HomeMy WebLinkAboutPOUDRE RIVER WHITEWATER PARK - - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTDRAINAGE, WATER QUALITY AND
EROSION CONTROL REPORT
FOR THE
POUDRE RIVER WHITEWATER PARK PROJECT
PREPARED FOR:
City of Fort Collins
Park Planning & Development
215 North Mason Street
Fort Collins, CO 80524
PREPARED BY:
Anderson Consulting Engineers, Inc.
375 East Horsetooth Road, Building 5
Fort Collins, CO 80525
(ACE Project No. COFC18.1)
June 6, 2017
DRAINAGE, WATER QUALITY AND
EROSION CONTROL REPORT
FOR THE
POUDRE RIVER WHITEWATER PARK PROJECT
PREPARED FOR:
City of Fort Collins
Park Planning & Development
215 North Mason Street
Fort Collins, CO 80524
PREPARED BY:
Anderson Consulting Engineers, Inc.
375 East Horsetooth Road, Building 5
Fort Collins, CO 80525
(ACE Project No. COFC18.1)
June 6, 2017
COFC18.1 Drainage Report (June 6 2017).docx i Anderson Consulting Engineers, Inc.
TABLE OF CONTENTS
I. INTRODUCTION ............................................................................................................................... 1
II. PROJECT LOCATION AND INFORMATION ........................................................................................ 2
2.1 Project Location .................................................................................................................. 2
2.2 Topographic Mapping ......................................................................................................... 2
2.3 Proposed Project Improvements ........................................................................................ 2
III. EXISTING DRAINAGE BASIN AND STORMWATER FACILITIES ........................................................... 4
3.1 Existing Basin Characteristics .............................................................................................. 4
3.2 Existing Stormwater Facilities ............................................................................................. 6
IV. DRAINAGE DESIGN CRITERIA ........................................................................................................... 7
4.1 Hydrologic Criteria .............................................................................................................. 7
4.2 Hydraulic Criteria ................................................................................................................ 7
4.3 Directly Connected Impervious Area (DCIA)/Stormwater Quality Management ............... 8
4.4 Low Impact Development (LID) Criteria ............................................................................. 9
4.5 Floodplain Regulations Compliance .................................................................................. 10
V. DRAINAGE FACILITY DESIGN .......................................................................................................... 11
5.1 Proposed Project Conditions ............................................................................................ 11
5.2 Fully Developed Project Conditions .................................................................................. 14
VI. SEDIMENT/EROSION CONTROL ..................................................................................................... 16
VII. CONCLUSIONS ................................................................................................................................ 17
VIII. REFERENCES ................................................................................................................................... 18
LIST OF FIGURES
Figure 2.1 Site Map for the Poudre River Whitewater Project ............................................................ 3
Figure 3.1 Effective FIRM Panel with Project Area .............................................................................. 5
LIST OF APPENDICES
Appendix A: Hydrologic and Hydraulic Documentation
Appendix B: Proposed Project Conditions Information and SWMM Results
Appendix C: Fully Developed with Project Conditions Information and SWMM Results
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I. INTRODUCTION
In October 2014, the City of Fort Collins completed the Poudre River Downtown Masterplan,
which covered approximately three miles of the Cache la Poudre River corridor from Shields Street to
Mulberry Street. The mission statement for this masterplan was “to plan and design integrated, and to
the extent possible, mutually supportive improvements related to habitat, recreation, and flood
mitigation.” The Poudre River Whitewater Park Project encompasses the vision that was set forth in Reach
3 (Museum of Discovery to BNSF Railroad) of the Downtown Masterplan. Improvements associated with
the project include: flood mitigation, wildlife habitat and ecological restoration including fish passage,
pedestrian access to and over the Cache la Poudre River, and outdoor recreational activities that include
whitewater river features for kayaking. The following report documents the procedures, assumptions,
and data utilized in preparing the drainage, erosion control, and water quality design for the Poudre River
Whitewater Park Project.
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II. PROJECT LOCATION AND INFORMATION
2.1 Project Location
A site map for the project area has been provided as Figure 2.1. The project area is located in
Sections 11 and 12, of Township 7N, Range 69W of Larimer County, Colorado and is located entirely within
the limits of the City of Fort Collins. As illustrated on Figure 2.1, the project area is generally bounded by
Vine Drive on the north, the Union Pacific Railroad on the west, the Cache la Poudre River on the south,
and the Burlington Northern and Santa Fe (BNSF) Railroad on the east. The project area encompasses
approximately 13.3 acres of land that is currently, or will soon be owned, by the City of Fort Collins. Xcel
Energy owns a natural gas regulation station just north of the river and west of the BNSF Railroad that is
excluded from the project area.
2.2 Topographic Mapping
All data utilized for this project is vertically referenced to the North American Vertical Datum of
1988 (NAV88). Detailed ground survey of the project area was collected by King Surveyors in 2015 and
2016. Outside of the project area, the ground survey information was supplemented with 1-foot
topographic mapping developed from LiDAR data that was collected by Ayres Associates in May 2013 for
the City of Fort Collins and Larimer County. The nearest City of Fort Collins benchmark to the project area
is Benchmark 1-00, which is located on a catch basin at the southeast corner of Vine Drive and College
Avenue.
2.3 Proposed Project Improvements
The proposed project consists of the following improvements:
• Cache la Poudre River Channel Improvements – Whitewater and grade control features will
be added upon removal of the Coy Ditch diversion dam and boat chute to provide flood
mitigation, fish passage, and increase recreational opportunities.
• Pedestrian Access – trails and a new pedestrian bridge will be added to connect the project
to surrounding areas and provide access to the river.
• Vine Drive – street improvements, including vertical curb, gutter, parallel parking, and storm
drainage facilities will be added on the south side of Vine Drive.
• Parking Lots – A 35 space parking lot will be constructed during Phase 1. An additional 27
parking spaces will be added as part of a second phase based on parking needs and funding.
• Stormwater Outfall and Water Quality Treatment – A storm sewer system and outfall to the
river will be added to provide water quality treatment and conveyance of rainfall-generated
runoff to the river.
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Figure 2.1 Site Map for the Poudre River Whitewater Project.
