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A simple coefficient chart works best. However, in the event you do not have access to such a chart; here is the general coefficient information that can be used to calculate Storm water Runoff: 1) Smooth, Impervious Surfaces, i.e., Tile, Roofing materials, Concrete walkways has a runoff coefficient of approximately 90% 2) Gravel surfaces and paved asphalt surfaces have a runoff coefficient of about 80% 3) Mitigated, engineered and or loose soils have a coefficient rating of 60% 4) Natural soils like that found in an undisturbed forest has a general coefficient rating of approximately 30% 5) Built landscape areas like "Green Roofs" should hold to and strive to reach the target of a 30% runoff coefficient rating. Use this calculation to calculate runoff: (CA) X (R) X (E) X (0.6) = Area runoff in gallons. Understanding the equation: (CA) = Catchment area in Sq. Ft. i.e., 1 Acre = 43,560 Sq.Ft. (R) = Rainfall expressed in inches (E)= efficiency expressed in decimal (0.6) = Gallons per Square feet for every inch of rain

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Q: How do you you determine storm water runoff coefficient?
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