HomeMy WebLinkAboutPOUDRE VALLEY PLAZA MIXED-USE - FDP220001 - DOCUMENT MARKUPS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT
Poudre Valley Plaza Mixed Use
Poudre Valley Plaza P.U.D. Lot 7
Fort Collins, CO
Prepared for:
Schuman Companies Inc.
Mark Morrison
7385 Greendale Road, Unit 104
Windsor, CO 80528
701.590.0434
Prepared by:
i2 Consultants, Inc.
16911 Potts Place
Mead, CO 80542
Phone: 970.217.9148
Project Number: 1024-3
October 6, 2021
i2
Consultants, Inc.
16911 Potts Place, Mead, CO
970.217.9148
troy@i2-consultants.com
October 6, 2021
Mr. Matt Simpson, PE, CFM
Development Review Engineer
City of Fort Collins Utilities
222 Laporte Avenue
Fort Collins, CO 80524
RE: Final Drainage Report for Poudre Valley Plaza Mixed Use
Lot 7, Poudre Valley Plaza P.U.D., Fort Collins, CO
Dear Mr. Simpson:
We are pleased to present this Final Drainage Report for Poudre Valley Plaza Mixed Use,
Lot 7, Poudre Valley Plaza P.U.D. for your review and approval. This report has been
prepared in accordance with the Fort Collins Stormwater Criteria Manual, September
2018.
We look forward to your favorable review of this project and report. Please do not hesitate
to contact our office if you have any questions.
Sincerely,
i2 Consultants, Inc.
Troy W. Campbell, PE
Senior Project Engineer
ENGINEER’S CERTIFICATION
I hereby certify that this report for the final drainage design of Poudre Valley Plaza Mixed Use, Lot
7, Poudre Valley Plaza P.U.D. was prepared by me (or under my direct supervision) in accordance
with the provisions of the Fort Collins Storm Drainage Criteria Manual for the owners thereof.
__________________________________________
Registered Professional Engineer
State of Colorado No. 41159
(Seal)
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 2
i2 Consultants, Inc.
Final Drainage Report
Poudre Valley Plaza Mixed Use
Lot 7, Poudre Valley Plaza P.U.D.
Located within the Northwest Quarter of Section 35,
Township 7 North, Range 69 West of the 6th P.M.
City of Fort Collins, County of Larimer, State of Colorado
TABLE OF CONTENTS Page
I. GENERAL LOCATION AND DESCRIPTION 3
A. Site Location
B. Description of Property
II. DRAINAGE BASINS AND SUB-BASINS 4
A. Major Basin
B. Sub-basin and Site Drainage
III. DRAINAGE DESIGN CRITERIA 4
A. Regulations
B. Development Criteria Reference and Constraints
C. Hydrological Criteria
D. Hydraulic Criteria
IV. DRAINAGE FACILITY DESIGN 5
A. General Concept
B. Specific Details
V. SEDIMENT, EROSION CONTROL AND STORMWATER QUALITY 7
A. Temporary Sediment and Erosion Control
B. Permanent Water Quality BMPs
VI. CONCLUSIONS 10
A. Compliance with Standards
B. Drainage Concept
VII. REFERENCES 11
VIII. APPENDICIES 12
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 3
i2 Consultants, Inc.
I. GENERAL LOCATION AND DESCRIPTION
A. Site Location:
The proposed development is located in the northwest quarter of Section 35,
Township 7 North, Range 69 West, of the 6th Principal Meridian, City of Fort Collins,
County of Larimer, State of Colorado. Furthermore, the project is north of Arbor
Street Avenue and east of Shields Street.
The legal description of the property is Lot 7, Poudre Valley Plaza P.U.D.
The subject site is currently vacant.
B. Description of Property:
The subject development lot consists of roughly 0.25 acres. The area considered
with this drainage report is roughly 0.43 acres. The proposed building will be within
Lot 7 and the parking, landscaping, walks and accesses will be located on Tract A
Poudre Valley Plaza P.U.D. The development of Lot 7 will consist of construction of
a single building, walks and landscaping. A portion of the existing parking to the
north of the building will be removed and replaced with this project.
