26004 DRAINAGE TECHNICAL REPORT
' Plmtnh'Ig, Engln9aYin8, A20ftecture. L071d7iaping lilehhcCluP9, "nA Survaying
CLC ASSC~~IATESr INC. ~
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SPOKA+iE, WA DL17VER, CO
DRA--NAGE r---'ECHN;CAL REPORr---"
for the
SPIZ~NGFIEUD I ST ADD-7710N
Ar--` AUr--nUMN CRES7-1
CLC No. 99141
OCTOBER 1999
Prepared for:
Linderman Construction
4823 Sky Meadows Lane
Greenacres, WA 99016
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Prepared By:
C. L. C. Associates, Inc.
707 W. 7th Avenue
Suite 200
Spokane, WA 99204
(509)458-6840
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DRAINAGE REPORT
for the
Springfield First 1 st Addition
at Autumn Crest Plat
Spokane County, Washington
October 1999
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This report has been prepared by Susan K. Murhpy of CLC Associates, Inc. under the direction of
, the undersigned professional engineer whose seal and signature appear hereon.
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EXPIRES 9/24Z'` °
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Springg) - eld 1 st Addition
Drainage Narrative
GEIVERAL
The Springfield First Addition at Autumn Crest plat is a 5.07 acre development of 14 single
family residential lots located east and south of Progress Road and 16' Avenue in the Spokane
Valley within Spokane County, Washington. The site is currently vacant with field grass as the
predominant land cover. This is the final phase of the Autumn Crest preliminary plat. Single
family residential development surrounds the plat location. A vicinity and location map have ✓
been included within the technical section of this document.
PURPOSE
The purpose of this report is to determine the extent of storm drainage facilities which will be
required to dispose of the increase in stormwater runoff created by the development of the
Springfield First Addition at Autum.n Crest plat. The storm drainage facilities on this project will
be designed to dispose of runoff from a ten year design storm for the onsite basins, as required by
the Spokane County Guidelines for Stormwater Management. This development is within the
Aquifer Sensitive Area of Spokane County and is subject to '208' requirements. For this project, /
the 10-year curve from the Spokane, Medical Lake, Reardon, Cheney and Rockford intensity
curves was used, as well as the SCS iso-pluvial rainfall curves.
ANALYSIS METHODOLOGY
Per the Spokane County Guidelines for Stormwater Manazement (GSM), the Rational Method, ~
which is recommended for basins less than ten acres in size, was used to determine the peak
discharges and runoff volumes for all onsite basins.
PROJECT DESCRIPTION
~ The SPringfield First Addition at Autumn Crest subdivision is located in Section 26> T. 25 N.> R.
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44 E., W.M. within Spokane County, Washington
TOPOGRAPHY
' The existing site generally drains to the northeast. Within the plat the natural topography was
used as much as possible to route storm drainage. Due to the flat slopes encountered, no ✓
concentrated pre existing flows were observed nor were there any signs that anything other than
sheet flow and ground absorption have occurred on this site. The general slopes within this plat
vary from flat to nearly flat with the maximum existing slope at 0.02 ft./ft. For development
purposes as stated the natural sloping was used for design and is maintained as possible
throughout the project.
CLC Associates, Inc. 1 Springfield !st Addition Plat
Drainage 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 one type of soil within the Class B type. This soil rype
is described as follows.
GmB - Garrison gravelly loam, 0 to 5 percent slopes: Soils within this soil type are somewhat
excessively drained, gravelly or stony soils of moderately rapid permeability, with a surface layer
, of gravelly loam, and a subsoil stratum of sand, loam and cobblestones. They formed under grass
in glacial outwash mixed in the uPPer Part with volcanic ash. Surface runoff is slow, and the ~
hazard of erosion is slight. Spokane Countv Guidelines for Stormwater Manapement indicate this
to be a Soil Group Type A and pre-approved for drywell installation.
Hydrologic Soil Classification - B
DRAINA GE NARRA TI VE
Offsite
Based on the natural topography and final design, there are no offsite flows. A copy of the basin
area is included for reference..
Onsite
As this plat is within the aquifer sensitive area of Spokane County all onsite drainage will be
collected and treated using the "208" runoff inethod as described in the Spokane County
Guidelines for Stormwater Management. To facilitate this analysis, the Springfield ls` Addition at ✓
Autumn Crest plat was divided into 8 permanent basins (A through H). Table 1 lists the basins
and pond combinations for easy reference.
DRAINAGE CALCULATIONS SUMMARY
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Bowstring calculations have been included for individual basins to determine the extent of storm
drainage facilities required for the 10-year storm event. Weighted "C" Runoff Coefficients were
~ calculated for each basin of less than 10 acres based on dwelling units per gross area, Table 1 pg ✓
6-2 of the GSM. Table No. 1 includes the basin size, number of dwelling units, and runoff
coefficients. The basin characteristics are summarized below with the remaining calculations in
the appendix.
CLC Associates, Inc. 2 Springfield 1 st Addition Plnt
Drainage Report
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Table No. 1- Basin Summary
~ ;~S~i:L.'~•,' F
Basin Tota~l D~,<~~ F=L: ~YY.;~ ,Runoff
t . . . . ; w.
. . Area , UNI~T''S
Coe- fficierit
~sir
AC)-
i .:H"., ♦.SJ. 1.Aa.>_ « l1]SKtY+S ~ CM - . .w • .
A1 14,390/0.330 - 0.45*
A2 14,623/0.226 - 0.48*
B 31,011/0.712 1/0.712=1.4 0.20
CF 39,418/0.905 2.5/0.0.905=2.8 0.25
DE 61,347/1.408 4.25/1.408=3.0 0.30
G 6,581/0.151 0.25/0.151=1.7 0.25
H 25,313/0.581 1.5/0.581=2.6 0.25
* No dwelling units are included in Basins A1 & A2. Weighted runoffcoefficienLs are calculated for the hvo basins.
'208' Calculatioos
Within each basin the streets are divided into sub-basins by high and low roadway profiles. These
facilities capture upstream stormwater runoff from the impervious street surface and direct the
runoff into grassy '208' ponds. 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.
Curb Inlets and Catch Basin Calculations
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It is necessary to check the adequacy of the curb inlets, inlets or catch basins provided to divert
the runoff from the gutter into the '208' ponds. The curb inlet calculation sheet included shows
the required lengths of curb openings, as well as the adequacy of the inlet grates or catch basin
grates.
CLC Associates. Inc. 3 Springfield Ist Addition Alat
Drainage Report
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Table No. 2- Pond RecLuir04 ent Summary
, . ` • , . . ' , p , . . , . . - -:v: ;,-i1R''F ` ,
Re"q'uired' ~~~'~.o~r
} ~S91prdS~F "~\~Y~/F4 ° - . . (S~. - ' . - . _ _ - r-+ils s..~
A 1 4800 400 400 1-Type B
A2(1) 2520 210 400 -
A2(2) 3845 320 400 1-Type B
B1 1224 102 76 '
B2 2180 182 176 -
B3 2780 232 277
B 6184 516 529 1-Type B
C 4,598 382 400 -
D 47525 377 400 -
E 6,154 ~ 513 808 2-Type B
' F 5,291 441 486 1-Type B
G 3,598 300 375 1-Type B
H 5,901 492 600 1-Type B
`208' area required/provided is based on bottom area only, @ 0.5' depth
Type A is a Spokane County Standard Drywell - Single Depth, Capacity 0.3 cfs
Type B is a Spokane County Standard Drywell - Double Depth, Capacity 1.0 cfs
I»let Calculations
~ Inlet calculations are provided for all inlets within the basin. The calculation worksheets for the
10 and 50-year storm events for uilets on continuous grades and in sump conditions are provided
in the appendix. By-pass flows were calculated for each inlet on a continuous grade, and added to
the downstream inlet.
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CONCL USION
As demonstrated by the calculations and body of this report the storm drainage facilities provided
in this design will adequately remove from the streets, store and dispose of the stormwater from
the site for the 10-year design storm as required by Spokane County. Additionally, the required
'208' treatment area is provided for the runoff from the street impervious areas.
