HomeMy WebLinkAboutCITY OF FORT COLLINS COMMUNITY RECYCLE CENTER - FDP - FDP150047 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT
Community Recycling Center
Prepared for:
City of Fort Collins
Operation Services
300 LaPorte Ave., Building B
Fort Collins, CO 80521
(970) 221-6610
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite C
Windsor, Colorado 80550
(970) 674-3300
May 19, 2015
Job Number 1165-012-12
ii
May 19, 2015
Mr. Dan Mogan
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522-0580
RE: Final Drainage Report for Community Recycling Center
Dear Dan,
I am pleased to submit for your review and approval, this Final Drainage Report for the
Community Recycling Center development. I certify that this report for the drainage design was
prepared in accordance with the criteria in the City of Fort Collins Storm Drainage Manual with
variances noted. City comments, dated May 7, 2015 have been addressed in this report.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Sincerely, Reviewed By:
Erika Schneider, P.E. Michael Oberlander, P.E., LEED AP
Colorado Professional Colorado Professional
Engineer No. 41777 Engineer No. 34288
iii
TABLE OF CONTENTS
TABLE OF CONTENTS ............................................................................................................ iii
1. GENERAL LOCATION AND DESCRIPTION ................................................................ 1
1.1 Location ........................................................................................................................... 1
1.2 Description of Property ................................................................................................. 1
2. DRAINAGE BASINS AND SUB-BASINS .......................................................................... 2
2.1 Major Basin Description ................................................................................................ 2
2.2 Sub-Basin Description ................................................................................................... 2
3. DRAINAGE DESIGN CRITERIA ...................................................................................... 2
3.1 Regulations ...................................................................................................................... 2
3.2 Directly Connected Impervious Area (DCIA) Discussion .......................................... 2
3.3 Development Criteria Reference and Constraints ...................................................... 4
3.4 Hydrological Criteria ..................................................................................................... 4
3.5 Hydraulic Criteria .......................................................................................................... 5
3.6 Floodplain Regulations Compliance ............................................................................. 5
4. DRAINAGE FACILITY DESIGN ....................................................................................... 5
4.1 General Concept ............................................................................................................. 5
4.2 Specific Flow Routing .................................................................................................... 6
4.3 Drainage Summary ........................................................................................................ 7
5. CONCLUSIONS .................................................................................................................... 7
5.1 Compliance with Standards .......................................................................................... 7
5.2 Drainage Concept ........................................................................................................... 7
6. DRAINAGE SYSTEM MAINTENANCE STANDARD OPERATING PROCEDURE 8
6.1 Rain Garden.................................................................................................................... 8
6.2 Storm Drain System (including SNOUT® Water Quality System) ........................... 8
6.3 Forebay-6” Curb with “V” Notches ............................................................................. 9
7. REFERENCES ...................................................................................................................... 9
APPENDIX A VICINITY MAP, DRAINAGE AND GRADING PLANS
APPENDIX B HYDROLOGIC COMPUTATIONS
APPENDIX C HYDRAULIC COMPUTATIONS
APPENDIX D WATER QUALITY AND DETENTION POND, RAIN GARDEN, SNOUT®
WATER QUALITY SYSTEM INFORMATION AND ALTERNATIVE
COMPLIANCE/VARIANCE APPLICATION
APPENDIX E SOILS INFORMATION, FIGURES, TABLES AND EXCERPTS FROM
REPORTS
1
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
The Community Recycling Center development is located in east Fort Collins. It is
located in the Northeast Quarter of Section 19, Township 7 North, Range 68 West of the
Sixth Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. Please
refer to the location map in Appendix A.
The project is located west of Timberline Road and south of the Timberline Substation.
The Power Trail and Union Pacific Railroad is located to the west of the project and the
un-platted Timberline Star property is located to the south.
1.2 Description of Property
The property consists of 4.56 acres and is owned by the City of Fort Collins. The project
is an open air facility and will not have any buildings (except for a service shed). It will
consist of a variety of hard surfaced areas for unloading and materials storage as well as a
circulation drive off of Timberline.
