SCS Method

A watershed has a drainage area of 1.5 square miles. The total watershed length (L) is 15,000 feet. A weighted CN number of 75 has been provided. The watershed slope is 1.2%.

1.) Compute the lag time using equation 15-4a from Chp 15 of Part 630 of the National Engineering Handbook,

2.) Compute the unit peak discharge for the basin for 1 inch of rainfall excess for a 6-hour storm of 4.5inches. Use the Equation for the SCS Triangular Unit Hydro graph .

3) Compute the excess rainfall for 4.5 inches of total rainfall following Equations 5.19 through 5.22 in Highway Hydrology

4.) Compute the Total Peak Discharge Knowing that the value in 2 is the result of 1 inch (unit) of rainfall.