HomeMy WebLinkAboutCIVIC CENTER PARKING STRUCTURE - PDP - 35-98 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Report
Civic Center Parking Structure
NOLTE and ASSOCIATES, Inc.
Engineers / Planners / Surveyors
REFERENCES
A. City of Fort Collins Storm Drainage Design Criteria and Construction Standards, City of
Fort Collins Stormwater Utility, May 1984.
B. Urban Storm Drainage Criteria Manual, Wright -McLaughlin Engineers, Inc., Denver
Regional Council of Governments, Denver 1969.
C. Old Town Drainage Basin Plan, City of Fort Collins, Resource Consultants and Engineers,
Inc, January 1993.
D. HEC-2 Commuter Program - Water Surface Profiles, U.S. Army Corp of Engineers
Hydraulic Engineering Center, Davis, California, 1990.
NOLTE and ASSOCIATES. Inc 10 N:\FC0053\civil\PKGStrDrainReport.doc
OIL Final Drainage Report
Civic Center Parking Structure
NOLTE and ASSOCIATES, Inc.
Engineers / Planners / Surveyors
5.2 DRAINAGE CONCEPT
The drainage system is designed to control storm water discharges , protect surface water quality,
and to safely convey runoff from the site in compliance with local regulations and consistent
with current studies of the major drainageway basin.
Nnl.TE and ASSOCIATES. Tnc. 9 N\FC0053\civil\PKGStrDrainRep66. 6i
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Final Drainage Report
F*4 -A- Civic Center Parking Structure
NOLTE and ASSOCIATES, Inc.
Engineers / Planners / Surveyors
The HEC2 model was run with the area occupied by the parking structure blocked out. This area
represents are small portion of the total conveyance available in the cross-section. The result is
that the parking structure will have no impact on the Old Town floodplain. Output from of the
analysis is summarized in Table 1.
In reviewing the HEC2 model and floodplain limits developed in the Master Plan, it is apparent
that this site is included in the floodplain because of a backwater condition. No part of the site
except for approximately 20 feet adjacent to Laporte Avenue was modeled as providing
conveyance for any flood discharges from the Old Town Basin.
The site is still subject to flooding, however, and first floor elevations for the commercial space
and parking structure have been set 1.5 feet above the 100-year flood elevation in Mason Street.
4.4 EROSION CONTROL AND WATER QUALITY
Erosion control during construction of this project will consist of silt fence installed around the
perimeter of the site. Once foundations are in place and floor slabs constructed, the potential for
erosion will be minimized. The Grading and Erosion Control Plan in the construction drawings
indicates the type and timing of proposed measures.
Water quality of stormwater discharge from the site in the long-term will be controlled by a
"Storm Ceptor" Manhole (Type 2400) to be installed within the site at the alley. The Storm
Ceptor has been shown to be effective in the removal of sediment, oil and grease, and other
pollutants of stormwater.
5.0 CONCLUSIONS/SUMMARY
5.1 COMPLIANCE WITH STANDARDS
The proposed storm drainage design for the site complies with the intent of the following
regulations, standards, and reports:
♦ City of Fort Collins Storm Drainage Design and Technical Criteria
♦ Old Town Master Drainage Plan for the City of Fort Collins, by Resource Consultants and
Engineers, dated January 1993.
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TABLE 1 PROFILE TABLE
ucr_coc Pimn Imnnrteri P12 River Rn/FR-1 Reach: Reach-1
Ar11-
-
Reach
,rarer
4980.40
4980.72
4980.54
4980.75
0.000532
0.80
69.60
98.92.
108.73
233,
240,91
24322
851
R0341
04�
0.4�
a
90.00
_
160.00
4980.40
4980.84
4980.68
4980.89
0.000611
1.24
Reach-1 -
288000
200.00
4980.40
4980.88
4980.73
4980.94
0.000720
1.47
R each-1
2 -
300.00
4980.40
4980.95
4980.82
4981.04
0.001034
2.00
126.09
247.27
6
Reach-1
2800
370.00
4980.401
4981.02
4980.88
4981.13
0.001078
2.26
142.39
250.00
_
0-58
2
�Reach-1
ch, 1
ch-1
1
reach---
3170
3
3170
3170
170.00
240.00
370.00
4980.90
4980.90
4980.90'i
4981 95
4982.08
4982.26'
4981.95
4982.08
4982.26
4982.114
4982.27
4982.44
0.002095
0.001901
0.0018241
3.49
3.77
4.27
51 77'
75.24
121.05:
158 5.5;
5
214.941
309.51
0.
p.83
0.811
0.83.
