HomeMy WebLinkAboutDrainage Reports - 05/01/2014City of Ft Collin prov P%ns
Approved ey-�
Date
Date: March 26, 2014
To: Wes Lamarque — City of Fort Collins Stormwater
From: Donald Harper, E.I.T., LEED AP, Karen Brigman
RE: Fort Collins Senior Center Expansion - Drainage Revisions Memo
JVA Job No. 2104c
Dear Mr. Lamarque:
JVA, Incorporated
25 Old Town Square
Suite 200
Fort Collins, CO 80524
Ph: 970.225.9099
Fax: 970.225.6923
Toll Free: 877.444.1951
Web site:
www.jvajva.com
E-mail:
info@jvajva.com
This memorandum has been prepared to summarize the revisions to the drainage concept, solutions
and changes in impervious area associated with the addition of Phase 2 & 3 parking lot site
improvements for the Senior Center Expansion located at 1200 Raintree Drive in the City of Fort
Collins.
Proposed Drainage Patterns
The proposed Phase 2 & 3 Senior Center parking lots consist of approximately 20,000 square feet of
additional impervious area over the previously designed and approved expansion project. See Figure
2: Developed Drainage Map for approximate areas of Phase 2 & 3 parking and revised hydrologic
basin boundaries. Although the original drainage calculations accounted for the future buildout of
Phase 2, the addition of 6,150 square feet for Phase 3 increases the site's percent impervious value
from 37.87% to 43.32% and consequently the 100-year peak storm flows are increased from 12.02
cfs to 13.01 cfs. This results in an increase in volume of stormwater runoff that is detained and
treated in the regional Detention Pond D of 0.007 acre feet, for a total of 0.237 acre feet. This water
ultimately discharges.into Spring Creek at a controlled rate that matches the historic 2 year release
rate. The only revised basin that discharges offsite into the New Mercer Canal (previously subbasin
D6, now 137) has been reduced in size by 0.24 acres for a difference in peak 100-year runoff of -0.23
cfs. Detention Pond D has been designed to detain the buildout 100-year storm event with additional
volume for water quality and has the capacity to handle this 0.007 acre feet increase in volume.
Detention Pond D's water quality plate had originally been slightly oversized in height, and
therefore the addition of Phase 3 does not necessitate a change to the outlet structure. See the
revised utility plan sheets, Rational Method runoff calculations, and water quality pond volume
calculations.
The permeable paver system has been expanded for the new impervious area and the underdrain
beneath it has been extended to the limits of the Phase 3 parking lot to the west. The City of Fort
Collins requires at least 25% of new pavement be treated using permeable pavement technology as
part of its Low Impact Development (LID) policy. The total percentage of new pavement being
proposed as permeable pavers with the addition of the Phase 2 & 3 improvements is 20%. A
variance is requested for this modification of standard with the following justifications: 1) site
constraints limit the effective areas for permeable paver installation so that 25% minimum is not able
to be achieved, and 2) 100% of the water quality capture volume for the site is treated in Detention
Pond D — volume reduction benefits for using LID practices were not calculated for this project. All
runoff treated by the permeable paver system is therefore in addition to the water quality treatment
provided by the pond design.
BOULDER I FORT COLLINS I WINTER PARK
Fort Collins Senior Center Expansion
March 26, 2014
Page 2 of 2
Proposed grading for the site has been designed to mimic the existing natural drainage patterns such
that runoff sheet flows north across the lot, where the majority is captured onsite by permeable
pavers located within downstream parking stalls (see Figure 2: Historic and Developed Drainage
Maps). Runoff filters through the stone drainage base course beneath the pavers, then into the
underdrain before being conveyed to the combination storm inlets and routed to Detention Pond D.