CLC Associates, Inc. 4 Spring(teld 1 st Addition Plat
Drainage Report
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APPENDIX
MAPS
VICIN.ITY MAP
SOILS MAP
DEVELOPED BOWSTRING CA.LCULATIONS
] 0-Year Design Storm
Inlet Calculations
BASIN MAP
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SOILS -MAP
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i SCS SOIL SURVEY OF SPOK:.ANE COUNTY
SHEET 76
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~ ICALCULATIONS
10-Year Storm Event
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Weighted Runoff Coefficient Calculation
, Project: Springfield First Addition
Basin: A1 IPE Job 99141
Total Area (acres): 0.33 Designer: SKM
' I mP. Area (acres): 0.13 Date: 10/19
Grass Area (acres): 0.20 I mp. Area "C": 0.90
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Grass Area ~~C,,. 0.15
(Imp. Area)(Imp. "C")= 0.1197
(Grass Area)(Grass "C")= 0.0296
0.3300 0.1493
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Weighted "C"= 0.1493
t = 0.45
0.3300
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PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT; SPRINGFIELD 1ST x
10-Yr Design Storm BASIN; A1 DETENTION BASIN DESIGN BASIN: A1
DESIGNER; SKM
Tot. Area 0.33 Acres 14390 SF DATE; 10120199
Imp. Area 4800 SF
C = 0.45
Time Increment (min) 5
Time of Conc, (min) 5.00
CASE 1 OutBow (cfs) 1.0
Design Year Flow 10
20 ft, Overland Flow Area (acres) 0.33
Impervious Area (sq fl) 4800
Ct = 0.15 'C' Factor 0.45
L= 20 ft. Area ' C 0.15
n= 0.02 Street Area 4800
S = 0.020
Tc = 0.28 min,, by Equabon 3-2 of Guidelines Time Time Inc. Intens, Q Devel. Vol.ln Vol.Out Storage
(min) (sec) (inlhr) (cfs) (cu ft) (cu ft) (cu ft)
100 ft. Gutter flow
5,00 300 3.18 0.47 190 300 -110
Z1 = 50.0 For Z2
Z2 = 1.0 Type A=1,0 5 300 3.18 0.47 190 300 -110
n= 0.016 Rolled = 3.5 10 600 224 0.33 200 600 -400
S= 0.0100 15 900 1.77 0.26 237 900 -663
' 20 1200 1.45 0.22 259 1200 -941
d= 0.115 ft, 25 1500 1.21 0.18 270 1500 -1230
30 1800 1.04 0,15 279 1800 -1521
A R Q Tc Tc total I Qc 35 2100 0.91 0.14 284 2100 -1816
40 2400 0.82 0.12 293 2400 -2107
0,34 0.06 0.47 1,21 5.00 3.18 0,47 45 2700 0.74 0.11 297 2700 -2403
50 3000 0.68 0.10 303 3000 -2697
Qpeak for Case 1= 0.47 cfs 55 3300 0.64 0.10 314 3300 •2986
60 3600 0.61 0.09 327 3600 -3273
65 3900 0.60 0.09 348 3900 -3552
CASE 2 70 4200 0.58 0.09 362 4200 -3838
75 4500 0.56 0.08 375 4540 -4125
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0.08 378 4800 4422
the peak flow =.90(3.18)(Imp. Area) = 0.32 cfs 85 5100 0,52 0,08 394 5100 -4706
90 5400 0,50 0.07 402 5400 -4998
95 5700 0.49 0.07 415 5700 •5285
So, the Peak flow for the Basin is the greater of the two flows, 100 6000 0.48 0A7 428 6000 -5572
0.47 cfs
208' DRAINAGE POND CALCULATIONS
Provided '208' Area 400 sq ft
Required'208' Area 400 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 200 cu ft Q 0.50' depth
Maximum Storage Required by Bowstring -110 cu ft
Number and Type of Drywelis Required 0 Single
1 Double
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Weighted Runoff Coefficient Calculation
~ Project: Springfield First Addition
Basin: A2 IPE Job 99141
Total Area (acres): 0.336 Designer: SKM
Imp. Area (acres): 0.15 Date: 10/19
Grass Area (acres): 0.19
Imp. Area "C": 0.90
Grass Area "C": 0.15
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(Imp. Area)(Imp. "C")= 0.1314
(Grass Area)(Grass "C")= 0.0285
0.3360 0.1599
Weighted "C"= 0.1599
0.48
0.3360
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PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST `''`•BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN; A2 kDETENTION BASIN DESIGN BASIN: A2
DESIGNER: SKM
Tot. Area 0.34 Acres 14623 i~ OATE: 10119/99
Imp. Area 6365 SF
.w,
C = 0,48
Time Increment (min) 5
;.Time of Conc. (min) 5.00 •
CASE 1 ; Outflow (cfs) 1.0
Design Year Flow 10
30 ft. Overland Flow ;Area (acres) 0.34
'w'Impenrious Area (sq ft) 6365
Ct = 0.15 ~'C Factor 0.48
aL= 30 ft. I Area' C 0,16
n= 0.02 Street Area 6365
S = 0.020
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Tc = 0,36 min., by Equation 3-2 of Guidelines Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
(min) (sec) (inmr) (cfs) (cu ft) (cu ft) (cu ft)
210 ft. Gutter flow
5,00 300 3.18 0.51 206 300 -94
Z1 = 50.0 For Z2 ;;~,.r . . Z2 = 1,0 Type A=1.0 5 300 3.18 0.51 206 300 -94
n= 0.016 Rolled = 3,5 10 600 2.24 0.36 217 600 -383
S= 0,0100 • 15 900 1.77 0.29 257 900 -643
20 1200 1.45 0.23 281 1200 -919
d= 0.119 ft. 25 1500 1.21 0.19 293 1500 -1207
;y 30 1804 1.04 0.17 302 1800 -1498
A R Q Tc Tc total I Qc 35 2100 0.91 0.15 308 2100 -1792
' 40 2400 0.82 0.13 317 2400 -2083
0,36 0.06 0.51 2.48 5.00 3.18 0.51 45 2700 0.74 0.12 322 2700 -2378
50 3000 0.68 0,11 329 3000 -2671
Qpeak for Case 1= 0.51 cfs 55 3300 0,64 0.10 340 3300 -2960
60 3600 0.61 0.10 354 3600 -3246
65 3900 0.60 0.10 377 3900 -3523
CASE 2 70 4200 0.58 0.09 393 4200 -3807
y~'~`~"~ 75 4500 0.56 0.09 406 4500 -4094
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0,53 0.09 410 4800 -4390
the peak flow =.90(3.18)(Imp. Area) = 0.42 cfs 85 5100 0,52 0.08 427 5100 -4673
90 5400 0,50 0.08 435 5400 -4965
95 5700 0.49 0.08 450 5700 - 5 2 5 0
So, the Peak fl
ow for the Basin is the greater of lhe two flows, 100 6000 0,48 0.08 464 6000 -5536
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0.51 cfs ~ 208' DRAINAGE POND CALCULATIONS
Provided'208' Area 800 sq ft
Required '208' Area 530 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 400 cu ft @ 0.50' depth
Maximum Storage Required by Bowstring -94 cu ft
. Number and Type of Drywells Required 0 Single
;,r-' 1 Double
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PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN: B DETENTION BASIN DESIGN BASIN: B
DESIGNER; SKM
Tot. Area 0.71 Acres 31011 SF ' DATE: 10119199
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Imp. Area 6184 SF
C = 0.20
Time Increment (min) 5
Time of Conc. (min) 5.00
CASE 1 Outflow (cfs) 0.3
Design Year Flow 10
35 ft. Overiand Flow Area (acres) 0.71
Impervious Area (sq ft) 6184
Ct = 0,15 'C Factor 0.20
L= 35 ft. Area " C 0.14
n= 0.02 _ • Street Area 6184
S = 0.020
Tc = 0.39 min., by Equation 3-2 of Guidelines Time Time Inc. intens. Q Devel. Vol,ln Vol,Out Storage
- . (min) (sec) (iNhr) (cfs) (cu ft) (cu fl) (cu fi)
290 ft. Gutter flow 5A0 300 3.18 0.45 182 90 92
Z1 = 50.0 For Z2 '
Z2 = 1.0 Type A=1.0 5 300 3.18 0.45 182 90 92
n= 0.016 Rolled = 3.5 10 600 2.24 0.32 192 180 12
S= 0.0100 15 900 1.77 0.25 227 270 -43
20 1200 1.45 0,21 248 360 -112
d= 0,114 ft, 25 1500 1.21 0.17 259 450 -191
30 1800 1.04 0.15 267 540 -273
A R Q Tc Tc total I Qc ~ 35 2100 0.91 0.13 272 630 -358
r, .
