Specifications a
r OFFICE COPY
CONSULTING ENGINEERS
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CS A
ENGINEERING EXCELLENCE R EC E V L D
I � b � O0 a- M5 JUN 2Z 2004
"1 CITY OF TIGARD
BUILDING DIVISION
STORM DRAINAGE CALCULATIONS
FOR
"BEVELAND OFFICE BUILDING"
CITY OF TIGARD, OREGON
City of Tigard
Approved Plans
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FOR
ZIMMLER DEVELOPMENT, LLC
7165 SE FIR LOOP, SUI'1`.b 100
TIGARD, OR 97223
CSA JOB# 04 -299
June 16, 2004
321 S.W. 4th, 4th Floor • Portland, Oregon 97204
(503) 228 -3848 E -mail: csa @integraonline.com FAX (503) 228 -0475
PURPOSE:
This report analyzes the surface water runoff from the proposed 0.83 AC commercial development
"BEVLAND OFFICE BUILDINGS ". This report includes hydrology calculations to determine water
quality storm requirements and detention system sizing as well as the peak stormwater runoff quantities
for hydraulic calculations to determine the capacity for the proposed storm drainage facilities.
SITE DESCRIPTION:
The site is located at 7155 & 7115 SW Bevland St., in Tigard, Oregon. The proposed site area is has
approximately 0.62 acres of pervious and 0.21 acres of impervious area existing. The site slopes
downward approximately 2 -5% in the westerly direction. The lot currently contains two single - family
home sites. The existing site drains via sheet flow to the northwest into the storm drainage -way located
along the northern portion of the property.
DESIGN PARAMETERS:
The SCS Type IA rainfall distribution, 24 -hour storm duration method for runoff parameters and the
Santa Barbara Urban Hydrograph (SBUH) method are being used to extract the peak runoff rates. The
Soil Survey of Washington County, August 2002, published by the Soil Conservation Service, was used
to determine the soil type. The site is comprised of various soil types; 1, Aloha silt loam, within
hydrologic group "C" and 45B, Woodburn, 3 to 7 % slopes, within hydrologic group "C ". Hydrologic
group "C" was utilized throughout the development. The rainfall intensities were provided by Clean
Water Services as follows:
Event Water Quality 2 -year 10- year 25 -year 100 -year
Intensity 0.36" 2.50" 3.45" 3.90" 4.50"
Duration 4 hrs 24 hrs 24 hrs 24 hrs 24 hrs
For the developed site, a curve number (CN) of 86 for pervious surfaces and a CN of 98 for impervious
surfaces was used. The undeveloped time of concentration for the site was determined to be 12.9' and the
developed time of concentration was determined to be less than 5 minutes, therefore a time of
concentration for the developed site of 5 minutes was used as a minimum for calculations.
SITE DESIGN:
The proposed additional impervious area is approximately 0.34 AC. The proposed stormwater water
quality will be provided by a Stormwater Management's StormFilter Manhole located at the connection
point to the public facility within the driveway area. All of the storm water conveyance system and the
detention system were designed per Clean Water Services standards for a 25 -year storm event. The entire
storm sewer system will be private with the property owner responsible for all maintenance.
WATER QUALITY DESIGN:
The site is designed utilizing a Stormwater Management proprietary system to provide the required
treatment. This resulted in the following design criteria:
® Pre- developed Runoff =0.03 cfs (SCS Type 1A)
® Post- developed Runoff= 0.11 cfs (SCS Type 1A)
• Water Quality Flow = 0.08 cf. (Post - Pre)
® Number of Cartridges = 3 (WQF x 449/15)
A sumped water quality /flow restriction manhole is provided immediately upstream from the water
quality facility.
CFA Consulting Engineers CLE 08:35 16- Jun -04
Project 04 -299
BEVLAND OFFICE BUILDING
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
PRE DEVELOPED FLOWS
2 -year, 24 -hour rainfall = 2.50"
flow type description coeff. distance fall slope T/C
1 overland sheet short grass,lawns n =0.15 100.0 2.0' 2.00% 11.1'
2 shallow concentrated short grass, lawns K =11 170.0 3.4' 2.00% 1.8'
total Time of Concentration = 12.9'
storm hyetograph: SCS TypelA
return period = 1 year
storm duration = 4 hr.
total rainfall = 0.36 in.
pervious area = 0.62 A CN = 86 Gp C:landscp,good cond.
impervious area = 0.21 A CN = 98
total site area = 0.83 A
hydrograph file: j:\ civil \_proje -1 \04- 299 \storm \wq- pre.hyd
peak flow = 0.03 cfs @ 1.39 hr.
runoff volume = 147 cu.ft.
