SEDIMENT BUDGETS ON RECLAIMED COAL SURFACE MINES IN CENTRAL PENNSYLVANIA.

摘要

Sediment budget investigations conducted within small scale (less than 21 hectares) reclaimed coal surface mine watersheds in central Pennsylvania document a complex spatial and temporal movement of sediment. Surface elevation measurements taken along eight different slope types over nearly one-and-one-half years following surface reclamation reveal that surfaces alternately aggrade and degrade. Sediment movement due to slope wash and rill processes decline during the second year following reclamation. The spatial movement of sediment along these surfaces is influenced by slope type and position. Convex converging slope forms yield more sediment via rilling than do non-converging slope types.;Knickpoint and gully channel segments within active gully-fan systems display cyclic aggradation and degradation during fall through spring and summer, respectively. Along fans, episodic degradation and aggradation can occur simultaneously within channels during individual storm events from fall through spring. Gully aggradation is initiated in the fall due to mass wasting of sidewalls and accelerates during the winter and early spring due to freeze-thaw. Early summer, intense storms erode sediment from within the gully, increasing sediment storage along the fan. Subsequent intense storms mobilize remaining sediment stored within the gully and produce additional sediment through knickpoint and gully channel scour. Generally, storms erode and deposit sediment throughout the gully-fan system depending upon storm character and timing, previous sediment storage history, and stream power conditioned by peak discharge of storm runoff and antecedent channel width and slope.;Multiple linear regression suggests that drainage basin length, maximum outslope relief, and the sum of drainage elements within reclaimed watersheds influence gully erosion for at least seven years following reclamation. Cross-profile surveys, rainfall, discharge, and grain size data taken over three years within two active gully-fan systems indicate that sediment production varies within seasonal and event-by-event time scales.