HomeMy WebLinkAboutSTREETS PARK - BASIC DEVELOPMENT REVIEW - BDR180010 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND
EROSION CONTROL REPORT
Streets Park
(Tract A, East Vine Streets Facility P.U.D.)
Prepared for:
City of Fort Collins Park Planning and Development
215 North Mason
Fort Collins, CO 80524
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite A
Windsor, Colorado 80550
(970) 674-3300
February 7, 2018
Job Number 1165-012-92
iii
TABLE OF CONTENTS
TABLE OF CONTENTS ............................................................................................................ iii
1. GENERAL LOCATION AND DESCRIPTION ................................................................ 1
1.1 Location ........................................................................................................................... 1
1.2 Description of Property ................................................................................................. 1
1.3 Floodplain Submittal Requirements ............................................................................. 2
2. DRAINAGE BASINS AND SUB-BASINS .......................................................................... 2
2.1 Major Basin Description ................................................................................................ 2
2.2 Sub-basin Description .................................................................................................... 3
3. DRAINAGE DESIGN CRITERIA ...................................................................................... 3
3.1 Regulations ...................................................................................................................... 3
3.2 Directly Connected Impervious Area (DCIA) Discussion .......................................... 4
3.3 Development Criteria Reference and Constraints ...................................................... 5
3.4 Hydrological Criteria ..................................................................................................... 6
3.5 Hydraulic Criteria .......................................................................................................... 6
3.6 Floodplain Regulations Compliance ............................................................................. 6
3.7 Modifications of Criteria ............................................................................................... 7
4. DRAINAGE FACILITY DESIGN ....................................................................................... 7
4.1 General Concept ............................................................................................................. 7
4.2 Specific Details ................................................................................................................ 8
5. CONCLUSIONS .................................................................................................................. 11
5.1 Compliance with Standards ........................................................................................ 11
5.2 Drainage Concept ......................................................................................................... 11
6. REFERENCES .................................................................................................................... 12
APPENDIX
VICINITY MAP AND DRAINAGE PLAN .............................................................................. A
POND CALCULATIONS ............................................................................................................ B
LID INFORMATION ................................................................................................................... C
1
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
The Streets Park project is located in the Northeast Quarter of Section 12, Township 7
North, Range 69 West of the Sixth Principal Meridian, in the City of Fort Collins,
Larimer County, Colorado. Please refer to the vicinity map in Appendix A.
Vine Drive and the BNSF Railroad Right of Way bound the site on the north; 9th Street
(Lemay Avenue) bounds the site on the east, the New Belgium Brewery is located on the
south, and the existing City Streets and Traffic facility is directly to the west. The site
was platted with the overall Streets Facility as Tract A of the East Vine Streets Facility
P.U.D. in 1993. Tract A was platted as a blanket Drainage and Access Easement and
provides water quality and detention for the East Vine Streets Facility P.U.D. (all of the
City land from 9th Street to Linden).
1.2 Description of Property
Tract A consists of 8.5 acres of land and was always planned to be a stormwater and
recreation facility. Today the existing driveway from 9th Street into the Streets facility
exists on the south side of the site. A railroad spur is located on the north portion of the
Tract. Water Quality Pond A is located on the west side of the site (south of the spur),
and Water Quality Pond B is located north of the spur. A basketball court, picnic shelter
and small parking area have been developed on the west side of the Tract adjacent to the
driveway. The remainder of the Tract is the detention pond for the Streets Facility. It
accepts discharges from both water quality ponds. The pond drains east to an existing
18” pipe and into the storm sewer system in 9th Street. There is an asphalt sidewalk on 9th
Street that currently acts as the initial spillway for the pond.
Tract A generally slopes east at approximately 0.5% to 2%. The land is currently vacant
except for the facilities described above. Based on previous reports, the only flow
contributing to the site is the City Street Facilities to the west. According to FEMA Panel
08069C0981G (6/17/2008), the site is in Zone X - Protected by a Levee.
The site has been studied numerous times in the past. Pertinent portions of these studies
will be discussed in this report regarding C values, release rates, and pond volumes.
2
1.3 Floodplain Submittal Requirements
The site is in Zone X, and because of this a Floodplain Submittal is not required and a
“City of Fort Collins Floodplain Review Checklist for 50% Submittals” has not been
included with this report.