The site currently is vacant but has been overlot graded with the Poudre Valley
Plaza P.U.D. improvements. The site is bound by Arbor Avenue to the south,
existing commercial development to the north, east and west.
The subject site generally slopes from south to north at varying slopes from 0% to
1%. A portion of the site drains to the east to the existing retention pond
constructed as part of Poudre Valley Plaza P.U.D. The existing runoff from the
subject property drains to the north in existing conveyances (curb, gutter, sheet
flow) to the existing detention pond in the northeast corner of Poudre Valley Plaza
P.U.D. The subject site was included in the approved Final Drainage and Erosion
Control Study for Poudre Valley Plaza, Fort Collins, Colorado, dated January 23,
1996, prepared by RBD, Inc. Engineering Consultants
According to the Natural Resources Conversation Service (NRCS) Web Soil
Survey, the native soils in this area are Altvan-Santanta loams, 0 to 3 percent
slopes (Map Unit Symbol #3), which is a Type B soil and Altvan-Satanta loams, 3 to
9 percent slopes (Map Unit Symbol #4), which is a Type B soil. Please refer to the
NRCS soils information in the Appendix.
Existing drainage facilities near or adjacent to the site include existing curb & gutter
installed with Poudre Valley Plaza P.U.D. as well as an existing retention pond east
of the site and existing detention pond north of the site. Furthermore, there is an
existing storm drain system in Arbor Avenue.
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 4
i2 Consultants, Inc.
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin:
This site is located within the Mail Creek Basin as shown on the City of Fort Collins
Master Drainage Plan. This basin historically generally flows from northwest to
southeast.
There no agricultural irrigation facilities within 100 feet of the property boundary for
the proposed site.
The site is shown on FEMA panel 08069C0986G, effective 05/02/2012. The
subject site is located with Zone X of the FEMA panel.
B. Sub-basin and Site Drainage:
The proposed site generally directs runoff north to existing improvements. A portion
of the site will drain east to the existing retention pond, due to existing grades and
site constraints.
The subject site is shown within Basins 1, 2 and 4 of the approved Final Drainage
and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado, dated
January 23, 1996, prepared by RBD, Inc. Engineering Consultants. There is a
small portion of this site in the southeast corner that flows offsite to Arbor Avenue
and was not accounted for in the above referenced report.
There is no offsite runoff that reaches the subject property.
The drainage patterns proposed with the subject improvements are generally
consistent with the drainage patterns proposed with the above referenced report.
III. DRAINAGE DESIGN CRITERIA
A. Regulations:
This report has been prepared in general accordance with the Fort Collins
Stormwater Criteria Manual, September 2018 and the Urban Storm Drainage
Criteria Manual (USDCM).
B. Development Criteria Reference and Constraints:
The subject site has been included in the following previous reports:
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 5
i2 Consultants, Inc.
· Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort
Collins, Colorado, dated January 23, 1996, prepared by RBD, Inc.
Engineering Consultants.
This report has been prepared in general accordance with the appropriate City and
USDCM criteria and previous reports.
C. Hydrological Criteria:
Fort Collins Stormwater Criteria Manual, September 2018, as well as the USDCM.
There are no deviations from the criteria in this report.
The design storms for this project are the 2-year and the 100-year recurrence
intervals. Runoff is calculated using the Rational Method since all basins are
smaller than 5 acres. The Rational Method calculations are computed by the
following:
Q = ciA where: Q = Runoff in cubic feet per second
c = Calculated runoff coefficient for design event
i = Storm intensity in inches/hour
A = Basin area in acres
Hydrological calculations have been prepared in accordance with the Fort Collins
Stormwater Criteria Manual, September 2018 as well as the USDCM.
D. Hydraulic Criteria:
Rational calculations were prepared using methodology outlined in the Fort Collins
Stormwater Criteria Manual, September 2018.