---+
each--1
---
I _70
31 _ �
I
500.001
4980.90
4982.35
1 4982.35
4982.571
0.001886
4.63
149.73
341.52
0.85
___--
Re h-1
13320_
90.00
4982.001
4982.27
4982.32
0.002542
i 2.23
49.59'
310.04
0.801
Reach-1
each-1
13320
3320 _
i
170.00
240.00
4982.00
4982.00,
4982.38
4982.46
4982.44
4982.53,
0.001787'
0.001407
2.41I
2.48
88.621
125.29'
385.01
464.39
0.72'
0.66
each-1
13320
1
370.00
4982.00
4982.591
4982.66
0.001100
1 2.59
; 191.72 ;
590.24
0.61 .
-
�each-1
�
13320
500.00
; ' 4982.00,
4982.70
;
�1 4982.76
0.000855;
2.56
256.48
631.92
0.55
Reach-1
13580 I
90.00
4981.40
4982.51
4982.34
4982.5211
0.000343
i _ 1.12 j
114.78 ,
434.79
0.32
Reach-1
)3586
170.00;
4981.40.,
4982.631
4982.40
4982.66
0.0004461
1.511
159.26;
449.32
0.37'
Reach-l-
3580
240.00;
4981.40
4982.71
4982.46
4982.74'
0.000520
1.79'
189.19�
457.23
0.41
Reach 1 -
35�
370.00
4981.40
! 4982.83
4982.55'1
4982.87
0.000648:
2.25
232.94 �
468.52
0.48
Reach-1
�3580
500.001
4981.40
4982.911
4982.62
4982.981
0.000785,
2.671
266.141
476.87.
0.53!
BEFORE PRO.1F[_T
sla-
90.00
4980.401
4980.72
4980.54
4-980 75
0.000532'
0.80
69.60''
233.85 i
0.34 :
WW A
2800
eaci,t
_
160.00,
4980.401
4980.84
4980.68
4980:89
0.000611
1.241
98.92
240.91
0.41
'Reach-1
280 ;; j
200.00,
4980.40i
4980.88
4980.73
4980.94
0.000720
1.47
108,73
243.22
0.45
Reach-1
2800
�
300.00
4980.40!
4980.95,
4980.82
4981.04
0.001034
2.00
126.09
247.27
0.56
Reach-1
2800
_
370.00
4980.401
4981.02
4980.88
4981.13
0.001078!
2.26
142.39
_250.00
Q
Reach 1
3170
90.00
4980.901
4981.68
4981.68
4981.
3057'
3.55
25.98
0.92
each-1
_
3170
170.00
4980.90
4981.94
4981.94
4982.14
0.002216,'
3.03
-- -
50.33
53.1
164.36
0.85
each-1
13170
240.00
4980.90:
4982.08
4982081
4982.27,
0.001949
3.84,
77.05
217.69
0-83
each-1
----
3170
370.001
4980.90
4982.25
4982.25
498244
' . `04,
.001999
4.44
120.84
306.3
0.86
'Reach-1
..-
13170
500.00
4980.90'
4982.42
4982.42'1
4982.55
0.001497,
3.45'
180.66
384.63
0.73
_...
_
Reach-1
3320
90.00
4982.00!4982.27
4982.32
0.002542
1 0.001735
2.23
_ 2.39
49.59
- 89.56
310.04
386.64
0.80
0.71
each3320
170.00 - 4982.00 4982.38'
4982.44
each-1
3320
240.00
4982.00,
4982.46
4982.531
0.001414
2.48
125.07
463.90
0.66
each-1
13320
370.00
4982.00!
4982.60
4982.66I
0.001046, _
2.55
195.49
596.59
0.59
eacheach=l
�3320
500.00.
4982.00.;
4982.67
4982.751
0.001039;
0.000269
2.75
0.96
240.24
128.55
623.29
429.63
0.60
0.28
Reach-1
3580
90.00: 4981.40 4982.49
4982.30I
4982.50
Reach-1
�3580
170.00:
4981.40'1
4982.60
4982.38
4982.621
0.0003401
126
179.77
446.29
0.32
Reach-1
43580
240.001
4981.401
4982.68
4982.41
4982.71
0.000381,
1. _
215.82
454.30
0.35
Reach-1
3580
370.00i
4981.40
4982.80
4982.501
4982.83
0.000454
268.84
465.83
0.40
-
��
Fran rani
ea�� wni
wcno no
AQR2 A71
4982.941
0-0005291
310.40
474.67"
0.44;
mom >.••W
Fort Collins Old Town Existing
River = RIVER-1 Reach = Reach-1 Section 78 IRS = 3320
.013- .013 - .013
Legend
WS 500-Year
WS 100-Year
WS 25-Year
4987
WS 10-Year
WS 5-Year
Ground
•
Bank Sta
4986
4985
c
0
9
m
W
4984
4983
MASON STREET PROFILE
4982;
0 200 400 600 800
Station (ft) 5
-11 A6" k!J
I in Horiz. = 100 ft 1 in Vert. = 1 ft
Fir1IRF
No Text
' , Final Drainage Report
■ Civic Center Parking Structure
NOLTE and ASSOCIATES, Inc.
