HomeMy WebLinkAboutSTREETS PARK - BDR180010 - SUBMITTAL DOCUMENTS - ROUND 4 - DRAINAGE REPORTFINAL DRAINAGE AND
EROSION CONTROL REPORT
Streets Park
Tract A, East Vine Streets Facility P.U.D., Lots 1A & 2A, a replat of
a portion of Lots 1 and 2, East Vine Streets Facility P.U.D., Major
Amended Final, Phase Two Final located in the northeast quarter of
Section 12, T-7-N, R-69-W of the Sixth Principal Meridian City of
Fort Collins, Larimer County, Colorado
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
November 28, 2018
Job Number 1165-012-92
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November 28, 2018
Mr. Dan Mogen
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, Colorado 80522-0580
RE: Final Drainage Report for Streets Park
Dear Dan,
I am pleased to submit for your review and approval, this Final Drainage Report for the Streets
Park development. I certify that this report for the drainage design was prepared in accordance
with the criteria in the City of Fort Collins Storm Drainage Manual and previous reports for this
site.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Sincerely,
Michael Oberlander, P.E., LEED AP
Colorado Professional
Engineer No. 34288
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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 .......................................................................................................... 7
3.6 Floodplain Regulations Compliance ............................................................................. 7
3.7 Modifications of Criteria ............................................................................................... 7
4. DRAINAGE FACILITY DESIGN ....................................................................................... 7
4.1 General Concept ............................................................................................................. 7
4.2 Specific Details ................................................................................................................ 9
5. CONCLUSIONS .................................................................................................................. 12
5.1 Compliance with Standards ........................................................................................ 12
5.2 Drainage Concept ......................................................................................................... 12
6. REFERENCES .................................................................................................................... 13
APPENDIX
VICINITY MAP AND DRAINAGE PLAN .............................................................................. A
EXISTING DRAINAGE REPORT SUPPORT MATERIAL .................................................. B
DRAINAGE INFORMATION .................................................................................................... C
POND CALCULATIONS ........................................................................................................... D
LID INFORMATION ................................................................................................................... E
STANDARD OPERATING PROCEDURE ............................................................................... F
STORMWATER ALTERNATIVE COMPLIANCE/VARIANCE ……………………………….G
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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 was an asphalt sidewalk on
9th Street that acted as the initial spillway for the pond. This walk and spillway was
recently rebuilt by the city in concrete.
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
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will be discussed in this report regarding C Values, release rates, and pond volumes.
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 100% 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 pond 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.
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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 - Existing Drainage Report Support Material for reference.
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
detention storage in the pond in conjunction with available storage volume in Water
Quality Pond A will be achieved with the “new” 1997 City of Fort Collins rainfall.
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
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“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 a release rate from the site and for recalculation of the required 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, with respect to the overall site.
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
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project.
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 park including the new parking spaces
was determined to be approximately 16,854 sf, by calculating the difference of
impervious areas between the proposed conditions to pre-project conditions.
The restroom and walks on the west side of the core area (approximately 3,713 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 – approximately 2,049 sf
impervious) will be treated within the subsurface of the playground. Inside the perimeter
of the playground will be a wood fiber media that will allow infiltration to a 3” layer of
drainage gravel below the wood fiber media and surrounding a perforated sub-drain (very
similar to a rain garden). The new impervious surfaces in this area were calculated to
require 81 cf of WQ storage with the rain garden calculator. Approximately 175 cf of
storage is available on the wood fiber media which will be bounded by a perimeter
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curb/barrier. This area is considered to be 100% treated by LID.
The remaining portions of the interior walks drain to the detention pond (approximately
10,445 sf), where the majority of walks sheet flow across an extensive amount of grass at
shallow grades. There is no reasonable expectation that these concrete walks need
additional water quality provisions, however 7,766 sf of these walks are being considered
as treated. This is due to this portion of 8’ wide walks draining across an average of 300’
or more of grass before exiting the detention pond, which would be over a 30:1 ratio of
impervious to pervious material. The 7,766 sf of walk treated by the grass buffer are
considered to be 100% treated by LID.
The new parking spaces and adjacent sidewalk will add 3,815 sf of impervious area.
