Predicting soil detachment from high-discharge concentrated flow

Field experiments were conducted on a loam and a silt loam soil to determine the effect of tillage on soil detachment in concentrated flow channels carrying high discharge rates. Soil detachment rates from tilled channels were an order of magnitude greater than rates from no-till channels. Based on a linear constant-parameter soil detachment model, soil erodibility was seven times greater for tilled soil than for no-till, while critical shear values for no-till were about twice that for tilled soil. The coefficient of determination for the soil detachment models improved when soil erodibility and critical shear were related to field measurements of a soil strength index, measured by a fall cone penetrometer and a vane shear device. The fall cone index resulted in better model fits (greater R2) than the vane shear index for modeling soil erodibility and critical shear. Both linear and exponential equations were used to model soil detachment rates. An exponential equation with detachment related to excess shear, which has both soil erodibility and critical shear as linear functions of soil strength, is the recommended form for modeling soil detachment from high discharge concentrated flow.