~+,,:a 40 2400 0.82 0.12 280 720 -440
.~:,w,.
0.33 0.06 0.45 3.52 5.00 3.18 0.45 45 2700 0.74 0.11 285 810 •525
50 3000 0.68 0.10 291 900 -609
. Qpeak for Case 1= 0.45 cfs 55 3300 0.64 0.09 301 990 -689
60 3600 0.61 0.09 313 1080 -767
65 3900 0.60 0.09 ' 333 1170 •837
CASE 2 ' ~70 4200 0.58 0.08 347 1260 -913
i'75 4500 0.56 0.08 359 1350 -991
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0.08 362 1440 -1078
the peak flow =.90(3.18)(Imp. Area) = 0.41 cfs 85 5100 0.52 0.07 378 1530 -1152
90 5400 0.50 0.07 385 1620 -1235
95 5700 0,49 0.07 398 1710 -1312
So, the Peak flow for the Basin is the greater of the two flows, a~~{ 100 6000 0.48 0.07 410 1800 -1390
0.45 cfs
,
y. :
1208' DRAINAGE POND CALCULATIONS
Provided'208' Area 529 sq ft
Required'208' Area 515 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 264,5 cu ft@ 0.50' depth
: Maximum Storage Required by Bowstring 92 cu ft
Number and Type of Drywells Required 1 Single
0 Double
~
~ ~ ~ w■ ~ ~ ~ ~w ~ w~ ~ ~ ~ ~ ~w ~ ~ ~ w~ r
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN; CF DETENTION BASIN DESIGN BASIN: CF
DESIGNER: SKM
Tot. Area 0,44 Acres 19205,02 SF DATE: 10119199
Imp. Area 9889 SF
C = 0,25
Lawns - 0,10 Time Increment (min) 5
Impervious - 0.90 Time of Conc. (min) 5.00
CASE 1 Outflow (cfs) 1.0
' Desfgn Year Flow 10
75 ft. Overland Flow Area (acres) 0.44
ImpeNious Area (sq ft) 9889
Ct = 0.15 'C' Factor 0,25
L= 75 ft. Area' C 0,11
n= 0.02 Street Area 9889
S = 0.010
Tc = 0.76 min., b E uation 3-2 of Guidelines
y q Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
min sec nmr cfs cu ft cu ft cu ft
( ) c ) ~i ~ c ) c ) c ) c )
368 fl,Gutterflow „ ;a~
' 5.00 300 3.18 0.35 141 300 -159
Z1= 50.0 For Z2 ....._._._.w__._____......_.. a_______.
~Y.
Z2 = 1.0 Type A=1.0 , 5 300 3.18 0.35 141 300 -159
n= 0.016 Rolled = 3.5 10 600 2.24 0.25 149 600 -451
S= 0.0148 15 900 1.77 0.20 176 900 -724
20 1200 1.45 0.16 192 1200 -1008
d= 0.096 ft. 25 1500 1.21 0,13 200 1500 -1300
30 1800 1.04 0.11 207 1800 -1593
A R Q Tc Tc total I Qc s 35 2100 0.91 0.10 211 2100 -1889
' 40 2400 0.82 0.09 217 2400 -2183
0.24 0.05 0.35 4.12 5,00 3.18 0.35 45 2700 0,74 0.08 220 2700 -2480
50 3000 0.68 0,07 225 3000 -2775
Qpeak for Case 1= 0.35 cfs ' 55 3300 0.64 0,07 233 3300 -3067
60 3600 0.61 0.07 242 3600 -3358
65 3900 0.60 0.07 258 3900 -3642
CASE 2 .,70 4200 0,58 0.06 269 4200 -3931
n~ ~ 75 4500 0.56 0.06 278 4500 -4222
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0.06 261 4800 -4519
the peak Flow =.90(3.18)(Imp. Area) = 0.65 cfs 65 5100 0.52 0.06 292 5100 -4808
90 5400 0.50 0.06 298 5400 -5102
95 5700 0.49 0.05 308 5700 -5392
So, the Peak flow for the Basin is the greater of the hvo flows, 100 6000 0.48 0.05 318 6000 -5682
0.65 cfs
ai1p 1{.`' a
208' DRAINAGE POND CALCULATIONS
, •
Provided'248' Area 886 sq ft
Required '208'Area 824 sq ft
~DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 443 cu ft@ 0.50' depth
r' Maximum Storage Required by Bowstring -159 cu ft
~ Number and Type of Drywells Required 0 Single
. 1 Double
`
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN: DE DETENTION BASIN DESIGN BASIN: DE
DESIGNER: SKM
Tot. Area 0,71 Acres 34,059 SF DATE: 10119/99
Imp. Area 10679 SF
C = 0.30
Lawns - 0.10 Time Increment (min) 5
Impervious - 0,90 Time of Conc, (min) 5.00
CASE 1 Oufflow (cfs) 2.0
Design Year Fiow 10
TO ft. Overland Flow •`~Area (acres) 0.71
~Y Impervious Area (sq ft) 10679
Ct = 0.15 'C' Factor 0.30
L= 70 fl. Area' C 021
n= 0,02 Street Area 10679
S = 0.020
~'L~57Ahr
Tc 0.59 min,, by Equation 3-2 of Guidelines Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
(min) (sec) (inlhr) (cfs) (cu ft) (cu ft) (cu ft)
~368 ft. Gutter flow ' 5.00 300 3,18 0.68 272 600 -328
„'q xr
Z1 = 50,0 For Z2
Z2 = 1.0 Type A=1.0 5 300 3,18 0.68 272 600 -328
n= 0.016 Rolled = 3.5 10 600 2.24 0.48 287 1200 •913
S= 0,0148 15 900 1,77 0,38 340 1800 -1460
20 1200 1.45 0.31 371 2400 -2029
d= 0.123 ft. 25 1500 1.21 0,26 387 3000 -2613
30 1800 1.04 0.22 399 3600 -3201
A R Q Tc Tc total I Qc 35 2100 0.91 0.19 407 4200 •3793
40 2400
0.39 0.06 0.68 3.49 5A0 3,18 0,68 x~"~' 0.82 0.17 419 4800 -4381
s>>;:x, 45 2700 0,74 0.16 426 5400 -4974
50 3000 0.68 0.14 435 6000 -5565
Qpeak for Case 1= 0 68 cfs '`-7 55 3300 0.64 0,14 450 6600 -6150
60 3600 0.61 0.13 468 7200 -6732
~ 65 3900 0,60 0.13 499 7800 -7301
CASE 2 70 4200 0.58 0.12 519 8400 -7881
75 4500 0.56 0,12 537' 9000 -8463
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0.11 542 9600 -9058
the peak flow =.90(3.18)(Imp. Area) = 0.70 cfs A6T85 5100 0.52 0,11 565 10200 -9635
90 5400 0,50 0.11 575 10800 -10225
95 5700 0.49 0.10 595 11400 -10805
So, the Peak flow for the Basin is the greater of the two flows, 1100 6000 0.48 0.14 614 12000 -11386
0.70 cfs
208' DRAINAGE POND CALCULATIONS
Provided '208'Area 1208 sq ft
Required'208' Area 890 sq ft
w'
,
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 604 cu ft@ 0,50' depth
~ Maximum Storage Required by Bowstring -328 cu ft
Number and Type of Drywells Required 0 Single
° 2 Double
~
i ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN: G DETENTION BASIN DESIGN BASIN; G
DESIGNER; SKM
Tot, Area 0.15 Acres 6581 SF DATE; 10/20I99
Imp. Area 3598 SF
C = 0.25
Lawns - 0.10 Time Increment (min) 5
Imperoious - 0.90 Time of Conc, (min) 5.00
CASE 1 Outflow (cfs) 1.0
Design Year Flow 10
40 ft. dverland Flow Area (acres) 0.15
Impervious Area (sq ft) 3598
Ct = 0.15 'C' Factor 0,25
L= 40 ft. Area * C 0.04
