surface runoff

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surface runoff (overland flow, Hortonian flow) The flow across the land surface of water that accumulates on the surface when the rainfall rate exceeds the infiltration capacity of the soil. The rate of infiltration, and therefore the possibility of surface runoff, is determined by such factors as soil type, vegetation, and the presence of shallow, relatively impermeable, soil horizons. Saturated overland flow can occur when a temporary rise of the water-table inhibits infiltration and causes flow over the surface.