Specifications , 5
LANPACIFIC
RECEIVED Clvii En9ineoi!ng
JUL 4 2006 Landscape Architeclure
CITY OF TIGARD land Use Planning
BUILDING DIVISION
STORM DRAINAGE REPORT
July 12, 2006
Dartmouth Square
Commercial Development
City of Tigard, Oregon
Prepared For:
Myrhe Group Architects
77 10 - Portland, Oregon 97214
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EXPIRES: I t 31 -61
Prepared By:
LanPacific
Eastbank Commerce Center
1001 SE Water Ave., Suite 360
Portland, OR 97214
Tel: 503 - 238 -2097
Project# MGA05 -008
TABLE OF CONTENTS
VICINITY MAP 1
GENERAL SITE INFORMATION 1
A. SITE DESCRIPTION 1
B. PROJECT DESCRIPTION 1
C. CLIMATE 1
D. SITE GEOLOGY 1
PRE - DEVELOPED CONDITIONS 2
A. TOPOGRAPHY 2
B. HYDROLOGIC ANALYSIS 2
C. HYDRAULIC ANALYSIS 2
POST - DEVELOPED CONDITIONS 3
A. TOPOGRAPHY 3
B. HYDROLOGIC ANALYSIS 3
C. HYDRAULIC ANALYSIS 3
WATER QUALITY 4
Water Quality GuidelineslCalculations 4
WATER QUANTITY 5
SUMMARY 5
TECHNICAL APPENDIX 6
Time of Concentration Equations 6
REFERENCES 7
Stormwater Management Maintenance Information In Back
LIST OF FIGURES
Figure 1 - Vicinity Map 1
LANPACIFIC
Dartmouth Development
Preliminary Storm Drainage Report
July 12, 2006
Page 1
VICINITY MAP
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Figure 1 - Vicinity Map
GENERAL SITE INFORMATION
A. Site Description
The site address is 11935 SW 70TH AVE, Tigard, Oregon, Tax Lot No. 1S136DC04400 and has
a total area of 83,075.35ft (1.91 acres). There is one existing single - family home and scattered
large and small trees, grasses and low -lying shrubs. The site slopes from the Northeast to the
Southwest with an average slope of 8 -14 %. Elevations range from a minimum of 224 feet at the
southwest corner to a maximum of 265 at the northeast corner of the property.
B. Project Description
The Dartmouth development will be developed into one commercial development with 128
parking spaces on the entire property. The public improvements include public and private road
construction, wet and dry utilities, individual lot grading, and a storm water quality /quantity facility.
C. Climate
The site is located in Washington County approximately 60 miles inland from the Pacific Ocean.
The climate in this region has gradual but defined seasonal characteristics. Average daily
temperatures range from 44 °F to 82 °F. Record temperatures recorded in this region of the state
are from -10 °F to 108 °F. The average annual rainfall recorded in this area is 40 -50 inches.
D. Site Geology
The soil groups as depicted on the Washington County Soils Survey Mapping (see Technical
Appendix - Soil Map) consist of 45C - Woodburn series. The hydrologic group for the soils is C
(see Technical Appendix - Water Features)
45C- Woodburn silt loam, 7 to 12 percent slopes.
This soil is moderately sloping. Included with this soil in mapping were areas of Aloha, Amity,
Willamette, Helvetia, and Dayton soils, which occupy as much as 15 percent of this mapping unit.
Runoff is medium, and the hazard of erosion is moderate. Capability unit Ile -2; wildlife group 2.
(ANPACIFIC
Dartmouth Development
Preliminary Storm Drainage Report
July 12, 2006
Page 2
PRE - DEVELOPED CONDITIONS
A. Topography
1. Land Cover: The site is covered with mostly landscaped grasses and trees. Most of the
trees fall along the perimeter of the site. The site has a gentle slope to it from the
southwest. The existing house sits on the easterly third of the site and will remain.
NOTE: The Pre - Developed areas used for calculating the pre - developed flow rates
were based on code compliance of using Lewis and Clark site conditions. Therefore, the
total area of the site was use as pervious area in our calculations.
2. On -Site Drainage Basin: Currently the site runoff sheet flows from the northeast to the
southwest. According to the existing conditions topography, the site receives no
significant runoff from the adjacent properties. The adjoining parcels are all developed as
single - family homes. The runoff from this parcel sheet flows to the southwest corner
where it enters into a piped conveyance channel. The existing drainage channel drains
west to the Fanno Creek basin.
