Laserfiche WebLink
June 16, 2022 <br />92 <br /> <br /> Source: NOAA. 1961. Technical Paper 40, Rainfall Frequency Atlas of the United States for Durations <br />from 30 Minutes to 24 Hours and Return Periods from 1 to 100 years. Washington, D.C. (50-60) <br /> <br />For pre-development computations, all runoff coefficients with the project shall be based on <br />actual land use assuming summer or good land cover conditions (see Table 15. Runoff <br />Coefficients below). Off-site land use conditions used to determine storm flows for designing <br />storm facilities shall be based on existing land uses assuming winter or poor land cover <br />conditions (see Table 15. Runoff Coefficients below). <br />3. The design of stormwater management collection facilities that service drainage areas <br />within the site shall be based upon a ten (10) year storm frequency event. <br />4. All developments must also include design provisions that allow for the overland <br />conveyance of the post Q100 year storm flows through the site without damage to any <br />private or public property. <br />5. Runoff calculations for on-site stormwater management facilities shall be based upon the <br />Rational method, where peak rate of discharge is termed Qp and is expressed as cubic feet <br />per second: <br />Qp = CIA <br />where <br />Qp = The peak runoff rate in cubic feet per second (CFS) <br />C = The runoff coefficient <br />I = The average rainfall intensity in inches per hour (in./hr.), occurring at the time of <br />concentration tc (min.) <br />A = The size of the drainage area <br />6. Criteria and assumptions to be used in the determination of stormwater runoff and design <br />of management facilities are as follows: <br />a. Runoff coefficients shall be based on the land use coefficients listed in Table 15. <br />Runoff Coefficients based on hydrologic soils group classification as defined in Table <br />16. <br />