These parking spaces need to drain to the south, as they are lower than the top of the
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 by LID.
The new impervious area created by the project that is treated by LID is 81%. There is a
small portion of sidewalk that cannot be treated for water quality (2565 sf). A variance is
included for this area. Please refer to Appendix E – LID Information for additional
information.
3.4 Hydrologic Criteria
Runoff computations have been prepared for the new park to demonstrate that there is no
appreciable change in the imperviousness of the overall site when the existing Streets
Facility is included.
The 1999 Report determined the composite C Value for the overall basin to be 0.62,
which yields an impervious value of 53% or 15.59 acres of hardscape on the 29.47 acre
site. Whereas the proposed conditions for Basin A (draining to the detention pond) will
add 0.24 acres of hardscape. In effect, this is a 1% increase in imperviousness for the
overall 29.47 acre site and it changes the C Value to 0.63.
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Basin B (draining offsite) today releases a Q100 of 5.9 cfs and with the parking and walks
added that cannot drain to the detention pond will produce 7.1 cfs in a 100 yr event,
which is 1.2 cfs more than what was calculated for the historic (existing) condition of the
site. To account for the 1.2 cfs increase in runoff from Basin B, the detention pond release
rate is being reduced to 9.3 cfs.
Please refer to Appendix C – Drainage Information for additional information.
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 located within a shaded FEMA Zone X, according to map number
08069C0981G. This Zone is for areas of 0.2% annual chance flood; areas of 1% chance
flood with average depths of less than 1 foot or within drainage areas less than 1 square
mile; and areas protected by levees from 1% annual chance flood. Based on the FEMA
Flood Map Service Center, the site is within an area with reduced flood risk due to levee.
3.7 Modifications of Criteria
The drainage design has been prepared assuming that the project’s 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
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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 old 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 survey for this project 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.
Since the survey for this project was performed, the asphalt sidewalk between 9th Street
and the pond has recently been reconstructed in concrete, with the previously submitted
proposed grading plan used as a guide for construction of a higher spillway elevation.
Proposed drainage scheme:
The existing 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 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 swale area will be planted in
a way that discourages pedestrians from crossing it.
The detention pond volume has been recalculated with the 1999 Report acreage, the new
proposed C Value (0.79) and new release rate (9.3 cfs), and with the current City of Fort
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Collins rainfall data. 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 9.3 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 within the detention pond.
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 west of the project were 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.
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 drainage gravel around it and
engineered wood fiber safety surface above it. The pipe will be readily accessible if any
maintenance is required.
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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 southeast 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.
Extended Detention Basin calculations were performed on all areas draining to the water
quality ponds. These calculations show a total required Water Quality Capture Volume of
0.65 acre-ft, so 1.34 acre-ft of excess storage is available.
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 layer of drainage gravel below that will surround 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
existing volume of the pond is more than was designed, but the spill elevation was
artificially raised with the construction of the asphalt 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
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18” outlet pipe. Using the acreage from the 1999 Report, along with the new C Value,
release rate, and rainfall data, the required detention pond volume is 5.20 acre-feet.
As mentioned previously, the asphalt sidewalk along the east rim of the detention pond
was recently reconstructed in concrete. The walk was rebuilt with an approximately 100’
long spill elevation of 4950.2 (design elevation of 4950.3). Calculations for the spillway
sizing are provided in Appendix D. 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 detention pond volume achieved with these various grading modifications is 4.57
acre-feet, not including any detention within the water quality ponds. The additional
required volume of 0.63 acre-ft to achieve the total volume of 5.2 acre-ft is available in
the excess volume of 1.34 acre-ft within Water Quality Pond A.
The proposed spillway for the detention spillway has been built approximately 100 ft
long. Using the FAA Detention spreadsheet and a time of concentration of 25 minutes
(Rational Urbanized Check), the flow over the spillway is 118 cfs and will flow at a depth
of 0.6 feet. A variance for this flow depth has been included.
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 = 5751 SF
Area of Concrete Pavement = 3,815 SF
Percent Impervious = 66 %
C Value = 0.70
Q (2-year for pan) = CiA = (0.70)*(2.85)*(5751/43,560) = 0.26 cfs
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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.