During heavy rainfall events, or in the event that the paver system becomes saturated or clogged, two
curb cuts and a concrete chase have been designed to channel runoff overland into Detention Pond
D. North American Green C-350 turf reinforcement mat has been specified along the flow path
behind the curb cuts to protect the pond side slopes from erosion. '
Conclusion
The proposed Phase 2 & 3 parking lot addition produces an overall increase in impervious area for
the site, but the resulting minor increase in stormwater runoff volume is captured and treated in
Detention Pond D before being discharged to Spring Creek. No modifications are required to the
pond as the original design accommodates these planned development phases. The overall 100-year
water surface elevation in Detention Pond D increases from an elevation of 5045.29 to 5045.34,
which still allows more than I foot of freeboard below the spillway elevation of 5047.50. One
variance is being requested to allow 20% of new pavement area to be permeable pavers instead of
25% per CoFC requirements. The proposed variance will not be detrimental to overall stormwater
quality treatment as the pond has been designed to treat 100% of the water quality capture volume.
The Phase 2 & 3 parking lot improvements are in compliance with City of Fort Collins stormwater
criteria and requirements.
Please feel free to contact myself or Karen Brigman to discuss any questions you may have.
Sincerely,
JVA, INCORPORATED
1
By..
Donald Hamer, E.I.T., LEED AP
Project Engineer
CC: The Neenan Company
Attachments: Figure 2: Developed Drainage Map
Rational Method Calculations
Water Quality Pond Volume Calculations
BOULDER I FORT COLLINS I WINTER PARK
PROPOSED DETENTION POND D c
WQCV = 0.049 AC -FT
DETENTION REQUIRED = 0237 AC -FT
TOTAL DETAINED VOLUME = 0.451 AC -FT
RELEASE RATE = 1.63 CFS
SPILLWAY 5048.5' ;A
(P
,r' a
CONC FES W/ RIPRAP
RI 5047.39 //
STEEL PLUGGED)
5034 9 8" PVC
503 69 8" PVC
503 .89 8" P"
503 .4 P CONNECT TO EXIST �D '
i I -� D(15TING -_ _ =S+P - _ - -
" = R�►vt�-S 9s "
POND B "-1512135'.80 8' PVC
SEE UTILITY PLANS (w) 5035_65 B=PC�L_-
FOR POND B. :_-_ -_ = _ _ - - COMBINATION INLET S
MODIFICATIONS NEW NERGs =�
V OF EXIST SS = _= COMBINATION INLET
RECORD PLAN)
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PROPOSED SPOT ELEVATION
tG
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PROPERTY LINE / ROW
PROPOSED DRAINAGE BASIN BOUNDARY (NAIOR BASIN)
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FC Senior Center Expansion
Critical Pond Elevations
Design Engineer:
D. Hamer
Design Firm:
JVA, Inc.
Project Number:
2104c
Date:
3/21/2014 (Revised for Phase 2 & 3 parking)
DESIGN CRITERIA
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001
Stage Storage
Volume (pond volume calculated using the prismoidal formula):
V (A, + A, + A, A2 Depth
3
CONTOUR (FT)
AREA (FT')
AREA (ACRE)
(VOLUME
ACRE -FT)
DEPTH (FT)
CUMULATIVE VOLUME
)
5044.00
0.000
0.000
0.00
0.000
5045.0
2,901.00
0,067
0.022
1.00
0.022
5046.0
4,028.00
0.092
0.079
2.00
0.101
5047.0
5,390.00
0.124
0.108
3.00
0.209
5048.0
7,035.00
0.162
0.142
4.00
0,351
5048.5
8,444.00
0.194
0.089
4.50
0.440
5049.0
9,419.00
0.216
0.102
5.00
1 0.542
5050.0
12,419.00
0.285
0.250
6.00
1 0.792
Required Water Quality Capture Volume =
0,049 Acre -Ft Interpolates to an Elev. of 5045.34 ft
Required 100-yr Detention Volume (including WQCV) _
0.286 Acre -Ft Interpolates to an Elev. of 5047.54 ft
DETENTION POND VOLUME
VERSUS ELEVATION
5051.00
5050.00
LL 5049.00
Z 5048.00
O 5047.00
5046.00
Lu
5045.00
5044.00
5043.00
0.0
0.2 0.4 0-6 0.8 1.0
DETENTION POND VOLUME (AC -FT)
Spillway
Senior Center PondCalcs West Parking Lot_2014-03-18.xls - Pond Stage Storage #1 JVA, Inc.