n= 0.02 Street Area 3598
S = 0.020
Tc = 0.42 min., by Equation 3-2 of Gufdelines Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
(min) (sec) (inlhr) (cfs) (cu ft) (cu ft) (cu ft)
115 ft, Gutter flow
5.00 300 3.18 0.12 48 300 -252
Z1 = 50.0 For Z2
Z2 = 1.0 Type A=1.0 5 300 3.18 0.12 48 300 -252
n= 0.016 Rolled = 3.5 10 600 2,24 0.08 51 600 -549
S= 0,0370 15 900 1,77 0.07 60 900 -840
20 1200 1.45 0.05 65 1200 -1135
d= 0.054 ft. 25 1500 1.21 0.05 68 1500 -1432
30 1800 1,04 0.04 70 1800 -1730
A R Q Tc Tc total I Qc 35 2100 0,91 0.03 72 2100 -2028
40 2400 0.82 0.03 74 2400 -2326
0.07 0.03 0.12 1.20 5,00 3.18 0.12 45 2100 0.74 0.03 75 2700 -2625
50 3000 0.68 0.03 77 3000 -2923
Qpeak for Case 1= 0.12 cfs 55 3300 0,64 0,02 79 3300 -3221
60 3600 6.61 0.02 82 3600 •3518
65 3900 0,60 0.02 88 3900 -3812
CASE 2 70 4200 0,58 0.02 91 4200 •4109
75 4500 0.56 0.02 95 4500 -4405
Case 2 assumes a Time of ConcentraGon less than 5 minutes so that 80 4800 0,53 0.02 95 4800 -4705
the peak flow =.90(3.18)(Imp, Area) = 024 cfs 85 5100 0.52 0.02 99 5100 -5001
90 5400 0.50 0.02 141 5400 -5299
95 5700 0.49 0.02 105 5700 -5595
So, the Peak flow for the Basin is the greater of the two flows, 100 6000 0,48 0.02 108 6000 -5892
0.24 cfs
208' DRAINAGE POND CALCULATIONS
Provided '208' Area 375 sq ft
Required '208'Area 300 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 187,5 cu ft@ 0.50' depth
Maximum Storage Required by Bowstring -252 cu ft
Number and Type of Drywells Required 0 Single
1 Double
~
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN: H DETENTION BASIN DESIGN BASIN: H
DESIGNER; SKM
Tot. Area 0.58 Acres 25313 SF DATE: 10120199
Imp. Area 5901 SF
C = 0.25
Lawns - 0.10 Time Increment (min) 5
Imperoious - 0.90 Time of Conc, (min) 5.00
CASE 1 Outflow (cfs) 1.0
Design Year Flow 10
100 ft. Overland Flow Area (acres) 0.58
Impervious Area (sq ft) 5901.21
Ct = 0.15 'C' Factor 025
L= 100 ft. Area' C 0.15
n= 0.02 Streel Area 5901.21
S = 0,040
Tc = 0.60 min., by Equation 3-2 of Guidelines Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
(min) (sec) (in/hr) (cfs) (cu ft) (cu ft) (cu ft)
150 ft. Gutter flow
5,00 300 3.18 0.46 186 300 -114
Z1 = 50.0 For Z2
Z2 = 1.0 Type A=1.0 5 300 3.18 0.46 186 300 -114
n= 0.016 Rolled = 3.5 10 600 2.24 0.33 196 600 -404
S= 0.0100 15 900 1.77 0.26 232 900 -668
20 1200 1.45 0.21 253 1200 -947
d= 0.115 ft, 25 1500 121 0.18 264 1500 •1236
30 1800 1.04 0.15 272 1800 -1528
A R Q Tc Tc total I Qc 35 2100 0.91 0.13 278 2100 -1822
40 2400 0.82 0,12 286 2400 -2114
0.33 0.06 0.46 1.82 5.00 3,18 0.46 45 2700 0,74 0.11 290 2700 -2410
50 3000 0.68 0,10 297 3000 -2703
Qpeak for Case 1= 0.46 cfs 55 3300 0.64 0.09 307 3300 -2993
60 3600 0.61 0.09 319 3600 -3281
65 3900 0.60 0.09 340 3900 -3560
CASE 2 70 4200 0.58 0.08 354 4200 -3846
75 4500 0.56 0.08 366 4500 -4134
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0,08 370 4800 -4430
the peak flow =.90(3.18)(Imp, Area) = 0.39 cfs 85 5100 0.52 0.08 385 5100 -4715
90 5400 0.50 0.07 392 5400 -5008
95 5700 0.49 0.07 406 5700 -5294
So, the Peak flow for the Basin is the greater of the two flows, 100 6000 0.48 0.07 419 6000 -5581
0.46 cfs
208' DRAINAGE POND CALCULATIONS
Provided'208' Area 600 sq ft
Required'208' Area 492 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 300 cu ft @ 0.50' depth
Maximum Storage Required by Bowstring •114 cu ft
Number and Type of Drywells Required 0 Single
1 Double ~
~
T
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CAY
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A
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SPRINGFIELD FIRST ADDITION
CURB INLET CALCULATIONS (10 YEAR) Continuous grade condition
Curb Inlet Depression = 2 in, .
Standard Curb Inlet Length = 4 ft.
Upstream Gutter Roughness Reciprocal Depth Length
Curb Drop Impervious Peak Flow Slope Coeff. Cross slope of Flow Required
Basin Station R1L Area c.f.s. S n Z Zln d` QalLa`" Q!(Qa1La) Remarks
- - - - - - - - ~
C 317 R 4589 0.30 0.0100 0.0160 50 3125 0.09 0.063 4.74 Need 1- 5' curb inlet
D 10+53 L 4525 0.30 0.0100 0.0160 50 3125 0.09 0.063 4.74 Need 1- 5' curb inlet
G 16+60 R 3598 0.24 0.3700 0,0160 50 3125 0.04 0.030 8.11 Need 2- 4' curb inlet
B1 52+25 R 1224 0.08 0.0200 0.0160 50 3125 0.05 0.034 2.36 Need 1- 4' curb inlet
62 51+20 R 2180 0.14 0,0040 0.0160 50 3125 0.08 0.057 2,48 Need 1- 4' curb inlet
A2(1) 13+20 R 2520 0.17 0.0112 0.0160 50 3125 0.07 0.050 3.39 Neetl 1- 4' curb inlet
Peak flow for intermediate ponds (those without a drywell) is based on Q=CIA, where 1= 3.18 in., C=0.90 and A= impervious area (acres) upstream of the curb inlet
Calculated per Figure 18 of Guidelines
Calculated per Figure 16 of Guidelines
A 4 foot curb drop with a 6" gutter has a
capacity of 4,0 cfs in sump condition.
~
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Ptannlrkg. FsglrraartM, Arrlsltdeturrr, Landaca" ArdtltocSUrk Land Surn¢qing
CLC A~SOCIATES, INC.
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r-+ i~iAL PUBLtC DOCl.lM'--~4~ .
~ 5'POKANF, C;OUNn ENGk~~ERS OFP1G~
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S138~~~AL# _ -
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~ SPOKANE, 'VIIA, ■ DEN VER, CO
'
'
:DRA--NAGE ^ECHNICA----, REPORT
for the
SPR:NGF--E--.::) I ST AD:D--T--ON
Ar---' AUr---'UMN CREST
' CLC No. 99141
NOVEMBER 1999
Prepared for:
' Linderman Construction
4823 Sky Meadows Lane
Greenacres, WA 99016
'
' Prepared By:
C.L. C. Associates, Inc.
