Run-Off

Definition

Run-off, also referred to as runoff or surface runoff, is the term used to refer to that part of precipitation in the water cycle that moves on the ground surface downslope or downstream away from the location where it first accumulated as rain or snow. Surface water run-off is part of the water cycle that also includes evaporation, infiltration, and storage (USGS 2016). Run-off is estimated from rainfall based on an empirical approach that is known as the rational method (Goyen et al. 2014)

$$ q=C\ A\ p $$

(1)

where q is the peak unit discharge in m³/s from a drainage basin at a point of interest, C is a dimensionless coefficient that represents the amount of run-off as a decimal fraction of precipitation, A is the drainage basin area in m² above the point of interest, and pis representative rainfall intensity in mm/hr for a meaningful duration and a desired return period. The duration for the rainfall intensity may be the time of concentration (the time required for...