HomeMy WebLinkAboutEASTGATE PDP - 10-04 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
IX. REFERENCES
o City of Fort Collins, Storm Drainage Design Criteria and Construction Standards;
March 1997
o City of Fort Collins, Erosion Control Reference Manual; January 1991
o City of Fort Collins, Land Use Code; January 9, 1999
o Urban Drainage and Flood Control District, Urban Storm Drainage Criteria Manual
Volume 1; March 1969
o Urban Drainage and Flood Control District, Urban Storm Drainage Criteria Manual
Volume 2; March 1969
o Urban Drainage and Flood Control District, Urban Storm Drainage Criteria Manual
Volume 3; September 1, 1999
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
2. See the Erosion Control Security Deposit Requirements document located in
Appendix III.
3. The erosion control security deposit is reimbursable.
4. The erosion control security deposit is equal to $1000.00.
VII. VARIANCE REQUEST
A. DETENTION POND FREEBOARD
1. According the City of Fort Collins Storm Drainage Design Criteria Section
9.2, one foot of freeboard is required for detention areas. This report is
requesting a variance for the 0.85 feet of freeboard in the detention pond for
Eastgate P.D.P.
VIII. CONCLUSIONS
A. COB4PLIANCE WITH STANDARDS
1. All drainage analysis has been perfonned according to the requirements of the
City of Fort Collins Storm Drainage Criteria Manual.
2. Proposed drainage improvements generally conform to the recommendations
of the City of Fort Collins Master Drainage Plan,
3. Proposed erosion control measures conform to the recommendations of the
City of Fort Collins standards.
B. DRAINAGE CONCEPT
1. The proposed drainage design for Eastgate P.D.P. is effective for the control
of storm runoff with a considerable reduction in potential downstream effects.
2. The proposed drainage design for Eastgate P.D.P. will have no affect on City
of Fort Collins Master Drainage Plan recommendations.
3. The proposed drainage design will release up to a 100-yr storm runoff at the
historic 2-yr storm runoff release.
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
ii. The bottom row will consist of one 3/4" hole set on -center.
iii. The top row will consist of one 5/8" hole set on -center
4. A water quality outlet device is specified in the plan set. A detail is provided
on the detail sheet.
5. A US Filter Stainless Steel well -screen will be provided in front of the water
quality orifice plate. This screen will have the following specifications:
i. Screen #93 VEE Wire Slot Opening 0.139.
ii. Support Rod Type #156 VEE
iii. Support Rod, On -Center, spacing = 3/4"
iv. Total Screen Thickness = 0.31"
v. Carbon Steel Frame Type = 3/8"xl.0" flat bar
6. For further specifics, please see water quality control in Appendix I.
C. SPECIFIC DETAILS— EROSION CONTROL MEASURES
1. The following temporary erosion control measures are specified on the
Drainage and Erosion Control Plan:
a. Wattles in the swales.
b. Wattles used for orifice plate protection.
z. The following permanent erosion control measures are specified on the
Drainage and Erosion Control Plan:
a. Seeding of the open areas, including the detention pond.
b. Water quality control pond in the base of the detention pond.
3. The erosion control deposit letter is attached in Appendix III.
D. EROSION CONTROL SECURITY DEPOSIT
1. An erosion control security deposit is required in accordance with City of Fort
Collins policy. In no instance shall the amount of the security be less than
$1000.00.
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
culvert. It has been determined that this development will not prevent this box
culvert from being implemented with a master drainage infrastructure design.
4. For additional information, please see future box option in Appendix I.
VI. EROSION CONTROL AND WATER QUALITY
A. GENERAL CONCEPT
1. Erosion control measures are specified on the Drainage and Erosion Control
Plan.
2. Maintenance of erosion control devices will remain the responsibility of the
contractor and the owner until the project is complete.
3. A water quality pond will be constructed in the east corner of the site within
the limits of the detention pond.
B. SPECIFIC DETAILS— WATER QUALITY POND
1. The water quality pond will be located in the base of the detention pond for
this site.
2. The water quality pond will be built to the following specifications:
a. The water quality pond will have a volume of 0.06 ac-ft (3066 co.
b. The water quality water surface elevation is 4838.80 ft.
c. This is based on a resultant impervious in the property of greater than fifty
percent (67.19%).
