Overland Flow

Overland flow consists of a thin film of water or tiny rivulets of water.

Overland flow occurs when the precipitation rate exceeds the infiltration rate of the ground's surface.

The infiltration rate is different for different surfaces.

Vegetated surfaces allow more water to infiltrate than bare surfaces (See the illustrations below).

Coarse textured soils (sands) have large pores which allow water to drain more easily than fine textured soils (clays). These coarse soils allow water to infiltrate more quickly.

Construction sites, urban areas, and haul roads produce large quantities of overland flow.

Since buildings, concrete, and asphalt do not allow water to infiltrate, water runs off of these surfaces immediately, resulting in higher peak flows in urban areas.

When impermeable surfaces prevent water from soaking into the ground, ground water recharge is reduced. This results in lower stream flows during periods when it is not raining.

Sources:

Leopold, Luna B. and Walter B. Langbein. A Primer on Water. U.S. Geological Survey. U.S. Government Printing Office: Washington D.C., 1960.

Back to Home | Back to River Channels, Sediment, and Runoff