HomeMy WebLinkAboutSPRING CREEK FARMS NORTH SECOND FILING - FDP - FDP120005 - REPORTS - DRAINAGE REPORTFinal Development Plan
Drainage Report
For
Spring Creek Farms North Filing No. 2
submitted to:
City of Fort Collins,
Colorado
August 29, 2012
760 Whalers Way
Bldg C, Suite 200
Fort Collins, CO 80525
970.226.0557 main
303.595.9103 metro
970.226.0204 fax
ideas@tstinc.com
www.tstinc.com
August 29, 2012
Mr. Glen Schlueter
City of Fort Collins
Stormwater Engineering Department
700 Wood Street
Fort Collins, CO 80521
Re: Spring Creek Farms North Filing No. 2
Project No. 1045.0039.00
Dear Mr. Schlueter,
We are pleased to resubmit this final drainage report for Spring Creek Farms
North Filing No. 2. The purposed of this report is to evaluate the drainage
conditions of the proposed project site. This report was prepared based on the
City of Fort Collins drainage criteria and we believe it satisfies all City
requirements for a final analysis. Comments from the July 30, 2012 review have
been incorporated into this resubmittal.
We look forward to your review and comments and will gladly answer any
questions that you may have.
Sincerely,
TST, INC. CONSULTING ENGINEERS
Eric M. Fuhrman, P.E.
EMF
Spring Creek Farms North Filing No. 2 Final Drainage Report
TABLE OF CONTENTS
1.0 Introduction
1.1 Scope and Purpose ..................................................................................................... 1
1.2 Project Location and Description ................................................................................. 1
1.3 Previous Studies ......................................................................................................... 1
2.0 Existing/Historic Conditions ............................................................................................. 3
3.0 Developed Conditions Plan
3.1 Design Criteria ............................................................................................................. 4
3.2 Drainage Plan Development ....................................................................................... 4
3.2.1 Street Capacity ................................................................................................... 5
3.2.2 Inlet Design ......................................................................................................... 5
3.2.3 Storm Sewer Design .......................................................................................... 5
3.2.4 Riprap Design ..................................................................................................... 6
3.2.5 Detention Pond Design ....................................................................................... 6
3.3 Erosion and Sediment Control .................................................................................... 7
4.0 Conclusion .......................................................................................................................... 8
5.0 References .......................................................................................................................... 8
Figures
Figure 1: Vicinity Map ................................................................................................................... 2
Appendices
Appendix A – Rational Method Hydrologic Analysis
Appendix B – Street Capacity Analysis
Appendix C – Inlet Analysis
Appendix D – Storm Sewer Design
Appendix E – Riprap Desgin
Appendix F – Detention Pond Design
Appendix G – Excerpts from Previous Reports
Appendix H – Excerpts from Spring Creek Farms Third Filing Drainage Report
Sheets
Drainage & Erosion Control Plan ........................................................................................ Sheet 1
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 1
1.0 Introduction
1.1 Scope and Purpose
This report presents the results of a final drainage evaluation for Spring Creek Farms North
Filing No. 2 which consists of Outlot A of the Spring Creek Farms North Subdivision. A
developed hydrologic analysis of the area is presented to show adherence to the overall
preliminary analyses presented to the City by Stantec in 2008 and then by Aspen Engineering in
2011. The allowable release rates, as set forth in those previous studies, will be adhered to and
are used to size the detention facility for the developed area.
1.2 Project Location and Description
Spring Creek Farms North Filing No. 2 is located in the Southeast Quarter of Section 19,
Township 7 North, Range 68 West of the 6th Principal Meridian. More specifically, the project is
located in Parcel B1 of the Amended Overall Development Plan for Spring Creek Farms North
located at the northwest quadrant of Timberline and Drake Roads in Fort Collins, Colorado. The
site is bounded on the north by Charles Brockman Drive (adjacent to the Police Station), on the
east by Timberline Road, on the south by Drake Road, and on the west by the future extension
of Joseph Allen Drive.
The project is planned for a multi-family community, consisting of approximately 314 residential
units in 11 buildings situated on a 16-acre site. These are apartment-style residential buildings
fronting a main loop road and parking areas within the site. The site will also include a club
house with pool and other active outdoor amenities such as community gardens and park areas.
A vicinity map illustrating the project location is provided in Figure 1. The proposed site is
located within the Foothills Master Drainage Basin.
The area undergoing development with this project includes the 16-acre site and the future
Joseph Allen Drive, resulting in a total developed acreage of 17.9 acres. The west half of
Timberline Road and the north half of Drake Road as they front the property are also included in
the analysis. The areas to the west of Joseph Allen Drive are not included in this analysis.
1.3 Previous Studies
The “Spring Creek Farms North Overall Drainage Exhibit”, prepared by Aspen Engineering and
dated February 22, 2011 presented drainage basin information for the entire Spring Creek
Farms North development area. This Drainage Exhibit referred to the approved Spring Creek
Farms North Drainage and Erosion Control Plan, prepared by Stantec and dated October 4,
2005.
The “100% Design Drainage Report for Interim Timberline Road Widening Drake to Prospect”
prepared by North Star Design and dated July 20, 2005 provided an overview of the master
drainage planning for the area along Timberline Road and for the Spring Creek Farms area.
The “Conceptual Drainage Report for Spring Creek Farms”, prepared by Manhard Consulting
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 2
Ltd and dated December 11, 2000 was also referred to for overall release rate allowances for
the area.
Figure 1. Vicinity Map
PROJECT
SITE
DRAKE ROAD
TIMBERLINE ROAD
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 3
2.0 Existing/Historic Conditions
The site generally slopes from northwest to the southeast at 0.5% to 1.0% toward the
southeastern most corner of the site at Timberline and Drake Roads where runoff is intercepted
in an existing area inlet at the North Tributary Storm Sewer system. The soil naturally occurring
on this site is classified as Type C by the Natural Resources Conservation Service (NRCS). The
existing condition of the land consists of natural grasses that appear to be regularly mowed
during summer months. Groundwater has been observed in geotechnical borings at depths
between 13 and 21 feet below the surface.
The multi-family site is surrounded by public roads: Timberline Road, Drake Road, Charles
Brockman Drive, and will be enclosed by the future Joseph Allen Drive on the west. Currently,
the west half of Timberline Road from Charles Brockman Drive to Drake Road drains onto the
site through a 10’ wide concrete sidewalk chase. The north half of Drake Road sheet flows
drains onto the site as there currently is no curb and gutter on the north side of Drake Road
from the railroad tracks to the Timberline intersection.
The allowed 100-year release from the entire Spring Creek Farms North area is 20 cfs over
approximately 55 acres. However, since the original drainage planning occurred for this area, a
few basins located near the north end are now directing storm runoff to the north toward the
Spring Creek Basin. These basins are shown on the Overall Drainage Exhibit prepared by
Aspen Engineering and are basins 6, 7, 8, 10, 11, and 12 and make up almost 10 acres of land.
Please refer to Appendix I for further illustration.
The remaining basins still draining toward the North Tributary Storm Sewer system are 1-5, and
9. These make up 48.27 acres. Of the basins draining toward the south, basin 5 is now the
existing Police Station. This site makes up approximately 8.6 acres total tributary area and has
a detained release rate of 3.10 cfs.
Therefore, the remaining allowable release into the North Tributary Storm Sewer system is 16.9
cfs (20 cfs – 3.1 cfs) over 39.67 acres (48.27 – 8.6 acres) released at 0.42 cfs/acre.
Each site that develops within the Spring Creek Farms North area is required to detain onsite
and release stormwater at their prorated share of the outfall capacity of the North Tributary
Storm Sewer system.
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 4
3.0 Developed Conditions Plan
This final drainage analysis for Spring Creek Farms North Filing No. 2 is intended to
demonstrate the sufficiency of the proposed drainage facilities and the conformance of the
drainage concept with the previous analyses.
3.1 Design Criteria
The drainage system presented in this report has been developed in accordance with the
criteria established by the Fort Collins Stormwater Criteria Manual (FCSCM) adopted December
2011. Design guidelines and information were also obtained from the Urban Drainage and Flood
Control District, Urban Storm Drainage Criteria Manual (USDCM) where applicable.
Peak design flows for the 2, 10, and 100 year storms were determined using the Rational
Method. City of Fort Collins rainfall data can be found in Appendix A of this report. A full
description of the Rational Method including the applicable runoff coefficients can be found in
Appendix B.
