HomeMy WebLinkAboutSite Certifications - 05/07/2003May 7, 2003
Basil Hamdan
City of Fort Collins
Storm water Utility
700 Wood Street
Fort Collins, CO 80521
Re: Atrix Laboratories — Sidewalk addition drainage certification
JR Project 39067.19
Dear Basil,
MAYE3M D
J•R ENGINEERING
A Subsidiary of Westrian
This letter is intended to document the changes in runoff associated with the addition of
approximately 180 feet of sidewalk to sub -basin 112 of the Atrix Laboratories site. This
sidewalk is proposed to wrap around the southeast corner of the building addition, and is shown
on the attached exhibit.
With this letter you will find runoff, water quality, and detention pond calculations taking into
account the addition of 717 square feet of impervious area due to the sidewalk addition in sub -
basin 112. These calculations revise those presented in the "Final Drainage and Erosion Control
Study Atrix Laboratories" (JR Eng. 2002). The sidewalk addition results in an increase in
runoff of 0.1 cfs in both the 10 and 100 year events. There was no change in the water quality
capture volume required.
A letter signed and dated January 30, 2003 by JR Engineering certifies that the as -built pond has
adequate detention and water quality volume. This record stage -storage analysis of the pond was
then checked to determine any impacts from the proposed sidewalk addition. According to this
analysis, the pond has adequate detention volume to accommodate the increase in drainage
volume from the sidewalk addition.
If you have any questions or comments, please do not hesitate to contact me at my office.
Si
Di tor•.of Operatiogs
AtatntApD
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X:\31)0(X)OO.all\31)00714\Ur, N%in s\4-19 SiticA,;iIk kc%ision\4-25 Sidewalk addition drainarc ICIM'Ahx
2620 East Prospect Road, Suite 190, Fort Collins, CO 80525
970-491-9888 • Fax: 970-491-9984 • www.irengineering.com
BUILDING ADDITION
SIDEWALK
TER QUALITY
TLET STRUCTURE
50 25 0 50 100
SCALE: 1 " = 50'
AREA OF INNUNDATION
(100—YEAR)
TOP OF POND
(SPILL ELEVATION)
ATRIX LABORATORIES
SIDEWALK ADDITION EXHIBIT
PROJECT NO. 39067.19
APRIL 28, 2003
J-R ENGINEERING
A&McrwydWesMm
60 Greenwood Plaza 9W - B*WOCKI, CO 8M
303-740-M- Fax 303--72>-M
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RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: ATRIX LABS
PROJECT NO: 9067.19
COMPUTATIONS BY: M. West
DATE: 4/28/2003
Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria
Recommended % Impervious from Urban Storrs Drainage Criteria Manual
Streets, parking lots (asphalt):
Sidewalks (concrete):
Roofs:
Lawns (flat <2%, sandy soil):
Runoff
%
coefficient
Impervious
C
--0.95-
- -100--
0.95
96
0.95
40
0.10
0
• JR Engineering
2620 E. Prospect Rd., Ste. 190
Fort Collins, CO 80525
SUBBASIN
DESIGNATION
TOTAL
AREA
(ac.)
TOTAL
AREA
(sq.ft)
ROOF
AREA
(sq.ft)
PAVED
AREA
(sq.ft)
SIDEWALK
AREA
(sq.ft)
LANDSCAPE
AREA
(sq.ft)
RUNOFF
COEFF.
(C)
%
Impervious
101.
0.57
24,981
23,632
793
185
371
0.94
89
102
0.28
12,247
0
6,566
2.728
2,953
0.75
75
103
1 0.48
20,743
0
12,175
1 1,199
7.370
0.65
1 64
--_-104' - _
0.15
6,361 -_
0 _
_ 4,173_
_ 1,400
768
_0.84
87
----
105
-
1,06-
-
45,988
25,075
0
--- --
750__ _
-- - -
20,163_
0.58_ _
51
106'
0.52
22,502
0
- 18,423 -
1,216 -
- 2,863 -
- 0.84
- 87
107
0.61
26,474
0
19,005
1,349
6,120
0.75
77
108
0.12
5,049
0
4,509
0
540
0.86
89
_109._ _
0.50
21,699
0
17,051
280
4,368
0.78
80
-110 _ _
- 0.53 .
