Question

Curve Number Assignment You need to calculate the curve number for a site which is composed of: 25 acres industrial buildings, 125 acres 1 acre lots, 60 acres parks/open space with good cover, 40 acres of commercial development, and 225 acres of meadows. The soil was determined to be 50% Sand, 25 % Silt and 25% Clay. a. Determine the Soils Type b. Determine Curve Number for AMC III.

Answer 1

Given,

Soil Conditions:

50 % Sand

25 % Silt

25 % Clay

Due to the presence of clay in the soil composure, it has very slow infiltration rates when thoroughly wetted.

a) The Soil Type belongs to HSG Group D

b) Curve Number for AMC III:

25 acres industrial buildings --> CN = 93 --> Adjusted CN = 93 * 1 = 93

125 acres 1 acre lots --> CN = 84 --> Adjusted CN = 84 * 1.07 = 89.88 ~ 90

60 acres parks/open space with good cover --> CN = 80 --> Adjusted CN = 80 * 1.14 = 91.2 ~ 91

40 acres of commercial development --> CN = 95 --> Adjusted CN = 95 * 1 = 95

225 acres of meadows --> CN = 78 --> Adjusted CN = 78 * 1.14 = 88.92 ~ 89

Curve Number = = 85.02 ~ 85

Curve Number for a site for AMC III = 85