3. Off -Site Drainage Basin: The existing off -site basin consists of approximately 7800 sf of
impervious surfaces in SW 70"' Ave.. The site frontage is about 590' long with catch
basins at each end. The low point for Dartmouth is at the southwest corner of the site.
See attached exhibits to show these areas.
B. Hydrologic Analysis
1. Curve numbers: CN = 86, Hydrologic Group = C with grass cover
conditions. See Appendix for Curve Number evaluation
2. Time of Concentration: 19.2 minutes(See Appendix for calculations)
3. Hvdroaraph Method: Santa Barbara Urban Hydrograph with SCS Type IA
hyetograph
4. Design Storm: 2 year, 24 hour storm 2.5 inches
10 year, 24 hour storm 3.4 inches
25 year, 24 hour storm 3.9 inches
100 year, 24 hour storm 4.5 inches
5. Onsite Peak Flow Runoff: 2 year, 24 hour storm 0.47 cfs
10 year, 24 hour storm 0.81 cfs
25 year, 24 hour storm 1.01 cfs
100 year, 24 hour storm 1.25 cfs
C. Hydraulic Analysis
1. Manning's 'n' values for Pipes: A Manning's 'n' value of 0.013 was selected for all of
the storm drain pipes per Clean Water Service guidelines. The Manning's 'n' value is 16
percent higher then the recommended Manning's 'n' value for concrete pipe (n= 0.012) in
order to account for entrance, exit, junction, and bend head losses. A Manning's 'n' value
of 0.025 was selected for all open channels except water quality swales for which
Manning's 'n' of 0.024 was selected.
I./ANPACIFIC
Dartmouth Development
Preliminary Storm Drainage Report
July 12, 2006
Page 3
POST - DEVELOPED CONDITIONS
A. Topography
1. Land Cover:. The proposed development will require minimal grading in the westem
two- thirds of the site. General topography of the site will remain mostly unchanged,
sloping from the northeast to the southwest. The land cover will change to fully
landscaped lots with grass and planted shrubs and trees.
2. Drainage Basin — Onsite and Offsite: The onsite storm water will be collected by a
small number of catch basins and roof drains and routed to the southeast corner of the
project site. The offsite improvements include AC and curb along the frontage of SW
Dartmouth and SW 70 Ave. Storm water from SW Dartmouth will be collected into two
catch basins and piped to an existing conveyance system west of the project site.
3. Area Calculation — Table
DESCRIPTION AREA
Total Impervious 1.49 Acres
Total Pervious 0.26 Acres
Total Area 1.75 Acres
B. Hydrologic Analysis
1. Curve numbers: CN = 86, Hydrologic Group = C with good landscape
conditions. See Appendix for Curve Number evaluation.
2. Time of Concentration: 5 minutes(See Appendix for calculations)
3. Hydroaraph Method: Santa Barbara Urban Hydrograph with SCS Type IA
hyetograph
4. Design Storm:, 2 year, 24 hour storm 2.5 inches
10 year, 24 hour storm 3.4 inches
25 year, 24 hour storm 3.9 inches
100 year, 24 hour storm 4.5 inches
5. Onsite Peak Flow Runoff: 2 year, 24 hour storm 1.50 cfs
10 year, 24 hour storm 2.37 cfs
25 year, 24 hour storm 2.79 cfs
100 year, 24 hour storm 3.36 cfs
C. Hydraulic Analysis
1. Manninct's 'n' Values for Pipes: A Manning's 'n' value of 0.013 was selected for all of
the storm drain pipes per Clean Water Service guidelines. The Manning's 'n' value is 16
percent higher than the recommended Manning's 'n' value for concrete pipe (n= 0.012) in
order to account for entrance, exit, junction and bend head losses. A Manning's 'n' value
of 0.025 was selected for all open channels except water quality swale for which
Manning's 'n' of 0.17 was selected.
IANP CFIC
Dartmouth Development
Preliminary Storm Drainage Report
July 12, 2006
Page 4
WATER QUALITY - ONSITE
Water Quality GuidelineslCalculations
The water quality facility was designed per Clean Water Services standards to facilitate the
treatment of all storm water runoff from the proposed improvements. The facility was designed
using a rainfall of 0.36" over a 4 -hour period with a return period of 96 -hours as outlined in section
3.12 of the Design and Construction Standards for Sanitary Sewer and Surface Water
Management issued in March 2004. Impervious areas and calculations are shown below:
Impervious surface area: 64,787 sf (1.49 ac)
Pervious area: 11,432 sf (0.26 ac)
WQV _ (0.36)(64,787 ft 2) = 1,944cf
(12in 1 ft)
WQF = 1 = 0.135cfs
14400 sec
Stormfilter vaults are chosen for water quality. The primary pollutants for the project are oil and
greases from the parking areas. The stormfilters have measured up to 85% removal of the oils.