2. DRAINAGE BASINS AND SUB-BASINS
2.1 Major Basin Description
The proposed development lies within the Dry Creek Master Drainage Plan. Outfall for
this site is the storm sewer system in 9th Street and then Dry Creek. The previously
approved release rate for the existing site is 10.5 CFS (more than the Master Plan
requirement of 0.2 CFS per acre).
The site was previously studied with the following reports.
• “Final Drainage, Erosion and Storm Water Quality Study, East Vine Streets
Facility P.U.D., Phase One Final”, by RBD, June 28, 1993. (The 1993 Report)
• “Final Drainage and Erosion Control Study, East Vine Streets Facility P.U.D.,
Major Amendment Final, Phase Two Final”, by The Sear Brown Group, August
3, 1999. (The 1999 Report)
• “Final Drainage and Erosion Control Report, East Vine Streets-Lot 5A City of
Fort Collins Traffic Operations Facility”, by The Sear Brown Group, March 25,
2002. (The 2002 Report)
The 1993 Report sized the two water quality ponds with the FAA/Rational Detention
Method (prior to UDFCD guidance) as well as the detention pond with the FAA Method.
The “C” value used for the sizing was 0.56 and the “old” City of Fort Collins Rainfall
was utilized with a contributing area of 29.8 acres and a release rate of 10.5 CFS. The
detention volume required was determined to be 2.77 acre-feet and the detention volume
provided was 1.33 acre-feet. The designer added the 1.5 acre-feet of water quality
volume to the provided detention volume to conclude that the required volume was
achieved.
3
The 1999 Report re-sized the facilities again with the FAA Method for all three ponds.
The “C” value used for the sizing was raised to 0.77 and the “old” City of Fort Collins
Rainfall was again utilized with a contributing area of 29.47 acres and a release rate of
10.5 CFS. The detention volume required was determined to be 4.17 acre-feet and the
detention volume provided was 2.61 acre-feet. The designer added the 1.6 acre-feet of
water quality volume to the provided detention volume to conclude that the required
volume was achieved.
The 2002 Report did not analyze the detention pond and will not be discussed further.
Please refer to Appendix B for reference material.
2.2 Sub-basin Description
Tract A mostly contains existing water quality and detention facilities. There are several
parking spaces, a picnic shelter, basketball court and the main access drive from 9th Street
on the site – all of these facilities were shown on the original construction plans for the
site and presumably were included in the drainage calculations. On Tract A, the existing
driveway sheet flows to the south and never drained to the detention facility. This
configuration will not be changed with the development of the park.
The proposed project will regrade the detention pond so that it will function adequately as
a recreation field with 1% minimum slope, install a restroom facility, larger picnic
shelter, and playground with safety surface. Additional parking is proposed along the
existing drive and LID treatment of this new impervious area is proposed. The core of
the new park (new structures and playground) will be elevated and will fill within some
of the existing detention pond volume. The project will regrade the pond so that the
standalone detention storage in the pond will be achieved with the “new” 1997 City of
Fort Collins rainfall and the water quality ponds will not be used as detention.
3. 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
4
“Urban Storm Drainage Criteria Manual” (UDFCD), developed by the Denver Regional
Council of Governments, has been used. The release rate approved in 1993 and 1999 was
used for the recalculation of detention volume.
3.2 Directly Connected Impervious Area (DCIA) Discussion
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process
for receiving water protection that focuses on reducing runoff volumes, treating the water
quality capture volume (WQCV), stabilizing drainageways and implementing long-term
source controls. The Four Step Process applies to the management of smaller, frequently
occurring events.
The park development will add very little impervious area. Many of these criteria are not
applicable to a project with such a minor drainage impact.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement
Low Impact Development (LID) strategies, including Minimizing Directly Connected
Impervious Areas (MDCIA).
The core area of the park will be within an existing detention facility. The west portion
of the core area will sheet flow into Water Quality Pond A and the east portion of the core
area will flow into the playground safety surface and underdrain (which is effectively like
a rain garden). The new parking proposed along the driveway will drain east and through
a new rain garden to meet LID requirements.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow
Release
A rain garden is proposed for the new parking along the driveway. This will result in a
slower release than if it simply sheet flowed south across the driveway.
Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate and volume of runoff during and following development. Because the site
will drain to an existing detention pond, bank stabilization is unnecessary with this
project.
