HomeMy WebLinkAboutBUCKING HORSE PARK - BDR210011 - DOCUMENT MARKUPS - ROUND 4 - DRAINAGE REPORT
March 9, 2022
FINAL DRAINAGE REPORT
Bucking Horse Park
Fort Collins, Colorado
Prepared for:
City of Fort Collins
Attn: Matt Schaefer
PO Box 580
Fort Collins, Colorado 80522
Prepared by:
200 South College Avenue, Suite 10
Fort Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 1748-002
This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is necessary, we recommend double-sided printing.
March 9, 2022
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Drainage and Erosion Control Report for
Bucking Horse Park
Dear Staff:
Northern Engineering is pleased to submit this Drainage and Erosion Control Report for your review.
This report accompanies the Basic Development Review (BDR) submittal for the proposed Bucking
Horse Park development.
This report was prepared in accordance with Fort Collins Stormwater Criteria Manual (FCSCM) and
serves to document the stormwater impacts associated with the proposed project. We understand
that review by the city is to assure general compliance with standardized criteria contained in the
FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
Northern Engineering Services, Inc.
Carlos Ortiz García Blaine Mathisen, PE
Project Engineer Project Engineer
Bucking Horse Park
Final Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ............................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 2
C. Floodplain.......................................................................................................................................... 3
II. DRAINAGE BASIN AND SUB-BASIN ........................................................................ 5
A. Major Basin Description .................................................................................................................... 5
B. Sub-Basin Description ....................................................................................................................... 5
III. DRAINAGE DESIGN CRITERIA ................................................................................. 5
A. Regulations........................................................................................................................................ 5
B. Development Criteria Reference And Constraints ............................. Error! Bookmark not defined.
C. Hydrological Criteria ......................................................................................................................... 6
D. Hydraulic Criteria .............................................................................................................................. 6
E. Modifications of Criteria ................................................................................................................... 6
F. Storm Management Strategy ............................................................................................................ 6
IV. DRAINAGE FACILITY DESIGN ................................................................................. 7
A. General Concept ............................................................................................................................... 7
B. Specific Details .................................................................................................................................. 8
C. LID Summary ..................................................................................................................................... 9
V. CONCLUSIONS ..................................................................................................... 10
A. Compliance with Standards ............................................................................................................ 10
VI. REFERENCES ........................................................................................................ 11
VII. EROSION CONTROL REPORT ................................................................................ 17
APPENDICES
APPENDIX A – Hydrologic Computations
APPENDIX B– Updated SWMM Model for Bucking Horse Second Filing
APPENDIX C– Hydraulic Computations
APPENDIX D– LID Sizing and Variance Request
APPENDIX E– Erosion Control Report and USDA Soils Report
LIST OF FIGURES
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2 – Proposed Site Plan ............................................................................................... 3
Figure 3 – Existing Floodplain Mapping .................................................................................. 4
MAP POCKET
Proposed Drainage Exhibit
Bucking Horse Park
Bucking Horse Park Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
Vicinity Map
A. LOCATION
1. Bucking Horse Park is located in the Southeast ¼ of Section 20, Township 7 North,
Range 68 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado. It is generally bound to the northwest by single family homes, the
east\northeast by the Great Western Railroad, the southwest by Miles Horse Avenue,
and the southeast by a daycare facility and Detention Pond 215.
2. An existing channel runs along the northeast boundary of the site parallel to the railroad
right-of-way, conveying stormwater from the surrounding area to Detention Pond 215.
Additional information regarding this swale can be found in subsequent sections.
3. Aside from the large channel that borders the site, offsite flows through the project area
are minimal. Refer to the Drainage Exhibit for offsite basin locations.
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Bucking Horse Park Drainage Report 2
B. DESCRIPTION OF PROPERTY
1. The project area is roughly 7.54± acres.
Figure 1 – Aerial Photograph
2. The subject property is an undeveloped parcel with native ground cover. The existing
ground generally slopes at moderate grades (1%–3%) from the southwest to the
northeast, towards the channel that borders the east side of the site. There is a soil
stockpile located on the southeast corner of the site.
