HomeMy WebLinkAboutUNIVERSITY CENTER PUD (UNIVERSITY MALL REDEVELOPMENT) - PRELIMINARY - 2-96 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTWIMM
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APPENDIX A
MAPS AND FIGURES
6.
7.
MISCELLANEOUS
6.1 Variances
There are no variances requested with the development of the University Town Center PUD,
6.2 Irrigation Ditches
As previously discussed, the eventual outfall for this project is the Sherwood Ditch Lateral
(as this is the existing outfall for this area).
6.3 Ditch Company Approval
Because this is the existing outfall for the drainage from this area, it is anticipated that the
Developer will work jointly with the City Stormwater Utility in order to obtain approval to
continue the release of flows into this structure.
6.4 Maintenance Agreements
The developer will be responsible for the maintenance of all temporary drainage structures.
REFERENCES
1. City of Fort Collins, "Storm Drainage Design Criteria and Construction Standards",
(SDDCCS), dated May, 1984.
2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes 1 and 2, dated March, 1969, and Volume 3 dated September,
1992.
3. "Spring Creek Master Drainageway", prepared by Engineering Professionals, Inc.,
dated March, 1988.
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4.1 PR.igL
Without Detention
10 Year
100 Year
Existing Runoff
Basins EEX5,E19
15.56 cfs
34.49 cfs
Developed Runoff
Basins DEX3,137,138,139,D10
26.46 cfs
44.60 cfs
Difference
- 10.90 cfs
- 10.11 cfs
With Parking Area Detention (Preliminary)
Existing Runoff
Basins EEX5,E19
15.56 cfs
34.49 cfs
Released
Developed Runoff
Basins D7,D8,D9
8.68 cfs
20.52 cfs
Developed Runoff
Basins DEX3,1310 -
5.48 cfs
11.30 cfs
Difference
1.40 cfs less than
Existing
2.67 cfs less than
Existing
As part of the preparation of the final plans for this site, the exact location and limits of the
detention area will be determined with the release rates limited to equal to or less than -the
existing 10-year and 100-year runoff rates.
5. EROSION CONTROL
The specific erosion control report and plan for this project are not included in this
preliminary report. Upon preparation of the Final Drainage and Erosion Control Report and
Plans for this project, this information will be determined (including detailed description,
calculations, schedule, and appropriate cost estimates) in accordance with the SDDCCS.
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1 3.8 Inlet Design
There are two (2) sump condition area inlets proposed with the University Town Center
PUD. These inlets (standard Type C) are located in the southwest portion of this site.
3.9 Storm Sewer Design
There is one underground storm sewer pipe system proposed with the development of
University Town Center PUD. This storm sewer pipe system (15" RCP) is located in the
southwest portion of the site and will be connected to the existing underground storm sewer
system.
4. DETENTION POND (PARKING AREA)
There is one detention pond proposed with the development of the University Town Center
PUD. This detention area is designed to reduce the flows to be released onto the existing
outfall swale in the northwest comer of this site to at or less than the existing 10-year and
100-year runoff rates.
Parking Area Detention
The proposed parking area detention pond has been sized on a preliminary basis as part of this
report. The size of the pond is limited by the 6 inch vertical curb along the east size of the
proposed storage unit areas and the proposed one percent (1%) cross slope for the parking
area between the University Town Center building and said curb line (for this area,
approximately 800 feet by 50 feet, the volume is 10,000 cubic feet).
In order to evaluate this detentionarea on the developed flows, preliminary calculations were
run (included in the Appendix) to determine if this was adequate. These calculations showed
the following (utilizing a total weir length of 18 feet (6 feet at each location):
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All hydrologic calculations associated with the sub -basins shown on Figure 3.1 are attached
in the Appendix of this report. Table 3.1 provides a summary of the design flows for all
Subbasins and Design Points (DP's) associated with this site.
CI00
Tc (2)
Tc (100)
Q (2)
Q (100
DESIGN
AREA
AREA
C10
POINT
DESIG.
