HomeMy WebLinkAboutHICKORY COMMONS - FDP - FDP130014 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage, Erosion Control and Water Quality Report
For
Hickory Commons
Fort Collins, Colorado
Prepared for:
CHARLES MESERLIAN
700 NORTH COLLEGE AVENUE
FORT COLLINS, CO 80524
Prepared by:
AAAApex pex
Engineering
908 LAPORTE AVENUE
FORT COLLINS, CO 80521
970-219-2834
MAY 1, 2013
Final Drainage Report
Hickory Commons
ENGINEER’S CERTIFICATION
I hereby state that this Drainage and Erosion Control report for the Hickory Commons
subdivision was prepared by me or under my direct supervision for the owners thereof and
meets or exceeds the criteria in the City of Fort Collins Storm Drainage Design Criteria
and Construction Standards.
-------------------------------------------
Stacy J. Gowing
Registered Professional Engineer
State of Colorado No: 34290
Final Drainage Report
Hickory Commons
TABLE OF CONTENTS
I. INTRODUCTION ............................................................................................. 3
II. GENERAL LOCATION AND DESCRIPTION .............................................. 3
A. Property Location ...................................................................................................................... 3
B. Description of Property ............................................................................................................ 3
III. DRAINAGE BASINS AND SUB-BASINS ...................................................... 4
A. Major Basin Description ........................................................................................................... 4
B. Existing Conditions ..................................................................................................................... 4
C. Developed Conditions .............................................................................................................. 4
IV. DRAINAGE DESIGN CRITERIA .................................................................... 5
A. Development Regulations ........................................................................................................ 5
B. Development Criteria Reference and Constraints ............................................................. 5
C. Hydrological Criteria ................................................................................................................. 5
D. Hydraulic Criteria ...................................................................................................................... 5
V. DRAINAGE FACILITY DESIGN ..................................................................... 5
A. General Concept ........................................................................................................................ 5
B. Specific Details – Detention ..................................................................................................... 6
C. Specific Details – Stormwater Quality .................................................................................. 7
D. Specific Details – Swales ........................................................................................................... 7
E. Specific Details – Inlets and Storm Sewer ............................................................................. 7
F. Specific Details – Curb Cuts ..................................................................................................... 8
VI. SEDIMENT/EROSION CONTROL ................................................................ 8
A. General Concept ........................................................................................................................ 8
VII. CONCLUSIONS ............................................................................................... 8
A. Compliance with standards ...................................................................................................... 8
B. Drainage Concept ....................................................................................................................... 9
VIII. REFERENCES .................................................................................................. 10
IX. APENDICES ..................................................................................................... 11
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Hickory Commons
I. INTRODUCTION
This report presents the pertinent data, methods, assumptions, and references used in
analyzing and preparing the final drainage, erosion control and water quality design for
the Hickory Commons subdivision project (the "project").
II. GENERAL LOCATION AND DESCRIPTION
A. Property Location
1. The project is located on the north side of Hickory Street. The legal
description is: A tract of land located in the Southeast One-quarter of Section
2, Township 7 North, Range 69 West of the Sixth Principal Meridian being all
of Lots 1 through 8, Block 21, of the Riverside Park Subdivision, a subdivision
of record in the City of Fort Collins, except the West 5 feet thereof and
together with the West Half of the vacated portion of Fourth Avenue; and all
of Lots 9 through 18, Block 21, of the said Riverside Park Subdivision, together
with the East Half of the vacated Alley and that part of the West Half of the
vacated portion of Fourth Avenue in Block 21 of the said Riverside Park
Subdivision, County of Larimer, State of Colorado.
SITE
Vicinity Map, NTS
B. Description of Property
1. The project site is currently undeveloped. The proposed use is multi-use
live/work project consisting of 26 two-story units in 7 separate buildings. The
project also includes widening of Hickory Street, utilities and site
improvements such as garages, parking areas, drive aisles, hardscape and
landscaping.
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Hickory Commons
III. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The project site lies within the City of Fort Collins Cache La Poudre River
Basin.
2. The project site is located outside the 100-year and 500-year floodplains, as
shown in the following image from the City of Fort Collins website:
SITE
B. Existing Conditions
1. The project site is currently undeveloped. The site is currently covered with
native and volunteer vegetation, and slopes gently from north to south at
approximately 1%.
C. Developed Conditions
1. The site will drain from north to south through a series of storm sewers and
overland flow paths. The majority of the developed flows will ultimate drain
through a detention/water quality pond to a proposed storm outfall pipe along
Hemlock Street towards the west. A small portion of the flows on the west,
east, and south edges of the site will run off the site un-detained. These flows
are significantly less than the existing flows leaving the site.
