75th Pl W-15625-BLD20080376-Rayresidence-stormwater_memo2.pdf
CITY OF EDMONDS
PLAN REVIEW COMMENTS
ENGINEERING DIVISION
(425) 771-0220
City Website: www.ci.edmonds.wa.us
DATE: July 9, 2009
TO: File
FROM: Jerry Shuster, P.E., Stormwater Engineering Program Manager
E: Application #: Bld20080376
R
Project: Ray Residence
Project Address: 15625 -75th Pl. W.
I have completed my review of the June 9, 2009 submittal from Donna L. Breske, P.E. for the aforementioned site
that I received on June 30, 2009.
Overall the methodology is sound in assessing the capacity of the existing downstream stormwater system. There
are a few changes that must be made to the document and they are as follows:
The derivation of the Curve Numbers for the modeling needs to be revised. The runoff contribution from
the roads are not accounted for in the calculations. The impervious percentages used for the single family
densities only include rooftop and sidewalk water and not runoff from the adjacent roadways. Please
recalculate the impervious area to include the approximately 24 foot wide paved road surfaces within the
the drainage basins.
The time of concentration calculation for the lower basin has a 1,188 ft reach of sheet flow. Page III-1-14
of the 1992 Ecology Stormwater Manual states that 300 ft is the limit for using the sheet flow equations.
Use the "Shallow Concentrated Flow" methodology for this reach and re-calculate.
The report states that the un-detained 100 -yr flow off the Ray residence is 0.08 cfs. Include the
calculations for this in this document so it is complete.
The modeling assumes no base flow. On a recent field visit to the area during the June to early July
prolonged drought witnessed a not insignificant base flowing off the upper basin. The lower basin had a
minor flow (est at 0.1 cfs). No action is required to address this issue, but it should be considered in future
submittals of this type.
Sincerely,
Jerry Shuster, P.E.
Stormwater Engineering Program Manager
City of Edmonds
121 5th Ave N.
Edmonds, WA 98020
Desk Phone: 425-771-0220 x1323
Fax: 425-672-5750
shuster@ci.edmonds.wa.us