3. A soils report (Project No. FC09343-125) was completed by CTL Thompson, Inc. on
May 8, 2020. The report contains the results of a complete geotechnical subsurface
exploration as well as pertinent geotechnical recommendations.
4. The proposed project site plan is composed of one small restroom building, numerous
park amenities, and open spaces. Please see Figure 2, on the following page, showing
the proposed site plan.
Bucking Horse Park
Bucking Horse Park Drainage Report 3
Figure 2 – Proposed Site Plan
C. FLOODPLAIN
1. The Bucking Horse Park is currently located within a FEMA Moderate Risk Flood Hazard
Area for the Cache la Poudre River. This area is designated as Zone X on Firm Panel
0992G, Revised May 2, 2012. Therefore, it falls outside of the regulated 100-year
floodway and floodplain fringe. (Figure 3 – Area Floodplain Mapping)
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Figure 3 – Existing Floodplain Mapping
It should be noted an updated floodplain map is being prepared by consultants for the
Colorado Water Conservation Board (CWCB) in coordination with the Federal Emergency
Management Agency (FEMA). This remapping is called RiskMAP. The updated mapping
will entirely remove the project site from any floodplain designations. Therefore, the
project site is not required to conform with the provisions of Chapter 10.
Figure 4 – Updated RiskMAP Floodplain Mapping
Bucking Horse Park
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II. DRAINAGE BASIN AND SUB-BASIN
A. MAJOR BASIN DESCRIPTION
The Bucking Horse Park is a part of the Foothills Drainage Basin. The Foothills Basin is
centrally located in Fort Collins and covers about 3,750 acres generally between Taft Hill
and Ziegler Road and Horsetooth Road and Drake Road. The basin is mostly developed with
commercial development and mixed-use. The basin drains from west to east through open
channels or storm sewer systems to the Fossil Creek Reservoir Inlet Ditch (FCRID).
B. SUB-BASIN DESCRIPTION
The subject property is located within the Bucking Horse Filing Two development and has
historically drained overland from southwest to northeast where runoff is detained and
treated in Detention Pond 215.
Bucking Horse Park drains to Detention Pond 215. This pond currently provides
approximately 32.4 ac-ft of storage volume. The pond also provides water quality as a 40-
hour dry extended detention basin (EDB).
The project area was modeled as part of the SWMM model for Bucking Horse Filing Two.
This model has been updated to reflect the constructed conditions within the study area and
to document the final required detention volume for Pond 215 and the peak flow for the
channel running along the east boundary of the site. (See Appendix B)
A description of the project drainage patterns follows in Section IV.B. below.
III. DRAINAGE DESIGN CRITERIA
A. REGULATIONS
Bucking Horse Park is submitting a variance request to reduce the percent of impervious
treated by LID. Please refer to variance request and subsequent LID section for additional
information.
B. ORIGINAL PROVISIONS AND PREVIOUS STUDIES
Large portions of the Bucking Horse neighborhood, including portions of Sidehill Filings 1 &
2 as well as Bucking Horse Filings 1, 2, 3 and 5 drain to Pond 215. Pond 215 is found
near the northeast corner of the Bucking Horse Park project site. Due to the size of the
drainage basin, a SWMM model was developed with the original filings to document the
overall drainage patterns in the study area.
The original SWMM model was developed by JR Engineering as part of the Sidehill
development. The SWMM model was subsequently updated with Bucking Horse Second
Filing. The purpose of the Bucking Horse Second Filing update was to document the change
in assumed impervious values from the previous models. These assumed impervious values
were reduced to be more accurate with what was being proposed during the Bucking Horse
Second Filing. This reduction in impervious reduced the amount of runoff being conveyed to
the large swale that runs parallel to the site along the northeast boundary. Bucking Horse
Second Filing showed a max conveyance of 341 cfs within the swale. Please refer to
Appendix D for snippets of the Bucking Horse Second Filing SWMM model.
