Journal of Natural Disaster Science

A METHOD FOR PREDICTING SEDIMENT YIELDS FROM WATERSHEDS

Saburo KOMURA
Professor, Department of Civil Engineering, Gifu University

(Received 4 June, 1984 and in revised form 27 Sept., 1984)

Abstract

General equations for soil erosion caused by rainfall and overland flow have been derived analytically by using the equations of motion and continuity for sediment transport, the dynamic and continuity equations for spatially varied flow with rainfall and the equations of boundary shear stress subject to rainfall. In 1976, I published general equations for soil erosion. From those general equations, I have developed a computational equation for predicting soil erosion rates. The equation for predicting the slope erosion rate is a function of the mean sediment size of the slope material, bare soil area ratio (ratio of the bare soil area to the total slope area), erodibility coefficient, unit weight of the eroded soil, runoff coefficient, rainfall intensity, slope length and the slope gradient.

The erodibility coefficient can be considered a function of the rill density, clay ratio, dispersion ratio, and compactness of the slope soil. An estimating equation for the erodibility coefficient has now been developed and is compared with previously published data on slope erosion. To demonstrate the applicability of these computational equations, computed results for slope erosion are compared with observed data.

The primary purpose of slope-erosion prediction procedures is to provide specific, reliable guides to help us select pertinent soil and water conservation practices for use on bare slope lands. The prediction procedure developed here also may be used to compute sediment yields from watersheds. This study was conducted mainly to develop a procedure for computing the sediment yields from watersheds.

Key words

slope erosion, sediment yield, soil erosion