Relation of Sediment Load Source to Rainfall Intensity

Soil erosion is a complex phenomenon and aggregate stability and soil texture are two influential factors governing soil erodibility.
Previous studies have shown that at the transport-limited regime, pre-detached particles and at the detachment-limited regime, soil
structure control sediment delivery. This study tried to analyze rule of factors and mechanisms governing interrill erodibility at different
rainfall intensities. Samples from 36 soil series with contrasting properties were collected from northwest of Iran. A rainfall simulator
with drainable tilting flume (1×0.5 m) at slope of 9 % was employed and interrill erodibility (Ki) was calculated for 20, 37, and 47 mm hr- 1 simulated rainfall intensities. Results showed a positive correlation (r = 0.286 - 0.804) between Ki and clay content. In contrast to
textural variables, the r values of Ki to the structure related indices (wet aggregate stability (WSA), mean weight diameter (MWD) and
geometric mean diameter (GMD)) turned to be greater and significant at higher rainfall intensities. These probably imply that at higher
rainfall intensities, soil detachment by raindrops limits sediment yield, but at lower intensities, transport limits sediment delivery. The
correlation of Ki to GMD was greater than that to MWD, implying that the proportion of smaller aggregates in sediment load was greater than larger aggregates.