HomeMy WebLinkAboutTHE GROVE AT FORT COLLINS - FDP - FDP110015 - REPORTS - DRAINAGE REPORT (5)Final Drainage and Erosion Control Report
for
at Fort Collins, Colorado
November 16, 2011
Prepared for:
Campus Crest at Fort Collins, LLC
2100 Rexford Road, Suite 414
Charlotte, North Carolina 28211
Prepared by:
200 South College Avenue, Suite 100
Fort Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 502-001
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 absolutely necessary, we recommend double-sided printing.
November 16, 2011
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage and Erosion Control Report
THE GROVE at Fort Collins
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage and Erosion Control Report
for your review. This report accompanies the 11.16.11 Final Plan submittal for the
proposed Grove at Fort Collins multi-family (student housing) development. Comments
from the Staff Review Letter dated October 28, 2011 have been addressed. Written
responses thereto can be found in the comprehensive response to comments letter on file
with Current Planning.
This report has been prepared in accordance to City of Fort Collins Storm Drainage Design
Criteria and Construction Standards (SDDCCS), and serves to document the stormwater
impacts associated with the proposed Grove at Fort Collins student housing project. We
understand that review by the City is to assure general compliance with standardized
criteria contained in the SDDCCS.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Aaron T. Cvar, PE
Senior Engineer
Nicholas W. Haws, PE Andrew G. Reese
Project Manager Project Engineer
Final Drainage and Erosion Control Report
TABLE OF CONTENTS
1.0 Scope ............................................................................................................ 1
2.0 Design Criteria and References ......................................................................... 1
3.0 Site Location and Description ........................................................................... 1
4.0 Existing Condition ........................................................................................... 2
5.0 Irrigation Facilities ........................................................................................... 5
6.0 Floodplain Encroachment ................................................................................. 8
7.0 Wetlands ..................................................................................................... 10
8.0 Proposed Development .................................................................................. 12
9.0 Proposed Drainage Plan ................................................................................. 12
10.0 Outfall ......................................................................................................... 14
11.0 Stormwater Quantity Detention ....................................................................... 16
12.0 Stormwater Quality Mitigation ........................................................................ 16
13.0 Erosion and Sediment Control ........................................................................ 20
14.0 Conclusions .................................................................................................. 21
References ............................................................................................................. 22
APPENDICES:
APPENDIX A – Rational Method Developed Runoff Calculations
APPENDIX B – Water Quality Calculations
APPENDIX C – Previous Drainage Memos and Correspondence
APPENDIX D – Floodplain Information
APPENDIX E – Street Capacity Calculations
APPENDIX F – Inlet and Curb Cut Calculations
APPENDIX G – Storm Line and Culvert Calculations
APPENDIX H – Prorated Culvert and Prorated WQ Pond Sizing Calculations
APPENDIX I – Erosion Control Cost Estimates and Riprap/Erosion Calculations
APPENDIX J – Supplemental Subsurface Water Investigation (by Applegate Group)
APPENDIX K – Geotechnical / Soils Information (by Earth Engineering Company)
APPENDIX L – Wetlands / Environmental Information (by Cedar Creek Associates)
MAP POCKET:
DR1 – Drainage Exhibit
FLOOD – Floodplain Exhibit
Final Drainage and Erosion Control Report 1
1.0 Scope
This Final Drainage and Erosion Control Report has been prepared for the proposed Grove at Fort
Collins student housing community, and is intended to document the associated stormwater
impacts. Major drainage items to be addressed are:
Historic drainage patterns and quantities of flow
Proposed overall drainage patterns and quantities of flow
Confirmation of existing facilities’ ability to convey and detain peak runoff from developed site
Proposed stormwater infrastructure design
Proposed water quality design
Confirmation that the proposed development will have no adverse drainage impacts
2.0 Design Criteria and References
Drainage criteria outlined in the City of Fort Collins Storm Drainage Design Criteria and Construction
Standards (SDDCCS) has been referenced in this study. The Rational Method has been used to
estimate the peak discharge rates for the minor and major storm events. The minor and major
rainfall events are considered to be the 2-yr and 100-yr storms, respectively. Runoff coefficients
and rainfall values utilized in the Rational Method computations are consistent with the SDDCCS.
The Urban Drainage and Flood Control District’s (UDFCD) Urban Storm Drainage Criteria Manual,
Volume III has been used for water quality design. Additionally, multiple previous studies and
reports have been referenced in the preparation of this document (see page 20 for a full listing).
3.0 Site Location and Description
The project site is located near the center of Section 23, Township 7 North, Range 69 West of the
6th Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. The site is bounded on
the south by the Larimer Canal No. 2, on the west by Care Housing at Windtrail Park, on the east
by Centre Avenue, and by the Sundering and Windtrail neighborhoods to the north. The Gardens on
Spring Creek is located immediately northeast of the property (note, the street stub constructed due
south of the Gardens on Spring Creek currently known as Rolland Moore Drive is expected to be re-
named as Botanic Place once the new Rolland Moore Drive is constructed and accepted). The land
is currently, and will continue to be, owned by the Colorado State University Research Foundation
(CSURF). The developer of the Grove has entered into a long-term ground lease with CSURF.
Existing ground cover is predominately a grass hayfield, with portions of non-native grassland along
the northern and eastern boundaries. Abandoned local irrigation ditches and control structures exist
along the southern property boundary, remnant of times when the land was an active hayfield.
Jurisdictional wetlands exist along the northern property line. (Refer to the Ecological
Characterization Study and Waters of the U.S. Delineation documents prepared by Cedar Creek
Associates for additional information related to the wetlands).
Final Drainage and Erosion Control Report 2
Existing Project Site
According to the NRCS Soil Survey, the site consists of loams and clay loam, which fall into
Hydrologic Soil Groups B and C. More site-specific exploration found an overburden layer of brown
and reddish brown sandy lean clay soils. Numerous soils bores and monitoring wells have been
drilled on the subject property, and subsurface exploration reports have been prepared by both
Earth Engineering Company (EEC) and Applegate Group. Copies of said reports can be found in
Appendices J and K of this document.
4.0 Existing Condition
4.1 Historic Site Drainage
The total area being subdivided is roughly 31.3 acres in size and currently consists of undeveloped
pasture land. The site slopes generally from southwest to northeast at slopes ranging from 6% to
12% near the southern site boundary, and 1% to 5% heading further north. Runoff currently sheet
flows to the north towards Spring Creek. The majority of flow is intercepted by a major
drainageway designed with Windtrail P.U.D.
This outfall channel was intentionally constructed as a wetland with the primary purpose of
conveying developed flows from neighborhoods to the north and west along the backyards of
Sundering Townhomes, as well as Windtrail Townhomes and Windtrail detached residences.
Variances were granted with the Windtrail P.U.D. to intentionally create wet, flat, natural appearing
drainage areas and man-made wetlands. This area is expected to hold water at times and have
drainage back-ups by design.
