HomeMy WebLinkAboutDrainage Reports - 05/18/2000..�.
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March 20, 2000
Mr. Basil Hamdan
City of Fort Collins Storm Water
700 Wood Street
Fort Collins, CO 80522
Re: New Belgium Brewery Administrative Change #3
Revision of the approved Office Addition (Phase III)
Basil;
This letter is intended to be an update to the Final Drainage and Erosion Control Report
for New Belgium Brewery First Filing prepared by JR Engineering, Ltd. dated December
23, 1997. Previous updates by North Star Design were completed for the Wastewater
Treatment Shed addition (dated October 19, 1998) and the Phase III Warehouse revision
(October 28, 1998).
The plans completed for New Belgium Brewery by JR Engineering dated December,
1997 and approved by the City of Fort Collins showed an office addition on the
southwest side of the existing building as Phase III. The office was proposed as 2400
square feet and was contained in Drainage Basin A.
New Belgium Brewery has reassessed their needs and determined that a larger office area
is needed. The proposed office addition is shown on the attached Grading, Drainage and
Utility plan. This revised office addition is 5500 square feet and encroaches on the
existing Detention Pond A. Also, based on existing conditions as surveyed, Basin A will
reduce in size and Basin E will increase in size by 0.13 acres (not previously accounted
for in Basin E). Because of the basin changes, the increased office area in Basin A and
the reduction of Detention Pond A, the hydraulic calculations for Basins A and E were
revised and are attached to this letter. The required detention for Pond A was
recalculated and the stage -storage curve was revised. These calculations are also
attached to this letter.
The proposed increased area in Basin E causes an increase of the c-value from 0.61 to
0.62. The runoff from the 10 year event increases from 7.3 cfs to 7.7 cfs and the runoff
from the 100 year event increases from 27.0 cfs to 28.6 cfs. This causes the required
1194 W. Ash Street, Suite B Windsor, Colorado 80550
970-686-6939 Phone 9.70-686-1188 Fax
detention to increase from 0.81 acre-feet to 0.85 acre-feet. Utilizing the same stage -
storage curve as the original report, the HWEL increases from 4948.89 to 4948.96.
The proposed changes in Basin A cause an increase of the c-value from 0.78 to 0.82. The
runoff from the 10 year event increases from 2.3 cfs to 3.8 cfs and the runoff from the
100 year event decreases from 10.1 cfs to 9.5 cfs. This causes the required detention to
change from 0.177 acre-feet to 0.125 acre-feet. The detention pond has been
reconfigured and accommodates the required volume at an elevation of 4951.8. The top
of the overflow is at 4951.9 and the top of the berm between the detention pond and the
irrigation ditch is 4952.15 which provides a freeboard of 0.35 feet. The City of Fort
Collins Storm Drainage Criteria requires a minimum of V of freeboard, therefore a
variance is being requested for this situation. The pond, if the outlet clogs, will overflow
into the irrigation ditch and will be conveyed downstream in this ditch. The detention
pond is very small and receives a minimal amount of runoff which, if conveyed
downstream, will have very minimal impact.
Because of the office addition, runoff from a portion of Basin A (patio near the entrance)
will need to be collected in an inlet and routed in a pipe to Detention Pond A. These
proposed storm facilities are shown on the attached Grading, Drainage and Utility Plan.
The existing concrete pan will be removed from the bottom of Detention Pond A. The
slope of the bottom of Detention Pond A is proposed to be 1.0%. This proposed change
is based on the desire of New Belgium Brewery to maintain a landscape with a minimal
of concrete drainage structures. This also allows for more detention volume than would
be provided by a 2% slope.
Proposed erosion control for this project is shown on the Grading, Drainage and Utility
Plan and is similar to the Phase III erosion control proposed on the JR Engineering plans.
This includes straw bale barriers in Detention Pond A and silt fence along the irrigation
ditch to prevent sediment from entering the ditch during construction.
Note that all of the calculations in this update were completed utilizing the rainfall
criteria that was in place when the original project was approved (prior to March 16,
1999)
I appreciate your time in reviewing this submittal.