The storm collection system routes storm water through the vault up to a flow of 0.14 cfs. Sizing
the Precast compost filter is determined by calculating the number of cartridges required.
(0.14 cfs * (449 gpm 11 cfs))1(15 gpm /1 Cartridge) = 4.5 or 5 Cartridges
Storm water Management Recommend Pre -cast Model 6 x 8
Outlet Orifice Diameter equation for StormGate Manhole
Q (cfs) = C * A* gh A
c* (2gh) ^ 2
C = 0.62, g = 32.2, h =1.0'
=
0.14
0.62 * *32.2 *1.0)
Orifice Area (A) = 0.0426 sf, A= pi(R) ^2, R= sgrt(a/pi), R = 0.027 ft, D = 0.65 inches
1ANPACIF
Dartmouth Development
Preliminary Storm Drainage Report
July 12, 2006
Page 5
WATER QUANTITY
Storm water detention is required for the project as per the pre - application meeting and will be
designed to meet the Clean Water Services R &O 04 -09 code requirements for Water Quality and
Water Quantity
The detention pipe has been sized to detain the full volume required for all the improvements
proposed with the McDonald Woods project. The pipe was sized to detain the 2 year, 10 year
and 25 year, 24 hour flows to be detained at their respective pre - developed flow rates. The pipe
will be sized to allow the 100 -year event to pass. For in -depth calculations please see the
attached detention routing calculation reports. Below is a summary table of pre - developed and
developed flows.
PreDeveloped Predeveloped Developed Design
Recurrence Peak Peak Release Rate
Interval (years) Flow (cfs) Flow (cfs) by Detention
2 Year 0.47 1.08 0.47
10 Year 0.81 1.52 0.81
25 Year 1.01 1.77 0.98
100 Year 1.25 2.07 2.07
Detention Pipe Peak Stage Elev Peak
Max Elevations (Bot. of Pipe =230) Volume
2 Year Storm 232.95 1,250 cf
10 Year Storm 233.76 1,634 cf
25 Year Storm 234.24 1,837 cf
100 Year Storm - - cf
WO / Detention Structure List: Elevation Orifice Size
Detention Orifice #1 230.00 3.30"
Detention Orifice #2 233.00 3.70"
The water quantity detention pipe was calculated using a length of 104' of 5' diameter detention
pipe. The construction plans call for three 60" manholes and one 72" manhole. The volume
available in the manholes and the connection pipe allow the 104' of detention pipe to reduce to
83'. Thus the two manhole, the two 36" connection pipes and 83' of detention pipe equal the
volume calculated for the 104' of 5' diameter pipe.
SUMMARY
Storm conveyance, water quality and water quantity designs followed Design and Construction
Standards for Sanitary and Surface Water Management by Clean Water Services, issued in
March 2004.
The storm water conveyance for the proposed site development of McDonald Woods will be in a
single storm system. Site run-off will be collected and treated in the Stormwater Management
compost filter vault before connecting into the storm system in McDonald Road and discharging
into the open channel at the southeast corner of the site.
The proposed onsite storm system will have sufficient capacity to handle all storm events up to
and including the 100 -year storm event. The existing downstream system won't experience any
flooding during the 100 -year storm event and will not impact any habitable structures.
tANPACIFIC
Dartmouth Development
Preliminary Storm Drainage Report
July 12, 2006
Page 6
TECHNICAL APPENDIX
Time of Concentration Equations
The time of concentration (Tc) as described in NEH-4 Chapter 15 is defined in two ways; the time
for runoff to travel from the furthermost point of the watershed to the point in question, and the
time from the end of excess rainfall to the point of inflection on the trailing limb of the unit
hydrograph. Time of concentration can be estimated from several formulas. The Clean Water
Services guidelines which are based on the SCS method were used in this analysis.
The minimum time of concentration is 5 minutes in highly developed urban areas (i.e. parking
lots) and the maximum is 100 minutes in rural areas. Several different times of concentration
were chosen for this project.
