HomeMy WebLinkAboutENCLAVE AT REDWOOD - FDP220014 - DOCUMENT MARKUPS - ROUND 2 - DRAINAGE REPORT (2)
FINAL DRAINAGE REPORT
FOR
ENCLAVE AT REDWOOD
Fort Collins, CO 80524
Date: August 18, 2021
Revised: October 19, 2021
Revised: December 22, 2021
Revised: October 19, 2022
Prepared for:
9555 South Kingston Court
Denver, CO 80112
Phone: 303-488-0061
Prepared by:
Mark A. West, P.E., C.F.M.
1120 Lincoln Street, Suite 1000
Denver, CO 80203
Ph: 303-623-6300, Fax: 303-623-6311
Harris Kocher Smith Project No. 201013
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................................................... 4
A. Site Location ....................................................................................................................................... 4
B. Description of Property ...................................................................................................................... 4
II. MASTER DRAINAGE BASIN DESCRIPTION .................................................................................................. 5
A. Floodplain........................................................................................................................................... 5
B. Master Drainage Basin ....................................................................................................................... 5
III. DRAINAGE DESIGN CRITERIA ................................................................................................................. 6
A. Regulations and Previous Studies ...................................................................................................... 6
B. Four-Step Process .............................................................................................................................. 6
C. Hydrologic Design Criteria ................................................................................................................. 7
D. Hydraulic Design Criteria .................................................................................................................... 8
E. Variances ............................................................................................................................................ 9
F. Erosion Control .................................................................................................................................. 9
IV. PROPOSED DRAINAGE SYSTEMS ............................................................................................................ 9
A. General Concept ................................................................................................................................ 9
B. Proposed Basins ............................................................................................................................... 10
C. Specific Details ................................................................................................................................. 11
V. CONCLUSIONS ......................................................................................................................................... 16
A. Compliance with Standards ............................................................................................................. 16
B. Drainage Concept ............................................................................................................................. 16
VI. REFERENCES ......................................................................................................................................... 17
VII. APPENDICES ......................................................................................................................................... 18
Appendix A – Vicinity Map, FIRM, Geotechnical Engineering Report ....................................................... A
Appendix B - Portions from Relevant Previous Studies ............................................................................ B
Appendix C – Subcatchment Hydrology .................................................................................................... C
Appendix D – Detention Storage Sizing ..................................................................................................... D
Appendix E – SWMM Model and Results .................................................................................................. E
Appendix F – Low Impact Development ................................................................................................... F
Appendix G – Drainage Map ..................................................................................................................... G
Enclave at Redwood
Engineer Certification
December 22, 2021
Engineer Certification
I hereby attest that this report for the drainage design of the Enclave at Redwood project was
prepared by me or under my direct supervision, in accordance with the provisions of the Fort
Collins Stormwater Criteria Manual. I understand that the City of Fort Collins does not and will not
assume liability for drainage facilities designed by others.
__________________________________ _______________________
Mark A. West, P.E., C.F.M. Date
State Of Colorado Registration No. 38561
On Behalf of Harris Kocher Smith
Enclave at Redwood
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December 22, 2021
I. GENERAL LOCATION AND DESCRIPTION
a. Site Location
The proposed Enclave at Redwood development (hereinafter referred to as “Site”) is located in the
southeast ¼ of Section 1, Township 7 north, Range 69 west of the sixth Principal Meridian, City of Fort
Collins, County of Larimer, State of Colorado. The Site is bounded by Redwood Street to the west and
East Suniga Road to the south. A small portion of the design exists south of East Suniga Road. Adjacent
developments include the Meadows at Redwood PUD Phase 1 (Redwood Meadows) to the west,
Northfield to the east and southeast, and Evergreen Park 3rd (Evergreen) to the north. Lake Canal exists
as an irrigation ditch adjacent to the Site to the east and southeast, and Redwood Channel lies adjacent
to the Site to the north. The Site will connect to Redwood St to the southwest, Lupine Dr in Redwood
Meadows to the west, Steeley Dr in Northfield to the southeast, and Collamer Dr in Northfield to the
east. See Appendix A for the Vicinity Map. The Site exists entirely within the Dry Creek master drainage
basin.
b. Description of Property
The Site is approximately 29.66 acres of undeveloped land. The undeveloped land is made up of various
native trees and grasses. The Site generally slopes from west to east at grades between roughly 0.3%
and 1% towards Lake Canal. Lake Canal is an irrigation ditch and discharging stormwater from the
developed Site to this ditch will require approval from the ditch ownership. Redwood Pond is an existing
regional pond to the northwest of the Site, it historically outfalls east into the Redwood Channel
drainage ditch that exists north of the Site. The proposed development of the Site will feature multi-
family housing, public and private roadways, walks, parks, a clubhouse with pool, landscaped areas, four
on-site detention facilities and low impact development systems.
Cole Garner Geotechnical prepared a Geotechnical Engineering Report for the Enclave at Redwood
Residential Development, dated August 11, 2021. The report analyzes existing soils information for the
Site. Ten borings were drilled to examine subsurface conditions in February of 2021. Groundwater was
encountered in all borings at the time of drilling and approximately two weeks after drilling at depths
ranging from 8 to 12 feet below existing Site grades. To account for seasonal groundwater fluctuations,
Cole Garner measured groundwater levels in the aforementioned borings again in September of 2021. It
was found that three of the ten borings saw no change in groundwater elevation, six of the ten borings
saw a rise in groundwater of less than 1.5 feet, and one of the borings saw a rise in groundwater of 4
feet. The drainage design of the Site will consider the readings from September to be the more accurate
reading indicative of the wet season. Due to shallow groundwater concerns, construction dewatering
may be required. All drainage facilities will be located at least 24 inches above groundwater. Please see
Appendix A for relevant portions of the Geotechnical Engineering Report and a table of the groundwater
readings taken in September of 2021.
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II. MASTER DRAINAGE BASIN DESCRIPTION
A. Floodplain
The Site is shown on the Federal Emergency Agency’s (FEMA) Flood Insurance Rate Map (FIRM)
Community Panel Numbers 08069C0977G and 08069C0981G, effective June 17, 2008. Lake Canal is
partially located within Zone X (0.2% annual chance flood hazard) and therefore the Site is partially
within this zone. Because the development of the Site will not involve altering of Lake Canal, no
floodplain modifications are necessary. Please refer to Appendix A for more details.
a. Master Drainage Basin
The Site exists in the Dry Creek Master Drainage Basin, but according to the City of Fort Collins, the Dry
Creek Master Drainage Plan is outdated and not specific to the Site. The North East College Corridor
Outfall Design Report prepared by Ayres Associates in August 2009 (NECCO Report) will be utilized to
impose drainage conditions on the Site instead of the Dry Creek Master Drainage Plan. Please see
Appendix B for relevant portions from the NECCO report. The report details the design and construction
of a regional pond that stores a large amount of runoff from the Dry Creek basin and conveys it to a new
storm main beneath E. Suniga St. The NECCO report also contains design plans to revise the existing
Redwood Pond’s grading and change its outfall location from the Redwood Channel drainage ditch north
of the Site to the NECCO storm main beneath E Suniga St south of the Site. The Redwood Pond changes
detailed in the NECCO report have not been constructed, and therefore the A2 lateral outlined in the
NECCO report has not been constructed either. The Site will require design and construction of the
proposed Redwood Pond outlet structure and the A2 lateral storm line that are detailed in the NECCO
report. No other proposed changes to the Redwood Pond will be constructed as part of this
development, as the Site contributes no runoff to the Redwood Pond. The A2 lateral storm line will
connect to an existing stub from the NECCO main and will act as the ultimate outfall of the developed
Site.
The basins from the NECCO report that were analyzed for this report include basins 113, 213, 313, 413,
and 812. The Site exists in basins 113, 313, and 413. Basin 413 will remain undeveloped and thus the A3
lateral detailed in the NECCO report will not be constructed, and runoff from this basin will continue to
follow historic patterns and release into Lake Canal undetained and untreated. The NECCO report calls
for future on-Site detention for basins 113 and 313, which will each require a 100-year release rate of
0.2 cubic-feet-per-second (CFS) per acre. Basin 213 consists of the Redwood Meadows development and
would require water quality treatment but no detention if redeveloped in the future. The Site will
provide inlets at various points between the border of the Redwood Meadows development and the
Site boundary in order to capture all runoff from basin 213 and route it to the A2 lateral storm line.
Basin 812 consists of the Redwood Pond, which the NECCO report details as requiring regrading and
redesign to allow for a 100-year detention volume of 7.70 acre-feet (ac-ft) and an additional 2.16 ac-ft of
storage for water quality. The redesign would entail adding additional pond facilities such as trickle
channels and forebays, as well as plugging the existing outlet, but leaving the existing berm and
overflow spillway. As stated above, because the Site will not contribute runoff to the Redwood Pond,
only the outlet structure and storm lateral A2 will be designed and constructed as part of this
development. Please see Section IV of this report for more information on the proposed redesign of the
Redwood Pond. The on-Site detention facilities will meet the release rate constraint of 0.2 CFS/acre
imposed by the NECCO Report.
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Also provided for the development of drainage for the Site was an existing conditions SWMM model
featuring the constructed NECCO storm main under E Suniga St and the regional pond designed in the
NECCO Report. This SWMM model was updated for the final drainage analysis.
Historic drainage analysis of the Site shows that the entirety of the Site (29.66 acres) discharges into
Lake Canal existing along the Site boundary running from the southeast to the northeast. The existing
Site has an imperviousness of 2% and an approximate 100-year runoff of 14 CFS, all of which discharges
into Lake Canal. Any stormwater discharging from the developed Site into Lake Canal will require
approval from the ditch ownership. The Site will contribute some undetained and untreated runoff to
Lake Canal due to the Site’s existing drainage patterns. Please see Section IV of this report for
approximate 100-year runoff values discharging to Lake Canal from the developed Site. Please note the
approximate runoff stated here and in Section IV is calculated using SWMM’s hydrologic calculator,
more accurate runoff calculations using the Rational Method will be included in a later version of this
report.