22,898 _ _ _
- 0 - _
-19,102 _
790_-.
_ _ 3.006 _ _ _
0.84 _
87
111
0.70
30,419
0
21,826
1,648
6,945
676
77
112
1.64
71,374
24,872
_ 0
2i707
43,795
m 0.43-
357
113
0.27
11,605
0
0
256
11,349
0.12
2
OS-1
0.37
16,046
0
0
0
1 16,046
0.10
0
__OS-2___
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6.915
0
1 0
0
6,915
0.10
0
- -- _
-
Total
7.45
324,558
73,579
- 111,448
13,309
;126,222
062
»59_. _
Equations
- Calculate_ d C coefficients& % Impervious are area weighted
C=E(Ci Ai) /At
Ci = runoffco efficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
'revised for sidewalk addition
'revised for sidewalk addition
9067FLOW 4-28-3.xls
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rJR Engineering
WATER QUALITY CAPTURE VOLUME SUMMARY
FOR EXTENDED DETENTION
PROJECT NAME:
ATRIX LABS
JR PROJECT NO:
9067.19
COMPUTATIONS BY:
M. West
DATE:
4/28/2003
Guidelines from Urban Strom Drainage Criteria! Manual, September1999
(Referenced figures are attached at the end of this section)
Use 40-hour brim -full volume drain time for extended detention basin
Water quality Capture Volume, W QCV = 1.0 ' (0.91, ' i3 -1.19 i2 + 0.78i)
Design. Volume: Vol = WOCV/12' Area' 1.2
MAJOR
BASIN
Trlti:
area
(acres)
Impervious
Ratio, Is
%Impervious
I =-lanoo
VdOCV
(watershed Indies)
Design
volume, Vol.
(ac-ft)
- - -PONDA
7.45
- -4 59,= ';-,,:, '
- -
0.59 _,��
- - -
023
- -
0.17-
'revised for sidewalk addition
Note : WOCV does not change
9067WO 4-28-3.)ds,4/28/2003,2:46 PM
0 0 JR Engineering
LOCATION:
PROJECT NO:
COMPUTATIONS BY
DATE:
Equations:
DETENTION VOLUME CALCULATIONS
Rational Volumetric (FAA) Method
100=Year Event
Atrix
9067.19
M. West
4/28/2003
Developed flow = Qp = CIA
Vol. In=Vi=TCIA=TOD
Vol. Out = Vo =K Opo T
storage = S = Vi - Vo
Area trib. to pond= 7.45 acre
C (100) � 0 8 ,?'revised for sidewalk addition
Developed C A = _ 5.8 acre
Release rate, Opo = 1.68 cfs
K = 0.95 (from fig 2.1)
Rainfall intensity from City of Fort Collins IDF Curve with updated,(3.67") rainfall
Storm
Duration, T
(min)
Rainfall
Intensity, I
(in/hr)
Op
(cfs)
Vol. In
% i
(ft)
Vol. Out
Vo
(ft)
Storage -
S
(ft)
Storage
S
(ac-ft)
5_ -
9:95-
57.5-
---17262 -
__ 480 -
16782
0.39
10_ _
7.77
_44.9
- 26948_
__960._ -
__ _25988_
0.60
20
5.62
32.5
39005
1919
37086
0.85
30_ _
4.47
25.8.
46512
2879
.43634
1.00
40
3.74
21.6
51907
3838
48068
1.10
50
3.23
18.7--
- 56103 -
4798-.
---51305- -
1-.18
60
2.86.
16.5 _ _
_ _59536_
_ 5757 _
53778 _ _
_ 1.23
-- --70 - -
2.57 - _
_ 14.9
62442
_ __ 6717
_
55725
1.28
80_ -
- - 2.34_
13.5..