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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
EXISTING DRAINAGE REPORT SUPPORT MATERIAL
1993 Report Calculations
1999 Report Calculations
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
C
APPENDIX C
DRAINAGE INFORMATION
Back Out of Original Sear-Brown Impervious % from C Value
Drainage Exhibit
Runoff Computations
Streets Park - Back out Original Sear Brown Impervious % from C Value
Interwest Consulting Group
8/10/2018
C (impervious - 1999 Report) 0.95 = 100%
C (pervious - 1999 Report) 0.25 = 0%
Overall Site - Original 1999 Design Overall Site - With Streets Park Adding 10,654 SF of Impervious
C (1999 Report)= 0.62 0.620 check C (1999 Report)= 0.63 0.626 check
Acreage 29.47 Acreage 29.47
Acres Impervious= 15.59 Acres Impervious= 15.83
Acres Pervious= 13.88 Acres Pervious= 13.64
% Impervious 53% % Impervious 54%
South Portion of Site - Original 1999 Design - To WQ Pond A North Portion of Site - Original 1999 Design - To WQ Pond B
C (1999 Report)= 0.81 0.810 check C (1999 Report)= 0.66 0.660 check
Acreage 14.85 Acreage 7.52
Acres Impervious= 11.87 Acres Impervious= 4.40
Acres Pervious= 2.98 Acres Pervious= 3.12
% Impervious 80% % Impervious 59%
WQ Pond A and B Contributing Area
C (1999 Report)= 0.76 0.759 check
Acreage 22.37
Acres Impervious= 16.27
Acres Pervious= 6.10
% Impervious 73%
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Streets Park (HISTORIC)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 6/15/2018
Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I
Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I
Type B Soils Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Gravel or Pavers: 0.50 40
Landscape Areas (Flat, heavy) : 0.15 0
Landscape Areas (Steep, heavy) : 0.20 0
SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS SIDEWALK LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
A 6.89 300,014 195 6,491 0 2,996 290,332 0.18 3
B 1.50 65,352 0 25,599 0 750 39,003 0.47 40
Equations
- Calculated C coefficients & % Impervious are area weighted
C = Σ (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
06-15-18 STREETS PARK_FC FLOW_HISTORIC.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 100 YR
LOCATION: Streets Park (HISTORIC)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 6/15/2018
100-yr storm Cf = 1.25 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I
SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASIN) tc
DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10
PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14)
A1 A 6.89 0.18 0.22 263 1.8 21.8 356 0.7 0.03 0.9 6.4 28.2 619 13.4 13.4
B1 B 1.50 0.47 0.59 58 0.9 7.6 751 0.5 0.03 0.7 17.0 24.7 809 14.5 14.5
EQUATIONS:
tc = ti + tt
ti = [1.87 (1.1 - CCf ) L0.5 ] / S 1/3
tt = L/Vel.
Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
06-15-18 STREETS PARK_FC FLOW_HISTORIC.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 100-Yr Storm)
LOCATION: Streets Park (HISTORIC)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 6/15/2018
100 yr storm, Cf = 1.25
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot
Design
Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
A1 A 6.89 0.22 13.4 6.84 10.4 10.4
B1 B 1.50 0.59 14.5 6.61 5.9 5.9
Q = C iA
Q = peak discharge (cfs)
C = runoff coefficient
i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99)
A = drainage area (acres) i = 84.682 / (10+ tc)
0.7975
06-15-18 STREETS PARK_FC FLOW_HISTORIC.xls
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Streets Park (PROPOSED)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 6/15/2018
Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I
Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I
Type B Soils Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Gravel or Pavers: 0.50 40
Landscape Areas (Flat, heavy) : 0.20 0
Landscape Areas (Steep, heavy) : 0.35 0
SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS SIDEWALK LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
A 6.89 300,014 1,573 2,619 0 16,119 279,703 0.25 7
B 1.50 65,352 0 29,490 0 3,090 32,773 0.57 50
Equations
- Calculated C coefficients & % Impervious are area weighted
C = Σ (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
06-15-18 STREETS PARK_FC FLOW_PROPOSED.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 100 YR
LOCATION: Streets Park (PROPOSED)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 6/15/2018
100-yr storm Cf = 1.25 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I
SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASIN) tc
DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10
PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14)
A1 A 6.89 0.25 0.31 263 1.8 19.6 356 0.7 0.012 2.2 2.6 22.3 619 13.4 13.4
B1 B 1.50 0.57 0.72 58 0.9 5.7 751 0.5 0.03 0.7 17.0 22.8 809 14.5 14.5
EQUATIONS:
tc = ti + tt
ti = [1.87 (1.1 - CCf ) L0.5 ] / S 1/3
tt = L/Vel.
Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
06-15-18 STREETS PARK_FC FLOW_PROPOSED.xls
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Streets Park (PROPOSED)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 8/10/2018
Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I
Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I
Type B Soils Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Gravel or Pavers: 0.50 40
Landscape Areas (Flat, heavy) : 0.20 0
Landscape Areas (Steep, heavy) : 0.35 0
SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS SIDEWALK LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
A 6.89 300,014 1,573 3,936 0 14,827 279,678 0.25 7
B 1.50 65,352 0 28,172 0 4,377 32,803 0.57 50
Equations
- Calculated C coefficients & % Impervious are area weighted
C = Σ (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
06-15-18 STREETS PARK_FC FLOW_PROPOSED.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 100 YR
LOCATION: Streets Park (PROPOSED)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 8/10/2018
100-yr storm Cf = 1.25 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I
SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASIN) tc
DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10
PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14)
A1 A 6.89 0.25 0.31 263 1.8 19.6 356 0.7 0.012 2.2 2.6 22.3 619 13.4 13.4
B1 B 1.50 0.57 0.72 58 0.9 5.7 751 0.5 0.03 0.7 17.0 22.8 809 14.5 14.5
EQUATIONS:
tc = ti + tt
ti = [1.87 (1.1 - CCf ) L0.5 ] / S 1/3
tt = L/Vel.
Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
06-15-18 STREETS PARK_FC FLOW_PROPOSED.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 100-Yr Storm)
LOCATION: Streets Park (PROPOSED)
PROJECT NO: 1165-012-92
COMPUTATIONS BY: laj
DATE: 8/10/2018
100 yr storm, Cf = 1.25
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot
Design
Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
A1 A 6.89 0.31 13.4 6.84 14.8 14.8
B1 B 1.50 0.72 14.5 6.61 7.1 7.1
Q = C iA
Q = peak discharge (cfs)
C = runoff coefficient
i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99)
A = drainage area (acres) i = 84.682 / (10+ tc)
0.7975
06-15-18 STREETS PARK_FC FLOW_PROPOSED.xls
D
APPENDIX D
POND CALCULATIONS
Actual Existing Pond Volumes based on 2017 Topographic Survey
Proposed FAA Detention Sizing with “New” City Rainfall
Overall WQCV Required for Both WQ Pond A & B
Proposed Volume Calculations (Detention and Water Quality Pond A)
Orifice Plate Sizing for 9.3 CFS
Spillway Calculation
Detention Pond Drain Time
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: LAJ
DATE: 8/10/2018
Equations: Area trib. to pond = 29.47 acre
Developed flow = QD = CIA C (100) = 0.79
Vol. In = Vi = T C I A = T QD Developed C A = 23.3 acre
Vol. Out = Vo =K QPO T Release rate, QPO = 9.30 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 9.95 231.6 69495 2790 66705 1.53
10 7.77 180.8 108487 5580 102907 2.36
20 5.62 130.9 157027 11160 145867 3.35
30 4.47 104.0 187253 16740 170513 3.91
40 3.74 87.1 208969 22320 186649 4.28
50 3.23 75.3 225862 27900 197962 4.54
60 2.86 66.6 239682 33480 206202 4.73
70 2.57 59.9 251382 39060 212322 4.87
80 2.34 54.5 261536 44640 216896 4.98
90 2.15 50.1 270515 50220 220295 5.06
100 1.99 46.4 278573 55800 222773 5.11
110 1.86 43.3 285888 61380 224508 5.15
120 1.75 40.6 292591 66960 225631 5.18
130 1.65 38.3 298783 72540 226243 5.19
140 1.56 36.3 304540 78120 226420 5.20
150 1.48 34.4 309924 83700 226224 5.19