III. DRAINAGE DESIGN CRITERIA
A. Regulations and Previous Studies
The principal design criteria used for this report come from the Fort Collins Stormwater Criteria Manual,
revised December 2018 (FCSCM). In addition, Mile High Flood District’s (MHFD) Urban Storm Drainage
Criteria Manual, Volumes 1-3 revised August 2018, September 2017, and January 2021 respectively,
were used (USDCM). The NECCO report also imposes drainage criteria on the Site that must be met.
a. Four-Step Process
b. Step 1: Employ Runoff Reduction Practices
The Site will feature numerous open areas dedicated for low-impact-development (LID), parks, and
above ground detention. Wherever possible, vegetated swales will be used to convey runoff to area
inlets and roof drains will be used to convey flow to these swales, directly to LID implements, or to
storm sewer structures.
c. Step 2: Implement BMPs That Provide a WQCV with Slow Release
There are four LID systems incorporated on-Site, with 3 of them being isolator row chamber systems,
and 4 of the . The systems are designed to treat over 75% of newly added impervious area after the
development of the Site, per the FCSCM. A majority of the remainder of the Site’s impervious areas will
be treated in the at-grade on-Site detention pond.
d. Step 3: Stabilize Streams
The Site will be far upstream of Dry Creek and the NECCO report has already considered developed
release rates from the Site entering Dry Creek. There will be no need to provide stream stabilization of
Dry Creek with the development of the Site.
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e. Step 4: Implement Site Specific and Other Source Control BMPs
Because the Site is not a new development or redevelopment of an industrial or commercial zone, Step
4 is not applicable to the Site.
f. Hydrologic Design Criteria
Design Frequencies – For the Site, the minor storm will be the 2-year and the major storm will be the
100-year. For detention volume and release rates, the WQCV and 100-year storm events have been
analyzed.
Rainfall Data - Fort Collins varies by runoff calculation method. For the purpose of this drainage report,
only SWMM was used in calculating runoff. Below is Table 4.1-4 which presents rainfall intensity values
for use in SWMM modelling.
Hydrologic Computation Method – As stated above, only EPA SWMM 5.1 was used to calculate runoff
for this drainage design. As of now the basins tributary to each of the ponds have not been broken into
smaller sub-basins for the purpose of inlet calculations. For future iterations of this report, the rational
method will be utilized to size inlets and storm drains. SWMM uses basin imperviousness, slope, area,
and width along with several default parameters to calculate runoff. SWMM inputs can be found in
Appendix E as well as Section IV of this report. The rational method uses weighted “C” coefficients based
upon surface type and a time of concentration to determine runoff. Fort Collins rational method IDF
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table and “C” coefficient table can be found in Appendix C along with SWMM subcatchment default
parameters and imperviousness by surface type tables. A summary of SWMM results for each
subcatchment can be found in Appendix C as well. The rational method “C” coefficient and water quality
event rainfall intensities were utilized in the Modified FAA Procedure to calculate the WQCV for the
isolator rows.
Detention Volume Computation Method – For project sizes greater than 20 acres, SWMM is required for
detention calculation. SWMM storage nodes are used to represent the ponds and require storage curves
(depth-area), SWMM then computes a volume based on these tables. SWMM outlet links are used to
represent a ponds outlet structure and require rating curves (depth-release). SWMM can also utilize
orifice, weir, or conduit links for a pond’s outlet structure. A mix of these different links were utilized for
the Site’s SWMM modelling. More discussion on pond modelling in the Site SWMM model can be found
in Section IV of this report, and all calculations relating to detention ponds and facilities can be found in
Appendix D. The FCSCM requires that the WQCV be added to the 100-year storage volume as opposed
to being included in said volume, thus the WQCV has been included in the SWMM model’s storage
nodes as an initial water depth value. Please see below for more information on computation of the
WQCV. See Appendix E for SWMM output results of storage nodes.
Water Quality Control Volume Calculation – The only LID systems implemented on-Site are isolator rows
featuring underground infiltration. Three of these systems are included as part of an underground
detention chamber system, and one other features isolator row chambers solely. For these isolator row
systems, a spreadsheet received from Advanced Drainage Systems (ADS) was used to determine the
number of chambers needed based on product choice, chamber volume, and required WQCV. For the
sizing of these systems, two different WQCV values are compared to determine which results in a higher
number of required chambers. The first is 120% of the WQCV based on a 12-hour drain time, which can
be calculated using UD-BMP’s rain garden tab and multiplying that value by 1.2. The second is the WQCV
calculated from the modified FAA procedure, which uses a weighted “C” coefficient, tributary area, and
maximum flow out of the chamber system. Whichever WQCV results in more chambers based on the
received spreadsheet discussed above is the utilized WQCV. The required WQCV for the above ground
on-Site detention pond was found using the UD-BMP extended detention basin tab. This tab computes a
WQCV based on a 40-hour drain time, which is then multiplied by a factor of 1.2 to meet the 120% of
the WQCV requirement from the FCSCM. See Appendix D for the calculation of the WQCV for the above
ground pond, and Appendix F for the calculation of the WQCV and chamber requirements for the
isolator rows.
g. Hydraulic Design Criteria
Detention Pond Infrastructure Sizing - Express Hydraflow will be used to calculate vegetated swale and
emergency overflow spillway capacities for the Site. The FCSCM requires that overflow spillway design
flow depth be no greater than 0.5 feet. UD-BMP will be used to size trickle channels, forebays, and
forebay notches for the above ground pond. Outlet structures for the Redwood Pond and on-Site above
ground detention ponds have been preliminarily designed, and only the Redwood Pond will feature a
rating curve in SWMM to act as an outlet. Pond 1 and Pond 3 have been designed in SWMM using
outfall conduits with their maximum flow values set at the 0.2 CFS/acre release rate criteria. This
ensures the facilities will have enough volume without needing to fully design their outlet structure (box
height, restrictor plates, orifice plates). These detention facilities’ outlet structures will be designed fully
in a future version of this report using stage-storage-discharge tables that result in a developed rating
curve. Stage-area-release tables for the ponds can be found in Appendix D.
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Street Capacity Calculation – Street sections upstream of proposed inlets will be analyzed using the
MHFD spreadsheet “MHFD-Inlet v5.01” released April 2021. These calculations will be presented in a
later version of this report.
Storm Sewer Sizing – Inlet sizing will be performed using the MHFD-Inlet spreadsheet. For the layout of
the storm network, inlet sizes were estimated based on contributing area and imperviousness. Inlet
Type 16 curb and valley inlets, Type R curb inlets, and Type C and D areas inlets were utilized for this
Site. Storm pipe sizing and vertical alignment will be analyzed using Bentley StormCAD CONNECT.
StormCAD computes losses and velocities and produces accurate HGLs and EGLs to prove the storm
sewer network works hydraulically.
h. Variances
The drainage design for the Site will not require any variance from criteria put forth in the FCSCM,
USDCM, and NECCO Report.
i. Erosion Control
The following drainage design will comply with all erosion control criteria put forth in the USDCM,
FCSCM, and NECCO Report. All erosion control materials will be provided with the final drainage report.
IV. PROPOSED DRAINAGE SYSTEMS
A. General Concept
The Site will include outlet structure design for the Redwood Pond in the northwest of the Site as
detailed in the NECCO report. For the design of the Site, the outlet structure has been designed to meet
the parameters presented in the NECCO report including pond regrading. The Site will include
development of the NECCO A2 storm lateral, which runs from the new Redwood Pond outlet structure
to an existing stub on the NECCO main line under E Suniga Rd. There are three proposed underground
chamber facilities and two proposed at-grade detention ponds, and the Redwood Pond, all of which will
feature some level of water quality treatment. All these ponds will meet the 0.2 CFS/ac release rate
criteria, and release to the NECCO A2 storm lateral. Site runoff will be conveyed to these ponds via roof
drains, swales, inlets and storm sewer pipes, and landscape drains. Runoff from basin 213 consisting of
Redwood Meadows will be captured by proposed on-Site inlets and routed directly into the NECCO A2
storm lateral. Further breakdown of the ponds and a summary table can be found below.
The Site will feature four LID systems all of which are underground infiltration isolator rows. These LID
features are designed to treat at least 75% of the Site’s impervious areas for the WQCV. Unlike the
detention facilities mentioned above, these LID systems are only designed to capture the areas tributary
to them and have been sized as such. The systems are conservatively sized by rounding up the
calculated imperviousness of their tributary areas for use in calculations. Runoff will be routed to these
systems via roof drains, swales, inlets and storm sewer pipes, and landscape drains, all to be designed in
a later version of this report. Any on-Site runoff that is not practicable to route to a stormwater facility
will leave the Site untreated, however more LID facilities may be added in a future revision to the Site’s
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drainage design to reduce the amount of area leaving the Site untreated. The at-grade detention pond
includes water quality detention but does not treat for any areas already accounted for by LID facilities.
Further breakdown of the LID areas and a summary table can be found in Table 3 of Section C.
For the SWMM analysis included in this report, only 4 subcatchments were used and the only storm line
included was the NECCO A2 storm lateral that receives the outfall from all ponds and runoff from basins
213 and 413. This is a high-level analysis of the Site’s drainage. Below is a breakdown of the seven
subcatchments as well as a table featuring their SWMM input parameters. Also found below is a table
summarizing SWMM model results.
See Appendix C for summary of subcatchments and SWMM input parameters. See Appendix D for
underground detention chamber layouts, stage-area tables for all ponds, SDI data sheets for all ponds,
and any other pond calculations and information. See Appendix E for SWMM schematic, input report
and output results. See Appendix F for LID calculations, summary table, and exhibit showing areas and
locations of facilities. See Appendix G for drainage map showing pond locations, basins, drainage
patterns, and storm layout.
a. Proposed Basins
Below is Table 1 featuring a summary of all basin input parameters for SWMM and other calculated
parameters.
Table 1:
Pond Subcatchment Summary Table
Basin Area
(ac)
Utilized
Imperviousness
(%)
Width
(ft)
Slope
(%)
2-Year
Peak
Runoff
(CFS)
100-
Year
Peak
Runoff
(CFS)
113_1 4.28 55 1863.8 0.75 6.65 32.61
113_2 7.86 50 1342.2 0.50 9.93 45.38
113_3 9.75 65 2831.8 0.80 17.21 77.77
113_4 5.58 68 2432.3 0.60 10.51 47.47
213 7.82 75 1946.5 0.40 14.41 67.65
413 2.19 7 374.3 1.00 0.45 6.62
812 3.75 2 544.5 0.50 0.22 7.21
Basin 113_1 lies on-Site and encompasses the southwestern portion of the Site. This basin consists of
multi-family housing, walks, roadways, alleys, open space, and Isolator Rows IR1 and at grade detention
Pond 1. Runoff from this basin will be conveyed to IR1 in the southern portion of this basin via roof
drains, swales, storm sewer systems, and landscape drains. It is assumed that some portions of this
basin will flow off-Site undetained and untreated into Redwood St or Lake Canal, but all of this basin is
tributary to Pond 1 for the purpose of this drainage analysis.