Final Drainage and Erosion Control Report 3
The ability for the Windtrail outfall swale to sufficiently convey stormwater is dependent upon
adequate maintenance of the wetland drainage facilities. The outfall swale falls within a drainage
easement, and according to the plans approved with Windtrail P.U.D., the homeowners association
shall be responsible for maintenance of the drainageway. Said easement and corresponding
maintenance obligations carries forward, regardless of future ownership changes or development
plans on the property. The Grove at Fort Collins subdivision plat preserves the pertinent drainage
easements of record to allow continued maintenance activities by the responsible parties.
A portion of the site also drains towards the triple 24” RCP culverts installed with the Centre for
Advanced Technology (CAT) 22nd Filing under the roadway stub near the service entrance drive to
the Gardens on Spring Creek. The culverts were designed to accept a 100-yr off-site flow of 57.6
cfs from the CSURF (Grove) parcel to the south. Said culverts discharge into the Horticulture
Center Outfall Channel. This outfall channel, constructed with CAT-22, will now serve as the outfall
for all off the developed runoff from the Grove student housing community.
4.2 Groundwater
The project site lies in a region containing rather shallow groundwater. The areas with the
narrowest depth to water (DTW) tend to lie along the Windtrail P.U.D. Outfall Swale. Not only does
this area along the northern subdivision boundary contain much of the shallowest groundwater, but
it also appears to be the least influenced by seasonal changes due to fluctuating water levels in
surrounding irrigation ditches.
Portions of the neighborhoods to the north and northwest of the Grove currently battle shallow
groundwater on a consistent basis. There are reports from residents of soggy crawlspaces and
nearly constant sump pump discharges. However, such problems are rather sporadic. While one
homeowner may have a routinely running basement sump pump, the neighbor next door or across
the street may be completely dry and have a sump pump that has never kicked on. This appears to
indicate that there are localized factors on a micro-level, in addition regional conditions, that
influence the groundwater on properties in this area. The difficulties that Windtrail, Sundering, and
other neighborhoods presently experience with shallow groundwater seemingly have very little to do
with conditions of property to be platted as The Grove at Fort Collins.
Rather, it is believed that groundwater along Spring Creek has much more to do with regional
geologic and subsurface hydrologic parameters. While the subject property does have the ability to
influence the local DTW, anything proposed within the Grove subdivision boundary would have
nominal affects to the surrounding neighborhoods and area-wide groundwater levels.
According to borings and other analysis performed by EEC, Applegate, and Miller Groundwater, the
DTW not only varies seasonally, but also differs horizontally across the site. As previously
mentioned, the areas with the shallowest groundwater tend to fall within the wetlands and
floodplain adjacent to Windtrail P.U.D. Therefore, the proposed site development and buildings are
placed to avoid the locations with the worst DTW. Additionally, underdrains will be installed to
further protect the buildings and roadways from potentially shallow groundwater. Note 8 is
included on the subdivision plat to explicitly prohibit basement construction for residential
structures.
Final Drainage and Erosion Control Report 4
Details of the underdrain system are included with the Final Utility Plans. The “subdivision-wide”
underdrain system generally follows the public street network, and has been designed in accordance
with Section 5.6 of the Larimer County Urban Area Street Standards (LCUASS). This underdrain
system will outfall into the Grove’s water quality control structure, downstream of the orifice plate,
thereby routing groundwater discharge into the CAT-22 outfall channel. The underdrain outfall
elevation is roughly 4994.1-ft. The peak groundwater discharge from the Grove’s underdrain
system is conservatively estimated to be on the order of 15 gpm, or roughly 0.03 cfs.
Additional recommendations and design parameters can be found in the Supplemental Subsurface
Water Investigation by Applegate Group (Appendix J). Not only does said report further expound on
the technical details of the underdrains and DTW levels, but it also contains modeling results to
approximate the affects of the proposed site grading and subsurface drainage system. Additionally,
the groundwater modeling has taken the Larimer Canal No. 2 ditch realignment into consideration
as well. It can be concluded that the proposed Grove development will have a negligible impact to
the historic groundwater condition along Spring Creek. The groundwater levels will neither lower
enough to adversely impact the existing wetlands nor raise enough to negatively affect surrounding
homes. Furthermore, permanently installed monitoring wells will allow for ongoing groundwater
measurements to assess any fluctuations in DTW. These monitoring wells and groundwater
readings will also aid in tracking the subsurface hydrology along the existing wetland channel. A
narrative describing Cedar Creek Associates’ proposed monitoring plan can be found in Appendix L.
Please see Section 5.0, below, for groundwater related to the Larimer Canal No. 2.
4.3 Off-Site Drainage
In addition to the on-site project area, six (6) off-site basins have also been delineated. Basins 0S1
– OS4 are south of the site boundary, and generally drain to the north. While the Larimer County
Canal No. 2 runs west to east through these basins, it is assumed to be full for the purposes of
stormwater analysis and drainage basin delineation. Basins OS5 and OS6 consist of the existing
Rolland Moore Drive stub (to be re-named) that will drain through new facilities to be constructed
with the Grove prior to reaching the Horticulture Center Outfall Channel.
Historic flows for the off-site basins have been computed and are utilized, where appropriate, in the
design of the Grove drainage improvements. All off-site flow patterns and quantities will continue in
their historic manner with the proposed student housing development. No provisions have been
made for the future development of any off-site basins outside the limits of the Grove subdivision
plat.
There are also historic flows that enter the site from off-site basins to the north and west of the
project boundary. However, since these flows travel directly to and/or through the Windtrail P.U.D.
outfall swale along the northern property line, no explicit computations are necessary. The limits of
development and other improvements associated with the Grove project will not be affected by, nor
have an effect on, the historic Windtrail drainageway. Not only will the existing drainage easements
be preserved with this development, but the entirety of Outlot A will be dedicated as a drainage
easement with The Grove at Fort Collins subdivision plat. Therefore, the ability for the Windtrail
and Sundering HOAs to fulfill their current channel maintenance obligations will not be impeded by
this project.
Final Drainage and Erosion Control Report 5
4.4 Major Drainage Basin
The site lies entirely within the Spring Creek Major Drainage Basin. More specifically, the Grove
resides within Basin 130 of the Spring Creek Master Drainage Plan. Two regional stormwater
studies have recently been conducted within the major drainage basin. The first is an analysis that
primarily deals with the conveyance and detention for the areas that drain to the Burlington
Northern Railroad (BNRR) pond south of the Fort Collins Hilton. Development boundaries and
percentage of impervious areas for the proposed Grove student housing community have been
shared with the parties involved in the study and modeling update. Please refer to the “Alternative
Analysis for the Design of the Mason Street Outfall” report by Ayres Associates dated November
2010 for additional information.
