Correspondence Nov 14 2007 9:05AM Harker Engineering, Inc. 3006992206 p.2
i
HARKER ENGINEERING INC. (360) 699 -2206
1403 Washington Vancouver, WA 98660
November 13, 2007 COPY
E1 E.
Project Coordinator
City of Tigard � �� , J t�
13125 SW Hall Blvd. V ax` � 0
Tigard Oregon 97223 ',11 2710 (o
Re Nelson Vial Site
Mans
This letter is to confirm that the construction of the bioswale at the Nelson Vial site on Varns
Road is in compliance with the general design and specifications approved by the City of Tigard.
I have observed the construction and have measured the final swale for grade and dimensions.
The swale is constructed with a slope of 1.2% ( 0.5% design). The constructed swale will provide
a residence time of 21 minutes where a residence time of 9 minutes minimum is required.
Attached are the calculations for the as built swale and the landscape plan for the upland area.
The facility does not have a Stormwater management product so no maintenance agreement will
be needed.
If you have any questions, please call me or email me at norm( aharkerengineering.com.
Sincerely ,
No an H. i er P.E.
1
Nov 14 2007 9:05AM Harker Engineering, Inc. 3606992206 p.3
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MAN -MADE CHANNELS
VARIABLES LIST:
Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE
Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS
VARIABLE TO BE SOLVED (Y,Q,B,M,S OR N) ? Y
Q (CFS) ? .005 RESULTS
B (FT) ? 2
M (FT /FT) ? 3 Y= 0.03 FT
S (FT /FT) ? .012 A= 0.06 SF
N (FT "1/6) ? .24 P= 2.19 FT
V= 0.08 FPS
F= 0.08 SUB- CRITICAL FLOW
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PROPOSED i
BUILDING fu
P'setaining Wall 1
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Water Quality Swale z u) 2 (II
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„.* 4 * * 3 of Incence Cedar ‘i et 3
1 (6) Ill > 0
— ne crIt
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25 Mix Dwarf Rhodo 6 (., g
J apanese Maple
to n
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t3ottom of the Swale: CO • IV 6 of Vine Maple
River Rock (2'-3/4") ir '
, cn
Placed on top of Jute Mat - 40 --i--- f 11 I DRMIN fly` 0
CO • ( t? Lb, HOA PHAM cn
CD
105 of Mexican Feather I Gal. Grass --7--.. A PLEV. LIAM CO
and 500 plugs of Slough Sedge Nov. 13 2007 IN)
Planted at the bottom of the Swale • cb, ' IV
MEET 17116 0
Seed Mix as per specs (CWS) water QUAXY Swain
------- Landzawe Plan
placed on the Freeboard Area — D -IL AS MR
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TO
3
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43 NORTH .
P.O.
Property Line (.5 S- 00
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MEV I1
Private Road scale:1/16= V-0" Al
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