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Basin 113_2 lies on-Site and encompasses the eastern portion and border of the Site. This basin consists
of multi-family housing, walks, roadways, alleys, open space, portions of Lake Canal irrigation ditch and
underground detention system UD2. Runoff from this basin will be conveyed to UD2 in the
southwestern portion of the basin via roof drains, swales, storm sewer systems, and landscape drains.
Basin 113_3 lies on-Site and encompasses the middle portion of the Site spanning from the Redwood
Meadows property boundary to the west to the northeastern corner of the Site. This basin consists of
multi-family housing, walks, roadways, alleys, open space, isolator rows, and above ground detention
pond Pond 3. A majority of the runoff from this basin will be conveyed to the isolator row system IR 3 in
the middle of the basin via roof drains, swales, storm sewer systems, and landscape drains. All other
runoff from this basin will be conveyed directly into Pond 3 instead of being routed through IR 3. The
area Pond 3 takes up will also be utilized as an open space park.
Basin 113_4 lies on-Site and encompasses the northern portion of the Site. This basin is consisting of
multi-family housing, walks, roadways, alleys, and open space. Runoff from this basin will be conveyed
to the Redwood Pond in the northwestern portion of the basin via roof drains, swales, storm sewer
systems, and landscape drains. Portions of this basin will contribute runoff north off-Site undetained and
untreated into the Redwood Channel drainage ditch.
Basin 213 lies off-Site to the west of the Site. This basin consists of the Redwood Meadows development
featuring walks, single-family homes, roadways, and open spaces. Runoff from this basin will not need to
be detained but will need to be conveyed to the NECCO A2 storm lateral. Two at-grade inlets are
proposed at the connection of Lupine Dr and the Site to collect runoff from the roadways of this basin.
An area inlet and swale are also proposed sitting just east of the Redwood Meadows development
meant to collect any runoff from this basin that is not collected by the roadways within the basin. This
basin slopes from the south to the northwest generally.
Basin 413 lies on-Site south of E Suniga St. This basin will remain undeveloped and consists entirely of
open space. Runoff from this basin will continue to follow historic patterns and discharge into Lake
Canal. The NECCO report details an additional storm lateral A3 for this basin but will not be constructed
because this lot will remain undeveloped.
Basin 812 lies off-Site to the northwest of the Site. This basin consists of the existing Redwood Pond.
Runoff from this basin will be collected by the Redwood Pond.
Progressing to the final drainage design allowed more area to be captured in the hydrological design of
the Site. Approximately 0.93 acres of the Site currently contributes flow off-Site untreated and
undetained, with 0.21 acres being captured by the NECCO A2 storm lateral, 0.28 acres discharging into
the Northfield development, 0.04 acres discharging into Redwood St, 0.60 acres discharging into
Redwood Channel, and 4.45 acres discharging into Lake Canal. Note that runoff discharging from the
developed Site into Lake Canal and Redwood Channel is mostly coming from open space. Further
analysis of these areas will be conducted with the final drainage design of the Site.
b. Specific Details
The Redwood Pond grading and outlet structure has been preliminarily designed as detailed in the
NECCO report. The NECCO report calls for a pond bottom invert of 4953.10, so the proposed outlet
structure has been set to this elevation and the pond regraded. The pond’s berm and spillway will
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remain the same at an elevation of 4962.10, and the existing outlet pipe into Redwood Channel will be
plugged as part of the ultimate condition for this pond. The stage-storage-discharge table presented in
Appendix D for this pond was used for information in the SWMM model and begin design of the outlet
structure. The final release rate for this pond will be equal to or less than 15.96 CFS, as presented in the
NECCO report. Basin 113_4 (5.58 ac) is tributary to this system, allowing for an additional release rate of
1.12 CFS for the 100-year storm event. The system releases directly into the NECCO A2 storm lateral.
The outlet manhole design to be included for final drainage design will feature an orifice plate, weir, and
restrictor plate to hold the release rate to 1.12 CFS. The Redwood Pond overflow spillway will direct
flows north into the Redwood Channel. Please see the table below for SWMM computed results for this
system. The WQCV for this system will be treated by standard
IR 1 is located in the southwestern portion of the Site and features an invert elevation of 4951.40. This
system will be comprised of 20 ADS MC-4500 Stormtech chambers with 9 inches of stone below the
chambers and 12 inches of stone above the chambers. The total height of the system is 6.75 ft, putting
the top of stone at an elevation of 4958.15. The minimum finished grade above the system is 4960.81
which is more than the 1 ft of required cover above the top of the system. The maximum groundwater
elevation below the system is 4949.40, which is 24 inches below the bottom of the facility, meeting
FCSCM criteria. Flows in excess of the LID event will bypass IR 1 and enter Pond 1. Basin 113_1 (4.28 ac)
is tributary to this system, allowing for a release rate of 0.86 CFS for the 100-year storm event. The
system releases directly into the NECCO A2 storm lateral. The outlet manhole design to be included for
final drainage design will feature an orifice plate, weir, and restrictor plate to hold the release rate to
0.86 CFS. The Pond3 overflow spillway will direct flows north into Collamer Drive. Please see the table
below for SWMM computed results for this system. The WQCV for this system will be treated entirely by
isolator rows included in the system, see below for more information on these chambers.
Underground detention system UD2 is located in the southwestern portion of the Site and features an
invert elevation of 4950.42. This system will be comprised of ADS MC-4500 Stormtech chambers with 9
inches of stone below the chambers and 12 inches of stone above the chambers. The total height of the
system is 7.75 ft, putting the top of stone at an elevation of 4957.17. The minimum finished grade above
the system is 4958.26 which is above the 1 ft of required cover above the top of the system. The
maximum groundwater elevation around the system is 4948.42, which is 2.0 ft below the invert of the
system. Basin 113_2 (7.86 ac) is tributary to the system, allowing for a release rate of 1.57 CFS for the
100-year storm event. The system releases directly into the NECCO A2 storm lateral. The outlet manhole
design to be included for final drainage design will feature an orifice plate, weir, and restrictor plate to
hold the release rate to 1.57 CFS. The UD2 overflow spillway will direct flows southwest to East Suniga
Street. Please see the table below for SWMM computed results for this system. The WQCV for this
system will be treated entirely by isolator rows included in the system, see below for more information
on these chambers.
Isolator rows IR3 are located in the middle portion of the Site, just upstream of Pond3. The sizing
process for these chambers is located above in Section III. The result is 42 ADS MC-3500 Stormtech
chambers. This system has a total height of 5.50 ft, requiring 2 ft below the system clear of
groundwater, and 0.5 ft above the system for cover. The minimum groundwater depth for this system is
approximately 11.50 ft, giving this system more than enough vertical clearance both ways. The 100-year
runoff entering this system will bypass the system to be detained in Pond 3.
Pond 3 is located in the middle portion of the Site and features a depth of 9.5 ft and a pond bottom
elevation of 4954.52. The spillway has a crest elevation of 4963.00 and a length of 76 ft. The spillway is
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situated on the northern edge of the pond and will discharge runoff above the 100-year event into
public roadway. Basin 113_3 (8.62 ac) is tributary to this pond, allowing for a release rate of 1.95 CFS for
the 100-year storm event. The runoff from basin 113_3 will be captured and treated for water quality by
the isolator row LID facility named IR3 directly upstream of the pond. Pond 3 has a WQCV water surface
elevation (WSEL) of 4958.34, modelled as an initial depth of 0.84 ft in the SWMM model. This pond will
feature varying side slopes and aesthetically pleasing design. An outlet box structure has been
preliminarily designed to release 1.95 CFS to the NECCO A2 storm so as not to cause overtopping of the
spillway during the 100-year storm. The main outlet box will feature orifice holes and a weir as typical to
treat the WQCV, and a restrictor plate to be designed during final drainage design that limits the release
rate to 1.95 CFS. The UD2 overflow spillway will direct flows southwest to East Suniga Street. The
minimum groundwater depth below this pond is 3.64 ft, with an elevation of 4950.88. Please see the
table below for SWMM computed results for this pond.
See below for Table 2 showing a summary of pond results from SWMM. The WQCV presented in this
table for the underground detention systems is from the LID isolator rows to be discussed below. The
WQCV for the above ground pond does not include any volume already treated by LID systems. The
WQCV WSELs have been inputted into SWMM and not computed.
Table 2:
Detention Pond Summary Table
Pond
100-
Year
Volume
(cu-ft)
100-
Year
Volume
(ac-ft)
100-Year
WSEL
WQCV
(cu-ft)
WQCV
WSEL
Max
Release
Rate (CFS)
Total Volume
Required (WQCV
+ Detention) (ac-
ft)
Total Volume
Provided (WQCV
+ Detention) (ac-
ft)
Pond1 36,562 0.84 4957.63 0.86
IR 1 3,147 4954.40 0.91 0.91
UD2 66,457 1.53 4951.92 1.57
IR2 5,354 4947.09 1.65 1.65
Pond3 81,471 1.87 4962.52 1.95
IR 3 7,304 4958.34 2.04 2.04
Redwood Pond 226,265 5.19 4958.19 4956.46 15.96
*WQCV in Underground Chamber Systems Explored Further in LID Exhibit and Calculations Found in
Appendix F of Final Drainage Report
**SWMM Model, Inputs, and Outputs Found in Appendix E of Final Drainage Report
Enclave at Redwood
Page 14
December 22, 2021
Isolator rows IR1, IR2, and IR3 are located within detention systems POND 1, POND 2, and POND 3
respectively. These isolator row chambers will match the inverts and dimensions of the systems they are
within. Table 3 below features a summary of the LID systems for the Site including tributary area,
imperviousness, impervious area, calculated WQCV, and provided WQCV.
Table 3:
Table 4 below features a summary of the SWMM results for nodes. Table 5 below features a summary of
the SWMM results for links. See Appendix E for a schematic calling out the nodes summarized below.
