An Evaluation of Unit Stream Power Theory for Estimating Soil Detachment and Sediment Discharge From Tilled Soils

Unit Stream Power (USP) and the associated Yang (1973) sediment transport equations were compared to soil detachment rates and sediment concentrations in runoff from eroding soils. Although USP was significantly correlated with rill detachment rates, potential energy dissipation rate per unit rill area was a better predictor of soil detachment rates. The Yang (1973) equations estimated sediment concentrations within a factor of 10 of the observed concentrations, if the median soil aggregate diameter was within the range of diameters used by Yang to estimate the equation parameters. When median aggregate sizes were less than 0.15 mm, the lower limit of Yang’s (1973) calibration range, the equations tended to produce unrealistically large estimates of sediment concentration.