3.2 Drainage Plan Development
Each site that develops within the Spring Creek Farms North area is required to detain onsite
and release stormwater at their prorated share of the North Tributary Storm Sewer outfall
capacity. The developed site will consist of the onsite basins, the east Joseph Allen Drive, the
west half of Timberline, and the north half of Drake road adjacent to the site. For the purposes
of this study, the western half of Joseph Allen Drive and the property to the west of Joseph Allen
Drive are assumed to be intercepted and detained with the sites that develop on the west side
of Joseph Allen Drive. Information regarding these basins can be found in the report applicable
to this area prepared by Aspen Engineering. In addition, they provided the information for the
design of the storm sewer within Joseph Allen Drive.
Basin A (sub-basins A1-A24) encompasses the majority of the site and the area that is tributary
to Pond 1. Storm drainage from the different sub-basins will be collected by inlets and pipes to
be conveyed to a detention pond in the southeast corner of the site. It will then be discharged
via storm sewer to the North Tributary Storm Sewer.
Onsite basin 2 directs runoff toward Charles Brockman Drive and ultimately into the detention
pond at the Police Station. The amount of runoff generated in the 100-year developed condition
in this basin is 5.09 cfs. It has been determined that the existing detention pond capacity at the
Police Station is adequate to accept this flow. The original required design volume per the
Police Station drainage report was 1.82 ac-ft and 2.11 ac-ft was provided. Checking the volume
requirements with adding Onsite basin 2 increases the required volume to 1.93 ac-ft using the
current release rate from that pond of 3.1 cfs. A mass balance with the increased area is
included in Appendix A. The street and inlet capacities on Charles Brockman Drive were
analyzed (see applicable sections) to verify there is adequate capacity to accept some
additional runoff from this multi-family site.
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 5
Basin OS5 is the south half of Charles Brockman Drive. This area was included in the Police
Station design and is included here to verify the street and inlet capacities with the addition of
onsite Basin 2.
The results of the Rational Method Hydrologic Analysis can be found in Appendix E.
3.2.1 Street Capacity
The public streets around the site were analyzed for street capacity. Timberline Road to the
east & Drake Road to the south are arterial roads, while the roads to the west and north are
local streets. On the local streets, flow depth was limited to the height of the crown so that
water did not overtop the crown and leave the site. The width of flow was also limited to the
back of walk if that became the controlling factor.
The applicable street encroachment criteria were taken from Table ST-2 (minor storm) and
Table ST-3 (major storm) of the FCSCM. All of the streets meet the applicable requirements
and will function below the allowed capacities. The results of the Street Capacity Analysis can
be found with supporting calculations in Appendix B.
3.2.2 Inlet Design
CDOT Type “R”, Type 13, Type 13 Combo, or area inlets were used to collect the 100-yr runoff
from low points. Ponding depths for the inlets were set based on the allowable depth for that
location. Along Joseph Allen & Charles Brockman, depths were limited to avoid overtopping the
crown. At two onsite locations, Design Points 5 & 13, ponding depths were set so that the flow
at those locations was balanced between the inlets on either side of the roads. The inlets are
connected to storm sewer systems that convey the runoff to the detention ponds.
At DP 20, there are existing sidewalk culverts to convey the drainage off of Timberline Road.
These culverts have been analyzed with the addition of a concrete rundown channel to convey
the drainage into the detention pond.
In emergency overflow conditions, all inlets will “spill” to a downstream location before impacting
any of the buildings.
The results of the Inlet Analysis & Design can be found with supporting calculations in Appendix
C.
3.2.3 Storm Sewer Design
The storm sewer lines were analyzed with NeoUDSewer v1.5.3. The pipes were sized such
that the hydraulic grade remains below the flow line of the proposed inlets.
Storm Sewer Lines ST-1 & ST-2 convey runoff from the site to Detention Pond 1. The 100-yr
water surface in Pond 1 was based on the volume of required detention.
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 6
Line ST-3 conveys runoff from Drake Road into Detention Pond 1.
Line ST-4 conveys the release from Detention Pond 1 to the North Tributary Storm Sewer.
The storm sewer line & west inlet in Joseph Allen has been sized and designed by Aspen
Engineering with their Spring Creek Farms North project. Information was provided by them for
inclusion of the construction of that line with this project. See their report for supporting
information.
The results of the Storm Sewer Design can be found with supporting NeoUDSewer results in
Appendix D.
3.2.4 Riprap Design
Riprap was placed at pipe outlets where exit velocities exceeded 5.0 fps. The results of the
Riprap Design can be found with supporting documentation in Appendix E.
3.2.5 Detention Pond Design
A water quality and detention pond was provided before discharge of the site runoff. The pond
was sized based on FCSCM criteria and the allowed release rate. For this multi-family project,
the basins included in the prorated share for allowable release are basins A1-24, for a total of
19.52 acres. The resulting release rate at 0.42 cfs/acre is 8.20 cfs.
The pond was provided with an orifice plate with multiple orifices to provide an extended drainage
time for water quality. The 100-yr storm will overtop the water quality structure and enter the
discharge pipe. An orifice plate on the discharge pipe controls the 100-yr discharge of the pond. At
the allowed release rates, the required water quality capture volume is 0.51 ac-ft with an additional
3.66 ac-ft of detention volume for the 100-yr storm for a total pond volume of 4.17 ac-ft required.
See Table 1 below for a summary of the volumes and water surface elevations.
Table 1. Detention Pond Design
Design
Total
Volume
Water
Surface
Element (acre-ft) Elevation
Pond Outlet n/a 4925.40
WQCV 0.51 4927.95
100-year Detention 4.19 4934.15
The 100-yr water surface elevation and required freeboard is below the adjacent sidewalks,
which have a low point elevation of 4935.30. Therefore, there is no need to create freeboard, or
storage, above the sidewalk elevation. Any pond overtopping will spill over the adjacent
sidewalk and into Timberline Road and Drake Road. The length of the available spill over the
sidewalk has been calculated to be 240’ with a maximum depth of 0.50’. No structures will be
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 7
inundated for this to occur. Due to this condition, no dedicated spillways have been sized.
A SWMM analysis of the pond was done for sizing purposes. This analysis and other
supporting calculations are provided in Appendix F.
3.3 Erosion and Sediment Control
The entire site is to be disturbed during construction. Erosion will be mitigated, as much as
possible, with seeding and mulching where applicable. Sedimentation will be controlled primarily by
temporary structural measures. This will include the installation of gravel filters around affected
proposed and existing inlets, silt fence adjacent to areas that drain onto public roadways and wattle
checks in swales. It will be the responsibility of the developer and the developer’s agents to
maintain all erosion and temporary sedimentation controls, in good working order, until risk of
erosion has been mitigated.
Upon completion of the utility work, the roads will be paved and the entire disturbed area of the site
will be reseeded and mulched to provide soil stabilization until build out. Elimination of bare soils by
pavement, and/or establishment of vegetation will help eliminate the potential of soil erosion caused
by storm runoff. The developer will be responsible for removing all of the temporary sedimentation
controls at such time that the risk of erosion has been mitigated by vegetative cover as approved by
the city. It will be necessary to leave the temporary structural sedimentation controls in place until
vegetative cover has been sufficiently established, to a minimum of 70% of original ground cover as
determined by pre-construction photos accepted by the City of Fort Collins and/or other governing
jurisdictions. It will also be necessary to flush and remove any accumulated sediment that may have
built up in the storm sewers and downstream detention ponds in such case that temporary
sedimentation controls were overwhelmed at any point during the construction process.
The drainage and erosion control plans, located in the plan set, show the location of the proposed
temporary and permanent erosion control measures. These erosion control plans are the minimum
level of protection needed and must be updated during the process of construction to maintain the
intent of the plans and reduce the risk of offsite discharge. See the separate Storm Water
Management Plan for additional information regarding erosion control.
Spring Creek Farms North Filing No. 2 Final Drainage Report
Page 8
4.0 Conclusion
The standards in the Fort Collins Stormwater Criteria Manual (FCSCM) and the Urban Storm
Drainage Criteria Manual, along with the overall allowable release requirements set forth in
previous studies of the Spring Creek Farms North site have been used to create an effective storm
drainage design. The proposed design is expected to collect and convey storm water runoff through
and around the site safely and effectively to the existing North Tributary Storm Sewer system.
According to the study presented, the site complies with the allowable releases into the North
Tributary Storm Sewer System and provides sufficient stormwater detention on-site to account for
the allowable releases from the site and adjacent roadway runoff. The North Tributary Storm Sewer
system will be tied into with a controlled release and water quality structure near the corner of
Timberline and Drake Roads.
5.0 References
1. Aspen Engineering, February 22, 2011, “Spring Creek Farms North Overall Drainage
Exhibit”
2. North Star Design, Inc., July 20, 2005 “100% Design Drainage Report for Interim
Timberline Road Widening Drake to Prospect”
3. Manhard Consulting, Ltd., December 11, 2000. “Conceptual Drainage Report for
Spring Creek Farms Fort Collins, Colorado”
4. City of Fort Collins, December, 2011. “Fort Collins Stormwater Criteria Manual,
Amendments to the Urban Drainage and Flood Control District Criteria Manual”
5. Urban Drainage and Flood Control District, 2001, “Urban Storm Drainage Criteria
Manual”.