Basin Area (sq-ft) Area (ac)
Calculated
Imperviousness
(%)
*Utilized
Imperviousness
(%)
Impervious
Area (sq-ft)
120% WQCV
(12-Hour Drain
Time) (cu-ft)
FAA
WQCV (cu-
ft)
LID Treatment
Provided
Volume in
LID (cu-ft)
IR-1 143024.90 3.28 65.6 70 93810 3147 1787 Isolator Rows 1 - Pond 1 3252
IR-2 223433.92 5.13 72.5 75 162057 5354 3855 Isolator Rows 2 - UD2 5366
IR-3 310215.35 7.12 71.1 74 220625 7304 4429 Isolator Rows 3 - Pond 3 7350
IR-4 198045.54 4.55 79.3 80 157030 not treated by LID
Total LID
Treated Area 676674.17 15.5 70.4 476492
Total Site Area 1196479.944 27.5 51.9 621093
77%Total LID Treated Impervious Area/Total Site Impervious Area (Must be > 75%)
LOW IMPACT DEVELOPMENT SUMMARY TABLE
**Isolator Rows were sized by comparing 120% of the WQCV based on a 12-Hour drain time and the City of Fort Collins Modified FAA Method
*In some cases imperviousness was rounded up to be more conservative in sizing LID facilities, exact imperviousness was used to prove 75% of new impervious areas
treated by LID
Enclave at Redwood
Page 15
December 22, 2021
Table 4:
SWMM Node Results Summary Table
Node Type Maximum
Depth (ft)
Maximum
HGL (ft)
Maximum Total
Inflow (CFS)
A2_1 JUNCTION 5.15 4951.84 68.25
A2_2 JUNCTION 5.48 4952.48 68.19
A2_3 JUNCTION 6.18 4954.67 69.26
A2_4 JUNCTION 6.00 4955.27 72.02
A2_5 JUNCTION 6.14 4955.71 74.07
A2_6 JUNCTION 6.24 4956.28 71.85
A2_7 JUNCTION 3.83 4955.91 75.65
A2_8 JUNCTION 3.91 4956.45 76.14
A2_9 JUNCTION 3.68 4956.50 13.39
A2_10 JUNCTION 3.90 4957.00 13.39
NECCO_A-11 JUNCTION 0.69 4956.97 89.97
308-Redwood STORAGE 5.02 4963.54 73.21
Pond1 STORAGE 6.23 4957.63 32.61
UD2 STORAGE 5.16 4951.92 46.95
Pond3 STORAGE 5.02 4962.52 77.77
Table 5:
SWMM Link Results Summary Table
Link Type Maximum
Flow (CFS)
Maximum
Velocity
(fps)
Maximum/Full
Flow
Maximum/Full
Depth
A2_1 CONDUIT 66.77 9 0.73 0.6
A2_2 CONDUIT 68.25 5.17 0.63 1.0
A2_3 CONDUIT 67.33 5.14 0.63 1.0
A2_4 CONDUIT 69.26 6.18 0.67 1.0
A2_5 CONDUIT 72.02 5.77 0.67 1.0
A2_6 CONDUIT 72.12 5.41 0.66 1.0
A2_7 CONDUIT 71.85 6.09 0.68 0.9
A2_8 CONDUIT 75.65 6.61 0.71 0.8
A2_9 CONDUIT 13.39 4.4 0.42 1.0
A2_10 CONDUIT 13.39 5.9 1.84 1.0
Redwood_Outlet DUMMY 13.53
POND1_Outlet CONDUIT 0.86 2.22 0.04 1.0
UD2_Outlet CONDUIT 1.57 12.84 0.04 1.0
POND3_Outlet CONDUIT 1.95 4.49 0.13 1.0
Enclave at Redwood
Page 16
December 22, 2021
V. CONCLUSIONS
A. Compliance with Standards
The drainage design is prepared in compliance with the FCSCM and the USDCM Volumes 1, 2, and 3.
As stated before, the NECCO report details utilizing a release of less than 15.96 CFS for the Redwood
Pond and less than 0.2 CFS/ac for the three on-Site ponds. This criteria has been met for the proposed
design.
a. Drainage Concept
The drainage design as described herein; if properly constructed and maintained, will effectively control
stormwater runoff in accordance with the criteria. The proposed development will provide water quality
and detention for the 100-year event with associated outlets and spillway overflow. This drainage design
for the proposed development does not have any impact on the NECCO report design. The drainage
design for this Site will have no adverse effects to any upstream or downstream adjacent properties.
4.13 Ayres Associates
The Regional Detention Pond has been sized for additional flows generated from the un-
developed portion of the Old Town North development. A storm sewer was not designed to
convey the flows north to the proposed Regional Detention Pond. When this storm sewer is
designed, special considerations must be given to the GWET and NEWT waterline
crossings. These clearances are very critical.
Laterals C6A and C6B are located just west of the regional detention pond along re-aligned
Vine Drive. Lateral C5A is at the intersection of Blondel and Future Vine Drive. This inlet
will reduce flows from Blondel Street. Laterals C4A and C4B are placed just east of College
Avenue and the future re-aligned Vine Drive.
The inlets located within the re-aligned Vine Drive were designed for the 10-year minor storm
event and the 100-year major storm event being handled within the road, based on current
COFC criteria.
Table 4.5 shows Storm Line C1 and C2, 10- and 100-Year Inlet Summary.
Table 4.5. Storm Line C1 and C2, 10- and 100-Year Inlet Summary.
ID Number
and Type Condition
10- / 100-Year
Flow to Inlet
(cfs)
10- / 100-Year
Capture %
10- / 100-Year
Carry-Over (cfs)
Carry-Over
Location
Inlet
C6A
3-Type 13
Combination On-Grade 5 / 11 90 / 83 1/ 2 A5A
Inlet
C6B
3-Type 13
Combination On-Grade 5 / 11 87/ 77 1 / 3 A5B
Inlet
C5A
1-Type 13
Combination On-Grade 5 / 5 100 - -
Inlet
C4A
2-Type 13
Combination Sump 4.5 / 10 100 - -
Inlet
C4B
3-Type 13
Combination Sump 10 / 27 100 - -
Inlet
C3A 3-Type C Orifice/Weir 24 / 60 - - -
A headwall with wing walls and scour stop are incorporated into the outlet of Storm Line C1
and C2. Scour stop was sized by the manufactured. Storm Line C1 will discharge
approximately 202 cfs to the regional pond during a 100-year storm. Storm Line C2 will
discharge approximately 50 cfs into the regional pond during a 100-year storm.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of the parallel Storm Sewer Lines C1 and C2.
The model results show the energy grade line of the system to be below the flowline of the
inlets, therefore the inlets will function properly during a 10- and 100-year event.
4.4 Redwood Pond
The existing Redwood Pond currently outfalls into existing drainage swale that conveys the
storm water to the Evergreen East Pond. The swale and downstream system does not meet
City of Fort Collins drainage criteria for the 100-year event. The improvements to the pond
included re-grading the pond to outlet at the southeast corner of the site. This outlet will
ultimately discharge into the proposed storm sewer in re-aligned Vine Drive. The re-graded
pond has the same footprint and top of berm elevation as the existing pond. A water quality
4.14 Ayres Associates
outlet structure is proposed prior to discharging into the proposed storm sewer system. A 4-
foot concrete trickle pan is incorporated into the pond bottom to direct low flows due to
minimal slope across the pond. The overall footprint encompasses approximately 3.5 acres
at an approximate depth of 6 ft. The required 100-year detention volume is 7.70 ac-ft with
an additional 2.16 ac-ft of storage below the detention storage for water quality. Table 4.6
shows the major characteristics of Redwood Pond.
Table 4.6. Redwood Pond.
Description
Elevation
(ft)
Pond Volume
(ac-ft)
Pond Depth
(ft)
Pond Invert 4953.10 --- ---
Outlet Structure
Elevation 4955.12 2.16 2.02
100-year WSEL 4957.75 9.86 4.65
Spillway into
Pond 4958.39 11.94 5.29
Top of Pond 4959 14.00 5.90
WSEL = Water Surface Elevation
The outlet structure for the redwood pond is a combination of two Type C inlets in series.
The inlets will be separated by a steel plate with an orifice opening sized to provide a 40-
hour drain time for the water quality portion of the pond. One of the frequent maintenance
issues associated with water quality structures is the clogging of the orifice plates. For this
reason we are proposing to install an 18F snout oil-water debris separator inside the first
Type C inlet over the water quality plate. The snout should prevent the orifice plate from
clogging. The second Type C inlet will be set at the water quality elevation and the outlet
pipe from the inlet controls the release rate from the pond.
Currently an undersized storm sewer system conveys flow from inlets along Redwood Street
into Redwood Pond. The series of existing inlets surcharge during the minor events creating
localized flooding at the intersection of Redwood Street and Conifer Street. The existing
inlets and storm sewer do not have the capacity for the 100-year runoff from the surrounding
basins. An adequate storm system would require large diameter storm pipe and deep inlets
to prevent surcharging. Due to existing water and sanitary conflicts in the area, and a
controlled invert into Redwood Pond, the only storm sewer system that could fit within the
existing constraints would be multiple shallow 12-inch diameter storm sewer culverts. These
storm sewer culverts would still not alleviate the minor and major storm flooding problem.
To mitigate the flooding, the design incorporates a 90-foot overflow weir graded into the
pond embankment. The 100-year storm event (approximately 85 cfs) will overtop the curb at
an elevation of approximately 4958.39 and be conveyed to the pond through the weir. Minor
event flows will continue to be captured by the existing inlets located north of the pond. This
design can be looked at in more detail during the final design process.
EPA SWMM Hydraulic Modeling
The proposed weir into Redwood Pond was modeled using a weir in EPA SWMM. The
transverse weir option was chosen with a discharge coefficient of 3.0. During a 100-year
event the 90 foot weir will convey approximately 80 cfs at a max depth of 0.45 ft.
4.15 Ayres Associates
The detention pond was given an initial depth of 2.02 ft to account for water quality storage.
The pond outlet structure was modeled using a combination of a low flow orifice and
overflow weir. A side calculation was performed to verify the accuracy of the generated EPA
SWMM rating curve out of the pond. Based on the calculations the discharge from the pond
is being controlled by the outflow pipe. The model results matched the side calculations (see
Appendix F for Redwood Pond Calculations).
4.5 East Vine Diversion Channel / Regional Detention Pond Outfall
The future East Vine Diversion Channel will serve as the outfall to the North East College
Corridor Outfall drainage system.
