25933 BSP-81-01 DRAINAGE REPORT
CLC
Associates, Inc.
707 West Th Avenue
Suite 200 2~01
Spokane, WA 99204 An Affillate M Colorodo Land Consultants, inc.
(509) 458-6840
(509) 458-6844 Fax November 28, 2001
cic-inc.com CLC #98560
Spokane, WA - Denver, CO
Spokane County
Division of Engineering and Roads _
1026 West Broadway Avenue
Spokane, Washington 99260-0170
Attn: Gary Nyberg, E.I.T.
~
Re: Howe Road Mobile Home Park
(i.e. Silver Pines Manufactured Home Park M~HP-1-99)
Dear Gary: .
Per the attached fax from Spokane County planner Jim Falk to Andrea gice of our
office, we have made a site visit to the Howe Mobile Home Park mid this morning and
' found Pond `A' to meet the design intent of the approved plans dated 8/24/99. Please
call if you have any questions or concerns.
Sincerely,
CLC ASSOCIAT S
~
,
,
,
-
Todd R. Whipple, P. . ~ 5462 Vice President
TRW/skm. E)EPtRES 9/24/
s.
cc: file .
tITY ENGINF~~s .
OFFlCM PUBUC DOCUMENT
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Landscape Architecture PROJECT
Land Surveying DATE ACCEPTED: ~ ~d
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Owner: ARTHUR, GARYIIKLEIN, DWAINE
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Owner: ARTHUR, GARYIIKLEIN, DWAINE
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Owner Address
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Parcel: 35231.1142
Owner: KLEIN, DWAINE R& C DOROTHEA
CoOwner:
Owner Address
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DRAINAGE REPORT
for
~ HOWE ROAD MOBILE HOME PARK
_ FEBRUARY 1999
IPE #98560
Prepared by: Inland Pacific Engineering Company
707 West 7th Suite 200; Spokane, WA 99204; (509)458-6840
The design improvements shown in this set of plans and calculations conform
to the applicable editions of the Spokane County Standards for Road and
Sewer Construction and the Spokane County Guidelfnes for Stormwater
T Management. All design deviations have been approved by the Spokane County
~ Engineer. I approve these plans (calculations) for construction. .
This report has been prepared by Matt Zarecor, E.I.T. and by the staff of Inland Pacific Engineering
~ Company under the direction of the undersigned professional engineer whose seal and signature appear
- hereon.
S
A.
wASy
~
~ ~b 99
22s1 s Q
- s~oNA1. EN
EXPIAES:
k~„ry~ •
Timothy A Schwab, P.E.
,
~
t
.
HO WE R OAD MOBILE HOME PARK
~ Storm Water Technical Evaluation
:i
-Narrative
~ i GENERAL
~ The Howe Road Mobile Home Park is an 11-lot development situated on approximately 1.57 acres.
~ t The site is located between Howe Road and Fancher Avenue approximate 330' south of Fourth
Avenue, in the Spokane Valley. The site is currently vacant with site vegetation that consists
primarily of field grass.
PURPOSE
~
~
The purpose of this drainage report is to determine generally the extent of storm drainage facilities
~ which will be required to dispose of stormwater runoff created by this development. The storm
;
` I drainage facilities on this project will be designed to dispose of runoff from a ten year design storm.
Additionally, the runoff from the 50-year storm will be checked for each basin to insure that they can
^ be contained within the ponds proposed. This development is within the Aquifer Sensitive Area of
Spokane County and is subject to '208' requirements. For this project the Intensity, Duration, and
Frequency (IDF) curve for the Spokane, Medical Lake, Reardon, Cheney and Rockford area was
~ used.
~ ANALYSIS METHODOLOGY
_ The Rational Method, which is recommended for basins less than ten acres in size, was used to -
determine the peak discharges and runoff volumes since none of the basins exceed 10 acres in size.
~ PROJECT DESCRIPTION
,T As stated previously, the proposed Howe Road Mobile Home Park is situated on approximately 1.57
acres. The project is located in the northeast 1/4 of Section 23, T. 25 N., R. 43 E., W.M. in Spokane
--County, Washington.
✓ TOPOGRAPHY
The site is virtually flat with all of the on-site and off-site slopes being one percent or less.
~
Inland Pacific Engineering Co. D 1 Howe Rood Mobile f•lome Pnrk Drninnge Report
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SOILS
~ As can be seen from the accomPanYing soils maP from the SPokane County Soils Survey as
performed by the SCS, the site consists of a Class B soil type. The soil description is as follows.
~
GgA - Garrison gravelly loam, 0 to 5 percent slopes: This complex of soil is a somewhat
excessively drained soil formed from a variety of igneous rock. Surface runoff is slow, and the
hazard of erosion is slight. Spokane County Guidelines for Stormwater Management indicate tlus to
be a Soil Group Type B and pre-approved for drywell installation.