707 W. 7th Avenue
' Suite 200
Spokane, WA 99204
(509) 458-6840
'
'
DRAINAGE REPORT
i ' for the
Springfield First 1 St Addition
at Autumn Crest Plat
Spokane County, Washington
November 1999
he desig~n improvemen~ts shown in t~his 141 of plans a~nd calculat~ions conform to the applicable
ed~itions of the Spok•ane Cou.n~ty St~andards fo' oad and Sewe Constrructiion and the ~ pokan
Cou~nty u'delines for Stormwater Ma 7a,geme ~t. All desigan deviations have been ap roved by the
Spo a e ounty : n~. ap mw- Qese *ns (calculations for const~ruction.
This report has been prepared by Susan K. Murphy of CLC Associates, Inc. under the direction of
the undersigned professional engineer whose seal and signature appear ereon.
wa l~
~
'
~a 9
5462
~
EXPIRES 9/24/'0 ~
Todd R. Whip le, P.E.
' Sp rin ield 1 st Addition
Drainage Narrative
'
GENERAL
The Springfield First Addition at Autumn Crest plat is a 5.07 acre development of 14 single
family residential lots located east and south of Progress Road and 16`h Avenue in the Spokane
Valley within Spokane County, Washington. The site is currently vacant with field grass as the
predominant land cover. This is the final phase of the Autumn Crest preliminary plat. Single
family residential development surrounds the plat location. A vicinity and location map have
been included within the technical section of this document.
PURPOSE
The purpose of this report is to determine the extent of storm drainage facilities which will be
required to dispose of the increase in stormwater runoff created by the development of the
' Springfield First Addition at Autumn Crest plat. The storm drainage facilities on this project will
be designed to dispose of runoff from a ten year design storm for the onsite basins, as requued by
the Spokane County Guidelines for Stormwater Management. This development is within the
Aquifer Sensitive Area of Spokane County and is subject to '208' requirements. For this project,
the 10-year curve from the Spokane, Medical Lake, Reardon, Cheney and Rockford intensity
curves was used, as well as the SCS iso-pluvial rainfall curves.
ANALYSIS METHODOLOGY -
Per the Spokane County Guidelines for Stormwater ManaQement (GSM), the Rational Method,
which is recommended for basins less than ten acres in size, was used to determine the peak
discharges and runoff volumes for all onsite basins.
PROJECT DESCRIPTION
, The Springfield First Addition at Autum.n Crest subdivision is located in Section 26, T. 25 N., R.
44 E., W.M. within Spokane County, Washington
r TOPOCRAPHY
The existing site generally drains to the northeast. Within the plat the natural topography was
~ used as much as Possible to route storm drainage. Due to the flat sloPes encountered, no
concentrated pre-existing flows were observed nor were there any signs that anything other than
sheet flow and ground absorption have occurred on this site. The general slopes within this plat
vary from flat to nearly flat with the maximum existing slope at 0.02 ft./ft. For development
purposes as stated the natural sloping was used for design and is maintained as possible
throughout the project.
CLC Associates, Inc. 1 Springfield 1 st Additron Plat
Drainage Report
'
'
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 one type of soil within the Class B type. This soil type
is described as follows.
GmB - Garrison gravelly loam, 0 to 5 percent slopes: Soils within this soil type are somewhat
excessively drained, gravelly or stony soils of moderately rapid permeability, with a surface layer
of gravelly loam, and a subsoil stratum of sand, loam and cobblestones.l`hey formed under grass
in glacial outwash mixed in the upper part with volcanic ash. Surface runoff is slow, and the
hazard of erosion is slight. Snokane Countv Guidelines for Stormwater Manap-ement indicate this
to be a Soil Group Type A and pre-approved for drywell installation.
, Hydrologic Soil Classification - B
DRAINAGE NARRATIVE
Offsite
Based on the natural topography and final design, there are no offsite flows. A copy of the basin
area is included for reference..
Onsite
As this plat is within the aquifer sensitive area of Spokane County all onsite drainage will be
collected and treated using the "208" runoff inethod as described in the Spokane County
Guidelines for Stormwater Management. To facilitate this analysis, the Springfield 1 S` Addition at
, Autumn Crest plat was divided into 8 permanent basins (A through H). Table 1 lists the basins
and pond combinations for easy reference.
DRAINAGE CALCULATIONS SUMMARY Bowstring calculations have been included for individual basins to determine the extent of storm
drainage facilities required for the 10-year storm event. Weighted "C" Runoff Coefficients were
calculated for each basin of less than 10 acres based on dwelling units per gross area, Table 1 pg
6-2 of the GSM. Table No. 1 includes the basin size, number of dwelling units, and runoff
l coefficients. The basin characteristics are summarized below with the remaining calculations in
the appendix.
CLC Associates, Inc. 2 Springfield 1 st Additron Plat
Drainage Report
~ Table No. 2- Pond Requirement Summary
' p ~ : ' . 208* r~ ~ S* ~ ► e ils
, e, , e, o _d e, •ll.e,
A 1 4966 414 420 1-Type B
A2(l) 2800 233 400 -
A2(2) 3845 320 400 1-Type B
B1 1350 113 76
B2 2180 , 182 176
B3 2780 232 277 -
~ B 6310 527 529 1-Type B
C 4,598 383 400 -
D 3,975 331 400 -
E 7,500 625 808 2-Type B
F 5,291 441 486 1-Type B
G 31598 300 375 1-Type B
'
H 51600 467 600 1-Type B
* `208' area requirecUprovided is based on bottom area only, @ 0.5' depth
Type A is a Spokane County Standard Drywell - Single Depth, Capacity 0.3 cfs
Type B is a Spokane County Standard Drywell - Double Depth, Capacity 1.0 cfs
Inlet Calculations
' Inlet calculations are provided for all inlets within the basin. The calculation worksheets for the
10 and 50-year storm events for inlets on continuous grades and in sump conditions are provided
in the appendix. By-pass flows were calculated for each inlet on a continuous grade, and added to -
, the downstream inlet.
CONCL USION
i
As demonstrated by the calculations and body of this report the storm drainage facilities provided
in this design will adequately remove from the streets, store and dispose of the stormwater from
the site for the 10-year design storm as required by Spokane County. Additionally, the required
'208' treatment area is provided for the runoff from the street impervious areas. CLC Associates, Inc. 4 Springrield lst Addition Plat
Drainage Report
'
'
APPENDIX
MAPS
VICINITY MAP
SOILS MAP
DEVELQPED BOWSTRING CALCULATIONS
10-Year Design Storm
Inlet Calculations
~
BASIN MAP
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Weighted Runoff Coefficient Calculation
, Project: Springfield First Addition
Basin: A1 I PE Job 99141
Total Area (acres): 0.33 Designer: SKM
r I mp. Area (acres): 0.14 Date: 11 /09
Grass Area (acres): 0.19
Imp. Area "C": 0.90
Grass Area "C": 0.15
(Imp. Area)(Imp. "C")= 0.1260
(Grass Area)(Grass "C")= 0.0?85
0.3300 0.1545
Weighted "C"= 0.1545
0.47
0.3300
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN: At DETENTION BASIN DESIGN BASIN: A1
DESIGNER; SKM
Tot, Area 0.33 Acres 14390 SF DATE: 11l09199
Imp. Area 6107 SF
C = 0.47
Time Increment (min) 5
Time of Conc, (min) 5.00
CASE 1 Outflow (cfs) 1.0
Design Year Flow 10
20 ft. Overland Flow Area (acres) 0.33
Impervious Area (sq ft) 6107
Ct = 0.15 'C' Factor 0.47
L= 20 ft. Area ' C 0.16
n= 0.02 Street Area 4966
S = 0.020
Tc = 0,24 min,, by Equation 3-2 of Guidelines Time Time Inc, Intens. Q Devel. Vol,ln Vol.Out Storage
(min) (sec) (inlhr) (cfs) (cu ft) (cu ft) (cu ft)
100 ft. Gutter flow
5.00 300 3.18 0.49 ' 198 300 -102
Z1 = 50.0 For Z2 . .