3. The release device for the water quality pond will allow a drain time of 40
hours and will be built to the following specifications:
a. The release rate will be 0.0213 cfs.
b. This release rate will be controlled by two (2) orifice holes placed
strategically in the metal plate on the northwestern side of the 2'x4' box in
the detention pond.
i. There will be two rows of orifices which will be set four inches (4")
apart.
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
i. The release rate is controlled by a 6 '/4 inch diameter orifice (See
orifice release in Appendix 1). This orifice plate will be placed inside
the box of the outlet structure.
ii. The release rate is controlled by two (2) orifices for the water quality
control pond. There will be one 3/4" orifice and one 5/8" orifice, which
together will allow a 40-hour drain time -release of 0.021 cfs.
c. In emergency situations with the detention pond being occupied while a
100-year storm occurs, the top of the berm along the eastern side of the
detention pond provides an emergency overflow weir. The overflow will
be conveyed historically towards the east.
i. The top of berm has an irregular height ranging from 4841.04 to
4842.00 ft and has an approximate 49 ft width.
ii. The water surface of 100-year storm passing over this berm is 4841.66
ft. This 100-year storm is 15.04 cfs flowing at a depth of 0.62 ft (See
detention in Appendix I).
6. For further specifics, please see detention and water quality volume
calculations in Appendix I.
C. SPECIFIC DETAILS -OPEN CHANNELS
1. Along the south side of the proposed building, an open channel will divert
runoff into the detention pond.
2. This open channel will have a depth of 0.49 ft, while conveying the 100-year
runoff rate of 2.69 cfs at this design point d2. This channel meets the 1 ft of
freeboard requirement.
D. SPECIFIC DETAILS— FUTURE Box CONDITION
1. Along the west side of Eastgate P.D.P., there is an existing 35' drainage
easement. This easement is for a possible future master drainage infrastructure
which would consist of a trapezoidal swale. This swale would have 4' bottom
width, 4:1 side slopes, 35' top width, and a longitudinal slope of 1.4%.
2. Haestad's Flowmaster v7 was used to determine the capacity of this
trapezoidal channel with one foot of required freeboard. The capacity of this
channel under these defined conditions is 336.09 cfs.
3. In order to have the future option to convey this flow past Eastgate P.D.P., the
equivalent box culvert was determined to be a 2'x10' reinforced concrete box
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
B. SPECIFIC DETAILS -DETENTION POND
1. The detention pond is located in the central area and in the western portion of
Eastgate P.D.P.
2. The release rate from the detention pond will match the 2-year historic runoff,
which is 1.20 cfs. Historically in a 100-year event, the detention pond restricts
the runoff to the capacity of the 12" RCP, which is obviously greater than 1.20
cfs. However, to conform to the City of Fort Collins Criteria, the proposed
detention pond will release at the 2-year historic runoff.
3. The total volume provided historically is 0.45 ac-ft. The total volume provided
in the developed condition will be 0.73 ac-ft.
4. The size of the detention pond will be built to the following specifications:
a. The detention pond will have volume of 0.45 ac-ft (19436 co. This
volume incorporates the water quality control volume of 0.07 ac-ft (3066
cf).
b. The detention pond has a 100-yr water surface elevation of 4840.15 ft.
c. The top of the bank for the detention pond has an elevation of 4841.00 ft,
which will provide 0.85 ft of freeboard. A variance is being requested for
this freeboard.
d. For additional specifics, please see Detention in Appendix I.
5. The release rate of the detention pond will be built to the following
specifications:
a. An outlet structure will be located at the eastern corner of the detention
pond to control release rates and ponding elevations.
i. On the northwest side of the outlet structure, a metal plate will be
placed to provide the proper release rates for water quality. Another
metal plate will be placed inside the outlet structure to release the
historic 2-year release rate.
ii. The outlet pipe from this structure will be the existing 12" inch RCP
pipe.
b. The release rate from the pond is restricted to 1.64 cfs.
Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
"Rational Method" for determining peak flows at various concentration points.
The Rainfall Intensity -Duration -Frequency Table was used in conjunction
with the Rainfall -Intensity -Duration curve, which provides the exact same
data (see Appendix II).