CFA Consulting Engineers CLE 09:14 16- Jun -04
Project 04 - 299
BEVLAND OFFICE BUILDING
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
POST DEVELOPED FLOWS
total Time of Concentration = 5.0'
storm hyetograph: SCS TypelA
return period = 1 year
storm duration = 4 hr.
total rainfall = 0.36 in.
pervious area = 0.13 A CN = 86 Gp C:landscp,good cond.
impervious area = 0.55 A CN = 98
total site area = 0.68 A
hydrograph file: j:\civil\_proje-1\04-299\storm\wg
peak flow = 0.11 cfs @ 1.33 hr.
runoff volume = 388 cu.ft.
•
STORMWATER CALCULATION DATA
FOR ON -SITE SYSTEM DESIGN
CFA Consulting Engineers CLE 14:01 16- Jun -04
Project 04 -299
BEVLAND OFFICE BUILDING
GRAVIY PIPE FLOW (Chezy- Manning)
OUTLET PIPE
2"
diameter = 12.0"
slope = 0.2%
material: ABS, PVC
Manning's n = 0.011
depth of flow = 41.00%
wetted perimeter = 1.39'
area = 0.30 s.f.
hydraulic radius = 0.22'
velocity = 2.14 fps
flow = 0.65 cfs
STORMWATER CALCULATION DATA
FOR DETENTION SYSTEM DESIGN
CFA Consulting Engineers CLE 08:34. 16- Jun -04
Project 04 -299
BEVLAND OFFICE BUILDING
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
PRE DEVELOPED FLOWS
2 -year, 24 -hour rainfall = 2.50"
flow type description coeff. distance fall slope TIC
1 overland sheet short grass,lawns n =0.15 100.0 2.0' 2.00% 11.1'
2 shallow concentrated short grass, lawns K =11 170.0 3.4' 2.00% 1.8'
total Time of Concentration = 12.9'
storm hyetograph: SCS TypelA
return period = 25 years
storm duration = 24 hr.
total rainfall = 3.90 in.
pervious area = 0.62 A CN = 86 Gp C:landscp,good cond.
impervious area = 0.21 A CN = 98
total site area = 0.83 A
hydrograph file: j: \civil \_proje -1 \04- 299 \storm \25yr - pre.hyd
peak flow = 0.55 cfs @ 8.00 hr.
runoff volume = 8,319 cu.ft.
CFA Consulting Engineers CLE 09:13 16- Jun -04
Project 04 - 299
BEVLAND OFFICE BUILDING
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
POST DEVELOPED FLOWS
total Time of Concentration = 5.0'
storm hyetograph: SCS TypelA
return period = 25 years
storm duration = 24 hr.
total rainfall = 3.90 in.
pervious area = 0.13 A CN = 86 Gp C:landscp,good cond.
impervious area = 0.55 A CN = 98
total site area = 0.68 A
hydrograph file: j:\ civil \_proje ' 1\04 - 299 \storm \25yr - pos.hyd
peak flow = 0.65 cfs @ 7.83 hr.
runoff volume = 8,477 cu.ft.
CFA Consulting Engineers CLE 09:42 16- Jun -04
Project 04 -299
BEVLAND OFFICE BUILDING
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
BYPASS POST DEVELOPED FLOWS
total Time of Concentration = 5.0'
storm hyetograph: SCS TypelA
return period = 25 years
storm duration = 24 hr.
total rainfall = 3.90 in.
pervious area = 0.15 A CN = 90 Gp C:landscp,fair cond.
impervious area = 0.00 A CN = 98
total site area = 0.15 A
hydrograph file: j:\ civil \proje =1 \04 - 299 \storm \25yr- byp.hyd
peak flow = 0.12 cfs @ 7.83 hr.
runoff volume = 1,538 cu.ft.
CFA Consulting Engineers CLE 09:45 16- Jun -04
Project 04 -299
BEVLAND OFFICE BUILDING
DETENTION ROUTING
DETENTION TUBE
flow (cfs)
0.8
0.6
0.4
0.2
0.0
0 5 10 15 20 25 30
time (hr)
DETENTION TUBE (stage - volume calculated)
diameter = 2.00'; length = 95.70'; slope = 0.19%; invert = 231.81'MSL
STAGE VOLUME
231.8 0
232.2 33
232.5 88
232.9 150
233.3 213
233.6 268
234.0 301
OUTLET TYPE ELEVATION SIZE
circ. orifice 231.8 dia.(in) = 3.75
inflow hydrograph: j: \civil \_proje =1\04- 299 \storm \25yr - pos.hyd
outflow hydrograph: j:\civil\_proje-1\04-299\storm\25yr-det.hyd
peaks: inflow = 0.65 cfs @ 7.83 hr.
outflow = 0.43 cfs @ 8.33 hr.
stage: 1.67 ft. volume: 245 c.f.