Mountaintop removal / valley fill (MTR/VF) operations are large scale extensions of what is commonly called surface mining, which is considered the greatest vector of land use change in the Central Appalachian Plateau of the eastern United States. While surface and some MTR mines remove overburden to expose coal seams, the landscape is returned to its approximate pre-mining contours. MTR/VF operations also remove overburden to expose coal seams, but a portion or all of the overburden is moved to adjacent valleys, permanently filling them. While surface mined areas may be reclaimed, the large earth moving equipment used generally compacts fill soils so that they are not capable of supporting vegetation communities that existed pre-mining, and infiltration rates are often an order of magnitude lower than nearby undisturbed sites. These factors have led many to believe the aggregate effect of surface mining is to exacerbate peak flow events. In this work we explore results from a wide range of published studies addressing surface mine effects on hydrologic response, and highlight key findings, specifically with regards to the question “Does surface mining increase downstream flood risk?” We then explore event analyses of 2 contemporary (2001 and 2009) storm events in West Virginia and Kentucky across watersheds with a wide range of mining operations.
Results/Conclusions
Surface mines generally increase peak flows but not all reports draw the same conclusion. Differences exist in methods used to analyze flood response, the time scales over which the studies were conducted, and the uncertainty associated with non-stationary land use. Another factor contributing to the variability in outcomes is related to scale (watershed size) with the majority of studies looking at impacts from small sites (less than 1-10 km2), while flood events are typically reported for larger watersheds (100-1000+ km2). Thus the proportion of a watershed impacted by mining may be very high at the local scale, with subsequent increases in peak flows reported locally, while at the scale of a larger river basin, the proportion mined may be far less, and peak flows attenuated by intervening land cover. However, experience at the local scale would imply that as mining operations impact larger proportions of a river basin, subsequent increases in peak flows (and flow variability overall) can be expected.
