20101019063748565.pdfCity of Edmonds
121 5"' Ave. North
Edmonds,' A 98020
6621 Foster Slough Rd. Ph: 425-334-9980
Snohomish, WA 98290 Fax: 425-334-7380
e-mail: donnabreske@corncast,net
Subject: Direct Drainage Discharge to Puget Sound
Reference: Michael & Nancy Gold, North Residence
7510 162nd ST. S.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
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 I 00 -year peak. flows.
As a result on-site detention is not proposed for the development of the site.
Sincerely,
Donna L. Breske, P.E.
VE� U 'T11/111"J" "A"
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VICINITY MAP
MIKE & NANCY GOLD., NORTH HOUSE
7510 162n d ST S. W.
EDMONDS, WA 95020
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DIRECT DRAINAGE DISCHARGE TO PUGET SOUND
MICHAEL, & NANCY GOLD — SINGLE FAMILY HOME -NOR]
7510 162 ID ST. SW, EDl' ONDS, WA 98020 o/1"
APRIL 5, 201 0, Iur�t;
The 1992 DDE Manual Minirnurn Requircrnent #r5; Strearnbank 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 strearn,
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 dernonstrated that the downstream pipe conveyance system, which outfalls to
Puget Sound, has sufficient capacity to accept the un -detained flows.
p 03KW1!_V72
Per Meadowdale Drainage Investigation prepared by R.W. Beck and dated April
2000, the pipes in Basin "D" and down to Maines Wharf have adequate capacity for full
build -out -1070 -year peals flows. The subject site lies within Basun "D" of the R.W. Beck
Report, (see attached map from the Report), Specifically, Section 3, Fuge l 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.
The site is located at 7510 162n' ST S.W. just uphill of Haines Wharf. The west
boundary of the site is approximately I00 -feet from the edge of the water of Puget Sound..
A single family horne is proposed for construction on the site. Access to the site is
currently from 162nd Ave S.W. and will continue to take access frorn the same point.
Currently, no structures exist on the site. An existing driveway bisects the site for access
to an unoccupied and uninhabitable hawse to the south. This driveway is proposed to be
removed. The house to the south is proposed to be demolished and a new access
provided from 75`' PL. W. will be used.
Michael & Nancy Gold -North House -Direct Storm Discharge
FURTHER DISCUSSION OF R.W. BECK DRAINAGE INVESTIGATION:
Per the R.W. Beck Report the flow for the 100 -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 100 -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
south, an additional 0.14 cfs for the 100 -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 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 162"d 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 -North House -Direct Storm Discharge
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O SUBBASIN DESIGNATION
SUBBASIN BOUNDARY
SLIDE BOUNDARY
500
SCALE IN FEET
FIGURE I
CITY OF EDMONDS, WASHINGTON
MEADOW13ALE DRAINAGE INVESTIGATION
STUDY AREA MAP
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FINDINGS AND RECOMMENDATIONS
from the south (Subbasin 0). 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
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.
s
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 lie 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 1591.0, 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
72"d 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 discharze to Puzet Sound in a 36 -
inch RCP. I All of these pipelines in Basin D and down to Haines Wharf have
ade� auate capacity for full build -out 100-vear weak flows.
X0017T 321 4A 710 0 R. W. Beck 3-11
1473 SF
1 7510 162nd ST. S.W.
I i 3889 SF
v
' L16220
DETENTION SYSTEMSUB-BASINBOUNDARYAREA=28,300 SF
TOTAL IMPERVIOUS AREA = 13,930 SF
0.32 AC
CN=98
TOTAL PERVIOUS AREA = 14,390 SF
0.33 AC
CN=86
2327 SF
FROM ECDC 18.30.010 DEFINITIONS
SECTIONS CC, RR, & TT
P2 = 1.5 IN PER 24 -HR
P10 = 2.5 IN PER 24 -HR
P100= 3.0 1N PER 24 -HR
DEVELOPED CONDITION -IMPERVIOUS AREA EXHIBIT
MIKE COLD PROJECTS
4-2-10
sF
DETEN770N SYSTEM„
'SUB -BASIN
BOUNDARY
AREA=27,965 SF
L -L Z
c "s
FROM ECDC 18.JD. 010 DEFINITIONS
SEC77ONS CC, RR, & TT
P2 = 1.5 IN PER 24 -HR
P10 25 IN PER 24 -HR TOTAL 4 ERWOUS AREA 27,965 SF
P1O0= 3.0 IN PER 24 -HR 0.642 AC
CN=85
TIME OF CONCENTRATION PRE-I)EVELOPEO SITE EXHIBIT
MIKE GOLD PROJECTS
4-2-10
3/15/10 1:40:10 pm
page 1
"2
Mike
Gold
Meac%owdale, 75th Ave
W.
.BASIN
SUMMARY
BASIN ID: A10OX
NAME: 10O YR
24HR EXISITNG
SBUH ME'T'HODOLOGY
TOTAL AREA.......:
0.64 Acres
BAS]EFLOWS: 0.00 cfs
RAINFALL TYPE...,:
TYPEIA
PERU
IMP
PRECIPI'T'ATION....:
3.00 inches
AREA..: 0.64 Acres
0.00 Acres
TIME IN`T'ERVAL....:
10.00 min
CN....: 85.00
0.00
TC..... 20.55 min
0.00 min
ABSTRACTION COEFF:
0.20
BEAK RATE: 0.18 cfs VOL: 0.08
Ac -ft TIME: 480 min
BASIN ID: AIOX
NAME: 10 -YR 24 HR EXISTING
SBH'H METHODOLOGY
TOTAL AREA........:
0.64 Acres
BASEFL+OWS: 0.00 cfs
r
RAINFALL TYPE....:
T'YPETA
DERV
IMP
PRECIPITATION .... :
.IME INTERVAL....:
2.50 inches
AREA..: 0.54 Acres
0.00 Acres
10.00 min
CN....: 85.00
0.00
TC....: 20.55 min
0.00 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 cads
RATNF°A,LL TYPE....
TYPEIA
DERV
IMP
PRECIPITATION....:
1.50 inches
AREA..: 0.64 Acres
0.00 Acres
TIME INTERVAL....:
10.00 min
CN....: 85.00
0.00
TC....: 20.55 min
0.00 min
ABSTRACTIONCOEFF:
'
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
"2
c
- ( i�
4/2/10 2:3:21 pm
Meadowdale, 75th Ave W.
Mike Gold
BASIN SUMMARY
page 1
BASIN ID: B100D
NAME: IOOYR,
R4 HR DEVELOPOED
SBUH METHODOLOGY
-
TOTAL AREA.......:
0.65 Acres
BASEFLOWS: 0.00 cfs
RAINFALL TYPE....:
TYPE1A
PERU
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
ABSTRACTION COEFF:
0.20
PEAK RATE: 0.32
cfs 7 VOL: 0.12
Ac -ft TIME': 480 min
BASIN TD; B10D
NAME: 10 YRT,
24HR DEVELOPED
SBUH METHODOLOGY
TOTAL AREA........
0.65 Acres
BASEFLOWS: 0.00 cfs
RAINFALL tYPE .... :
TYPEIA
PERV
IMP
PRECEPITATION....:
2.50 inches
AREA..; 0.3,3 Acres
0.32 Acres
Ilk
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
PERU
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: 430 min