Ca
c
he
La Po
u
dre
R
iver
Vine Dr
Linden Street
Cherry St
College Ave
Project Area
Union Pacific Railroad
Burlington Northern Railroad
Jerome St
0 250 500 1,000
Feet
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III. EXISTING DRAINAGE BASIN AND STORMWATER FACILITIES
The project site lies within the Cache la Poudre River Basin. The Cache la Poudre River has its
origins in the Rocky Mountains, in both Roosevelt National Forest and Rocky Mountain National Park,
located west of the City of Fort Collins, Colorado. The river conveys flows from the mouth of the Poudre
Canyon, southeast to its confluence with the South Platte River east of Greeley, Colorado. The Cache la
Poudre River is regulated by the Federal Emergency Management Agency (FEMA) as part of the National
Flood Insurance Program (NFIP). The Effective Flood Insurance Rate Map (FIRM) for the project is
#08069C0977G, dated June 17, 2008. As illustrated on Figure 3.1, the majority of the project area is
situated within the effective 1-percent annual chance (100-year) floodplain (Zone AE) and the
southwestern portion of the project site located within the floodway.
3.1 Existing Basin Characteristics
The proposed project area includes the western portion of the Gustav Swanson Natural Area and
approximately 970 linear feet of the Poudre River. The site consists of residential/commercial property
along Vine Drive, with open space between these properties and the river. The abandoned Coy Ditch runs
through the middle of the property and previously fed the two man-made ponds, which are referred to
as the Eastern and Western Coy Ponds throughout this report. An existing stormwater retention pond is
the located in northeastern corner of the project site and retains stormwater runoff from the
Inverness/Innosphere development properties located on the north side of Vine Drive.
In general, the site is relatively level with an approximate 1.0%-0.50% slope towards the Cache la
Poudre River. Existing vegetation of the site consists of upland herbaceous, sub-canopy, riparian forest,
and developed land. Additionally, there are four wetland areas located along the Coy Ditch/Ponds. The
vegetation of the site and wetland areas were classified as part of the ecological characterization study
(ECS) that was conducted by Biohabitats and submitted to the City as part of the development review
process for this project. Due to the extensive river work and small impact to existing wetland areas, the
procurement of a 404-permit from the U.S. Army Corps of Engineers (ACOE) will be required prior to
construction. It is noted that an initial 404-permit application was submitted to the ACOE on November
2, 2016, with a revised submittal application provided on April 4, 2017. Reference is made to the 404-
permit application and supplemental information prepared by Ecology and Environment, Inc.
Existing soils general consist of a thin layer of top soil that overlays silty/clayey sands and gravels.
Depth to groundwater varies throughout the site, with general depths of 5-10 feet. Due to the proximity
to the river and coarse soil material, groundwater depths fluctuate seasonally. Depth to bedrock also
varies throughout the site, but is generally located at depths of 15-20 feet. Reference is made to the soils
report for the project developed by Earth Engineering Consultants (EEC) Inc called “Subsurface Exploration
Report, proposed City of Fort Collins’ – Poudre River Whitewater Park and Vine Drive Roadway
Improvements” December 8, 2016.
Figure 3.1 Effective FIRM Panel with Project Area.
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Legend
Project Area
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3.2 Existing Stormwater Facilities
Existing site drainage generally consists of overland flow from north to south. Off-site drainage
enters the project site from properties north of Vine Drive. The majority of rainfall-generated runoff in
this basin is conveyed as overland flow and is captured by the Coy Ditch, or the adjacent man-made ponds
(Eastern and Western Coy Ponds). A small storm sewer system, consisting of four single valley grate inlets
and a 12-inch pipe, collects runoff from the western portion of Vine Drive and conveys it to the Western
Coy Pond. When the capacity of this system is exceeded, flow overtops Vine Drive west of Jerome Street
and is conveyed overland into the Western Coy Pond. It is presumed that most of the rainfall-generated
runoff that reaches the Coy Ditch or Coy Ponds infiltrates into the groundwater table. Flow that does not
infiltrate is conveyed off site via the Coy Ditch through a culvert underneath the BNSF railroad.
As part of the Inverness Innovation Park (Innosphere) development, a storm sewer system was
installed on Vine Drive, east of Jerome Street, to collect and convey runoff generated from a 100-year
rainfall event into a retention pond located on the south side of Vine Drive. The pond was sized to retain
and infiltrate the entire 100-year runoff volume from both the currently developed Innosphere site and
future development located to the east of the Innosphere site. It is noted that the future development
property located to the east of the existing Innosphere building currently drains to an existing 18-inch
storm drain pipe underneath Vine Drive that discharges to an open channel swale. This swale drains to
the Coy Ditch through an existing culvert underneath the BNSF railroad. However, the three 24-inch storm
drainage pipes that cross Vine Drive and drain into the retention pond, which were installed as part of the
Inverness development, are intended to convey runoff from the future development of the property
located to the east of the Innosphere building.
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IV. DRAINAGE DESIGN CRITERIA
The City of Fort Collins Stormwater Criteria Manual and Construction Standards were utilized to
develop the design for this project. Due to the abandonment of the Coy Ditch as a conveyance system for
irrigation water, it was learned early in the design phase of this project that the City Stormwater
Department was investigating the potential of plugging the Coy Ditch culvert at the BNSF railroad to
reduce potential flooding of downstream properties caused by the ditch capturing excess
stormwater/Poudre River flood flows west of the BNSF. It was realized that the design of the Poudre River
Whitewater Park project could help alleviate potential local drainage issues that would be created by the
plugging of the Coy Ditch culvert. Therefore, in partnership with the City Stormwater Department, it was
decided that the EPA SWMM 5.0 model would be utilized to develop a small Stormwater Masterplan for
the localized drainage basin.
4.1 Hydrologic Criteria
For the this study, the project area was delineated into 14 drainage basins for determining flow
rates at specific design locations. The rainfall intensity-duration-frequency curves provided in Table RA-9
from the City Stormwater Criteria Manual were utilized in the EPA-SWMM 5.0 model to generate basin
runoff. Percent imperviousness was calculated based on aerial imagery and proposed site improvements.
Basin slopes were calculated based on topographic information. Hydrologic input parameters for the
project are summarized and provided in Appendix A.
4.2 Hydraulic Criteria
The proposed hydraulic design for this study follows the Stormwater Criteria Manual and
Construction Standards for all improvements. The EPA SWMM 5.0 model was utilized to generate and
route basin runoff through the project site. Proposed conveyance element sizes and slopes were
developed based on an iterative process to meet criteria. Detention element areas/volumes were
obtained from topographic mapping. Per criteria, Urban Drainage’s UDInlet was utilized to determine the
capacity of existing inlets and to size proposed inlets. UDBMP was also utilized to determine the water
quality capture volume for the proposed retrofit of the Inverness retention pond to a traditional extended
detention water quality pond. Hydraulic documentation and spreadsheet calculations are provided in
Appendix A.
