Runoff and water-quality characteristics of surface-mined lands in Illinois

Seven watersheds--three in western Illinois (Fulton County), two in south-western Illinois (St. Clair County), and two in southern Illinois (Williamson County)--were selected to assess the effect of surface mining on the quality and quantity of surface runoff. Each area had one site draining an unmined basin and a nearby site(s) draining a partly surface-mined basin. Flow-duration curves for streams draining surface-mined land had lower variability than those from unmined land. By adjusting an index of variability according to the percentage of surface-mined land in a basin, present techniques can be used to develop synthetic flow-duration curves. Surface mining changes basin characteristics so that peak flows decrease and low flows increase. Regression equations were developed relating storm runoff volume and peak discharge to basin characteristics and climatological data. Concentrations of dissolved solids, sulfate , and calcium were higher in streams draining extensively mined areas. Different mining areas of Illinois yield regional differences in concentrations of these substances. Surface-mined basins had lower suspended-sediment yields than unmined basins. (USGS)