Water Quality



VSA Processes

Variable Source Area Hydrology is the concept that the majority of runoff exiting a watershed is driven by a relatively small portion of the watershed. The abundance of these runoff generating sources may increase and decrease depending on temporal and spatial variability.

August field conditions (Dry) March field conditions (Wet)
Agricultural field conditions in August (Dry)
Agricultural field conditions in March (Wet)

The contribution to runoff by these variable source areas is governed by two major processes:

Animated VSA Hydrology Processes
(Examples of Saturation Excess Overland Flow):

VSA Processes

Watch a model of VSAs throughout the year:


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