WITHIN-STORM VARIATIONS IN RUNOFF AND SEDIMENT EXPORT FROM A RAPIDLY ERODING COAL-REFUSE DEPOSIT

Measurements of rainfall, runoff and sediment export from a barren dep osit of coal mine refuse in south-western Indiana were collected durin g three storms in the summer and autumn of 1990. Interfluve sheetwash, sediment mass flux, sediment concentration and, to a lesser extent, t runk gully discharge all responded quickly to changes in rainfall inte nsity. Grain-size distributions varied considerably during storms, con taining exclusively fine-grained sediment at low sediment discharges b ut very large quantities of coarse (> 2 mm) sediment at peak sediment discharges. Although data from a fairly long, multipulsed storm indica te that sediment production is limited by supply, the imbricated layer of flat chips that exists at the surface of the deposit is apparently mobilized during most high-intensity pulses of rainfall, thereby prod ucing large volumes of coarse sediment during summer thunderstorms.