Composite Curve Number With An Unconnected Impervious Area

This calculation is to be used for calculating the composite CN for area with an unconnected impervious area and a total impervious area of less than 30%.


CNp - Pervious runoff curve number
Pimp - Percent imperviousness
R - Ratio of unconnected impervious area to total impervious area
CNc - Composite runoff curve number