HomeMy WebLinkAboutTHE OVERLOOK/SENECA CENTER AT ARAPAHOE FARM PUD - FINAL - 55-87P - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT (2) N
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FINAL DRAINAGE AND
EROSION CONTROL REPORT
OVERLOOK/
SENECA CENTER P.U.D.
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Prepared for:
Wheeler Commercial Property Services
—111 1027 West Horsetooth Road,Suite 200
Fort Collins, CO 80526
Prepared by:
North Star Design
1200 Carousel Drive, Suite 201
Windsor, Colorado 80550
(970) 686-6939
September 14, 1999
Job Number 103-02
North Star
iikew design
September 14, 1999
Basil Hamdan
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522-0580
RE: Final Drainage Report for Overlook/Seneca Center P.U.D.
Dear Basil,
111 I am pleased to submit for your review and approval, this Final Drainage Report for Overlook /
Seneca Center P.U.D. I certify that this report for the drainage design of Seneca Center was
prepared in accordance with the criteria in the City of Fort Collins Storm Drainage Manual.
I appreciate your time and consideration in reviewingthis submittal. Please call if you have any
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questions.
Sincerely,
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Patricia Kroetch, P.E.
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1200 Carousel Drive, Suite 201 Windsor, Colorado 80550
970 - 686 - 6939
Phone & Fax
TABLE OF CONTENTS
TABLE OF CONTENTS iii
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location 1
1.2 Description of Property 1
2. DRAINAGE BASINS AND SUB-BASINS
2.1 Major Basin Description 1
2.2 Sub-Basin Description 2
3. DRAINAGE DESIGN CRITERIA
3.1 Regulations 2
3.2 Development Criteria Reference and Constraints 2
3.3 Hydrologic Criteria 2
3.4 Hydraulic Criteria 3
4. DRAINAGE FACILITY DESIGN
4.1 General Concept 3
4.2 Specific Flow,Routing 3
4.3 Drainage Summary 5
5. EROSION CONTROL -
5.1 General Concept 5
5.2 Specific Details 5
6. CONCLUSIONS
6.1 Compliance with Standards 6
6.2 Drainage Concept 6
7. REFERENCES 7
APPENDICES
A Vicinity Map
B Hydrologic Computations
C Hydraulic Calculations
D Erosion Control Calculations
E Figures and Tables
F Excerpts from Previous Reports
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1. GENERAL LOCATION AND DESCRIPTION
III 1.1 Location
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II This site is located within the Overlook/Gates development in Fort Collins, at the
southwest corner of the intersection of Seneca Street and Harmony Road. The project is
II bounded to the northeast by the Harmony Road, to the northwest by the back lots of the
Overlook at Woodridge, First Filing, and to the south by the old alignment of Harmony
Road.
IN
More precisely the proposed development is located in the Southwest Quarter of Section
111 34, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins;
Larimer County, Colorado. The project site is shown on the Vicinity Map in Appendix
A.
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III1.2 Description of Property
The Overlook at Arapahoe P.U.D. site contains approximately 3.2 acres and is generally
4 undeveloped at the present. The existing site is presently open ground covered with
native grasses. The site slopes gradually to the southeast of approximately 2.0% to 3.0%
ill and historically drains to an existing roadside ditch running along the south boundary of
the site and to Harmony Road along the northeast boundary of the site.
111 The project will consist of three buildings,
p J dings, a car wash and associated parking. One
building will contain a convenience store, one will be a combined office and residential
and the third building will contain retail or commercial, uses. The site will access off
Harmony Road and Seneca Street.
2. DRAINAGE BASINS AND SUB-BASINS
III 2.1 Major Basin Description
Ili" The project site is located in the McClellands/Mail Creek Basin. It is more particularly
detailed in the "Preliminary Master Drainage Study for Woodridge", December 1991,
II RBD Inc.
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2.2 Sub-basin Description
For the most part, this site is delineated as Basin 7C on the "Preliminary Grading and
Drainage Plan" for Woodridge, by RBD Inc. A portion of that plan is included in
Appendix A.
The site is split by the proposed new Seneca Street, which runs northeast to southwest in
the eastern boundary of the site. As mentioned before, there is an existing roadside ditch
running along the south property line of the site, but this will be removed with this
development.