Three components are considered for determining the T sheet flow, shallow concentrated flow,
and channel / pipe flow. The T, values for the property were determined based on the following
equations:
Sheet Flow
0.007(nL } °'
T, — (p 0 0.5 s 0.4
2
Tt = Travel Time (hours)
n = Manning's "n" of slope
L = Length of flow (ft)
P2 = 2 -Year, 24 -hour rainfall (in)
s Slope(ft /ft)
Shallow Concentrated Flow
_
T' 3600V
T = Travel Time (hours)
L = Flow Length (ft)
V = Average Velocity (ft / s)
3600 = seconds / hour
Channel / Pipe Flow
Using Manning's Equation, the velocities were calculated in the channels and / or pipes, and then
this velocity was divided the flow length.
1
=
L
V n T` = 3600V
V = Average Velocity (ft/s)
r = Hydraulic Radius = a / P
a = Cross - sectional Area (ft
P = Wetted Perimeter (ft)
s = Channel Slope (ft / ft)
n = Manning's °n" of channel
The time of concentration values used for the stormwater analysis are shown in Table 4 below.
These values were computed according to Technical Release 55: Urban Hydrology for Small
Watersheds.
lANPACIHC
Dartmouth Development
Preliminary Storm Drainage Report
July 12, 2006
Page 7
Curve Numbers
The major factors for determining the Curve Number (CN) are hydrologic soil group, type of plant
cover, treatment and antecedent runoff conditions. Curve Number is going to be greatly affected
by the way impervious surface is connected to the drainage system (impervious area outlet
directly to drainage system or whether the flow spreads over pervious areas before entering the
drainage system).
REFERENCES
1. Soil Survey of Washington County Area
2. Technical Release 55 — Urban Hydrology of Small Watersheds
U.S. Department of Agriculture, NRCS
3. Design and Construction Standards Resolution and Order 04 -9 (R &O 04 -9) — Clean
Water Services, Washington County, Oregon.
lANPACIFIC
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LAN PACT F I C OVELOPLIDIL DARTMOUTH DEVELOPMENT DRAM: A4.
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LANDSCAPE
1001 SE Writer Menge, Suite 36Q Po/gM
P, Oregon 97214
SW DARTMOUTHST. AND SW 70TH AVE. 1
ARCNTIECRINE
!! 5031 238 -2097 FAX: 5031 238 -2447 RD, OREGON 2
www.fonpocific.com
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PROJ 0 DD-DASE
eilMI OW
IfIlaftERWC PROPOSED SITE AND GRADING PLAN DATE: 04/17/06
DRAWN: JSE ,
LAN PACIFIC Z 14 DARTMOUTH DEVELOPMENT LOT
ARporrcanc
/0;
1001 SE 'toter Avenue, Suite 380. Portland. SW DARTMOUTHST. AND SW 70TH AVE 2 nd. Oregon 97214
ir 503 1 238-2057 FAX: 503 1238 TICiARD, OREGON
....t.poefic.com
,
•
LanPacific, Inc. JSSApri1 17, 2006
Project MGA05 -008.
Dartmouth Development
DETENTION ROUTING
DETENTION - 2 YEAR STORM EVENT
flow (cfs)
2.00
1.50
1.00 — _ A —
0.50 -- -___..
0.00
0 5 10 15 20 25 30
time (hr)
DETENTION TUBE (stage - volume calculated)
diameter = 5.00'; length = 104.00'; elope = 0.00%; invert 230.00'MSL
STAGE VOLUME
230.0 0
230.8 224
231.7 596
232.5 1021
233.3 1446
234.2 1818
235.0 2042
OUTLET TYPE ELEVATION SIZE
circ. orifice 230.0 dia.(in) = 3.30
circ. orifice 233.0 dia.(in) = 3.70
inflow hydrograph: j : \mga05- 008 \drain \dev- 002.hyd
peaks: inflow = 1.08 cfs e 7.83 hr.
outflow = 0.47 cfs e 8.67 hr.
stage: 2.95 ft. detained volume: 1,250 c.f.