APPENDIX A
Rational Method Hydrologic Analysis
Spring Creek Farms North Filing No. 2 Final Drainage Report
C2 C
10 C100
Streets: Paved 0.03 0.95
Lawn, Heavy, <2% Slope 0.81 0.20
Streets: Paved 0.02 0.95
Lawn, Heavy, <2% Slope 0.38 0.20
Roofs 0.24 0.95
Streets: Paved 0.47 0.95
Lawn, Heavy, <2% Slope 0.21 0.20
Roofs 0.25 0.95
Streets: Paved 0.00 0.95
Lawn, Heavy, <2% Slope 0.11 0.20
Roofs 0.08 0.95
Streets: Paved 0.90 0.95
Lawn, Heavy, <2% Slope 0.43 0.20
Roofs 0.14 0.95
Streets: Paved 0.49 0.95
Lawn, Heavy, <2% Slope 0.22 0.20
Roofs 0.23 0.95
Streets: Paved 0.83 0.95
Lawn, Heavy, <2% Slope 0.29 0.20
Roofs 0.21 0.95
Streets: Paved 0.11 0.95
Lawn, Heavy, <2% Slope 0.01 0.20
Roofs 0.03 0.95
Streets: Paved 0.17 0.95
Lawn, Heavy, <2% Slope 0.08 0.20
Roofs 0.09 0.95
Streets: Paved 0.30 0.95
Lawn, Heavy, <2% Slope 0.13 0.20
Roofs 0.20 0.95
Streets: Paved 0.01 0.95
Lawn, Heavy, <2% Slope 0.19 0.20
Roofs 0.16 0.95
Streets: Paved 0.16 0.95
Lawn, Heavy, <2% Slope 0.09 0.20
Roofs 0.09 0.95
Streets: Paved 0.01 0.95
Lawn, Heavy, <2% Slope 0.11 0.20
Roofs 0.08 0.95
Streets: Paved 0.14 0.95
Lawn, Heavy, <2% Slope 0.02 0.20
Roofs 0.00 0.95
Streets: Paved 1.34 0.95
Lawn, Heavy, <2% Slope 0.44 0.20
45.0%
87.5%
80.4%
78.2%
93.3%
76.5%
79.4%
47.2%
73.5%
Percent
Impervious
3.6%
40.6%
77.4%
Spring Creek Farms North Filing No. 2 Final Drainage Report
Basin Overland Flow Average Channelized Channel Channel Channelized
Length, L Overland Slope Tov Tov Tov Flow Length Slope Velocity Time (Tt)
(ft) (%) 2-year 10-year 100-year (ft) (%) (ft/s) (min) 2-year 10-year 100-year
A1 0.23 0.23 0.28 25 32 3 3 2 165 0.1 0.5 5.5 9 9 8
A2 0.50 0.50 0.63 22 6 3 3 2 416 1 1.5 4.6 8 8 7
A3 0.78 0.78 0.98 45 2 3 3 1 355 0.6 1.6 3.7 7 7 5
A4 0.52 0.52 0.64 40 7 4 4 3 130 1.8 2 1.1 5 5 5
A5 0.73 0.73 0.91 45 2 4 4 2 715 0.5 1.5 7.9 12 12 10
A6 0.77 0.77 0.97 70 2 4 4 2 435 0.7 1.7 4.3 8 8 6
A7 0.79 0.79 0.98 20 2 2 2 1 570 0.5 1.5 6.3 8 8 7
A8 0.90 0.90 1.00 65 3 2 2 1 0 0 0 0.0 5 5 5
A9 0.77 0.77 0.97 70 3 4 4 1 130 0.7 1.7 1.3 5 5 5
A10 0.80 0.80 0.99 70 3 3 3 1 113 0.6 1.6 1.2 5 5 5
A11 0.55 0.55 0.69 42 7 3 3 3 125 2 2.1 1.0 5 5 5
A12 0.75 0.75 0.94 70 3 4 4 2 125 0.6 1.6 1.3 5 5 5
A13 0.54 0.54 0.67 42 10 3 3 2 110 2 2.1 0.9 5 5 5
A14 0.86 0.86 1.00 21 2 2 2 1 170 0.9 1.9 1.5 5 5 5
A15 0.80 0.80 1.00 95 3 4 4 1 639 0.7 1.7 6.3 10 10 7
A16 0.81 0.81 1.00 65 2 3 3 1 375 0.9 1.9 3.3 6 6 5
A17 0.74 0.74 0.93 85 3 4 4 2 55 2 2.9 0.3 5 5 5
A18 0.75 0.75 0.94 40 2 3 3 2 155 1.2 2.1 1.2 5 5 5
A19 0.57 0.57 0.71 45 7 3 3 3 180 1.5 1.9 1.6 5 5 5
A20 0.73 0.73 0.92 100 3.8 4 4 2 73 1.2 2.1 0.6 5 5 5
A21 0.63 0.63 0.79 80 5.8 4 4 3 0 0 0 0.0 5 5 5
A22 0.65 0.65 0.81 50 2 5 5 3 660 1 2 5.5 11 11 9
A23 0.69 0.69 0.87 85 2 6 6 3 1140 0.5 1.5 12.7 19 19 16
A24 080 080 100 55 2 3 3 1 525 05 15 58 9 9 7
Table A-2
Basin Time of Concentration
Frequency Adj. Runoff Coefficients (C*Cf)
C2 C10 C100
Overland Travel Time Time of Concentration
Tc = Tov + Tt (min)
A24 0.80 0.80 1.00 55 2 3 3 1 525 0.5 1.5 5.8 9 9 7
2 0.62 0.62 0.78 60 2 5 5 4 375 0.7 1.7 3.7 9 9 8
OS5 0.82 0.82 1.00 15 2 2 2 1 450 0.7 1.7 4.4 6 6 5
Appendix A
Spring Creek Farms North Filing No. 2 Final Drainage Report
2 - year 10 - year 100 - year 2 - year 10 - year 100 - year 2 - Year 10 - Year 100 - Year 2 - Year 10 - Year 100 - Year
A1 0.84 0.23 0.23 0.28 9 9 8 2.30 3.93 8.38 0.44 0.75 2.00 A1
A2 0.64 0.50 0.50 0.63 8 8 7 2.40 4.10 8.80 0.78 1.32 3.55 A2
A3 0.93 0.78 0.78 0.98 7 7 5 2.52 4.31 9.95 1.83 3.13 9.03 A3
A4 0.19 0.52 0.52 0.64 5 5 5 2.85 4.87 9.95 0.28 0.48 1.22 A4
A5 1.47 0.73 0.73 0.91 12 12 10 2.05 3.50 7.72 2.20 3.76 10.36 A5
A6 0.94 0.77 0.77 0.97 8 8 6 2.40 4.10 9.31 1.75 2.98 8.47 A6
A7 1.33 0.79 0.79 0.98 8 8 7 2.40 4.10 8.80 2.51 4.29 11.51 A7
A8 0.15 0.90 0.90 1.00 5 5 5 2.85 4.87 9.95 0.38 0.66 1.49 A8
A9 0.34 0.77 0.77 0.97 5 5 5 2.85 4.87 9.95 0.75 1.28 3.27 A9
A10 0.63 0.80 0.80 0.99 5 5 5 2.85 4.87 9.95 1.43 2.44 6.23 A10
A11 0.36 0.55 0.55 0.69 5 5 5 2.85 4.87 9.95 0.57 0.97 2.48 A11
A12 0.34 0.75 0.75 0.94 5 5 5 2.85 4.87 9.95 0.73 1.24 3.18 A12
A13 0.20 0.54 0.54 0.67 5 5 5 2.85 4.87 9.95 0.31 0.52 1.34 A13
A14 0.16 0.86 0.86 1.00 5 5 5 2.85 4.87 9.95 0.39 0.67 1.59 A14
A15 2.24 0.80 0.80 1.00 10 10 7 2.21 3.78 8.80 3.97 6.80 19.71 A15
A16 0.37 0.81 0.81 1.00 6 6 5 2.67 4.56 9.95 0.80 1.36 3.68 A16
A17 0.29 0.74 0.74 0.93 5 5 5 2.85 4.87 9.95 0.61 1.05 2.68 A17
A18 0.56 0.75 0.75 0.94 5 5 5 2.85 4.87 9.95 1.20 2.04 5.22 A18
A19 0.43 0.57 0.57 0.71 5 5 5 2.85 4.87 9.95 0.69 1.19 3.03 A19
A20 1.14 0.73 0.73 0.92 5 5 5 2.85 4.87 9.95 2.38 4.07 10.39 A20
A21 0.35 0.63 0.63 0.79 5 5 5 2.85 4.87 9.95 0.63 1.07 2.74 A21
A22 2.14 0.65 0.65 0.81 11 11 9 2.13 3.63 8.03 2.96 5.04 13.93 A22
A23 2.52 0.69 0.69 0.87 19 19 16 1.65 2.82 6.30 2.89 4.93 13.77 A23
A24 0.96 0.80 0.80 1.00 9 9 7 2.30 3.93 8.80 1.77 3.02 8.45 A24
2 0.78 0.62 0.62 0.78 9 9 8 2.30 3.93 8.38 1.12 1.91 5.09 2
OS5 0.41 0.82 0.82 1.00 6 6 5 2.67 4.56 9.95 0.91 1.55 4.11 OS5
Time of Concentration, Tc (min)
Table A-3
Basin Peak Discharge
Basin Rainfall Intensity (in/hr) Peak Discharge (cfs) Basin
Basin Area
(ac)
Frequency Adj. Runoff Coefficients
Appendix A
Spring Creek Farms North Filing No. 2 Final Drainage Report
Design Contributing Contributing Area