The second regional stormwater effort currently underway is a proposed Physical Map Revision
(PMR) to the Spring Creek floodplain. This includes updates to both the MODSWMM hydrology as
well as the HEC-RAS hydraulic modeling. Pertinent drainage parameters have been shared
between City Staff, their consultants, and the Grove engineers. As a result, it is neither appropriate
nor required that the Applicant for the Grove conduct any further modeling. The practical and
preferred approach is to ensure consistent data and enable a more thorough and accurate effort by
those already conducting larger-scale studies. The Grove student housing development remains
consistent with the governing master drainage studies.
5.0 Irrigation Facilities
All existing on-site irrigation facilities are assumed to be abandoned, and will be removed within the
limits of work. The Larimer County Canal No. 2 roughly parallels the southern property boundary.
The ditch is elevated in this area and has relatively steep banks. The proposed Grove subdivision
boundary lies approximately 20’ – 40’ north of the existing top of ditch. Alternatively, the boundary
line is intended to follow the toe of slope along the elevated portion of the Larimer Canal No. 2.
Another consideration regarding the ditch that runs along the southern property line is the potential
for seepage. It is a known fact that the Larimer Canal No. 2 seeps in the area near Care Housing at
Windtrail Park. The horizontal separation of the Grove property boundary, as well as the additional
buffer provided by Outlot B, offers a certain level of protection for the buildings and roadways.
Additionally, The Grove at Fort Collins will install an underdrain system to safeguard the structural
integrity of the foundations and subgrade. The potential for the Larimer Canal No. 2 to overtop in
major rainfall events is no different than any other irrigation ditch elsewhere in Fort Collins, and is
not a consideration or concern in selecting this site for development.
Neither the subdivision boundary nor the limits of development for the proposed Grove student
housing community impact existing ditch company rights-of-way, easements, integrity, or ability to
access and maintain ditch company facilities. Nonetheless, the Larimer County Canal No. 2
Irrigating Company has been notified of the proposed project and copies of the applicable
development plan documents have been provided for their review. Additionally, the final
construction plans for the Grove will be routed to the ditch company for their approval and signature
to confirm that there are no adverse impacts to their facilities.
Final Drainage and Erosion Control Report 6
The proposed Grove Project Development Plan has been discussed with Ditch Company
representatives on multiple occasions since this project was first envisioned. Concerns of seepage,
slope stability, large tree intrusion, access, and maintenance have been the main topics of
conversation to date. The Ditch Company has issued multiple letters on the matter. Copies of said
correspondence can be found in Appendix C.
In order to address the concerns related to potential seepage and slope stability, additional testing
and analysis has been performed by Applegate Group, Miller Groundwater and Earth Engineering
Company (EEC) to further resolve these issues. The supplementary data has afforded a more
accurate understanding of how much of an effect, if any, the May to July irrigation flows in the
Larimer No. 2 canal have on downhill groundwater and slope stability. Brief memos further
describing the additional testing efforts can be found in Appendix J (Applegate) and Appendix K
(EEC).
Development adjacent to the canal must be done with great care. The fact that the student housing
buildings will not have basements or crawlspaces is one significant advantage. Cuts will not be
allowed below the ditch while the canal is running. Slope stability measures and retaining wall
construction shall follow the strict recommendations of EEC. Slopes previously proposed at 2:1 or
3:1 in proximity to the ditch have been revised such that all design slopes are 4:1 or less.
Additionally, a free-draining mechanically stabilized earth (MSE) retaining wall with modular
concrete block facing will be constructed behind Buildings 3, 4, and 5.
As alluded to above, CSURF, the Ditch Company, and Campus Crest have entered into a three-party
agreement to realign the Larimer No. 2 Canal further south on land also owned by CSURF. The
Fort Collins Planning and Zoning Board added a condition of approval to the Grove at Fort Collins
PDP requiring the canal to be realigned prior to issuance of the first certificate of occupancy. As
such, the final groundwater modeling and underdrain design take the ditch realignment into
account.
The ditch relocation will help achieve numerous objectives benefitting multiple parties. First of all,
the newly cut and compacted clay-lined channel section will have significantly less seepage than
the existing ditch. Obviously the Ditch Company and its shareholders will benefit from the
decreased seepage. Additionally, downhill land owners will have increased peace-of-mind and
future construction north of the canal will be safer and more cost effective as a result.
The proposed ditch realignment will offer additional horizontal separation from the active canal and
The Grove at Fort Collins development plan. This again is an improvement for the Ditch Company,
not only to gain distance, but to get away from the steep slope that currently exists downhill of the
present alignment. Concerns of slope stability effectively go away from their perspective.
The canal is currently lined with numerous large cottonwood trees, many of which protrude into the
ditch embankment and are nearing the end of their maximum lifetime. These trees pose major
concerns to the Ditch Company in terms of water loss, as well as safety and liability. In fact, the
Superintendent for the Larimer Canal No. 2 has gone on record to say that if the ditch remains in its
present alignment, that he will have to remove multiple significant trees along the channel.
Final Drainage and Erosion Control Report 7
The trees in question offer substantial habitat value to the wildlife corridor, as well as contributing
to the aesthetic landscape of the area. Realigning the ditch will allow the existing trees to remain
as-is. The intent is to restore the abandoned channel section to a more natural condition; therefore,
a reclamation plan has been prepared to specify the planting of additional trees, shrubs, and native
grasses. The new canal route will provide an additional wildlife corridor, essentially creating a
refuge in the middle. The end result will offer a substantially improved natural habitat from what
would occur to the wildlife corridor if the Ditch Company were to remove the large trees and keep
the single channel where it is. The 04.04.11 memo from Senior Wildlife Biologist, T. Michael
Phelan, further describes the benefits of realigning the ditch from a habitat perspective.
As of the date of this report, the contact information of record for the Larimer County Canal No. 2
Irrigating Company is as follows:
John Moen - Superintendent 970.482.3309 (970.218.0726 – mobile)
John Strachan - President 970.223.5231
Brent Bartlett - Attorney 970.407.9000 ext.217
Final Drainage and Erosion Control Report 8
6.0 Floodplain Encroachment
The majority of Outlot A falls within the Spring Creek floodplain. Both 100-yr floodway (dark blue)
and flood fringe zones (cyan) run along the northern property line. There is no erosion buffer zone
associated with Spring Creek. Spring Creek is a regulatory FEMA floodplain. A copy of FIRM Panel
0987F with an effective date of 12.19.06 can be found in Appendix D. Please note, a Physical
Map Revision (PMR) is currently being reviewed by FEMA for the Spring Creek floodplain.
The placement of fill and the construction of new residential dwellings (including mixed-use
development) is allowed in the Spring Creek 100-yr flood fringe. The City of Fort Collins has
prepared a Quick Guide for all floodplain regulations other than the Poudre River. This document
helps to clearly depict and explain the code allowance to fill in the flood fringe. A copy of this Quick
Guide is included in Appendix D for reference.
