Runoff

Definition

Runoff is water that flows over the land surface instead of soaking in. It can carry soil, nutrients and pollutants into streams and drains, which is why muddy rivers after storms are a sign of erosion upstream. Runoff increases where the ground is bare, crusted, compacted, sealed under pavement or very steep, and it grows more damaging when it concentrates into a track or channel. Slowing and spreading it is a core aim of terraces and contour lines. See also: Infiltration, Erosion, Terrace, and the guide "Soil Erosion by Water and Wind: Mechanisms and Warning Signs".