2. The 2- and 100- year storms were analyzed in accordance with Table 3-1 of
the City of Fort Collins Storm Drainage Design Criteria Manual for
commercial sites.
3. After coordinating with the City of Fort Collins Stormwater Department, the
runoff coefficients for areas zoned employment district (E-D) or low -density,
mix -use neighborhood will be 0.85 and 0.60 respectively.
D. HYDRAULIC CRITERIA
1. Open channel capacities are based on the Manning's Equation. The
Manning's coefficient is in accordance with the City of Fort Collins Storm
Drainage Criteria Manual. Haestad Method Flowmaster v7 was used in the
calculation of stone sewers and channel capacities.
V. DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
1. The historic flow patterns will be maintained with the development of this
site. In developed conditions, stonnwater will be conveyed through the site via
a combination of overland flow, swales, and gutters.
2. The existing detention pond will be improved to provide a building area along
Montgomery Street.
a. This detention pond was designed as part of Eastgate P.U.D. prepared by
James H. Stewart & Associates in 1978. A drainage report was not
available.
b. This detention pond will be adequate to detain the 100-year storm for the
contributing area.
c. In addition to detaining the 100-year storm, water quality will be provided
with this development.
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
a. The pond will be designed to accommodate a majority of Lots 1, 3 and 4
fully developed with a employment district (E-D) use.
3. Referring to the Historic Drainage Exhibit, there are 1.82 acres contributing to
design point "h." Portions of Lots 12 through 17, which are zoned low -
density, mix -use neighborhood, contribute to this design point. Also, a small
portion of Lots 1 through 4 and a portion of Lot 5, which are zoned
employment district (E-D), contribute to this design point
4. Referring to the Drainage and Erosion Control Plan, the same area contributes
to the detention pond as delineated in the Historic Drainage Exhibit. However,
sub -basin D2 was delineated to determine the amount of runoff in the swale
along the south side of the proposed four-plex townhome unit.
IV. DRAINAGE DESIGN CRITERIA
A. REGULATIONS
1. Design Criteria from the City of Fort Collins Storm Drainage Design Criteria
Manual and options for storm drainage improvements discussed with the City
of Fort Collins were considered.
2. Water quality control measures and erosion control criteria were considered
from the Urban Storm Drainage Criteria Manual by the Urban Drainage and
Flood Control District.
B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
1. The surrounding areas are completely developed, except for a few lots along
Riverside Avenue.
2. All grading along the north, south, east, and west property lines will match
existing grades.
3. Water quality provisions are required for and within the limits of this site.
4. Additional detention will be provided in order to restrict release rates from the
site to less than or equal to historic release rates and to account for the water
quality control volume.
C. HYDROLOGICAL CRITERIA
1. The Rainfall -Intensity -Duration curves for the City of Fort Collins were used
(Figure 3-1, attached for reference in Appendix 11), in conjunction with the
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
4. In the new developed condition, a portion of Tract B will be regraded to
provide space for a building pad for a four-plex townhome unit.
a. There will be 2.63 acres contributing to this detention pond in the
developed condition.
b. Water quality will be provided in the developed detention pond.
c. The release rate from the developed detention pond will match the release
rate from the historic detention pond.
III. DRAINAGE BASINS AND SUB -BASINS
A. MAJOR BASIN DESCRIPTION
1. The site is located within the Spring Creek Basin as defined on the City of
Fort Collins Master Stormwater Basin Map (See Appendix M. The City has
completed updating the master plan for this basin.
2. Spring Creek is the major watercourse that flows from Spring Canyon Dam at
Horsetooth Reservoir to its confluence with the Poudre River.
3. In accordance with the City of Fort Collins Conceptual Review Team notes on
October 6, 2003, there is a possibility of master drainage improvements along
the east side of Montgomery Street. This design will not inhibit the future
possibility of these master drainage improvements.
B. SUB -BASIN DESCRIPTION
1. A portion of the Eastgate development slopes towards the detention pond.
a. The pond was initially designed in 1978 to meet City of Fort Collins storm
drainage criteria current at that time.
b. The pond will be redesigned and expanded to meet current City of Fort
Collins storm drainage criteria and water quality requirements for the
actual developed area currently contributing to the pond.
c. Historically, there is 1.82 acres contributing to this detention pond.
