HomeMy WebLinkAboutDrainage Report 989600018MOe n nec
WNEK ENGINEERING
Consulting Civil Engineer
3388 NW Byron St., Suite 200 Silverdale, WA 98383
(360}692-3802
Engineered Drainage Report
Gould SFR
33 Elston Ave
Parcel#:989600018
bested ft
JEFFERSON COUNTY
lElffk50fJ COUNTY
prepared W.
Barbara Gould
103 N Lyter
Port Townsend, WA
date:
September 25, 2014
Overview: This report covers the parcel proposed for residential construction. The parcel
contains a single family residence with a septic system and downspouts currently
tightlined to two CPE pipes laid at the top of the steep slope on the north side of the
property. Each pipe handles approximately 50% of the roof area. The driveway will have a
drain installed to route stormwater to the eastern pipe. The site plan on file with the county
shows splash blocks for the downspouts instead of direct discharge over the bluff. The
grading around the house does not indicate that splash blocks would be feasible; the
tightline system will be used to direct flow to two dry wells sized to infiltrate the storm
runoff. Because the reserve drainfield and house both have setbacks to infiltration
features, the drywells will be constructed linearly instead of the typical circular design. The
required gravel, depths and cover will not be changed from the DOE design
specifications.
NOTE: DRI.WNG COPY Is INSCRIRED MIH DIGITIZED
SIGNATURE k DATE. WICINAL SIGNED DRAWNG IS
APbMED IN WE SIGNATURE ENGINEER'S oRSE.
MFW Project Number: 642
By the seal and signature here affixed,
1 certify that the enclosed report was
accomplished by myself, and that 1 am
currently a registered engineer of good
standing in the State of Washington.
Drywell Calculation:
DOE design criteria specifies 60 ft' per 1000 ft2 of impervious area served. The area available for the use
of drywells is limited by setbacks to the house and reserve drainfield. In order to fit the drywells into the
area available, the drywells have been converted into rectangular wells instead of circular wells. The
same volume of gravel will be used to store and infiltrate storm runoff. The drywell minimum depth is 4
feet, which is the design depth forthe project drywells. The drywells will also be 2 feet wide. The areas
routed to the drywells and required lengths are as follows:
Description
Area (ft2)
Required Gravel
Volume (ft')
Length of Drywell
(ft)
Total Volume of
Drywell(ft3)'
East Roof
933
Driveway
359
Total
1292
81.12
10.25
82.00
West Roof
933
Total
933
59.58
7.50
60.00
Length x Width (2 -ft) x Depth (4 -ft)
All drywell sizing is based on DOE Volume III, Section 3.1.1 Design Criteria for Infiltration Drywells and
Figure 3.1.4 Typical Downspout Infiltration Drywell
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