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4.3 Directly Connected Impervious Area (DCIA)/Stormwater Quality Management
The Urban Drainage and Flood Control District (UDFCD) recommends a Four-Step Process for
reducing the impacts of urban runoff and effectively designing stormwater quality BMPs. This section
describes the UDFCD Four-Step Process and how it was applied to the current project.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanized areas, implement Low
Impact Development (LID) strategies, including measures to "minimize directly connected impervious
areas" (MDCIA). These practices reduce unnecessary impervious areas and route runoff from impervious
surfaces over permeable areas to slow runoff (increase time of concentration) and promote onsite storage
and infiltration (Urban Storm Drainage Criteria Manual, Volume 3 – Best Management Practices, UDFCD,
2010).
Increased impervious area within the project site has been minimized to the extent possible, being
limited to the proposed parking lot near the northeast corner of the site, widening of the south side of
Vine Drive, the sidewalk along Vine Drive, and several concrete trails. All runoff emanating from the
parking lot, Vine Drive and the sidewalk along Vine Drive, as well as many of the trails, will be pre-treated
with Snout Hood BMPs in stormwater inlets and/or conveyed through grass-lined swales and non-
regulatory wetland areas prior to being released to the Poudre River. Utilizing new drainage swales,
enhanced wetland areas of the Coy Ponds, and an enhanced wetland corridor along the abandoned Coy
Ditch will reduce runoff volumes, peak flow rates, and pollutant loads entering the Poudre River.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume (WQCV) with Slow Release
After runoff has been reduced, the remaining runoff must be treated through capture and slow
release of the WQCV. WQCV facilities may provide both water quality and runoff reduction benefits,
depending on the BMP selected (Urban Storm Drainage Criteria Manual, Volume 3 – Best Management
Practices, UDFCD, 2010).
The existing retention pond near the northeast corner of the project site is being reconfigured to
provide a WQCV with a metered release which has been designed to accommodate street runoff and the
parking lot expansion which will be constructed during Phase 2 of this project. In addition, runoff directed
into existing wetland areas associated with the Coy Ponds will slow runoff, promote infiltration, and
provide water quality treatment.
Step 3: Stabilize Drainageways
During and following urban development, natural drainageways are often subject to bed and bank
erosion due to increases in the frequency, rate, duration, and volume of runoff. Although Steps 1 and 2
help to minimize these effects, some degree of drainageway stabilization is required (Urban Storm
Drainage Criteria Manual, Volume 3 – Best Management Practices, UDFCD, 2010).
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All drainage swales within the project area have been designed such that stabilization can be
provided by vegetative cover, which will be beneficial in terms of maximizing the effectiveness in
disconnecting impervious surfaces. Stabilization will be provided in the form of buried rock riprap at the
outlets of culverts, as well as along the sill of the emergency spillway serving the water quality pond.
Step 4: Implement Site Specific and Other Source Control BMPs
Frequently, site-specific needs or operations require source control BMPs. This refers to
implementation of both structural and procedural BMPs (Urban Storm Drainage Criteria Manual, Volume
3 – Best Management Practices, UDFCD, 2010).
In addition to the LID and BMP strategies identified above that will be implemented throughout
the project area, source pollution will be controlled using the following methods. All proposed inlets will
be constructed with recessed floors to trap sediment generated from Vine Drive and the proposed parking
lot. These inlets will also be fitted with Snout Hoods to minimize the potential for trash and other debris,
as well as greases and oils, from passing downstream into the vegetated swales and wetlands. It is
anticipated that these inlets will be maintained by City Stormwater maintenance crews. It is noted that
the contractor will be responsible for the implementation and maintenance of BMPs during construction.
4.4 Low Impact Development (LID) Criteria
Per City of Fort Collins development criteria, 50% of newly added or modified impervious area
must be treated by LID techniques and 25% of new paved areas must be pervious or 75% of all newly added
or modified impervious area must be treated by LID techniques. Since this project is not proposing to
install pervious pavement, 75% of all newly added or modified impervious area will be treated by LID
techniques. LID/water quality treatment requirements will be met through the use of a new water quality
pond and enhancements to wetland areas associated with the Coy Ditch and Ponds. Per previous
discussion with City Stormwater and Environmental Planning staff, the proposed enhancement of the
existing wetland areas associated with the Coy Ditch and Coy Ponds will meet the City’s LID requirements
for this project.
The project proposes to add 69,550 square feet (sf) of new impervious area that is associated with
the concrete trails, walks, and parking lot (both Phase 1 and 2). Runoff from the entire Phase 2 parking
lot, 10,515 sf, will be pre-treated with a Snout Hood BMP, prior to being discharged into the proposed
water quality pond for additional treatment. Water released from the water quality pond will receive
even further treatment as it is conveyed along the wetland channel of the Coy Ditch and into the wetlands
of the Eastern Coy Pond that will be enhanced as part of this project. Runoff from the entire Phase 1
parking lot, 22,855 sf, will also be pre-treated with a Snout Hood BMP prior to being discharged into the
enhanced wetlands of the Coy Ditch and Eastern Coy Pond, and ultimately released to the river. In
addition, runoff from 26,110 sf of concrete trail and walk will be pre-treated with natural grass buffers
and swales, prior to being conveyed into the enhanced wetlands of the Coy Ponds.
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In total, 56,225 sf (81%) of the new or modified impervious area proposed by the project will be
treated with a water quality pond and/or enhancements to existing wetland areas along the Coy Ditch
and Coy Ponds. Thus, meeting the City development criteria for LID techniques.
4.5 Floodplain Regulations Compliance
As illustrated on Figure 3.1 (FRIM Panel #08069C0997G), the majority of the project area is
situated within the effective 1-percent annual chance (100-year) floodplain (Zone AE) and the
southwestern portion of the project site located within the floodway. Due to the project’s proposed
improvements within the floodplain and floodway, the procurement of a Conditional Letter of Map
Revision (CLOMR) from FEMA and a floodplain use permit from the City will be required prior to the
initiation of construction. It is noted that information necessary to support the CLOMR and Floodplain
Use Permit will be submitted as part of a separate report entitled “Hydraulic Analysis of the Cache la
Poudre River Between Linden Street and the Lake Canal Diversion Dam (Prepared in Support of a
Conditional Letter of Map Revision for the Poudre River Whitewater Park)”.
In addition to federal floodplain regulations, the project will be required to meet the requirements
and regulations set forth in Chapter 10 of the City Code. A completed “City of Fort Collins Floodplain
Review Checklist for 50% Submittals” has been included in Appendix B. Floatable project infrastructure
(trash cans, benches, park equipment, bike racks, etc…) located within the floodplain will be anchored per
an approved plan as part of the floodplain use permit. After construction of the project has been
completed and as-built survey has been collected, a Letter of Map Revision (LOMR) will be prepared and
submitted to the City and FEMA for review and approval.