Table 4.7 represents the tailwater rating curve that was used in the EPA SWMM model for
the downstream boundary condition (Storm Line A1) at the future East Vine Diversion
Channel. This rating curve is based on a conceptual design of the future channel and was
taken from the preliminary HEC-RAS model of the East Vine Diversion Channel from the
DC3 project (Dry Creek Connection Channel).
Table 4.7. Dry Creek Tailwater Rating Curve.
Time (hr) Tailwater (ft)
100-year Storm Event
0.0 4934.24
0.3 4939.31
1 4937.88
1.19 4938.29
2 4937.31
3 4936.94
4 4936.86
5 4936.79
6 4936.42
4.5.1 Storm Line A1
Storm Line A1 is a major component of the proposed storm drainage system east of
Redwood Street. Storm Line A1 starts at the outlet of the regional pond and continues east
along re-aligned Vine Drive. This system will outfall into the future East Vine Diversion
Channel. Storm Line A1 will collect flow from the Redwood Pond outlet (Storm Line A2), the
Old Town North detention pond (Storm Line A3), and the Green briar Outfall (Storm Line
A4). The storm line consists of a storm sewer ranging in diameter from 48- to 54-inch RCP,
4 ft x 7 ft and 4 ft x 12 ft RCBC, contains 4 storm laterals, a total of 25-Type 13 combination
inlets, snout oil-water debris separators for water quality, and a crossing at Lake Canal.
Box culverts are required at the downstream end of the Storm Line A1 due to cover
constraints. The box culvert is mainly located so the outside edge of the box coincides with
the outside edge of the 6-foot sidewalk of the future re-aligned Vine Drive.
4.17 Ayres Associates
The 60-inch GWET and 42-inch NEWT water lines were also in conflict with the proposed
storm sewer in several locations along Storm Line A1, primarily at the storm lateral locations.
As mentioned previously, Storm Line A1 system is constrained by the upstream and
downstream inverts. The laterals are constrained by the hydraulics of the system.
Discussions between the City of Fort Collins and the City of Greeley occurred during the
initial design stages. The engineers from both sides offered alternatives and made
accommodations where possible. An agreement was made to allow the Greeley waterlines
to be within 6 inches (outside diameter) of the proposed storm sewer. Manhole risers were
incorporated into the storm sewer design where the hydraulics permitted to allow shallow
storm laterals. The construction drawings reflect GWET and NEWT waterline elevations as
Boyle Engineering submitted to the City of Fort Collins in May 2008.
The potential for future development of the land north of the re-aligned Vine Drive required
Ayres to look at the feasibility of future utilities. After investigating potential sanitary sewer
access locations, it was determined that any development in this area would not be able to
have basements. The sanitary sewer on the east side of Redwood Street posed the
greatest concern. The proposed storm sewer and Greeley waterlines create a utility barrier
along re-aligned Vine Drive. Existing sanitary sewer is currently located in Alta Vista, Lemay
Avenue, and Redwood Street. The sewers located in Lemay Avenue and Redwood Street
do not pose a connection problem, however, the sewer located on the west side of Alta Vista
would required to run at minimum grade and drop manholes would be needed to tie into this
system. Other areas west and east of Redwood should not have issues connecting to
existing utilities.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of the Storm Sewer Lines A1. The proposed
design shows the energy grade line of the system to be underground at the inlets, therefore
the inlets will function properly during a 10- and 100-year event.
4.5.2 Storm Line A2
Storm Line A2 outlets Redwood Pond, continues south and connects into Storm Line A1.
This system consists of storm sewer ranging in diameter from 15- to 48-inch RCP, contains
1 storm lateral and a total of 3-Type C inlets and one snout oil-water debris separator for
water quality.
Storm lateral A6 is placed near the cul-de sac just south of Lupine Drive. Inlet A6 will
replace an existing 12-inch pipe that currently conveys flows north to the existing channel
where Redwood Pond outfalls. Runoff (approximately 73 cfs) from the development will be
re-directed into the proposed system.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of Storm Sewer Lines A2. The analysis shows
the energy grade line of the system to be below the flowline of the inlets, therefore the inlets
will function properly during a 10- and 100-year event.
1-HR Rainfall
City of Fort Collins 1-hr Rainfall (NOAA Atlas 14 PPFE) City & County of Denver Criteria (Amended November 2013)
Return 1-hour Return 1-hour
Interval (YR)Rainfall Interval (YR)Rainfall
WQ 0.60 WQ 0.60
1 0.751 1 unknown
2 0.878 2 0.950
5 1.16 5 1.34
10 1.47 10 1.55
25 1.99 25 unknown
50 2.48 50 2.25
100 3.04 100 2.57
500 3.68 500 unknown
CALCULATED BY: AML
DATE: 6/24/2022 Storm Drainage System Design
CHECKED BY: < >Rational Method Procedure
PROJECT MANAGER: < >Proposed Development
SUB-BASIN(s)DESIGN POINT (DP)AREA (AC)RUNOFF COEFFTc (min)C x A (AC)I (IN/HR)Q (CFS)Tc (MIN)S(C x A) (AC)I (IN/HR)Q (CFS)SLOPE (%)STREET FLOW (CFS)CAPACITY: 1/2 STREET (TO LESSER OF TOP/CURB OR CROWN),ALLEY (FULL SECTION TO EOP)(CFS)RWP FLOW N/A N/A N/A N/A N/A 15.96
OS1 4.37 0.25 10.8 1.09 2.30 2.51
RWP + OS1 1 10.8 1.09 2.30 15.96
A1 0.22 0.72 5.0 0.16 2.98 0.47
OS2 1.54 0.58 5.0 0.89 2.98 2.66
A1 + OS2 2 5.0 1.05 2.98 3.13
A2 0.27 0.73 5.0 0.20 2.98 0.59
OS3 3.13 0.56 5.6 1.76 2.89 5.09
A2 + OS3 3 5.6 1.96 2.89 5.67
DP2 + DP3 4 5.6 3.01 2.89 8.71
DP1 + DP4 5 10.8 4.10 2.30 25.40
A3 0.26 0.25 12.3 0.07 2.18 0.14
OS4 3.16 0.55 5.0 1.74 2.98 5.20
A3 + OS4 6 12.3 1.81 2.18 3.95
DP5 + DP6 7 12.3 5.91 2.18 28.87
A4 2.06 0.33 5.0 0.67 2.98 2.00
Pond3 FLOW N/A N/A N/A N/A N/A 1.95
A4 + P3 8 5.0 0.67 2.98 1.95
DP7 + DP8 9 12.3 6.58 2.18 32.28
A5 0.26 0.25 5.0 0.07 2.98 0.19
A6 0.10 0.25 5.0 0.03 2.98 0.07
A5 + A6 10 5.0 0.09 2.98 0.27
A7 0.08 0.22 5.0 0.02 2.98 0.05
DP10 + A7 11 5.0 0.11 2.98 0.32
A8 0.40 0.67 5.0 0.27 2.98 0.80
DP11 + A8 12 5.0 0.38 2.98 1.12
A9 0.96 0.68 5.0 0.65 2.98 1.93
DP12 + A9 13 5.0 1.02 2.98 3.05
A10 0.16 0.23 5.0 0.04 2.98 0.11
DP13 + A10 14 5.0 1.06 2.98 3.16
Pond1 FLOW N/A N/A N/A N/A N/A 0.50
5.0 0.04 2.98 0.61
A11 1.85 0.54 5.0 0.99 2.98 2.95
Pond1 + A11 15 5.0 0.99 2.98 0.50
DP9 + DP15 16 12.3 7.57 2.18 34.94
A12 0.13 0.23 5.0 0.03 2.98 0.09
A13 0.23 0.28 5.0 0.07 2.98 0.19
A12 + A13 17 5.0 0.09 2.98 0.28
A14 0.17 0.43 5.0 0.07 2.98 0.22
DP17 + A14 18 5.0 0.17 2.98 0.50
A15 0.17 0.41 5.0 0.07 2.98 0.21
DP18 + A15 19 5.0 0.24 2.98 0.71
A16 0.49 0.40 5.0 0.20 2.98 0.59
DP19 + A16 20 5.0 0.43 2.98 1.29
A17 0.64 0.91 5.0 0.58 2.98 1.74
A18 0.70 0.81 5.0 0.57 2.98 1.68
A17 + A18 21 5.0 1.15 2.98 3.42
DP20 + DP21 22 5.0 1.58 2.98 4.71
A19 0.33 0.16 5.0 0.05 2.98 0.15
A20 0.33 0.61 5.0 0.20 2.98 0.60
A19 + A20 + DP22 23 5.0 1.84 2.98 5.47
A21 0.34 0.57 5.0 0.19 2.98 0.58
DP23 + A21 24 5.0 2.03 2.98 6.05
A22 0.35 0.20 5.0 0.07 2.98 0.20
DP24 + A22 25 5.0 2.10 2.98 6.25
DIRECT RUNOFF TOTAL RUNOFF STREET (approx, compare to Inlet calcs)
CALCULATED BY: AML Standard Form SF-2 (modified)
DATE: 6/24/2022 Storm Drainage System Design
CHECKED BY: < >(Rational Method Procedure)
PROJECT MANAGER: < >Proposed Development
SUB-BASIN(s)DESIGN POINT (DP)AREA (AC)RUNOFF COEFFTc (min)C x A (AC)I (IN/HR)Q (CFS)Tc (MIN)S(C x A) (AC)I (IN/HR)Q (CFS)RWP FLOW N/A N/A N/A N/A N/A 15.96
OS1 4.37 0.31 10.8 1.37 7.96 10.87
RWP + OS1 1 10.8 1.37 7.96 15.96
A1 0.22 0.89 5.0 0.20 10.31 2.03
OS2 1.54 0.73 5.0 1.12 10.31 11.52
A1 + OS2 2 5.0 1.31 10.31 13.55
A2 0.27 0.92 5.0 0.25 10.31 2.55
OS3 3.13 0.70 5.6 2.20 10.02 22.05
A2 + OS3 3 5.6 2.45 10.02 24.53
DP2 + DP3 4 5.6 3.76 10.02 37.69
DP1 + DP4 5 10.8 5.13 7.96 56.80
A3 0.26 0.31 12.3 0.08 7.56 0.61
OS4 3.16 0.69 5.0 2.18 10.31 22.49
A3 + OS4 6 12.3 2.26 7.56 17.10
DP5 + DP6 7 12.3 7.39 7.56 71.82
A4 2.06 0.41 5.0 0.84 10.31 8.64
Pond3 FLOW N/A N/A N/A N/A N/A 1.95
A4 + P3 8 5.0 0.84 10.31 1.95
DP7 + DP8 9 12.3 8.23 7.56 80.10
A5 0.26 0.31 5.0 0.08 10.31 0.84
A6 0.10 0.31 5.0 0.03 10.31 0.32
A5 + A6 10 5.0 0.11 10.31 1.16
A7 0.08 0.28 5.0 0.02 10.31 0.23
DP10 + A7 11 5.0 0.13 10.31 1.39
A8 0.40 0.84 5.0 0.33 10.31 3.45
DP11 + A8 12 5.0 0.47 10.31 4.84
A9 0.96 0.85 5.0 0.81 10.31 8.37
DP12 + A9 13 5.0 1.28 10.31 13.21
A10 0.16 0.29 5.0 0.05 10.31 0.48
DP13 + A10 14 5.0 1.33 10.31 13.69
Pond1 FLOW N/A N/A N/A N/A N/A 0.50
5.0 0.05 10.31 0.98
A11 1.85 0.67 5.0 1.24 10.31 12.78
Pond1 + A11 15 5.0 1.24 10.31 0.50
DP9 + DP15 16 12.3 9.47 7.56 89.96
A12 0.13 0.28 5.0 0.04 10.31 0.38
A13 0.23 0.35 5.0 0.08 10.31 0.84
A12 + A13 17 5.0 0.12 10.31 1.22
A14 0.17 0.53 5.0 0.09 10.31 0.93
DIRECT RUNOFF TOTAL RUNOFF
Project Name:Enclave at Redwood
Project No:201013
Date:01/18/22
Design by:MW
Preliminary Design
Stage-Storage-Discharge
Proposed On-Site Pond 1 Max V SWMM = 0.92 ac-ft
W.S. Elevation Total Discharge Q Area Area incremental accumulated Vol.
