The Impact Of Three Longwall Coal Mines On Streamflow In The Appalachian Coalfield

The objectives of this study were to document the hydrologic impacts of longwall mining on streams, identify the factors affecting the extent of stream dewatering, and develop empirical trends to predict the extent of dewatering and recovery of streams in advance of mining. This study on stream impacts is a companion to a stud; conducted on ground water impacts from longwall mining, which was done as part of the same research project at the' same locations and times. The study areas are three mine sites in north- central West Virginia. Mine A, located in Upshur County, has relatively thin mine overburden under the valley streams (105-115 feet). Stream monitoring there continued the earlier work of Cifelli and Rauch (1). Stream dewatering was severe with streams often going dry over the longwall panels during baseflow conditions. The lost water was probably flowing to the mine. Dewatering began in streams over the mine entry areas adjacent to the panels and as much as 380 feet from the nearest panel edge. The angles of dewatering influence ranged 22 to 72 degrees with respect to the nearest mined panel edge. Discharge then typically increased as the streams- flowed across the panel edge, but then decreased again over the panels. These streams were often ponded by local reversals in hydraulic gradient caused by land subsidence, and often dried up after flowing a few hundred feet across the panels. This occurred over panels that were previously mined up to eight months before. Mine B, located in Monongalia County, has relatively thick mine overburden (475-485 - feet) under the major stream. Stream dewatering was severe there during warm season baseflows, with complete dewatering occurring then over the longwall panels. This dewatering occurred over mined panels up to five years old, probably in response to a major anticlinal axis lineament and fracture zone in the stream valley. Mine C. located on the West Virginia -Pennsylvania border, has relatively thick mine overburden (about 585-630 feet) under the monitored streams there. stream dewatering was only partial, and these streams typically recovered their lost discharge downstream of the mine, indicating that lost water was not recharging to the mine. Only longwall panels less than one year old were associated with stream dewatering.