HomeMy WebLinkAboutDrainage Reports - 11/29/2017City of Fort Collins Approved Plans
Approved by:
PfP--E Engineering [Nate: "!, -t Zoe
908 Laporte Avenue • Fort Collins. Colorado 80521 • 970.219.2834 • bob@apex-engineer.com
August 23, 2017
Mr. Shane Boyle, P.E.
Stormwater Department
City of Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80521
RE: Drainage Memo
Red Truck Brewery - Minor Amendment
Dear Shane,
This purpose of this letter is to examine the potential impacts of the proposed site
improvements associated with the above referenced Minor Amendment (MA) project on
the existing drainage facilities located on the project site. As we discussed in our
meeting on 5/31/2017, the project consists of exterior and interior remodeling of the
existing Fort Collins Brewery located at 1020 East Lincoln Avenue. There is also an
elevated deck proposed over the existing detention pond. The deck is supported by 38
12"xl2" concrete piers and four 24"x24" concrete piers. The total plan area of the 42
proposed piers is 54 square feet.
The changes in impervious cover created by the revisions to the site design are as
follows:
Removal of concrete from parking area and sidewalk (190)
Expansion of existing patios and sidewalk (906 SF)
A gravel trail along the west side of the building (1283 SF)
In preparing this drainage memo, the following approved documents prepared by Apex
Engineering for the Fort Collins Brewery (FCB) project are referenced:
• Utility Plans (and subsequent drawings of record), dated 4/20/2009
• Final Drainage, Erosion Control and Water Quality Report, dated 4/20/2009
• Drainage Certification, dated 9/24/2010
Runoff Parameters
The net effect of the removal and additions listed above, the weighted composite runoff
Coefficient (C) and percentage of impervious area changes very slightly. The following is
a comparison of the existing and proposed values (calculations attached):
-C % Imo.
Existing 0.852 82.1%
Proposed 0.857 83.0%
Detention Storaoe
The original FTB detention analysis was based on a proposed C of 0.852 for full build out
of both phases of the project. The original analysis was modified to reflect the higher
proposed C of 0.857. The results indicate that these revisions do not increase required
detention volume. Please note that this result is to be expected since the City's detention
volume calculation spreadsheet adds a 25% factor of safety to all runoff coefficients.
Therefore, the resultant detention volume calculation is based on an identical C of 1.00
for both conditions.
Water Quarrhr
As noted above, the percentage of impervious increases slightly due to the proposed
improvements. The slightly higher figure was used to recalculate the Water Quality
Capture Volume (WOCV) using the same methodology as the FCB project. The revised
design spreadsheet is attached, and the results are summarized below:
% Imp. WOCV
Existing 82.1% 0.092ac-ft
Proposed 83.0% 0.094 ac-ft
Pond Volume Rating Curve
The revised WQCV and detention volumes were then used to modify the original as -built
pond stage -storage calculations, which was attached to the original drainage
certification for the FTB project. This spreadsheet was also modified to reflect the
proposed piers by subtracting 54 square feet from the area of each elevation in the
analysis. The revised spreadsheet is attached, and the results are summarized below:
WQCV WSE 100-Year WSE
Existing 4936.60 4940.59
Proposed 4936.63 4940.60
As noted in the Drainage Certification for the FfB project, the design emergency spillway
elevation was 4940.60. The proposed very slight increase in 100-year WSE of 0.01' is
insignificant since it is at the design spillway elevation.
This analysis reveals that the increased elevations in the pond are insignificant, and
contained within the existing detention pond system. The increases are not significant
to water quality treatment or detention functionality of the existing pond. Therefore, it is
concluded that no modifications to the existing pond are needed to accommodate the
Red Truck improvements as included in the Minor Amendment for the property.
I appreciate your time and consideration in reviewing this submittal. Please contact me
at (970) 219-2834 should you have any questions or concerns.
Best Regards,
Bob Gowing, P.E.
