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,