Z2 = 1.0 Type A=1.0 5 300 3.18 0.49 198 300 -102
n= 0.016 Rolled = 3.5 10 600 2,24 0.35 209 600 -391
S= 0,0100 15 900 1,77 0.27 248 900 -652
20 1200 1.45 023 271 1200 -929
d= 0.117 ft, 25 1500 121 0.19 282 1500 -1218
30 1800 1,04 0.16 291 1800 •1509
A R Q Tc Tc total I Qc 35 2100 0,91 0.14 297 2100 -1803
40 2400 0.820.13 306 2400 •2094
0.35 0.06 0.49 1.19 5.00 3.18 0.49 45 2700 0.74 0.11 310 2700 -2390
50 3400 0.68 0.11 317 3000 -2683
Qpeak for Case 1= 0.49 cfs 55 3300 0.64 0,10 328 3300 -2972
60 3600 0.61 0.09 341 3600 -3259
65 3900 0.60 0.09 363 3900 -3537
CASE 2 70 4200 0.58 0.09 378 4200 -3822
75 4500 0,56 0.09 391 4500 -4109
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0.08 395 4800 -4405
the peak flaw =.90(3.18)(Imp. Area) = 0.40 cfs 85 5100 0.52 0,08 412 5100 -4688
90 5400 0,50 0.08 419 5400 -4981
95 5700 0,49 0.08 434 5700 -5266
So, the Peak flow for the Basin is the greater of the two Bows, 100 6000 0,48 0,07 447 6000 -5553
0.49 cfs
208' DRAINAGE POND CALCULATIONS
Provided '208' Area 400 sq ft
Required'208'Area 414 sqft
DRYWELL REQUIREMENTS • 10 YR DESIGN STORM
Provided Storage Volume 200 cu ft@ 0,50' depth
Maximum Storage Required by BowsUing •102 cu ft
Number and Type of Drywells Required 0 Single
1 Double
Weighted Runoff Coefficient Calculation
Project: Springfield 1 st Addn.
Basin: A2 IPE Job 99141
Total Area (acres): 0.336 Designer: SKM
I mp. Area (acres): 0.19 Date: 11 /08
Grass Area (acres): 0.15
Imp. Area "C": 0.90
Grass Area "C": 0.15
(Imp. Area)(Imp. "C")= 0.1682
(Grass Area)(Grass "C")= 0.0224
0.3360 0.1906
Weighted "C"= 0.1906
0.57
0.3360
~
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT; SPRINGFIELD 1ST
10•Yr Design Storm BASIN; A2 DETENTION BASIN DESIGN BASIN: A2
DESIGNER; SKM
Tot. Area 0.34 Acres 14623 DATE: 10/19199
Imp. Area 8140 SF
C = 0.57
Time Increment (min) 5
Time of Canc. (min) 5.00
CASE 1 OuMow (cfs) 1.0
Design Year Flow 10
30 ft, Overland Flow Area (acres) 0.34
Impervious Area (sq ft) 8140
Ct = 0.15 'C' Factor 0.57
L= 30 ft, Area " C 0,19
n= 0.02 Street Area 6536
S = 0.020
Tc = 0.31 min., by Equation 3-2 of Guidelines Time Time Inc, Intens. Q Devel. Vol,ln Vol.Out Storage
(min) (sec) (inlhr) (cfs) (cu ft) (cu ft) (cu ft)
210 ft,Gutterflow
5,00 300 3.18 0.61 ' 245 300 -55
Z1= 50.0 For Z2
Z2 = 1.0 Type A=1.0 5 300 3,18 0.61 245 300 -55
n= 0.016 Rolled = 3.5 10 600 2.24 0.43 258 600 -342
S= 0.0100 15 900 1.77 0.34 305 900 -595
20 1200 1,45 0.28 333 1200 -867
d= 0.127 ft, 25 1500 121 0.23 348 1500 -1152
30 1800 1.04 0.20 359 1800 -1441
A R Q Tc Tc total I Qc 35 2100 0.91 0.17 366 2100 -1734
40 2400 0.82 0.16 377 2400 -2023
0.41 0.06 0.61 2,37 5.00 3.16 0.61 45 2700 0,74 0.14 383 2700 -2317
50 3000 0.68 0.13 391 3000 -2609
Qpeak for Case 1= 0.61 cfs 55 3300 0.64 0,12 404 3300 -2896
60 3600 0.61 0.12 420 3600 -3180
65 3900 0.60 0,11 448 3900 -3452
CASE 2 70 4200 0.58 0.11 466 4200 -3734
75 4500 0.56 0.11 482 4500 -4018
Case 2 assumes a Time of Concentrafion less than 5 minutes so that 80 4840 0.53 0.10 487 4800 4313
the peak flow =.90(3.18)(Imp. Area) = 0.53 cfs 85 5100 0.52 0.10 508 5100 -4592
90 5440 0.50 0.10 517 5400 -4883
95 5700 0.49 0.09 535 5700 -5165
So, the Peak flow for the Basin is the greater of the two flows, 100 6000 0.48 0,09 551 6000 -5449
0.61 cfs
208' DRAINAGE POND CALCUI.ATIONS
Provided'208' Area 800 sq ft
Required'208' Area 545 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 400 cu ft Q 0.50' depth
Maximum Storage Required by Bowstring -55 cu ft
Number and Type of Drywells Required 0 Single
1 Dauble
'
Weighted Runoff Coefficient Calculation
Project: Springfield 1 st Addn.
Basin: B IPE Job 99141
Total Area (acres): 0.712 Designer: SKM
' Imp. Area (acres): 0.18 Date: 11/10
Grass Area (acres): 0.53
Imp. Area "C": 0.90
' Grass Area "C": 0.15
(Imp. Area)(Imp. "C")= 0.1611
(Grass Area)(Grass "C")= 0.0799
0.7120 0.2411
~
Weighted "C"= 0.2411
0.34
0.7120
~
'
'
~■ir ~ ~ ~ ~ ~ ~ ~ ~ ri ~ ~ r~ ~r ~ r ~ ~
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN; B DETENTION BASIN DESIGN BASIN: B
DESIGNER: SKM
Tot. Area 0,71 Acres 31011 SF DATE: 10h9/99
Imp, Area 6310 SF
C = 0.34
Time Increment (min) 5
Time of Conc. (min) 5,00
CASE 1 Outflow (cfs) 0.3
Design Year Flow 10
35 ft. Overland Flow Area (acres) 0,71
Impervious Area (sq ft) 6310
Ct = 0.15 'C Factor 0,34
L= 35 ft. Area ' C 0.24
n= 0.02 Street Area 6310
S = 0.020
Tc = 0.39 min., by Equation 3-2 of Guidelines Time Time Inc. Intens. Q Devel. Vol.in Vol.Out Storage
(min) (sec) (inlhr) (cfs) (cu ft) (cu ft) (cu ft)
290 ft, Gutter flow
5,00 300 3.18 0,77' 309 90 219
Z1 = 50.0 For Z2 •
Z2 = 1.0 Type A=1.0 5 300 3.18 0.77 309 90 219
n= 0.016 Rolled = 3,5 10 600 2.24 0.54 326 180 146
S= 0.0100 15 900 1,77 0.43 386 270 116
20 1200 1,45 0.35 422 360 62
d= 0.139 ft. 25 1500 1.21 0.29 440 450 -10
30 1800 1.04 0.25 454 540 •86
A R Q Tc Tc total I Qc 35 2100 0.91 0.22 463 630 -167
40 2400 0.82 020 477 724 -243
0.49 0.07 0.77 3.09 5.00 3,18 0.77 45 2700 0.74 0.18 484 810 -326
50 3000 0.68 0.16 494 900 -406
Qpeak for Case 1= 0.77 cfs 55 3300 0.64 0.15 511 990 -479
60 3600 0.61 0.15 532 1080 -548
65 3900 0.60 0.15 567 1170 -603
CASE 2 70 4200 0.58 0.14 590 1260 •670
75 4500 0.56 0.14 610 1350 -740
Case 2 assumes a Time of ConcentraGon less than 5 minutes so that 80 4800 0.53 0,13 616 1440 -824
the peak flow =.90(3.18)(Imp, Area) = 0.41 cfs 85 5100 0.52 0,13 642 1530 -888
90 5400 0.50 0.12 654 1620 -966
95 5700 0.49 0.12 676 1710 -1034
So, the Peak flow for the Basin is the greater of the two flows, 100 6000 0.48 0.12 697 1800 •1103
0.77 cfs
208' DRAINAGE POND CALCULATIONS
Provided '208'Area 529 sq ft
Required'208' Area 529 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 264.5 cu ft@ 0.50' depth
Maximum Storage Required by Bowstring 219 cu ft
Number and Type of Drywells Required 1 Single
0 Double
~
Weighted Runoff Coefficient Calculation
' Project: Spn'ngfield 1 st Addn.
