3. Curve Number and SCS Travel Time Assignment (2 pts) 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.

Solution :

It is given that the soil consists of :

Sand -- 50 %

Silt -- 25 %

Clay -- 25 %

Clay is present in the soil and so it has a very slow infiltration rates when the soil is thoroughly wetted.

a). Therefore the type of soil bis HSG Group D.

b). It is give that :

  Industrial building is 25 acres, i.e.

  CN = 93

  adjusted CN = 93 x 1 = 93

  I acre lots is 125 acres, i.e.

  CN = 84

  Adjusted CN = 84 x 1.07 = 89.88

                                          = 90 (approx.)

  60 acres of open or park space, i.e.

   CN = 80

  Adjusted CN = 80 x 1.14 = 91.2

                                          = 91 (approx.)

  225 acres of the meadows

  CN = 78

  Adjusted CN = 78 x 1.14 = 88.92

                                          = 89 (approx.)

  Commercial development of 40 acres, i.e.

  CN = 95

  Adjusted CN = 95 x 1 = 95

  Therefore the curve number is given by :

Thus, the curve number for the site for AMC III = 85

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