HomeMy WebLinkAboutPOUDRE RIVER WHITEWATER PARK FORMERLY DOWNTOWN PARK - PDP160039 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTVill. 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), TBD.
Biohabitats, Ecological Characterization Study of Poudre River Whitewater Park odplain Modeling Report
for the McMurray Natural Area Ecological Restoration Project — Phase 2 (Prepared in Support of
a Conditional Letter of Map), April 2013.
Ecology and Environment Inc., Application for Department of the Army Permit (33 CFR325) Poudre River
Whitewater Park Fort Collins Colorado — Supplement to Engineering Form 345 (404 Permit
Submittal), November 2016
United States Environmental Protection Agency, National Risk Management and Research Laboratory,
Storm Water Management Model, Version 5.1.010, 2015.
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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 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.
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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 final design and construction of the project will be conducted as part of the
Construction Manager/General Contractor (CMGC) delivery method. Once a contractor has been selected
for the project, a detailed approach for temporary erosion control will be developed. However, it is
anticipated that that following temporary erosion control measures will be utilized during construction of
this project:
• Staging of disturbed areas
• Silt fencing
• Vehicle tracking pads
• Bypass channels for river work
• Inlet bags/filters
• Straw bales/waddles
• Sediment basins
• Check Dams
• Terracing and mulching of slopes
• Erosion control blankets
• Dust control
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of the Innosphere development (Subbasin 12). Conceptual detention was also not assumed
for Subbasin 6, which represents the future parking lot area.
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.
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• Outfall to River: Proposed project improvements include the installation of a 30-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
prosed 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 30-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).
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 6, 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
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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: A 5-foot Type R inlet and 18-inch storm sewer is proposed to collect runoff from
the parking lot and convey it to the existing Coy Ditch/Eastern Coy Pond. 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.
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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 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
Drawings depicting the proposed site improvements and grading plan have 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 24-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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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 UDlnlet 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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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.
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.
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 man-made 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 develop meted 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.
COFC18.1 Preliminary Drainage Report (Dec 6 2016).docx 6
ANdERSON CONSULTING ENGINEERS, INC.
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COFC18.1 Preliminary Drainage Report(Dec S2016).doa S ANdERSON CONSUMING ENGINEERS, INC.
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. 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)".
3.1 Existing Basin Characteristics and Stormwater Facilities
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 the 404-permit application was submitted to the ACOE on November 2,
2016. Reference is made to the 404-permit application and supplemental information prepared by
Ecology and Environment, Inc.
COFC18.1 Preliminary Drainage Report (Dec 6 2016).docx 4 ANd ERSON CONSUITiNG ENGINEERS, INC.
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COFC18.1 Preliminary Drainage Report (Dec 6 2016).docx 3 ANdERSON CONSULTING ENGINEERS, INC.
11. 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 12.5 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 Lot — A 35 space parking lot will be added with room for future expansion.
• 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.
COFC18.1 Preliminary Drainage Report (Dec 6 2016).docx 2 ANdERSON CONSULTING ENGINEERS, INC.
i
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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IV
0
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VII
TABLE OF CONTENTS
INTRODUCTION...............................................................................................................................1
PROJECT LOCATION AND INFORMATION........................................................................................2
2.1 Project Location..................................................................................................................
2
2
2.2 Topographic Mapping .... *'**
.........................
EXISTING DRAINAGE BASIN AND STORMWATER FACILITIES...........................................................4
3.1 Existing Basin Characteristics and Stormwater Facilities....................................................4
DRAINAGEDESIGN CRITERIA............................................................................................................7
4.1 Hydrologic Criteria..............................................................................................................7
4.2 Hydraulic Criteria...............................................................................................I................7
DRAINAGEFACILITY DESIGN............................................................................................................8
5.1 Proposed Project Conditions..............................................................................................8
5.2 Fully Developed Project Conditions............................................................................I.....10
SEDIMENT/EROSION CONTROL....................................................................................................12
CONCLUSIONS.............................................................................................................................13
Vill. REFERENCES...................................................................................................................................14
LIST OF FIGURES
Figure2.1 Site Map..............................................................................................................................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
COFC18.1 Preliminary Drainage Report (Dec 62016).docx I ANd ERSON CONSULTING ENGINEERS, INC.
PRELIMINARY
DRAINAGE, WATER QUALITYAND
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 Nos. COFC18.1)
December 6, 2016
ZANdERSON CONSU[TING ENGINEERS, INC.
— Civil • N,uter Resowres • Environnnenrtnl