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V. DRAINAGE FACILITY DESIGN
In general, the concept of the drainage facility design for this project was to create an outfall for
the drainage basin that would be capable of safely conveying runoff generated from a 100-year rainfall
event on the basin to the Poudre River with no adverse impact to existing or proposed facilities. The
proposed design will utilize the existing infrastructure to the fullest extent possible to convey and detain
stormwater flows. New inlets, storm sewer pipes, and open channels are proposed to collect and convey
water from the Vine Drive street improvements. In addition, the project proposes modifications to the
existing Innosphere retention pond to maintain water quality treatment while providing room for a future
parking lot and proposes a new storm sewer outfall to the Poudre River.
5.1 Proposed Project Conditions
A half-size copy of the Utility Plans has been provided in Appendix B. A figure depicting the
proposed project condition subbasin and conveyance elements is provided as Sheet 1 in Appendix B.
Tabular results from the proposed project condition EPA SWMM model have also been provided in
Appendix B. Electronic copies of the fully developed project condition EPA SWMM models are provided
as digital data on the disk included with this report. A description of proposed project improvements is
provided below:
• Vine Drive Storm Sewer Improvements: The capacity of the existing storm sewer system
west of Jerome Street was estimated at approximately 4 cfs (1 cfs per inlet). Therefore,
rainfall events that generate flows in excess of 4 cfs will pond along the street and overtop
Vine Drive at its low point, located to the west of Jerome Street. Based on the results of the
SWMM model this will occur for events less than the 2-year, which violates street drainage
criteria. Proposed project improvements associated with Vine Drive include the construction
of vertical curb and gutter along the south side of the road. In order for the proposed
improvements to meet criteria, new inlets and a storm sewer system will be installed. Due to
the widening of the street cross section as part of the project, the existing inlet on the south
side of the road will be removed, relocated and replaced with a standard 5-foot Type R inlet.
The existing 12-inch pipe that conveys flow from the existing inlet to the Western Coy Pond
will be filled and abandoned in place. The existing 12-inch pipe under Vine Drive will be
extended to the new inlet and a new 18-inch storm sewer pipe will be installed to convey flow
from the inlet eastward to the proposed storm water conveyance channel/grass-lined and
vegetated swale. A new inlet and 18-inch storm sewer pipe will also be installed at the
proposed sump location in Vine Drive to capture and convey flow to the conveyance channel.
The bottom of the new inlets will be suppressed and a Snout Hood BMP will be installed to
provide initial water quality treatment with respect to floatable debris and sediment. Based
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on the results of the SWMM model, the proposed design will capture and convey the 100-
year event that is tributary to these inlets from the south side of the road. It is noted that
excess flows from the north of the road will continue overtop Vine Drive. Flows exceeding
the capacity of the system will overtop the curb/sidewalk and be discharged into the storm
water swale. It is further noted that drainage improvements to the north side of Vine Drive
were outside the scope of this project. However, as discussed in Section 5.2 of this report,
the proposed drainage facilities were designed to accommodate peak flow rates associated
with future fully developed conditions.
• Poudre River Trail Culverts: Flow captured by the Vine Drive Storm Sewer system will be
conveyed to the Western Coy Pond via an open stormwater channel. The channel will be
vegetated with plantings that will further promote water quality treatment and the removal
of pollutants. Prior to discharging into the Western Coy Pond, the channel will be piped
underneath the proposed Poudre River trail. To eliminate trail overtopping, the culverts were
designed to pass the 100-year event, which required two 24-inch culverts to accommodate
cover constraints. Flows in excess of the 100-year will overtop the trail and be conveyed into
the Western Coy Pond.
• Innosphere Retention Pond Modifications: As previously mentioned, the pond associated
with the Inverness development was sized to retain the 100-year volume from the two
development properties located on the north side of Vine Drive. Due to the proposed project
improvements, an adequate outfall can now be constructed for the pond. Consequently, the
project is proposing to modify the existing pond from a full retention pond to a water quality
pond with overflow spillway to allow the western half of the existing pond to be filled and
reserved for a future parking lot. It is noted that the pond property is privately owned by the
Inverness developers, but the City Stormwater Department is currently in negotiations to
acquire the pond and take over maintenance obligations as part of this project. Assuming the
City is successful in acquiring the pond parcel, it has been discussed that the conversion of
the retention pond to a water quality pond would be acceptable. Documentation utilized to
size the water quality capture volume of the proposed modified pond is provided in Appendix
A. Other identified improvements to the existing pond include the rerouting of flow from the
adjacent stormwater swale into the pond so that stormwater flows can be diverted from the
Coy Ditch and the culvert underneath the BNSF railroad can be plugged. It is noted that these
improvement, if implemented, would be constructed separately by the City Stormwater
Department.
• Parking Lot: The proposed parking lot will be constructed in two phases. The first phase, a
35-space parking lot, will be constructed as part of the initial project. A 5-foot Type R inlet
and 18-inch storm sewer is proposed to collect runoff from the Phase 1 parking lot and convey
it to the existing Coy Ditch/Eastern Coy Pond. The bottom of the new inlet will be suppressed
and a Snout Hood BMP will be installed to provide initial water quality treatment with respect
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to floatable debris and sediment. The system was designed to convey the 100-year rainfall
runoff from the parking lot. Flows in excess of the 100-year will overtop the curb/sidewalk
and be discharged into the existing Coy Ditch/Eastern Coy Pond.
The second phase, a 27-space parking lot located to the east of the first phase, will be
constructed at a future date based on parking needs and funding. Similar to the first phase
parking lot, a 5-foot Type R inlet and 18-inch storm sewer pipe is proposed to collect runoff
from the Phase 2 parking lot and convey it to the proposed water quality pond. The existing
15-inch ADS storm sewer that collects water from an inlet on Vine Drive and discharges into
the retention pond will be extended and connected into the proposed inlet box. The bottom
of the new inlet will be suppressed and a Snout Hood BMP will be installed to provide initial
water quality treatment with respect to floatable debris and sediment. The system was
designed to convey the 100-year rainfall runoff from the parking lot.
• Outfall to River: Proposed project improvements include the installation of a 27-inch and 18-
inch storm sewer pipe to convey flow from the Western and Eastern Coy Ponds, respectively,
to the river. To limit impacts to the river and reduce construction costs, a junction box is
proposed to combine the two pond outlet pipes into a single 36-inch pipe that will outfall to
the northern river bank. The outfall system was designed to convey the 100-year event
assuming no tailwater impacts due to river levels. To prevent the surcharging and flooding of
the outfall system due to high river levels, flap gates are proposed to be installed on the
downstream ends of the 27-inch and 18-inch storm sewer pipes inside the junction box. It is
anticipated that these flap gates will reduce the capacity of the drainage system as river levels
rise until a level is reached where the flap gates will no longer be operational. For this scenario
and for flow events that exceed the capacity of the system, overtopping of both the Western
and Eastern Coy Pond will occur. Overtopping flows will not be concentrated and will
generally flow overland and return to the river where the northern bank will be lowered
adjacent to the Xcel regulation station. It is anticipated that the river will overtop its banks
and completely inundate the entire drainage system for flow events in excess of the 10-year
discharge (approximately 5,800 cfs).
