Report 1 C
•
DESIGN, INC. v ' >
DBE / WBE FIRM
Final Drainage Report
for
Spectrum /SW 67 Avenue
Tigard, Oregon
Prepared for:
Spectrum Development
Attn: Kurt Dalbey
25115 SW Parkway Ave
Bldg. A, Suite C
Wilsonville, OR 97070
Prepared By:
DL Design, Inc.
9045 SW Barbur Blvd., Suite 101
Portland, Oregon 97219
. PROp
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I EXPIRES 12 -31 -2004 I
December 26, 2003
BIS11
9045 SW Barbur Boulevard, Suite 101 0 Portland, Oregon 97219 ♦ Phone: 503.225.1679 0 Fax: 503.525.9266
PROJECT OVERVIEW
The 0.15 -acre commercial development is located at 12705 SW 67 Avenue in Tigard.
The site can be found in tax map 25101AD and has a tax lot number 1000 (See Figure 1).
EXISTING CONDITIONS
The site has a topographic gradient to the west with an average slope of 1.5 %. A map of
the existing property is provided in Figure 2.
The site is currently has approximately 3,448 sq. ft of impervious surface that includes a
house, a garage, asphalt pavement. Runoff on this site is currently draining to west of the
property.
The Soil Survey of Washington County identifies the site soil as Woodburn silt loam and
is classified as Hydrologic Soil Group C. The soil has slow permeability, the Woodburn
silt is moderately well drained. The runoff for the soil is described as being slow, and the
hazard for erosion is slight. Soil information from the Soil Survey is contained in
Appendix B.
PROPOSED DRAINAGE
Stormwater runoff for the development will be managed as described below. Figure 3 is
included for reference, which shows the proposed storm system improvements, as well as
the development's building, parking and landscaped area.
• Roof runoff from the roof will be conveyed by a storm lateral and connected to the
catch basin storm filter.
• Runoff from the parking lot will be collected and treated by catch basin storm filter at
the low point prior to discharging into the existing 24 -inch storm main in SW 67
Avenue.
HYDROLOGIC ANALYSIS
Hydrologic analyses for the site have been completed according to the Santa Barbara Unit
Hydrograph (SBUH) method, with modeling by the WaterWorks computer program. This
program enables the user to develop runoff hydrographs. Analysis calculations,
supporting information, and computer output are contained in Appendix A.
Impervious and Pervious Surface Areas
The site covers 0.15 acre. The impervious and pervious areas for the pre - development
were estimated from field visit. For the post development actual roof, pavement, and
landscaped areas were used. The areas used for the analyses are summarized in Table 1.
The net increase of new impervious area is approximately 2500 sq. ft. and is less than
5,000 sq. ft., therefore detention is not required (per City of Tigard).
Preliminary Drainage Report DAK01
Dakar Car Lot Page 1 06/21/03
Curve Numbers
Curve numbers used for the analyses are based on characterization of the site's soils as
primarily Type C soils (as described above). The curve numbers represent values
appropriate for wet antecedent moisture conditions, which is typical of the wet - weather
conditions for the area. Curve numbers of 80 and 98 were used for pervious and
impervious, respectively.
Time of Concentration
The pre -and post- development times of concentrations are summarized below.
Calculations are presented in Appendix A.
Impervious and Pervious Areas
Existing Site Developed Site
Area Description Area (acre) CN Area (acre) CN
Pervious Surface 0.07 80 0.01 80
Impervious Surface 0.08 98 0.14 98
Time of Concentration 5 minutes 5 minutes
•
• WATER QUALITY
Design Criteria and Treatment Flow
Runoff from the development will be treated in the catch basin stormfilter onsite. In
accordance with the requirements of Cleanwater Services, the peak treatment flow is
generated from 100% runoff from a basin's impervious area for 0.36 inches of rain falling
in a 4 -hour period. To simplify water quality design, all impervious areas were used to
size the catch basin stormfilter. One cartridge can treat up to 0.033 cfs and this site has a
flow of 0.0011 cfs therefore one cartridge is more than adequate.