No floodplain modeling is required as part of this proposed development, as it will result in no
change to the FEMA regulatory mapped flood hazard zones. However, a City of Fort Collins
Floodplain Use Permit, along with ancillary support documents, will be required for each structure
(Buildings 10 and 11) and each site construction element (stormwater swale and pond, paths,
parking lots, streets, utilities, etc.) in the floodplain. Furthermore, FEMA Elevation Certificates shall
be completed and approved before the Certificates of Occupancy are issued for Building 10 and
Building 11.
Final Drainage and Erosion Control Report 9
A portion of the 100-yr flood fringe encroaches slightly into Tract A, Lot 1, Block 1 and Lot 1, Block
2. No structures are proposed within the floodplain on either Tract A or Lot 1, Block 1. The only
structures proposed within the (12.19.06) 100-yr floodplain are portions of Building 10 and
Building 11, located on Lot 1, Block 2. Both buildings are multi-family residential structures with
identical floor plans. There will be no basements or crawl spaces associated with any structure
within the Grove student housing community. All building foundations will be slab-on-grade with
thickened perimeter footings (see schematic detail on Floodplain Exhibit). All construction within
the floodplain shall be in compliance with Chapter 10 of the City of Fort Collins Municipal Code.
Specifically, the Lowest Floor and all HVAC equipment shall be elevated above the Regulatory Flood
Protection Elevation. Buildings 10 and 11 are explicitly prohibited from being converted to critical
facilities, as defined by Chapter 10 of the City Code.
The controlling Base Flood Elevation (BFE) for Building 10 is 5004.31 feet (NAVD 88), and for
Building 11 is 5002.81 feet (NAVD 88). Since the City of Fort Collins (and thus, the proposed
Grove student housing development) is on the “original” NGVD 1929 (unadjusted) vertical datum,
3.0 feet was subtracted to convert the BFE’s to the project datum. Therefore, the resulting BFE
affecting Building 10 is 5001.31, feet NGVD 29 (unadjusted), and Building 11 is 4999.81 feet,
NGVD 29 (unadjusted). The Regulatory Flood Protection Elevation is eighteen (18) inches above
the Spring Creek BFE. The consequent Regulatory Flood Protection Elevation for Building 10 is
5002.81 feet, NGVD 29 (unadjusted) or 5005.81 feet, NAVD 88 and the Regulatory Flood
Protection Elevation for Building 11 is 5001.31 feet, NGVD 29 (unadjusted) or 5004.31 feet,
NAVD 88.
Regulatory Flood Protection Elevations
Final Drainage and Erosion Control Report 10
7.0 Wetlands
As previously mentioned, an Army Corps of Engineers (ACOE) jurisdictional wetland currently exists
along the northern property line. The wetland roughly follows the floodplain passing through Outlot
A. A descriptive project history, including more than twenty (20) site plan alternatives, has been
prepared by Ripley Design, Inc. to document the extensive effort that has been taken to create a
plan that meets the City’s codes and objectives, while minimizing the impact to the existing
wetlands. The proposed Grove at Fort Collins development plan preserves 100% of the existing on-
site ACOE jurisdictional wetlands.
ACOE Wetland Delineation Map
An existing clay tile underdrain is shown on the Windtrail P.U.D. Outfall Swale drawings, which
roughly parallels the existing wetlands. Another underdrain line appears to have been installed
parallel to the southern boundary of Sundering Townhomes as part of the Care Housing detention
pond outfall. Since there will be no disturbance within the main wetland channel, it is not
anticipated that the aforementioned drain tiles will be affected by the Grove.
A very small (0.015-acre) pocket of non-jurisdictional wetlands exists near the northern corner of
Building 11. Although this loss could be argued as nominal and inconsequential, the Applicant will
be mitigating this area nonetheless through substantial buffer habitat enhancements, additional
planting, and structural diversity augmentation within Outlot A.
Final Drainage and Erosion Control Report 11
Since this project will not be disturbing any jurisdictional wetlands, no 404 permit or other specific
approval is necessary from the Army Corps of Engineers. However, the Applicant still intends to
inform the ACOE of the proposed development plan and measures taken to protect the wetlands.
Additionally, the Grove will conduct a monitoring program for a minimum of three (3) years after
construction. The monitoring plan will include visual observations and recording of wetland
vegetation, soils, and groundwater levels. Pre-construction monitoring has already begun as of April
2011 to establish baseline data. A copy of the proposed monitoring plan, as well as results to date,
can be found in Appendix L.
Results of the ongoing monitoring program will be provided to the City of Fort Collins Natural
Resources Department. Obviously it is desired to have no adverse changes to the existing wetlands
as a result of the development. However, the monitoring plan will ensure that objective data is
available for accurate evaluation. Should there be any issues of concern, the Grove and the City will
work together to make certain that the development adheres to its intent and promise to have no
negative impacts to the existing wetlands.
As previously mentioned, the existing wetlands were created (man-made) with the Windtrail P.U.D.
subdivision, and receive substantial surface water runoff from surrounding neighborhoods and
upstream development. This is considered to be a significant source of irrigation to the existing
wetlands. Since the delivery of such surface water is not impacted by the Grove, it is doubtful that
there will be a material reduction in wetland vegetation as a result of this development.
Final Drainage and Erosion Control Report 12
8.0 Proposed Development
The proposed development will include construction of a 12-building, 218-unit student housing
apartment community, including a clubhouse, pool, and other outdoor amenities capable of
supporting 612 residents. Additionally, Rolland Moore Drive will be extended from its current
terminus east of Shields Street towards a new intersection at Centre Avenue across from the
southern entrance to the Natural Resources Research Center. Two new streets, Native Plant Way
and Perennial Lane, along with supporting earthwork, utility infrastructure, and stormwater
improvements are also a part of the proposed Grove development.
Site Plan
9.0 Proposed Drainage Plan
9.1 Drainage Basins
The developed site has been broken into six (6) major drainage basins. The major basins have
been further divided, where appropriate, into fifteen (15) total sub-basins. Basins A – D generally
consist of the areas currently being developed as The Grove at Fort Collins student housing
community, whereas Basin X is reserved for the future development of CSURF’s Tract A, and Basin
CH is a small area at the west end of Rolland Moore Drive near the Care Housing subdivision.
Basin A consists of public roadways, private parking lots and drive aisles, as well as buildings and
landscape areas. Sub-basin A4 is comprised of Building 1 and the adjacent Lot 1, Block 1 parking
area. This sub-basin drains into Storm Line 1, which travels east in Outlot A and north/northeast
through sub-basins A3 and A2 into Swale 1. This swale then conveys flow east in Outlot A toward
the water quality pond located in sub-basin A1.