Basin. CF IPE Job 99141
Total Area (acres): 0.905 Designer: SKM
' Imp. Area (acres): 0.39 Date: 11 /10
Grass Area (acres): 0.52
Imp. Area "C": 0.90
' Grass Area "C": 0.15
(Imp. Area)(Imp. "C")= 0.3510
(Grass Area)(Grass "C")= 0.0773
0.9050 0.4283
Weighted "C"= 0.4283
0.47
0.9050
,
i
1
1
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT; SPRINGFIELD 1ST
10-Yr Design Storm BASIN: CF DETENTION BASIN DESIGN BASIN: CF
DESIGNER; SKM
Tot. Area 0.90 Acres 39418 SF DATE: 11110l99
Imp. Area 10489 SF
C = 0,41
Lawns - 0.15 Time Increment (min) 5
Imperoious - 0.90 Time of Conc. (min) 7.70
CASE 1 Outflow (cfs) 1,0
Design Year Flow 10
75 ft. Overland Flow Area (acres) 0.90
Imperoious Area (sq ft) 10489
Ct = 0.15 'C' Factor 0.47
L= 75 ft. Area ` C 0.43
n= 0.40 Street Area 9889
S = 0.010
Tc = 4.60 min., by Equation 3-2 of Guidelines Time Time Inc. Intens. Q Devel, Vol.ln Vol.Out Storage
, (min) (sec) (in/hr) (cfs) (cu ft) (cu ft) (cu ft)
368 ft. Gutter flow
7.10 462 2.56 1.09 ~ 615 462 213
Z1= 50.0 For Z2
Z2 = 1.0 Type A=1,0 5 300 3.18 1.35 544 300 244
n= 0.016 Rolled = 3,5 10 600 2.24 0.95 574 600 -26
S= 0,0148 15 900 1.77 0.75 679 900 •221
20 1200 1.45 0.62 742 1200 -458
d= 0.147 ft. 25 1500 1.21 0.51 773 1500 •727
30 1800 1.04 0.44 797 1800 -1003
A R Q Tc Tc total I Qc 35 2100 0.91 0.39 814 2100 -1286
40 2400 0.82 0.35 838 2400 -1562
0.55 0.07 1.09 3.10 7.70 2.56 1,09 45 2700 0.74 0.31 851 2700 -1849
50 3000 0.68 0,29 868 3000 -2132
Qpeak for Case 1= 1.09 cfs 55 3300 0.64 0.27 899 3300 -2401
60 3600 0.61 0.26 935 3600 •2665
65 3900 0.60 0.26 996 3900 -2904
CASE 2 70 4200 0.58 0.25 1037 4200 •3163
75 4500 0.56 0.24 1072 4500 •3428
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0,23 1083 4800 •3717
the peak flow =,94(3.18)(Imp, Area) = 0.69 cfs 85 5100 0.52 0.22 1129 5100 -3971
90 5400 0.50 0.21 1149 5400 -4251
95 5700 0.49 0.21 1188 5704 -4512
So, the Peak flow for the Basin is the greater of the lwo flows, 100 6000 0.48 0.20 1225 6000 -4775
1.09 cfs
208' DRAINAGE POND CALCULATIONS
Provided'208' Area 886 sq ft
Required'208' Area 824 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 443 cu ft@ 0.50' depth
- Maximum Storage Required by Bowstring 244 cu ft
Number and Type of Drywells Required 0 Single
1 Double
,
Weighted Runoff Coefficient Calculation
1 Project: Springfield 1 st Addn.
Basin: DE IPE Job 99141
Total Area (acres): 1.408 Designer: SKM
' I mp. Area (acres): 0.54 Date: 11 /1 0
Grass Area (acres): 0.86
Imp. Area "C": 0.90
' Grass Area "C": 0.15
(Imp. Area)(Imp. "C")= 0.4896
(Grass Area)(Grass "C")= 0.1 ?96
1.4080 0.6192
Weighted "C"= 0.6192
0.44
1.4080
'
'
'
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1 ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN: DE DETENTION BASIN DESIGN BASIN; DE
DESIGNER: SKM
Tot. Area 1.41 Acres 61,347 SF DATE: 10119199
Imp. Area 22930 SF
C = 0.44
• Lawns - 0.15 Time Increment (min) 5
Imperoious - 0.90 Time of Conc, (min) 6.34
CASE 1 Outflow (cfs) 2.0
Design Year Flow 10
70 ft. Overland Flow Area (acres) 1,41
Impervious Area (sq fl) 22930
Ct = 0.15 'C Factor 0.44
L= 70 ft, Area ' C 0.62
n= 0,40 Street Area 11480
S = 0.020
Tc = 3.58 min., by Equation 3-2 of Guidelines Time Time inc. Intens. Q Devel. Vol.ln Vol.Out Storage
(min) (sec) (inlhr) (cfs) (cu ft) (cu ft) (cu ft)
368 ft. Gutter flow
6,34 380 2.81 1.74 - 887 761 126
Z1 = 50.0 For Z2
Z2 = 1.0 Type A=1,0 5 300 3.18 1.91 792 600 192
n= 0.016 Rolled = 3.5 10 600 2.24 1,39 836 1200 •364
S= 0,0148 15 900 1.77 1.10 989 1800 •811
20 1200 1.45 0,90 1080 2400 -1320
d= 0.175 ft. 25 1500 121 0.75 1126 3000 •1874
30 1800 1.04 0.64 1161 3600 -2439
A R Q Tc Tc total I Qc 35 2100 0.91 0.56 1185 4200 -3015
40 2400 0.82 0.51 1220 4800 -3580
0.78 0,09 1.74 2.76 6.34 2.81 1.74 45 2700 0.74 0.46 1239 5400 -4161
50 3000 0.68 0.42 1265 6000 4735
Qpeak for Case 1= 1.74 cfs 55 3300 0.64 0.40 1309 6600 -5291
60 3600 0.61 0.38 1361 7200 -5839
65 3900 0.60 0.37 1450 7800 -6350
CASE 2 70 4200 0.58 0.36 1510 8400 •6890
75 4500 0.56 0.35 1562 9000 -7438
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0.33 1577 9600 -8023
the peak flow =,90(3.18)(Imp. Area) = 1.51 cfs 85 5100 0,52 0.32 1644 10200 •8556
90 5400 0.50 0.31 1673 10800 •9127
95 5700 0.49 0.30 1731 11400 -9669
So, the Peak Flow for the Basin is the greater of the two flows, 100 6000 0.48 0.30 1785 12000 -10215
1.74 cfs
208' DRAINAGE POND CALCULATIONS
Provided'208' Area 1208 sq ft
Required '208'Area 957 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 604 cu ft Q 0.50' depth
Maximum Storage Required by Bowstring 192 cu ft
Number and Type of Drywells Required 0 Single
2 Double
Weighted Runoff Coefficient Calculation
~ Project: Springfield 1 st Addn.
Basin: G I PE Job 99141
Total Area (acres): 0.151 Designer: SKM
, I mp. Area (acres): 0.10 Date: 11 /08
Grass Area (acres): 0.05
Imp. Area "C": 0.90
Grass Area "C": 0.15
(Imp. Area)(Imp. "C")= 0.0909
(Grass Area)(Grass "C")= 0.0075
0.1510 0.0984
Weighted "C"= 0.0984'
0.65
0.1510
~
~
~
~ r ~ ~r ~r ~r ~r ~ ~r ~ ~ ~■r r ~ ~ ~ ~ r ~r
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT; SPRINGFIELD 1ST
10-Yr Design Storm BASIN: G DETENTION BASIN DESIGN BASIN: G
DESIGNER: SKM
Tot. Area 0.15 Acres 6581 SF DATE: 11/08/99
Imp. Area 4400 SF
C = 0.65
Lawns - 0.15 Time Increment (min) 5
Imperoious - 0.90 Time of Conc. (min) 5.00
CASE 1 Outflow (cfs) 1.0
Design Year Flow 10
40 ft. Overland Flow Area (acres) 0.15
Imperoious Area (sq ft) 4400
Ct = 0.15 'C' Factor 0.65
L= 40 ft, Area' C 0,10
n= 0.02 Street Area 3598
S = 0.020
Tc = 0.37 min., by Equation 3-2 of Guidelines Time Time Inc. Intens. Q Devel. Vol,in Vol.Out Storage
(min) (sec) (inmr) (cfs) (cu ft) (cu ft) (cu ft)
115 ft. Gutter flow
5.00 300 3.18 0.31 125 300 -175
Z1 = 50.0 For Z2 .