Bucking Horse Park is modifying the existing swale slightly by moving the concrete pan that
runs along the bottom north to help align the swale with the future trails project by the city.
The current swale is outlet controlled near the northeast corner of the Bucking Horse Pipe
by a 36” RCP culvert. The 36” RCP culvert does not have the capacity to convey the 341
Bucking Horse Park
Bucking Horse Park Drainage Report 6
cfs therefore during the 100-yr event the runoff safely overtops the existing berm that the
36” RCP culvert is in. During the 100-year event the tailwater backs up to a height of
4889.96, as shown in the HY-8 analysis in Appendix C. The normal flow depth during the
100-year event is 2.83’, refer to Hydraflow Express analysis in Appendix C for additional
information. Therefore, at elevation 4887.13 (4889.96 – 2.83 = 4887.13) the depth
transitions from tailwater depth to normal flow depth. This elevation is shown on sheet G1
of the Bucking Horse Park Utility Plans. As shown in the Hydraflow Express analysis during
normal flow depth the swale has well over one foot of freeboard. Additionally, the revised
swale top of bank along the northside is set at an elevation of 4890.01 so during the
backwater conditions there is still no overtopping along the north bank. Please refer to sheet
G1 of the Bucking Horse Park Utility plans for additional information.
C. HYDROLOGICAL CRITERIA
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure 3.4-1 of the FCSCM, serve as the source for all hydrologic computations
associated with the proposed development. Tabulated data contained in Table 3.4-1
was utilized for Rational Method runoff calculations.
2. The Rational Method was employed to compute localized stormwater runoff utilizing
coefficients contained in Tables 3.2-1 and 3.2-2 of the FCSCM.
3. The previously approved SWMM model that was approved with Bucking Horse Filing
Two was used to size the adjacent swale that runs parallel to the project site.
4. Two separate design storms were utilized to address distinct drainage scenarios. The
first event analyzed is the “Minor” or “Initial” Storm, which has a two-year recurrence
interval. The second event considered is the “Major” Storm, which has a 100-year
recurrence interval.
5. No other assumptions or calculation methods were used with this development that are
not referenced by the current City of Fort Collins Stormwater Criteria Man.
C. HYDRAULIC CRITERIA
1. As previously noted, the subject property maintains historical drainage patterns.
2. All drainage facilities proposed with the project are designed in accordance with the
criteria outlined in the FCSCM and/or Mile High Flood District (UDFCD) Urban Storm
Drainage Criteria Manual.
3. As previously mentioned, this project is not subject to any floodplain regulations.
D. MODIFICATIONS OF CRITERIA
A variance request has been submitted with Bucking Horse Park. The variance is requesting
that LID requirements be loosened to allow for less impervious area to be treated than the
required 50% of newly modified or added impervious areas. Please refer to the subsequent
LID section for additional information as well as Appendix D.
E. STORM MANAGEMENT STRATEGY
The overall stormwater management strategy employed with the Bucking Horse Park
development utilizes the "Four Step Process" to minimize adverse impacts of urbanization on
receiving waters. The following describes how the proposed development has incorporated
each step.
Step 1 – Employ Runoff Reduction Practices.
Bucking Horse Park
Bucking Horse Park Drainage Report 7
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use to a park.
Providing large swaths of vegetated land to promote natural infiltration and filtration.
Routing runoff generated from the basketball court, ping-pong court, and some
sidewalk through a rain garden in the northeast corner of the site.
No parking lot or vehicular access paths have been proposed to help minimize the
amount of impervious area.
Step 2 – Implement Best Management Practices (BMPs) that provide a Water Quality
Capture Volume (WQCV) with slow release.
The efforts taken in Step 1 will help to minimize excess runoff from frequently occurring
storm events; however, development still generates additional stormwater runoff beyond
historical conditions. The primary water quality treatment and volume control will occur in a
detention pond previously calculated in the Bucking Horse Second Filing by Northern
Engineering, dated July 2012. However, the Bucking Horse Park is also proposing to install
a rain garden at the northeast corner of the project site. Additionally, Bucking Horse Park
has a calculated impervious area of 13% with most of the impervious area being conveyed
via overland flow over wide areas of vegetated land. This low percent impervious along with
the large amount of open space will promote natural infiltration and filtration.