Final Drainage and Erosion Control Report 13
It should be noted that a small portion of Swale 1, as well as a small portion of the slope grading in
Outlot A north of Rolland Moore Drive, have side slopes of 3:1. These areas are located within the
natural habitats buffer, and will be restored with native plantings. As such, they will not be
manicured turf maintained by riding mowers. These slopes will be privately maintained in a
manner that respects the buffer, and the Applicant acknowledges the presence of 3:1 slopes.
These slopes are designed to prevent encroachment into the floodway and wetlands, described in
Sections 6.0 and 7.0, respectively. This is the exclusive reason for exceeding 4:1 side slopes.
Basin B is comprised of public roadway, private parking lots and drive aisles, as well as buildings
and landscape areas. Sub-basins B1 and B2 drain to sump inlets in Rolland Moore Drive located
west of Buildings 5 and 7. An RCP storm drain will convey runoff from the inlets into Storm Line 1,
which ultimately discharges into the main water quality pond near the west end of the Rolland
Moore Drive (to be renamed) street stub.
Basin C consists of roadway, parking lot and drive aisles, as well as buildings, amenities and
landscape areas. Sub-basins C1 and C2 drain to sump inlets in Native Plant Way located east of
Building 10. Sub-basin C3 drains to a sump inlet south of Buildings 10 and 11. Sub-basin C4
drains to a sump inlet in the private parking lot south of Building 9, which discharges into Swale 1
via Storm Line 2. Storm Line 3 will convey runoff from sub-basins C1-C3 into Swale 1. All of
Basin C ultimately passes through Swale 1 prior to reaching the main water quality pond northeast
of Building 11.
Basin D is predominantly composed of public roadway along with portions of the clubhouse,
Building 11, and adjacent landscaping. This basin drains to sump inlets located immediately south
of the west end of the Rolland Moore Drive (to be renamed) street stub. Storm Line 4 will convey
runoff from the inlets directly into the water quality pond on the west side of Perennial Lane.
Basin X is currently comprised of undeveloped grassland owned by CSURF (Tract A). However,
Basin X is subject to future development in accordance with the ODP of record (E zoning district).
While the development of this parcel is not a part of The Grove at Fort Collins student housing
project, certain assumptions have been made in the drainage computations contained within this
report. A 90% impervious value has been assumed for Basin X. This basin drains north towards
the intersection of Perennial Lane and the Rolland Moore Drive (to be renamed) street stub. Flared-
end-sections will convey flows through Storm Line 4 under Perennial Lane into the Grove’s water
quality pond. Both the storm line and water quality pond have been “up-sized” to accommodate
the fully developed future flows from Basin X. (See Appendix H for documentation of the
proportionate size increase necessary to allow Tract A to develop without any on-site detention or
water quality.)
Basin CH is comprised of the public right-of-way of Rolland Moore Drive (RMD), as well as the
adjacent vegetated area that sheet flows into the roadway. This basin represents a very small area
at the western-most end of RMD. Runoff from Basin CH drains west to existing sump inlets
installed with Care Housing at Windtrail Park. While this area leaves the Grove subdivision
boundary “undetained,” runoff does receive quantity and quality mitigation through the existing
drainage system. The Care Housing design assumed a small off-site area would drain from the east
to the existing sump inlets. The area corresponds to the high point in Rolland Moore Drive roughly
50’± east of the current end of pavement. The Grove roadway plan (thus, corresponding tributary
area) matches the design assumptions made with the Care Housing project; therefore, no further
analysis or improvements are necessary for the runoff from Basin CH. Likewise, Basin CH has been
excluded from the on-site “developed” stormwater computations since this area drains to a different
outfall.
Final Drainage and Erosion Control Report 14
9.2 Developed Drainage Concept
The Windtrail P.U.D. Outfall Swale currently drains a good portion of the site. The downstream end
of this swale is located immediately east of 602 Gilgalad Way, which is also the limiting ‘pinch
point’ of the outfall channel. The swale has a 100-yr design flow of approximately 130.7 cfs, with
a maximum allowable capacity of 139.8 cfs. The swale was “over-sized” specifically to
accommodate future developed flow from the land currently being platted as the Grove (then known
as the CSURF/McCoy Land Swap).
Therefore, previous Windtrail P.U.D. drainage designs would appear to provide sufficient capacity to
drain a substantial portion of the Grove development. However, current homeowners in the
neighborhoods north of Outlot A have expressed noted concerns with both surface and subsurface
waters. Some of the issues regarding the backup of stormwater could be a result of the original
design intent to achieve flat areas, subtle ponding, and created wetlands. Others could be a result
of insufficient channel maintenance, over-irrigation, and sump pump discharge.
Regardless of the factors currently causing water troubles for the Sundering and Windtrail
neighborhoods, it is the strong desire and intent of the Applicant of the Grove to not exacerbate
these problems in any way. Rather than sending developed runoff towards the Windtrail P.U.D.
Outfall Swale, as it was originally intended, the Grove will design and install a completely separate
outfall. Additionally, groundwater flows intercepted by the underdrain system will also be
discharged away from existing homes in an effort to further ensure there are no adverse affects from
the Grove development. A much better outfall for this project is the Horticulture Center Outfall
Channel, which was constructed with the CAT-22 Gardens on Spring Creek improvements.
10.0 Outfall
The CAT-22 Horticulture Center Outfall Channel currently flows behind the Gardens on Spring
Creek. A concrete trail separates this outfall channel from the Windtrail P.U.D. outfall swale. The
CAT-22 channel conveys flow from the current terminus of the Rolland Moore Drive stub (to be
renamed) north towards Spring Creek. Dual 1.5’ x 6’ box culverts allow stormwater to pass under
the Sherwood Lateral prior to reaching Spring Creek.
The outfall channel was originally designed to convey 57.6 cfs from The Grove at Fort Collins
project area in the 100-yr event. The 100-yr peak flow expected at this design point from the
proposed student housing and future CSURF development is roughly 92.9 cfs. However, that does
not necessarily imply that the outfall channel is insufficient to accommodate the developed runoff
from the Grove. A simplified analysis of both the channel section itself, as well as the box culverts,
estimated a 100-yr capacity in excess of 132 cfs. These cursory computations were calculated
both with and without an assumed 34 cfs groundwater baseflow (extremely conservative). In all
scenarios, the outfall could easily accept the fully developed 100-yr peak discharge from the Grove
without overtopping.
However, the Horticulture Center Outfall Channel cannot be fully evaluated with such simple
analyses, as this channel is heavily influenced by the tailwater conditions in Spring Creek. Such
correlation was witnessed as recently as this past fall of 2010 when there had been a build-up of
debris immediately downstream of the outfall channel. The backwater effects caused the box
culverts under the Sherwood Lateral to be nearly submerged. Fortunately, the City Stormwater
Utility has since cleared the blockage in Spring Creek to provide unobstructed drainage.
Nevertheless, this occurrence does prove the close correlation between the CAT-22 outfall channel
and the water level in Spring Creek.
