EFFECTS OF DIRECT REVEGETATION ON THE HYDROLOGY, EROSION AND SEDIMENT YIELD OF AN ABANDONED DEPOSIT OF COAL-MINE REFUSE

As part of the feasibility studies at a large abandoned coal-mining complex, an elevated deposit of weathered pyritic refuse was monitored before and after treatment by a method referred to as dir-ect revegetation. The monitoring was concentrated in three small watersheds that were instrumented to quantify the effects of the reclamation method on storm runoff, yield of coarse- and fine-grained sediment, chemistry of soil water and surface runoff, and morphologic evolution of gullies. Prior to treatment, about 30 percent of the warm-season rainfall was shed as storm runoff (overland flow); interfluve surfaces were lowering about 0.4 cm yr(-1) and gullies were backwearing about 2.5 cm yr(-1). The annual sediment yield was about 10.4 kg m(-2), more than half of which was coarse grained and highly acidic. The surface incorporation, by discing, of amendments (principally limestone) and placement of small rip-rap checkdams and water bars promoted the establishment of vegetation and resulted in increased rainfall infiltration (warm-season runoff declined to about 13 percent of rainfall). The yield of coarse-grained sediment was virtually eliminated, and the annual yield of fine-grained sediment was reduced from about 4.5 to 0.3 kg m(-2). The chemistry of storm runoff changed from acidic (acidities sometimes exceeded 700 mg l(-1) prior to treatment) to alkaline (75 mg l(-1), on average). Gully sidewalls continued to retreat, but the colluvial sediment accumulated on the gully floor (rather than being flushed away by storm runoff) and the gully cross-sections developed a more subdued and stable form.