Engineers / Planners / Surveyors
1
4.0 DRAINAGE FACILITY DESIGN
4.1 GENERAL CONCEPT
Runoff from the site will be collected on the top level of the parking structure at inlets and floor
' drains which are connected with the floor drains on lower levels. The structure drains will be
connected to single outlet pipe on the east side of the building (Design Point 1 on the Drainage
' Exhibit). At this location, runoff will be routed through a Storm Ceptor manhole for water
quality purposes before being discharged into the existing storm sewer system in the alley.
1 4.2 BASIN DESCRIPTION
For the purpose of calculating runoff, the entire site is considered completely impervious. The
site is comprised of a single basin, identified by the letter A, as shown on the Drainage Exhibit.
Potential off -site discharges from the west will be conveyed in Laporte Avenue on the north side
of the property. No off -site flows will be conveyed through the site. No analysis has been
performed for landscaping which will occur within the right-of-way of Laporte Avenue and
Mason Street.
Basin A consists of the parking structure and commercial space within the boundary of the
property. Discharges from the site into the storm sewer inlet will be conveyed by a 15" RCP.
This storm sewer is designed for the minor event. Major event flows will be partially intercepted
by the storm sewer, and the remainder will surcharge the inlet and discharge directly into the
alley.
4.3 IMPACTS TO THE FLOODPLAIN
The Old Town floodplain was delineated in the Master Plan using the HEC2 computer program
(Reference D). Input and output files are listed in the Technical Addendum, Volume I, to the
Master Plan. The HEC2 input file for Reach 6 was copied and run as part of this analysis to
duplicate the results of the Master Plan, and to determine the affect this project will have on
1' existing flood elevations. The HEC2 input and output files from the Master Plan are included in
the Appendix to this report.
Two hydraulic cross -sections, numbered 77 and 78, define the flood elevations at this site. These
cross -sections are illustrated in Figures 2 and 3 on the following pages. The parking structure
will occupy a small area adjacent to Laporte Avenue in cross-section 77, but will not affect
r section 78. The location of the parking structure is indicated in cross-section 77, Figure 2.
NOLTE and ASSOCIATES, Inc. 4 N:\FC0053\civil\PKGStrDrainReportdoc ..
■, Final Drainage Report
Civic Center Parking Structure
NOLTE and ASSOCIATES, Inc.
Engineers / Planners / Surveyors
1.0 GENERAL LOCATION AND DESCRIPTION
1.1 LOCATION
The proposed civic center parking structure and commercial facility is located on the northwest
quadrant of Block 21 in downtown Fort Collins. It is located in the northeast '/< of Section 11,
Township 7 North South, Range 69 West of the Sixth Principal Meridian, see Figure 1, Vicinity
Map.
To the south of the site is a single story commercial building; to the north across Laporte Avenue
is Washington's bar, the Old Fort Collins Freight Depot and new Temporary Parking; to the east
is more commercial buildings with store fronts on College Avenue; and to the west across Mason
Street is the proposed Larimer County Justice Center.
Within the alley right-of-way on the east, storm sewer lines are existing which discharge through
downtown Fort Collins to the Poudre River.
1.2 DESCRIPTION OF PROPERTY
The parking structure lot is approximately 1.75 acres in area and is currently paved and used for
surface parking. The ground slopes downward from the west to east at approximately 1.0
percent. The overall change in grade across the lot is just over two feet, from a maximum
elevation of 4982.4 to a minimum of 4980.
The proposed development will include a single three-story building for parking, with a single
story building for commercial uses along Mason Street. There are no landscape areas proposed,
so the site will be virtually impervious.
1.3 PREVIOUS REPORT AND STUDIES
The site is in the drainageway known as Old Town Basin. The flood prone areas were delineated
in a master planning study, and are documented in a report entitled, Old Town Master Drainage
Basin Plan, City of Fort Collins, (Master Plan) prepared by Resource Consultants and Engineers,
Inc., dated January 1993 (Reference Q. This report includes a hydrologic model, evaluation of
the downtown area storm sewer system, delineation of the floodplain, and recommendations for
future improvements to alleviate flooding problems. The Civic Center Parking Structure is
adjacent to Reach 6 of the Old Town Basin drainageway. The Master Plan calls for a future
diversion channel to be constructed upstream (west) of Mason Street which will significantly
reduce flooding problems in the vicinity of the Civic Center Parking Structure.