Final Drainage and Erosion Control Report 15
This relationship was first documented by Anderson Consulting Engineers (ACE) in their 2002
“Hydraulic Analysis of the Horticulture Center Outfall Channel.” A HEC-RAS model was developed
for the outfall channel, and 100-yr stormwater elevations were computed at both the peak time in
Spring Creek as well as the peak of the local basin tributary to the storm drain feeding the outfall
channel.
The 2002 ACE report was based upon older Spring Creek drainage models. Northern Engineering
has since obtained the most current modeling data from the City of Fort Collins, and has re-run the
analysis on the Horticulture Center Outfall Channel. Additionally, the 2002 ACE report had
assumed a time of concentration of 37 minutes for the CSURF basin upstream of the triple culverts.
The new results reflect the latest modeling data as well as an actual time of concentration for the
Grove of 26 minutes. The channel proves to have sufficient capacity to accept the 100-yr peak
discharge of 92.9 cfs from The Grove at Fort Collins. Additional information on this analysis can be
found in Appendix C.
Even if one were to consider a catastrophic, worst-case scenario, such as the culverts being clogged
or a rainfall event exceeding the 100-yr design storm, the emergency spill path would be to the
east/northeast. Such an emergency overflow would likely occur via shallow overland flow traveling
across City-owned property towards Spring Creek. It is practically impossible for any water from the
Horticulture Center Outfall Channel to ever reach the neighboring homes in Windtrail under any
circumstance. This is all the more reason to utilize the Horticulture Center Outfall Channel rather
than the Windtrail P.U.D. outfall swale for the Grove’s developed runoff. It also should be noted
that it is accepted design practice for culverts to be submerged at depths one-and-a-half-times their
height during major rain events.
Not only is the CAT-22 channel an appropriate stormwater outfall, but it currently serves to relieve
groundwater in the area as well. In fact, a perennial baseflow can be observed trickling in the
bottom of this channel even in the dead of winter. The underdrain system to be installed with the
Grove will also outfall directly into this channel rather than routing through the Windtrail wetland
drainage. The underdrain outfall will connect into the outlet structure of the water quality pond,
downstream of the orifice plate.
The underdrain outfall will also have an invert elevation higher than the triple culverts draining the
outlet structure. These measures will help minimize the potential for stormwater to backup into the
underdrain system. While routine rain events are unlikely to cause backwater in the underdrains,
the potential does exist for major storms to backup into a portion of the outfall line. However, the
underdrain outfall within Outlot A is solid PVC. The invert elevation crossing the right-of-way of
Native Plant Way is roughly 4995.7-ft, whereas the 100-yr tailwater elevation at the outfall is
approximately 4994.9-ft. The WQCV WSEL is around 4997.7-ft; however, the WQCV and the
underdrain outfall are hydraulically disconnected. An inline backflow preventer could be installed
on the underdrain outfall line just upstream of the outlet structure should there be remaining
backwater concerns.
The peak discharge of the underdrain outfall is expected to only be around 1.53 cfs (15 gpm, or
0.03 cfs, from groundwater and 1.5 cfs from the rain gardens), and has a negligible impact on the
outfall channel (see Appendix J for further details on the underdrain system). Nonetheless, the floor
of the concrete outlet structure will be sloped to prohibit groundwater discharge from trickling to the
south and saturating the area in front of the water quality plate.
Final Drainage and Erosion Control Report 16
11.0 Stormwater Quantity Detention
The effective Spring Creek Master Drainage Plan assumes a set area and impervious value for Basin
130. As such, stormwater quantity detention is not required if development patterns are at or
below the assumed basin parameters. The actual impervious value for the developed area within
the Grove subdivision boundary (including future CSURF development of Tract A) is just over 62%.
Therefore, it is prudent to run the applicable modeling to ensure that on-site detention is not
required and that downstream conveyance is sufficient.
Fortunately, such additional analysis has been conducted to be absolutely certain that the proposed
Grove development will not have any adverse drainage impacts to downstream properties. Further
examination was given to Basin 130 in the City’s MODSWMM for the Spring Creek Master Drainage
Plan. Ayres Associates recently completed a large-scale study and analysis of the stormwater
system in this portion of the Spring Creek basin.
The November 2010 “Alternative Analysis for the Design of the Mason Street Outfall” assumed a
developed area of 24 acres with a percent impervious value of 90% associated with the proposed
Grove project. These parameters were modeled with the larger Spring Creek Master Plan, and the
output resulted in no rise in water surface elevation to Pond 303 (aka, BNRR Pond). Therefore, it
is further proven that the proposed Grove student housing development and future CSURF
development of Tract A can free release without any on-site quantity detention. In fact, the Grove’s
actual developed area and percent impervious values are closer to 23 acres and 59%, respectively,
so there should be more than enough capacity in the downstream regional pond.
12.0 Stormwater Quality Mitigation
12.1 Water Quality Pond
Regardless of whether or not on-site quantity detention is required, mitigation to address the
stormwater quality of developed runoff is necessary. Water quality treatment for the Grove student
housing community will primarily be achieved in the water quality pond located at the
east/southeast corner of Outlot A. This pond will be designed as a standard dry extended detention
basin (EDB), per City of Fort Collins guidelines.
The water quality capture volume (WQCV) will help remove sediment and other pollutants from
developed runoff. Criteria for a 40-hour drain time treating the 80th percentile runoff event, as
outlined in the Urban Storm Drainage Criteria Manual, Volume 3 – Best Management Practices
(BMPs) by the Urban Drainage and Flood Control District has been used to design the WQCV. The
required water quality volume is approximately 0.53 ac-ft, and over 0.81 ac-ft is provided. The
primary reason the extra volume (depth) is designed in the pond is to provide additional head to
allow the developed 100-yr flow to fully pass through the outlet structure.
Technically speaking, the EDB will fully satisfy the minimum water quality requirements for the
Grove development. However, this project is going above and beyond the minimum requirements.
Nearly every drop of developed runoff will pass over or through some sort of vegetated surface prior
to leaving the project boundary. Swale 1 is intended to function as an infiltration swale, thereby
offering additional water quality enhancement upstream of the water quality pond. Additionally, the
CAT-22 outfall channel itself is designed as a water quality grassed swale. Therefore, there will be
multiple BMPs in series between the developed runoff from the Grove and the receiving waters of
Spring Creek.
Final Drainage and Erosion Control Report 17
Rain Garden Precedence Photographs
Photos courtesy of www.portlandonline.com
12.2 Rain Gardens
One more water quality concept worth noting is the pursuit of rain garden planters within the curb
extensions of Rolland Moore Drive. These roadside planters will serve to treat the stormwater from
the public right-of-way. Gutter flows will be routed through the curb extension areas to create
ecological rain gardens. An area-wide underdrain system will already be employed, and the same
drains will extend under the rain garden areas for subsurface drainage relief. Engineering details of
the rain gardens, including a specification for the bioretention sand media (BSM) can be found on
Sheet D10 of the Utility Plans. Additional landscaping details, including planting, cobbles, and
other surface treatments, can be found on the Landscape Plans by Ripley Design, Inc.