2. The off-site storm outfall pipe will be a public line, serving adjacent properties
as well as the Hickory Commons site.
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IV. DRAINAGE DESIGN CRITERIA
A. Development Regulations
1. Design criteria from the City of Fort Collins Storm Drainage and Design
Criteria and Construction Standards were followed for this drainage report.
B. Development Criteria Reference and Constraints
1. The proposed storm water release rate is 4.71 CFS, which is the capacity of an
18” RCP pipe at 0.2%. The outfall pipe is proposed as a 21” RCP, which has
capacity for 7.11 CFS. The remaining capacity of 2.4 CFS is allocated to
adjacent properties as shown on the enclosed Drainage and Erosion Control
Plan.
C. Hydrological Criteria
1. Peak flow rates for the 100-year storm have been calculated in accordance
with the City of Fort Collins Storm Drainage and Design Criteria and
Construction Standards. Please see these calculations in the Hydrology section
of Appendix I.
D. Hydraulic Criteria
1. The City of Fort Collins Storm Drainage and Design Criteria and Construction
Standards are used to determine the adequacy of the hydraulic structures
associated with the project.
2. Analyses are performed using methodologies presented in Urban Storm
Drainage Criteria Manual Volumes 1 and 2; Urban Drainage and Flood Control
District, Denver, Colorado, September, 1999. Please see the various
computation spreadsheets in the Hydraulics section of Appendix 1.
V. DRAINAGE FACILITY DESIGN
A. General Concept
1. The general direction of proposed storm water flow is from north to south.
2. Storm water from the improved section along Hickory Street and the majority
of the site flow though a series of storm sewers to a proposed detention pond
located at the southwest corner of the site. Additional detention is provided
within the drive aisle. The detention pond ultimately discharges to a proposed
off-site storm outfall pipe located within the ROW for Hemlock Street. This
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Hickory Commons
pipe ultimately discharges to a natural drainage way near the entrance to the
McMurry Natural Area.
3. Although the off-site storm sewer is entirely located within the right-of-way for
Hemlock, an easement has been obtained from the City of Fort Collins Natural
Areas to accept the drainage discharge for conveyance to the river.
B. Specific Details – Detention
1. The drainage area for the site is 2.09 acres, which includes the project site and
Hickory Street located along the frontage of the site. Only 1.89 acres on the
project site is able to drain to the detention pond, however 2.09 acres is the
calculated area that will be treated for detention and water quality by the new
detention pond.
a. The release rate for the project is proposed to be 4.71 CFS, which is the
capacity of an 18” RCP at 0.2% slope. It should be noted that additional
capacity is provided in the 21” RCP outfall storm pipe to allow for adjacent
properties to drain to this public storm drain pipe as discussed above.
b. The drainage basin is 80% impervious, which requires 0.069 acre-feet of
extended detention volume. The water quality volume is provided at
elevation 4973.23’. The calculations for the water quality volume are located
in the appendix.
c. The required detention volume was calculated using the City’s rational
formula based detention pond design worksheet. The required detention
volume is 0.196 acre-feet. The total required volume of 0.265 acre-feet is
provided at elevation 4974.62’. The calculations for the detention volume
are located in the appendix.
d. A relatively small amount of detention volume is provided in the drive aisle.
The maximum depth of the 100-year ponding in the drive aisle is 0.5’.
e. There are 0.20 acres of the site on the west, south, and east borders that
will not drain to the detention pond and will instead runoff the site un-
detained and untreated. These flows are generated by Basin B and C and
total 1.01 CFS for the 100-year storm and 0.19 CFS for the 2-year storm.
This is less than the existing 100-year runoff from the site, which is 2.79 CFS,
but more than the existing 2-year runoff from the site which is only 0.06
CFS. It should be noted that conveyance to the river for all these un-
detained flows is provided with this project.
2. As previously mentioned, the detention pond drains to a proposed public off-
site storm outfall pipe located within the ROW for Hemlock Street, ultimately
discharging to the Cache La Poudre River.
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3. An emergency spillway path is provided in the emergency vehicle access off
Hemlock Street. The spill elevation for this structure is 4974.62’. The depth
required to convey the developed un-detained 100-year discharge from the
site is 0.5’.
C. Specific Details – Stormwater Quality
1. Water quality will be provided in accordance with Best Management Practices
as presented in the Urban Storm Drainage Criteria Manual Volume 3, Best
Management Practices; Urban Drainage and Flood Control District, Denver,
Colorado, September, 1999.
2. Permanent structural BMP’s will consist of extended detention within the
proposed detention pond. See the above discussion of the detention pond for
more details.
