bld20131338-Jacobsens Marine-storm capacity.pdfJanuary 3, 2014
File No. 242014.913.001
Mr. Robert McChesney
Port of Edmonds
336 Admiral Way
Edmonds, WA 98020
Subject: Storm Line Capacity Analysis Downstream of Jacobsen's Marine
Dear Mr. McChesney:
Jacobsen's Marine is planning a new facility at the Port of Edmonds (Port). The facility
will be located on the east side of Admiral Way adjacent to the Port's boatyard and
across the street from the Yacht Club. Stormwater from Jacobsen's facility will be
collected and discharged into an existing catch basin (CB) on the east side of Admiral
Way adjacent to the Port's boatyard. The Port has requested an analysis of the capacity
of the stormwater piping system downstream from the point of connection of Jacobsen's
stormwater discharge. This letter provides a summary of the stormwater system
capacity analysis.
The stormwater system that the Jacobsen stormwater will connect to consists of the
following:
• A CB and 12 -inch HDPE line from the Port's boatyard to the CB on the east side
of Admiral Way. This CB in Admiral Way is designated as CB#4 in the
calculations.
• Two 8 -inch ductile iron pipes from CB#4 running under Admiral Way to CB#3
on the west side of the roadway.
• A 12 -inch ductile iron pipe from CB#3 to CB#2 in the parking area north of the
Port Administration Building.
• A 12 -inch ductile iron pipe from CB#2 to CB#1 in the parking area north of the
Port Administration Building near the office entrance.
• A 12 -inch PVC pipe from CB#1 to an outfall discharging to the marina and
Puget Sound.
ti
Mr. Robert McChesney
Port of Edmonds
January 3, 2014
File No. 242014.913.001
Page 2
Because the stormwater piping system will discharge directly to Puget Sound,
stormwater detention is not required as long as the piping system has adequate capacity
to discharge the runoff through the outfall. Per the Stormwater Code Supplement to
Edmonds Community Development Code Chapter 18.30, an analysis of the capacity of
the storm drainage line to convey the 50 -year storm event was conducted.
The tributary areas for the storm drainage lines in the analysis included the Jacobsen's
site, the Port's boatyard, a 400 -foot section of Admiral Way, the Port Administration
office, and the parking area between the Port Administration office and the Yacht Club.
This tributary area is approximately 2.83 acres. Similar to the analysis for the on-site
Jacobsen's stormwater analysis, the SBUH method was used to calculate the peak
stormwater flow from the tributary areas, and the Manning Equation was used to
calculate the capacity of the existing pipe system (see attached calculations).
Based on the analysis, the existing stormwater drainage piping system has sufficient
capacity to convey the 50 -year storm to the outfall for discharge into the marina;
therefore, no detention facilities for the stormwater from Jacobsen's facility and no
modification of the existing piping system should be required.
If you have any questions or comments please call me.
Sincerely,
Reid Middleton, Inc.
W
Shannon Kinsella, P.E.
Principal
Attachments
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Port of Edmonds Jacobsen's Marine and Downstream Basins Event
1/3/2014
Summary:
Precipitation:
P2 = 1.5 in
P25=2.5in
Pyo = 2.7 in
P100 = 3.0 in
BasinlD
Peak Q
Peak T
Area
Method
Raintype
Event
0.20
(cfs)
(hrs)
ac
/Loss
Area
CN
CB 4 to CB 3 (Eastside & East Admiral)
1.23
8.00
2.08
SBUH/SCS
TYPE1A
25 yr
CB 4 to CB 3 (Eastside & East Admiral)
1.33
8.00
2.08
SBUH/SCS
TYPE1A
50 yr
CB 4 to CB 3 (Eastside & East Admiral)
1.49
8.00
2.08
SBUH/SCS
TYPE1A
100 yr
CB 3 to CB 2 (Eastside & All Admiral)
1.39
8.00
2.08+0.28
SBUH/SCS
TYPE1A
25 yr
CB 3 to CB 2 (Eastside & All Admiral)
1.51
8.00
2.08+0.28
SBUH/SCS
TYPE1A
50 yr
CB 3 to CB 2 (Eastside & All Admiral)
1.69
8.00
2.08+0.28
SBUH/SCS
TYPEIA
100 yr
CB 2 to CB 1 (Eastside, Admiral, prkng)
1.60
8.00
2.36+0.36
SBUH/SCS
TYPEIA
25 yr
CB 2 to CB 1 (Eastside, Admiral, prkng)
1.74
8.00
2.36+0.36
SBUH/SCS
TYPE1A
50 yr
CB 2 to CB 1 (Eastside, Admiral, prkng)
1.94
8.00
2.36+0.36
SBUH/SCS
TYPEIA
100 yr
CB 1 to outfall (Eastside, Admiral, prkng)
1.67
8.00
2.72+0.11
SBUH/SCS
TYPEIA
25 yr
CB 1 to ouffall (Eastside, Admiral, prkng)
1.81
8.00
2.72+0.11
SBUH/SCS
TYPEIA
50 yr
CB 1 to ouffall (Eastside, Admiral, prkng)
2.02
8.00
2.72+0.11
SBUH/SCS
TYPEIA
100 yr
Drainage Area: Jacobsen's Marine and Downstream Basins
Hyd Method: SBUH Hyd
Loss Method;:
SCS CN Number
Peak Factor: 484.00
SCS Abs:
0.20
Storm Dur: 24.00 hrs
Intv:
10.00 min
Area
CN
TC
Pervious 2.83 ac
98.00
0.08 hrs
Impervious 0.00 ac
Total 2.83 ac
Supporting Data:
Pervious CN Data:
Landscape
90.00
0.0000 ac
Impervious CN Data:
Pavement
98.00
2.8300 ac
Impervious TC Data:
Flow type: Description:
Length:
Slope: Coeff: Travel Time
Sheet Pavement
200.00 ft
2.00% 0.0110 3.08 min