• Future Restroom: Due to funding constraints and floodplain regulations, a permanent
restroom will not be installed as part of this project. However, a fill pad will be constructed
in the northwestern corner of the site to elevate the existing ground above the proposed post-
project base flood elevation for the future restroom. As identified on the Floodplain Plan
provided as part of the Utility Plan drawings, the proposed base flood elevation at the future
restroom location is 4964.0 NAVD88. The proposed elevation of the fill pad is 4966.0,
approximately 2-feet above the proposed base flood elevation. When the LOMR for the
project has been approved, the fill pad will be located above/outside the 100-year floodplain
and will eliminate future floodplain permitting and regulations associated with the
construction of the permanent restroom.
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• Poudre River Pedestrian Bridge: As part of the City’s masterplan for the Poudre River Trail
system, the trail will eventually be relocated to the northern side of the river between Linden
Street and the BNSF Railroad when improvements to the Linde Street Bridge are
implemented. In order to reconnect Poudre River trail users with the current trail as it passes
underneath College Avenue, and to provide a pedestrian connection across the river for
residents and businesses in northern Fort Collins, a new pedestrian bridge will be installed
across the Poudre River as part of the project. The bridge will be 185-feet long and 15-feet
wide. As identified on the Floodplain Plan provided as part of the Utility Plan drawings, the
low chord elevation of the bridge (4964.0 NAVD88) will be located approximately 0.5-feet
above the proposed/post-project base flood elevation of 4963.5. The bridge will also span
the proposed/post-project floodway limits and a minimum 8-foot clearance will be provided
between the low chord and proposed trails beneath the bridge. Since the bridge will be
located above the base flood elevation, it will be designed as a non-breakaway bridge and will
be incorporated into the hydraulic modeling conducted for the CLOMR/LOMR as part of this
project.
5.2 Fully Developed Project Conditions
Based on coordination with City stormwater staff, it was decided that a fully developed condition
scenario would be developed to evaluate the sizing of proposed project infrastructure to accommodate
fully developed conditions, as well as generate a conceptual drainage plan for future improvements. A
figure depicting the fully developed project condition conveyance elements is provided as Sheet 2 in
Appendix C. Tabular results from the fully developed project condition EPA SWMM model are also
provided in Appendix C. Electronic copies of the fully developed project conditions EPA SWMM models
are provided as digital data on the disk included with this report. A description of the fully developed
proposed project condition is provided below:
• Fully Developed Basins and Conceptual Detention Ponds: Subbasins 9, 11, 13, and 14 were
assumed to be fully developed with increased impervious areas. Per the direction of City
Stormwater staff, conceptual detention ponds were assumed for the three privately owned
properties located north of Vine Drive (Subbasins 9, 11, and 14) to detain and release fully
developed 100-year flows to a 2-year historic rate. It is noted that the conceptual detention
ponds were simulated with a two-point rating curve. Conceptual detention for Subbasin 13
was not assumed per the development agreement between the City and the developer for
this property. Fully developed flows from this basin will be conveyed underneath Vine Drive
and into the water quality pond via the existing storm sewer system that was installed as part
of the Innosphere development (Subbasin 12).
COFC18.1 Drainage Report (June 6 2017).docx 15 Anderson Consulting Engineers, Inc.
• Conceptual Future Vine Drive Improvements: In order to meet stormwater criteria, a 5-foot
Type R inlet was conceptually assumed in the sump area on the north side of Vine Drive. Flow
collected by this inlet, along with the detained released from Subbasins 9 and 11 is
conceptually conveyed underneath Vine Drive in an 18-inch pipe. This pipe conceptually
connects to the inlet on the south side of the street and into the storm drainage system
proposed by the project. The installation of the inlet on the north side of the street will reduce
the frequency of road overtopping for events less than the 50-year.
COFC18.1 Drainage Report (June 6 2017).docx 16 Anderson Consulting Engineers, Inc.
VI. SEDIMENT/EROSION CONTROL
Permanent BMP Snout Hoods will be installed inside all stormwater inlets that are proposed for
the project. The Snout Hoods will capture the majority of sediment that could potentiality enter the site
from the western portion of Vine Drive and the proposed parking lot. The existing Inverness retention
pond located in the northeastern corner of the site will be modified to provide water quality treatment
and will act as a sediment basin for sediment entering the site from the Inverness/Innosphere
development properties and the future parking lot. It is noted that the Snout Hoods and water quality
pond will provide pre-treatment of almost all offsite runoff from impervious surfaces. The use of the
existing Coy Ditch and associated ponds for stormwater conveyance will provide an opportunity for
further water quality treatment prior to runoff being discharged to the river.
During construction, erosion control measures will be implemented in accordance with the
Colorado Department of Public Health Stormwater Discharge Permit and City of Fort Collins construction
standards. It is noted that construction of the project will be conducted as part of the Construction
Manager/General Contractor (CMGC) delivery method. A separate report entitled “Erosion
Control/Stormwater Management Plan for Poudre River Whitewater Park” June 6, 2017 provides detailed
information with respect to the development and implementation of a stormwater management plan for
the project. This report was developed as part of a joint effort between Anderson Consulting Engineers
and ECI, the selected general contractor for the project.
COFC18.1 Drainage Report (June 6 2017).docx 17 Anderson Consulting Engineers, Inc.
VII. CONCLUSIONS
Based on the hydrologic and hydraulic analysis documented in this report, the proposed
stormwater drainage design conforms to the City of Fort Collins stormwater criteria manual and Standard
Construction Specifications. The proposed stormwater drainage system will safely convey runoff
generated from a 100-year rainfall event on the basin to the Poudre River with no adverse impact to
existing or proposed facilities. The proposed inlet Snout Hoods and water quality pond will capture
sediment from off-site flows and provide initial water quality treatment. The use and enhancement of
the wetlands associated with the existing Coy Ditch and Coy Ponds for stormwater conveyance will
provide an opportunity for infiltration and additional water quality treatment prior to runoff being
discharged to the river.
COFC18.1 Drainage Report (June 6 2017).docx 18 Anderson Consulting Engineers, Inc.