D. Specific Details – Swales
1. There is an 8’ wide swale with 5:1 side slopes to the east of the property
boundary on City of Fort Collins Parks property. This swale is designed to
convey 133% of the 100-year storm for Basin B. This 8’ wide swale and
landscaping adjacent to the 10’ wide concrete trail will be maintained by the
developer as per an agreement between the two parties.
E. Specific Details – Inlets and Storm Sewer
1. Runoff discharges from Hickory Street are collected in a proposed Type R inlet
located in a sump condition. The drainage area to this inlet is quite small,
and a 5’ Type R inlet is more than adequate to collect the developed 100-
year runoff discharge.
2. The majority of the discharges from the site are collected by proposed Type
13 inlets in the drive aisle. These flows are conveyed along with the flows
from Hickory Street through a series of storm sewers to the detention pond.
3. The minor flows on the western side of the site will be collected in a swale
within the sidewalk and conveyed to an inlet. This inlet also includes a storm
sewer stub to the adjacent property to the west for future extension into
that property.
4. 100-year flows are conveyed through the site with a combination of storm
sewers and the swale created by the inverted crown of the drive aisle.
There is a small amount of bypass flow past Inlet 2 of 0.8 CFS and inlet 1 of
4.2 CFS. Storm sewer calculations are included in the appendix.
5. An off-site storm sewer is proposed to convey discharges from the site to the
Poudre River. This 21” RCP has a capacity of 7.11 CFS. As previously
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discussed, the release rate for the project site has been established as 4.71
CFS. Since the release rate for future developments contributing to this
storm sewer is 0.20 CFS/acre, the excess capacity of 2.40 CFS will
accommodate 12 acres of additional development from adjacent properties.
The only property that does not have the ability to connect to this new
storm outfall is the property immediately to the west. This property
(identified as basin OS1) is 1.09 acres in size, and will generate 0.22 CFS of
discharge in the developed and detained condition. A pipe is currently being
shown to the western property boundary which could allow that property to
connect to this property’s storm sewer system. Any additional excess
capacity will be available for other properties in the area as needed.
F. Specific Details – Curb Cuts
1. There are no curb cuts proposed with the project.
VI. SEDIMENT/EROSION CONTROL
A. General Concept
1. Temporary erosion control measures will be installed with this project.
These measures will include:
a. Silt fence along the property lines.
b. Straw bale barriers surrounding the inlets and the discharge structure of
the pond.
c. Water trucks and soil terracing to address construction dust abatement.
d. Vehicle tracking pad at the construction entrances.
e. The detention pond will act as a sediment basin during construction.
2. Permanent sediment\erosion control measures will consist of paving,
concrete hardscape, and landscaping to stabilize the disturbed areas.
3. Maintenance of all sediment\erosion control devices will remain the
responsibility of the contractor until the project is completed.
VII. CONCLUSIONS
A. Compliance with standards
1. All drainage design conforms to the criteria and requirements of City of Fort
Collins Storm Drainage and Design Criteria and Construction Standards.
2. Proposed drainage improvements conform to the concepts and
recommendations of the Dry Creek Basin master plan.
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3. Proposed sediment/erosion control measures conform to the
recommendations of City of Fort Collins Storm Drainage and Design Criteria
and Construction Standards and generally accepted erosion control
procedures.
B. Drainage Concept
1. The proposed drainage plan concept for the project will be effective for the
control of stormwater runoff and water quality for the proposed site and
conforms to City of Fort Collins standards.
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VIII. REFERENCES
• City of Fort Collins Storm Drainage and Design Criteria and Construction Standards
• The Dry Creek Basin Master Plan
• Urban Storm Drainage Criteria Manual Volume 1; Urban Drainage and Flood Control
District, Denver, Colorado, March, 1969.
• Urban Storm Drainage Criteria Manual Volume 2; Urban Drainage and Flood Control
District, Denver, Colorado, March, 1969.
• Urban Storm Drainage Criteria Manual Volume 3, Best Management Practices; Urban
Drainage and Flood Control District, Denver, Colorado, September, 1999.
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IX. APENDICES
Appendix I - Hydrologic Calculations
Runoff Curve Number
Time of Concentration and Peak Discharge
Appendix II - Hydraulic and Detention Calculations
Water Quality Calculations
Detention Pond Sizing Worksheet
Pond Stage-Storage Worksheet
Storm Sewer Calculations
Appendix III - Mapping and Plans
Drainage and Erosion Control Plan (24”x36”)
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Appendix 1 – Hydrology
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Appendix II - Hydraulics
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Appendix III – Mapping and Plans