3. DRAINAGE DESIGN CRITERIA
3.1 Regulations
This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage
MIDesign Criteria.Manual" specifications. Where applicable, the criteria established in the
"Urban Storm Drainage Criteria Manual" (UDFCD), 1984, developed by the Denver
Regional Council of Governments, has been used. -
® 3.2 Development Criteria Reference and Constraints
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The criteria established by the "Preliminary Master Drainage Study for Woodridge",
December 1991 by RBD Inc. and the "Final Drainage and Erosion Control Study for
Arapahoe FarmsTownhomesP.
U.D.",P.U.D. , July 15, 1994 by RBD Inc. were used for
designing the drainage facilities for this site.
This site was not planned to require on-site detention. Based on the "Preliminary Master
111 Drainage Study for Woodridge" and the "Final Drainage and Erosion Control Study for
Arapahoe Farms Townhomes P.U.D.", the site drains undetained into the proposed storm
drain beneath Harmony Road. The revised IDF curve compiled by the City of Fort
Collins (implemented on March 26, 1999) was used in calculating the runoff from the
site.
3.3 Hydrologic Criteria
The Rational Method for determining surface runoff was only used for the project site.
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The 10-year and 100-year storm event criteria and the revised IDF curve were used in
calculating runoff values.
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All hydrologic calculations associated with the basins are included in Appendix B of this
report. Standard Form 8 (SF-8) provides time of concentration calculations for all sub-
.! basins. Standard Form 9 (SF-9) provides a summary of the design flows for all Sub-
basins and Design Points associated with this site.
3.4 Hydraulic Criteria
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All hydraulic calculations within this report have been prepared in accordance with the
City of Fort Collins Drainage Criteria and are also included in Appendix C of this report.,
4. DRAINAGE FACILITY DESIGN
4.1 General Concept
The on-site runoff will drain via on-site swales and curb & gutter to inlets at low points,
will be collected in storm pipe and conveyed to the existing 30" storm pipe at the
southwest corner of the intersection of Seneca and Harmony, behind one of the proposed
buildings. The proposed drainage and erosion control plan-is included in the back pocket
of this report.
4.2 Specific Flow Routing
Per the "Preliminary Grading and Drainage Plan" for Woodridge and the "Final Drainage
and Erosion Control Study" for Arapahoe Farms Townhomes P.U.D., it was proposed
that 36.6 cfs be released from this site during the major storm into the existing 30" storm
pipe.
The drainage from the Harmony Road %-street width along the northeast property line of
this site was accounted for in the "Preliminary Master Drainage Study for Woodridge".
Basically, all of the Harmony Road runoff coming from upstream of Seneca Street is
collected in the existing 17" type `R' inlet (ST-3). This curb inlet was designed to
capture a portion of the flows coming from the areas and streets upstream of Seneca
Street. This stormwater is then routed to Detention Pond #2. The storm sewer plan and
profile by RBD is included in the back pocket for reference.
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Basin 1 contains the north
o h half of the north most building, a grassed swale (Swale A-A)
and the back half of 7 lots in the Overlook First Filing. Runoff from this basin is
collected in Swale A-A and is conveyed to an area inlet (Inlet #1). The water is then
conveyed in an 18" storm pipe to Inlet#2.
Basin 2 contains the south half of the north most building, the east half of the southwest
building, the west half of the convenience store, the car wash building, the refueling
islands and the majority of the parking lot and drive areas. Runoff from this basin is
collected in a 10' type `R' inlet (Inlet #2), is combined with runoff from other basins and
114 conveyed in a 24"storm pipe to Storm Manhole #1.
Basin 3 contains the west half of the southwest building, the parking area and driveways
for the residential use and the back half of one lot in the Overlook First Filing. Runoff
from this basin is conveyed in curb and gutter to a 5' type `R' inlet (Inlet #3). The water
is then conveyed in an 18" storm pipe to Storm Manhole#2 and then to Inlet#2.
store 4 contains the east half of the convenience and a small green area behind the
store. The runoff is conveyed in grass swales to an area inlet (Inlet #4). The water then
flows to Storm Manhole #1 where it combines with runoff from other basins and flows in
the existing 30" storm pipe to Detention Pond#2.