Hydraulic capacities were calculated using Hydraflow Express Extension for
Autodesk Civil 3D, Version 2021.
IV. DRAINAGE FACILITY DESIGN
A. General Concept:
The drainage patterns associated with the proposed improvements are generally
consistent with the existing drainage patterns, flow and the drainage patterns
proposed with the Final Drainage and Erosion Control Study for Poudre Valley
Plaza, Fort Collins, Colorado.
The proposed site generally directs runoff north to the existing detention pond in the
northeast corner of Poudre Valley Plaza P.U.D. A portion of the site will drain south
to Arbor and east to the existing retention pond, due to existing grades and site
constraints, as depicted within the Final Drainage and Erosion Control Study for
Poudre Valley Plaza, Fort Collins, Colorado.
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 6
i2 Consultants, Inc.
The runoff for the site was determined using the Rational Method, as detailed
above. The proposed improvements have been divided into seven (7) drainage
basins. The basins have been created to direct runoff to existing and proposed
facilities.
B. Specific Details:
Basin A1
Basin A1 (0.01 acres) is in the northwestern portion of the site and contains the
northwestern portion of the proposed building. The basin generally drains from
south to north. The runoff from the building will be captured in a proposed planter
with rain garden for water quality purposes.
Basin A2
Basin A2(0.11 acres) is in the northwestern portion of the site and contains a portion
of the northern section of the proposed building. The basin generally drains from
south to north. The runoff from the building will be captured in a proposed planter
with rain garden for water quality purposes. The landscape area on the west side of
the building will drain to the existing eastern flowline of the existing access.
Basin B
Basin B (0.11 acres) is in the northeastern portion of the site and contains the
northeastern portion of the proposed building, concrete sidewalks and landscaping.
The runoff from the building will be captured in a proposed planter with rain garden
for water quality purposes.
Basin C
Basin C (0.03 acres) is along the northeastern portion of the site and contains
proposed concrete sidewalks and landscaping. The basin drains to an existing
slotted drain installed with the Poudre Valley Plaza P.U.D. and to the existing
retention pond located east of Lot 7.
Basin D
Basin D (0.13 acres) is along the southwestern portion of the site and contains the
southern portion of the proposed building and landscaping. The basin generally
drains from north to south. The runoff from the building will be captured in a
proposed rain garden for water quality. The basin will be released from the rain
garden to the existing eastern flowline of the existing access.
Basin E
Basin E (0.02 acres) is along the southeastern portion of the site and contains
landscaping and a sidewalk from the building. The basin generally drains from
north to south. The basin will be released south the northern flowline of Arbor
Drive, in a pattern similar to what is shown in the Final Drainage and Erosion
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 7
i2 Consultants, Inc.
Control Study for Poudre Valley Plaza, Fort Collins, Colorado, dated January 23,
1996, prepared by RBD, Inc. Engineering Consultants.
Basin F
Basin F (0.01) acres is in the southeastern portion of the site and will contain
landscaping. This basin is in a low area of the subject site and will drain to the
existing retention pond east of Lot 7.
The subject site was considered in Basins 1 and 2 of the Final Drainage and
Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado. The
imperviousness for the basins are provide below:
Basin 1: 68.3% (0.81 “C” Value)
Basin 2: 79.6% (0.87 “C” Value)
The composite imperviousness calculated for this development is 56.6%, with
a “C” value of 0.62. These values are below the assumed values in the overall
development drainage report. No additional detention is required as a result
of the proposed development of Lot 7.
The drainage design for the subject development will reduce the amount of runoff
into the retention pond. A portion of the subject site was designed to drain to the
retention pond in the overall report. With the proposed layout and constraints of the
proposed development, a small portion of runoff will drain north to the existing pond
in the northeast corner of the site and not into the retention pond. The additional
flow will be from roughly 700 s.f. of sidewalk to the north of the proposed building.
The drainage design for the subject site will generally conform to the overall
drainage design for Poudre Valley Plaza P.U.D. The flow patterns proposed with
the subject development generally follow the patterns of the overall drainage report,
with exceptions noted above.