(cfs) (sf) (acre) volume (ac-ft) (ac-ft)
0.00 4954.15 1 0.00 - -
0.85 4955.00 1323.43 0.03 0.009 0.009
1.85 4956.0 3929.07 0.09 0.058 0.066
2.85 4957.0 7548.39 0.17 0.130 0.196
3.85 4958.0 11028 0.25 0.212 0.408
4.85 4959.0 14241.29 0.33 0.289 0.697
5.85 4960.0 17156 0.39 0.360 1.057
6.15 4960.3 0.86 18033 0.41 0.121 1.178 100-year
Proposed On-Site Pond UD2 Max V SWMM = 1.74 ac-ft
W.S. Elevation Total Discharge Q Area Area incremental accumulated Vol.
(cfs) (sf) (acre) volume (ac-ft) (ac-ft)
0.00 4950.42 7,807 0.18 - -
0.91 4951.3 7,807 0.123
0.75 4951.2 7,807 0.18 0.134 0.134 WQCV
1.00 4951.4 16,944 0.39 0.069 0.204
2.00 4952.4 16,401 0.38 0.383 0.587
3.00 4953.4 15,473 0.36 0.366 0.952
4.00 4954.4 14,010 0.32 0.338 1.291
5.00 4955.4 11,435 0.26 0.292 1.582
6.00 4956.4 1.57 1.802
6.00 4956.4 7,807 0.18 0.220 1.802 100-year
6.67 4957.1 7,807 0.18 0.120 1.922
Proposed On-Site Pond 3 Max V SWMM = 2.19 ac-ft
W.S. Elevation Total Discharge Q Area Area incremental accumulated Vol.
(cfs) (sf) (acre) volume (ac-ft) (ac-ft)
0.00 4954.53 1 0.00 - -
0.47 4955.0 878.65 0.02 0.003 0.003
1.47 4956.0 13482 0.31 0.136 0.017
2.47 4957.0 21020.74 0.48 0.393 0.396 WQCV
3.47 4958.0 24683.34 0.57 0.524 0.920
4.47 4959.0 28229.9 0.65 0.607 1.527
5.47 4960.0 31729.4 0.73 0.688 2.215
6.47 4961.0 1.95 35175 0.81 0.768 2.983
7.47 4962.0 38771 0.89 0.848 3.831 100-year
8.47 4963.0 43525.51 1.00 0.944 4.775
Proposed On-Site Pond 4
Max WQCV Rain Garden= 0.12 ac-ft
Max V SWMM = 0.26 ac-ft
W.S. Elevation Total Discharge Q Area Area incremental accumulated Vol.
(cfs) (sf) (acre) volume (ac-ft) (ac-ft)
4960.0 4,343 0.10 - -
4961.0 6,481 0.15 0.123 0.123
4961.7 42.41 0.255 WQCV
4962.0 9,016 0.21 0.177 0.301 100-year
Proposed Redwood Pond
Max V SWMM = 5.26 ac-ft
W.S. Elevation Total Discharge Q Area Area incremental accumulated Vol.
(cfs) (sf) (acre) volume (ac-ft) (ac-ft)
0.0 4954.0 26 0.00 - -
1.0 4955.0 5767 0.13 0.047 0.047
2.0 4956.0 18687 0.43 0.267 0.31
3.0 4957.0 47833 1.10 0.738 1.052
4.0 4958.0 67065 1.54 1.313 2.364
5.0 4959.0 97301 2.23 1.876 4.240 Water Quality Volume
6.0 4960.0 130041 2.99 2.600 6.841 100-year Max V SWMM
7.0 4961.0 9.860
7.0 4961.0 141866 3.26 3.120 9.961 Max NECCO V
8.0 4962.0 151158 3.47 3.363 13.324
StormTech888-892-2694 | WWW.STORMTECH.COM®Chamber System4640 TRUEMAN BLVDHILLIARD, OH 430261-800-733-7473DATE: DRAWN: JMPROJECT #: CHECKED: N/ATHIS DRAWING HAS BEEN PREPARED BASED ON INFORMATION PROVIDED TO ADS UNDER THE DIRECTION OF THE SITE DESIGN ENGINEER OR OTHER PROJECT REPRESENTATIVE. THE SITE DESIGN ENGINEER SHALL REVIEW THIS DRAWING PRIOR TO CONSTRUCTION. IT IS THE ULTIMATERESPONSIBILITY OF THE SITE DESIGN ENGINEER TO ENSURE THAT THE PRODUCT(S) DEPICTED AND ALL ASSOCIATED DETAILS MEET ALL APPLICABLE LAWS, REGULATIONS, AND PROJECT REQUIREMENTS.DATEDRWCHKDESCRIPTIONENCLAVE - UD2FORT COLLINS, COSHEETOF26NOTES•MANIFOLD SIZE TO BE DETERMINED BY SITE DESIGN ENGINEER. SEE TECH NOTE #6.32 FOR MANIFOLD SIZING GUIDANCE.•DUE TO THE ADAPTATION OF THIS CHAMBER SYSTEM TO SPECIFIC SITE AND DESIGN CONSTRAINTS, IT MAY BE NECESSARY TO CUT AND COUPLE ADDITIONAL PIPE TO STANDARD MANIFOLDCOMPONENTS IN THE FIELD.•THE SITE DESIGN ENGINEER MUST REVIEW ELEVATIONS AND IF NECESSARY ADJUST GRADING TO ENSURE THE CHAMBER COVER REQUIREMENTS ARE MET.•THIS CHAMBER SYSTEM WAS DESIGNED WITHOUT SITE-SPECIFIC INFORMATION ON SOIL CONDITIONS OR BEARING CAPACITY. THE SITE DESIGN ENGINEER IS RESPONSIBLE FORDETERMININGTHE SUITABILITY OF THE SOIL AND PROVIDING THE BEARING CAPACITY OF THE INSITU SOILS. THE BASE STONE DEPTH MAY BE INCREASED OR DECREASED ONCE THIS INFORMATION ISPROVIDED.•NOT FOR CONSTRUCTION: THIS LAYOUT IS FOR DIMENSIONAL PURPOSES ONLY TO PROVE CONCEPT & THE REQUIRED STORAGE VOLUME CAN BE ACHIEVED ON SITE.CONCEPTUAL ELEVATIONSMAXIMUM ALLOWABLE GRADE (TOP OF PAVEMENT/UNPAVED):12.75MINIMUM ALLOWABLE GRADE (UNPAVED WITH TRAFFIC):8.25MINIMUM ALLOWABLE GRADE (UNPAVED NO TRAFFIC):7.75MINIMUM ALLOWABLE GRADE (TOP OF RIGID CONCRETE PAVEMENT):7.75MINIMUM ALLOWABLE GRADE (BASE OF FLEXIBLE PAVEMENT):7.75TOP OF STONE:6.75TOP OF MC-4500 CHAMBER:5.7518" x 18" TOP MANIFOLD INVERT:3.2024" ISOLATOR ROW PLUS INVERT:0.9418" x 18" BOTTOM MANIFOLD INVERT:0.9118" BOTTOM CONNECTION INVERT:0.91BOTTOM OF MC-4500 CHAMBER:0.75BOTTOM OF STONE:0.00PROPOSED LAYOUT495STORMTECH MC-4500 CHAMBERS24STORMTECH MC-4500 END CAPS12STONE ABOVE (in)9STONE BELOW (in)40STONE VOID85016INSTALLED SYSTEM VOLUME (CF)(PERIMETER STONE INCLUDED)(COVER STONE INCLUDED)(BASE STONE INCLUDED)19561SYSTEM AREA (SF)886.2SYSTEM PERIMETER (ft)*INVERT ABOVE BASE OF CHAMBERMAX FLOWINVERT*DESCRIPTIONITEM ONLAYOUTPART TYPE29.37"18" TOP PARTIAL CUT END CAP, PART#: MC4500IEPP18T / TYP OF ALL 18" TOP CONNECTIONSAPREFABRICATED END CAP2.26"24" BOTTOM PARTIAL CUT END CAP, PART#: MC4500IEPP24B / TYP OF ALL 24" BOTTOMCONNECTIONS AND ISOLATOR PLUS ROWSBPREFABRICATED END CAP1.97"18" BOTTOM PARTIAL CUT END CAP, PART#: MC4500IEPP18B / TYP OF ALL 18" BOTTOMCONNECTIONSCPREFABRICATED END CAPINSTALL FLAMP ON 24" ACCESS PIPE / PART#: MC450024RAMP (TYP 2 PLACES)DFLAMP29.36"18" x 18" TOP MANIFOLD, ADS N-12EMANIFOLD1.97"18" x 18" BOTTOM MANIFOLD, ADS N-12FMANIFOLD16.5 CFS IN30" DIAMETER (24.00" SUMP MIN)GNYLOPLAST (INLET W/ ISOPLUS ROW)8.0 CFS OUT30" DIAMETER (DESIGN BY ENGINEER)HNYLOPLAST (OUTLET)4" SEE DETAILIINSPECTION PORTISOLATOR ROW PLUS(SEE DETAIL)PLACE MINIMUM 17.50' OF ADSPLUS175 WOVEN GEOTEXTILE OVER BEDDINGSTONE AND UNDERNEATH CHAMBER FEET FOR SCOUR PROTECTION AT ALLCHAMBER INLET ROWSBED LIMITS50'25'0341.94'101.17'331.49'99.17'IDBCAGEFH
StormTech888-892-2694 | WWW.STORMTECH.COM®Chamber SystemINSPECTION & MAINTENANCESTEP 1)INSPECT ISOLATOR ROW PLUS FOR SEDIMENTA.INSPECTION PORTS (IF PRESENT)A.1.REMOVE/OPEN LID ON NYLOPLAST INLINE DRAINA.2.REMOVE AND CLEAN FLEXSTORM FILTER IF INSTALLEDA.3.USING A FLASHLIGHT AND STADIA ROD, MEASURE DEPTH OF SEDIMENT AND RECORD ON MAINTENANCE LOGA.4.LOWER A CAMERA INTO ISOLATOR ROW PLUS FOR VISUAL INSPECTION OF SEDIMENT LEVELS (OPTIONAL)A.5.IF SEDIMENT IS AT, OR ABOVE, 3" (80 mm) PROCEED TO STEP 2. IF NOT, PROCEED TO STEP 3.B.ALL ISOLATOR PLUS ROWSB.1.REMOVE COVER FROM STRUCTURE AT UPSTREAM END OF ISOLATOR ROW PLUSB.2.USING A FLASHLIGHT, INSPECT DOWN THE ISOLATOR ROW PLUS THROUGH OUTLET PIPEi)MIRRORS ON POLES OR CAMERAS MAY BE USED TO AVOID A CONFINED SPACE ENTRYii)FOLLOW OSHA REGULATIONS FOR CONFINED SPACE ENTRY IF ENTERING MANHOLEB.3.IF SEDIMENT IS AT, OR ABOVE, 3" (80 mm) PROCEED TO STEP 2. IF NOT, PROCEED TO STEP 3.STEP 2)CLEAN OUT ISOLATOR ROW PLUS USING THE JETVAC PROCESSA.A