160 1.41 32.8 314983 89280 225703 5.18
170 1.35 31.3 319756 94860 224896 5.16
180 1.29 30.0 324277 100440 223837 5.14
190 1.24 28.8 328573 106020 222553 5.11
200 1.19 27.7 332667 111600 221067 5.07
210 1.15 26.7 336579 117180 219399 5.04
Required Storage Volume: 226420 ft3
5.20 acre-ft
08-10-18 STREETS PARK POND_LAJ.xls,FAA-100yr (A-E))
Design Procedure Form: Extended Detention Basin (EDB) - Sedimentation Facility
LOCATION: Streets Park - Overall WQCV Required for Both WQ Pond A & B
PROJECT NO:
COMPUTATIONS BY: LAJ
DATE: 8/10/2018
1. Basin Storage Volume
A) Tributary Area's Imperviousness Ratio (i=Ia/100) Ia = 73 %
i = 0.73
B) Contributing Watershed Area (Area) A = 22.37 acres
C) Water Quality Capture Volume (WQCV) WQCV = 0.29 watershed inches
(WQCV = 1.0 * (0.91 * i3 - 1.19 * i2 + 0.78i) )
D) Design Volume: Vol = WQCV/12 * Area * 1.2 Vol. = 0.65 ac-ft
Proposed Detention Pond - Stage/Storage
LOCATION: STREETS PARK
PROJECT NO:
COMPUTATIONS BY: LAJ
DATE: 11/8/2018
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
Detention Pond Water Quality Pond A Summary
Surface Incremental Total Surface Incremental Total 5.20 acre-ft
Stage Area Storage Storage Stage Area Storage Storage 4.57 acre-ft
(ft) (ft
2
) (ac-ft) (ac-ft) (ft) (ft
2
) (ac-ft) (ac-ft) 0.63 acre-ft
46.2 1 46.2
46.5 1218 0.00 0.00 46.5 0.00 0.00 1.99 acre-ft
47.0 8312 0.05 0.05 47.0 0.00 0.00 0.65 acre-ft
47.5 21334 0.16 0.22 47.5 0.00 0.00 1.34 acre-ft
47.8 30795 0.18 0.39 47.8 0.00 0.00
48.0 37534 0.16 0.55 48.0 0.00 0.00
48.5 54984 0.53 1.08 48.5 100 0.00 0.00 0.71 acre-ft
49.0 73961 0.74 1.82 49.0 18666 0.08 0.08
49.5 95407 0.97 2.79 49.5 35618 0.31 0.38
49.8 109321 0.70 3.49 49.8 40817 0.26 0.65
50.0 117558 0.52 4.01 50.0 43263 0.19 0.84
50.1 121344 0.27 4.28 50.1 44337 0.10 0.94
NEW SPILL 50.2 122656 0.28 4.57 50.2 45295 0.10 1.04
50.3 128926 0.29 50.3 46393 0.11 1.15
50.4 50.5 48465 0.22 1.37
50.5 NEW OVERTOP TO DET 51.0 59776 0.62 1.99
NEW TOP OF BERM 51.3 EX SPILL TO SOUTH 51.6
WQCV Required
Solution: Provide Remaining Detention
Required from Volume Available in WQ
Pond A. Remaining Volume Available in WQ
Pond A
Volume Available in WQ Pond A
Detention Required (per FAA Method)
Provided in Detention Pond
Remaining Detention Required
Volume of Water Quality Pond A
11-08-18 STREETS PARK POND_LAJ.xls
DETENTIONPOND
100-yr Event, Outlet Sizing
LOCATION: STREETS PARK
PROJECT NO:
COMPUTATIONS BY: LAJ
DATE: 9/20/2018
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 = 9.30 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 = 50.23 ft - 100 yr WSEL
Co = 0.65
solve for effective area of orifice using the orifice equation
Ao = 1.079 ft2
= 155.4 in2
orifice dia. = d = 14.07 in
Check orifice discharge coefficient using Figure 5-21 (Hydraulic Engineering )
d/ D = 0.78
kinematic viscosity, v = 1.22E-05 ft2/s
Reynolds no. = Red = 4Q/(πdv ) = 8.28E+05
Co = (K in figure) = 0.65 check
A o = 1.079 ft 2 = 155.38 in 2
Qmax = 9.30 cfs
orifice - 100yr, 09-20-18 STREETS PARK POND_LAJ.xls
Detention Pond
Emergency Overflow Spillway Sizing
LOCATION: STREETS PARK
PROJECT NO:
COMPUTATIONS BY: LAJ
DATE: 8/13/2018
Equation for flow over a broad crested weir
Q = CLH3/2
where C = weir coefficient = 2.6
H = overflow height
L = length of the weir
The pond has a spill elevation equal to the maximum water surface elevation in the pond
Design spillway with 0.5 ft flow depth, thus H = 0.6 ft
Size the spillway assuming that the pond outlet is completely clogged.
