Channel Enlargement as a Function of Impervious Cover
Notes:
Evidence that stream channels enlarge in response to watershed development lies in research studies that have tracked the change in the cross-sectional area of stream channels over time. One simple way to quantify these changes is to define an �enlargement ratio,� which represents the ratio of a stream�s current cross-sectional area to its pre-development cross-sectional area (or, in some cases, a cross-section from an adjacent undeveloped stream of equivalent watershed area).
The graph in this slide shows the relationship between impervious cover and the ultimate channel enlargement ratio from about 60 channel reaches of alluvial streams in Texas, Maryland, and Vermont. This provides watershed managers a rough sense of how much channel enlargement can be expected for different levels of impervious cover. It should be noted that this general curve does not apply to stream channels with a rock bed or rock banks.