5
Step 4: Implement Site Specific and Other Source Control BMPs
As a park, the proposed development will not increase pollutants that require treatment.
The parking spaces (which could have sands, salts, and leaking fluids from cars) will
drain to a rain garden.
3.3 Development Criteria Reference and Constraints
The runoff from this site has been routed to conform to the requirements of the City
Stormwater Department and previously approved reports for the overall site. The
detention calculations were approved in 1999 with the “old” City rainfall (apparently the
site submitted for review prior to the rainfall change in early 1999 and was vested).
The existing water quality facilities on the west side of the site are upstream of the project
and intended to treat the Streets Shops and Facilities. These ponds will not be upgraded
or changed with this project.
LID techniques are required – pavers are not proposed, so no less than seventy-five
percent of any newly added impervious area must be treated using one or a combination
of LID techniques. New impervious area in the core of the park including the new
parking spaces is 8,060 sf.
The restroom and walks on the west side of the core area (1,353 sf impervious) will drain
west and into Water Quality Pond A. It is our understanding that the City would like to
upgrade this water quality pond to a rain garden in the future, but at this time, this
impervious area is not considered treated by LID.
The east portion of the core area (shelter and playground – 2,890 sf impervious) will be
treated within the safety surface of the playground and in 325 linear feet of 0.5% grass
swale at the toe of the proposed slope on the south side of the detention pond. Inside the
perimeter of the playground will be a wood fiber media draining to a perforated sub-drain
(very similar to a rain garden). The wood media is removed every few years and
replaced. This area is considered to be treated by LID.
The new parking spaces and adjacent sidewalk will add 3,820 sf of impervious area.
These parking spaces need to drain to the south, or they will be lower than the top of the
6
detention pond berm. The design will capture the minor storm in a new 4’ trickle pan on
the south side of the new parking spaces and take that minor flow east and to a new rain
garden. Any flows that overwhelm the pan or the rain garden will sheet flow to the south
over the existing driveway and then east to 9th Street in a swale on the south side of the
driveway. The parking spaces are considered to be 100% treated.
The new trails around the perimeter of the park will not be treated – they are located
either on top of the detention pond berm or within the pond. There is no reasonable
expectation that the concrete trail needs additional water quality provisions.
The new impervious area created by the project that is treated by LID is 83%.
Please refer to Appendix C for LID calculations and information.
3.4 Hydrologic Criteria
Runoff computations have not been prepared for the new park. There is no appreciable
change in the imperviousness of the overall site when the existing Streets Facility is
included.
3.5 Hydraulic Criteria
No hydraulic calculations have been prepared. Two existing storm pipes will be extended
with the project – these new pipes have been sized larger than the existing pipes.
3.6 Floodplain Regulations Compliance
The project is not within any regulated FEMA or City of Fort Collins mapped floodway;
therefore, Floodplain Regulations Compliance is not required.
7
3.7 Modifications of Criteria
The drainage design has been prepared assuming that the detention release rate can
remain at the previously approved rate of 10.5 cfs.
4. DRAINAGE FACILITY DESIGN
4.1 General Concept
Existing drainage scheme:
The latest pertinent design of the East Vine Streets Facility (the 1999 Report), routed the
southwestern portion of the overall facility (14.85 acres) to Water Quality Pond A and the
northwestern portion of the facility (7.52 acres) to Water Quality Pond B. The water
quality ponds released individually into the detention pond. A concrete pan exists from
the outlet pipes to the 18” detention pond outlet pipe at 9th Street. The detention was
undersized because the City’s old rainfall criterion was used. The 1999 Report design
showed the invert of the pond at elevation 46.2 and the spillway to 9th Street at 4949.2
with a design volume of 2.61 acre-feet.
At some point after the construction of the ponds, curb and gutter was added to 9th Street
as well as an asphalt sidewalk between 9th Street and the pond. The asphalt sidewalk
appears to have significantly raised the spillway elevation of the detention pond with the
lowest point of the walk being at elevation 4950.1. The current survey indicates that the
pond (with the additional 0.9’ of depth) exceeds the 1999 design volume with a detention
volume of 4.97 acre-feet. The pond is deficient in that there is a low point in the
driveway at elevation 4950.3, so if the pond ever were to spill, it would spill both east to
9th Street and to the south towards New Belgium Brewing once a water surface elevation
of 4950.3 was exceeded.