(ACRES)
CFS
(CFS
DI
0.56
0.92
1.00
5.0
10.0
2.89
3.991
D2
0.60
0.91
1.00
5.0
10.0
3.06
4.2
D3
0.25
0.86
1.00
5.0
10.0
1.20
1.7
D4
0.75
0.93
1.00
5.0
10.0
3.89
5.3
DEXI
0.16
0.50
0.63
5.0
10.0
0.45
0.71
D5
0.79
0.91
1.00
5.0
10.0
4.02
5.621
DEX1,D5
0.95
0.84
1.00
5.6
10.0
4.33
6.7
DEX2
0.09
0.50
0.63
5.01
10.0
0.25
0.4
D6
0.63
0.93
1.00
5.0
10.0
3.26
4.4
DEX2,D6
0.72
0.87
1.00
7.0
10.0
3.18
5.13
D7
1.38
0.95
1.00
5.0
10.0
7.32
9.8
D8
1.55
0.94
1.00
5.1
10.0
8.09
11.0
D9
2.13
0.94
1.00
5.0
10.0
11.17
15.1
D7,D8,D9
5.06
0.94
1.00
5.11
10.0
26.49
36.0
DEX3
0.36
0.501
0.63
5.0
10.0
1.00
1.6
D10
1.38
0.871
1.00
9.1
10.0
5.53
9.8
DEX3,D10
1.74
0.791
0.99
13.1
12.2
5.48
11.3
DEX3,D7,
6.80
0.901
1.00
13.1
12.2
26.46
44.6
D8,D9,D10
DI 1
0.65
0.951
1.001
5.01
10.0
3.45
4.63
3.7 Allowable Street Flow Capacities
The University Town Center PUD does not affect flows on any existing or proposed streets.
Therefore, calculations for allowable street capacities for surrounding, existing streets are not
included.
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The runoff from the combination of Subbasins DEX3 and D7, D8, D9 and D10 is
routed to the existing outfall swale as stated in the previous paragraphs.
3.6 Hydrologic Analysis of the Proposed Drainage Conditions
The Rational Method was used to determine both 10-year and 100-year peak runoff values
for each Subbasin. Runoff coefficients were assigned utilizing Table 3-2 of the SDDCCS
Manual.
As stated above, the Rational Method was used for all hydrologic analyses for the project site.
The Rational Method utilizes the SDDCCS equation:
Q = CrCIA (1)
where Q is the flow in cfs, A is the total area of the basin in acres, Cf is the storm frequency
adjustment factor, C is the runoff coefficient, and I is the rainfall intensity in inches per hour.
The frequency adjustment factor, Cs is 1.0 for the initial 10-year storm and 1.25 for the major
100-year storm.
The appropriate rainfall intensity information was developed based on rainfall intensity
duration curves in the SDDCCS Manual.
In order to utilize the rainfall intensity curves, the time of concentration is required. The
following equation was used to determine the time of concentration:
tC=ti+tt
; (2)
where t. is the time of concentration in minutes; t is the initial or overland flow time in
minutes, and tt is the travel time in the ditch, channel, or gutter in minutes. The initial or
overland flow time is calculated with the SDDCCS Manual equation:
ti = [1.87(1.1 - CCf)L0.5]/(s)0.33
(3)
where L is the length of overland flow in feet (limited to a maximum of 500 feet), S is the
average slope of the basin in percent, and C and Cf are as defined previously.
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flow.
The runoff from Subbasin DEM is routed onto Subbasin D5 via overland flow.
Runoff from Subbasin D5 is conveyed into a proposed sump condition area inlet to
be located west of the proposed building in the southwest portion of this site via sheet
flow.
The runoff from the combination of Subbasins DEXI and D5 are routed to the
proposed sump condition area inlet as previously stated.
The runoff from Subbasin DEX2 is routed onto Subbasin D6 via overland flow.
Runoff from Subbasin D6 is conveyed into a proposed sump condition area inlet to
be located east of the proposed building in the southwest portion of this site via sheet
flow.
The runoff from the combination of Subbasins DEX2 and D6 are routed to the
proposed sump condition area inlet as previously stated.