64964
7676
57288
1.32
90
2.15
12.4
67194
8636
58559
1.34
100
1.99
11.5
69196
- - -9595
59601-
----1.37
1.10
1.86_ -
10.8 - _
__71013 -
10555
_60458_
1.39_
--- 120 -
- - 175- -
-
---10:1--
--
--72678-
11514
61164
1.40
130
1.65_ - _
9.5
74216
12474
61742
1.42
140
1.56
9.0
75646
13433
62213
1.43
150
1.48
8.6
76983
14393
- -62590
1.44
.160
1.41
8.1
78240
15352_
62887
_-1.44__ _
170
_. 1.35-
7.8 -__
-'79426-
16312
63114 -
1.45 -
180_
1.29_ _
_ 7.5_____.
_ 80548
17271 _
63277
1.45
-T- 190
- 1.24
7.2
-81616
18231
63385
1.46
200
-1.19 _ _
_ _ 6.9_ _ _
82633
- 1919.1 _ _
_ 63442 _ .
_ _ _ 1.46 _
210 --
- -1 15-- -
-6.6--
___83604
-- 20150
63454
1.46
220----
- - __ 1.11. _
6.4_
__ _ 84535
- 21110 -1
63425
1.46
Required Storage Volume: I '-'
454 ftg -revised for sidewalk addition
146 acre=ft-.;
9067POND-cert 4-28-3.xls,FAA-100yr
0
JR Engineering
WATER QUALITY CAPTURE VOLUME SUMMARY
FOR EXTENDED DETENTION
PROJECT NAME:
ATRIX LABS
A PROJECT NO:
9067.19
COMPUTATIONS BY:
M. West
DATE:
4/28/2003
Guidelines from Urban Strom Drainage Criteria! Manual, September 1999.
(Referenced figures are attached at the end of this section)
Use 46-hour brim -full volume drain time for extended detention basin
Water quality Capture Volume, WQCV = 1.0 " (0.91 ' i3 - 1.19 " iZ + 0.78i)
Design Volume: Vol = WQCV/12 ` Area ' 1.2
NWOR
BASIN
Trib.
area
- (ate)
impervious
Ratio, la
%Impervious
I - IaMoo
WQOV
(watershed Inches)
Design
Volume, Vol.
(ac.fl)
PONDA
7.45
59 :_
0.59 ,.._.:
6.23
0.17
'revised for sidewalk addition
Note: WQCV does not change
9067WQ.4-28-3.)ds,4/28/2003,3:12 PM
0
0
Detention Pond
Record Detention Pond = Stage/Storage
LOCATION:
PROJECT NO:
COMPUTATIONS BY:
SUBMITTED BY:
DATE:
WQCV-
100-yr WSEL-
Spill Elev. -
top of berm -
Atrix
9067.19
A West
JR ENGINEERING
4/28/2,003
V= 1/3d (A+B+sgrt.(A'B))
where V = volume between contours, ft3
d depth between contours, ft
A = surface area of contour
POND AS -BUILT
With sidewalk addition
Stage
(ft)
-Surface -
Area
02)
Incremental
Storage
Total
Storage
5036.9
0
_ 5037.0 _ _
_ _ _ _611
- _0.00
0.00.
5037.5
3052
0.02
0.02
--_5038 0 -
5493
_ _0.05
0.07
5038.45
13895
0.10
0.17
5038.5
14828
_ _ _0.02 _
0.18
5039.0
22483
0.21
0.39
_ 5039.5
26564 _ _
_ 0.28'.
0.68,
5040.0
28671
0.32
0:99
5040.5_
_ _ _30851 _
_ 0.34 _
1.33
5040.90
32601
0.29
1.63
_ 5041..0
33039 _ _
_ 008
- 1.70 .
5041.54
35215
0.42
2.12
5041.89 _
- _ 36841- _
0:29
_ 2.45
Required Water Quality Volume =
0.17
Required Detention Volume =
1.46
Total Required Volume =
1.63
Total Provided Volume =
2.12
9067POND-cert 4-28-3.xls