LanPacific, Inc. JSEApri1 17, 2006
Project MGA05 -008
Dartmouth Development
DETENTION ROUTING
DETENTION - 10 YEAR STORM EVENT
flow (efa)
2.00
1.50 - - -- _ _ _, ____._
1.00 _
k 0.50 — — ._..__ _ �__ __......._..._ _____—
o.00
0 5 10 15 20 25 30
time (hr)
DETENTION TUBE (stage - volume calculated)
diameter = 5.00'; length = 104.00'; slope = 0.00 %; invert = 230.00'NSL
STAGE VOLUME
230.0 0
230.8 224
231.7 596
232.5 1021
233.3 1446
234.2 1818
235.0 2042
OUTLET TYPE ELEVATION SIZE
circ. orifice 230.0 dia.(in) = 3.30
circ. orifice 233.0 dia.(in) = 3.70
inflow hydrograph: j: \mga05- 008 \drain \dev- 010.hyd
peaks: inflow = 1.52 cfs e 7.83 hr.
outflow = 0.81 cfs 0 8.50 hr.
stage: 3.76 ft. detained volume: 1,634 c.f.
LanPacific, Inc. JSEApri1 17, 2006
Project MGA05 -008
Dartmouth Development
DETENTION ROUTING
DETENTION - 25 YEAR STORM EVENT
flow (cfs)
2.00
1.50
1.00
0.50
J r-
0.00
0 5 10 15 20 25 30
time (hr)
DETENTION TUBE (stage - volume calculated)
diameter = 5.00'; length = 104.00'; slope = 0.00 %; invert = 230.00'MSL
STAGE VOLUME
230.0 0
230.8 224
231.7 596
232.5 1021
233.3 1446
234.2 1818
235.0 2042
OUTLET TYPE ELEVATION SIZE
circ. orifice 230.0 dia.(in) = 3.30
circ. orifice 233.0 dia.(in) a 3.70
inflow hydrograph: j: \mga05- 008 \drain \dev- 025.hyd
peaks: inflow 1.77 cfs @ 7.83 hr.
outflow = 0.98 cfs @ 8.33 hr.
stage: 4.24 ft. detained volume: 1,837 c.f.
•
LanPacific, Inc. JSEApri1 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
Developed - 2 Year
total Time of Concentration = 5.0'
storm hyetograph: SCS TypeIA
return period = 2 years
storm duration = 24 hr.
total rainfall = 2.50 in.
pervious area = 0.26 A CN = 74 GpC:Open.space,gd.cnd
impervious area = 1.65 A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05- 008 \drain \dev- 002.hyd
peak flow = 1.08cfs @ 7.83 hr.
runoff volume = 14,175 cu.ft.
•
LanPacific, Inc. JSEApri1 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
Developed - 10 Year
total Time of Concentration = 5.0'
storm hyetograph: SCS TypeIA
return period = 10 years
storm duration = 24 hr.
total rainfall = 3.40 in.
pervious area = 0.26 A CN = 74 GpC:Open.space,gd.cnd
impervious area = 1.65 A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05- 008 \drain \dev- 010.hyd
peak flow = 1.52cfs rep 7.83 hr.
runoff volume = 20,073 cu.ft.
•
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LanPacific, Inc. JSEApri1 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN RYDROGRAPH
Developed - 25 Year
total Time of Concentration = 5.0'
storm hyetograph: SCS TypeIA
return period = 25 years
storm duration = 24 hr.
total rainfall = 3.90 in.
pervious area = 0.26 A CN = 74 GpC:Open.space,gd.cnd
impervious area = 1.65 A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05- 008 \drain \dev- 025.hyd
peak flow = 1.77cfs @ 7.83 hr.
runoff volume = 23,391 cu.ft.
•
LanPacific, Inc. JSPApti1 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
Developed - 100 Year
total Time of Concentration = 5.0'
storm hyetograph: SCS TypeIA
return period = 100 years
storm duration = 24 hr.
total rainfall = 4.50 in.
pervious area = 0.26 A CN = 74 GpC:Open.space,gd.cnd
impervious area = 1.65 A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05- 008 \drain \dev- 100.hyd
peak flow = 2.07cfs @ 7.83 hr.
runoff volume = 27,401 cu.ft.
•
LanPacific, Inc. JSEApri1 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN RYDROGRAPB
•
Pre - Developed - 2 Year
2 -year, 24 -hour rainfall = 2.50"
flow type description coeff. distance fall slope T/C
1 overland sheet dense.grasses n =0.24 250.0 25.0' 10.00% 17.7'
2 shallow concentrated high.grass K =9 220.0 13.0' 6.19% 1.6'
total Time of Concentration = 19.2'
storm hyetograph: SCS TypeIA
return period = 2 years
storm duration = 24 hr.
total rainfall = 2.50 in.
pervious area = 1.91 A CN = GpC:Open.space,pr.cnd
impervious area = 0.00 A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05- 008 \drain \pre- 002.hyd
peak flow = 0.47cfs @ 8.00 hr.
runoff volume = 8,619 cu.ft.
