E

Abstract

The purpose of this paper is to describe practical methods used by the Office of Surface Mining to evaluate environmental impacts from a landslide and devise a mitigation strategy. On January 27, 2005, a 10-hectare (25-acre) landslide occurred on a steep mountainside at High Point Mountain in Scott County, TN. The landslide included spoil from a pre-law contour coalmine and a reclaimed cross-ridge coalmine. Sediments from the landslide washed into Smoky Creek, a tributary to New River, which flows into the Big South Fork of the Cumberland River. Initial suspended sediment concentrations below the landslide were about 5000 mg/L, while total sediment concentrations peaked at about 24,000 mg/L. After 4 months, the landslide had stabilized and suspended sediment concentrations fell to less than 10 mg/L. Sand and gravel sized particles settled out within 610 m (2000 ft) below the landslide tributary, while fine silts and clays were carried over 32 km (20 miles) downstream. Groundwater from the adjacent mine spoils was modeled using the USGS MODFLOW software; results indicated mine spoil discharges would reach equilibrium within 292 days. Acid- base accounting accurately predicted no acid mine drainage would occur. Stormwater was modeled using the TVA TENN-I double triangle model, and net sediment erosion was modeled using the ERODE-I model. Model results compared well with actual field data and should be useful in evaluating other landslides. Biological evaluations were conducted on the impacted stream and compared to adjacent streams to show area productivity. Steams were sampled for fish, benthic invertebrates, crayfish, and amphibians by biologists with the Tennessee Wildlife Resources Agency, National Park Service and Tennessee Valley Authority. Aquatic life, while initially smothered, had begun to recover after 22 months. The NRCS WEPP model was used to evaluate different mitigation strategies. Mitigation consisted of seeding the landslide with grasses, planting trees, and implementing vegetative filters. In conclusion, the landslide resulted in an intense short-term release of sediments similar to a construction site, which subsided in about 3 months. Models proved satisfactory in estimating impacts.