Pond
Q (100) = 118.0 cfs (peak flow into pond)
Spill elev = 50.30 ft
Min top of berm elev.= 51.20
Weir length required:
L = 98 ft
Use L = 100 ft
v = 1.90 ft/s
spillway, 08-13-18 STREETS PARK POND_LAJ.xls
Qpeak @ 25 minutes
Note: Spillway Peak Flow (Qpeak)
was determined by the following:
Total Length of Basin = 2700' approx.
Urbanized Check: (L/180) +10
(2700/180) +10 = 25 min.
(design elevation)
Stormwater Facility Name:
Facility Location & Jurisdiction:
User (Input) Watershed Characteristics User Defined User Defined User Defined User Defined
Watershed Slope = 0.007 ft/ft Stage [ft] Area [ft^2] Stage [ft] Discharge [cfs]
Watershed Length-to-Width Ratio = 6.00 L:W 0.00 0 0.00 0.00
Watershed Area = 24.97 acres 0.30 1,218 4.00 9.30
Watershed Imperviousness = 54.0% percent 0.80 8,312 5.10 118.00
Percentage Hydrologic Soil Group A = 0.0% percent 1.30 21,334
Percentage Hydrologic Soil Group B = 0.0% percent 1.60 30,795
Percentage Hydrologic Soil Groups C/D = 100.0% percent 1.80 37,534
2.30 54,984
2.80 73,961
3.30 95,407
3.60 109,321
User Input: Detention Basin Characteristics 3.80 160,821
WQCV Design Drain Time = 0.00 hours 3.90 165,681
4.00 167,951
4.10 175,319
4.30 48,465
4.80 59,776
5.10 0
After completing and printing this worksheet to a pdf, go to:
https://maperture.digitaldataservices.com/gvh/?viewer=cswdif,
create a new stormwater facility, and
attach the pdf of this worksheet to that record.
Routed Hydrograph Results
Design Storm Return Period = WQCV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year
Two-Hour Rainfall Depth = 0.53 0.98 1.36 1.71 2.31 2.91 3.67 in
Calculated Runoff Volume = 0.001 1.048 1.759 2.431 3.687 4.851 6.462 acre-ft
OPTIONAL Override Runoff Volume = acre-ft
Inflow Hydrograph Volume = 0.001 1.047 1.759 2.430 3.687 4.850 6.453 acre-ft
Time to Drain 97% of Inflow Volume = 1 4 5 7 8 10 11 hours
Time to Drain 99% of Inflow Volume = 1 4 6 7 9 10 12 hours
Maximum Ponding Depth = 0.01 1.78 2.28 2.65 3.20 3.62 4.01 ft
Maximum Ponded Area = 0.000 0.845 1.241 1.562 2.092 2.612 3.863 acres
Maximum Volume Stored = 0.000 0.547 1.065 1.583 2.597 3.561 4.912 acre-ft
Workbook Protected Worksheet Protected
Stormwater Detention and Infiltration Design Data Sheet
Streets Park
Fort Collins, CO
09-20-18 STREETS PARK_DRAIN TIME.xlsm, Design Data 9/20/2018, 11:35 AM
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Stormwater Detention and Infiltration Design Data Sheet
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APPENDIX E
LID INFORMATION
Drainage Exhibit
Trickle Pan for New Parking Area
Rain Garden Calculations
Project Description
Flow Element: Triangular Channel
Friction Method: Manning Formula
Solve For: Normal Depth
Section Data
Roughness Coefficient: 0.013
Channel Slope: 0.35000 %
Normal Depth: 1.65 in
Left Side Slope: 12.00 ft/ft (H:V)
Right Side Slope: 12.00 ft/ft (H:V)
Discharge: 0.26 ft³/s
4' TRICKLE PAN
Cross Section for Triangular Channel - 1
Project Description
Flow Element: Triangular Channel
Friction Method: Manning Formula
Solve For: Normal Depth
Input Data
Roughness Coefficient: 0.013
Channel Slope: 0.35000 %
Left Side Slope: 12.00 ft/ft (H:V)
Right Side Slope: 12.00 ft/ft (H:V)
Discharge: 0.26 ft³/s
Results
Normal Depth: 1.65 in
Flow Area: 0.23 ft²
Wetted Perimeter: 3.32 ft
Top Width: 3.31 ft
Critical Depth: 0.12 ft
Critical Slope: 0.00625 ft/ft
Velocity: 1.14 ft/s
Velocity Head: 0.02 ft
Specific Energy: 0.16 ft
Froude Number: 0.76
Flow Type: Subcritical
GVF Input Data
Downstream Depth: 0.00 in
Length: 0.00 ft
Number Of Steps: 0
GVF Output Data
Upstream Depth: 0.00 in