Step 3 – Stabilize Drainageways.
As stated in Section III.B there is a swale that runs along the northeast project boundary.
This swale is being modified to adequately and safely convey the 341 cfs, per Bucking
Horse Second Filing, to Pond 215 which is directly southeast of the existing 36” culvert.
The drainageway will be stabilized using erosion control blankets to get vegetation stabilized
along the 4:1 slopes. Additionally, there is a 2’ concrete pan at the bottom of the swale to
convey nuisance flows to help prevent wetland development.
Step 4 – Implement Site Specific and Other Source Control BMPs.
This step typically applies to industrial and commercial developments. However, localized
trash bins with lids have been placed around the site to decrease the potential impacts
of garbage making its way downstream.
IV. DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
1. The main objectives of the project drainage design is to maintain existing drainage
patterns and ensure no adverse impacts to any adjacent properties and downstream
infrastructure.
2. Detention and traditional water quality for Bucking Horse Park are provided in Detention
Pond 215.
3. The site was broken into twelve (12) onsite basins and one (1) offsite basins for design
purposes. Anticipated drainage patterns for proposed drainage basins are described
below.
Bucking Horse Park
Bucking Horse Park Drainage Report 8
B. SPECIFIC DETAILS
Basin 1
Basin 1 is consists of sidewalks, gravel, and open areas. This basin will convey flows via
overland flow to a swale that will route the runoff to a proposed 12” HDPE culvert. From the
culvert the runoff will be conveyed to the existing swale which will route the runoff to
Detention Pond 215.
Basin 2
Basin 2 conveys runoff from the crusher fines path and open field via overland flow. Runoff
is then collected in a Nyloplast inlet and then conveyed via a storm drain to the existing
swale that runs along the northeast of the project site. Runoff from Basin 2 eventually
makes it to Detention Pond 215.
Basin 3
Basins 3 is associated with a planter bed, a small amount of concrete, and the bathrooms.
Runoff from Basin 3 is conveyed via overland flow, collected in a storm drain, and routed to
the existing swale that borders the project site along the northeast boundary. Runoff
generated from Basin 3 eventually makes it to Detention Pond 215.
Basin 4
Basin 4 consists of a large amount of vegetation (sod), crusher fine path, and concrete
sidewalks. Just like Basins 2 & 3 runoff is collected in a storm drain and eventually makes
its way to the existing swale. Basin 4 eventually makes it to Detention Pond 215.
Basin 5
Basin 5 consists of a large amount of vegetation (sod), crusher fine path, and concrete
sidewalks. Just like Basins 2, 3, and 4 runoff is collected in a storm drain and eventually
makes its way to the existing swale. Basin 5 eventually makes it to Detention Pond 215.
Basin 6
Basin 6 consists of a large amount of vegetation (sod), crusher fine path, and concrete
sidewalks. Just like Basins 2, 3, 4, and 5 runoff is collected in a storm drain and eventually
makes its way to the existing swale. Basin 6 eventually makes it to Detention Pond 215.
Basin 7
Basin 7 encompasses the playground area and some concrete sidewalks. Runoff from Basin
7 is conveyed to the existing swale that runs parallel to the project site via overland flow.
Basin 7 eventually makes it to Detention Pond 215.
Basin 8
Basin 8 encompasses the hammock garden and some concrete sidewalks. Runoff from
Basin 8 is conveyed to the existing swale that runs parallel to the project site via overland
flow. Basin 8 eventually makes it to Detention Pond 215.
Basin 9
Basin 9 encompasses some landscaping and concrete sidewalks. Runoff from Basin 9 is
conveyed to an existing Type R inlet in Mile House Avenue. From there the runoff enters an
existing 36” RCP that conveys the runoff to the existing swale that runs parallel to the
project site. Basin 9 eventually makes it to Detention Pond 215.