2. Within the Replat of Tract "A" Eastgate, First Filing, Lots 2, 6, and 7 through
16 are developed. Lots 1, 3, 4, and 5 are not developed. These are commercial
lots.
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
I. INTRODUCTION
1. This report presents the pertinent data, methods, assumptions, references and
calculations used in analyzing and preparing the final drainage and erosion control
design for Eastgate P.D.P.
II. GENERAL LOCATION AND DESCRIPTION
A. LOCATION
1. Eastgate P.D.P. is located near the center of Section 18, Township 7 North,
Range 68 West of the 6th P.M., Fort Collins, Colorado.
2. More specifically, it is located on the east side of Montgomery Street
approximately 250 feet south of the intersection of Riverside Avenue and
Montgomery Street.
3. Eastgate P.D.P. will be a Replat of Tract B, Replat of Tract A, Eastgate, First
Filing. Tract B was designed primarily as a detention pond according to the
design prepared by James H. Stewart & Associates in 1978.
B. DESCRIPTION OF PROPERTY
1. Historically, this site exists in the Replat of Tract "A", Eastgate, First Filing.
Within in this existing development, Eastgate P.D.P. is Tract "B."
2. The lots bordering Riverside Avenue have been zoned "Employment,"
according to the City of Fort Collins Land Use Code. The lots within the
Replat of Tract "A" Eastgate, First Filing, not bordering Riverside Avenue are
zoned low -density, mix -use neighborhood.
3. In the historic condition, a detention pond exists within this project site and
services a portion of the property for the Replat of Tract "A" Eastgate, First
Filing.
a. Historically, approximately 1.82 acres contributes to this detention pond.
b. No water quality is provided for the contributing area for the detention
pond.
c. This detention pond has a 12" RCP acting as the outlet.
d. Eastgate P.D.P. has a net area of approximately 0.77 acres.
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Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
APPENDIX I
- DRAINAGE CALCULATIONS
APPENDIX II
- CHARTS AND FIGURES
APPENDIX III
- EROSION CONTROL
APPENDIX IV
- STUFFER ENVELOPE
Final Drainage and Erosion Control Report for Eastgate P.D.P.
Project No. 1466-50-03
TABLE OF CONTENTS
TITLE PAGE
VICINITY MAP
TABLE OF CONTENTS
I. INTRODUCTION
H. GENERAL LOCATION AND DESCRIPTION
A. PROJECT LOCATION
B. DESCRIPTION OF PROPERTY
III. DRAINAGE BASINS AND SUB -BASINS
A. MAJOR BASIN DESCRIPTION
B. SUB -BASIN DESCRIPTION
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2
4
4
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4
5
5
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IV. DRAINAGE DESIGN CRITERIA 6
A. REGULATIONS 6
B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 6
C. HYDROLOGAL CRITERIA 6
D. HYDRAULIC CRITERIA 7
V. DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
B. SPECIFIC DETAILS - DETENTION POND
C. SPECIFIC DETAILS - OPEN CHANNELS
D. SPECIFIC DETAILS - FUTURE BOX OPTION
VI. EROSION CONTROL AND WATER QUALITY
A. GENERAL CONCEPT
B. SPECIFIC DETAILS - WATER QUALITY POND
C. SPECIFIC DETAILS - EROSION CONTROL MEASURES
D. EROSION CONTROL SECURITY DEPOSIT
VII. VARIANCE REQUEST
A. DETENTION POND FREEBOARD
VIII. CONCLUSIONS
A. COMPLIANCE WITH STANDARDS
B. DRAINAGE CONCEPT
IX. REFERENCES
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PROJECT SITE
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Final Drainage and Erosion Control Report
For
Eastt!ate P.D.P.
Replat of Tract B, Replat of Tract A, Eastgate, First Filing
Fort Collins, Colorado
Prepared for:
Premier Custom Builders,1
1420 G Blue Spruce Drive
Fort Collins, Colorado 8052
Prepared by:
Shear Eneineering Corporation
Project No: 1466-50-03
Date: February, 2004
4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 Fax (970) 282-0311 www.shearenginecring.com