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 direct 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 1−1 prior to treatment) to alkaline (75 mg 1−1, 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.