Partial Area Contributions to Storm Runoff in a Small New England Watershed

Abstract

During an experimental study of runoff producing mechanisms in a small drainage basin, the major portion of storm runoff was produced as overland flow on a small proportion of the watershed. Where the water table intersected the ground surface before and during a storm, water escaped from the soil surface and ran quickly to the stream at velocities 100 to 500 times those of the subsurface system. Direct precipitation onto the saturated area was another major contributor of storm flow. Storage of water within these source areas was small and travel times out of them were short. Runoff from them was largely controlled by rainfall intensity. These partial areas contributing quick runoff could expand or contract seasonally or during a storm. Their position and expansion can be related to geology, topography, soils, and rainfall characteristics. In the study basin, water that remained below the ground surface on its way to the main stream channel was a relatively minor contributor to the storm hydrograph. The response of subsurface flow to rainfall was heavily damped by storage and transmission within the soil. Measurements of water table elevation and runoff from experimental plots in another small watershed with different geologic conditions confirmed the results outlined above. Runoff records from a large number of small basins of the Sleepers River experimental watershed indicate the more general applicability of these findings.