DETENTION VOLUME BY THE MODIFIED FAA METHOD
(See USDCM Volume 2 Storage Chapter for description of method)
Project: FC Senior Center Expansion
Basin ID: Proposed West Parking Lot - Detention Pond D (Revised for Phase 2 & 3 parking)
(For catchments leas than 160 acres only. For larger Detai n ent., use hydrograph routing method)
(NOTE: forcatchments larger than 90 acres, CUHP hydrograph and routing are recommended)
Detemtination of MINOR Detention Volume Using Modified FAA Method I Determination of MAJOR Detention Volume Using Modified FAA Method I
calDlmem oramge Impemowross
CatcMnnnt Drarust. A.
Preddwiopmem [ARCS Soo Group
Return Penod for DetenDon Control
Time of concentration of Walemned
Ahavaele Un Release Rate
OnchoW Prewpnallon
Design Rainfall OF Formula I=C: P,f(C,rTJ"Cf
Coefficient One
Coercion[Two
Coefficient Three
1, =
0-36
percent
A =
2599
BLba
Tyac=
B
A. B,C, o,0
T =
2
yays (2. 5, 10, 25. 50, or 100)
T,_ =
10
oo d o
D=
063
sbusc.
P.=
082
inches
C. 28.W
10
C,= oTe
Cauchmenl Drainage lmnen,D4ircas
Camhmenl Drainage Ame
Predel,a1.pm0nl NRCS Sall Group
Return Paned for Desertion Connor
Time of Concemm4on of W atonsred
Allowable llml Release Rate
OmAn.ur Prenp;moon
Design RalnMIIIDFFOrmYla I•Cj Prl(CpTJ4Cr
Coefficient One
Coefficient Twn
Coefficient Three
I. =
4336
1lemem
A =
2 590
soled
Tyre=
B
A, B. C, DID
T =1
100
'am (2.5. 10. 16, SO. or 100)
Tic =
10
rmwlDe
q =
0.83
clefacra
P,=
2.SB
Irlcred
C, =
2aso
Cf =
t0
C,=
0787
Runoff Coelbuem C= 025
Inflow Pea4 Ru»fl a"= 141 cue
AIIoeole Peel, Curfew Rale Op-ow� IA3 efs
Mod. FAA Minof Storage Volume v 51 E Mat
Mod. FAA Minor Storage Volume= e00f coma
10 Value isi 51or54.ertaii
Runolr Coolficient C=
IMIow Peali Rwgll Dp+ -
Allmint Pa. Oul6ow Raln 00 out
Mod. FAA of Store,. Volume•
Mod. FM Major Storage Volume •
0.50
9.82
i.93
10,311
=7
cud
cis
Cubic kal
•craft
Ranil
RaMMI
Ir410w
AdllaplMM
Awmga
OIA11ow
Storage
Ranldl
Rental
Ind'"
Adbam+enl
AMmge
OIAOow
Sbrepe
Ou2ti0n
Intensity
Volume
Factor
Odessa
Volume
Volume
DMaOan
Inemlty
Volune
Factor
OIdIaW
Vollane
Volume
mirlules
Inches f N
cubic lest
Ns
cVeto feel
cu5ic reel
minuMs
Inches I M
cubic feel
cla
Cubic feet
cubic fell
ul
