§ 84-8. Flow from upstream tributary areas.

Stormwater runoff from areas tributary to the property shall be considered in the design of the property's stormwater management system. Whenever practicable, undetained stormwater runoff from upstream areas that are not providing detention should be routed around the basin being provided for the applicant's property.

(1)

Upstream tributary areas. The following shall apply to upstream tributary areas:

a.

If upstream tributary flows are passed through the applicant's basin, then a detention volume safety factor of five percent shall be added to storage volume required for the applicant's property.

b.

If upstream tributary flows are passed through the applicant's detention basin, the final design release rates shall be based on the total tributary area (the applicant's property and upstream areas tributary to the applicant's property).

(2)

Regional detention evaluation. When upstream property tributary to the applicant's property does not meet the stormwater runoff storage and release requirements of this chapter, regionalized detention on the applicant's property shall be explored by the applicant. The following steps shall be followed:

a.

The applicant shall compute the storage volume needed for his property alone using the applicable release rates from this chapter, the applicant's property area, and the procedures described in this chapter.

b.

Upstream areas tributary to the applicant's property not meeting the storage and release rate requirements of this chapter shall be identified.

c.

The applicant shall compute the combined storage volume needed for the total area (the applicant's property and upstream areas tributary to the applicant's property) using the applicable release rates from this chapter, the total area, and the procedures described in this chapter.

d.

If upstream tributary areas are not currently developed, a reasonable fully developed land cover, based on anticipated zoning, shall be assumed for the purposes of computing storage.

e.

Once the necessary combined storage is computed, the city may choose to pay for increasing the size of the applicant's detention basin to accommodate the upstream area flows. The applicant's responsibility will then be limited to the required storage for his property alone.

f.

If regional storage is selected by the city, then the combined-storage design computed above shall be implemented.

(Ord. No. O16-2017, § 1, 4-18-2017)