A number of field soil erosion tests were successfully accomplished on newly constructed highway fills at Putnamville and Evansville, Indiana, in 1985 and 1986. The slope steepnesses ranged from 9 to 50 percent. It is possible to use the universal soil loss equation (USLE), which is widely applied for prediction of soil erosion, for highway slopes. However, the empirical slope steepness factor (S) in the USLE has been developed for slopes of from 3 to 18 percent. Because most highway slopes exceed this range, it was necessary to generate original experimental data. The modified rainfall simulator needed to obtain the data and its use are briefly described. The S factor reflects the development of rills, and the impact of raindrops, and appears to reach a maximum value of 1.5 at an intermediate value of slope steepness of 20 percent (11.2 degrees). The S factor may change with slope length, soil properties, and elapsed time, and accordingly is not an independent factor. In this study, the ratios of total erosion (which consists of the erosion in dry, wet, and very wet runs) to the erosion due to very wet runs are close to a constant. The mean value is 6.348 with a coefficient of variation of 4.90 percent.
Abstract