SOIL DETACHMENT BY SHALLOW FLOW

Abstract

A precise understanding of soil detachment rates is necessary to establish a basic understanding of soil erosionand to develop a fundamentally based erosion model. This study was conducted to investigate the relationships between soildetachment rates and flow discharge, slope gradient, flow depth, mean flow velocity, shear stress, unit stream power, andstream power. A 5m long
0.4m wide hydraulic flume with constant artificial roughness upstream of and surrounding thesample area was used. Flow discharge ranged from 0.25 to 2.0 L s 1 and slope gradient varied from 3.5% to 46.6%. Theexperimental results indicated that detachment rates increased with both greater flow discharge and slope gradient.Detachment rate was affected more by discharge than by slope gradient. The influence of slope gradient on detachment ratewas greater at high slopes. The effect of flow depth on soil detachment rate was also dependent on slope gradient. Stepwisevariable selection analyses indicated that detachment rate could be predicted by a power function of discharge and slopegradient (R 2 = 0.97). Substituting flow depth for discharge gave a poorer prediction (R 2 = 0.92). Mean flow velocity was moreclosely correlated to detachment than was any other hydraulic parameter (r 2 = 0.90). Flow detachment rates were bettercorrelated to a power function of stream power (r 2 = 0.89) than to functions of either shear stress or unit stream power. Theresults of this study suggest that soil detachment by shallow flow is more closely related to flow energy than to shear stress.