Proposed drainage scheme:
The pan from the two water quality ponds runs through the center of the proposed core of
the park. Several options to reroute this pan were investigated, but in each case, the
reroute would take the pan between the playground/shelter and the turf field, which will
8
be a high traffic area. The goal of the project was to avoid any park users from having to
cross this trickle.
The current design solution will reroute the pipe from Water Quality Pond B into Water
Quality Pond A and then route the outlet pipe from Water Quality Pond A through the
playground and to the south side of the site. A swale will be built at the toe of the south
embankment at 0.5% to the detention pond outlet pipe. This 0.5% swale area will be
planted in a way to discourage crossing.
The detention pond volume has been recalculated with the 1999 Report acreage, C value
and release rate, but with the current City of Fort Collins rainfall. The core area of the
park is encroaching into the existing pond volume and the regrading of the bottom of the
pond (to get a standard 1% slope) will also take some of the existing volume. To
counteract this, the spillway will be lengthened and raised slightly, and the south berm of
the pond will also be raised to an elevation 12” above the spillway (to remove chances of
spilling over the drive). A headwall and orifice plate will be added to the pond outlet
structure to reduce the flow to the 10.5 cfs release rate.
Parking will be added to the drive, but it will be treated in a rain garden prior to the
underdrain releasing to the 0.5% swale.
4.2 Specific Details
A summary of the drainage patterns within specific areas of the project is provided in the
following paragraphs. Hydrology of the basins was not analyzed as the previous reports
were used for overall C values and no new conveyance pipes are proposed. Please refer
to Appendix A for the drainage plan.
Water Quality Pond B is north of the railroad spur and currently has 0.56 acre-feet of
volume prior to water spilling over the railroad tracks into Water Quality Pond A.
Presently, the pond drains through a 12”x18” HERCP pipe (15” equivalent) to the trickle
pan in the detention pond. The proposed design will add a manhole on this pipe on the
south side of the railroad spur and extend an 18” pipe to Water Quality Pond A.
9
Water Quality Pond A is south of the railroad spur and west of the proposed park core
area and the detention pond. It accepts runoff from the existing streets facility both
overland through a curb cut and from an existing 30” pipe. The pond has an existing
volume of 1.59 acre feet prior to spilling east into the detention pond. The pond outlet is
an 8” steel pipe which currently drains to the existing trickle pan in the detention pond.
The proposed design will add a junction box (area inlet) on the downstream side of this
8” pipe. A new, solid 12” PVC pipe will be run through the proposed playground and
will discharge into the detention pond on the south side of the core area. This 12” pipe
will be placed on the subgrade of the playground with wood safety surface above it. The
pipe will be readily accessible if any maintenance is required.
Additionally, the grading of the east side of Water Quality Pond A will be changed.
Today the spill elevation of the pond is 4950.7. This spill location is directly adjacent to
the proposed restroom and core area. With the new grading design of the detention pond,
Water Quality Pond A will spill northeast at an elevation of 4951.0. The bottom of the
detention pond will sheet flow at 1% to the northeast and be the new spillway for the
Water Quality Pond. No erosion protection will be necessary as it will basically just spill
into a flat field. With the increase in the spill elevation, the new volume associated with
Water Quality Pond A will be 1.99 acre-feet. It is assumed that in the future the streets
department will reconfigure this pond into a rain garden or some LID treatment basin.
Preliminary calculations indicate that much less volume than the 1.99 acre feet available
would be necessary.
The Core Area is located north of the existing drive and new parking, and between
Water Quality Pond A and the Detention Pond. It will contain a new restroom (set 12”
higher than the top of the detention pond berm), planting beds, walkways, an open air
picnic shelter and the playground for the park. The core area is elevated above existing
grade and will drain west and east. The west portion of the site will drain overland into
Water Quality Pond A, the east portion of the site will drain into the playground safety
surface. The safety surface is an engineered wood fiber that will be at least 18” deep with
a 6” perforated pipe in the bottom to drain runoff to the detention pond.
