ERODIBILITY AND SEDIMENT YIELD BY NATURAL RAINFALL FROM RECONSTRUCTEDMINE SOILS

Standard erosion plots, 4.6 m x 22.1 m with a 9% slope, were establish ed at the Alston Surface Mine in Ohio County, Kentucky. Topsoil, subso il, and mine spoil were reconstructed according to contemporary reclam ation techniques using bulldozers and scraper pans. The following para meters were evaluated under natural rainfall conditions: runoff, erodi bility, and sediment yield. Mine spoil yielded significantly greater r unoff volumes, compared with reconstructed topsoil and subsoil. Averag e curve numbers (CN) were 89.1, 90. 1, and 94.7 for bare topsoil, subs oil, and mine spoil, respectively. The subsoil plot generated the larg est amount of sediment and was significantly more erodible than topsoi l and mine spoil. The average annual erodibility (K) factor was .046 f or topsoil, .067 for subsoil, and .051 for mine spoil, with units of M g ha h (ha MJ mm)-1. Erodibility of the mine spoil in this study was m ore than twice that measured from an earlier rainfall simulation study at this same site. Differences in the degree of physical weathering w ere believed to be the primary contributing factor and, therefore, hav e important implications when assessing the erodibility of highly weat hered spoil materials (e.g., abandoned mine lands). Compared with the soil interpretation record's K factor estimate for the soil series eva luated in this study, the reconstructed topsoil was not inherently mor e erodible than when existing in its natural, undisturbed condition. T herefore, factors that the mine operator can control (e.g., slope, veg etative cover, management practices) will likely have a greater impact on whether erosion losses from reconstructed soils are significantly greater than losses that occur under pre-mining conditions.