Evaluating WEPP-Predicted Furrow Irrigation Erosion

Abstract

The Water Erosion Prediction Project (WEPP) model allows users to predict furrow irrigation erosion. However, an initial model evaluation showed that 1) WEPP default erodibility values had to be reduced for simulating furrow irrigation erosion and 2) the WEPP model overpredicted sediment transport capacity. Therefore, the purpose of this study was to investigate the applicability of the governing equations used in the WEPP model to calculate sediment detachment and transport. Sediment detachment data were collected from 53 irrigation furrows, 9 m long, on a Portneuf silt loam with flow rates varying from 2 to 50 L min -1 among furrows. Hydraulic shear measured in irrigation furrows varied from 0.4 to 1.7 Pa, which is less than the 2.6 to 8.8 Pa shear measured during WEPP rainfall simulation on the same soil. The linear relationship between shear and detachment rate used by the WEPP model may be appropriate for predicting both rainfall and furrow irrigation erosion as long as separate erodibility values are identified for furrow irrigation. A power function relating shear and detachment rate may allow one relationship to be used for both the low shear conditions in irrigation furrows and the high shear conditions in rills during intense rain storms. Although transport capacity could not be thoroughly evaluated with this data set, sediment detachment seemed to be limited by factors other than transport capacity,. Additional model evaluation is needed with data from other soils before changes to the model can be recommended or the model can be implemented for predicting furrow irrigation erosion.