FIXED CULVERT CLEANING NOZZLE WITH REAR FACING SPREAD OF 45" (1.1 m) OR MORE IS PREFERREDB.APPLY MULTIPLE PASSES OF JETVAC UNTIL BACKFLUSH WATER IS CLEANC.VACUUM STRUCTURE SUMP AS REQUIREDSTEP 3)REPLACE ALL COVERS, GRATES, FILTERS, AND LIDS; RECORD OBSERVATIONS AND ACTIONS.STEP 4)INSPECT AND CLEAN BASINS AND MANHOLES UPSTREAM OF THE STORMTECH SYSTEM.NOTES1.INSPECT EVERY 6 MONTHS DURING THE FIRST YEAR OF OPERATION. ADJUST THE INSPECTION INTERVAL BASED ON PREVIOUSOBSERVATIONS OF SEDIMENT ACCUMULATION AND HIGH WATER ELEVATIONS.2.CONDUCT JETTING AND VACTORING ANNUALLY OR WHEN INSPECTION SHOWS THAT MAINTENANCE IS NECESSARY.CATCH BASINORMANHOLEMC-4500 ISOLATOR ROW PLUS DETAILNTSSTORMTECH HIGHLY RECOMMENDSFLEXSTORM INSERTS IN ANY UPSTREAMSTRUCTURES WITH OPEN GRATESCOVER PIPE CONNECTION TO END CAP WITH ADSGEOSYNTHETICS 601T NON-WOVEN GEOTEXTILEMC-4500 CHAMBEROPTIONAL INSPECTION PORTMC-4500 END CAP24" (600 mm) HDPE ACCESS PIPE REQUIRED USEFACTORY PRE-CORED END CAPPART #: MC4500REPE24BC OR MC4500REPE24BWONE LAYER OF ADSPLUS175 WOVEN GEOTEXTILE BETWEENFOUNDATION STONE AND CHAMBERS10.3' (3.1 m) MIN WIDE CONTINUOUS FABRIC WITHOUT SEAMSSUMP DEPTH TBD BYSITE DESIGN ENGINEER(24" [600 mm] MIN RECOMMENDED)INSTALL FLAMP ON 24" (600 mm) ACCESS PIPEPART #: MC450024RAMPNOTE:INSPECTION PORTS MAY BE CONNECTED THROUGH ANY CHAMBER CORRUGATION VALLEY.STORMTECH CHAMBER8" NYLOPLAST INSPECTION PORTBODY (PART# 2708AG4IPKIT) ORTRAFFIC RATED BOX W/SOLIDLOCKING COVERCONCRETE COLLARPAVEMENT12" (300 mm) MIN WIDTHCONCRETE SLAB6" (150 mm) MIN THICKNESS4" PVC INSPECTION PORT DETAIL(MC SERIES CHAMBER)NTSCONCRETE COLLAR NOT REQUIREDFOR UNPAVED APPLICATIONS4" (100 mm)SDR 35 PIPE4" (100 mm) INSERTA TEETO BE CENTERED ONCORRUGATION VALLEY4640 TRUEMAN BLVDHILLIARD, OH 430261-800-733-7473DATE: DRAWN: JMPROJECT #: CHECKED: N/ATHIS DRAWING HAS BEEN PREPARED BASED ON INFORMATION PROVIDED TO ADS UNDER THE DIRECTION OF THE SITE DESIGN ENGINEER OR OTHER PROJECT REPRESENTATIVE. THE SITE DESIGN ENGINEER SHALL REVIEW THIS DRAWING PRIOR TO CONSTRUCTION. IT IS THE ULTIMATERESPONSIBILITY OF THE SITE DESIGN ENGINEER TO ENSURE THAT THE PRODUCT(S) DEPICTED AND ALL ASSOCIATED DETAILS MEET ALL APPLICABLE LAWS, REGULATIONS, AND PROJECT REQUIREMENTS.DATEDRWCHKDESCRIPTIONENCLAVE - UD2FORT COLLINS, COSHEETOF46
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =74.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.740
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.24 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 198,046 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =3,885.78 cu ft
Vol = (WQCV / 12) * Area
Design Procedure Form: Rain Garden (RG)
MW
HKS
December 21, 2021
Enclave at Redwood
Redwood Pond - Additional WQ from Basin 113_4 (IR4)
UD-BMP (Version 3.07, March 2018)
IR4 MHFD.xlsm, RG 12/21/2021, 3:23 PM
dfsghdfgndgfhndcgfhncdgfhdgfhmdgfhmdg
Filepath: K:\201013\ENGINEERING\EXHIBIT\UNDERGROUND DETENTION EXHIBIT.DWG Layout: IR17 XREFs: e-base, e-legal, e-offsite, keymap, p-base, p-legal, p-utilPlotted: TUE 12/21/21 9:50:23A By: Mark West NO CHANGES ARE TO BE MADE TO THIS DRAWING WITHOUT WRITTEN PERMISSION OF HARRIS KOCHER SMITH.1120 Lincoln Street, Suite 1000Denver, Colorado 80203P: 303.623.6300 F: 303.623.6311HarrisKocherSmith.com0SCALE: 1" =10102010'UNDERGROUND DETENTION EXHIBIT - IR1KEY MAPSCALE 1" = 500'REDWOOD ST
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Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =70.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.700
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.22 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 143,025 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =2,622.41 cu ft
Vol = (WQCV / 12) * Area
Design Procedure Form: Rain Garden (RG)
MW
HKS
December 21, 2021
Enclave at Redwood
POND1 - Isolator Rows
UD-BMP (Version 3.07, March 2018)
UD1 MHFD.xlsm, RG 12/21/2021, 9:38 AM
AB C DE F GH IJKLMNVAULT IDTOTAL REQUIRED WQCV(CF)WQ FLOW (CFS) CHAMBER TYPERELEASE RATE/CHAMBER(CFS)CHAMBER VOLUME(CF)CHAMBER VOLUME + AGGREGATE(CF)NUMBER OF CHAMBERSCOMBINED RELEASE RATE WQCV METHOD(CFS)FAA REQUIRED STORAGE VOLUME (CF)NUMBER OF CHAMBERS (FAA)TOTAL VOLUME (CHAMBERS ONLY)(CF)COMBINED RELEASE RATE FAA METHOD (CFS)TOTAL NUMBER OF CHAMBERS REQUIREDTOTAL SYSTEM VOLUME (CF)3146.892 0 MC‐45000.026106.5162.620 0.52 1787.29 17 1811 0.4420 3252CONFIRM CONFIRMA MHFD Rain Garden UD‐BMP WQCV * 120%B 1/2 of the 2‐year developed flow rate for the basin being sizedC Chamber type based on site constraintsD Flwo rate thru the bottom of the isolator row chamber which is equal to the area of the bottom of the chamber multiplied by the flow rate per unit area (see calculations below)E Volume within chamber only, not accounting for void spaces in surrounding aggregate (standard spec)F Volume includes chamber and void space (40%) in surrounding aggregate , per chamber unit. (standard spec)G Number of chambers required to provide full WQCV within total installed system, include aggregate = A / FH Release rate per chamber times number of chambers = D * G I FAA calc based on Flow, WQ and Total Release RateJ Number of chambers required to provide required FAA staorage volume stored within the chamber only (no aggregate stone) = I / EK Volume provided in chambers only (no aggregate storage). This must meet or excheed the required FAA storage volume. Greater of G or J * E L Release rate per chamber times number of chambers = D * J M Total number of chambers (Greater of J or G)N Total system volume. Includes number of chambers plus aggregate. This must meet or exceed required WQCVMC‐4500 MC‐3500 SC‐740 SC‐310 SC‐160LP60.0 45.0 30.0 16.0 12.0100.0 77.0 51.0 34.0 25.048.3 86.0 85.4 85.4 85.433.5 46.0 30.2 20.2 14.8106.5 109.9 85.9 14.7 6.9162.6 175.0 74.9 31.0 15.0CHAMBER FLOW RATE CONVERSION (GPM/SF TO CFS)0.35 GPM/SF1 CF = 7.48052 GAL1 GALLON = 0.133681 CF 1 GPM = 0.002228 CFS*FLOW RATE BASED ON 1/2 OF NOV 07 QMAX IN FIGURE 17 OF UNH TESTING REPORTMC‐4500 MC‐3500 SC‐740 SC‐310 SC‐160LP0.0262 0.036 0.024 0.016 0.012 (COLUMN D)FLOW RATE / CHAMBER (CFS)STORMTECH CHAMBER VOLUME AND RELEASE RATE CALCULATIONSFLOOR AREA (SF)CHAMBER VOLUME (CF)CHAMBER/AGGREGATE VOLUME (CF)STORMTECH CHAMBER DATAFLOW RATE*CHAMBER FLOW RATECHAMBER DIMENSIONSWIDTH (IN)INSTALLED LENGTH (IN)HEIGHT (IN)