The Detention Pond was designed in 1993 with the first construction phase of the East
Vine Streets Facility P.U.D. Today the detention pond outlets to an uncontrolled 18” pipe
in the southeast corner of the pond and into the storm sewer system in 9th Street. The
10
existing pond has a volume of 4.97 acre-feet at the existing spill elevation of 4951.1 over
the 9th Street asphalt sidewalk. The pond has a secondary spill location on the north side
of the existing driveway at elevation 4951.3. The existing volume of the pond is more
than was designed, but the spill elevation was artificially raised with the construction of
the sidewalk on 9th Street, and the pond bottom is much flatter than was designed with
slopes as flat as 0.40%.
The construction of the park core area will fill within the existing detention volume as
will steepening the bottom of the pond to 1% minimum (required for usable turf fields).
The goal of the project was to calculate the required pond volume with the current City of
Fort Collins rainfall and control the release of the pond with a new orifice plate on the
18” outlet pipe. Using the acreage, C value, and release rate from the 1999 Report, along
with the new rainfall, the required detention pond volume is 4.81 acre-feet. The project is
required to reconstruct the existing asphalt sidewalk in concrete, so the walk will be
rebuilt with a 100’ long spill elevation of 4950.3. The south side of the pond will also be
reconstructed to a minimum elevation of 4951.3 so that the secondary pond spillway is
removed. The bottom of the pond has been designed with a 1% minimum slope in the
open field areas, and a 0.5% grass channel on the south toe of the pond (which will
receive flows from the core area and Water Quality Pond A). The pond volume achieved
with these various grading modifications is 4.84 acre-feet, which meets the project’s
goals.
The New Parking Spaces are located on the north side of the existing driveway. The
driveway in this area is lower than the top of the detention pond, so it is not possible to
sheet flow the parking spaces into the pond. In an effort to provide water quality for this
new hard surface area, a 4’ trickle pan will be run on the north edge of the driveway to
accept the concrete parking spaces and the adjacent walk. This pan will be graded at
0.35% to the east and drain to a new, small rain garden. The sizing of the pan and rain
garden follow:
Total area of “New Parking Spaces” Basin = 4,620 SF
Area of Concrete Pavement = 3,820 SF
Percent Impervious = 83%
C value = 0.82
Q (2-year for pan) = CiA = (0.82)*(2.85)*(4,620/43,560) = 0.25 cfs
11
Calculations for the rain garden are included in the appendices. It will have an 80 SF
bottom at elevation 5049.5 and will pond 9” deep prior to overtopping the north edge of
the driveway.
The Existing South Driveway is south of the detention pond. The driveway is already
lower than the existing pond spillway and it is impossible to drain the driveway to the
pond. The original design of the Streets Facility showed this configuration.
5. CONCLUSIONS
5.1 Compliance with Standards
All computations that have been completed within this report are in compliance with the
City of Fort Collins Storm Drainage Design Criteria Manual and the previously approved
reports for the site.
5.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provides for stormwater quantity and quality treatment of proposed
impervious 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 will be required.
12
6. REFERENCES
1. City of Fort Collins, “Fort Collins Stormwater Criteria Manual Amendments to
the Urban Drainage and Flood Control District Criteria Manual”, adopted
December 2011.
2. Urban Drainage and Flood Control District, “Urban Storm Drainage Criteria
Manual”, Volumes 1 and 2, dated June 2001, and Volume 3 dated November
2010.
3. “Final Drainage, Erosion and Storm Water Quality Study, East Vine Streets
Facility P.U.D., Phase One Final”, by RBD, June 28, 1993.
4. “Final Drainage and Erosion Control Study, East Vine Streets Facility P.U.D.,
Major Amendment Final, Phase Two Final”, by The Sear Brown Group, August
3, 1999.