The land currently slopes to the north at about 8%. The land is currently vacant. The
majority of the ground cover is dry land vegetation. There is offsite flow onto the
property parallel to Timberline Road. Flow from the Timberline Star property to the
south enters a drainage ditch at the southeast corner of the property. The ditch is adjacent
to Timberline and directs flow north to an existing pipe in the Railroad Right-of-Way.
The majority of existing soil type on-site consists of Larimer-Stoneham complex which is
classified as Type B by the Natural Resources Conservation Service. Soil information is
located in Appendix E.
2
2. DRAINAGE BASINS AND SUB-BASINS
2.1 Major Basin Description
The proposed development lies within the Spring Creek Master Drainage Basin. It is also
a portion of Basin 13 of the Timberline Road Widening Drake to Prospect Drainage
Report, by North Star Design, Inc. dated April 6, 2005.
Excerpts from the City approved “100% Design Drainage Report for Interim Timberline
Road Widening Drake to Prospect” can be found in Appendix E of this report. The
Developed Drainage Plan for the Timberline Road Widening is also located in Appendix
E.
2.2 Sub-basin Description
The existing site drains to the north where it is intercepted by an existing 24” storm
system in the RR right-of-way that discharges into Spring Creek.
3. DRAINAGE DESIGN CRITERIA
3.1 Regulations
This report was prepared to meet or exceed the “City of Fort Collins Storm Drainage
Design Criteria Manual” specifications. Where applicable, the criteria established in the
“Urban Storm Drainage Criteria Manual” (UDFCD), developed by the Denver Regional
Council of Governments, has been used.
3.2 Directly Connected Impervious Area (DCIA) Discussion
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process
for receiving water protection that focuses on reducing runoff volumes, treating the water
quality capture volume (WQCV), stabilizing drainageways and implementing long-term
source controls. The Four Step Process applies to the management of smaller, frequently
occurring events.
3
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement
Low Impact Development (LID) strategies, including Minimizing Directly Connected
Impervious Areas (MDCIA).
Runoff for the site will be routed through vegetated areas, a SNOUT® water quality
device with a sump and a forebay along the north curb and gutter thereby reducing runoff
from impervious surfaces over permeable areas to slow runoff and increase the time of
concentration and promote infiltration.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow
Release
Once runoff has been minimized, the remaining runoff shall be treated through the water
quality pond (rain garden) located north of the project.
Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate and volume of runoff during and following development. Because the site
will drain to a proposed detention and water quality pond, bank stabilization is
unnecessary with this project.
Step 4: Implement Site Specific and Other Source Control BMPs
Proactively controlling pollutants at their source by preventing pollution rather than
removing contaminants once they have entered the stormwater system or receiving waters
is important when protecting storm systems and receiving waters. This can be
accomplished through site specific needs such as construction site runoff control, post-
construction runoff control and pollution prevention / good housekeeping.
4
3.3 Development Criteria Reference and Constraints
The runoff from this site has been routed to conform to the requirements of the City
Stormwater Department. Water quality facilities are required for the new construction
proposed on the site. Water quality will be met through the use of a rain garden at the
bottom of the detention pond. Onsite detention is required for the runoff volume
difference between the 100 year developed inflow rate and the 2 year historic release rate
of 3.6 cfs, which works out to be approximately 0.6 cfs/acre, and will be provided in the
proposed water quality and detention pond.
Runoff reduction practices (LID techniques) are also required. No less than fifty percent
of any newly added impervious area must be treated using one or a combination of LID
techniques. This project will incorporate a SNOUT® water quality system, a forebay in
the form of a 6” curb with “V” cuts every 6’ along the north curb and gutter, and a rain
garden as LID techniques. The project added 83,329 sf of new impervious area. Using
the LID techniques, 100% of the new impervious area will be treated which exceeds the
50% requirement.
No less than twenty five percent of any newly added pavement areas must be treated
using a permeable pavement technology. Because of the significant water quality
facilities on the site and the nature of the heavy traffic and flow patterns, porous
pavement is not proposed. The only useful location for pavers is the main drive which
will have frequent truck traffic potentially damaging the paver system. Reversing the site
operation (such as moving the drive to the south) in order to find a good place for the
porous pavement would not be a good option because driveway spacing with the
warehouse to the south would be too short. The 100% LID techniques of the SNOUT®,
forebay and rain garden are intended to offset the need for pavers.