Z2 = 1.0 Type A=1.0 5 300 3,18 0.31 125 300 -175
n= 0.016 Rolled = 3.5 10 600 2.24 0.22 131 600 -469
S= 0.0370 15 900 1.77 0,17 156 900 -744
20 1200 1.45 0.14 170 1200 -1030
d= 0.077 ft. 25 1500 1.21 0,12 177 1500 -1323
30 1800 1.04 0.10 183 1800 -1617
A R Q Tc Tc total I Qc 35 2100 0,91 0.09 186 2100 -1914
40 2400 0.82 0.08 192 2400 -2208
0,15 0.04 0.31 0,94 5.00 3,18 0.31 45 2700 0.74 0.07 195 2700 -2505
50 3000 0.68 0.07 199 3000 -2801
Qpeak for Case 1= 0.31 cfs 55 3300 0.64 0.06 206 3300 -3094
60 3600 0.61 0.06 214 3600 -3386
65 3900 0.60 0.06 228 3900 •3672
CASE 2 70 4200 0.58 0.06 238 4200 -3962
75 4500 0.56 0.05 246 4500 -4254
Case 2 assumes a Time of Concentration less than 5 minutes so that 80 4800 0.53 0.05 248 4800 -4552
the peak flow =.90(3.18)(Imp, Area) = 0.29 cfs 85 5100 0,52 0.05 259 5100 -4841
90 5400 0.50 0.05 263 5400 -5137
95 5700 0.49 0.05 272 5700 -5428
So, the Peak flow for the Basin is the greater of the two flows, 100 6000 0.48 0.05 281 6000 -5719
0.31 cfs
208' DRAINAGE POND CALCULATIONS
Provided'208' Area 375 sq ft
Required'208' Area 300 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 187.5 cu ft@ 0.50' depth
Maximum Storage Required by Bowstring •175 cu ft
Number and Type of Drywelis Required 0 Single .
1 Double
Weighted Runoff Coefficient Calculation
' Project: Springfield 1 st Addn.
Basin: H IPE Job 99141
Total Area (acres): 0.581 Designer: SKM
I mp. Area (acres): 0.31 Date: 11 /10
Grass Area (acres): 0.27
Imp. Area "C": 0.90
Grass Area "C": 0.15
(Imp. Area)(Imp. "C")= 0.2772
(Grass Area)(Grass "C")= 0.0410
0.5810 0.3182
Weighted "C"= 0.3182
0.55
0.5810
~
PEAK FLOW CALCULATION PROJECT: SPRINGFIELD 1ST BOWSTRING METHOD PROJECT: SPRINGFIELD 1ST
10-Yr Design Storm BASIN: H DETENTION BASIN DESIGN BASIN: H
DESIGNER: SKM
Tot. Area 0.58 Acres 25313 SF DATE: 11110l99
Imp. Area 7731 SF
C = 0.55
Lawns - 0,15 Time Increment (min) 5
Impervious - 0.90 Time of Conc, (min) 5.09
CASE 1 Outflow (cfs) 1,0
Design Year Flow 10 '
100 ft. Overland Flow Area (acres) 0.58
Imperoious Area (sq ft) 7731
Ct = 0.15 'C' Factor 0.55
L= 100 ft. Area ' C 0.32
n= 0.40 Street Area 5901
S = 0.040
Tc = 3,60 min., by Equation 3-2 of Guidelines Time Time Inc. Intens. Q Devel. Vol.ln Vol.Out Storage
(min) (sec) (iNhr) (cfs) (cu ft) (cu ft) (cu ft)
150 ft. Gutter flow
5,09 306 3.16 1.01 ~ 413 306 107
Z1 = 50.0 For Z2 a . .
Z2 = 1.0 Type A=1.0 5 300 3.18 1,02 409 300 109
n= 0.016 Rolled = 3.5 10 600 2.24 0.72 431 600 -169
S= 0.0100 15 900 1.77 0.57 510 900 -390
20 1200 1.45 0.46 557 1200 -643
d= 0,154 ft. 25 1500 121 0.39 581 1500 -919
30 1800 1,04 0,33 599 1800 -1201
A R Q Tc Tc total I Qc 35 2100 0.91 0,29 611 2100 -1489
40 2400 0.82 0.26 629 2400 -1771
0.60 0.08 1.01 1,49 5.09 3.16 1.01 45 2700 0.74 0.24 639 2700 -2061
50 3000 0.68 0.22 652 3000 -2348
Qpeak for Case 1= 1.01 cfs 55 3300 0.64 0,20 675 3300 -2625
60 3600 0.61 0,19 702 3600 -2898
65 3900 0.60 0.19 748 3900 -3152
CASE 2 70 4200 0,58 0.19 779 4200 -3421
75 4500 0.56 0.18 806 4500 •3694
Case 2 assumes a Time of ConcentraGon less than 5 minutes so that 80 4800 0.53 0.17 813 4800 -3987
the peak Flow =.90(3.18)(Imp. Area) = 0.51 cfs 85 5100 0.52 0,17 848 5100 -4252
90 5400 0.50 0.16 863 5400 -4537
95 5700 0.49 0.16 893 5700 -4807
So, the Peak flow for the Basin is the greater of the two flows, 100 6000 0.48 0.15 921 6000 -5079
1.01 cfs
208' ORAINAGE POND CALCULATIONS
Provided'208' Area 600 sq ft
Required '208' Area 492 sq ft
DRYWELL REQUIREMENTS -10 YR DESIGN STORM
Provided Storage Volume 300 cu ft @ 0.50' depth
Maximum Storage Required by Bowstring 109 cu ft
Number and Type of Drywells Required 0 Single
1 Double
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SPRINGFIELD FIRST ADDITION
CURB INLET CALCULATIONS (10 YEAR) Continuous grade condition
Curb Inlet Depression = 2 in.
Standard Curb Inlet Length = 4 ft.
Upstream Gutter Roughness Reciprocal Depth Length
Curb Drop ImpeNious Peak Flow Slope Coeff. Cross slope of Flow Required
Basin Station WL Area c.f.s. S n Z Z!n d' Qa/La"" QI(QalLa~__ Remarks
-C 317 R 4598 0.30 0.0100 4.0160 50 3125 0,09 0,063 4.74 Need 1- 5' curb inlet
D 10+53 L 3975 0.26 0.0100 0.4160 50 3125 0.09 0.060 4.33 Need 1- 5' curb inlet
G 16+60 R 4400 0.29 0.3700 0.0160 50 3125 0.05 0.032 9.13 Need 2- 4' curb inlet
B1 52+25 R 1355 0.09 0.0200 0.0160 50 3125 0.05 0.035 2.54 Need 1- 4' curb inlet
B2 51+20 R 2180 0.14 0.0040 0.0160 50 3125 0.08 0.057 2.48 Need 1- 4' curb inlet
A2(1) 13+20 R 2800 0.18 0.0112 0,0160 50 3125 0.07 0.051 3.52 Need 1- 4' curb inlet
Peak flow for intermediate ponds (those without a drywell) is based on Q=CIA, where 1= 3,18 in., C=0.90 and A= impervious area (acres) upstream of the curb inlet
Calculated per Figure 18 of Guidelines
Calculated per Figure 16 of Guidelines
A 4 foot curb drop with a 6" gutter has a
capacity of 4.0 cfs in sump condition.
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