§ 1-15. Design storms and hydrologic methods.

A.

Unless otherwise specified, the prescribed design storms are one hundred twenty (120) percent of the one-year, two-year, ten-year, twenty-five-year, fifty-year and one hundred-year twenty-four-hour storms using the rainfall precipitation frequency data recommended by the U.S. National Oceanic and Atmospheric Administration (NOAA) Atlas 14, Volume 2 Version 3.0. Partial duration time series, as adjusted by the City of Virginia Beach Public Works Design Standards Manual, shall be used for the precipitation data.

B.

Unless otherwise specified, all hydrologic analyses shall be based on the existing watershed characteristics and how the ultimate development condition of the subject project will be addressed.

C.

Except as allowed in subsection D. below, all analysis shall use dynamic modeling. Predeveloped vs. post-developed runoff comparisons shall be performed using the same method of analysis.

D.

When total land disturbance is less than twenty thousand (20,000) square feet or the proposed impervious area is at least ten (10) percent less than the existing impervious area, stormwater design may use any computer design program that utilizes the twenty-four-hour design storm hyetograph with increased precipitation and the static tailwater provided by the City of Virginia Beach. Analysis of upstream and downstream impacts is not required under these conditions.

(Ord. No. 3337, 4-22-14, eff. 7-1-14; Ord. No. 3618, 6-16-20)

(Ord. No. 3337, 4-22-14, eff. 7-1-14; Ord. No. 3618, 6-16-20)