Point Basins Design Points (acres) 2 - year 10 - year 100 - year 2 - year 10 - year 100 - year 2 - year 10 - year 100 - year 2 - year 10 - year 100 - year
18 + 19 A21, A22 2.49 11 11 9 0.65 0.65 0.81 2.13 3.63 8.03 3.4 5.8 16.1
17 A20 18, 19 3.63 11 11 9 0.67 0.67 0.84 2.13 3.63 8.03 5.2 8.9 24.5
13W A16, A17 0.66 6 6 5 0.78 0.78 0.97 2.67 4.56 9.95 1.4 2.3 6.4
13 A15 13W 2.90 10 10 7 0.80 0.80 0.99 2.21 3.78 8.80 5.1 8.7 25.3
15 A18, A19 0.99 5 5 5 0.67 0.67 0.84 2.85 4.87 9.95 1.9 3.2 8.2
13 + 15 13, 15 3.89 10 10 7 0.76 0.76 0.95 2.21 3.78 8.80 6.6 11.2 32.6
10 A12,A13,A14 13, 15 4.59 10 10 7 0.76 0.76 0.94 2.21 3.78 8.80 7.7 13.1 38.0
10 + 17 10, 17 8.22 11 11 9 0.72 0.72 0.90 2.13 3.63 8.03 12.6 21.5 59.2
8 A10,A11 10, 17 9.21 11 11 9 0.72 0.72 0.90 2.13 3.63 8.03 14.1 24.0 66.3
7 A9 8 9.55 11 11 9 0.72 0.72 0.90 2.13 3.63 8.03 14.7 25.0 68.9
5N (surface) A6,A7 2.27 8 8 7 0.78 0.78 0.98 2.40 4.10 8.80 4.3 7.3 19.5
5N (pipe) A6,A7,A8 2.42 8 8 7 0.79 0.79 0.98 2.40 4.10 8.80 4.6 7.8 20.8
5 (surface) A5,A6,A7 3.74 12 12 10 0.76 0.76 0.95 2.05 3.50 7.72 5.8 10.0 27.5
5 (pipe) A5 5N 3.89 12 12 10 0.77 0.77 0.95 2.05 3.50 7.72 6.1 10.4 28.6
1 A1,A2,A3,A4,
A23,A24 5, 7 19.52 19 19 16 0.70 0.70 0.88 1.65 2.82 6.30 22.6 38.7 107.8
30 2, OS5 1.19 9 9 8 0.69 0.69 0.86 2.30 3.93 8.38 1.9 3.2 8.6
Table A-4
Attenuation of Peak Discharge
Time of Concentration, Tc (min) Weighted Runoff Coefficient Rainfall Intensity (in/hr) Peak Discharge (cfs)
Appendix A
Spring Creek Farms North Filing No. 2 Final Drainage Report
POLICE STATION POND - WITH ONSITE BASIN 2
DETENTION POND MASS BALANCE - 100 YR (MAJOR)
0.89
3.1 cfs
Area = 9.38 ac.
8.6 AC police + 0.78 ac Basin 2 Detention provided = 2.11 ac-ft
MAX = 1.934 (AF)
t (min) Intensity (in/hr) Q in (cfs) V in (ft3) Q out (cfs) V out (ft3) V detained (AF)
5 9.95 83.065 24919.38 3.10 930 0.551
10 7.72 64.448 38668.86 3.10 1860 0.845
15 6.52 54.430 48987.24 3.10 2790 1.061
20 5.60 46.750 56099.90 3.10 3720 1.202
25 4.98 41.574 62361.05 3.10 4650 1.325
30 4.52 37.734 67920.96 3.10 5580 1.431
35 4.08 34.061 71527.38 3.10 6510 1.493
40 3.74 31.222 74933.44 3.10 7440 1.549
45 3.46 28.885 77988.88 3.10 8370 1.598
50 3.23 26.965 80894.06 3.10 9300 1.644
55 3.03 25.295 83473.65 3.10 10230 1.681
60 2.86 23.876 85953.07 3.10 11160 1.717
65 2.70 22.540 87906.55 3.10 12090 1.741
70 2.60 21.705 91162.34 3.10 13020 1.794
75 2.50 20.871 93917.25 3.10 13950 1.836
80 2.40 20.036 96171.26 3.10 14880 1.866
85 2.30 19.201 97924.39 3.10 15810 1.885
90 2.20 18.366 99176.62 3.10 16740 1.892
100 2.05 17.114 102682.86 3.10 18600 1.930
110 1.90 15.862 104686.43 3.10 20460 1.934
120 1.75 14.609 105187.32 3.10 22320 1.902
130 1.65 13.775 107441.33 3.10 24180 1.911
140 1.56 13.023 109394.81 3.10 26040 1.914
150 1.48 12.355 111198.02 3.10 27900 1.912
160 1.41 11.771 113001.24 3.10 29760 1.911
170 1.35 11.270 114954.71 3.10 31620 1.913
180 1.29 10.769 116307.12 3.10 33480 1.901
Runoff Coefficient =
Q out Pond A =
Spring Creek Farms North Filing No. 2 Final Drainage Report
Appendix A
Developed Runoff
Developed condition runoff was evaluated in accordance with the criteria established by the City
of Fort Collins Storm Drainage Design Criteria and Construction Standards Manual (SDDC)
dated May 1984 and revised in January 1997. Design guidelines and information were also
obtained from the Denver Regional Council of Government Urban Storm Drainage Criteria
Manual (USDCM) where applicable. A full description of this method is available through those
manuals; this appendix is to serve as a reference for Willow Brook Filing No. 3. The Rational
Method computes only the peak flow at a design point and does not provide hydrograph
information.
Rational Method
City of Fort Collins
The Rational Method calculates peak runoff using the equation:
Q = CCfIA
Where: Q = The maximum rate of runoff (cfs)
C = Rational Method Runoff Coefficient for the design storm frequency. City of Fort
Collins runoff coefficients are found in Table 3-3 of the SDDC manual.
Cf = Storm Frequency Coefficient found in Table 3-4 of the SDDC manual.
I = Average intensity of rainfall in inches per hour for a duration equal to the time of
concentration, Tc. City of Fort Collins rainfall intensity data are shown in this
Appendix.
A = Basin Area (acres)
Rational Method Runoff Coefficients, C, are a function of the basin land use and the design
storm frequency. They are listed in Table 3-3 of the Storm Drainage Design Criteria manual. For
basins containing more than one land use, a weighted average runoff coefficient has been
computed.
Time of Concentration, Tc, is the sum of the overland travel time, to, and the channel or conduit
flow time, tt. Time of concentration is used to select the correct rainfall intensity for the rational
method equation.
T c = t i + t t
where: Tc = Time of Concentration (min),
to = Overland Travel Time (min),
tt = Channel or Conduit flow time (min).
Spring Creek Farms North Filing No. 2 Final Drainage Report
Appendix A
Overland Travel Time, to, is computed using the frequency adjusted runoff coefficient
and is applicable to all design storm intervals.
( ) 3
1
1 . 8 ( 1 . 1 ) 0 . 5
S
t CC f L
o
−
=
Where:
to = Overland Travel Time (min)
C5 = The Rational Method runoff coefficient for the 5 – year storm
L = Length of overland flow (ft), Maximum = 400 feet.