o W
o N
omN
o N
0
u
O N
O N
OmN
a N
O ul
(Output)
5
278
539
t 00
10
489
51
5
968
3762
1.00
1.63
489
3?73
15
1.86
1,083
065
138
1,245
-163
15
848
7,551
085
155
1,245
6.306
25
1,43
1,385
071
1,16
1,734
-us
25
4.97
9.659
071
116
1734
7,925
35
117
1.591
OAS
1Do
2,223
ii32
35
4.08
11.00
085
1A6
2,223
8.874
45
100
1747
062
1.DO
2.211
-"a
AS
348
12,184
062
100
2711
9,422
55
0,88
1.972
0.60
097
3,200
-1,32a
0
3.06
loose
060
087
3.2D0
9.857
65
078
1.91772
058
0.95
3.699
4,712
65
273
13,789
058
OAS
3.680
10,100
75
071
2,061
057
0,93
4,179
4,111
TB
247
14.419
057
093
4,1711
10,241
85
0as
2.146
0.%
0,91
s,eBB
.2,520
85
2.27
14,972
ass
0,91
A,ti66
10,305
95
060
2.217
0.56
0.SO
5.155
-2,958
95
2.10
15.466
056
0.90
5,156
10,311
105
0.56
2,281
a 55
0 N
5,644
5,30
105
195
15.9111
0.55
0.90
5.644
10,270
115
0.52
2.340
0.55
0a
16.133
5.1,93
115
1.0
16,323
0.55
0.89
6.133
10,190
125
0.49
2.394
054
am
6621
4,327
125
V2
16,700
0.54
age
6,621
loan
135
017
2.4M
05A
on
7.110
Aegis
135
1.63
12,050
0.S1
ON
7.110
0910
145
044
2491
a54
0.87
7,599
S,ioa
145
1154
17,377
0.54
0.87
7,599
one
155
042
2.535
0.53
087
8.088
5.552
155
1,47
17,684
0.53
0.87
81088
9,596
165
040
2.577
0.53
087
8.519
8000
165
1A0
17,973
0.53
087
8,576
9.397
175
0.39
2,616
053
O56
9.065
-6.448
175
1.a4
18,247
0.53
a86
9.065
9.182
185
037
2.653
053
OAS
9.554
-9.901
185
1.29
18,507
0.53
086
9,55a
8.954
195
035
Zero
053
0.86
10.042
-7,354
195
124
18,755
055
0.86
10,042
8.713
205
0.34
2,723
050
056
10,531
-),BOB
205
1.19
18,982
063
0so
10.531
8.461
215
0.33
2,755
0.52
085
11.020
8.285
215
1.is
19,219
0.S2
D85
11.020
8.199
225
0,32
2.71116
0.52
0.S5
11,509
A.722
225
111
ISA36
052
0.85
11.509
7.928
235
031
2,016
0.52
OAS
11.91117
.9.181
235
105
19.645
Du
0.85
11.997
2,648
245
a."
2.845
a52
0.85
12.486
8,641
245
104
19,847
052
0.85
12,485
7,361
255
029
2.873
0.52
am
12,975
-10.102
255
101
20,041
0S2
0.a5
12.975
7,066
265
0a
2.900
052
0m
13.464
40,584
285
ass
10,229
0.52
on
13.484
6.765
275
0.27
2926
052
0,85
13,952
-11,026
275
088
20,411
0.52
offs
13,02
6,4.Sa
285
0,27
2,951
0.52
am
14."1
41190
285
0.93
20,587
0.52
0.84
14,441
6,146
NO
0,26
2.976
0.52
ON
14,930
-11.954
285
0,91
2070
052
0."
