Report s /7 - csovtt
RECEIVED
JUL 11 2003
CITY OF TIGAF D
• HYDROLOGY BUILDING DIVIS ON
• REPORT
B.A.P.S. TEMPLE WEST
Washington County, OR
Prepared by:
TRT Engineering, Inc.
2636 S.E. Market Street
Portland, OR 97214
(503) 235 -7592
January 3, 2001"
Revised July 10, 2003
•
•
Prepared by: Timothy R. Turner, P.E. •
PROP
�5 NE 4 i
k. .14,494 7 4 ,
O 0
G< g ����v
1
O T'S'Y 2 R R. -0T 11iul03
�� 613010+
•
EXISTING CONDITIONS AND ASSUMPTIONS
The present site slopes southerly on a 5 percent gradient. There appears to be
some offsite area from the north that contributes some runoff across the site. For
ease of comparison, this area is not included in either the pre or post-
e development hydrologic analysis. Rear lot and side lot swales will convey runoff
• from this area directly to either of the abutting street right -of -ways for
conveyance. Frontage improvements are required and these'drainage areas will
be addressed separately from the on -site areas.
•
Proposed Stormwater Management System
The stormwater quality and quantity control facility will be located in the
southwest corner of the site. This location is near the existing field inlet (at the
edge of pavement) that presently collects runoff from this site.
Runoff from the parking areas and travel lanes, roof . area, and landscaped areas
will be collected in a storm drain system with conveyance directly to a water
quality treatment swale. The outflow rates will be controlled by a standard
system of two ditch inlets. The first structure provides flow control with an orifice
(for low flows) and high flows will enter the second structure. This structure also
provides for emergency overflow capability.
•
•
•
•
•
•
•
•
•
•
I
COMPARISON OF THE EXISTING AND PROPOSED PEAK DISCHARGE
RATES TO THE OFFSITE STORM DRAIN SYSTEM
STORM ' : ' :.: ; ; > xIsnNG" : P OPt SE . RELEASE RATE
Peak Peak
r Di . Discharge (Os);
Subcat 1 Subcat 10 Pond 10 (symbol)
2 0.32 0.7 0.13
5 0.48 1.00 0.24
10 0.58 1.13 0.38
25 0.71 1.30 0.61
•
50 0.79 1.42 0.83
•
• Existing condition of "field grass" on HSG C soils
Y CN 71 from Table 2 -2c. SCS TR -55, 1986 ED. for cover type -
Meadow w /continuous grass,, protected from grazing and generally
mowed for hay. To account for weather conditions in the Northwest,
CN 86 was used for AMC III.
• Proposed condition of.Iawn and landscaping on HSG C soils
CN 74 from Table 2 -2a. SCS TR -55, 1986 ED. for cover type - Open
space (lawns, parks, golf - courses, cemeteries, etc.) - good condition is
AMC II. To account for weather conditions in the Northwest; CN 88
was used for AMC Ill. .
•
• .2
•
•
WATER QUALITY DESIGN
In general, stormwater runoff from the site is collected and conveyed to a WQ
treatment swale prior to being discharged. The swale was designed in
accordance with Unified Sewerage Agency (USA) standards for water quality
. control. The proposed swale has a total length of 106 lineal feet with a 3.5 -foot
base width and a slope of 1.5 percent. The swale was designed to provide 9
minutes of treatment for a water quality runoff of 0.26 cfs. The water quality
runoff was computed from the approximately 1.05 acres of impervious area
associated with this project. USA's water quality storm distribution has a total
precipitation of 0.36 inches with a storm duration of 4- hours. A more detailed
summary of the water quality design and analysis for each of the post - developed
sub - basins is provided below.
ON -SITE AREA
•
•
The proposed impervious area on -site, is approximately 1.05 acres. The
developed site has two separate sub - basins. A summary of the water quality
design and analysis is outlined below. Please reference the attached maps to
assist in your review.
•
Sub -Basin #10
The majority of the post - developed site, 1.60 Ac, is contained within the site
and collected in the storm drain system. During the water quality storm event,
the associated runoff (0.10 cfs) is discharged through a "low -flow' orifice into
the into the existing storm drain piping at the intersection of SW Tigard Road
and SW 115 Ave.
Determine Water Quality Flow:
QD1 - P(A) ; P = water quality precipitation (inches)
D A = impervious area (ac)
D = storm duration (hr)
QD1 0.36(1.05) ; converting units yields
4
Water Quality Flow, Qot = 0.095 cfs
The design water quality flow rate of 0.10 cfs receives approximately 9.3
• minutes of-residence time through the biofilter swale. This is in excess of the
9 minutes required by Unified Sewerage Agency (USA). Please reference
the attached WQ treatment swale calculations.