APEX Engineering
Attachments:
• Proposed Runoff Coefficients and Percent Impervious Calculations
• Proposed Water Quality Capture Volume Calculations
• Proposed Pond Volume Rating Curve Calculations
• Original Drainage Certification for the Fort Collins Brewery
Developed Weighted Runoff Coefficients
Red Truck Beer
Composite Calculations
Basins Total Area Sum CaA Composite C
P-1, EA 3,64 3.12 0.857
Li Use or Suri Characteristics
Percent lmpe-vbusness
Business:
Commercial areas
95
Neighborhood areas
85
Reetalimdal:
Om le-famA
'
Multiunit detache0
60
Multiunit(altacheE)
75
Half -acre lot or larger
'
Apartments
so
Industrial:
L ht areas
80
Heavy areas
90
Parks, cemeteries:
5
Playgrounds;
10
Schools:
50
Railroad yard areas:
15
Undeveloped areas:
Historical Flow Analysis
2
Greenness, agnalltwal
Off -site flow analysis
(when land use not defined)
45
severe:
P9ved
100
Gravel(packed)
40
Drivesra sand sidewalks:
90
Reots:
90
Lawns. sandy soil
a
Lawns, clayey soil
0
'Refer to Figures RO-3 through RO-5 in Runoff Chapter
Notes.
1. Net increase in concrete area = 535 SF
2. Net increase in gravel area = 1340 SF
1 32 AM
APEXENG(NEERING 8232017
100 Year
This is to convert % imp. to a C value
100-year
(must insert % imp. and C pervious).
Required
detention
'C'value
'C" 1.25
Area
0.86
1
3.64 acres
ft3
acre-ft.
Modified
Modified
Release Rate
0.73
M. FATER
D. JUDISH
C. I -I
Nov-98
5/95 Nov-97
POND SIZING
TIME INTENSITY Q 100 Runoff Release Required
cum 100 year Volume Cum total Detention
(secs) (in/hr) (cfs) (ft^3) (ft^3) (ft^3)
0 0 0.00 01 0.0 0.0
300 9.950 36.22 10865.4' 218.4_1 10647.0
600 7.720 28.10 16860.481 436.8 16423.7
900 6.520 23.73 21359.52 655.2 20704.3
1200 5.600 20.38 24460.81 873.6 23587.2
1500 4.980 18.13 27190.8 1092.0 26098.8
1800 4.520 16.45 29615,04 1310.4 28304.6
2100 4.080 14.85 31187.52 1528.8 29658.7
2400 3.740 13.61 32672.64 1747.2 30925.4
2700 3.460 1259 34004.88 1965.6 32039.3
3000 3.230 1176 35271.6 2184.0 33087.6
3300 3.030 11.03 36396.36 2402.4 33994.0
3600 2.860 1041 37477.44 2620.8 34856.E
3900 2.720 9.90 38613.12 2839.21 35773.6
4200 2.590 943 39596.923057.6 36538.3
4500 2.480 9.031 40622.4 3276.0 37346A
4600 2.380 8.66 41583.36' 3494.4 38089.0
5100 2.290 8.34 42511.56 3712 8 38798.8
5400 2.210 8.04 43439.76 3931.2 39508.6
DETENTION
TIME
Required
(mins)
Detention
(ac-ft)
0
0.0000
5
10
15
0.2444
0.3770
0.4753
20
0.5415
25
0.5991
30
35
0.6498
0.6809
40
0.7100
45
0.7355
50
0.7596
55
0.7804
60
0.8002
65
0.8213
70
75
80
85
0
go!
0.8388
0.8574
0.8744
0.8907
0.9070
95 5700 2.130
7.75
44193.24
4149.6
40043.61
0.9193
100 6000 2.060
7.50
44990.4 4368.0
40622.4
0.9326
105 6300 2.000
7.28
45864 4586.4
41277.6
0.9476
110 6600 1.940 7.06 46606.56 4804.8 41801.8
115 6900 1.890 6.88 47469.24 5023.2 42446.01
120 7200 1.840 6.70 48 222.72 5241.6 42981.1
0.9596
0.9744
0.9867
Page 1
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Red Truck
Detention Pond
As Built Detention Pond Volume Rating Curve
Based on As -Built Topography of Existing Detention Pond
35.50
332
0.008
0.001
0.001
36.00
3,495
0.080
0.019
0.020
36.50
7,007
0.161
0.059
0.079
36.627
37.00
7,059
0.162
0.081
0.160
37.50
7,097
0.163
0.081
0.241
38.00
7,136
0.164
0.082
0.322
38.50
7,518
0.173
0.084
0.406
39.00
9,004
0.207
0.095
0.501
39.50
9,653
0.222
0,107
0.608
40.00
16,220
0.372
0.147
0.755
40.50
28,703
0.659
0.254
1.009
40.60
31,206
0,716
0.069
1.078
40 604
(100 year Volume) Required = 0.99 acre-ft
WQCV Required = 0.094 acre-ft
(100 year Volume+ WQCV) Required = 1.08 acre-ft
100-year WSEL =
WQ WSEL =
V = ld�A+B+ AB)
where:
V = volume between contour interval
d = elevation - elevation.,
A = area of elevation_, contour
B = area of elevation„ contour
1:33 AM
APEX ENGINEERING 8/23/2017
ENGINEERING
238 Walnut Street ■ Suite 200 ■ Fort Collins, Colorado 80524 a 970.797.2906
September 24, 2010
Mr. Jay Barber
City of Fort Collins, Stormwater Department
700 Wood Street
Fort Collins, CO 80521
RE: Fort Collins Brewery - Drainage Certification
Dear Jay
The purpose of this letter is to provide as -built information for the drainage facilities
constructed as part of the Fort Collins Brewery project.