The proposed drainage from this site is not anticipated to have a negative impact on
the existing facilities as the existing detention pond will provide for attenuation of the
developed runoff.
V. SEDIMENT, EROSION CONTROL AND STORMWATER QUALITY
A. Temporary Sediment and Erosion Control:
Several sediment and erosion control measures will be incorporated into the initial
phase of construction. The initial sediment and erosion control measures to be
installed shall include sediment control logs, as well as a vehicle tracking control
mat at the construction entrance, inlet protection in Arbor Avenue and rock socks
within the existing flowline of the access. An initial control measure will be the
installation of construction fence around the development perimeter.
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 8
i2 Consultants, Inc.
Furthermore, additional measures for sediment and erosion control shall consist of
providing an area designated for a concrete washout area. A stabilized staging
area is proposed in the parking area to the north of the subject site. The initial
measures for sediment and erosion control shall be maintained and updated as
necessary during the interim and final stages of the project.
Additionally, any area that has been disturbed by construction activities and left
exposed for more than fourteen (14) days, shall receive drilled seeding and straw
mulch at 2 tons/acre, until permanent landscaping or ground cover has been
provided.
Four Step Process to Minimize Adverse Impacts of Urbanization
Employing runoff reduction practices: Water Quality will be utilized with this
development. There will be landscaping around each side of the site and no
new parking areas are proposed with this development.
Implementing best management practices (BMPs): Water Quality will be
provided in the form of rain gardens to capture runoff from the proposed
building. An underdrain will be installed in the rain gardens along the
southern portion of the site.
Stabilizing Streams: The runoff from the subject site drains to paved
surfaces and existing detention facilities. The runoff release from the overall
development will be controlled by these existing facilities.
Implementing site specific and other source control BMPs: A stabilized
staging area will be provided to the north of the subject site on existing
asphalt. Appropriate erosion and pollution control shall be installed around
the staging area.
B. Permanent Water Quality BMPs
Rain gardens will be installed along the southern portion of the proposed building to
provide permanent water quality. Furthermore, water quality planters/rain gardens
will be installed at three (3) areas along the northern portion of the proposed
building. These rain gardens will treat runoff prior to being released to existing
conveyances to the north of the site. The design volume is larger than the required
volume (120% of WQCV) for each planter.
A rain garden will also be installed along the southern portion of the building. The
rain garden will capture and treat runoff from the building, prior to being released to
the existing access. The design volume for each rain garden along the southern
side of the building is larger than the required (120% of WQCV) volume.
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 9
i2 Consultants, Inc.
These measures were selected for permanent water quality due to the site
constraints regarding the proposed layout and tight tolerance for elevations. Please
refer to the Appendix for water quality/rain garden calculations.
The existing detention pond in the northeast corner of the overall development does
not contain a water quality component. The retention pond will provide water quality
for runoff that reaches the pond.
Required Treatment Area
The proposed development utilizes water quality practices to the extent practical for
the project. Rain gardens are proposed on the northern and southern portions of
the building to treat roof runoff. 100% of the proposed building runoff will be treated
in the proposed rain gardens.
Portions of new and modified impervious areas are not able to be treated to the
existing conditions surrounding the subject site. Proposed and modified sidewalk
and modified parking areas drain away from the subject site to existing
conveyances and therefore are not able to be treated.
Treatment Summary
Treated New Impervious Area 9,260 sf (62.0% of Total Impervious Area)
Untreated New or
Modified Impervious Area 5,670 sf (38.0% of Total Impervious Area)
Total New or
Modified Impervious Area 14,930 sf
The proposed development is not able to comply with City of Fort Collins criteria for
LID treatment based on the surrounding and existing conditions.
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 10
i2 Consultants, Inc.
VI. CONCLUSIONS
A. Compliance with Standards:
The drainage design is in general compliance with the Fort Collins Stormwater
Criteria Manual, September 2018 as well as the Urban Storm Drainage Criteria
Manual (USDCM). Furthermore, the design is in general conformance with the
approved Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort
Collins, Colorado, dated January 23, 1996, prepared by RBD, Inc. Engineering
Consultants.