• 3
•
•
OFF -SITE AREA (STREET)
Sub -Basin # 20
Development of the project requires half -width improvements to SW Tigard
Road and SW 115 Ave. along the entire site frontage. The new impervious
area associated with the improvements is approximately 0.35 acres.
Determine Water Quality Flow:
Q = P(A) ; P = water quality precipitation (inches)
D A = impervious area (ac)
D = storm duration (hr)
Q = 0.36(0.35) ; converting units yields
4
•
Water Quality Flow, :Q = 0.03 cfs
Treatment for this surface area and WQ flow will be provided for in a standard
water quality manhole. The.25 -year flow is 0.31 cfs and does not exceed the
required sump volume limit of 20 cubic ft / 1.0 cfs flow rate.
WATER QUALITY SUMMARY
The storm drainage system for the proposed site was designed to be in
conformance with the water quality control standards set forth by the USA. The
proposed water quality treatment swale provides in excess of 9 minutes of
residence time for the required water quality flows. .
The storm drainage system for the street improvements also provides the water
quality treatment criteria of the USA.
WATER QUANTITY DESIGN
The storm drainage system for the proposed site was designed to limit the post -
development discharge rate to existing storm sewer to pre - development
discharge rates for the 2, 5, 10, 25, and 50 -year storm events. Stormwater
runoff will be detained in the control facility. Post - development discharge rates
will be control by an 1.7 -inch orifice plate installed in the facility flow control
structure.
,4
•
""' • L—I
\ 1 1
r - , .. -
209.5 x
1_ x ° - -�
r 1 v ,
Q
•
Q �� 1
_ e \ l
11 lik n (4, 9 -L _k . 0 sa p Bq 0 .. l0
C
ui i ll - (3 . : 7 . ft -----____
D 1 1 %////////0 Q ',
0 Q 5 -17,
RDPosEn , iti - � - . 4 r - we iv /.... .1,6 !J • tEvA • LL
! fl. S 1TE • D i i i' 4% 14 ' IL ---_. I ( — '\ \ ---__,,,
❑ 1 - II
•' . _ _ .190.3 S.W. 1-16/11;t0 ST
- 1:SFH Pet, ! ,.... i_ �I �� rt.** �' � + Sub -basin Map 1 Fr ] 34DC tax 1 t 7 . o p � From Map # 1 S o 00 00 Ike
ir � �� Zit '� � ' Scale: 1" =100' "`
- 13 P. __ awl, iii I Air M .H . ` - -. • ' 'f - �'-.�, -
�!' --
DETERMINE FLOW VELOCITY FOR WQ TREATMENT
Worksheet for Trapezoidal Channel :
•
• Project Description -
Project File d:lhaestadlfmw11904baps.fm2
Worksheet WQ TREATMENT SWALE
Flow Element Trapezoidal Channel
Method Manning's Formula
Solve For Channel Depth
Input Data
Mannings Coefficient 0.240
Channel Slope 0.016000 ft/ft
Left Side Slope 4.000000 H : V
Right Side Slope 2.000000 H : V
Bottom Width 3.50 ft
Discharge 0.10 cfs
•
Results - •
Depth 0.13 •' ft .
Flow Area 452 fr. -
Wetted Perimeter 4.35 ft
Top Width' 4.31 ft
•
Critical Depth 0.03 ft
Critical Slope 2.758757 ft/ft
Velocity 0.19 ft/s
Velocity Head 0.57e -3 ft
Specific Energy 0.13 ft
Froude Number 0.10
Flow is subcritical.
7r — L V ( o.i9) — 9. 3 "�ti •
‘d
•
12/22//0 • _ 'FlowMaster v5.15
02:21:31 PM Haestad Methods, Inc. 37 Brookslde Road Waterbury, CT 06708 (203) 755 -1666 Page 1 of 1',
•
Cross Section •
Cross Section for Trapezoidal Channel
Project Description
Project File d:lhaestad1fmw\1904baps.fm2
• Worksheet WQ TREATMENT SWALE
Flow Element Trapezoidal Channel
Method Manning's Formula
Solve For Channel Depth
Section Data
Mannings Coefficient 0.240
Channel Slope 0.016000 ft/ft
Depth 0.13 ft
Left Side Slope 4.000000 H : V 3. rock u,
Right Side Slope 2.000000 H : V
Bottom Width 3.50 ft S ;de siOpef
Discharge 0.10 cfs .
•
•
•
•
•
•
• Z
V7 'sr ' 0.13
•
1
3.50ft V N
H
NTS
•
12 22100 FlowMaster v5.15
10.23:17 AM • Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06700 (203) 755-1666 Page 1 of 1
•