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Final Drainage Report
�- Civic Center Parking Structure
NOLTE and ASSOCIATES, Inc.
' Engineers I Planners / Surveyors
2.0 DRAINAGE BASINS AND SUB -BASINS
2.1 MAJOR BASIN DESCRIPTION
The proposed development lies within the Old Town Drainage Basin. The Basin is located in the
' central part of Fort Collins and is almost completely developed. There is no major drainage
channel, and runoff is carried within a network of storm sewers and street sections to the Poudre
' River. The Basin is also subject to discharges resulting from irrigation surcharge flows occurring
in the basin upstream of Shields Street. Although this project is within the Old Town Basin
floodplain, the proposed structures are above the 100-year flood elevations.
2.2 SUB -BASIN DEVELOPMENT
As shown on the Drainage Exhibit at the back of this report, the site historically drained overland
to the east to an existing storm sewer in the alley, and north to an existing storm sewer in Laporte
' Avenue. The site has accepted sheet flows from the offsite area to thewest which may
infrequently overtop Mason Street. Upon development, the site will drain to the storm sewer
' system in the alley on the east.
3.0 DRAINAGE DESIGN CRITERIA
3.1 CRITERIA
This drainage report was prepared in accordance with the City of Fort.Collins' Storm Drainage
' Design Criteria and Construction Standards Manual (Reference A). The design rainfall data
used to calculate runoff for the site was obtained from the Time -Intensity -Frequency curves
contained within the City's Criteria Manual.
1 The site drainage plan was prepared with consideration given to the Master Plan for Old Town
Basin prepared by Resource Consultants, Inc. There are no specific site constraints that will
adversely impact the drainage.
3.2 RUNOFF CALCULATIONS
The Rational Method has been used to calculate peak runoff from the 10-year and 100-year
recurrence interval storms. Storm water detention is not provided, but discharges from the site
will not be increased over the "existing" conditions because the site was completely paved before
this project. Peak flow calculations are listed in the Appendix and summarized on the Drainage
Exhibit.
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Final Drainage Report
°r,£
Civic Center Parking Structure
NOLTE and ASSOCIATES, Inc.
Engineers / Planners / Surveyors
CERTIFICATION
I hereby affirm that this report for the final drainage design of the Civic Center Parking Structure
was prepared under my direct supervision in accordance with the provisions of the City of Fort
Collins Storm Drainage Design Criteria for the owners thereof. I understand that the City of
Fort Collins does not and will not assume liability for drainage facilities designed by others.
JOHN S. GRIFFITH, Professional Engineer
State of Colorado No. 16030
I
■k
NOLTE and ASSOCIATES, Inc.
Engineers / Planners / Surveyors
Final Drainage Report
Civic Center Parking Structure
TABLE OF CONTENTS
PAGE
CERTIFICATION........................................................................................................... ii
1.0. GENERAL LOCATION AND DESCRIPTION..............................................................1
1.1 Location................................................................................................................1
1.2 Description of Property ..............................................................................::::.......1
1.3 Previous Report and Studies.................................................................................1
FIGURE1 - VICINITY MAP..........................................................................................2
2.0 DRAINAGE BASINS AND SUB-BASINS....................................................................3
2.1 Major Basin Description.......................................................................................3
2.2 Sub -Basin Development ................................................. ...................................... 3
3.0 DRAINAGE DESIGN CRITERIA...................................................................................3
3.1 Criteria..................................................................................................................3
3.2 Runoff Calculations..............................................................................................3
4.0 DRAINAGE FACILITY DESIGN...................................................................................4
4.1 General Concept....................................................................................................4
4.2 Basin Descriptions................................................................................................4
4.3 Impacts to the Floodplain......................................................................................4
4.4 Erosion Control and Water Quality ......................................................................8
5.0 CONCLUSIONS/SUMMARY.........................................................................................8
5.1 Compliance with Standards..................................................................................8
5.2 Drainage Concept..................................................................................................9
REFERENCES...............................................................................................................10
APPENDIX
DRAINAGE EXHIBIT
j
S F
CIVIC CENTER PARKING STRUCTURE
FINAL DRAINAGE REPORT
for
Parsons and Associates
432 Link Lane Plaza
Fort Collins, Colorado 80524
(970) 221-2400
705
Nolte and Associates, Inc.
7000 S. Yosemite Street, Suite 200
Englewood, Colorado 80112
(303) 220-1001
July 1998