Effect of Slope Length and Rainfall Intensity on Runoff and Erosion Conversion from Laboratory to Field

Abstract

Predictions of soil and water loss at large extents often relies on data obtained from laboratory flume experiments. It is necessary to have a reliable approach to extrapolate from laboratory collected data to larger field areas. In this study, a series of experiments were designed using rainfall simulator on laboratory flumes with varying surface areas (ranging from 0.5 to 2.5 m²) as well as field plots ranging in surface areas between 4 and 20 m². Both the flumes and field plots had the same slope gradient (20°), surface trait (bare slope) and soil type (red soil). We varied rainfall intensities from 30 to 150 mm/h, and measured runoff and erosion. Results confirmed that actual erosion in field cannot be simply extrapolated from laboratory data, rather we showed that erosion modulus directly relates to surface area and rainfall intensity in both the laboratory and field experiments. However, the effect of surface area on runoff is more complicated. Compared to surface area, rainfall intensity showed more pronounced influence on runoff. Based on our experimental results, a conversion calculation method was investigated and a conversion coefficient model, which is a function of rainfall intensity and ratio of field area to laboratory area, was introduced. The model provides a reference for laboratory to field conversions and allows for soil erosion prediction at larger extents in the field.