S = Average basin slope (%)
Channel or Conduit Travel Time, tt, is determined from the velocity of flow computed
for the hydraulic properties of the channel, ditch, gutter, pipe or sewer. For the purposes
of this report, the following equation was used:
V
tt 60 L *
=
Where:
tt = Channel or Conduit Travel Time (min)
L = Length of channel or conduit flow (ft)
V = Velocity of flow (fps), determined from Figure 3-2
Spring Creek Farms North Filing No. 2 Final Drainage Report
Appendix A
Spring Creek Farms North Filing No. 2 Final Drainage Report
City of Fort Collins
Rational Method Runoff Coefficients
Runoff
Coefficient
Lawn, Heavy, <2% Slope 0.20
Lawn, Heavy, >7% Slope 0.35
Lawn, Heavy, 2-7% Slope 0.25
Lawn, Sandy, <2% Slope 0.10
Lawn, Sandy, >7% Slope 0.20
Lawn, Sandy, 2-7% Slope 0.15
Roofs 0.95
Streets: Gravel 0.50
Streets: Paved 0.95
From Table 3-3 of the City of Fort Collins, SDDCCS
Appendix A
Spring Creek Farms North Filing No. 2 Final Drainage Report
Rational Method Frequency Adjustment Factors
Min year Max year Frequency Factor, Cf
2101
11 25 1.1
26 50 1.2
51 100 1.25
From Table 3-4 in the City of Fort Collins, SDDCCS
Appendix A
Spring Creek Farms North Filing No. 2 Final Drainage Report
City of Fort Collins
IDF Curves
Duration 2-yr 10-yr 100-yr
5 2.85 4.87 9.95
6 2.67 4.56 9.31
7 2.52 4.31 8.80
8 2.40 4.10 8.38
9 2.30 3.93 8.03
10 2.21 3.78 7.72
11 2.13 3.63 7.42
12 2.05 3.50 7.16
13 1.98 3.39 6.92
14 1.92 3.29 6.71
15 1.87 3.19 6.52
16 1.81 3.08 6.30
17 1.75 2.99 6.10
18 1.70 2.90 5.92
19 1.65 2.82 5.75
20 1.61 2.74 5.60
21 1.56 2.67 5.46
22 1.53 2.61 5.32
23 1.49 2.55 5.20
24 1.46 2.49 5.09
25 1.43 2.44 4.98
26 1.40 2.39 4.87
27 1.37 2.34 4.78
28 1.34 2.29 4.69
29 1.32 2.25 4.60
30 1.30 2.21 4.52
31 1.27 2.16 4.42
32 1.24 2.12 4.33
33 1.22 2.08 4.24
34 1.19 2.04 4.16
35 1.17 2.00 4.08
36 1.15 1.96 4.01
37 1.13 1.93 3.93
38 1.11 1.89 3.87
39 1.09 1.86 3.80
40 107 183 374
Intensity Duration Frequency Curve
40 1.07 1.83 3.74
41 1.05 1.80 3.68
42 1.04 1.77 3.62
43 1.02 1.74 3.56
44 1.01 1.72 3.51
45 0.99 1.69 3.46
46 0.98 1.67 3.41
47 0.96 1.64 3.36
48 0.95 1.62 3.31
49 0.94 1.60 3.27
50 0.92 1.58 3.23
51 0.91 1.56 3.18
52 0.90 1.54 3.14
53 0.89 1.52 3.10
54 0.88 1.50 3.07
55 0.87 1.48 3.03
56 0.86 1.47 2.99
57 0.85 1.45 2.96
58 0.84 1.43 2.92
Spring Creek Farms North Filing No. 2 Final Drainage Report
From the Town of Timnath Design Criteria Manual and Construction Specifications
y = -1.373ln(x) + 6.9169
R² = 0.9964
y = -2.804ln(x) + 14.129
R² = 0.9964
0.00
2.00
4.00
6.00
8.00
10.00
12.00
010203040506070
Rainfall Intensity (in/hr)
Storm Duration (min)
City of Fort Collins IDF Curves
2-yr
10-yr
100-yr
Log. (2-yr)
Log. (10-yr)
Intensity Duration Frequency Curve
APPENDIX B
Street Capacity Analysis
Spring Creek Farms North Filing No. 2 Final Drainage Report
Street Classification Slope Max Depth Flow @ Q2-yr Meets Max Depth Flow @ Q100-yr Meets
(ft/ft) (ft) Max Depth (cfs) Criteria? (ft) Max Depth* (cfs) Criteria?
67% A22 Joseph Allen Local 0.010 0.50 13.8 2.0 Yes 0.70 18.5 9.3 Yes
A23 Timberline Arterial 0.005 0.50 9.7 2.9 Yes 0.82 53.0 13.8 Yes
A24 Drake Arterial 0.005 0.50 9.7 1.8 Yes 0.82 53.0 8.4 Yes
77% OS5 (w/ 2) Charles Brockman Local 0.007 0.50 10.5 1.5 Yes 0.70 10.5 6.6 Yes
A15 Private - East Drive Private 0.007 0.33 10.0 4.0 Yes
A15+A16 Private - East Drive Private 0.007 0.50 32.4 11.7 Yes
A7 Private - South Dr. Private 0.007 0.33 2.6 2.5 Yes
50% A5 + A7 Private - South Dr. Private 0.007 1.00 66.4 8.3 Yes
Flow @ Max Depth computed using UD Inlet v_3.1
Design Basin
Minor Storm (2-yr or 10-yr - CHECK SUB CRITERIA) Major Storm (100-year)
Table B-1
Street Capacity
Appendix B
APPENDIX C
Inlet Analysis
Spring Creek Farms North Filing No. 2 Final Drainage Report
Design Grade Inlet Allowable 100-yr Allowable Length Evenly Divided
Point Condition Type Ponding Depth Design Flow Capacity Flow?
(in) (cfs) (cfs) (ft)
3 Sump Curb Cut 12 9.0 9.1 2-2' chases No
5 Sump Combo 8.4 13.7 16.2 9', 3 units Yes (1/2 shown)
6 Sump Combo 9.6 1.5 7.7 3', 1 unit No
7 Sump Type R 8.4 5.3 13.3 7' Includes DP8 bypass
8 Sump Type 13 6.3 6.2 4.2 6', 2 units Add bypass to DP7
9 Sump Area 12 2.5 4.3 15" Dome No
10 Sump Combo 6 3.2 3.6 3', 1 unit No
11 Sump Area 12 1.3 4.3 15" Dome
12 Sump Combo 6 1.6 3.6 3', 1 unit No
13 Sump Type 13 8.4 12.9 13.3 12', 4 units Yes (1/2 shown)
14 Sump Combo 6 2.7 3.6 3', 1 unit No
15 On Grade Type 13 6 5.2 2.9 6', 2 units Add bypass to DP13
16 Sump Area 12 3.0 4.3 15" Dome No
17 Sump Combo 9 10.4 15.1 6', 2 units No
18 Sump Area 12 2.7 4.3 15" Dome No
19 Sump Type R 7 13.9 14.6 15' No
20 Sump Type R 9.8 13.8 15.2 7' No
21 Sump Type R 9.8 8.4 10.5 5' No
30 Sump Type R 5.8 8.6 9.6 5' (existing) No
Table C-1
Inlet Design
Appendix C
APPENDIX D
Storm Sewer Design
Spring Creek Farms North Filing No. 2 Final Drainage Report
Design From To UD Sewer Design Flow Pipe Diameter
Basin/Point (Downstream) (Upstream) Pipe ID (cfs) (in)
7 ST-1 FES 1-1 INLET 1-1 1 68.9 60 RCP
8 ST-1 INLET 1-1 INLET 1-2 2 66.3 60 RCP
ST-1 INLET 1-2 STMH 1-1 4 59.2 54 RCP
10 ST-1 STMH 1-1 INLET 1-3 5 38.0 42 RCP
ST-1 INLET 1-3 STMH 1-2 8 32.6 36 RCP
15 ST-1 STMH 1-2 INLET 1-4 12 8.2 18 RCP
16 ST-1 INLET 1-4 AREA INLET 4 13 3.0 12 RCP
9 ST-1A INLET 1-2 AREA INLET 1 3 2.5 18 RCP
17 ST-1B STMH 1-1 INLET 1B-1 14 24.5 36 RCP
ST-1B INLSET 1B-1 STMH 1B-1 15 16.1 36 RCP
ST-1B STMH 1B-1 STMH 1B-2 16 16.1 36 RCP
ST-1B STMH 1B-2 STMH 1B-3 18 13.9 30 RCP
19 ST-1B STMH 1B-3 INLET 1B-2 19 13.9 30 RCP
11 ST-1C INLET 3 AREA INLET 2 6 1.3 12 RCP
12 ST-1D INLET 1-3 INLET 1D-1 7 1.6 18 RCP
13 ST-1E STMH 1-2 INLET 1E-1 9 25.3 36 RCP
ST-1E INLET 1E-1 INLET 1E-2 10 14.3 24 RCP
ST-1E INLSET 1E-2 INLET 1E-3 11 2.7 18 RCP
5 ST-2 FES 2-1 INLET 2-1 1 28.6 30 RCP
ST-2 INLET 2-1 INLET 2-2 2 15.2 24 RCP
6 ST-2 INLET 2-2 INLET 2-3 3 1.5 18 RCP
21 ST-3 FES 3-1 INLET 3-1 1 8.4 18 RCP
1 ST-4 OUTLET POND 1 7.45 18 RCP
18 ST-7 STMH 1B-2 INLET 7-3 17 2.7 12 HDPE
Table E-1
Storm Sewer Summary
Line Pipe Material
Appendix D
APPENDIX E
Riprap Design
Spring Creek Farms North Filing No. 2 Final Drainage Report
Storm Flow Velocity Pipe Depth @ Depth in Froude Minimum Expansion Req. Area Extra Length Length Width Riprap
Sewer Dia. Outlet Pipe # Yt/D
c or Q/D
1.5
or Q/D
2.5
or Da
= (Dc+Y
n)/2 Yt
/Da or Q/D
a
1.5
or Q/Da
2.5
or Diameter Factor At
if Q/Da
2.5
Lp W
p Type
(cfs) (fps) (ft) Yt
(ft) Yn (ft) Y
t/H Q/WH
0.5
Q/WH
1.5
(ft) Yt