Analysis Parameter Value
Precipitation 0.36 inches
Duration 4 hours
Impervious Area 0.14 acres
Water Quality Volume 183 cf
Water Quality Flow 0.0011 cfs
Preliminary Drainage Report DAK01
Dakar Car Lot Page 2 06/21/03
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/I I PRIOR TO CONNECTING
TO EX. STORM MAIN & ORDERING,
CATCH BASIN 5FORMFILTER,
/ \ CONTRACTOR MALI VERIFY
SW 67TH AVE. SCALE 1 ■10' EX. SO SIZE AND IE nry C3.2
/ (CONNECT WITH #NSERTA TEE)
/) !0 52.50 f0
S EX. 24" SD MAIN(PUBLIC) SD 7 SD SD SD
0 SD SD-
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MIN. S -0.01
S EX. SAN. MAIN SS SS ! SS . SS SS
1170 SS SS --
~ „ EX. 12" WATER (TVWD)
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COUPLING EXTEND CATCH BASIN STORM FILTER A m
4 III S 0.02(M1 RIM 253.81
# U IE 250.51 10" OUT (E) { = _ -- IE 251.81 4" IN (W) NIPT
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BL SETBACK EASEMENT - 1 I . : 11 CONNECT & EXTEND
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Appendix A
Calculations & Supporting Information
12/29/03 3:53:35 pm Shareware Release page 1
BASIN SUMMARY
BASIN ID: lopre NAME: 10 -yr pre
SCS METHODOLOGY
TOTAL AREA • 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE TYPE2 PERV IMP
PRECIPITATION • 3.45 inches AREA..: 0.15 Acres 0.00 Acres
TIME INTERVAL 10.00 min CN • 86.00 0.00
TC • 5.00 min 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.41 cfs VOL: 0.02 Ac -ft TIME: 730 min
BASIN ID: lOpst NAME: 10 -yr pst
SCS METHODOLOGY
TOTAL AREA 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE TYPE2 PERV IMP
PRECIPITATION 3.45 inches AREA..: 0.01 Acres 0.14 Acres
TIME INTERVAL " 10.00 min CN 86.00 98.00
TC 5.00 min 5.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.55 cfs VOL: 0.04 Ac -ft .TIME: 730 min
BASIN ID: 25pre NAME: 25 -yr pre
SCS METHODOLOGY
TOTAL AREA 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE • TYPE2 PERV IMP
PRECIPITATION 3.90 inches AREA..: 0.15 Acres 0.00 Acres
TIME INTERVAL 10.00 min CN 86.00 0.00
TC 5.00 min 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.48 cfs VOL: 0.03 Ac -ft TIME: 730 min
BASIN ID: 25pst NAME: 25 -yr pst
SCS METHODOLOGY
TOTAL AREA 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE TYPE2 PERV IMP
PRECIPITATION • 3.90 inches AREA..: 0.01 Acres 0.14 Acres
TIME INTERVAL 10.00 min CN • 86.00 98.00
TC 5.00 min 5.00 min
ABSTRACTION COEFF: 0.20
---,PEAK RATE: 0.62 cfs VOL: 0.04 Ac -ft TIME: 730 min
12/29/03 3:53:35 pm Shareware Release page 2
BASIN SUMMARY
BASIN ID: 2pre NAME: 2 -yr pre
SCS METHODOLOGY
TOTAL AREA • 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE • TYPE2 PERV IMP
PRECIPITATION 2.50 inches AREA..: 0.15 Acres 0.00 Acres
TIME INTERVAL 10.00 min CN • 86.00 0.00
TC 5.00 min 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.25 cfs VOL: 0.01 Ac -ft TIME: 730 min
BASIN ID: 2pst NAME: 2 -yr pst
SCS. METHODOLOGY
TOTAL AREA 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE TYPE2 PERV IMP
PRECIPITATION 2.50 inches AREA..: . 0.01 Acres 0.14 Acres
TIME INTERVAL • 10.00 min CN • 86.00 98.00
TC 5.00 min 5.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.39 cfs VOL: 0.03 Ac -ft TIME: 730 min
BASIN ID: 5pre NAME: 5 -yr pre
SCS METHODOLOGY
TOTAL AREA 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE TYPE2 PERV IMP
PRECIPITATION 3.10 inches AREA..: 0.15 Acres 0.00 Acres
TIME INTERVAL 10.00 min CN 86.00 0.00
TC 5.00 min 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.35 cfs VOL: 0.02 Ac -ft TIME: 730 min
BASIN ID: 5pst NAME: 5 -yr pst
SCS METHODOLOGY
TOTAL AREA • 0.15 Acres BASEFLOWS: 0.00 cfs
RAINFALL TYPE TYPE2 PERV IMP
PRECIPITATION 3.10 inches AREA..: 0.01 Acres 0.14 Acres
TIME INTERVAL 10.00 min CN 86.00 98.00
TC • 5.00 min 5.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.49 cfs VOL: 0.03 Ac -ft TIME: 730 min
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Appendix B
Soils Information
•
•
48 SOIL SURVEY
medium acid (pH 5.6)..; gradual, smooth Aloha, Amity, Willamette, Helvetia, and Dayton soils, r`
boundary. 0 to 7 inches thick. which occupy as much as 15 percent of this mapping
B21t -16 to 26 inches, dark -brown (10YR 4/3) unit. i.
