Overland Flow

Synonyms

Hortonian overland flow; Infiltration excess overland flow; Saturation excess overland flow; Surface runoff

Definition

Overland flow is the movement of water over the land, downslope toward a surface water body.

Overland flow is a very important aspect of the water cycle and can be generated under two different physical mechanisms. The infiltration excess overland flow is formed (named also Hortonian overland flow after Horton E. R.), when the rainfall intensity exceeds the soil infiltration capacity in an area (Liu et al., 2004). Then water accumulates on the soil and starts moving downslope, due to gravity, towards the hydrographic network. The second mechanism occurs when the soil saturation exceeds its maximum level due to groundwater uplifting, baseflow, and lateral subsurface water discharges, resulting in the appearance of saturation excess overland flow (Beven, 2001).

Factors such as soil permeability, topographic slope, and type and density of vegetation affect the...