Loading...
HomeMy WebLinkAbout2022-01-20 Drainage Letter to City.pdfJonathan Chavez, P.E. Civil Engineer III City of Renton Development Engineering Decision 1055 S Grady Way 6th Floor Renton, WA 98057 jchavez@rentonwa.gov RE: 600 SW 10th Parking Lot CCP Mr. Chavez, I, on behalf of EV 600, LLC, am the property owner and applicant for the proposed parking lot expansion at 600 SW 10th Street, Renton, WA 98057 otherwise described as King County Tax Parcel Number 2146000050. The City or Renton has provided comments on the CCP plans to provide catch basin spacing that meets the requirements for catch basin spacing in Table 4.2.1.A1 in the 2022 City of Renton Surface Water Design Manual (Manual), and further interprets that these spacing requirements are intended for application in a roadway with a crowned center. This interpretation therefore limits the tributary drainage area for a catch basin to one side of the crowned roadway. The proposed parking expansion is a paved lot with a proposed grading design including several high and low points creating multiple tributary drainage areas for which each has a catch basin capturing and conveying runoff from the pavement. As designed, these areas, in some cases, exceed those outlined in Manual based on the City’s interpretation of a crowned roadway. The Manual, in Core Requirement #4, requires that a proposed conveyance system, utilizing the Backwater Analysis Method, must convey and contain the 25-year peak flow. As designed, the proposed conveyance system successfully conveys and contains the 100-year peak flow, thus exceeding the conveyance requirements of Core Requirement #4. As the proposed conveyance system proves, through the Backwater Analysis Method, that it can convey flows in excess of those required by the Manual, I understand that the proper standard of care in design of the proposed stormwater conveyance system has been provided and accept the potential flooding risk that could be caused by the tributary drainage area to a single catch basin in excess of that allotted for in Table 4.2.1.A1. Kind Regards,