~J Hydrologic Soil Classification - B
i,
;
DRAINAGE NARRATIVE
Off-site
~ Howe Road along the west side of this project is 36 feet wide with no curbs or sidewalks. The
runoff from Howe Road runs off the sides and infiltrates. Fancher Road along the east side of the
-J project is an unimproved gravel road that generates little or no runoff. No runoff onto or from the
_ site is anticipated due to the shallow slopes, free-draining soils, and dense native vegetation.
On-site
All on-site drainage will be collected and treated using the "208" runoff inethod as described in the
~ Spokane County Guidelines for Stormwater Management. The entire project is contained in one
- basin, Basin A. The runoff from Basin A is directed to Pond A. Only the asphalt drive aisle itself
was used in sizing the "208" pond since the runoff from the roofs of the homes must flow over 20 to
~ 30 feet of grass at less than one percent before getting to the drive aisle. Also, the individual parking
areas generally are concrete in this type of development. The basin and pond are shown on the basin
map at the back of this report.
~ 11208" Calculations
~ As shown on the '208' calculation worksheets included, the '208' storage volume provided is
adequate to perform'208' treatment for the runoff created by the first half inch of rainfall upon the
J asphaltic surfaces within the basin it serves.
i DRAINAGE CALCULATIONS SUMMARY
~Bowstring calculations have been included for individual basins to determine the extent of storm
drainage facilities required for the 10-year event. The runoff produced by the 50-year event was also
f checked to verify that the ponds would adequately contain the storms. The basin characteristics are
~
~ I Inland Pacifrc Engineering Co. D2 Howe Roact Mobile Nome Park Drainnge Report
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summarized below with the remaining calculations in the appendix.
Table No. 1- Basio Summary Table - Areas
~
Total Impervious Runoff .
--=,~Basin;:;,,~:~:;: _Ar.ea (acres) Area (S~ Coefficient
~ On-site A 1.57 30,480 0.48 .
-J Runoff coefficient is based upon "c" value of 0.15 for pervious area and 0.90 for impervious area.
Table 2 summarizes the requirements of the ponds by basin.
_ Table No. 2- 208 Basin Summary .
iL BASIN: S. Y
~.-~y, • ~rr.,Gr- c+ qc- a , _ . _ . . ,y.,~..., a-~ '
rt`~~^lfi^. . `.s
ondi,~:;,;~;~~ ~:sz208GAr,ea;,Required~(s~ ,~208 Area Provided (sn Drywells~Rec~uire`d~:* .
~
s
On-site A 1,330 1,400 1-Type B
Type A is a Spokane Standard Drywell - Single Depth, Capacity 0.3 cfs
Type B is a Spokane Standard Drywell - Double Depth, Capacity 1.0 cfs
CONCL USION
~ As demonstrated by the calculations and body of this report the storm drainage facilities provided in
the design will adequately store and dispose of the storm water from the site. Even though the
^ minimum design criteria is the 10-year storm, the ponds in this development will contain the 50-year
~ event without overtopping. Additionally, the "208" area required for the asphaltic surfaces of the
paved surfaces is provided.
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tnland Pncific Engineering Co. D 3 Howe Rond Mobile Home Park Drninnge Reporl
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APPENDIX _
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MAps
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' VICINITY MAP
>
SOILS MAP
BOWSTRING CALCULATIONS
ON-SITE. 10-Yr., 50-Yr. A 1-A2
a
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BASIN MAP
BASIN MAP
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Inland Pacific Engineering Ca D4 Howe Rocrd Mobile Home Pnrk Drainage Report
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VICINITY -MAP
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SCS SOIL SUR.VEY OF SPOK:ANE COUNTY
~l SHEET 74
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~ BOWSTRING CALCULATIONS,
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BOWSTRING METHOD PROJECT: Howe Road Mobile Home Park
PEAK FLOW CALCULATION PROJECT: Howe Road Mobile Home Park DETENTION BASIN DESIGN BASIN: A
