(A) The Soil Conservation Service (SCS) Method may be used for the following: to calculate storm runoff volume; to calculate peak rate of discharge; to develop runoff hydrographs for basins and sub basins; and to calculate the required storage volume for storm water control facilities.
(B) The SCS Method is the preferred method for performing hydrologic analysis. The SCS Method shall utilize the formulas, constants and data as currently provided by the Soil Conservation Service. The SCS Method utilizes a 24-hour storm duration, which is considered to be acceptable for the county. When the SCS Method is used, the Type II rainfall distribution shall be used. The rainfall depths for the 24-hour storm are found in the Weather Bureau Technical Paper 40 or the Rainfall Frequency Values for Kentucky, Engineering Memorandum No. 2, 6-1-1979, and are included in Table 1 below:
Table 1 - 24-Hour Storm Rainfall Depths | |
Storm Frequency | 24-Hour Rainfall Depth (In Inches) |
2-year | 3.20 |
10-year | 4.50 |
25-year | 5.20 |
50-year | 5.70 |
100-year | 6.30 |
(C) The curve number (CN) needed for SCS computations is similar to the runoff coefficient used in the Rational Method in that it is based on the surface conditions of the project site. The CN can be determined from tables in SCS TR-55 or in the Louisville Metropolitan Sewer District Design Manual. Soil Conservation Service publications may be used for detailed information.
(Ord. 012-118, passed 10-8-2012)