Profile Description: N/A
Profile Headloss: 0.00 ft
Downstream Velocity: 0.00 ft/s
Upstream Velocity: 0.00 ft/s
Normal Depth: 1.65 in
Critical Depth: 0.12 ft
Channel Slope: 0.35000 %
Critical Slope: 0.00625 ft/ft
Worksheet for Triangular Channel - 1
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 59.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.590
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.19 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 1,454,904 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 22,586 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 = 10 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 20.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 15057 sq ft
D) Actual Flat Surface Area AActual = 18666 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 40844 sq ft
F) Rain Garden Total Volume VT= 24,795 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)
mo
August 13, 2018
Streets Park - Basin B Parking Spaces - Rain Garden
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 12.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.120
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.06 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 15,664 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 81 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 = 0.25 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 54 sq ft
D) Actual Flat Surface Area AActual = 8406 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 8406 sq ft
F) Rain Garden Total Volume VT= 175 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)
LAJ
November 8, 2018
Streets Park - Playground Gravel Bed Below Safety Surface
F
APPENDIX F
STANDARD OPERATING PROCEDURE (SOP)
Playground Surfacing Maintenance Plan
Routine Maintenance Table (Summary adapted from Chapter 6 of UDFCD, Volume 3)
Required Action Maintenance Objective Frequency of Action
Debris and
Litter Removal
Remove debris and litter from the
infiltrating surface to minimize clogging of
the media.
Routine - Including just before
annual storm seasons (April and
May), end of storm season after
leaves have fallen (October), and
following significant rainfall
events.
Sediment Removal
and Media
Replacement
Maintain adequate infiltration rates to
drain the playground surfacing within 24
hours. Upon replacement of EWF and/or
clogging is observed. Inspection of the
geotextile fabric and drainage gravel below
the EWF should be performed. If either
item is preventing proper infiltration, it
should be replaced per design
specifications.
Non-routine – Maintenance
activities to restore infiltration
capacity of playground surfacing
will vary with the degree and
nature of the clogging. The
frequency of media replacement
will depend on site-specific
characteristics that have the
potential to clog the playground
surfacing and drainage gravel.
Replacement of
Engineered Wood
Fiber (EWF)
Maintain a level play surface with raking of
existing EWF and add additional EWF as
necessary to achieve a level surface and
proper depths. Where playground
equipment is less than 4 feet in height, the
minimum EWF depth required is 8 inches
after compaction. Where playground
equipment exceeds 4 feet in height, the
minimum EWF depth required is 12 inches
after compaction.
Non-Routine – As needed and
inspect EWF conditions at least
twice annually following
precipitation events.
Inspections
Determine if the playground surfacing area
is providing acceptable infiltration, and
outlet structures are not obstructed. Check
for erosion and repair as necessary.
