Changing Waters: Trends in Central Appalachian Streamflow in the Presence of Mountaintop Mining

• Baseflow: Baseflow is the water in a stream that is not directly associated with a specific precipitation events (i.e., event runoff). It is usually comprised of groundwater flow and slower shallow subsurface flow components including soil water drainage. • Drainage area/catchment/watershed: A watershed is the geographic area that contributes water to the same single point in a river or stream. In this paper, I use the terms drainage area, catchment, and watershed synonymously. • Flow duration curves (FDCs): FDCs show exceedance probabilities for all runoff values observed in a watershed. They help us visualize the flow regime of a stream. The 95 th percentile, for example, is the runoff value that is exceeded 95% of the time (usually a low baseflow value), while the 5 th percentile is the runoff value that is only exceeded 5% of the time. • Flow regime: Flow regime describes the seasonal pattern of streamflow in a certain river (Kundzewicz & Robson, 2000). • Hydrograph: A graph of stream discharge over time past a specific point (cross section) in the stream. • Hyetograph: A graph of the amount of rainfall over time in a particular place (e.g., at a precipitation gage). • Runoff ratio: The ratio of amount of runoff from an area divided by the amount of precipitation (RR = Q/P) in a stream. This ratio describes the amount of precipitation that leaves the watershed via the stream. • Stationarity: The assumption that all natural processes occur at the same rate as in the past, i.e., no changes/trends over time (Milly et al., 2008). 4 • Streamflow/runoff: Streamflow is the amount of water leaving the watershed over time past a stream gauge. • Stream gauges are measuring devices in streams that can record water height. Water height can be converted to a flux and then to area-normalized runoff in millimeters (by dividing a water flux (e.g., m 3 /s) by the watershed area). Executive Summary Mountaintop mining (MTM) became popular in the 1970s in Central Appalachia and today remains the dominant form of coal mining in the region (Ross et al., 2016). Approximately 6-7% of the Appalachian Coalfield Region in West Virginia, Kentucky, Virginia, and Tennessee is covered by mountaintop mining operations (Lindberg et. al, 2011). MTM involves stripping mountain surfaces by up to 300 vertical meters of rock material (" overburden ") to gain access to thin coal seams (Lindberg et al., …