Characterizing runoff responses in a mountaintop mine impacted and forested catchment in the coalfields of West Virginia

Abstract

Mountaintop mining (MTM) represents the largest land cover/landuse change in the Central Appalachian region. By 2012, the U.S. EPA estimates that MTR will have impacted approximately 6.8% of the predominately forested Appalachian Coalfield region of West Virginia (WV), Kentucky, Tennessee, and Virginia with nearly 4,000 miles of headwater streams buried under valley fills (VF). In spite of the scale and extent of MTM, its hydrologic impacts are poorly understood. Several devastating floods in the region have been attributed to MTM, but there is little evidence to either confirm or refute this belief. Existing research on the hydrologic impacts of MTM has documented a range of potential impacts to the storm hydrograph and seasonal flow regimes but has also revealed considerable variability in hydrologic responses to differing storm events, extents of disturbance, and stage of reclamation. Additional uncertainty stems from our poor understanding runoff processes of forested catchments in the southern coalfields of West Virginia. This study begins to address this knowledge gap by exploring rainfall-runoff relationships in two headwater catchments in southern West Virginia: a predominantly forested catchment with no active surface mining and another undergoing active MTM and VF that disturbs 20% of its catchment area. Streamflow (Q) and precipitation (P) were measured in each catchment from 01 September 2011 to 30 September 2012 and 23 discrete storm events were selected for analysis. Both catchments responded rapidly to precipitation inputs but the MTM-impacted catchment experienced significantly greater total runoff (3x), higher peak runoff (2x), greater runoff ratios (Q/P) (2x), greater baseflows, and shorter time lags from peak precipitation to peak runoff (2x). Hydraulic response time, a fundamental hydraulic parameter that controls the conversion of rainfall to runoff, was modeled with a transfer function rainfall-runoff model and found to be more rapid in the MTM-impacted catchment. The source of these differences is likely attributable to some combination of three factors: surface disturbance of MTM/VF operations, the smaller drainage area of the MTM-impacted catchment and additional water inputs from legacy underground mining in the MTM-impacted catchment. Results from this study reflect the hydrologic complexity of runoff generation the southern coalfields of West Virginia. Future research efforts should quantify the physical processes that control hydrologic response in these heavily disturbed landscapes.