/Ha Q/WH
a
0.5
Q/WHa
1.5
d50 (ft) 1/(2Tanθ)
(ft
2
) > 6 (ft) (ft)
ST-1 68.90 8.7 5.0 8.25 2.12 1.21 3.56 2.32 10.26 2.88 0.18 6.75 7.92 1.25 16.3 20.0 TYPE L
ST-2 28.60 10.6 2.5 8.25 1.35 1.79 1.93 4.29 10.71 5.56 0.08 4.75 2.70 0.63 8.1 10.0 TYPE L
ST-3 8.40 6.6 1.50 7.25 3.17 1.22 2.34 3.10 2.35 1.01 0.00 6.75 1.27 0.00 4.5 6.0 TYPE L
Rundown 13.77 45.7 2.00 8.15 0.14 22.81 1.07 7.62 12.44 11.63 0.00 4.25 0.30 0.50 6.0 8.0 TYPE L
Table E-1
Storm Sewer Outlet Riprap Design
(Froude # < 1, Subcritical Flow) (Froude # > 1, Supercritical Flow )
Appendix E
Spring Creek Farms North Filing No. 2 Final Drainage Report
Required Rock Size
The required rock size may be selected from Figure MD-21 for circular conduits and from Figure MD-22 for
rectangular conduits. Figure MD-21 is valid for Q/Dc
2.5
of 6 or less and Figure MD-22 is valid for Q/WH1.5 of 8.0
or less. The parameters in these two figures are:
1. Q/D
1.5 or Q/W
0.5 in which Q is the design discharge in cfs, Dc is the diameter of a
circular conduit in feet,and W and H are the width and height of a rectangular conduit in
feet.
2. Yt/Dc or Yt/H in which Yt is the tailwater depth in feet, Dc is the diameter of a circular conduit in feet,
and H is the height of a rectangular conduit in feet. In cases where Yt is unknown or a hydraulic jump is
suspected downstream of the outlet, use Yt/Dt = Yt/H = 0.40 when using Figures MD-21
and MD-22.
3. The riprap size requirements in Figures MD-21 and MD-22 are based on the non-dimensional
parametric Equations MD-18 and MD-19 (Steven, Simons, and Lewis 1971 and Smith 1975).
Circular culvert:
0 . 023
Q
D
D
Y
D
d
2 . 5
c
1 . 2
c
t
c
50
=
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
(MD-18)
Rectangular culvert:
0 . 014
Q
H H
WH
d Y
1 . 5
Spring Creek Farms North Filing No. 2 Final Drainage Report
Extent of Protection
The length of the riprap protection downstream from the outlet depends on the degree of protection desired. If
it is necessary to prevent all erosion, the riprap must be continued until the velocity has been reduced to an
acceptable value. For purposes of outlet protection during major floods, the acceptable velocity is set at 5.5
ft/sec for very erosive soils and at 7.7 ft/sec for erosion resistant soils. The rate at which the velocity of a jet
from a conduit outlet decreases is not well known. For the procedure recommended here, it is assumed to be
related to the angle of lateral expansion, θ, of the jet. The velocity is related to the expansion factor,
(1/(2tanθ)), which can be determined directly using Figure MD-23 or Figure MD-24, assuming that the
expanding jet has a rectangular shape:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⎟ −
⎠
⎞
⎜
⎝
⎛
θ
= W
2 tan
1
Y
L A
t
t
p (MD-22)
where:
Lp = length of protection (ft)
W = width of the conduit in (ft) (use diameter for circular conduits)
Yt = tailwater depth (ft)
θ = the expansion angle of the culvert flow
and:
V
Q
At = (MD-23)
where:
Q = design discharge (cfs)
V = the allowable non-eroding velocity in the downstream channel (ft/sec)
At = required area of flow at allowable velocity (ft²)
In certain circumstances, Equation MD-22 may yield unreasonable results. Therefore, in no case should Lp be
less than 3H or 3D, nor does Lp need to be greater than 10H or 10D whenever the Froude parameter, Q/WH1.5
or Q/D2.5, is less than 8.0 or 6.0, respectively. Whenever the Froude parameter is greater than these
maximums, increase the maximum Lp required by ¼ Dc or ¼ H for circular or rectangular culverts,
respectively, for each whole number by which the Froude parameter is greater than 8.0 or 6.0, respectively.
APPENDIX F
Detention Pond Design
Spring Creek Farms North Filing No. 2 Final Drainage Report
Table F-1
Outlet Structure Design
Design Q in Q out Normal 100-year Depth Area Dia. Length Top Width Angle Length Spillway Depth Top Width
Point (cfs) (cfs) WSEL WSEL (ft) (ft2) (in) (ft) (ft) (Deg.) (ft) Elevation (ft) (ft)
Pond 1 107.80 8.2 4928.75 4934.15 5.4 0.75 11.71 236 4935.3 .50* 10.0
* Maximum overflow depth = 0.50'. Varies from 0-0.5' along spillway.
Table F-2
Detention Pond Design
Design Volume Water Surface
Element (acre-ft) Elevation
Pond Outlet N/A 4925.40
Water Quality 0.51 4927.95
100-year Detention 4.19 4934.15
Outlet Orifice Outlet Weir Emergency Overflow Weir
Orifice Design
An orifice plate has been placed over the outlet pipe to function as the 100 – year flow restriction. For a single orifice flow can be
determined using the following equation:
in which:
Q = 2.82 cfs (the orifice flow rate)
Co = 0.61 (discharge coefficient)
Ao = 0.45 ft2
(area of orifice)
Ho = 1.62 ft (difference in head between 100-year surface water in the pond and centroid of the orifice)
g = 32.2 ft/sec2
(gravitational acceleration )
( ) 0 . 5
Q = C o A o 2 g H o
Appendix F
[TITLE]
[OPTIONS]
FLOW_UNITS CFS
INFILTRATION HORTON
FLOW_ROUTING DYNWAVE
START_DATE 06/28/2012
START_TIME 00:00:00
REPORT_START_DATE 06/28/2012
REPORT_START_TIME 00:00:00
END_DATE 06/28/2012
END_TIME 12:00:00
SWEEP_START 01/01
SWEEP_END 12/31
DRY_DAYS 0
REPORT_STEP 00:01:00
WET_STEP 00:05:00
DRY_STEP 01:00:00
ROUTING_STEP 0:01:00
ALLOW_PONDING NO
INERTIAL_DAMPING PARTIAL
VARIABLE_STEP 0.75
LENGTHENING_STEP 0
MIN_SURFAREA 0
NORMAL_FLOW_LIMITED BOTH
SKIP_STEADY_STATE NO
FORCE_MAIN_EQUATION H-W
LINK_OFFSETS DEPTH
MIN_SLOPE 0
[EVAPORATION]
;;Type Parameters
;;---------- ----------
CONSTANT 0.0
DRY_ONLY NO
[RAINGAGES]
;; Rain Time Snow Data
;;Name Type Intrvl Catch Source
;;-------------- --------- ------ ------ ----------
;100-yr
Gage1 INTENSITY 0:5 1.0 TIMESERIES 100-yr
[SUBCATCHMENTS]
;; Total Pcnt. Pcnt. Curb Snow
;;Name Raingage Outlet Area Imperv Width Slope Length Pack
;;-------------- ---------------- ---------------- -------- -------- -------- -------- -------- --------
S1 Gage1 POND 19.52 67 600 0.5 0
[SUBAREAS]
;;Subcatchment N-Imperv N-Perv S-Imperv S-Perv PctZero RouteTo PctRouted
;;-------------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
S1 .016 .025 .1 .3 1 OUTLET
[INFILTRATION]
;;Subcatchment MaxRate MinRate Decay DryTime MaxInfil
;;-------------- ---------- ---------- ---------- ---------- ----------
S1 .51 0.5 6.5 7 0
[OUTFALLS]
;; Invert Outfall Stage/Table Tide
;;Name Elev. Type Time Series Gate
;;-------------- ---------- ---------- ---------------- ----
Out1 4925.5 FREE NO
[STORAGE]
;; Invert Max. Init. Storage Curve Ponded Evap.