The subject site is treating 100% of proposed roof runoff in proposed rain
gardens/bioretention areas on the north and south sides of the site. There are new
and modified impervious areas, such as sidewalks and parking that are not able to
be treated, per City criteria, since these areas drain away from the subject site to
existing conveyances and there is not existing infrastructure to support necessary
items such as an underdrain. The subject site is the last undeveloped property in
the overall development.
B. Drainage Concept:
The runoff from this site will be conveyed by existing and proposed storm drainage
improvements, including proposed curb, gutter, swales and rain gardens. The
drainage design for this project should not negatively impact improvements
downstream or the existing storm system.
Permanent water quality for the site will be provided through rain gardens to slow
runoff and provide a filter for runoff prior to leaving the subject site.
Final Drainage Report
Poudre Valley Plaza Mixed Use, Fort Collins, CO
October 6, 2021 Page 11
i2 Consultants, Inc.
VII.REFERENCES
1. Fort Collins Stormwater Criteria Manual, dated September 2018.
2. Urban Drainage and Flood Control District, Drainage Criteria Manual Volumes 1,
Revised August 2018, Volume 2, Revised September 2017 and the Volume 3, dated
November 2010 and Updated October 2019.
3. Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins,
Colorado, dated January 23, 1996, prepared by RBD, Inc. Engineering Consultants.
T
E
TRACT A
P0UDRE VALLEY PLAZA P.U.D.
ARBOR DRIVEPRIVATE ACCESSDRIVELOT 7
LOT 6
EXISTING
BUILDING
EXISTING
RETENTION
POND
EXISTING
TRASH
ENCLOSURE
PROPOSED BUILDING
FF = 5083.70
PROPOSED BUILDING
FF = 5082.45
JLB LID TREATMENT PLANLID-1
Know what's below.
before you dig.Call
R
LEGEND OF SYMBOLS
SURVEY NOTES:
SHEET
OF SHEETSPOUDRE VALLEY PLAZA MIXED USEUTILITY PLANSCITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADONORTHWEST 1/4, SECTION 35, TOWNSHIP 7 NORTH, RANGE 69 WEST13
PRELIMINARY
NOT FOR CONSTRUCTION
10/06/2021
C:\Users\troy\Dropbox\I2\Projects\1024-3 PVP\DWG\Exhibits\PVP_BMP_2021-09-27.dwg, 10/6/2021 7:44:11 AM
TRACT A
P0UDRE VALLEY PLAZA P.U.D.
ARBOR DRIVEPRIVATE ACCESSDRIVELOT 6
EXISTING
BUILDING
EXISTING
RETENTION
POND
EXISTING
TRASH
ENCLOSURE
PROPOSED BUILDING
FF = 5082.45
LOT 7
WQEL=5086.15; EMERG. CREST AT 5086.15; V = 141 CU.FT.WQEL=5086.15; EMERG. CREST AT 5086.15; V = 148 CU.FT.
WQ OVERFLOW AT 5082.43; V = 182 CU.FT.
5083
5083 50815082
PROPOSED BUILDING
FF = 5083.70
JLB
7 FINAL DRAINAGE PLANC-7
NOTES
Know what's below.
before you dig.Call
R
LEGEND OF SYMBOLS
SURVEY NOTES:
SHEET
OF SHEETSPOUDRE VALLEY PLAZA MIXED USEUTILITY PLANSCITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADONORTHWEST 1/4, SECTION 35, TOWNSHIP 7 NORTH, RANGE 69 WEST13
PRELIMINARY
NOT FOR CONSTRUCTION
10/06/2021
BASIN RUNOFF SUMMARY
WATER QUALITY SUMMARY
C:\Users\troy\Dropbox\I2\Projects\1024-3 PVP\DWG\Sheets\PVP_DR.dwg, 10/6/2021 7:43:34 AM