VIII. REFERENCES
Anderson Consulting Engineers, Hydraulic Analysis for the Cache la Poudre River Between Linden Street
and the Lake Canal Diversion Dam (Prepared in Support of a Conditional Letter of Map Revision
for the Poudre River Whitewater Park), Draft, April 11, 2017.
Anderson Consulting Engineers and ECI, Erosion Control/Stormwater Management Plan for Poudre River
Whitewater Park Project, June 6, 2017
Biohabitats, Ecological Characterization Study of Poudre River Whitewater Park, November 2016.
Biohabitats, Poudre River Whitewater Park Ecological Characterization Study: Addendum for 101 East Vine
Drive (the Krush Property), January 2017.
City of Fort Collins, Stormwater Criteria Manual (Amendments to the Urban Drainage and Flood Control
District Manual), December 2011
City of Fort Collins Stormwater Construction Standards and Details
Earth Engineering Consultants, Inc., Subsurface Exploration Report, Proposed City of Fort Collins’ – Poudre
River Whitewater Park and Vine Drive Roadway Improvements, December 2016
Ecology and Environment, Inc., Application for Department of the Army Pert (33 CFR 25) Poudre River
Whitewater Park, Fort Collins, Colorado: Supplement to Engineering Form 4345, Final Draft, April
4, 2017
United States Environmental Protection Agency, National Risk Management and Research Laboratory,
Storm Water Management Model, Version 5.1.010, 2015.
Urban Drainage and Flood Control District, Urban Storm Drainage Criteria Manual, Volumes 1 and 2,
Updated January 2016, Volume 3 Updated November 2015.
APPENDIX A
HYDROLOGIC AND HYDRAULIC
DOCUMENTATION
Basin Name Area (ac)
Width
(ft)*
OFL (ft) % Slope
% Impervious
(Proposed
Conditions)
% Impervious
(Fully Developed)
Description for Fully Developed Condition
B-1 2.78 1211 100 2.00 60 60 Assumes 100% impervious for ponded area
B-2 3.34 1455 100 3.00 50 50 Assumes 100% impervious for ponded area
B-3 0.56 76 320 1.20 90 90
B-4 0.35 152 100 0.50 90 90
B-5 0.80 290 120 2.00 75 75
B-6 0.33 287 50 2.00 75 75
B-7 1.38 194 310 1.00 50 50 Assumes 100% impervious for ponded area
B-8 0.74 101 320 1.20 90 90
B-9 4.68 371 550 1.00 45 85 Assumes property is fully developed
B-10 1.50 163 400 0.90 90 90
B-11 0.89 194 200 0.50 45 85 Assumes property is fully developed
B-12 2.50 573 190 4.40 85 85
B-13 2.77 710 170 1.00 25 85 Assumes property is fully developed
B-14 2.51 497 220 0.50 25 85 Assumes property is fully developed
*Width is calculated from area and Overland Flow Length (OFL)
SWMM MODEL INPUT PARAMETERS
Stage AutoCAD AutoCAD Unit Total Total Stage AutoCAD AutoCAD Unit Total Total
(NAVD 88) Area Area Depth Volume Volume (NAVD 88) Area Area Depth Volume Volume
(ft) (ft2) (acre) (ft) (ft3) (acre-ft) (ft) (ft2) (acre) (ft) (ft3) (acre-ft)
4955.5 9407 0.22 0.0 N/A N/A 4953 0 0.00 0.0 N/A N/A
4956 14280 0.33 0.5 5880 0.13 4954 2450 0.06 1.0 817 0.02
4957 23013 0.53 1.5 23567 0.54 4955 13074 0.30 2.0 7878 0.18
4958 33813 0.78 2.5 51807 1.19 4956 26934 0.62 3.0 27469 0.63
4958.5 40100 0.92 3.0 68929 1.58 4957 39506 0.91 4.0 60489 1.39
Spill will occur over trail at southeast corner at El. = 4958.5 4958 65918 1.51 5.0 112641 2.59
4958.5 79822 1.83 5.5 149020 3.42
Spill will occur south towards river at El. = 4958.5
Stage AutoCAD AutoCAD Unit Total Total Stage AutoCAD AutoCAD Unit Total Total
(NAVD 88) Area Area Depth Volume Volume (NAVD 88) Area Area Depth Volume Volume
(ft) (ft2) (acre) (ft) (ft3) (acre-ft) (ft) (ft2) (acre) (ft) (ft3) (acre-ft)
4955.2 0 0.00 0.0 N/A N/A 4955 0 0.00 0.0 N/A N/A
4956 3422 0.08 0.8 913 0.02 4958.99 0 0.00 3.99 0 0.00
4957 5120 0.12 1.8 5155 0.12 4959 111 0.00 4.0 0 0.00
4958 6570 0.15 2.8 10985 0.25 4960 3706 0.09 5.0 1486 0.03
4959 9153 0.21 3.8 18811 0.43 4961 23896 0.55 6.0 13824 0.32
4960 11700 0.27 4.8 29211 0.67 4961.4 33722 0.77 6.4 25291 0.58
Weir for WQCV set at El. = 4958.0
Detention Node #1 (Western Coy Pond) Detention Node #2 (Eastern Coy Pond)
Detention Node #3 (Modified Innosphere Pond) Detention Node #4 (Existing Parking Lot)
PROPOSED CONDITION DETENTION NODE STORAGE CURVES
Input Parameters from SWMM Model Results
Q100 40 cfs SWMM Node = P-1 Definitions
V 5 ft/s Assumed 5 ft/sec based on vegetated soil Lp Length of Protection (ft)
At 8.0 ft2
At Required Area of Flow at Allowable Velocity (ft2)
W or D 3 ft Yt Tailwater Depth (ft)