3.4 Hydrologic Criteria
Runoff computations were prepared for the 2-year and 10-year minor and 100-year major
storm frequency utilizing the rational method.
All hydrologic calculations associated with the basins are included in Appendix B of this
report.
5
Water quality volume and detention were calculated using the methods recommended in
the “Urban Storm Drainage Criteria Manual”. All calculations are located in Appendix
D.
3.5 Hydraulic Criteria
All hydraulic calculations are prepared in accordance with the City of Fort Collins
Drainage Criteria. All calculations are included in Appendix C of this report.
3.6 Floodplain Regulations Compliance
The site is not within a City of Fort Collins floodway or FEMA special flood hazard area
(Panel 08069C1000F). Therefore, a completed “City of Fort Collins Floodplain Review
Checklist” has not been included with this report.
4. DRAINAGE FACILITY DESIGN
4.1 General Concept
The majority of the proposed development (including the adjacent west half of the
ultimate Timberline road) will be collected and conveyed to the proposed water quality
and detention pond on the northern most portion of the site where it will be treated before
being released. The water quality capture volume for a 12-hour drain time (rain garden)
is 3,259 cf and will be accomplished with the rain garden built in the invert of the pond
with a maximum of 12 inches depth. Detention will be in addition to this water quality
capture volume. The pond outfall will discharge to an existing 18-inch storm pipe and
swale that discharges north to an existing 24-inch storm system in the Railroad right-of-
way. This system discharges into Spring Creek. An emergency overflow spillway will be
constructed and is designed to pass the 100-year flow of the site plus the 100-year
existing condition of the Timberline Star property (sub-basin OS-2) located just south of
the site.
6
4.2 Specific Flow Routing
A summary of the drainage patterns within each basin is provided in the following
paragraphs.
Basin A is 4.56 acres and includes the majority of the site. Runoff from this basin will
flow north to the forebay curb and gutter and then to the water quality and detention pond
located to the north. Basin A contains the water quality and detention pond. Discharge
from the pond will be directed north to the existing 18-inch storm pipe and swale that
discharges north to the existing 24-inch storm system in the Railroad right-of-way.
Basin OS-1 is 1.26 acres and includes the west half of the ultimate condition of
Timberline Road and a small portion in the southeast of the project site. The basin drains
to a CDOT Type C sump inlet (design point 1) that contains a SNOUT® water quality
system and sump. Flow will be then be directed north to the water quality and detention
pond.
Basin OS-2 is 4.82 acres and includes the Timberline Star property located just south of
the site. Runoff from this basin enters a drainage ditch at the southeast corner of the
property. The ditch is adjacent to Timberline and directs flow north to the Type C inlet at
design point 1. Existing conditions remain and flow from this basin will be passed over
the water quality and detention pond’s emergency spillway.
Water from the site will be detained and treated for water quality in the water quality and
detention pond located north of the site. The existing 2-year rate for basins A and OS-1 is
3.6 cfs. A 640’ long and 6’ wide swath along the bottom of the pond will also be
designed as a rain garden with underdrain for water quality treatment. After treatment,
water will be released to the north to an existing storm system and eventually to Spring
Creek. Please refer to Appendix D for pond information.
Because of the significant water quality facilities on the site and the nature of the heavy
traffic and flow patterns, porous pavement is not proposed.
7
4.3 Drainage Summary
Drainage facilities located outside of the right of way (including water quality and
detention pond, proposed storm drain system, rain garden and the pond outlet) will be
maintained by the operational staff of the facility.
5. CONCLUSIONS
5.1 Compliance with Standards
All computations that have been completed within this report are in compliance with the
City of Fort Collins Erosion Control Reference Manual for Construction Sites and the
Storm Drainage Design Criteria Manual.
Because of the significant water quality facilities on the site and the nature of the heavy
traffic and flow patterns, porous pavement is not proposed and we request a variance
from the porous pavement requirement of 25%. Please refer to Appendix D.
