Interrill Erosion and Runoff on Very Steep Slopes

Interrill erosion and runoff were measured from a 504-mm-square box filled with disturbed Hagerstown silty clay loam under a simulated 20-min, 92-mm/h rainfall at six slopes ranging from 5 to 85%. Steady-state wash soil loss (soil suspended in the runoff) increased linearly with slope, with measured rates ranging from 3.34 g m–2 min–1 at 5% slope to 22.47 g m–2 min–1 at 85% slope. For soil splashed off the plot, downslope splash increased, upslope splash decreased, and across-slope splash showed a slight increase with slope. Total splash detachment (downslope + upslope) increased with slope. Net downslope splash transport (downslope – upslope) also increased, at an increasing rate, reaching 3.5 g m–1 min–1 at 85% slope. Ninety-nine percent of splash moved downslope at the 85% slope. There were no differences between steady-state runoff rates for slopes from 15 to 85%, with a mean runoff rate of 66.5 mm/h.