A
APPENDIX A
VICINITY MAP AND DRAINAGE PLAN
SITE
Vicinity Map
Scale: 1" = 1000'
B
APPENDIX B
POND CALCULATIONS
1993 Report Calculations
1999 Report Calculations
Actual Existing Pond Volumes based on 2017 Topographic Survey
Proposed FAA Detention Sizing with “New” City Rainfall
Proposed Volume Calculations (Detention and Water Quality Pond A)
Orifice Plate Sizing for 10.5 CFS
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on May-10-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
Existing Detention Pond - Stage/Storage
LOCATION: STREETS PARK
PROJECT NO:
COMPUTATIONS BY: MPO
DATE: 2/7/2018
V = 1/3 d ( A + B + sqrt(A*B))
where V = volume between contours, ft
3
d = depth between contours, ft
A = surface area of contour
Main Detention Pond at Lemay Water Quality Pond A (SOUTH) Water Quality Pond B (NORTH)
Surface Incremental Total Surface Incremental Total Surface Incremental Total
Stage Area Storage Storage Stage Area Storage Storage Stage Area Storage Storage
(ft) (ft
2
) (ac-ft) (ac-ft) (ft) (ft
2
) (ac-ft) (ac-ft) (ft) (ft
2
) (ac-ft) (ac-ft)
46.2 0 46.2 46.2
46.5 85 0.00 0.00 46.5 0.00 0.00 46.5 0.00 0.00
47.0 2913 0.01 0.01 47.0 0.00 0.00 47.0 0.00 0.00
47.5 12101 0.08 0.09 47.5 0.00 0.00 47.5 0.00 0.00
48.0 27047 0.22 0.31 48.0 0.00 0.00 48.0 0.00 0.00
48.5 52919 0.45 0.76 48.5 100 0.00 0.00 48.5 0.00 0.00
49.0 101873 0.87 1.64 49.0 18666 0.08 0.08 49.0 0.00 0.00
49.5 131750 1.34 2.97 49.5 35620 0.31 0.38 49.5 0.00 0.00
49.8 145695 0.95 3.93 49.8 40844 0.26 0.65 49.8 0.00 0.00
50.0 153886 0.69 4.62 50.0 43316 0.19 0.84 50.0 0 0.00 0.00
EX SPILL LEMAY 50.1 158202 0.36 4.97 50.1 44394 0.10 0.94 50.1 1 0.00 0.00
EX SPILL SOUTH 50.3 166935 0.75 5.72 50.3 45341 0.21 1.15 50.3 31 0.00 0.00
50.5 48397 0.22 1.36 50.5 200 0.00 0.00
50.7 50567 0.23 1.59 50.7 550 0.00 0.00
51.0 3230 0.02 0.02
51.5 11500 0.10 0.10
52.0 20000 0.18 0.28
52.5 33100 0.54 0.56
1-16-18 STREETS PARK POND MPO.xls
Interwest Consulting Group
DETENTION VOLUME CALCULATIONS
Rational Volumetric (FAA) Method
100-Year Event
LOCATION: STREETS PARK - 1999 POND SIZING WITH NEW RAINFALL
PROJECT NO:
COMPUTATIONS BY: MPO
DATE: 2/7/2018
Equations: Area trib. to pond = 29.47 acre
Developed flow = QD = CIA C (100) = 0.77
Vol. In = Vi = T C I A = T QD Developed C A = 22.7 acre
Vol. Out = Vo =K QPO T Release rate, QPO = 10.50 cfs
storage = S = Vi - Vo K = 1 (from fig 2.1)
Rainfall intensity from City of Fort Collins IDF Curve with updated (3.67") rainfall
Storm Rainfall QD Vol. In Vol. Out Storage Storage
Duration, T Intensity, I (cfs) Vi Vo S S
(min) (in/hr) (ft3) (ft3) (ft3) (ac-ft)
5 9.95 225.8 67735 3150 64585 1.48
10 7.77 176.2 105741 6300 99441 2.28
20 5.62 127.5 153052 12600 140452 3.22
30 4.47 101.4 182512 18900 163612 3.76
40 3.74 84.9 203678 25200 178478 4.10
50 3.23 73.4 220144 31500 188644 4.33
60 2.86 64.9 233614 37800 195814 4.50
70 2.57 58.3 245017 44100 200917 4.61
80 2.34 53.1 254915 50400 204515 4.70
90 2.15 48.8 263667 56700 206967 4.75
100 1.99 45.3 271520 63000 208520 4.79
110 1.86 42.2 278650 69300 209350 4.81
120 1.75 39.6 285184 75600 209584 4.81
130 1.65 37.3 291219 81900 209319 4.81
140 1.56 35.3 296830 88200 208630 4.79
150 1.48 33.6 302078 94500 207578 4.77
160 1.41 32.0 307008 100800 206208 4.73
170 1.35 30.6 311661 107100 204561 4.70
180 1.29 29.3 316067 113400 202667 4.65
190 1.24 28.1 320255 119700 200555 4.60
200 1.19 27.0 324245 126000 198245 4.55
210 1.15 26.0 328058 132300 195758 4.49