BASIN: A 10-Year Design Storm DESIGNER: MBZ
Tot. Area 1.57 Acres DATE: 02108199
Imp. Area 30480 SF 68389
C = 0.48
Time Increment (min) 5
CASE 1 , Time of Conc. (min) 13.89
Outflow (cfs) 1
60 ft. Overland Flow Design Year Flow 10
Area (acres) 1,57
Ct = 0.40 Impervious Area (sq ft) 30480
L= 60 ft. 'C' Factor 0.48
n= 0.40 '208' Volume Provided 700
S= 0.010 Area * C 0.76
Total Asphaltic Area 15960
Tc = 10.72 min., by Equation 3-2 of Guidelines
Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
270 ft, Gutter flow (min) (sec) (in/hr) (cfs) (cu ft) (cu ft) (cu ft)
Z1= 50.0 For Z2 13.89 833 1.86 1.41 1578 833 745
Z2 = 50 Type B =1.0
n= 0.016 Rolled = 3.5 5 300 3.18 2.42 972 300 672
S= 0.008 10 600 2,24 1.70 1369 600 769
15 900 1,77 1.35 1217 900 311
d= 0.141 ft. 20 1200 1.45 1.10 1328 1200 128
25 1500 1,21 0.92 1384 1500 -116
A R Q Tc Tctotal I Qc 30 1800 1,04 0.79 1427 1800 -373
,
35 2100 0.91 0.69 1456 2100 -644
0.99 0,07 1.41 3.17 13,89 1.86 1.41 40 2400 0.82 0.62 1499 2400 -901
45 2700 0.74 0.56 1522 2700 -1178
Qpeak for Case 1= 1.41 cfs 50 3000 0.68 0.52 1553 3000 •1447
55 3300 0.64 0.49 1608 3300 -1692
60 3600 0.61 0.46 1672 3600 -1928
CASE 2 65 3900 0.60 0.46 1781 3900 -2119
70 4200 0.58 0.44 1854 4200 -2346
Case 2 assumes a Time of Concentration less than 5 minutes so that the 75 4500 0.56 0.43 1918 4500 -2582
peak flow =.90(3.18)(Irnp. Area) = 2,00 cfs 80 4800 0.53 0.40 1936 4800 •2864
85 5100 0.52 0.40 2018 5100 -3082
90 5400 0.50 0.38 2055 5400 -3345
So, the Peak flow for the Basin is the greater of the two flows, 95 5700 0.49 0.37 2125 5700 -3575
2.00 cfs 100 6000 0.48 0.36 2191 6000 -3809
208' DRAINAGE POND CALCULATIONS
Provided "208" Volume 700 cu ft
Required "208" Volume 665 cu ft
DRYWELL REQUIREMENTS • 10 YR DESIGN STORM
Maximum Storage Required by Bowstring 769 cu ft
Al Provided Storage Volume 1400 cu ft
Number and Type of Drywells Required 0 Single
1 Double
,
1 ~.___J ~ 1 ~ l I ~ 1 f ) ( I ~ ~ ~ _ 1 ( I ) i i ~ J t_ 1 J C~~
50-year STORM BOWSTRING METHOD PROJECT: Howe Road Mobile Home Park
PEAK FLOW CALCULATION PROJECT; Howe Road Mobile Home Park DETENTION BASIN DESIGN BASIN; A
BASIN: A DESIGNER; MBZ
Tot. Area 1,57 Acres DATE: 02h 1199
Imp, Area 30480 SF 68389
C = 0.48
Time Increment (min) 5
CASE 1 Time of Conc. (min) 13.62
Outflow (cfs) 1
60 ft. Overland Flow Design Year Flow 50
Area (acres) 1.57
Ct = 0.40 Impervious Area (sq ft) 30480
L= 60 ft. 'C' Factor 0.48
n= 0.40 50-year Volume Provided 700
S= 0.010 Area' C 0.76
Total Asphaltic Area 15960
Tc = 10.72 min., by Equation 3-2 of Guidelines
Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
270 ft. Gutter flow ' (min) (sec) (iNhr) (cfs) (cu ft) (cu ft) (cu ft)
Z1= 50.0 13.62 817 2.63 2.00 2193 817 1376
Z2 = 50
n= 0.016 , 5 300 4.58 3.48 1400 300 1100
S= 0.008 10 600 3.20 2.43 1956 600 1356
15 900 2,45 1.86 2194 900 1294
d= 0.161 ft. 20 1200 1.95 1.48 2191 1200 991
25 1500 1.62 1.23 2190 1500 690
A R Q Tc Tc total I Qc 30 1800 1.56 1.19 2464 1800 664
35 2100 1.28 0.97 2314 2100 214
1.30 0.08 2.01 2.90 13,62 2.63 2.00 40 2400 1,19 0,90 2413 2400 13
45 2700 1,08 0,82 2445 2700 -255
Qpeak for Case 1= 2.00 cfs 50 3000 0,99 0.75 2467 3000 -533
55 3300 0.92 0.70 2503 3300 -797
60 3600 0.87 0.66 2565 3600 -1035
CASE 2 65 3900 0.82 0.62 2605 3900 -1295
70 4200 0.80 0.61 2724 4240 -1476
Case 2 assumes a Time of Concentration less than 5 minutes so that the 75 4500 0.77 0.59 2797 4500 -1703
peak flow =.90(4.58)(Imp. Area) = 2.88 cfs 80 4800 0.15 0.57 2895 4800 -1905
85 5100 0.72 0.55 2944 5100 -2156
90 5400 0.71 0,54 3065 5400 -2335
So, the Peak flow for the Basin is the greater of the two flows, - 95 5700 0,69 0,52 3136 5700 -2564
2.88 cfs 100 6000 0,67 0.51 3198 6000 •2602
208' ORAINAGE POND CALCULATIONS
Provided "208" Volume 700 cu ft
Required "208" Volume 665 cu ft
DRYWELL REQUIREMENTS - 50 YR DESIGN STORM
Maximum Storage Required by Bowstnng 1376 cu ft
Provided Storage Volume 1400 cu ft
Number and Type of Drywells Required 0 Single
1 Double
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INLAND PACIFIC ENGINEERING