Determination of the erodibility factor of soils and lignite spoils

Abstract

Surface strip mining is currently the fastest way to recover lignite and bituminous coal. The strip mining results in the disturbance of large acreages of land. However, specific management of the spoils is required to protect the environment when potential erosion and pollution hazards are evident. Samples representing a wide range of chemical and physical characteristics were collected from strip mining areas at the Gulf Coast Region so that the inferences resulting from this study can be applied to a broad range of conditions. The rotating disk rainfall simulator was used to measure the erodibility factor on small samples of soils and lignite spoils from the Gulf Coast Region. The 100-year 30-minute rainfall was applied to the samples on three slopes (2, 9 and 18%) and two antecedent moisture conditions (dry and wet). Direct extrapolation of the simulated rainfall results to field conditions is not possible because of the small dimensions of the experimental plot (0.61 m length) as compared to the standard Unit Plot in the USLE (22.14 m). However, by computing an adjusted topographic factor LS, an adjusted K factor was calculated from the experimental results. The assumption is made that by using this adjusted K in the USLE, subtle differences among samples that can be detected under simulated rainfall can be exploited along with the large background of data existing for the other parameters in the USLE. In the same line of thought, any equation accurately predicting the adjusted K can be used effectively in the USLE. In general, equations reported in the literature to estimate K were found of little value in predicting the sheet erosion loss from spoils under simulated rainfall, while some equations developed using multiple regression analysis on the chemical and physical characteristics of the samples showed high prediction ability. Parameters involving infiltration had the largest influence on K and were included in all the selected models. In topsoils, K measured using the Wischmeier nomograph and the adjusted K measured in the rainfall simulator showed similar values, but spoils were less erodible than the nomograph suggested.