13.25.045 Drainage design and low impact development – Required.
(1) All development proposals shall conduct a low impact development site analysis in accordance with the minimum requirements outlined in Chapter 7 of the Design and Construction Standards. The site analysis shall be submitted with a request for a preapplication meeting in accordance with Chapter 14.35 CMC. Site analysis findings shall be a component of the development project submittal requirements.
(2) Projects that exceed the thresholds provided in CMC 13.25.040 shall submit a drainage report together with the required calculations, plans, and details. The drainage report and supporting plan documents shall address the applicable minimum requirements and include the proposed BMPs to mitigate stormwater impacts.
(3) Projects that are below the threshold for submitting a drainage report but are above the threshold requiring stormwater review shall submit plans that document the proposed BMPs to mitigate stormwater impacts. The proposed BMPs shall address the applicable minimum requirements.
(4) Projects that propose $100,000 or more of improvements to a previously developed site are subject to the minimum requirements for redevelopment projects. The Director of Public Works will determine the minimum requirements applicable to the project that shall be addressed in the drainage report.
(5) Stormwater generated on site from all new impervious surfaces shall be managed through a combination of LID BMPs, in accordance with this chapter and the Design and Construction Standards, or other LID best management practices approved by the city through the design deviation process in CMC 13.25.050, unless site and soil conditions make LID infeasible as determined by the Public Works Director.
(6) If the Public Works Director determines that LID is not feasible due to site and soil conditions, the applicant shall evaluate LID alternatives provided in CMC 13.25.047.
(7) The following low impact development stormwater management BMPs are permitted outright and shall be designed in accordance with the adopted stormwater manuals:
(a) Bioretention Areas. All bioretention areas shall be designed and constructed in accordance with the adopted stormwater manual. Bioretention areas shall be used instead of a conventional stormwater vault, or wet pond or permanent pool ponds.
(b) Amending construction site soils in accordance with Chapter 14.60 CMC.
(c) Permeable Pavements Not Subject to Vehicular Use. Pervious surfacing for areas of a site that are typically impervious, not subject to vehicular use, shall be designed and constructed in accordance with the adopted stormwater manual and the manufacturer’s recommendations.
(d) Disperse Stormwater into a Critical Area, Where Outright Permitted in Accordance with Chapter 18.65 CMC. Stormwater dispersion shall comply with the design standards set forth in the adopted stormwater manual and pursuant to City biologist approval. (Ord. 26-16 § 6)