A mechanism for storm runoff generation during large rainfall events
McKinnon, Robert Joseph
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A series of subsurface gutter experiments, situated on the mid-slope of a Piedmont catchment, were conducted to investigate a potential mechanism for the rapid mobilization of storm runoff from the unsaturated zone. Covered gutters were 1.45 m long and installed approximately 10 cm below the ground surface. Nearly a year of natural and artificial rainfall monitoring data showed a close relationship between rainfall intensity and runoff in the subsurface gutters. The gutter response closely followed the onset of intense rainfall and “switched off” with the cessation of storm events. This behavior is not indicative of a saturated subsurface flow mechanism. Deuterium analysis of runoff samples demonstrated that stormflow was comprised primarily of pre-event soil water. The data suggest that runoff from large storm events occurs when high intensity rainfall generates pressure waves that rapidly travel through the soil and produce pre-event water.