Runoff from Subbasin D7 is conveyed westerly to the proposed parking lot detention
area and released onto Subbasin D10 through a proposed curb cut (weir structure).
Runoff from Subbasin D8 is conveyed westerly to the proposed parking lot detention
area and released onto Subbasin D10 through a proposed curb cut (weir structure).
Runoff from Subbasin D9 is conveyed westerly to the proposed parking lot detention
area and released onto Subbasin D10 through a proposed curb cut (weir structure).
The runoff from the combination of Subbasins D7,,D8 and D9 is routed onto
Subbasin D10 as stated in the previous paragraphs.
The runoff from Subbasin DEX3 is routed onto Subbasin D10 via overland flow.
Runoff from Subbasin D10 is conveyed northerly in a proposed swale between the
proposed storage buildings and outfalls into the existing swale at the northwest corner
of this site.
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3.4 General Flow Routing
The final drainage pattern for this area has been developed to provide a drainage system that
is compatible with the surrounding area. This has been accomplished by utilizing existing
drainage patterns to the extent possible and routing flows to limit the amount of required
drainage facilities.
The proposed drainage facilities for this site consist of existing area inlets and outfall pipes,
proposed inlets and pipe in the southwest corner of the site, and parking lot detention in the
rear of the site.
The proposed drainage system meets the requirements for providing drainage relief by
reducing the impact of the flows generated by the re -development of portions of this site on
downstream areas (restricting release rates to existing) and meets the criteria in the SDDCCS.
(See attached "Preliminary Drainage Plan" for the location of all drainage facilities.)
3.5 Proposed Drainage Plan
A qualitative summarization of the drainage patterns within each sub -basin and at each design
point is provided in the following discussion paragraphs. Discussions of the detailed design
of drainage facilities identified in this section are included in Sections 3.7.
Note: The drainage for the portion of this site between the existing mall and College Avenue
(north of McDonalds) does not change as a result of this project. Therefore, developed flows
were not calculated for these areas nor described below.
Runoff from Subbasin D1 is conveyed into three (3) existing sump condition area
inlets adjacent to the north side of McDonalds via sheet flow.
Runoff from Subbasin D2 is conveyed into an existing sump condition area inlet
adjacent to the south side of McDonalds via sheet flow.
Runoff from Subbasin D3 is conveyed into an existing sump condition area inlet in
the parking area south of McDonalds via sheet flow.
Runoff from Subbasin D4 is conveyed into a proposed sump condition area inlet to
be located east of the proposed building in the southwest portion of this site via sheet
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3.
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DEVELOPED FLOWS
3.1 Method
The Rational Method was used to determine both the 10-year and 100-year flows for the sub -
basins indicated in this drainage report. A detailed description of the hydrologic analysis is
provided in Section 3.6 of this report.
The historic (existing) flows for this site are included as part of this report. The resulting 10-
and 100-year runoff values were used to compute discharges at specific design points.
3.2 Exterior Flows
i Exterior flows enter this site from the west (the existing Burlington Northern Railroad). All
g lands lying within these areas have been assigned land use characteristics reflecting their
I current, developed conditions. These areas are identified on the attached "Preliminary
Drainage Plan" and calculations are included in the Appendix of this report.
3.3 Onsite Flows
Flows within this site will take the form of overlot and swale flow. The existing drainage
patterns have been maintained where possible. All grading has been designed to carry flows
away from structures to the proposed drainage facilities.
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The proposed re -development of portions of this site does not result in changes to the flows
and drainage structures on the east side of the this site. Therefore, the basins were delineated
and flows calculated for reference. However, further analysis of said existing system is not
warranted and is well outside the scope of this report.
The outfall from the rear of the site (the existing outfall swale) flows have been determined
and the developed flows will be limited to the existing 10-year and 100-year runoff rates.
AREA
AREA
CIO C 100
Tc 2
Tc 100
Q 2
Q 100
DESIG.