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Basin 5 contains Seneca Street north of the high point. Seneca Street was designed by
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TST Consulting Engineers and the proposed grading for the street is being shown for
reference. This basin receives runoff from Basin 6 and the combined runoff will flow
into Harmony Road. All runoff in Harmony will flow to Inlet ST-3 (17' type `R') and
eventually to Detention Pond#2.
Basin 6 contains the entrance drive to the site from Seneca. The existing site grading
constraints and the proposed grading on Seneca restrict the ability to collect runoff from
this basin and convey it in the storm system. The runoff from this basin, therefore, is
r,e . conveyed in the curb and gutter to Seneca Street, to Harmony Road and into Inlet ST-3.
rr,
Basin 7 contains a small strip of green area on the south boundary of the site. Runoff
from this basin will flow south and off site. The amount of water generated by this basin
is less than the historic flows to the south and will have minimal impact on the
development adjacent to the south.
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The total runoff from this site in the 100 year event was calculated to be 34.69 cfs which
is less than the allowable 36.6 cfs,release rate from this site. All runoff calculations were
completed utilizing the revised rainfall criteria.
4.3 Drainage Summary
The storm conveyance system is primarily a sub-surface system. The project owner or
subsequent owner will be responsible for the maintenance of all storm pipe and inlets on
the site and the City of Fort Collins will be responsible for maintenance of the existing
storm drainage facilities located within the right-of-way.
5. EROSION CONTROL
5.1 General Concept
This site lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort
Collins Zone Maps. The potential exists for silt movement from the site and into the
existing storm system during construction. Potential also exists for tracking of mud onto
existing streets which could then wash into existing storm systems.
Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and
related calculations in Appendix D, the erosion control performance standard for the
'` subject site is 80.9%. The erosion control plan gives a performance standard of 78.7%.
The erosion control plan as designed does not achieve the performance standard required
for the site but the erosion control plan as shown is adequate. All erosion control
measures necessary to minimize sediment transport have been designed into this site.
Additional measures implemented simply to achieve the desired performance standard
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!Ill would be redundant and add unnecessary costs to the project.
The erosion control escrow amount is $5700.
5.2 Specific Details
To limit the amount of silt leaving the site several erosion control measures shall be
implemented during construction. The inlets shall be protected with a gravel filters, the
III swale around the building on the north shall have straw bales, and the south and east
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boundaries shall have silt fence installed. Vehicle tracking pads shall be installed at the
entries to control the mud being tracked onto the existing pavement. During overlot
grading, disturbed areas are to be kept in a roughened condition and watered to reduce
wind erosion.
6. CONCLUSIONS
6.1 Compliance with Standards
All computations that have been completed within this report are in compliance with the
City of Fort Collins Erosion Control Reference Manual for Construction Sites and the
r'y Storm Drainage Design Criteria Manual.
.0 , 6.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provide for the conveyance and release of developed on-site flows into the
proposed 30" RCP storm drain and into the existing curb & gutter on Harmony Road. No
on-site detention was proposed with this project, but the amount of stormwater leaving
the site does not exceed the allowable release for the site established with Woodridge and •
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Arapahoe Farms Townhomes P.U.D. The existing Detention Pond downstream at the
4' southeast corner of the Woodridge development has been designed and built to account
for flows released from the Overlook/Seneca Center P.U.D. site.
If groundwater is encountered at the time of construction, a Colorado Department of
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Health Construction Dewatering Permit will be required.
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7. REFERENCES
4 1. Storm Drainage Design Criteria and Construction Standards, by the City of Fort
Collins, Colorado, May 1984, revised January 1991.
2. Erosion Control Reference Manual for Construction Sites, by the City of Fort
II Collins, Colorado, January 1991.
3. Preliminary/Master Drainage Study for Woodridge, by RBD, Inc., Fort Collins,
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Colorado, December 1991.
4. Final Drainage and Erosion Control Study for Arapahoe Farms Townhomes
a P.U.D., by RBD, Inc., Fort Collins, Colorado, July 15, 1994.
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APPENDIX A
VICINITY MAP
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