Direct Discharge Approval.pdfApril 5, 2010
City of Edmonds
121 5'h Ave. North
Edmonds, WA 98020
6621 Foster Slough Rd. Ph: 425-334-9980
Snohomish, WA 98290 Fax: 425-334-7380
e-mail: donnabreske@comcast.net
Subject: Direct Drainage Discharge to Puget Sound
Reference: Michael & Nancy Gold, South Residence
1626b 75" PL. W., Edmonds, WA 98020
Please find attached a narrative prepared by this engineer and information from
city records which concludes that on-site detention for the above referenced project is not
required.
The site is in very close proximity to Puget Sound and a Meadowdale Drainage
Investigation Report prepared in April 2000 by R.W. Beck concludes the piping
conveyance systems within the drainage basin have adequate capacity for full build -out
of 100 -year peak flows.
As a result on-site detention is not proposed for the development of the site.
Sincerely,
2 13,"1
Donna L. Breske, P.E.
VICINITY MAP
M1KE & NANCY COLD, SOUTH HOUSE
16220 75th PL W.
EDMONDS. WA 98020
DIRECT DRAINAGE DISCHARGE TO PUGET SOUND
MICHAEL & NANCY GOLD --- SINGLE FAMILY HOME -SOUTH LOT
1622075 TH PL.W., EDMONDS, WA 98020
APRIL 1, 2010
REASON FOR REPORT:
The 1992 DOE Manual Minimum Requirement #5; Streambank Erosion Control
applies only to situations where stormwater runoff is discharged directly or indirectly to a
stream. Thus, per the 1992 DOE since discharge from this site does not enter a stream,
no detention is required. Furthermore, per the city of Edmonds detention system fro new
impervious area may be eliminated, if the site is in close proximity to Puget Sound, and if
it can be demonstrated that the downstream pipe conveyance system, which outfalls to
Puget Sound, has sufficient capacity to accept the un -detained flows.
CONCLUSION:
Per Meadowdale Drainage Investigation prepared by R.W. Beck and dated April
2000, the pipes in Basin "D" and down to Haines Wharf have adequate capacity for full
build -out -100 -year peak flows. The subject site lies within Basin "D" of the R.W. Beck
Report, (see attached map from the Report), Specifically, Section 3, Page I I of said
report states, "All of these pipelines in Basin "D" and down to Haines Wharf have
adequate capacity for full build -out 100 -year peak flows.
It I 1 alp,z
The site is located at 16220 75" PL. W., just uphill of Haines Wharf. The west
boundary of the site is approximately 100 -feet from the edge of the water of Puget Sound.
A single family home is proposed for construction on the site. An existing unoccupied
and uninhabitable house is currently on the site. The house is proposed to be demolished
and a new access provided from 75th PL. W. will be used for the new house.
Michael & Nancy Gold -South House -Direct Storm Discharge
FURTHER DISCUSSION OF R.W. BECK DRAINAGE INVESTIGATION:
Per the R.W. Beck Report the flow for the I00 -year full build -out of Basin "D" is
calculated at 7.8 cfs. Additionally, per the R.W. Report, the existing conditions, April
2000, for the I00 -year storm are 4.2 cfs. (See Table 2, Stormwater Peak Flows from the
R.W. Beck Report).
For this project, coupled together with the adjacent Mike Gold project to the
north, an additional 0.14 cfs for the I00 -year storm will be added to Basin "D". (See
attached Water Works Calculations and supporting Exhibits prepared by this engineer).
This 0.14 cfs adds to the April 2000 calculated 100 -year rate of 4.2 cfs, and contributes
to a portion of the overall 100 -year full build -out rate of 7.8 cfs as identified in the R.W.
Beck Report.
DOWNSTREAM PIPING SYSTEM DISCUSSION:
Storm drainage flows from the site will be connected, via a drainage easement
from the site to the north, to an exiting catch basin which is labeled 1-90 within a Basin
Map from the R.W. Beck Report and attached herein. Flows will be directed downhill to
the west in a 15" CMP pipe segments within the city right-of-way of 162nd Ave. S.W.
Then the flows will enter a catch basin and head north in another 15' CMP in the city
right of way of 75th Ave. W. at which point they enter another CB and are directed to the
west. From this CB, the pipe increases to a 36" CP and travels under the BNRR and
outflows to Puget Sound.
Prepared By:
Donna L. Breske P.E.
