(A) Design conditions. All storm water management facilities shall be designed for ultimate development. Three development conditions shall be analyzed for each development. (See Table 153.1040(A) below.)
(B) Design storm event. Facilities with drainage areas under 100 acres shall be designed for a 25-year storm. Facilities with drainage areas over 100 acres or areas within a designated floodplain shall be designed for a 100-year storm or a 25-year storm, plus freeboard, if that elevation is higher. Detention facilities and streets are exceptions to the frequency criteria cited in this section. Detention facility outflows will be designed for five-, 25- and 100-year frequency storms.
(C) Responsibility to accept storm water.
(1) The owner or developer of property to be developed is responsible for the conveyance of all storm water flowing through the property. This responsibility includes storm water flowing onto the property by any other developed property as well as the drainage naturally flowing through the property by reason of topography.
Condition | Design Parameters |
Existing conditions | Current development conditions in the watershed and on site. Use as the baseline analysis for determining the impact of development. |
Proposed conditions | Existing conditions with the proposed development added. Use to determine if the increased run-off from the proposed development results in an adverse impact to other properties. |
Ultimate conditions | Ultimate development conditions within the watershed used to design the drainage facilities. May be used in lieu of proposed conditions to determine if the increased runoff from the ultimate watershed development results in an adverse impact to other properties. |
(2) Future upstream development shall be accounted for by assuming ultimate development when sizing drainage systems as specified in this section.
(Ord. 3020, passed 9-10-2013, § 5.22.5)