;;Name Elev. Depth Depth Curve Params Area Frac. Infiltration Paramet
[LOSSES]
;;Link Inlet Outlet Average Flap Gate
;;-------------- ---------- ---------- ---------- ----------
[CURVES]
;;Name Type X-Value Y-Value
;;-------------- ---------- ---------- ----------
PondA Storage .5 8823
PondA 1.5 17550
PondA 2.5 19681
PondA 3.5 20833
PondA 4.5 22295
PondA 5.5 23986
PondA 6.5 25121
PondA 7.5 27008
PondA 8.5 29518
PondA 9.5 55320
[TIMESERIES]
;;Name Date Time Value
;;-------------- ---------- ---------- ----------
100-yr 0 0
100-yr 0:5 1
100-yr 0:10 1.14
100-yr 0:15 1.33
100-yr 0:20 2.23
100-yr 0:25 2.84
100-yr 0:30 5.49
100-yr 0:35 9.95
100-yr 0:40 4.12
100-yr 0:45 2.48
100-yr 0:50 1.46
100-yr 0:55 1.22
100-yr 1 1.06
100-yr 1:05 1.00
100-yr 1:10 .95
100-yr 1:15 .91
100-yr 1:20 .87
100-yr 1:25 .84
100-yr 1:30 .81
100-yr 1:35 .78
100-yr 1:40 .75
100-yr 1:45 .73
100-yr 1:50 .71
100-yr 1:55 .69
100-yr 2 .67
[REPORT]
INPUT NO
CONTROLS NO
SUBCATCHMENTS ALL
NODES ALL
LINKS ALL
[TAGS]
[MAP]
DIMENSIONS 0.000 0.000 10000.000 10000.000
Units None
[COORDINATES]
;;Node X-Coord Y-Coord
;;-------------- ------------------ ------------------
Out1 5192.982 2654.971
POND 3684.211 2608.187
[VERTICES]
EPA STORM WATER MANAGEMENT MODEL - VERSION 5.0 (Build 5.0.022)
--------------------------------------------------------------
*********************************************************
NOTE: The summary statistics displayed in this report are
based on results found at every computational time step,
not just on results from each reporting time step.
*********************************************************
****************
Analysis Options
****************
Flow Units ............... CFS
Process Models:
Rainfall/Runoff ........ YES
Snowmelt ............... NO
Groundwater ............ NO
Flow Routing ........... YES
Ponding Allowed ........ NO
Water Quality .......... NO
Infiltration Method ...... HORTON
Flow Routing Method ...... DYNWAVE
Starting Date ............ JUN-28-2012 00:00:00
Ending Date .............. JUN-28-2012 12:00:00
Antecedent Dry Days ...... 0.0
Report Time Step ......... 00:01:00
Wet Time Step ............ 00:05:00
Dry Time Step ............ 01:00:00
Routing Time Step ........ 60.00 sec
WARNING 04: minimum elevation drop used for Conduit C1
************************** Volume Depth
Runoff Quantity Continuity acre-feet inches
************************** --------- -------
Total Precipitation ...... 5.969 3.669
Evaporation Loss ......... 0.000 0.000
Infiltration Loss ........ 0.767 0.471
Surface Runoff ........... 5.122 3.149
Final Surface Storage .... 0.113 0.070
Continuity Error (%) ..... -0.569
************************** Volume Volume
Flow Routing Continuity acre-feet 10^6 gal
************************** --------- ---------
Dry Weather Inflow ....... 0.000 0.000
Wet Weather Inflow ....... 5.122 1.669
Groundwater Inflow ....... 0.000 0.000
RDII Inflow .............. 0.000 0.000
External Inflow .......... 0.000 0.000
External Outflow ......... 5.122 1.669
Internal Outflow ......... 0.000 0.000
Storage Losses ........... 0.000 0.000
Initial Stored Volume .... 0.000 0.000
Final Stored Volume ...... 0.000 0.000
Continuity Error (%) ..... 0.005
***************************
Time-Step Critical Elements
***************************
Link C1 (99.40%)
********************************
Highest Flow Instability Indexes
********************************
All links are stable.
*************************
***************************
Subcatchment Runoff Summary
***************************
--------------------------------------------------------------------------------------------------------
Total Total Total Total Total Total Peak Runoff
Precip Runon Evap Infil Runoff Runoff Runoff Coeff
Subcatchment in in in in in 10^6 gal CFS
--------------------------------------------------------------------------------------------------------
S1 3.67 0.00 0.00 0.47 3.15 1.67 120.85 0.858
******************
Node Depth Summary
******************
---------------------------------------------------------------------
Average Maximum Maximum Time of Max
Depth Depth HGL Occurrence
Node Type Feet Feet Feet days hr:min
---------------------------------------------------------------------
Out1 OUTFALL 0.86 0.90 4926.40 0 00:31
POND STORAGE 4.89 7.85 4933.35 0 02:09
*******************
Node Inflow Summary
*******************
-------------------------------------------------------------------------------------
Maximum Maximum Lateral Total
Lateral Total Time of Max Inflow Inflow
Inflow Inflow Occurrence Volume Volume
Node Type CFS CFS days hr:min 10^6 gal 10^6 gal
-------------------------------------------------------------------------------------
Out1 OUTFALL 0.00 8.20 0 00:31 0.000 1.669
POND STORAGE 120.85 120.85 0 00:40 1.670 1.669
**********************
Node Surcharge Summary
**********************
Surcharging occurs when water rises above the top of the highest conduit.
---------------------------------------------------------------------
Max. Height Min. Depth
Hours Above Crown Below Rim
Node Type Surcharged Feet Feet
---------------------------------------------------------------------
POND STORAGE 5.81 4.853 1.647
*********************
Node Flooding Summary
*********************
No nodes were flooded.
**********************
Storage Volume Summary
**********************
--------------------------------------------------------------------------------------------
Average Avg E&I Maximum Max Time of Max Maximum
Volume Pcnt Pcnt Volume Pcnt Occurrence Outflow
Storage Unit 1000 ft3 Full Loss 1000 ft3 Full days hr:min CFS
--------------------------------------------------------------------------------------------
POND 89.266 41 0 159.283 72 0 02:09 8.20
***********************
Outfall Loading Summary
***********************
-----------------------------------------------------------
Flow Avg. Max. Total
Freq. Flow Flow Volume
Outfall Node Pcnt. CFS CFS 10^6 gal
Out1 99.98 7.72 8.20 1.669
-----------------------------------------------------------
System 99.98 7.72 8.20 1.669
********************
Link Flow Summary
********************
-----------------------------------------------------------------------------
Maximum Time of Max Maximum Max/ Max/
|Flow| Occurrence |Veloc| Full Full
Link Type CFS days hr:min ft/sec Flow Depth
-----------------------------------------------------------------------------
C1 CONDUIT 8.20 0 00:31 4.46 1.23 0.65
***************************
Flow Classification Summary
***************************
-----------------------------------------------------------------------------------------
Adjusted --- Fraction of Time in Flow Class ---- Avg. Avg.
/Actual Up Down Sub Sup Up Down Froude Flow
Conduit Length Dry Dry Dry Crit Crit Crit Crit Number Change
-----------------------------------------------------------------------------------------
C1 1.00 0.00 0.00 0.00 1.00 0.00 0.00 0.00 0.33 0.0001
*************************
Conduit Surcharge Summary
*************************
----------------------------------------------------------------------------
Hours Hours
--------- Hours Full -------- Above Full Capacity
Conduit Both Ends Upstream Dnstream Normal Flow Limited
----------------------------------------------------------------------------
C1 0.01 0.01 0.01 7.30 0.01
Analysis begun on: Fri Aug 24 11:56:53 2012
Analysis ended on: Fri Aug 24 11:56:53 2012
Total elapsed time: < 1 sec
SWMM 5 Page 3
WATER QUALITY CAPTURE VOLUME SUMMARY
FOR EXTENDED DETENTION
PROJECT NAME: Spring Creek Farms North Filing No. 2
PROJECT NO: 1045.0039.00
COMPUTATIONS BY: emf
DATE: 06/29/12
Guidelines from Urban Strom Drainage Criterial Manual, September 1999
(Referenced figures are attached at the end of this section)
Use 40-hour brim-full volume drain time for extended detention basin
Water quality Capture Volume, WQCV = 1.0 * (0.91 * i3 - 1.19 * i2 + 0.78i)
Design Volume: Vol = WQCV/12 * Area * 1.2
MAJOR Trib. % Impervious Impervious WQCV Design
BASIN area Ia Ratio (watershed inVolume, Vol.
