Evaluating Wepp-Predicted Infiltration, Runoff, and Soil Erosion for Furrow Irrigation

The Water Erosion Prediction Project (WEPP) model contains a furrow irrigation component to simulatehydrology and erosion in irrigation furrows. It currently is the only multiple-event furrow erosion simulation modelavailable for public use. However, the furrow irrigation component has not been evaluated yet. Therefore, we evaluatedthe WEPP model for furrow irrigation by comparing predicted infiltration, runoff, and soil loss with field measurementsfrom three southern Idaho studies on Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic XericHaplocalcids). Baseline effective hydraulic conductivity, rill erodibility, and critical shear were calibrated using datameasured from the upper quarter of two fields. Calibrated effective hydraulic conductivity was within the range of WEPPdefinedvalues for Portneuf soil. Calibrated rill erodibility of 0.0003 s m1 was almost two orders of magnitude less thanthe WEPP-defined value of 0.02 s m1, while calibrated critical shear of 1.2 Pa was about one-third of the WEPP-definedvalue of 3.5 Pa. Predicted infiltration correlated poorly with measured infiltration for most fields. Regression coefficientsfor predicted versus measured infiltration ranged from 0.07 to 0.35, indicating that predicted infiltration did not varywith measured infiltration. Predicted soil loss correlated well (R2 = 0.57) with measured soil loss from the upper end ofthe two fields used to calibrate erodibility parameters. At the field ends however, runoff was underpredicted and soil losswas overpredicted. When runoff was predicted reasonably well for an irrigation, cumulated predicted soil erosion acrossa field did not match cumulated measured erosion at field quarter segments because transport capacity wasoverpredicted. Deposition was not predicted unless runoff was greatly under-predicted. The WEPP model cannot berecommended for use with furrow irrigation until erodibility parameters and sediment transport are better defined forirrigation furrows.