5.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provide for stormwater quantity and quality treatment of proposed impervious
areas.
If, at the time of construction, groundwater is encountered, a Colorado Department of
Health Construction Dewatering Permit will be required.
8
6. DRAINAGE SYSTEM MAINTENANCE STANDARD OPERATING
PROCEDURE:
Records shall be kept regarding perpetual maintenance activities. The records shall show
when and which facilities have been inspected and cleaned. Spill and illegal dumping
incidents and responses to both incidents shall also be documented and tracked.
6.1 Rain Garden
Inspect the infiltrating surface at least twice annually following precipitation events to
determine if the rain garden pond area is providing acceptable infiltration. If standing
water persists for more than 24 hours after runoff has ceased, clogging should be further
investigated and remedied. Additionally, check for erosion and repair as necessary.
Remove debris and litter from the infiltrating surface to minimize clogging of media.
Remove debris and litter from the overflow area.
Maintain healthy, weed-free vegetation.
If ponded water is observed in an infiltration pond for more than 24 hours after the end of
a runoff event, check outfall location for blockages. If clogging is primarily related to
sediment accumulation of the filter surface, remove excess accumulated sediment and
scarify the surface of the filter with a rake. If the clogging is due to migration of
sediments deeper into the pore spaces of the media, remove and replace all or a portion of
the media. Full media removal and replacement is anticipated every 5-10 years.
6.2 Storm Drain System (including SNOUT® Water Quality System)
Inspect and clean as needed all drainage catch basins (inlets) at least once a year.
Remove as much debris, silt, trash and sediment as possible from the storm drain system
when cleaning. Prevent material from washing into adjacent storm sewers, streams or
channels.
Monitor the SNOUT® monthly during the first year of new installation after the site has
been stabilized. Measurements should be taken after each rain event of 0.5 inches or
9
more, or monthly, as determined by local weather conditions. The structure should be
cleaned when the sump is half full (2 feet of material collected in a 5 foot sump). The
structure should also be cleaned if a spill or other incident causes a larger than normal
accumulation of pollutants in the structure. Maintenance is best done with a vacuum
truck. Finally, annual inspection of the anti-siphon vent and access hatch are
recommended. Flush the vent or gently rod with a flexible wire is required to maintain
the anti-siphon properties.
6.3 Forebay-6” Curb with “V” Notches
Street sweep every month along the curb to clean out the forebay. Remove as much
debris, silt, trash and sediment as possible from the notches when cleaning. Prevent
material from washing to the pond slope.
7. REFERENCES
1. City of Fort Collins, “Storm Drainage Criteria Manual”, (SDCM), dated March,
1986.
2. Urban Drainage and Flood Control District, “Urban Storm Drainage Criteria
Manual”, Volumes 1 and 2, dated June 2001, and Volume 3 dated September
1999.
3. North Star Design, “100% Design Drainage Report for Interim Timberline Road
Widening Drake to Prospect”, dated April 6, 2005.
Detention Pond - Stage/Storage
LOCATION: Intergrated Recycling Center
PROJECT NO: 1165-012-12
COMPUTATIONS BY: es
DATE: 5/19/2015
V = 1/3 d ( A + B + sqrt(A*B))
where V = volume between contours, ft3
d = depth between contours, ft
A = surface area of contour
Surface Incremental Detention Total
Stage Area Storage Storage Storage
(Elev) (Ft^2) (Ac-ft) (Ac-ft) (Ac-ft)
4929.9 0
Bottom Rain Garden 4930.0 7900 0.01 0.01
Top Rain Garden 4931.0 16300 0.27 0.00 0.28
100 year Detention 4932.0 25300 0.47 0.47 0.75
Spillway 4933.0 34600 0.68 1.16 1.44
Top Berm 4934.0 44300 0.90 2.06 2.34
REQUIRED WQCV ( RAIN GARDEN 3,259 CF)= 0.07 AC-FT
PROVIDED WQCV= 0.28 AC-FT
REQUIRED DET VOL= 0.65 AC-FT
PROVIDED DET VOL= 0.75 AC-FT
5-19-15 Pond Volume.xls