ACRES
CFS
CFS
EXl
0.82
0.95
1.00
5.01
10.0
4.35
5.841
1
0.51
0.92
1.00
5.01
10.0
2.621
3.6.3
EX1,E1
1.33
0.941
1.00
5.01
10.0
6.971
9.4
2
0.71
0.891
1.00
5.01
10.0
3.511
5.05
3
0.25
0.831
1.00
5.01
10.0
1.161
1.7
4
0.84
_0.921
1.00
5.01
10.0
4.331
5.9
5
0.28
0.90
1.00
5.0
10.0
1.40
1.9
6
0.98
0.87
1.00
5.0
10.0
4.78
6.9
7
0.16
0.81
1.00
5.0
10.0
0.72
1.1
8
0.07
0.95
1.00
5.0
10.0
0.37
0.5
9
0.41
0.951
1.00
5.01
10.0
2.171
2.9
10
0.56
0.951
1.00
5.01
10.0
2,971
3.9
11
0.58
0.901
1.00
5.01
10.0
2.911
4.13
12
0.29
0.951
1.00
5.0
10.0
1.54
2.0
13
0.74
0.931
1.00
5.0
10.0
3.84
5.2
14
0.64
0.871
1.00
5.0
10.0
3.10
4.5
15
0.47
0.741
0.93
9.1
10.0
1.61
3.11
EX2
0.18
0.501
0.63
5,01
10.0
0.50
0.8
16
1.64
0.21
0.26
12.3
12.3
1.40
2.8
EX2,E16
1.82
0.24
0.30
12.3
12.3
1.77
3.5
EX3
0.23
0.50
0.63
5.0
10.0
0.64
1.0
17
1.39
0.72
0.90
6.1
10.0
5.27
8.8
EX3,E17
1.62
0.69
0.86
6.1
10.0
5.88
9.91
EX4
0.0610.501
0.63
5.0
10.0
0.17
0.2
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Town Center PUD, including consideration of all on -site and tributary off -site runoff.
1.5 Design Criteria
(�
This report was prepared to meet or exceed the submittal requirements established in the City
ail of Fort Collins' "Storm Drainage Design Criteria and Construction Standards" (SDDCCS),
dated May 1984. Runoff computations were prepared for the 10-year minor and 100-year
�I major storm frequency utilizing the rational method.
Where applicable, the criteria established in the "Urban Storm Drainage Criteria Manual"
(UDFCD), 1984, developed by the Denver Regional Council of Governments, has been
utilized.
1.6 Master Drainage Basin
This site falls within the Spring Creek Major Drainage Basin and a report entitled "Spring
Creek Master Drainageway Plan"was prepared by Engineering Professionals, Inc. in March
1988. This report provides a detailed storm drainage planning analysis for Spring Creek
(®I through the City of Fort Collins, but the University Mall Redevelopment will not have an
impact on the Spring Creek Major Drainage Basin.
2. HISTORIC (EXISTING) DRAINAGE
The historic flows for this site looked at with respect to the proposed development consist
of the currently existing drainage patterns.
In general, the existing drainage patterns for this site consist of the routing of flows to existing
area inlets in the east parking area of this site, the loading ramps at the rear of King Soopers,
the existing businesses on the north and south, and the existing dirt area in the southwest
corner of this site.
The drainage from the westerly portion of this site is conveyed northerly along the westerly
edge of the existing asphalt parking area to an existing swale which runs from the northwest
corner of subject site and outfalls into the existing Sherwood Lateral.
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1. INTRODUCTION
1.1 Project Location
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University Town Center PUD is the proposed re -development of portions of the University
�I Mall. This project is located in the Southeast One -Quarter of Section 23, Township 7 North,
Range 69 West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County,
Colorado. (See FIGURE 1 - VICINITY MAP.)
This project is bounded on the south by existing commercial development (McDonalds and
the K-Mart Plaza Expansion, on the west by the Burlington Northern Railroad, on the north
by Montgomery Wards, and on the east by College Avenue. More specifically, this site can
be found on the west side of College Avenue, north and south of Columbia Road.