Yt 1 ft Assumed 1 ft for tailwater on river W or D Diameter of Circular Conduits (ft)
Yt/D 0.33 θ Expansion angle of the culvert flow
Fr=Q/D2.5 2.6 V Allowable Non-Eroding Velocity in the Downstream Channel (ft/s)
Q Design Discharge (cfs)
EF Expansion Factor
Rock Size (Section 3.2.3 from Urban Drainage) T Width of Protection (ft)
Definitions Fr Froude Number
Q Design discharge (cfs) Equations
Dc Diameter of Circular Conduit At =Q/V
EF =1/(2tan(θ)) Determined Using Figure 9-35
Check: θ =tan-1(1/(2expansionfactor))
Q/Dc2.5
2.6 =<6.0 Use Figure 9-38 From USDCM Volume 2 Lp =(EF)(At/Yt-W) 3D≤Lp≤10D
T = 2(Lptanθ)+W
Q/D1.5 7.7
Yt/D 0.33 Apron Length (Section 3.2.1)
Riprap Size
d50 =(0.023Q)/(Yt1.2Dc0.3) Equation 9-16
Yt/D 0.33
d50
: 0.66 ft Q/Dc2.5
2.6
7.9 inches EF 3.8 Per chart
θ 0.13
T 8 ft Width of Protection at Furthest Downstream Point
Extent of Protection NOTE:
3W or 3D 9 Lp should be a minimum of 3W or 3D if Fr<8
Lp 19.0 Lp should be a maximum of 3W or 3D if Fr<6
Lp 19 ft If Fr>8 then Lpmin=3D+[D/4(Fr-8)]
If Fr>6 then Lpmax=10D+[D/4(Fr-6)]
Selected Riprap Size Type M (12")
Selected Riprap Width 8 ft
Selected Riprap Length 19 ft
*Note: Riprap bank protection along river will serve as
erosion protection for culvert
Per Figure 9-38: Use Type L
Poudre River Whitewater Park Project: 36" RCP Outfall to River
Per COFC Code Upsize to Type M
Input Parameters from SWMM Model Results
Q100 25 cfs SWMM Node = P-4 (divided by 2 for two pipes) Definitions
V 5 ft/s Assumed 5 ft/sec based on vegetated soil Lp Length of Protection (ft)
At 5.0 ft2
At Required Area of Flow at Allowable Velocity (ft2)
W or D 2 ft Yt Tailwater Depth (ft)
Yt 1.6 ft Based on depth of Western Coy Pond W or D Diameter of Circular Conduits (ft)
Yt/D 0.80 θ Expansion angle of the culvert flow
Fr=Q/D2.5 4.4 V Allowable Non-Eroding Velocity in the Downstream Channel (ft/s)
Q Design Discharge (cfs)
EF Expansion Factor
Rock Size (Section 3.2.3 from Urban Drainage) T Width of Protection (ft)
Definitions Fr Froude Number
Q Design discharge (cfs) Equations
Dc Diameter of Circular Conduit At =Q/V
EF =1/(2tan(θ)) Determined Using Figure 9-35
Check: θ =tan-1(1/(2expansionfactor))
Q/Dc2.5
4.4 =<6.0 Use Figure 9-38 From USDCM Volume 2 Lp =(EF)(At/Yt-W) 3D≤Lp≤10D
T = 2(Lptanθ)+W
Q/D1.5 8.8
Yt/D 0.80 Apron Length (Section 3.2.1)
Riprap Size
d50 =(0.023Q)/(Yt1.2Dc0.3) Equation 9-16
Yt/D 0.80
d50
: 0.27 ft Q/Dc2.5
6.0
3.2 inches EF 3.8 Per chart
θ 0.13
T 4 ft Width of Protection at Furthest Downstream Point
Extent of Protection NOTE:
3W or 3D 6 Lp should be a minimum of 3W or 3D if Fr<8
Lp 4.3 Lp should be a maximum of 3W or 3D if Fr<6
Lp 6 ft If Fr>8 then Lpmin=3D+[D/4(Fr-8)]
If Fr>6 then Lpmax=10D+[D/4(Fr-6)]
Selected Riprap Size Type M (12")
Selected Riprap Width 4 ft
Selected Riprap Length 6 ft
*Note: Riprap width will be doubled at a minimum
due to dual culverts
Poudre River Whitewater Park Project: Dual 24" Trail Culverts
Per Figure 9-38: Use Type L
Per COFC Code Upsize to Type M
Input Parameters from SWMM Model Results
Q100 10.2 cfs SWMM Node = P-5 (fully developed conditions) Definitions
V 5 ft/s Assumed 5 ft/sec based on vegetated soil Lp Length of Protection (ft)
At 2.0 ft2
At Required Area of Flow at Allowable Velocity (ft2)
W or D 1.5 ft Yt Tailwater Depth (ft)
Yt 1.5 ft Pipe fully submerged during 100-year W or D Diameter of Circular Conduits (ft)
Yt/D 1.00 θ Expansion angle of the culvert flow
Fr=Q/D2.5 3.7 V Allowable Non-Eroding Velocity in the Downstream Channel (ft/s)
Q Design Discharge (cfs)
EF Expansion Factor
Rock Size (Section 3.2.3 from Urban Drainage) T Width of Protection (ft)
Definitions Fr Froude Number
Q Design discharge (cfs) Equations
Dc Diameter of Circular Conduit At =Q/V
EF =1/(2tan(θ)) Determined Using Figure 9-35
Check: θ =tan-1(1/(2expansionfactor))
Q/Dc2.5
3.7 =<6.0 Use Figure 9-38 From USDCM Volume 2 Lp =(EF)(At/Yt-W) 3D≤Lp≤10D
T = 2(Lptanθ)+W
Q/D1.5 5.6
Yt/D 1.00 Apron Length (Section 3.2.1)
Riprap Size
d50 =(0.023Q)/(Yt1.2Dc0.3) Equation 9-16
Yt/D 1.00
d50
: 0.13 ft Q/Dc2.5
3.7
1.5 inches EF 6.8 Per chart
θ 0.07
T 2 ft Width of Protection at Furthest Downstream Point
Extent of Protection NOTE:
3W or 3D 4.5 Lp should be a minimum of 3W or 3D if Fr<8
Lp -1.0 Lp should be a maximum of 3W or 3D if Fr<6
