Semester

Spring

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Henry W. Rauch.

Abstract

Six streams were studied in Ohio, Pennsylvania, and West Virginia to evaluate subsidence impacts from active and abandoned longwall coal mines on stream discharge. Mined longwall panels included in this study ranged in age from five months to fifteen years old and in depth from 100 to 600 feet (30.5 to 182.9 m) beneath the studied streams.;Significant stream flow losses and gains were detected in each stream studied. Comparing longwall panel locations to stream flow measurements, geophysical surveys, and geomorphology surveys, it was concluded that longwall mine subsidence caused some of the detected stream flow losses and gains. Data collected suggests that longwall mine subsidence can impact stream flow and that the impact can be different for different baseflow conditions. The impact on a stream can vary across a longwall panel and the significance of an impact is related to many factors.;The greatest stream flow changes are across the upstream and downstream edges of the longwall subsidence basins, corresponding to zones of tension. Tension zones form fractures within the surface-rock fracture zone (soil zone). Naturally occurring fractures located within the tension zone may also dilate during longwall subsidence and enhance its hydraulic conductivity. Effects to stream discharge from mine subsidence depends on the baseflow conditions. In most cases, normalized stream discharges increase across the fractured tension zones during high baseflow conditions, and declined during low baseflow condition. These characteristics are caused by the increased permeability and storage capacity of dilated fractures within the tension zones.;All streams in the study had a normalized discharge decline across subsided longwall panels. This characteristic is caused by in increase in fractures throughout the panel increasing underflow rates and bank storage potential.;Sediment thickness and particle size distribution fluctuated at measuring stations spaced across the mined longwall panel. Erosion over the upstream tension zone thinned the sediment as the stream entered the subsidence basin. The coarsest and thickest sediment is over the upstream quarter-panel reach where the largest and greatest amount of sediment is deposited from the upstream erosion. A downstream fining trend is detected. This characteristic is caused by the slope of the subsidence basin and its impact on stream power causing it to decrease from the upstream quarter-panel to the downstream quarter-panel.

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