Implementing these curb extension rain garden planters will have multiple benefits, the most
obvious of which is the water quality treatment. However, there will also be the opportunity for the
rain gardens to serve as a pilot project and case study for the region. Unfortunately, current Fort
Collins street standards do not allow for such low-impact stormwater strategies; thus, a formal
variance request has been from the Engineering Department to allow them within the public right-
of-way.
The City of Fort Collins Engineering/Streets Department had initially expressed concerns regarding
the long-term viability, and potential replacement, of such facilities. Admittedly, the ongoing
operation and maintenance of the curb extension areas are unknown at this time since there is little
data or precedence in our region for such facilities. Fortunately, subsequent meetings have helped
to expose and formulate remedies to the major concerns. The concepts depicted above were
discussed at two Utility Coordination Meetings (04.14.10 and 01.20.11), and received no
objections from the providers. A design charrette was also held on 10.26.10 to specifically address
the pavement management concerns, opportunities, and constraints. A subsequent design meeting
was held on 11.03.11 with multiple City Staff Departments to further discuss the design details of
the already agreed to rain gardens.
Additionally, the City of Fort Collins Stormwater Utility will be providing the necessary assurance for
the rain gardens. As a thought-partner in these concepts, City Stormwater Staff has agreed to help
champion these efforts and truly create 21st Century Utilities. The curb extension planters fall very
much inline with the current trends in Green Streets and sustainable infrastructure. In fact, such
techniques coincide perfectly with the recent Plan Fort Collins objectives to innovate, sustain, and
connect. Rolland Moore Drive has the potential to become a showcase example of a multi-
functioning street. Furthermore, the Urban Water Center at Colorado State University has expressed
Final Drainage and Erosion Control Report 18
interest in another partnership project with the City of Fort Collins to install sampling stations and
monitor the above-described rain gardens.
Exhibit 1, above, illustrates the rain garden concept to be implemented with The Grove at Fort
Collins. Stormwater runoff from the curb and gutter of Rolland Moore Drive will enter the rain
gardens through 2’ wide curb openings with 2” depressed gutter sections. Cemented cobble
forebays will be installed at the entrances to all rain gardens. While these forebays do take away a
small amount of area from the infiltration zone, their benefit of collecting large trash, debris, and
sediment far outweighs the reduced permeability. The forebays will provide much easier long-term
maintenance, and will extend the life of the infiltration swale and adjoining bioretention sand media.
Small weep drains will be installed in the cemented forebays to allow them to complete drain free of
standing water.
Downstream of the forebays, flow will enter the infiltration zone. A cobble swale will define the low
flow path down the center of rain gardens. The flowline of the infiltration swale is aligned with the
underdrain system, which extends under each rain garden. The underdrains from the rain gardens
connect into the same outfall described in Section 4.2, above. To the side and elevated slightly
above the infiltration swale is the vegetated zone. The plantings in this zone will be situated above
the bioretention sand media. Non-floatable gravel mulch will be utilized, and drip irrigation will be
installed for initial establishment and to ensure the long-range viability of the vegetation.
Where pedestrian ramps cross the infiltration swales, sidewalk chases with decorative grates will be
installed. The downstream end of each rain garden will have an overflow control weir integrated
with the vertical curb and gutter. The overflow weir section consists of a 2’ wide opening with 4:1
side slopes. This will enable the rain gardens to pond to a maximum downstream depth of 4”
above the adjacent street elevation prior to overtopping into the curb and gutter of Rolland Moore
Drive. This shallow ponding depth is expected to allow full infiltration of the frequent storm events,
while major storm events can safely spill in a controlled manner and reach the downstream storm
inlets.
Final Drainage and Erosion Control Report 19
The perimeters of the rain gardens will be lined with cobbles. The cobbles will be partially
embedded into the underlying soil such that their tops are roughly flush with the adjacent curb
heads and sidewalks. The cobble edge treatment will be situated on a 2’ wide section of
compacted subgrade to provide stability to the concrete curb/gutter and sidewalk on either side.
The compacted subgrade section then slopes down at 1.3:1 to the bottom of the underdrain
section, helping to provide additional stability and drainage protection.
One primary topic of discussion at the 11.03.11 rain garden meeting was the retrofit design
alternative. The issue of concern regarded what would happen to the curb extension areas in the
event that the infiltration component were to be abandoned. The two major considerations are
what happens to the landscaping and what happens to the flows in the curb and gutter of Rolland
Moore Drive. Exhibit 2, below, depicts the retrofit option.
The ‘corrective plan’ is really quite simple. From the surface, the curb extensions will look nearly
identical. The cobbles would be moved aside of the infiltration zone while the underlying sand is
replaced with base material capable of supporting a concrete trickle pan. A concrete channel would
then be installed, and some or all of the previous cobbles would be cemented into the channel, very
similar to the forebay. This essentially puts a concrete lining under the swale section, and removes
the low-flow infiltration component. The overflow weirs at the downstream end of each rain garden
would be cut-out to provide a 2’ curb opening. The curb extensions would then become ‘pass-
through’ landscape areas, and both frequent and major storm events would reach the downstream
inlets in Rolland Moore Drive.
Final Drainage and Erosion Control Report 20
13.0 Erosion and Sediment Control
An Erosion and Sediment Control Plan (along with associated details) is included with the final
construction drawings. It should be noted, however, that any such Erosion and Sediment Control
Plan serves only as a general guide to the Contractor. Staging and/or phasing of the BMPs
depicted, and additional or different BMPs from those included may be necessary during
construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan will address both temporary measures to be implemented
during construction, as well as permanent erosion control protection. Best Management Practices
from the UDFCD and the City of Fort Collins Erosion Control Reference Manual for Construction
Sites will be utilized. Expected measures include: silt fencing along the disturbed perimeter, gutter
protection in the adjacent roadways, and inlet protection at existing and proposed storm inlets and
culverts. Special care and attention shall be given to the wetland drainageway in Outlot A. Vehicle
tracking control pads, spill containment and clean-up procedures, designated concrete washout
areas, and job site restrooms shall also be provided by the Contractor.
Final Drainage and Erosion Control Report 21
14.0 Conclusions
This Final Drainage and Erosion Control Report has taken into consideration the comments and
concerns raised with the previous development plan proposed for the subject property. The new
analysis and updated Site Plan mitigate most, if not all, of the previous concerns. In addition to
comments raised by City of Fort Collins Stormwater Staff, the Applicant also acknowledges receipt
of Memorandums from the Windtrail and Sundering Townhomes Homeowners Associations dated
10.15.10 and 04.25.11, respectively; as well as concerns expressed by Mr. Terence H. Podmore,
Ph.D. to the Ditch Company (Gene Fischer) on 01.27.11 and to the Fort Collins City Council on
04.19.11. All relevant engineering concerns voiced in said citizen comments have been diligently
addressed.