silty clay loam, light yellowish brown Runoff is slow, and the hazard of erosion is 21101. _+
(10YR 6/4) dry; moderate, fine, and C a i i y un rfIe -2; wildlife group 2.
very fine, . subangular blocky structure; 45C— Woodburn silt loam, 7 to 12 percent slopes.
hard, firm, slightly sticky and plastic; This soil is moderately sloping.
many fine roots ; many, very fine, tubular. . Included with this soil in mapping were areas of ;
pores ; thick clay films on peds and in Aloha, Amity, Willamette, Helvetia, and Dayton soils,
pores; medium acid (pH 5.8) ; clear, which .occupy as much as 15 percent of this mapping i
smooth boundary. 7 to 10 inches thick. unit.
B22t -26 to 31 inches, dark -brown (10YR 4/3) Runoff is medium, and the hazard of erosion is mod -
silty clay loam, pale brown. (10YR 6/3) erate. Capability unit IIe-2; wildlife group 2.
dry ; common fine, distinct, dark grayish- 45D— Woodburn silt loam, 12 to 20 percent slopes.
brown (10YR 4/2) and grayish -brown This moderately steep soil is along terrace escarp -
(2.5YR 5/2) mottles; weak, medium, ments.
and fine, subangular blocky structure; Included with this soil in mapping were areas of
hard; firm; . slightly sticky and plastic; Aloha, Amity, Willamette, Helvetia, and Dayton soils,
few fine roots; many, fine and very fine, which occupy as much as 15 percent of this mapping
tubular pores ; common thick clay films unit.
in pores and on peds ; few, fine, black Runoff is medium, and the hazard of erosion is mod-
manganese stains ; medium acid (pH erate. Capability unit IIIe -5 ; wildlife group 2.
6.0) ; gradual, smooth boundary. 4 to 10
inches thick. Xerochrepts and Haploxerolls, very steep
B3 - to 41 inches, dark grayish -brown (10YR
4/3) silty clay loam, pale brown (10YR 46F— Xerochrepts and Haploxerolls very steep. This
6/3) dry; common, fine, distinct, dark undifferentiated group is about 45 percent Xerochrepts
grayish -brown (10YR 4/2) and grayish- and about 45 percent Haploxerolls. It occurs as steep
brown (2.5YR 5/2) mottles; weak, me- to - very steep escarpments along the small streams that
dium and fine, subangular blocky have cut deeply into the valley terraces and where the
structure;, hard, firm, slightly sticky and terraces meet the bottom lands and flood plains along
slightly plastic; few fine and medium . major streams and rivers. These soils are well drained,
roots; common, fine and very fine, tubular They formed in a mixture of silt, sand, and an accumu-
pores ; few thick clay films in larger lation of material that has moved downslope. The short
pores; medium acid (pH 6.0) ; gradual, slopes range from 20 to 60 percent. Elevation is 50 to
smooth boundary. 0 to 12 inches thick. 450 feet. 'Vegetation is Douglas -fir, Oregon white oak,
C-41 to 60 inches, dark grayish -brown (10YR shrubs, forbs, and grasses. The average annual precipi-
4/2) silt loam, light brownish gray tation is 40 to 60 inches, average annual air tempera-
(10YR 6/2) dry; many, distinct, grayish- ture is 50° to 54° F, and the frost -free period is 165
brown (2.5YR 5/2) dark grayish -brown to 210 days.
(10YR 4/3) and dark yellowish -brown Included in mapping were areas of Hillsboro,
(10YR- 4/4) mottles; .massive, hard, Quatama,' Willamette, and Woodburn soils, which .
firm, slightly sticky and slightly plastic; make up' as much as 15 percent of this mapping unit.
few fine roots ; very few, fine, tubular Small seep spots and wet- season springs are also in
pores ; medium acid (pH 6.0) . eluded.
