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DATE: 11/4/03 North Star
SCALE: 1" = 1000' LOT 1, IN -SITU SUBDIVISION -��. design, inc.
FORT COLLINS, CO 700 Automation Drive, Unit I
DRAWN BY: SB VICINITY MAP Windsor, Colorado
JOB NO.: 174-02 Fax:970-686-1188
APPENDIX A
VICINITY MAP
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1 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
Storm Drainage Design Criteria Manual.
Floodplain and floodway documentation is located in Appendix F of this report. A FEMA
Elevation Certificate must be completed and approved prior to the issuance of a
Certificate of Occupancy for the building expansion.
6.2. Drainage Concept
' The proposed drainage concepts presented in this report and on the construction plans
adequately provide for stormwater detention of improved areas. Conveyance elements
have been designed to pass required flows and to minimize future maintenance.
If, at the time of construction, groundwater is encountered, a Colorado Department of
Health Construction Dewatering Permit would be required.
7. REFERENCES
1. Ayres Associates, "Hydraulic Analysis for the Cache La Poudre River Floodway
Revisions", dated August 2000.
2. City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March,
r 1986.
3. FEMA, Flood Insurance Rate Map, Community -Panel Number 080102 0004 C,
Revised March 18, 1996.
4. FEMA, Letter of Map Amendment Determination Document (Removal)
5. Urban Drainage and Flood Control Districf,- "Urban Storm Drainage Criteria
Manual", Volumes 1 and 2, dated June 2001 and Volume 3, dated September
2001.
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' Basin 4 (0.44 acres) is located to the south of Basin 3 and adjacent to the Poudre River.
Runoff from this basin will sheet flow, undetained, into the Poudre River. The only
impervious area in this basin is from the Poudre River Trail and. connecting walkways.
Peak runoff from Basin 4 is 0.54 cfs for the 10-year storm and 1.44 cfs for the 100-year
' storm.
4.3.. Drainage Summary
Drainage facilities located outside of the right-of-way (including the water quality pond,
' proposed storm drain systems, and the pond outlet) will be maintained by the owners of
the property. A water quality detention pond is proposed that will treat a portion of the
site (Basins 1, 2, and 3). The treated water will be released into the Poudre River. Basin
4 will sheet flow into the Poudre River undetained.
5. EROSION CONTROL
' 5.1. General Concept
This site lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort
Collins and into adjacent properties. Potential also exists for tracking of mud onto
existing streets which could then wash into existing storm systems. The required
performance standard for the site is 79.1%. During construction and after paving, this
figure has been exceeded with the use of silt fence, straw bales, and by using the water
quality pond as a sediment trap during construction. All erosion control calculations are
included in Appendix D of this report.
The erosion control escrow amount is $9,400.
5.2. Specific Details
To limit the amount of silt leaving the site several erosion control measures shall be
implemented during construction. Straw bales will be used where appropriate and the
south, east, and west boundaries shall have silt fence installed. A vehicle tracking pad
shall be installed at the east entrance to East Lincoln' Avenue to control the mud being
tracked onto the existing pavement. During overlot grading, disturbed areas Ore to be
kept in a roughened condition and watered to reduce wind erosion. The water quality
pond will be used as a sediment trap during construction.
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4. DRAINAGE FACILITY DESIGN
4.1. General Concept
' All proposed flow patterns will remain the same as existing flow patterns. The site is
split into four drainage basins. Basins 1 through 3 will be collected in the proposed -water
quality and detention pond and will be detained before being released into.the Poudre
River. Basin 4 will sheet flow from the site into the River.
' 4.2. Specific Flow Routing
A summary of the drainage patterns within each basin is provided in the following
paragraphs.
Basin 1 (2.24 acres) is the located in the northwest portion of the site and contains the
' west portion of the building, all of the proposed and future parking lot, and adjacent
walks. The adjacent portion of the southern half of East Lincoln Avenue is also included
in the hydrology calculations for this basin. Runoff from this basin will flow via sheet
flow to the proposed concrete pan located at the center of the parking lot. From there,
runoff will be conveyed in the pan to the proposed detention pond. Peak runoff from
Basin 1 is 7.88 cfs for the 10-year storm and 22.28 cfs for the 100-year storm.
