Estimation of runoff critical shear stress for soil erosion from soil shear strength

Critical shear stress is an important soil parameter governing detachment by runoff which appears in numerous erosion models. Soil shear strength has been often presented as the best soil property to predict critical shear stress. However, only a few studies have documented the relationship between soil shear strength and critical shear stress, and the results obtained have sometimes seemed contradictory. This is why we have put together all available data about the relationship between critical shear stress and soil shear strength in order to analyse and discuss its significance and its generality. Results showed that contradictions between different studies mainly arise because total shear stress is a poor predictor of detachment on rough soils. When grain shear stress is used rather than total shear stress, a significant relationship between saturated soil shear strength and critical shear stress does exist. Soil shear strength may thus be used to predict critical grain shear stress. However, it is recalled that in general only total shear stress is predicted by erosion models, which makes detachment predictions difficult on rough natural soils.