basin has an average CN of 67.29 calculated by the formula below.
CN = ΣCiAi / ΣAi
This curve number can be used to calculate S, the maximum soil water retention parameter. Hadley Valley has a maximum soil water retention parameter of 4.861.
S = ((1000 / CN) – 10)
An accumulated runoff volume, Q in inches, may be computed for a particular storm event. In Rochester, Minnesota these are Type II precipitation events. This is a connective, high intensity storm occurring in inland areas. This method estimates total runoff and factors in infiltration losses, Ia. Losses also include initial abstractions from interception due to vegetation and surface storage.
Q = (P - Ia)2 / P – Ia + S
Ia = .2S
Total precipitation, P must be larger than Ia. These formulas are influenced by AMC, or antecedent moisture. AMC I is a dry condition where little or no precipitation occurs prior to the calculated event. A rainfall of 3.0 inches under these conditions in Hadley Valley watershed produces .60 inches of runoff.
Figure 14 depicts locations with highest potential for runoff in Hadley Valley watershed. No runoff occurs in black wetlands. Yellow shows minimal runoff in permeable soils and naturally vegetated areas. As humans influence through residential living or commerce