Bucking Horse Park
Bucking Horse Park Drainage Report 9
Basin 10
Basin 10 encompasses some landscaping and concrete sidewalks. Runoff from Basin 10 is
conveyed to an existing Type R inlet in Mile House Avenue. From there the runoff enters an
existing 36” RCP that conveys the runoff directly to Detention Pond 215.
Basin 11
Basin 11 encompasses the basketball court, ping-pong court, concrete sidewalk, and some
crusher fines path. Runoff from Basin 11 is conveyed via overland flow and concentrated
flow (storm drain) to a rain garden near the northeast corner of the project site. The rain
garden will promote infiltration and filtration for the water quality storm event. From the rain
garden the runoff will be conveyed directly to Detention Pond 215 via HDPE piping.
Basin 12
Basin 12 consists of sidewalk and vegetated open space. Runoff is conveyed via a swale to
an open field where it then sheet flows to the northeast and enters Detention Pond 215.
Basin OS1
Basin OS1 is the only offsite basin that gets routed through the project site. Basin OS1 is
associated with the back of lots that are adjacent to the northwest project boundary. Runoff
is routed to Basin 1 via overland flow. From there the runoff is conveyed just like Basin 1
and it eventually makes its way to Detention Pond 215.
C. LID SUMMARY
1. Bucking Horse Park is submitting a variance request to reduce to modify the standards
set forth in Chapter 7 Section 6 of the FCSCM. Per Section 6 “50% of all newly added
or modified impervious area must be treated by LID techniques.” However, because the
Bucking Horse Park has such a low percent impervious (13%) it is proposing to treat
only 27% of the new impervious area through a recognized LID treatment (rain garden)
per the FCSCM. The rational behind this is that because Bucking Horse Park is not
providing on-site parking and is considered a “Low Intense Use” which drastically
reduces the migration of pollutants such as oil, magnesium chloride, gas, etc.
Additionally, Bucking Horse Park also has large swaths of open space that naturally
promotes infiltration and filtration of runoff.
Basin ID LID Treatment Impervious Area
(i%>=90%)(sq.
ft.)
Impervious Area
Treated By LID (sq. ft.)
Percent of Impervious
Treated by LID
11 Rain Garden 6781 6781 100%
Total Site 25492 6781 27%
Table 1 LID SUMMARY
2. Please refer to the formal variance request within Appendix D for additional information.
3. An LID Exhibit can be found in Appendix D.
4. The rain garden was sized using Mile High Flood Control District criteria and sizing
spreadsheets. These calculations can also be found in Appendix D.
Bucking Horse Park
Bucking Horse Park Drainage Report 10
V. CONCLUSIONS
A. COMPLIANCE WITH STANDARDS
1. The drainage design proposed with the proposed project complies with the City of Fort
Collins Stormwater Criteria Manual, as well as previous drainage studies from which
downstream stormwater infrastructure was constructed
2. The drainage design proposed with this project complies with requirements for the
Foothills Basin.
3. The drainage plan and stormwater management measures proposed with the proposed
development are compliant with all applicable State and Federal regulations governing
stormwater discharge.
Bucking Horse Park
Bucking Horse Park Drainage Report 11
VI. REFERENCES
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention
Facilities, November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility
Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by
Ordinance No. 174, 2011, and referenced in Section 26-500 (c) of the City of Fort
Collins Municipal Code.
3. Larimer County Urban Area Street Standards, Adopted January 2, 2001,
Repealed and Reenacted, Effective October 1, 2002, Repealed and Reenacted,
Effective April 1, 2007.
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources
Conservation Service, United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Mile High Flood Control
District, Denver, Colorado, Updated January 2016.
6. Geotechnical Investigation Proposed Improvements Bucking Horse Park, Fort
Collins, Colorado, May 8, 2020, CLT Thompson. (Project No. FC09343-125)
7. Final Drainage Report Bucking Horse Filing One, Dated September 19, 2012,
by Northern Engineering.
8. Final Drainage Report Bucking Horse Filing Two, Dated December 17, 2012, by
Northern Engineering