Patricia Kroetch,
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DETENTION E
'DETENTION VOLUME CALCULATION - FAA METHOD
Detention Pond E
(100-YEAR)
LOCATION: NEW BELGIUM BREWERY
PROJECT NO:
COMPUTATIONS BY: PPK
SUBMITTED BY: NORTH STAR DESIGN
DATE: 1/14/00
Equations: A trib. To pond =
5.25 acre
Qo = CIA C (100) =
0.77
Vi = T C I A= T Qo Developed C A=
4.0 acre
Vo = QPo T QPo =
1.15 cis
S=Vi -Vo
1
Rainfall intensity from City of Fort Collins OF Curve
Storm
Duration, T
(min)
Rainfall
Intensity, I
(in/hr)
Qo
(cfs)
Vol. In
Vi
(ft)
Vol. Out
Vo
(ft)
Storage
S
(ft'')
Storage
S
(ac-ft)
5
9.00
36.4
10915
345
10570
0.243
10
7.28
29.4
17658
690
16968
0.390
20
5.18
20.9
25128
1380
23748
0.545
30
4.08
16.5
29688
2070
27618
0.634
40
3.40
13.7
32987
2760
30227
0.694
50
2.93
11.8
35534
3450
32084
0.737
60
2.58
10.4
37547
4140
33407
0.767
70
2.32
9.4
39390
4830
34560
0.793
80
2.11
8.5
40942
5520
35422
0.813
90
1.93
7.8
42131
6210
35921
0.825
100
1.79
7.2
43416
6900
36516
0.838
110
1.67
6.8
44556
7590
36966
0.849
120
1.56
6.3
45405
8280
37125
0.852
Required Storage Volume: 37125 ft
0.85 acre-ft
Page 1
New Belgium Brewery Detention Pond E - Stage/Storage
LOCATION: NEW BELGIUM BREWERY
PROJECT NO:
COMPUTATIONS BY: PPK
SUBMITTED BY: NORTH STAR DESIGN
DATE: 1/14/00
V = 1/3 d (A + B + sgrt(A*B))
where V = volume between contours, ft3
d = depth between contours, ft
A = surface area of contour
Stage
(ft)
Surface
Area
(ft)
Incremental
Storage
(cu-ft)
Total
Storage
(cu-ft)
Total
Storage
(ac-ft)
4946
0
0.00
0.00
0.00
4947
8150
2716.67
2716.67
0.06
4948
18710
13069.51
15786.18
0.36
4948.96
25804
21275.88
37062.06
0.85
4949
26100
22302.74
38088.92
0:87
Required volume =
0.85 acre-feet
Total volume =
0.87 acre-feet @ 4949
100 yr HWEL =
4948.89
Volume Provided =
0.85 acre-feet @ 4948.96
Page 1
------------------------------------------------------------------------------
------------------------------------------------------------------------------
DETENTION POND SIZING BY FAA METHOD
Developed by
Civil Eng. Dept., U. of Colorado
Supported by Denver Metro Cities/Counties Pool Fund Study
Denver Urban Drainage and Flood Control District, Colorado
------------------------------------------------------------------------------
------------------------------------------------------------------------------
PROJECT TITLE: New Belgium Brewery Office Addition
**** DRAINAGE BASIN DESCRIPTION
BASIN ID NUMBER = A
BASIN AREA (acre)= 1.06
RUNOFF COEF = 0.82
***** DESIGN RAINFALL STATISTICS
DESIGN RETURN PERIOD (YEARS) = 100.00
INTENSITY(IN/HR)-DURATION(MIN) TABLE IS GIVEN
DURATION 5 10 20 30 40 50 60 80 100' 120 150 180
INTENSITY 9.0 7.2 5.2 4.2 3.5 3.0 2.6 2.1 .1.7 1.5 1.2 1.0
***** POND OUTFLOW CHARACTERISTICS:
MAXIMUM ALLOWABLE RELEASE RATE _ .85 CFS
OUTFLOW ADJUSTMENT FACTOR = .98
AVERAGE RELEASE RATE _ .8330001 CFS
AVERAGE RELEASE RATE = MAXIMUM RELEASE RATE * ADJUSTMENT FACTOR.
***** COMPUTATION OF POND SIZE
RAINFALL
RAINFALL
INFLOW
OUTFLOW
REQUIRED
DURATION
INTENSITY
VOLUME
VOLUME
STORAGE
MINUTE
INCH/HR
ACRE -FT
ACRE -FT
ACRE -FT
-----------------------------------------------------
0.00
0.00
0.00
0.00
0.00
5.00
9.00
0.05
0.01
0.05
10.00
7.20
0.09
0.01
0.08
15.00
6.19
0.11
0.02
0.09
20.00
5.18
0.13
0.02
0.10
25.00
4.68
0.14
0.03
0.11
30.00
4.17
0.15
0.03
0.12
35.00
3.84
0.16
0.04
0.12
40.00
3.50
0.17
0.05
0.12
45.00
3.25
0.18
0.05
0.12
50.00
3.00
0.18
0.06
0.12
55.00
2.80
0.19
0.06
0.12
60.00
2.61
0.19
0.07
0.12
65.00
2.47
0.19
0.07
0.12
70.00'
2.34
0.20
0.08
0.12
75.00
2.20
0.20
0.09
0.11
-----------------------------------------------------
THE REQUIRED POND SIZE _ .124924 ACRE -FT
THE RAINFALL DURATION FOR THE ABOVE POND STORAGE= 45 MINUTES
NEW BELGUIM BREWERY
Detention Pond A - Stage/Storage
LOCATION:
PROJECT NO:
COMPUTATIONS BY:
SUBMITTED BY:
DATE:
100-yr WSEL-
Overilow elev
New Belguim Brewery
110-03
twc
NORTH STAR DESIGN
1/14/00
V= 1/3d(A+B+sgrt(A'B))
where V = volume between contours, ft3
d = depth between contours, It
A = surface area'of contour
Stage
(ft)
Surface
Area
W)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
49.62
0
50
482
0.00
0.00
51
4085
0.05
0.05
51.8
4324
0.08
0.125
51.9
4350
0.09
0.134
Total required detention = 0.125 Ac. Ft.
detention.xls
Cost Est
EROSION CONTROL COST ESTIMATE
Project: New Belguim Brewery Office Addition
Prepared by: 110-03
ITEM
IQUANTITY
JUNIT
COST/UNIT
ITO=ST
Silt Fence
290
LF
$3
$870
Straw Bale Barrier
2
EA
$150
$300
Gravel Inlet Filter
0
EA
$150
$0
Construction Entrance
0
EA
$550
$0
Subtotal
Contingency (50%)
Total
$1,170
$585
$1,755
CITY RESEEDING COST
Reseed/Mulch
0.47
ACRE
1 $650
$306
Subtotal
Contingency (50%)
Total
$306
$153
$458
EROSION CONTROL ESCROW AMOUNT $1,755
Page 1