Abstract
Soil transportation by the tractive force of surface water flow has been investigated in experiments using uniform surface water flow as a model, but very few papers have dealt with the mechanism of soil transportation by non-uniform and unsteady surface water flow appearing in sloped soil layer during natural rainfall. In this study, we analyzed the mechanism of soil transportation involving a non-uniform surface water flow produced by a computer controlled surface water flow generator. Experiments were performed under the same hydraulic conditions as had been set in previous experiments for the study of uniform surface water flow.
The comparison between the results of the non-uniform flow and the uniform flow reveals the following. 1) The quantity of soil transportation increased with an increase in the volume of surface water flow in both cases. 2) When the soil layer was exposed to the same volume of surface water flow, the non-uniform flow case showed smaller values than the uniform flow for the rate of increase in the quantity.of soil transportation. 3) The relation between the dimensionless quantity of surface water flow shown by qw/qwc (qw: surface water flow, qwc: critical surface water flow) and the dimensionless quantity of soil erosion qe/u*dk (qe: quantity of soil erosion, u*: friction velocity, dk: average clod size) had been reported in the case of the uniform flow. Therefore, we applied these relations to the results of the measurements in this experiment and obtained a new equation with a nonuniform surface flow. That equation would be expected to be applied to the estimation of the quantity of soil transportation occurring in a field subjected of a natural rainfall.