Detention Pond:
The detention pond area was surveyed by Edmonds Land Surveying on September 3, 2010.
The results of that survey were used to recalculate the pond volumes using the same
methodology as that used for the design. A copy of the revised detention pond volume
rating curve is attached.
The results of the volume calculation indicate that there is adequate volume within the
pond for the required detention volume of 1.08 acre-feet. This volume corresponds to a
water surface elevation of 4940.59 within the pond. Although slightly higher than the design
elevation, this is still lower than the emergency spillway elevation of 4940.60.
In addition, the final finished floor elevation for the adjacent building was surveyed, and that
elevation was found to be 4942.08. This elevation provides 1.49 feet of freeboard from the
100-year water surface elevation to the finished floor. It should be noted that several
elements of the building structure are immediately adjacent to and subject to inundation
from the detention pond. This situation was known to the owner, architect and structural
engineer during the design process, and we have no reason to believe that this was not
accounted for adequately. We simply mention this because Apex Engineering does not
provide architectural, structural or geotechnical services and has no way to check or verify
this. We make no statements concerning, and are not responsible for, any impacts that this
situation may cause to the building, sidewalks, paving, or other structural elements of the
project.
There are several aspects of the construction of the pond which may present future
maintenance issues to the owner. Those include less than ideal slopes in the bottom of the
pond and the riprap at the pipe outfalls in the pond. The pond bottom shows several areas
which may not drain completely, and the riprap installation is not as large as designed.
Neither of these issues should affect the detention or water quality performance of the
pond, and the owner has been advised (via this letter) that these areas may need occasional
maintenance in the future.
Culverts. Inlets and Pipes:
The drainage infrastructure such as culverts, inlets and pipes show many minor deviations
from design. The as -built elevations, inverts and slopes are shown on the enclosed Record
Drawings and are based on survey information provided by Edmonds Land Surveying.
Street Drainage
There are two areas where drainage along the sides of the adjacent streets is less than
optimal. Both of these areas were addressed by minor field adjustments as coordinated
with the Engineering Inspector and other City Engineering Staff. In particular, the throats of
the two type R inlets accepting drainage from Lemay and Lincoln Avenues were constructed
and the storm manhole along storm line B was constructed higher than design with a solid
cover, which was not in accordance with design. This resulted in minor pending at the
handicap ramp near the intersection and along the western edge of paving for Lemay
Avenue. Drainage near the ramp was provided by a small channel which was ground into
the existing asphalt, and a small gravel drain to the Type R inlet along Lincoln Avenue. It
was determined at a field meeting with Wayne Lenard, Tracy Dyer and Marc Virata that the
proposed solution was adequate and the small area of minor ponding adjacent to Lemay
was not an issue since the adjacent street improvements are interim.
Site Drainage:
Many of the privately owned and maintained areas within the site were not graded as per
design. These include the drive aisles, parking areas, sidewalks and the open areas
throughout the site. Most of the variances from design are minor, but several field changes
related to paving slopes were undertaken by the Owner and Contractor for reasons related
to the decision to use concrete paving instead of asphalt paving as shown in the design
documents. These as -built areas were not analyzed in detail since they are private and the
Owner is responsible for maintenance implications of the changes. Based on our visual
observation these changes do not appear to affect the overall drainage concepts or drainage
infrastructure design for the site as a whole.
Enclosed please find the following supporting information:
Drawings of Records for drainage improvements (PDF format).
Detention pond volume calculations
Drainage Site Certification Checklist
The above stated opinions and calculations are based on the survey information provided by
Edmonds Land Surveying and information provided by the owner and contractor.
Please contact me should you need additional information.
Sincerely,
Bob Gowing, P.E.
CC: Tom Peters, Fort Collins Brewery