1.2 Site Characteristics `
The general topography of this site consists primarily of existing asphalt parking lot, buildings
and curb, gutter and sidewalk. The southwest comer and westerly portion of the site consists
of poorly to very poorly covered range type land. The slopes range from 0.5 to 3 percent.
1.3 Soils
The soils for this site are comprised of the Nunn clay loams (73,74). (See FIGURE 2 - SOIL
MAP )
The Nunn clay loams complex consists of nearly level soils on high terraces and fans.
Pertinent characteristics of this soil include slow to medium runoff and a slight to moderate
hazard of wind and water erosion. Nunn clay loams are categorized in Hydrologic Group C.
The source for soil data is the "Soil Survey for Larimer County Area, Colorado', prepared
by the United States Department of Agriculture Soil Conservation Service.
1 1.4 Purpose and Scope of Report
This report defines the proposed preliminary drainage and erosion control plan for University
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ITABLE OF CONTENTS
IPAGE
TABLE OF CONTENTS ..................................................... i
1. INTRODUCTION.....................................................1
1.1 Project Location.................................................1
1.2 Site Characteristics...............................................
1
1.3 Soils..........................................................1
1.4 Purpose and Scope of Report .......................................1
1.5 Design Criteria..................................................2
1.6 Master Drainage Basin ............................................
2
2.
HISTORIC (EXISTING) DRAINAGE .....................................
2
3.
DEVELOPED FLOWS ........... ........ `:........::...................
3.1 Method.......................................................4
4
3.2 Exterior Flows..................................................4
3.3 Onsite Flows...................................................4
3.4 General Flow Routing .............................................
5
3.5 Proposed Drainage Plan ...........................................5
3.6 Hydrologic Analysis of the Proposed Drainage Conditions .................
7
3.7 Allowable Street Flow Capacities ....................................
8
3.8 Inlet Design....................................................9
3.9 Storm Sewer Design.............................................9
5.
EROSION CONTROL ................................................
10
6.
MISCELLANEOUS..................................................11
6.1 Variances.....................................................11
6.2 Irrigation Ditches...............................................II
6.3 Ditch Company Approval .........................................
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6.4 Maintenance Agreements .........................................
11
7.
REFERENCES......................................................II
APPENDIX A - MAPS AND FIGURES
APPENDIX B - HYDROLOGIC CALCULATIONS
APPENDIX C - DETENTION CALCULATIONS
T" Engineering, Ltd.
(�J 4812 South College Avenue
Fort Collins, Colorado 80525
(970) 282-4335 • FAX (970) 282-4340
January 22, 1996
Mr. Basil Hamdan
City of Fort Collins
Stormwater Utility
235 Mathews Street
Fort Collins, Colorado 80524
Re: Preliminary Drainage and Erosion Control Report
University Town Center PUD
Fort Collins, Colorado
Dear Basil:
4935 North 30th Street
Colorado Springs, Colorado 80919
(719) 593-2593 • FAX (719) 528-6613
6110 Greenwood Plaza Blvd.
Englewood, Colorado 80111
(303) 740-9393 • FAX (303) 721-9019
JR Engineering, Ltd. is pleased to submit the attached Preliminary Drainage and Erosion Control
Report for University Town Center PUD for your review and approval. The hydraulic and hydrologic
evaluation of the site was performed in accordance with the specifications set forth in the City of Fort
Collins' "Storm Drainage Design and Criteria Manual".
If you have any questions regarding the procedures, methodology, or results presented herein, please
do not hesitate to contact me at your convenience.
Sincerely,
JR Engineering, Ltd.
F. Scott Waterman, E.I.
Project Engineer
`�W -C
David W. Klockeman, P.E.
Project Manager
Attachment
Recycled
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
UNIVERSITY TOWN CENTER PUD
Prepared for:
ZTI GROUP
1220 SOUTH COLLEGE AVENUE
FORT COLLINS, COLORADO 80524
Prepared by
JR ENGINEERING, LTD.
4812 South College Avenue
Fort Collins, Colorado 80525
(970)282-4335
January 22, 1996
Job Number 9059.00
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PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
UNIVERSITY TOWN CENTER PUD
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