Phone: 425-334-9980
Michael & Nancy Gold -South House -Direct Storm Discharge
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SUBBASJN DESIGNATION
SUBBASIN BOUNDARY
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SCALE IN FEET
FIGURE I
CITY OF EDMONDS, WASHINGTON
MEADOWDALE DRAINAGE INVESTIGATION
STUDY AREA MAP
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SCALE IN FEET
FIGURE I
CITY OF EDMONDS, WASHINGTON
MEADOWDALE DRAINAGE INVESTIGATION
STUDY AREA MAP
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FINDINGS AND RECOMMENDATIONS
from the south (Subbasin C3). Portions of this branch precede the 1984 work and
are in fair condition. The branch cuts across the valley bottom and was intended
to collect at least a portion of a small stream. The area also appears to be a small
wetland and has been reported as a seepage area. The vegetation and deposition
is limiting the effectiveness of this line, eliminating any inflow from the stream
and perhaps allowing outflow from the system. Although it is no longer
g desirable to collect the stream flow, the system should be cleaned to prevent
' outflows. Installation of solid catch basin/manhole covers would stop collection
and would reduce maintenance_
The small stream is collected into the North Meadowdale Road trunk at the west
end of the subbasin (see Report Map). The intake for the small stream now has a
small trashrack that is subject to clogging. A replacement trashrack and headwall
is recommended to ensure better collection. Overflows down North
Meadowdale Road have been reported. A detail of a trashrack and headwall
' with adequate surface area is shown in Appendix C.
Two other inlets he on the north side of the North Meadowdale Road trunk.
Both should have larger trashracks installed.
Six seepage or wet areas were identified during the 1984 work. One, discussed
above, should remain as is. Another is currently being eliminated by
construction of a house (16123 North Meadowdale Road). The area at 16119
North Meadowdale Road is very small. The area near 15910, 15917 and 15920
72nd Avenue W appears to be adequately handled by private french drains.
Both slides and seepage have been reported on the Johanson property. The
slides did not involve public property or drainage facilities. The uphill property
owner, Mrs. Glantz, reportedly installed the additional drainage system
requested by the City. Slope stability at this location remains the responsibility of
the property owners. This property was the location of the stream prior to road
and pipe installation. It still rests in the low point in the valley. Seepage in this
area is to be expected. Elimination of seepage here would require that seepage
following the topographic bottom of the valley would have to be collected. This
would require a very deep french drain that would not be cost effective.
BASIN D
Basin D covers 21.5 acres and includes the steep and moderate slopes between
72nd Avenue W and 75' Place W. Seepage is heavy along the steep slope in the
middle of the basin. The basin is partially developed, probably inhibited by steep
slope and, stability concerns
The existing collection system includes both surface and groundwater
components. Three separate groundwater collection systems lie along the slope.
These feed into a surface system along 75' Place W. Flow from Basin D combines
with flow from Basin C near Haines Wharf and discharge to Puget Sound in a 36 -
inch RCP. I All of these pipelines in Basin D and down to Haines Wharf have
adequate cavacity for full build -out 100-vear peak flows.
X001 121 V17/00 R. W. Beck 3-11
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�- 1473 SF
l 7510 162nd
3889 SF
1 1 �
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DETENTION SYSTEM 1
SUB -BASIN 1
BOUNDARY o
AREA=28,300 SF ` 1
TOTAL IMPERVIOUS AREA = 13, 930 Sr
0.32 AC
CN=98
TOTAL PERVIOUS AREA = 14,390 SF
0.33 AC
CN=BS
16220 75th
2327 SF
5811 SF
FROM ECDC 18.30.010 DEFINITIONS
SECTIONS CC, RR, & TT
P2 = 1.5 IN PER 24 -NR
P1O = 2.5 IN PER 24 -NR
P1O0= 3.0 IN PER 24 -NR
I
DEVELOPED COND1 TION-IMPERWOUS AREA EXHIBIT
MIKE GOLD PROJECTS
4-2-10
/*
DETENTION SYSTEM
I'SUB-BASIN 1',BOUNDARY
AREA=27,965 SF
A
I f
FROM ECDC 18,30,010 DEFIN17IONS
SECTIONS CC, RR, & TF
P2 = 1.5 IN PER 24 -HR
P10 = 2.5 IN PER 24 -HR TOTAL IMPERVIOUS AREA = 27,965 SF
P100= 3.0 IN PER 24 -HR 0.642 AC
CN=85
TIME OF CONCENTRA TION PRE -DEVELOPED SITE EXHIBIT
MIKE GOLD PROJECTS
4-2-10
3/15/10 1:40:10 pm
Mike Gold
Meadowdale, 75th Ave W.