Lp 4.5 ft If Fr>8 then Lpmin=3D+[D/4(Fr-8)]
If Fr>6 then Lpmax=10D+[D/4(Fr-6)]
Selected Riprap Size Type M (12")
Selected Riprap Width 2 ft
Selected Riprap Length 4.5 ft
*Note: Use this design for all 18" storm sewer pipe outlets
Poudre River Whitewater Park Project: 18" Storm Sewer Outlets
Per Figure 9-38: Use Type L
Per COFC Code Upsize to Type M
APPENDIX B
PROPOSED PROJECT CONDITIONS
INFORMATION AND SWMM RESULTS
COLLEGE AVENUE
CACHE LA POUDRE RIVER
BNSF RAILROAD
UNION PACIFIC RAILROAD
JEROME STREET
LINDEN STREET
REDWOOD STREET
VINE DRIVE
COY DITCH
COY DITCH
LAKE CANAL
LAKE CANAL
Anderson Consulting Engineers, Inc
Civil ▪ Water Resources ▪ Environmental
375 East Horsetooth Road, Building 5, Fort Collins, CO 80525
Phone (970) 226-0120 / Fax (970) 226-0121
www.acewater.com
CITY OF FORT COLLINS
POUDRE RIVER
WHITEWATER PARK
PROPOSED PROJECT
CONDITION
SUBBASIN AND
CONVEYANCE
ELEMENTS MAP
1
Basin Name Area (ac)
2-Year Peak
Runoff (cfs)
10-Year Peak
Runoff (cfs)
100-Year Peak
Runoff (cfs)
100-Year Peak
Unit
Runoff Rate
(cfs/acre)
B-1 2.78 4.78 10.46 25.64 9.2
B-2 3.34 4.81 11.13 29.33 8.8
B-3 0.56 1.17 2.29 5.20 9.3
B-4 0.35 0.84 1.59 3.43 9.8
B-5 0.80 1.69 3.41 7.71 9.6
B-6 0.33 0.72 1.52 3.25 9.8
B-7 1.38 1.79 3.55 9.15 6.6
B-8 0.74 1.54 3.03 6.87 9.3
B-9 4.68 4.96 9.90 25.23 5.4
B-10 1.50 2.77 5.64 13.23 8.8
B-11 0.89 1.07 2.14 5.65 6.3
B-12 2.50 5.94 11.45 24.63 9.9
B-13 2.77 1.99 4.65 15.18 5.5
B-14 2.51 1.75 3.69 11.02 4.4
PROPOSED CONDITION BASIN RUNOFF RESULTS
SWMM
Element
2-Year Peak
Discharge (cfs)
10-Year Peak
Runoff (cfs)
100-Year Peak
Runoff (cfs)
Description
N-7 1.1 2.1 5.7
S-4 0.8 1.7 4.7
N-6 10.0 20.1 49.9
S-3 6.9 16.9 47.0
P-7 3.0 3.0 3.0
N-5 4.2 5.3 7.4
P-6 4.1 5.2 5.7
S-2 0.0 0.0 2.0
N-4 0.8 1.6 8.0
P-5 0.8 1.5 4.9
N-3 11.8 23.6 55.2
S-1 11.1 22.1 50.2
N-2 11.1 22.1 50.2
P-4 10.6 21.2 50.2
D-1 14.4 30.2 73.8
P-3 7.8 16.4 32.5
N-10 3.7 8.3 26.2
S-6 3.3 7.3 25.0
D-4 3.3 7.3 25.0
P-10 3.4 7.7 13.5
N-9 9.2 17.0 29.5
P-9 9.1 16.9 29.5
N-8 9.1 16.9 29.5
P-8 9.0 16.8 29.4
D-3 11.4 21.8 41.7
S-5 0.6 8.9 29.3
D-2 6.5 14.5 61.9
P-2 4.1 7.8 12.2
N-1 11.1 21.9 39.8
P-1 11.1 21.9 39.8
O-1 11.1 21.9 39.8
PROPOSED CONDITION DISCHARGE RESULTS
Eastern Flow Path Western Flow Path
Out-
fall
APPENDIX C
FULLY DEVELOPED WITH PROJECT CONDITIONS
INFORMATION AND SWMM RESULTS
COLLEGE AVENUE
CACHE LA POUDRE RIVER
BNSF RAILROAD
UNION PACIFIC RAILROAD
JEROME STREET
LINDEN STREET
REDWOOD STREET
VINE DRIVE
COY DITCH
COY DITCH
LAKE CANAL
LAKE CANAL
Anderson Consulting Engineers, Inc
Civil ▪ Water Resources ▪ Environmental
375 East Horsetooth Road, Building 5, Fort Collins, CO 80525
Phone (970) 226-0120 / Fax (970) 226-0121
www.acewater.com
CITY OF FORT COLLINS
POUDRE RIVER
WHITEWATER PARK
FULLY DEVELOPED
CONDITION
SUBBASIN AND
CONVEYANCE
ELEMENTS MAP
2
Basin Name Area (ac)
2-Year Peak
Runoff (cfs)
10-Year Peak
Runoff (cfs)
100-Year Peak
Runoff (cfs)
100-Year Peak
Unit
Runoff Rate
(cfs/acre)
B-1 2.78 4.8 10.5 25.6 9.2
B-2 3.34 4.8 11.1 29.3 8.8
B-3 0.56 1.2 2.3 5.2 9.3
B-4 0.35 0.8 1.6 3.4 9.8
B-5 0.80 1.7 3.4 7.7 9.6
B-6 0.33 0.7 1.5 3.3 9.8
B-7 1.38 1.8 3.6 9.2 6.6
B-8 0.74 1.5 3.0 6.9 9.3
B-9 4.68 7.5 15.7 38.3 8.2
B-10 1.50 2.8 5.6 13.2 8.8
B-11 0.89 1.8 3.5 8.1 9.1
B-12 2.50 5.9 11.5 24.6 9.9
B-13 2.77 6.2 11.9 26.6 9.6
B-14 2.51 4.9 9.8 22.7 9.0
FULLY DEVELOPED CONDITION BASIN RUNOFF RESULTS
SWMM
Element
2-Year Peak
Discharge (cfs)
10-Year Peak
Runoff (cfs)
100-Year Peak
Runoff (cfs)
Description
D-6 1.8 3.5 8.1
P-17 0.8 0.9 1.1
N-7 0.8 0.9 1.1
P-16 0.8 0.9 1.1
D-5 7.5 15.7 38.3
P-15 3.1 3.9 5.0
N-6 1.5 3.0 7.3
S-3 0.0 0.0 4.2
N-14 2.8 5.6 16.6
S-4 0.0 0.0 7.3
P-14 2.8 5.6 6.7
N-13 5.3 7.0 9.4
P-13 5.3 7.0 9.4
P-7 1.5 3.0 3.0
N-5 2.7 5.3 7.0
P-6 2.7 5.1 5.7
S-2 0.0 0.0 1.0
N-4 6.0 8.6 12.6
P-5 6.0 8.6 10.2
N-3 8.7 13.7 22.5
S-1 7.7 12.3 20.1
N-2 7.7 12.3 20.1
P-4 7.5 11.6 18.5
D-1 10.7 20.8 40.1
P-3 6.8 12.3 23.2
D-4 4.9 9.8 22.7
P-12 1.2 1.4 1.8
N-12 1.2 1.4 1.8
P-11 1.2 1.4 1.8
N-11 1.7 1.7 1.9
P-10 1.3 2.1 2.1
N-10 6.2 11.9 26.6
S-6 5.5 11.4 26.0
N-9 12.0 23.7 50.9
P-9 12.0 20.1 50.9
N-8 12.0 20.1 50.9
P-8 11.8 20.1 50.9
D-3 14.2 24.4 63.3
S-5 2.8 12.9 44.0
D-2 6.5 19.4 76.0
P-2 4.1 8.1 11.4
N-1 9.6 19.3 32.4
P-1 9.6 19.3 32.4
O-1 9.6 19.3 32.4
FULLY DEVELOPED CONDITION DISCHARGE RESULTS
Eastern Flow Path Western Flow Path
Out-
fall