Stormwater runoff from areas tributary to the property shall be considered in the design of the property's drainage system. Whenever practicable, flows from upstream areas that are not to be detained should be routed around the basin being provided for the site being developed.
A. Upstream Areas Not Meeting Division Requirements: When there are areas not meeting the storage and release rates of this division, tributary to the applicant's property, regionalized detention on the applicant's property shall be explored by the applicant. The following steps shall be followed:
2. Areas tributary to the applicant's property, not meeting the storage and release rate requirements of this division, shall be identified;
3. Using the areas determined in paragraph A2 of this section plus the applicant's property area, total storage needed for the combined properties shall be computed;
Allowable release rates shall be computed using the combined property areas. Storage shall be computed as described in section 10-10-7 of this division. If tributary areas are not developed, a reasonable fully developed land cover, based on local zoning, shall be assumed for the purposes of computing storage.
Once the necessary combined storage is computed, the county may choose to pay for oversizing the applicant's detention basin to accommodate the regional flows. The applicant's responsibility will be limited to the storage for his property as computed in paragraph A1 of this section. If regional storage is selected by the county, then the design produced in paragraph A3 of this section shall be implemented. If regional storage is rejected by the county, the applicant shall bypass all tributary area flows around the applicant's basin whenever practicable. If the applicant must route upstream flows through his basin and the upstream areas exceed one square mile in size, the applicant must meet the provisions of paragraph 10-10-7I3 of this division for on stream basins.
B. Upstream Areas Meeting Division Requirements: When there are areas which meet the storage and release rate requirements of this division, tributary to the applicant's property, the upstream flows shall be bypassed around the applicant's detention basin, or be routed through the applicant's detention basin if this is the only practicable alternative. Storage needed for the applicant's property shall still be computed as described in paragraph A1 of this section. However, if the county decides to route tributary area flows through an applicant's basin, the final design stormwater releases shall be based on the combined total of the applicant's property plus tributary areas. It must be shown that at no time will the runoff rate from the applicant's property exceed the allowable release rate for his/her property alone. (Ord., 2-22-1999)