(A) The selection of a design storm is the basis for all runoff calculations and facility design for a project site. The storm water conveyance system shall be designed to adequately handle the runoff from storms having various frequencies of occurrence from different types of development in accordance with the general categories set forth below in this section.
(B) To ensure the adequacy of the storm water conveyance system, the following minimum design storms shall be used, where applicable.
(1) The ten-year storm shall be used for all public storm sewer inlets and closed pipe systems. The ten-year storm shall also be used for all channels and ditches, which should be capable of conveying the ten-year storm flow within their banks.
(2) The 100-year storm shall be used as a check storm for sewer systems designed for a ten- year storm to confine containment at levels below the rim opening to prevent surcharging.
(3) The two-year storm, ten-year storm, 25-year storm and 100-year storm shall be used to calculate pre-development runoff from a site for detention, retention and sediment control basins.
(4) The two-year storm, ten-year storm, 25-year storm and 100-year storm shall be used to calculate post-development runoff from a site for detention, retention and sediment control basins.
(5) The 100-year storm shall be used for all detention, retention or sediment control basins as a check storm to ensure against flooding or surcharging.
(6) The 100-year storm shall be used in the design of flood control facilities. The post-development peak flow rates shall be less than or equal to the pre-development peak flow rates for the two year storm, 10-year storm, 25-year storm and 100-year storm events.
(7) The 100-year Storm shall be used in comparison with established flood elevations from property owners, observations, state’s Department of Transportation drainage folder data, Federal Emergency Management Agency maps and other applicable records to minimize the impacts of flooding.
(8) Additional controls or localized restrictions may be placed on specific sites, such as deemed necessary by the approving agency.
(Ord. 012-118, passed 10-8-2012)