Routine - Inspect the infiltrating
surface at least twice annually
Playground Drain Pipe Lines Maintenance Plan
Routine Maintenance Table
Required Action Maintenance Objective Frequency of Action
Debris Removal from Inlets and
Catch Basins
Remove debris and trash from
inlets to prevent them from
continuing downstream or
clogging and reducing the flow
capacity of the system.
Non-routine – Remove debris as
needed after storm events or
seasonally such as during the Fall
with heavy amounts of leaves
and twigs entering the system.
Debris Removal from Storm
Pipes
Ensure the pipe systems function
as intended. Reduced capacities
in the pipes will cause the system
to back up and increase the
frequency of surface flooding
that could damage property.
Non-routine – Pipe cleaning is
recommended as needed based
on the results of inspections or
when the system is no longer
able to regularly convey routine
storm flows from the site.
Inspection Use a video camera to inspect
the condition of the storm drain
pipes looking for sediment
buildup and structural integrity.
Clean out pipes as needed. If the
integrity of the pipe is
compromised, then repair the
damaged section(s).
Routine – Visually Inspect pipes
and inlets at least annually or
after major storm events. Every
2-5 years the pipes should be
inspected with a video camera.
Bioretention/Bioswale
Routine Maintenance Table (Summary from Chapter 6 of UDFCD)
Required
Action
Maintenance Objective Frequency of Action
Lawn mowing
and vegetative
care
Occasional mowing of grasses and weed
removal to limit unwanted vegetation.
Maintain irrigated turf grass as 2 to 4
inches tall and non-irrigated native turf
grasses at 4 to 6 inches.
Routine – Depending on aesthetic
requirements, planting scheme and cover.
Weeds should be removed before they flower.
Debris and litter
removal and
snow stockpiling
Remove debris and litter from
bioretention area and upstream
concrete forebay to minimize clogging
of the sand media. Remove debris and
litter from the pond area and outlet
orifice plate to minimize clogging.
Remove debris and litter from curb
channel and sidewalk chase outlets
adjacent to pond if applicable to
minimize clogging. Avoid stockpiling
snow in the bioretention area to
minimize clogging from sediment
accumulation.
Routine – Including just before annual storm
seasons and after snow season (April or May),
end of storm season after leaves have fallen,
and following significant rainfall events.
Inspections
Inspect detention area to determine if
the sand media is allowing acceptable
infiltration. If standing water persists
for more than 24 hours after storm
runoff has ceased, clogging should be
further investigated and remedied.
Routine – Biannual inspection of the hydraulic
performance.
Growing media
replacement
Restore infiltration capacity of
bioretention facilities.
Non-routine – Performed when clogging is due
to the migration of sediments deep into the
pore spaces of the media. The frequency of
replacement will depend on site-specific
pollutant loading characteristics.
Perforated Subdrain
The perforated subdrain system storm drain outfall at the bottom of the Low Impact Development (LID) system is
critical to the overall function of the system subbase. As such, special maintenance has been identified to ensure
these perforated drain systems perform as they were designed.
Perforated subdrains leading away from the LID system is designed to provide faster release of water when
accumulation occurs under the LID system. Outflow should be seen into downstream storm boxes. If not seen it is
recommended that the system is inspected using a video camera to verify no clogging has occurred.
Perforated subdrains leading toward the LID system are designed to provide an opportunity for infiltration. These
subdrains may lead to a drywell where additional infiltration capacity is available to reduce runoff per the stated
LID goals adopted by the City.
Routine Maintenance Table
Required
Action
Maintenance Objective Frequency of Action
Inspection
Use a video camera to inspect the
condition of the perforated drain
pipes. Cleanout pipes as needed. If the
integrity of the pipe is compromised,
then repair the damaged section(s).
Every two to five years.
Inspection
Where accessible, expose inlet and/or
outlet of perforated pipe and watch
for water inflow and/or outflow.
Minimum Annually
G
APPENDIX G
STORMWATER ALTERNATIVE COMPLIANCE/VARIANCE
following precipitation events.
Check for obvious problems during
routine maintenance visits,
especially for plugging of outlets
and erosion.
09-20-18 STREETS PARK_DRAIN TIME.xlsm, Design Data 9/20/2018, 11:35 AM