Basin 2 (0.65 acres) is located in the northeast portion of the site and includes the
remainder of the building and the adjacent portion of the southern half of East Lincoln
Avenue. Runoff from this basin will be conveyed via a proposed concrete pan (behind
the building) through Basin 3 and into the proposed detention pond. Runoff from Basin 2
is 1.45 cfs for the 10-year storm and 4.06 cfs for the 100-year storm.
Basin 3 (1.20 acres) is located to the south of the proposed parking lot and future
building and includes the proposed detention pond. Peak runoff from Basin 3 is 1.23 cfs
for the 10-year storm and 3.14 cfs for the 100-year storm. Combined runoff from Basins
1, 2, and 3 will be released into the Poudre River at a rate of 6.8 cfs. Total storage
volume provided in the proposed pond is 0.097 acre-feet for extended water quality
detention and 0.356 acre-feet for runoff volume detention, for a total of 0.446 acre-feet of
storage in the pond. The pond has been designed without a trickle pan and with a 1%
bottom slope. This will result in shallow ponding, which is preferred by the owner.
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A floodway modeling report has been completed by Ayres Associates (08/2000), but no
floodplain modeling report has been completed for the site. A FEMA LOMR has been
approved for the site by JR Engineering. The LOMR case number is 02-08-485A. A
FEMA Elevation Certificate must be completed and approved prior to the issuance of a
' Certificate of Occupancy for the proposed building.
3.2. Development Criteria Reference and Constraints
The runoff from this site has been routed to conform to the requirements of the City
' Stormwater Department. Detention is not required for this site, but will be provided in
order to reduce the size of the outlet pipe. All calculations have been done assuming
IPhase 2 buildout of the building and parking lot.
This project complies with the requirements of Chapter 10 of the City Code. Constraints
' on the site include the "no fill" requirements for the floodway and that all proposed
buildings be elevated at least 2.0' above the 100-year Base Flood Elevation (BFE). The
Phase 1 building elevation is 2.5' above the BFE at the building (4943.7). The Phase 1
building is out of the floodplain, but the Phase 2 expansion will be inside the floodplain.
All necessary floodplain documents will be completed for the Phase 2 expansion at that
time.
3.3. Hydrologic Criteria
Runoff computations were prepared for the 10-year minor and 100-year major storm
' frequencies utilizing the Rational Method. All hydrologic calculations associated with
the basins are included in Appendix B of this report. Water quality volume was
calculated using the method recommended in the "Urban Storm Drainage Criteria
Manual". All detention and water quality calculations are included in Appendix C of this
report.
3.4. Hydraulic Criteria
All hydraulic calculations within this report have been prepared in accordance with the
City of Fort Collins Drainage Criteria and are included in the Appendix B of this report.
Proposed on -site storm sewer includes a culvert section that will allow free -flow between
the two detention areas and the proposed outlet pipe. All basins will release into the
�j Poudre River.
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2.
3.
Phase 1
Phase 2
FEMA 100-Year Base Flood Elevation
NA
4943.7
FEMA Regulatory Flood Protection Elevation
NA
4945.7
Proposed Lowest Floor Elevation(Finished Floor
4946.20
4946.20
Proposed HVAC Elevation
4946.20
4946.20
DRAINAGE BASINS AND SUB -BASINS
2.1. Major Basin Description
The proposed development lies within the Old Town Drainage Basin. The outfall point
for this site is the Poudre River. Extended water quality detention is required for this site
and is being provided. Runoff volume detention is not required but will be provided in
order to reduce the size of the outfall pipe from the site to the Poudre River.
2.2. Sub -basin Description
This site was split into 4 sub -basins. The existing drainage patterns will remain with the
proposed improvements. All basins drain from north to south and, with the exception of
Basin 4, are collected in the proposed detention pond. After being detained, runoff will
be released into the Poudre River. Refer to Section 4 of this report for a more detailed
summary of on -site drainage patterns.