14,930
5.828
305
025
3,000
052
am
15!19
-12419
SOS
0.88
20,023
0.52
Deaf
15419
5.505
315
035
3,023
052
0.84
15.9D7
-12,886
315
0.86
21,085
052
084
15.907
5.177
325
024
3.045
0.52
am
16,396
13,351
325
0.64
21,242
Doc
0.84
16.396
4,846
335
024
3,067
0.52
am
16'es5
-13,818
335
0,83
21,39A
0.52
0,1111
16,885
4,510
Sao
am
SON
0.52
0"
17,373
-14,255
us
Doe
215A3
052
O.Bs
17,373
4,170
355
0.23
3, 1Do
0.51
0.84
17,862
-14,753
355
0.99
21 eggs
0.51
084
17,BB2
3,826
365
on
3,130
0.51
OBI
18,351
-15,221
us
077
21.830
031
am
18.351
3A79
325
o22
3,119
0.51
0BI
18.940
-15.690
375
075
21.969
05,
0,1113
19.8A0
3.129
Day
0.21
3,169
0.51
08A
19.328
-16.160
3115
074
22,104
051
am
to.=
2,T26
385
0.21
3,1811
051
084
19.817
-151519
See
072
22,237
05,
am
19,817
2,420
AM
020
3.206
0.51
a.84
20,306
-17,099
AN
071
22,366
051
DP
20.306
2.061
415
on
3,225
0.51
084
20.795
17,570
415
070
22A93
051
DAM
20,195
1899
425
O]
3.242
0.5,
0"
21,30
-sew
425
0"
22,618
051
0.0
21.2a3
1,334
A35
019
3.280
051
on
21772
-111,512
43S
0.67
22.740
0.51
083
21,772
96B
445
0.19
3.2T7
0.51
0.03
22,261
-19,98a
4d5
0,86
22,859
Del
083
2?261
Soo
age
DAIS
3,2B4
0,51
0,83
22,750
-1o4S6
455
OA5
22977
c51
083
22.750
227
465
0.18
3.310
0.51
aM
23,238
19.928
465
0.64
23.092
0.51
0.83
23,238
446
475
Ole
3.327
ass
OA3
23,727
30,400
475
0.63
23205
051
0.83
23,727
-522
485
Ole
3,343
0.51
0.83
24,216
-20,873
485
0.62
23.316
0.51
0.83
24246
899
AM
0.1T
3,355
DS1
0.83
24,704
21,3a6
495
0.61
23426
0.51
0.83
24,7o4
-1.279
505
0.17
3,374
0,51
0,83
25.193
21,820
505
Moo
23,533
0.51
083
25,193
-1,660
515
0.17
3.359
0.51
083
25,682
-22.293
515
east
23639
0.51
0.83
25,692
-2.043
525
017
3.404
0.51
0.83
26,171
.22.767
525
0,5a
23743
051
0.83
26,171
.2,428
535
016
3,41a
0.51
0.a3
26,659
23,241
535
0.57
23,845
0.51
083
26,659
-2,814
546
Ole
3433
0.51
0.33
27,14a
-23.715
545
0.57
23.946
0.51
OAS
27,148
-3.202
555
0.16
3447
0.51
0.83
27,637
-24.190
555
01%
24,045
0.51
0s.3
27.637
-3.592
585
Ole
3,461
0.51
0.83
25.126
-24,665
565
0.55
241 a3
0.51
083
28.126
J.M
575
OA6
3475
0.51
0.83
26.514
-25.140
575
0.54
24,239
0,51
083
25,614
4.375
595
O15
3488
0.51
0,53
29.103
.25,615
585
OS4
24334
0,51
0.83
29,103
4,769
5%
DID
3.502
0.51
0.83
29.592
�26.090
585
0.53
26A27
0,51
0.83
29,592
-5.164
Iaoa. raw ameramnge Iommelouo.. nP m aqa. I. Molar smrage mmmalouteo D.i- ..all
Mad. FM Miner Storage Vatent. leeraAb)• 0.0012 Mod. FM M nor Storage Volume here -MI = 0.2367
UDFCD DETENTION VOLUME ESTIMATING WORKBOOK Version 2.2, Released January 2010
2104c Senior Center West Parent; Lot IW Oelemwn_2 2 2014-03-11i As, Modified FM 3rzt12014, 1 64 PM
I 11
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