The proposed Grove at Fort Collins student housing development conforms to all governing drainage
criteria and regulations. The proposed stormwater system will adequately treat the developed runoff
for water quality before leaving the site. Regional conveyance and attenuation of peak discharge is
provided off-site, and can safely accommodate full development of the subdivision. No adverse
stormwater impacts are expected as a result of this project. The Grove will have a completely
separate drainage system from Windtrail P.U.D.; thereby ensuring adjacent homeowners will not be
affected by the Grove’s developed runoff. The proposed development complies with Chapter 10 of
the City of Fort Collins Municipal Code – “Flood Prevention and Protection.” Final drainage
improvements have been designed in accordance with applicable City of Fort Collins and UDFCD
criteria.
Extensive site analysis and alternative plan investigations have been conducted over the course of
2+ years. The resulting development plan best accommodates the multiple environmental and
stormwater constraints of the site, while providing a great asset to the community. The Grove at
Fort Collins will offer students a place to live that is close to campus and the Mason Corridor BRT,
thereby lessening the vehicular impacts to local roadways and the environment. It also helps to
consolidate students into an appropriate location (per vested ODPs, Master Plans, and compliant
with City zoning and Land Use Code), and may relieve the stress on overburdened rental houses in
single-family residential neighborhoods throughout the City.
From a progressive stormwater management perspective, the rain gardens proposed along Rolland
Moore Drive offer another opportunity to achieve the City’s vision for a 21st Century Utility. This
collaborative effort is a true occasion to innovate, sustain, and connect. The Grove aligns with Plan
Fort Collins objectives, moves towards multi-functioning (green) streets, helps create sustainable
infrastructure, and promotes a high performing community.
Final Drainage and Erosion Control Report 22
References
1. Addendum to the Final Drainage Report for the Windtrail P.U.D., Townhomes Site,
March 1, 1995, Lidstone & Anderson, Inc. (LA Project No. COTST18.8).
2. Alternative Analysis for the Design of the Mason Street Outfall, November 2010,
Ayres Associates.
3. 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.
4. Ecological Characterization Study Report (ESCR) Update for The Grove 11/29/10 Concept
Plan, November 30, 2010, Cedar Creek Associates.
5. Erosion Control Reference Manual for Construction Sites, January 1991, City of Fort Collins.
6. Flood Insurance Rate Map (FIRM) Panel 0987F, Effective Date December 19, 2006,
Federal Emergency Management Agency (FEMA).
7. Fort Collins Municipal Code (Chapter 10 – Flood Prevention and Protection), 1987,
Colorado Code Publishing Company, Fort Collins, Colorado.
8. Hydraulic Analysis of the Horticulture Center Outfall Channel, September 4, 2002,
Anderson Consulting Engineers, Inc.
9. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007
10. Monitor Well Installation and Slope Stability Assessment Status, September 7, 2010,
Earth Engineering Company (EEC Project No. 09-01-032).
11. Project Development Drainage and Erosion Control Report, Center for Advanced
Technologies 22nd Filing “Community Horticultural Center,” January 2003,
EDAW Inc. (Job No. 7F082.20).
12. Revised Subsurface Exploration Report, The Grove at Fort Collins, Fort Collins, Colorado,
December 7, 2010, Earth Engineering Company, Inc.(EEC Project No. 09-01-032).
13. Slope Stability Assessment, The Grove at Fort Collins, Fort Collins, Colorado,
October 7, 2010, Earth Engineering Company, Inc., EEC Project No. 09-01-032).
14. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
15. Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado,
Updated April 1999.
16. Supplemental Subsurface Water Investigation – The Grove at Fort Collins,
December 8, 2010, Applegate Group (AG File No. 10-132).
17. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Updated June 2001.
APPENDIX A
RATIONAL METHOD DEVELOPED RUNOFF CALCULATIONS
APPENDIX B
WATER QUALITY CALCULATIONS
APPENDIX C
PREVIOUS DRAINAGE MEMOS AND CORRESPONDENCE
C.1 – Horticulture Center Outfall Channel Modeling
C.1.a – Narrative
C.1.b – MODSWMM: Spring Creek 100-yr PMR
C.1.c – HEC-RAS: Truncated Spring Creek
C.1.d – HEC-RAS: Horticulture Center Channel
C.2 – Simplified Horticulture Center Outfall Analysis
C.3 – BNRR Pond Capacity Confirmation
C.4 – Ditch Company Letters
APPENDIX C.1
HORTICULTURE CENTER OUTFALL CHANNEL MODELING
C.1.a – Narrative
C.1.b – MODSWMM: Spring Creek 100-yr PMR
C.1.c – HEC-RAS: Truncated Spring Creek
C.1.d – HEC-RAS: Horticulture Center Channel
APPENDIX C.1.a
HORTICULTURE CENTER OUTFALL CHANNEL MODELING
Narrative
APPENDIX C.1.b
HORTICULTURE CENTER OUTFALL CHANNEL MODELING
MODSWMM: Spring Creek 100-yr PMR
APPENDIX C.1.c
HORTICULTURE CENTER OUTFALL CHANNEL MODELING
HEC-RAS: Truncated Spring Creek
APPENDIX C.1.d
HORTICULTURE CENTER OUTFALL CHANNEL MODELING
HEC-RAS: Horticulture Center Channel
APPENDIX C.2
SIMPLIFIED HORTICULTURE CENTER OUTFALL ANALYSIS
APPENDIX C.3
BNRR POND CAPACITY CONFIRMATION
APPENDIX C.4
DITCH COMPANY LETTERS
APPENDIX D
FLOODPLAIN INFORMATION
APPENDIX E
STREET CAPACITY CALCULATIONS
APPENDIX F
INLET AND CURB CUT CALCULATIONS
APPENDIX G
STORM LINE AND CULVERT CALCULATIONS
APPENDIX H
PRORATED CULVERT AND PRORATED WQ POND SIZING CALCULATIONS
APPENDIX I
EROSION CONTROL COST ESTIMATE AND RIPRAP/EROSION CALCULATIONS
APPENDIX J
SUPPLEMENTAL SUBSURFACE WATER INVESTIGATION
(BY APPLEGATE GROUP)
APPENDIX K
GEOTECHNICAL / SOILS INFORMATION
(BY EARTH ENGINEERING COMPANY)
APPENDIX L
WETLANDS / ENVIRONMENTAL INFORMATION
(BY CEDAR CREEK ASSOCIATES)
MAP POCKET
DR1 – DRAINAGE EXHIBIT
FLOOD – FLOODPLAIN EXHIBIT