The A horizon has moist value of 2 or 3, chroma of Permeability is moderate to moderately slow. Avail-
2 or 3, and hue of 10YR. Dry value is 4 or 5, and chroma able water capacity is 10 to 12 inches. Water- supplying
is 2 or 3. Between depths of 10 and 20 inches, moist capacity is 22 to 26 inches. Effective rooting depth is
value and chroma range to 4. Distinct mottles are more than 60 inches.
within a depth of 30 inches. The B2 horizon ranges Runoff is rapid, and the hazard of erosion is severe.
from heavy silt loam to silty clay loam. Horizons below These soils are used for pasture, recreation, home -
a depth of 30 inches are firm to very firm and are brit- sites, and wildlife habitat. Capability unit VIe ; wild-
tle. The solum is slightly acid to medium acid. life group 2.
45A— Woodburn silt loam, 0 to 3 percent slopes.
This nearly level soil has the profile described as repre- Xerochrepts - Rock outcrop complex
sentative of the series.
Included with this soil in mapping were areas of 47D— Xerochrepts•Rock outcrop complex. This com-
Aloha, Amity, Willamette, Helvetia, and Dayton soils, plex is about 50 percent Xerochrepts and 30 percent
which occupy as much as 15 percent of this mapping Rock outcrop. It occurs in •irregularly shaped areas
unit. southeast of Sherwood and is composed of shallow and
Runoff is slow, and the hazard of erosion is slight. very shallow soils and barren exposures of basalt bed -
Ca ility unit IIw -1; wildlife group 2. rock. Slope is 5 to 30 percent. The Xerochrepts formed
45 Woodburn silt loam, 3 to 7 percent slopes. in a mixture of silt and sand too variable to map. Vege-
This soil is gently sloping. tation is low shrubs, Oregon white oak, Douglas -fir,
Included with this soil in mapping were areas of grasses, and forbs. The average annual precipitation is
is {;
S OIL SURVEY
122 ;��•�
TABLE 13. - Soil ands
how
Flooding
Hydro- it
Soil name and logic &i.
map ..
symbol p group Frequency Duration Months ij'y
��.
Klickitat:
25E, 25F, 25G B None .4,
2 '
Knappa:
Al
26 a. B None - - -- -- -- - - -- -- K
:b
Labish
27 D Frequent Very long Dec -Apr ____________ __ ,n
Laurelwood
28B, 28C, 28D, 28E, 29E, 29F B None
# :j
McBee
30 B Frequent Brief Nov -May
Melbourne: ) '1
3113, 310, 31D, 31E, 31F B None , i
Melby:
32C, 32D, 32E, 33E, 33F, 33G C None
Olyic:
34C, 34D, 34E, 35E, 35F, 35G B None
Pervina:
360, 360, 36E, 36F C None
Quatama :
37A, 37B, 370, 37D C None
Saum:
38B, 38C, 38D, 38E, 38F C None
Tolke:
39E, 39F B None
U difluvents :
40 B • Frequent Very brief Nov -Apr
Verboort:
42 D • Frequent Brief Dec -Apr
Wapato:
43 D Frequent Brief Dec -Apr
Willamette:
44A, 4413,44C, 44D B None
> Woodbur
45A, 5, 450, 45D 11_ j None
Xerochrepts:
' 46F:
Xerochrepts part B None
Haploxerolls part C None
'47D:
Xerochrepts part D None
Rock outcrop part.
' This mapping unit is made up of two or more dominant kinds of soil. See mapping unit description for the composition and
behavior of the whole mapping unit.
,' WASHINGTON COUNTY, OREGON 123 ,
■
' ter f eatur es—Continued
5 High water table Bedrock
1 `.
.1I ;' ! . - Depth Kind Months Depth Hardness
a
4 Ft In
i li >6.0 ----------------------------------------- __ 40 -50 Hard.
iy; >6.0 >60
d (
4'; 0 -1.0 Perched Dec —Apr >60
�,:,`, >6.0 -------=-------- - - - - -- >60
' 2.0 -3.0 Apparent Nov —Apr >60
,? 6.0 > 60
>6.0 40 -60 Rippable.
'' 40 -60 Hard.
>6.0
i , ` >6.0 >60 Rippable.
2.0 -3.0 Perched Dec —Apr >60 --
tt
1 X 6.0
40 -60 Hard.
Al
>6.0
X 60
>60
0 -6.0 Apparent Nov —Apr
di!' 0 -2.0 Perched Dec -Apr >60
0 - 1.0 Apparent Dec —Apr >60
>6.0 >60
2.0 -3.0 Perched Dec —Apr >60
3.0 -4.0 Perched Dec —Apr >60
3.0 -4.0 Perched Dec —Mar >60
6.0 0 -15 Hard.