HomeMy WebLinkAboutEASTGATE - PDP (RESUBMITTAL) - 10-04A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
X. 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
14
Final Drainage and Erosion Control Report for Eastgate, 2°d Filing
Project No. 1466-50-03
B. DRAINAGE CONCEPT
1. The proposed drainage design for Eastgate, 2nd Filing is effective for the
control of storm runoff with a considerable reduction in potential downstream
effects.
2. The proposed drainage design for Eastgate, 2nd Filing 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.
13
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
a. Wattles in the swales.
b. Wattles used for orifice plate protection.
2. 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.
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. CONCLUSIONS
A. COMPLIANCE WITH STANDARDS
1. All drainage analysis has been performed 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.
12
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
a. The water quality pond will have a volume of 0.06 ac-ft (3066 cf).
b. The water quality water surface elevation is 4838.08 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 0.021 cfs.
b. The release rate is controlled by two (2) orifices for the water quality
control pond. There will be one 3/4" orifice and one 1/2" orifice, which
together will allow a 40-hour drain time release of 0.021 cfs.
i. There will be two rows of orifices which will be set four inches (4")
apart.
ii. The bottom row will consist of one 3/4" hole set on -center.
iii. The top row will consist of one 1/2" 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"x 1.0" flat bar
6. For further specifics, please see water quality control in Appendix I.
C. SPECIFIC DETAILS- EROSION CONTROL MEASURES
t. The following temporary erosion control measures are specified on the
Drainage and Erosion Control Plan:
11
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
D. SPECIFIC DETAILS— FUTURE BOX CONDITION
1. Along the west side of Eastgate, 2nd Filing, 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, 2nd Filing,
the equivalent box culvert was determined to be a 2'x10' reinforced concrete
box culvert. It has been determined that this development will not prevent this
box culvert from being implemented with a master drainage infrastructure
design.
4. Due to the grading required to insure that the City will still have the option of
placing this box culvert, Sub -basin D3 has been delineated for stormwater that
conveys into Montgomery Street. The 2- and 100- year events contribute 0.37
and 1.29 cfs, respectively, to design point d3.
5. 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:
10
Final Drainage and Erosion Control Report for Eastgate, 2„ d Filing
Project No. 1466-50-03
i. On the northwest side of the outlet structure, a metal plate will be
placed to provide the proper release rates for water quality.
ii. The outlet pipe from this structure will be the existing 12" inch RCP
pipe, which will restrict runoff to historic release rates from the
detention pond.
b. The release rate from the pond is restricted to 5.68 cfs, and the historic
release rate for the pond is 6.66 cfs.
i. The release rate is controlled by the existing 12" RCP orifice for the
detention pond (See orifice release in Appendix I).
c. In emergency situations with the detention pond being occupied while a
100-year storm occurs, there will be an overflow weir and channel that
will convey stormwater on Lot 4 in the interim condition. In the ultimate
condition, the overflow weir and channel should be shared between Lots 3
and 4, once Lot 4 develops.
i. In the interim condition, the overflow channel have side slopes of 1.5:1
on the left side and 3:1 on the right side. The overflow from the pond
will have a depth of 0.43 ft at the weir and the channel conveying the
stormwater will have a depth of 1.18 ft.
ii. In the interim condition, the overflow channel have side slopes of 3:1
on each side. The overflow from the pond will have a depth of 0.41 ft
at the weir and the channel conveying the stormwater will have a depth
of 1.05 ft.
6. Sub -basin D3 contributes stormwater to Montgomery Street; however, the
detention pond calculations and overflow spillway have been design as if Sub -
basin D3 contributed all stormwater to the detention pond.
7. 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.
0
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
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.
B. SPECIFIC DETAILS -DETENTION POND
1. The detention pond is located in the central area and in the western portion of
Eastgate, 2nd Filing
2. The release rate from the detention pond will be less than the historic release
rate of the 12" RCP that currently restricts the detention pond. With this
development, a water quality release structure will be built, and the 12" RCP
will continue to restrict the runoff. However, this detention pond will be
expanded and an overflow weir will be placed to lower the water surface
elevation. Thus, the release into the 12" RCP will be less than the historic
conditions. For additional information see the orifice release rate comparisons
in the detention section of Appendix I.
3. The total maximum volume provided historically is 0.16 ac-ft. The total
maximum volume provided in the developed condition will be 0.23 ac-ft.
4. The size of the detention pond will be built to the following specifications:
a. The detention pond will have volume of 0.23 ac-ft (10,030 co. This
volume incorporates the water quality control volume of 0.07 ac-ft (3066
cf).
b. The detention pond will have a 100-yr water surface elevation of
4839.78 ft.
c. The top of the bank for the detention pond has an elevation of 4841.00 ft,
which will provide 1.22 ft of 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.
E-3
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
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
The Rainfall -Intensity -Duration curves for the City of Fort Collins were used
(Figure 3-1, attached for reference in Appendix II), in conjunction with the
"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. Please note that
these values will meet or exceed any runoff coefficient for future developed
conditions of undeveloped lots.
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 storm 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, stormwater 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.
7
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
a. The pond will be designed to accommodate a majority of Lots 1, 3 and 4
fully developed with an 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, except for
the driveways leading up to the four-plex townhome units.
a. Sub -basin D2 was delineated to determine the amount of runoff in the
swale along the south side of the proposed four-plex townhome units.
b. Sub -basin D3 was delineated for the driveways are leading up to the four-
plex townhome units. The grading has been designed to insure that the
possibility of a box culvert will not be inhibited for future master drainage
improvements. However, the constraints for this grading design forces
drainage conveyance into Montgomery Street.
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.
T
Final Drainage and Erosion Control Report for Eastgate, 2°d Filing
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 be less than or
equal 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 1I). 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.
5
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
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, 2"d Filing.
II. GENERAL LOCATION AND DESCRIPTION
A. PROJECT LOCATION
Eastgate, 2nd Filing 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, 2nd Filing 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, 2nd Filing 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, 2nd Filing has a net area of approximately 0.77 acres.
4
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
APPENDIX I
- DRAINAGE CALCULATIONS
APPENDIX H
- CHARTS AND FIGURES
APPENDIX HI
- EROSION CONTROL
APPENDIX IV
- STUFFER ENVELOPE
Final Drainage and Erosion Control Report for Eastgate, 2"d Filing
Project No. 1466-50-03
TABLE OF CONTENTS
TITLE PAGE
VICINITY MAP
TABLE OF CONTENTS
I. INTRODUCTION
II. 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
IV. DRAINAGE DESIGN CRITERIA
A. REGULATIONS
B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
C. HYDROLOGAL CRITERIA
D. HYDRAULIC CRITERIA
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. CONCLUSIONS
A. COMPLIANCE WITH STANDARDS
B. DRAINAGE CONCEPT
X. REFERENCES
2
4
4
4
4
5
5
5
6
6
6
7
7
7
7
8
9
10
10
10
10
I
12
1.2
12
13
14
2
PROJECT SITE
(TRACT B)
VICINITY MAP
V =2000'
j
SHEAR
ENGINEERING
CORPOWON
Final Drainage and Erosion Control Report
For
nd •
Eastimte, 2 Film
Replat of Tract B, Replat of Tract A, Eastgate, First Filing
Fort Collins, Colorado
Prepared for:
Premier Custom Builders, Inc.
1420 G Blue Spnice Drive
Fort Collins, Colorado 80524
Prepared by:
Shear En2ineerina Corporation
Project No: 1466-50-03
Date: October 2004
4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 Fax (970) 282-0311 www.shearengineering.com