Watershed sediment yield prediction for soils containing rock fragments

Estimates of soil erosion and sediment yield from watersheds are needed to select the best management practices for sediment yield abatement and protection of water quality. The ‘ANSWERS’ model predicts sediment yield from agricultural watersheds for individual rainfall events. Conventional values of the soil erodibility factor, K, for soils containing rock fragments may result in an overestimation of sediment concentration present in the runoff. In this study, the effect of K factor adjustment to predict a more accurate sediment yield by the ANSWERS model was investigated. The value of the K factor was adjusted for the volumetric fraction of rock fragment. This resulted in a higher level of agreement between the predicted and observed values of sediment concentration in the watershed runoff. Therefore, it is concluded that the volumetric fraction of rock fragment should be determined for watershed soils containing rock fragments and be applied for modification of published K values