•
LanPacific, Inc. JSEApril 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
Pre - Developed - 10 Year
2 -year, 24 -hour rainfall = 2.50"
flow type description coeff. distance fall slope T/C
1 overland sheet dense.grasses n =0.24 250.0 25.0' 10.00% 17.7'
2 shallow concentrated high.grass K =9 210.0 13.0' 6.19% 1.6'
total Time of Concentration = 19.2'
storm hyetograph: SCS TypeIA
return period = 10 years
storm duration = 24 hr.
total rainfall = 3.40 in.
pervious area = 1.91 A CN = 86 GpC:Open.space,pr.cnd
impervious area = 0.00 A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05- 008 \drain \pre- 010.hyd
peak flow = 0.81cfs O 8.00 hr.
runoff volume = 13,933 cu.ft.
•
•
LanPacific, Inc. JSEApr1 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
Pre - Developed - 25 Year
2 -year, 24 -hour rainfall = 2.50"
flow type description coeff. distance fall slope T/C
1 'overland sheet dense.grasses n =0.24 250.0 25.0' 10.00% 17.7'
2 shallow concentrated high.grass K =9 210.0 13.0' 6.19% 1.6'
total Time of Concentration = 19.2'
storm hyetograph: SCS TypeIA
return period = 25 years
storm duration = 24 hr.
total rainfall = 3.90 in. •
pervious area = 1.91 A CN = 86 GpC:Open.space,pr.cnd
impervious area = 0.00.A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05 -008 \drain \pre- 025.hyd
peak flow = 1.01cfs @ 8.00 hr.
runoff volume = 17,025 cu.ft.
•
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LanPacific, Inc. JSEApri1 17, 2006
Project MGA05 -008
Dartmouth Development
RUNOFF by the SANTA BARBARA URBAN HYDROGRAPH
Pre - Developed - 100 Year
2 -year, 24 -hour rainfall = 2.50"
flow type description coeff. distance fall slope T/C
1 overland sheet dense.grasses n =0.24 250.0 25.0' 10.00% 17.7'
2 shallow concentrated high.grass K =9 210.0 13.0' 6.19% 1.6'
total Time of Concentration = 19.2'
storm hyetograph: SCS TypeIA
return period = 100 years
storm duration = 24 hr.
total rainfall = 4.50 in.
pervious area = 1.91 A CN = 86 GpC:Open.space,pr.cnd,
impervious area = 0.00 A CN = 98
total site area = 1.91 A
hydrograph file: j: \mga05- 008 \drain \pre- 100.hyd
peak flow = 1.25cfs @ 8.00 hr.
runoff volume = 20,819 cu.ft.
•
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http: / /ice.or.nres. usda. gov /website /wash_or/MapFrame.htm 4/19/2006
Water Features
Washington County, Oregon
[Depths of layers are In feet. See text for definitions of terms used in this table. Estimates of the frequency of ponding and flooding apply to the whole year rather than to Individual months. Absence of
an entry indicates that the feature is not a concem or that data were not estimated]
Water table Ponding Flooding
Map symbol Hydrologic Surface runoff Month
and soil name group Upper limit lower limit Surface depth Duration Frequency Duration Frequency
Ft Ft Ft
13:
Cove D. — January 0.0 -1.0 >6.0. — — None.. Brief Frequent
• March
0.0 -1 0 >6.0 .. ; Norre Brief Frequent
Decemb 0-1 Bn F q nt
37B:
. March :,>: 2030.. ,... � >g p .:....:.. • — : , Norte :.. None
N
• :...:. .......:: :.. December 2.03.0. 6.. None . ... .
Norre one
> 0
45C:
Woodburn'.'. C: January 2.03.0 2.53.3: .: -- - None — None
February 2.0 -3.0 2.53.3 — — None. , — None
—
....... . .. ......: March 2.03.0:: :... 2:53.3`:...., . None .': None
April 2.03.0: ..:.:253 3 None Nona
Decembe 203 0 53 3 — — None None
USDA Natural Resources This report stows only the major soils In each ntap unit. our ntay eat
Tabular Data Version: 2
Conservation Service Tabular Data Version Date: 12/13/2005 Page 1 of 1