Required Storage Volume: 209584 ft3
4.81 acre-ft
1-16-18 STREETS PARK POND MPO.xls,FAA-100yr (A-E))
Proposed Detention Pond - Stage/Storage
LOCATION: STREETS PARK
PROJECT NO:
COMPUTATIONS BY: MPO
DATE: 2/7/2018
V = 1/3 d ( A + B + sqrt(A*B))
where V = volume between contours, ft3
d = depth between contours, ft
A = surface area of contour
Main Detention Pond at Lemay Water Quality Pond A
Surface Incremental Total Surface Incremental Total
Stage Area Storage Storage Stage Area Storage Storage
(ft) (ft2) (ac-ft) (ac-ft) (ft) (ft2) (ac-ft) (ac-ft)
46.2 0 46.2
46.5 800 0.00 0.00 46.5 0.00 0.00
47.0 7100 0.04 0.04 47.0 0.00 0.00
47.5 19900 0.15 0.19 47.5 0.00 0.00
48.0 36800 0.32 0.51 48.0 0.00 0.00
48.5 55000 0.52 1.03 48.5 100 0.00 0.00
49.0 75100 0.74 1.78 49.0 18666 0.08 0.08
49.5 96200 0.98 2.76 49.5 35620 0.31 0.38
49.8 110000 0.71 3.47 49.8 40844 0.26 0.65
50.0 117800 0.52 3.99 50.0 43316 0.19 0.84
50.1 122200 0.28 4.27 50.1 44394 0.10 0.94
NEW SPILL 50.3 129400 0.58 4.84 50.3 45341 0.21 1.15
50.4 133700 0.30 5.15 50.5 48397 0.22 1.36
50.5 137300 0.31 5.46 NEW OVERTOP TO DET 51.0 60000 0.84 1.99
NEW TOP OF BERM 51.3 EX SPILL TO SOUTH 51.6
1-16-18 STREETS PARK POND MPO.xls
DETENTIONPOND
100-yr Event, Outlet Sizing
LOCATION: STREETS PARK
PROJECT NO:
COMPUTATIONS BY: MPO
DATE: 2/7/2018
Submerged Orifice Outlet:
release rate is described by the orifice equation,
Qo = CoAo sqrt( 2g(h-Eo))
where Qo = orifice outflow (cfs)
Co = orifice discharge coefficient
g = gravitational acceleration = 32.20 ft/s
Ao = effective area of the orifice (ft2)
Eo = greater of geometric center elevation of the orifice or d/s HGL (ft)
h = water surface elevation (ft)
Qo = 10.50 cfs
outlet pipe dia = D = 18.0 in
Invert elev. = 46.20 ft (inv. "D" on outlet structure)
Eo = 47.50 ft (downstream HGL for peak 100 yr flow - from FlowMaster)
h = 50.30 ft - 100 yr WSEL
Co = 0.65
solve for effective area of orifice using the orifice equation
Ao = 1.203 ft2
= 173.2 in2
orifice dia. = d = 14.85 in
Check orifice discharge coefficient using Figure 5-21 (Hydraulic Engineering )
d/ D = 0.83
kinematic viscosity, v = 1.22E-05 ft2/s
Reynolds no. = Red = 4Q/(πdv ) = 8.85E+05
Co = (K in figure) = 0.65 check
A o = 1.203 ft 2 = 173.23 in 2
Qmax = 10.50 cfs
orifice - 100yr, 1-16-18 STREETS PARK POND MPO.xls
C
APPENDIX C
LID INFORMATION
LID Exhibit
Trickle Pan Capacity for New Parking
Rain Garden Calculation
75% On-Site Treatment of New Impervious by LID (No Pavers Proposed)
New Impervious Area 8,060 sq. ft.
Required Minimum Impervious Area to be Treated 6,045 sq. ft.
Core Area Draining East (Playground Safety Surface / 0.5% Swale) 2,890 sq. ft.
New Parking Area (Rain Garden) 3,820 sq. ft.
Total Impervious Area Treated 6,710 sq. ft.
Actual % On-Site Treated by LID 83%
LID TABLE
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 83.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.830
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.28 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 4,620 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 107 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 9 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 71 sq ft
D) Actual Flat Surface Area AActual = 80 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 600 sq ft
F) Rain Garden Total Volume VT= 255 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
MPO
February 7, 2018
Streets Park - Overall Rain Garden Requirement based on Aerial