BASIN SUMMARY
BASIN ID: A10OX
NAME: 100 YR
24HR EXISITNG
SBUH METHODOLOGY
0.32
e
TOTAL AREA.......:
0.64 Acres
BASEFLOWS: 0.00 cfs
RAINFALL TYPE....:
TYPEIA
PERV
PRECIPITATION....:
3.00 inches
AREA..: 0.64 Acres
TIME INTERVAL....:
10.00 min
CN....: 85.00
TC..... 20.55 min
ABSTRACTION COEFF:
0.20
PEAK RATE: 0.18 cfs VOL:j 0.08
Ac -ft TIME: 480 min
BASIN ID: AIOX
NAME: 10 -YR 24 HR EXISTING
SBUH METHODOLOGY
TOTAL AREA.......:
0.64 Acres
BASEFLOWS: 0.00 cfs
RAINFALL 'IfYPE-....:
TYPEIA
PERV
PRECIPITATION....:
IME INTERVAL....:
2.50 inches
AREA..: 0.64 Acres
10.00 min
CN....: 85.00
TC.. ... 20.55 min
ABSTRACTION COEFF:
0.20
PEAK RATE: 0.12 cfs
VOL: 0.06
Ac -ft TIME: 480 min
BASIN ID: A2X
NAME: 2YR, 24
HR EXISTING
SBUH METHODOLOGY
TOTAL AREA.......:
0.64 Acres
BASEFLOWS: 0.00 cfs
RAINFALL TYPE....:
TYPEIA
PERV
PRECIPITATION....:
1.50 inches
AREA..: 0.64 Acres
TIME INTERVAL....:
10.00 min
CN..:.: 85.00
TC..... 20.55 min
ABSTRACTION COEFF:
0.20
TcReach - Sheet L:
41.00 ns:0.4000
p2yr: 1.50 s:0.2380
TcReach - Sheet L:
18.00 ns:0.4000
p2yr: 1.50 S:0.4440
TcReach - Sheet L:
52.00 ns:0.4000
p2yr: 1.50 s:0.1150
TcReach - Sheet L:
19.00 ns:0.4000
p2yr: 1.50 s:0.2000
PEAK RATE: 0.04 cfs
VOL: 0.02 Ac -ft TIME: 490 min
page 1
IMP
0.00 Acres
0.00
0.00 min
.IMP
0.00 Acres
0.00
0.00 min
IMP
0.00 Acres
0.00
0.00 min
(00 -yr
Oeu
100 -yr
EXsf
0.32
e
16
Js 14 c creacjp
4/2/10 2:3:21 pm page 1
mike Gold
Meadowdale, 75th Ave W.
BASIN SUMMARY
BASIN ID: B100D
NAME: 10OYR,
,24 HR DEVELOPOED
SBUH METHODOLOGY
--
TOTAL AREA .......
0.65 Acres
BASEFLOWS: 0.00 cfs
RAINFALL TYPE....:
TYPEIA
PERV
IMP
PRECIPITATION....:
3.00 inches
AREA..: 0.33 Acres
0.32 Acres
TIME INTERVAL....:
10.00 min
CN....: 86.00
98.00
TC..... 6.30 min
6.30 min
is ABSTRACTION COEFF:
0.20
PEAK RATE: 0.32
cf s'l VOL: 0.12
Ac --ft TIME: 480 min
BASIN ID: B10D
NAME: 10 YRT,
24HR DEVELOPED
SBUH METHODOLOGY
TOTAL AREA.......:
0.65 Acres
BASEFLOWS: 0.00 cfs
RAINFALL tYPE.... :
TYPEIA
PERV
IMP
PRECIPITATION .... :
2.50 inches
AREA..: 0.33 Acres
0.32 Acres
IME INTERVAL....:
10.00_ min
CN....: 86.00
98.00
TC.... 6.30 min
6.30 min
ABSTRACTION COEFF:
0,20
PEAK RATE: 0.25
cfs VOL: 0.09
Ac -ft TIME: 480 min
BASIN ID: B2D
NAME: 2YR, 24
HR DEVELOPED
SBUH METHODOLOGY
TOTAL AREA.......:
0.65 Acres
BASEFLOWS: 0.00 cfs
RAINFALL TYPE....:
TYPEIA
PERV
IMP
PRECIPITATION....:
1.50 .inches
AREA..: 0.33 Acres
0.32 Acres
TIME INTERVAL....:
10.00 min
CN....: 86.00
98.00
TC..... 6.30 min
6.30 min
ABSTRACTION COEFF:
0.20
PEAK RATE: 0.12
cfs VOL: 0.05
Ac -ft TIME: 480 min