(acres) i=Ia/100 (ac-ft)
Site 19.52 67.1 0.671 0.26 0.51
Spring Creek Farms North Filing No. 2 Final Drainage Report
Project:
Basin ID:
Design Information (Input):
From the pond site grading plan, enter water surface elevations
and measured contour areas in ascending order.
Water Eq-elev. Volume
Surface Contour above
Elevation Area Datum
ft square feet acre-ft
(input) (input) (output)
4925.40 0 0.00
4926.00 3,271 0.02
4927.00 11,572 0.19
WQCV Elev 4927.95 17,059 0.51
4928.00 17,275 0.52
4929.00 21,031 0.96
4930.00 23,238 1.47
4931.00 26,016 2.04
4932.00 28,121 2.66
4933.00 30,993 3.34
4934.00 33,213 4.07
100yr Elev 4934.15 33,495 4.19
STAGE-STORAGE FOR IRREGULAR GEOMETRY
Spring Creek Farms North Filing No. 2
Pond Volume
Detention Volume
APPENDIX G
Excerpts from Previous Reports
760 Whalers Way Bldg C, Suite 200 Fort Collins, CO 80525 ideas@tstinc.com
970.226.0557 main 303.595.9103 metro 970.226.0204 fax www.tstinc.com
PROJ. NO.
DRAWN:
CHECKED:
DATE:
REVISIONS
SCALE:
SHEET NUMBER
SHEET TITLE:
ISSUED FOR:
DESIGNED:
Timberline Road & Drake Road
Fort Collins, Colorado 80525
C.30
AS NOTED
08/29/12
FINAL DEVELOPMENT
PLAN
DRAINAGE PLAN
SPRING CREEK FARMS
NORTH FILING NO. 2
1045.0039.00
EMF
H.E.M.
EMF
FILE: 0039_DRAINAGE FDP
-----------------------------------------------------------
SWMM 5 Page 2
Routing Time Step Summary
*************************
Minimum Time Step : 0.75 sec
Average Time Step : 1.17 sec
Maximum Time Step : 60.00 sec
Percent in Steady State : 0.00
Average Iterations per Step : 2.00
SWMM 5 Page 1
;;Link X-Coord Y-Coord
;;-------------- ------------------ ------------------
[Polygons]
;;Subcatchment X-Coord Y-Coord
;;-------------- ------------------ ------------------
S1 441.520 3149.123
S1 3260.234 3149.123
S1 3248.538 8646.199
S1 441.520 8634.503
[SYMBOLS]
;;Gage X-Coord Y-Coord
;;-------------- ------------------ ------------------
Gage1 713.450 9111.111
SWMM 5 Page 2
;;-------------- -------- -------- -------- ---------- -------- -------- -------- -------- -------- --------------------
POND 4925.5 9.5 0 TABULAR PondA 0 0
[CONDUITS]
;; Inlet Outlet Manning Inlet Outlet Init. Max.
;;Name Node Node Length N Offset Offset Flow Flow
;;-------------- ---------------- ---------------- ---------- ---------- ---------- ---------- ---------- ----------
C1 POND Out1 10 .013 0 0 0 8.2
[XSECTIONS]
;;Link Shape Geom1 Geom2 Geom3 Geom4 Barrels
;;-------------- ------------ ---------------- ---------- ---------- ---------- ----------
C1 CIRCULAR 3 0 0 0 1
SWMM 5 Page 1
1 . 2
50 t
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
(MD-19)
The rock size requirements were determined assuming that the flow in the culvert barrel is not supercritical. It
is possible to use Equations MD-18 and MD-19 when the flow in the culvert is supercritical (and less than full)
if the value of Dc or H is modified for use in Figures MD-21 and MD-22. Whenever the flow is supercritical in
the culvert, substitute Da for Dc and Ha for H, in which Da is defined as:
( )
2
D D c Y n
a
+
= (MD-20)
in which the maximum value of Da shall not exceed D, and
()
2
H Y
H n
a
+
= (MD-21)
in which the maximum value of Ha shall not exceed H, and:
Da = parameter to use in place of D in Figure MD-21 when flow is supercritical
Dc = diameter of circular culvert (ft)
Ha = parameter to use in place of H in Figure MD-22 when flow is supercritical
H = height of rectangular culvert (ft)
Yn = normal depth of supercritical flow in the culvert
59 0.83 1.42 2.89
60 0.82 1.40 2.86
From the City of Fort Collins Storm Drainage Design Criteria and Construction Standars
Intensity Duration Frequency Curve
42.1%
70.7%
Basin/ Sub- Composite C
Basin Area (ac)
Frequency Adjusted Runoff Coefficients (C*Cf)
Table A-1
Basin Composite Runoff Coefficients
Attribute Attribute Area
(ac)
Runoff
Coefficient, C
0.23 0.23
0.50
0.77
A1 0.84 0.23 0.28
0.63
0.78 0.98
0.73 0.91
A2 0.64 0.50 0.50
0.52 0.64
A3 0.93 0.78 0.78
A4 0.19 0.52 0.52
0.97
A5 1.47 0.73 0.73
A6 0.94 76.6% 0.77 0.77
0.90 1.00
A7 1.33 0.79 0.79 0.79 0.98
A8 0.15 0.90 0.90
0.80 0.99
A9 0.34 0.77 0.77 0.77 0.97
A10 0.63 0.80 0.80
0.75 0.94
A11 0.36 0.55 0.55 0.55 0.69
A12 0.34 0.75 0.75
0.86 1.00
A13 0.20 0.54 0.54 0.54 0.67
A14 0.16 0.86 0.86
A15 2.24 Lawn, Heavy, 2% Slope 0.44 0.20 0.80 0.80 0.80 1.00
Roofs 0.46 0.95
Streets: Paved 0.27 0.95
Lawn, Heavy, <2% Slope 0.07 0.20
Roofs 0.03 0.95
Streets: Paved 0.16 0.95
Lawn, Heavy, <2% Slope 0.08 0.20
Roofs 0.05 0.95
Streets: Paved 0.27 0.95
Lawn, Heavy, <2% Slope 0.15 0.20
Roofs 0.14 0.95
Streets: Paved 0.02 0.95
Lawn, Heavy, <2% Slope 0.22 0.20
Roofs 0.19 0.95
Streets: Paved 0.48 0.95
Lawn, Heavy, <2% Slope 0.33 0.20
Roofs 0.33 0.95
Streets: Paved 0.08 0.95
Lawn, Heavy, <2% Slope 0.15 0.20
Roofs 0.12 0.95
Streets: Paved 1.03 0.95
Lawn, Heavy, <2% Slope 0.86 0.20
Roofs 0.25 0.95
Streets: Paved 1.61 0.95
Lawn, Heavy, <2% Slope 0.86 0.20
Roofs 0.05 0.95
Streets: Paved 0.77 0.95
Lawn, Heavy, <2% Slope 0.19 0.20
Roofs 0.00 0.95
Streets: Paved 0.14 0.95
Lawn, Heavy, <2% Slope 0.34 0.20
Roofs 0.30 0.95
Streets: Paved 0.34 0.95
Lawn, Heavy, <2% Slope 0.07 0.20
A1-A24 Total % Imp. 67.1%
56.4%
82.8%
48.8%
71.1%
57.1%
59.8%
65.9%
80.2%
80 %
81.1%
72.4%
73.2%
OS5 0.41 0.82 0.82 0.82 1.00
20.78 0.62 0.62 0.62 0.78
0.81 1.00
5 080 080 080 00
A16 0.37 0.81 0.81
0.75 0.94
A17 0.29 0.74 0.74 0.74 0.93
A18 0.56 0.75 0.75
0.73 0.92
A19 0.43 0.57 0.57 0.57 0.71
A20 1.14 0.73 0.73
0.65 0.81
A21 0.35 0.63 0.63 0.63 0.79
0.80 1.00
A23 2.52 0.69 0.69 0.69 0.87
A24 0.96 0.80 0.80
A22 2.14 0.65 0.65
Appendix A