[pp.21-28]

Revision of an Equation to Predict Water Erosion from Agricultural Lands – Consideration of the Effect 21 of Length and

Kingshuk ROY, Tatsuro KUSAKA and Mitsuo FUKADA （Nihon University / Yamaguchi University）

Abstract:
As an essential step of soil conservation, the authors previously proposed a soil loss equation with regard to rainfall types (qe = aKeLdαsinβθqrγ ) to predict soil erosion in inclined fields. A number of experiments and observations had been carried out to make the equation applicable to the practical farmlands. Later, the authors proposed an extended form of the equation (qe = aKeLdαsinβθNdδqrγ ), which considered the effect of the small amount of rainfall (less than 1mm/10min intensity) on soil loss. The present study is aimed at to improve the applicability of the equation with a further revised form (qe = aKeLdαsinβθWdεNdδqrγ ), which included the inter-effect between the length (Ld ) and the lateral width (Wd ) of a slope on soil erosion. In the study, runoff, soil loss and rainfall data collected from two bare-surfaced experimental test plots (termed as ‘Standard plot’ and ‘Comparison plot’ in this paper) during the period of 1981 to 1994 had been analyzed. The study result indicates that the revised form of the equation could achieve higher applicability for both of the test plots while predicting soil erosion by rainfall with different intensities.

Key Word:
soil erosion, soil loss equation, rainfall, runoff, slope length, slope width

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