DRAINAGE DESIGN CRITERIA
3.1.. Regulations
This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage
Design 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.
Since this site is located in the Poudre River Floodplain, it is also subject to Chapter 10 of
the City Code "Flood Prevention and Protection". Both Phase 1 and Phase 2 of the
building, as well as the proposed HVAC unit are in compliance with this Code (2.0' of
freeboard).
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1. GENERAL LOCATION AND DESCRIPTION
1.1. Location
' This project is located at 105 East Lincoln Avenue on Lot 1 of In -Situ Subdivision. This
project is located in the Southeast Quarter of Section 12, Township 7 North, Range 69
West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County,
Colorado. See the location map in Appendix A of this report. The project is located on
' the south side of Lincoln Avenue. The project is bounded on the south by the Poudre
River and on the east and west by existing commercial properties.
' 1.2. Description of Property
Presently, the site consists of a small building on blocks with a shed and semi trailers.
Existing drainage patterns on -site are to the south into the Poudre River at approximately
1 %. Existing vegetation consists mainly of native grasses and weeds.
' Improvements proposed with this project include a 16,000 square foot building with a
' planned future addition and associated drives, parking, and walks. The building will be a
slab on grade foundation. Existing drainage patterns will be maintained with proposed
runoff flowing to the south into a proposed detention and water quality pond, then
' releasing into the Poudre River.
The southern portion of this site is within the Poudre River Floodplain and Floodway
' (FEMA Panel 080102 0004 C, March 18, 1996). A LOMR was submitted by JR
Engineering and approved by FEMA in September of 2002. The LOMR case number is
02-08-485A. There is no City floodplain map for the Poudre River. The Phase 1
building is not in the floodplain, but the Phase 2 building will be. The proposed building
meets the 2.0' minimum freeboard requirement from the flood elevation. Refer to the
"Grading Plan" and "Drainage and Erosion Control Plan" for specific information related
to the building elevations
A FEMA Elevation Certificate must be completed an4tapproved prior to the issuance of a
Certificate of Occupancy for the proposed building. See Appendix F of this report for
information related to the floodplain and the Floodplain Use Permit. The following table
lists the elevations required for the building.
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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..........................................................................................2 ,
2.2 Sub -Basin Description.............................................................................................2
3. DRAINAGE DESIGN CRITERIA
3.1 Regulations..............................................................................................................2
3.2 Development Criteria Reference and Constraints....................................................3
3.3 Hydrologic Criteria..................................................................................................3
3.4 Hydraulic Criteria....................................................................................................3
4. DRAINAGE FACILITY DESIGN
4.1 General Concept.......................................................................................................4
4.2 Specific Flow Routing.............................................................................................4
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....................................................................................................................6
APPENDICES
A Vicinity Map
B Hydrologic and Hydraulic Computations
C Detention and Water Quality Pond Sizing
D Erosion Control Calculations
E Figures and Tables
F Floodplain and Floodway Documentation
iii
North Star
design, inc.
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' November 4, 2003
Basil Hamdan
' City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522-0580
RE: Final Drainage and Erosion Control Study for Lot 1, In -Situ Subdivision
Dear Basil,
I am pleased to submit for your review and approval, this Final Drainage and Erosion Control
Report for Lot 1, In -Situ Subdivision. I certify that this report for the drainage design was
prepared in accordance with the criteria in the City of Fort Collins Storm Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Sincerely,
North Star Design, Inc.
Prepared By:
Aaw� Rve�
Shane Boyle, EIT
Reviewed By:
Michael Oberlander, P.E., L.S.I.
700 Automation Drive, Unit I Windsor, Colorado 80550
970-686-6939 Phone . 970-686-1 188 Fax
FINAL DRAINAGE AND EROSION
CONTROL REPORT
FOR.
LOT 1, IN -SITU SUBDIVISION
Prepared for:
DOHN CONSTRUCTION, INC.
2642 Midpoint Drive, Unit A
Fort Collins, CO 80525
Prepared by:
North Star Design
700 Automation Drive, Unit I
Windsor, Colorado 80550
(970) 686-6939
November 4, 2003
Job Number 174-02