses the Green and Ampt equation with ponding to compute infiltration. Infiltration data from simulated rainfall were collected at the USDA-ARS Conservation and Production Research Laboratory in Bushland, Texas. The March 1994 version (version 94.300) of the WEPP erosion model was used to predict infiltration using the best approximation of the soil physical conditions at Bushland, Texas. Model efficiency and correlation coefficient methods were used to evaluate the degree of agreement or correlation between measured data and predicted results. In general, validation results showed a wide range of correlation between measured data and predicted results, with R values ranging from 0.825 to 0.997. Model efficiency values ranged from-0.843 to 0.950. Model predicted results for infiltration volume were better than those for infiltration rate. The poor correlation between measured and predicted values for some of the data is explained by the fact that the infiltration parameter estimation techniques in WEPP are not good enough. Sensitivity analyses showed that the key to improving the prediction of runoff and infiltration in WEPP is to improve the parameter estimation procedures. Results indicated that WEPP model version 94.300 was valid for predicting cumulative infiltration volume on irrigated lands. However, the validity of the model to predict infiltration rate on irrigated lands was not established within this study. It is important to note that the difference between the measured data and the predicted results may be partly due to inaccuracies in the collection of field data, and not completely due to the inability of the WEPP model to predict infiltration on irrigated lands.