Filepath: K:\201013\ENGINEERING\EXHIBIT\UNDERGROUND DETENTION EXHIBIT.DWG Layout: UD27 XREFs: e-base, e-legal, e-offsite, keymap, p-base, p-legal, p-utilPlotted: TUE 12/21/21 12:26:18P By: Mark West NO CHANGES ARE TO BE MADE TO THIS DRAWING WITHOUT WRITTEN PERMISSION OF HARRIS KOCHER SMITH.1120 Lincoln Street, Suite 1000Denver, Colorado 80203P: 303.623.6300 F: 303.623.6311HarrisKocherSmith.com0SCALE: 1" =20204020'UNDERGROUND DETENTION EXHIBIT - UD2KEY MAPSCALE 1" = 500'REDWOOD ST
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Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =75.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.750
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.24 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area =223433.92 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =4,461.70 cu ft
Vol = (WQCV / 12) * Area
Design Procedure Form: Rain Garden (RG)
JMR
HKS
December 21, 2021
Enclave at Redwood
UD2 - Isolator Rows
UD-BMP (Version 3.07, March 2018)
UD2 MHFD.xlsm, RG 12/21/2021, 10:45 AM
X
F
M
RXFMR XFMRFilepath: K:\201013\ENGINEERING\EXHIBIT\UNDERGROUND DETENTION EXHIBIT.DWG Layout: IR37 XREFs: e-base, e-legal, e-offsite, keymap, p-base, p-legal, p-utilPlotted: TUE 12/21/21 12:25:40P By: Mark West NO CHANGES ARE TO BE MADE TO THIS DRAWING WITHOUT WRITTEN PERMISSION OF HARRIS KOCHER SMITH.1120 Lincoln Street, Suite 1000Denver, Colorado 80203P: 303.623.6300 F: 303.623.6311HarrisKocherSmith.com0SCALE: 1" =20204020'UNDERGROUND ISOLATOR ROW EXHIBIT - PARK AREA (IR3)KEY MAPSCALE 1" = 500'REDWOOD ST
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Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =74.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.740
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.24 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 310,215 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =6,086.63 cu ft
Vol = (WQCV / 12) * Area
Design Procedure Form: Rain Garden (RG)
MW
HKS
December 21, 2021
Enclave at Redwood
IR3 - Isolator Rows
UD-BMP (Version 3.07, March 2018)
IR3 MHFD.xlsm, RG 12/21/2021, 10:08 AM
IR1 ISOLATOR ROW VOLUME CALCULATION: MODIFIED FAA METHOD FROM FORT COLLINS IDF
Project #201013
Project Name Enclave at Redwood *Unused
Designer MW
Date 10/12/2021
0.7549
7.122 310215.35 sq‐ft
1.51
Time (min)WQCV Intensity (1/2 of 2‐Year
Intensity) (in/hr)
Volume In
(cu‐ft)
Out
Factor*
Adjusted
Release (CFS)
Volume Out
(cu‐ft)
Storage
(cu‐ft)
5 1.425 2298.270 1.00 1.5100 453.000 1845.27
10 1.105 3564.334 1.00 1.5100 906.000 2658.33
15 0.935 4523.962 1.00 1.5100 1359.000 3164.96
20 0.805 5193.283 0.95 1.4345 1721.400 3471.88
25 0.715 5765.834 0.86 1.2986 1947.900 3817.93
30 0.65 6290.001 0.80 1.2080 2174.400 4115.60
35 0.585 6604.501 0.76 1.1476 2409.960 4194.54
40 0.535 6902.873 0.73 1.1023 2645.520 4257.35
45 0.495 7185.116 0.70 1.0570 2853.900 4331.22
50 0.46 7418.975 0.68 1.0268 3080.400 4338.58
55 0.435 7717.347 0.66 0.9966 3288.780 4428.57
60 0.41 7935.078 0.65 0.9815 3533.400 4401.68
65 0.39 8177.001 0.64 0.9664 3768.960 4408.04
70 0.365 8241.514 0.63 0.9513 3995.460 4246.05
75 0.35 8467.309 0.62 0.9362 4212.900 4254.41
80 0.33 8515.693 0.61 0.9211 4421.280 4094.41
85 0.32 8773.745 0.61 0.9211 4697.610 4076.13
90 0.305 8854.386 0.60 0.9060 4892.400 3961.99
95 0.29 8886.642 0.59 0.8909 5078.130 3808.51
100 0.28 9031.796 0.59 0.8909 5345.400 3686.40
105 0.27 9144.693 0.59 0.8909 5612.670 3532.02
110 0.26 9225.334 0.58 0.8758 5780.280 3445.05
115 0.255 9459.193 0.58 0.8758 6043.020 3416.17
120 0.245 9483.386 0.58 0.8758 6305.760 3177.63
4428.57
Qout (From ADS maximum chamber flow rate)(CFS)
FAA Method Table
Maximum Storage Represents Required WQCV
C (From Fort Collins Storm Criteria Manual)
Area (ac)
DSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDS DSDSDSDSDSDSDSDSDS DS DS DSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDS
DSDS
DSDSDSDSDSDSDSDSDSDSDSDSDSDSDS DSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDS
DSDS
DSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSD
S
DSDSDSD
S
DS DSDSDS DSDSDS
DS DSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDS DS DS DS DS DSDSDSDSDSDSDSDSDSDSDSDSDSDS DS DS DS DS DS DS DSDSDSDSDSDSDSDSDS
DSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDS
D
SDSD
SDSD
SDSDS
DS
D
S
DSDSD
SDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDS
DSDS
DS DSDSDSDS
DS DSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSD
S
DSDSDSDS
DSDSDSDSDSDS
DSDSDSDSDSDSDSDSDS
DS
DS
DSDSDSDSDS
DSDS
DSDSDSDSDSDSDSDSDS
DS
DS
DSDSDSDSDSRAMPRAMPRAMPRAMPRAMPRAMPACBASINAREAIMP%113_26.5380%ACBASINAREAIMP%113_38.6280%ACBASINAREACMINORMAJOR2138.530.80ACBASINAREACMINORMAJOR8124.370.516ACBASINAREACMINORMAJOR113_13.820.67ACBASINAREACMINORMAJOR113_45.380.868SHEET NUMBERISSUE DATE:DATEREVISION COMMENTSDESIGNED BY:CHECKED BY:DRAWN BY:PROJECT #:1120 Lincoln Street, Suite 1000Denver, Colorado 80203P: 303.623.6300 F: 303.623.6311HarrisKocherSmith.comKnow what's below.Call before you dig.®FILEPATH: K:\201013\ENGINEERING\DRAINAGE\FINAL DRAINAGE PLAN.DWG LAYOUT: DETENTION BASIN MAP11 XREFs: aerial[U], cd - drainage map labelling, dhi_logo, e-base, e-legal, e-offsite[U], e-util, p-base, p-legal[U], p-storm, p-utilPLOTTED: WED 10/19/22 1:00:44A BY: AIDAN LOWE
201013ENCLAVE AT REDWOODDETENTION BASIN MAP9494OF140 10-19-2022JMRMAWJMR NO CHANGES ARE TO BE MADE TO THIS DRAWING WITHOUT WRITTEN PERMISSION OF HARRIS KOCHER SMITH.0SCALE: 1" =808016080'BASINDESIGNATIONBASIN SIZEIN ACRESC COEFFICIENTOS 10.671.23ACBASINAREAC1BASIN DESIGN POINTMAJORMINOR100-YR SWMMSubcatchment Summary TableBasinOutfall IDArea (ac)CalculatedImperviousness(%)UtilizedImperviousness(%)100-Year TotalRunoff Volume(ac-ft)2-YearPeakRunoff(CFS)100-YearPeakRunoff(CFS)2-Year SWMMCalculatedRunoffCoefficient100-Year SWMMCalculatedRunoffCoefficient113_1Pond13.810042%45%0.896.6529.640.5160.771113_2UD26.460040%40%1.449.9337.690.4610.737113_3Pond38.610050%50%2.2417.2175.450.6030.855113_4Redwood Pond9.960032%40%1.8710.5153.090.6320.747213NECCO A2 StormLine7.8200N/A752.1214.4167.650.6890.889413Existing NECCOStub2.1900N/A70.400.456.620.0740.585812Redwood Pond3.7500N/A20.580.227.210.0250.516Detention Pond Summary TablePond100-YearVolume(cu-ft)100-YearVolume(ac-ft)100-YearWSELWQCV(cu-ft)WQCVWSELMax ReleaseRate (CFS)Total VolumeRequired (WQCV +Detention) (ac-ft)Total VolumeProvided (WQCV +Detention) (ac-ft)Pond136,5620.844957.630.86IR 13,1474954.400.910.91UD266,4571.534951.921.57IR25,3544947.091.651.65Pond381,4711.874962.521.95IR 37,3044958.342.042.04Redwood Pond226,2655.194963.544961.8815.96*WQCV in Underground Chamber Systems Explored Further in LID Exhibit and Calculations Found in Appendix Fof Preliminary Drainage Report**SWMM Model, Inputs, and Outputs Found in Appendix E of Preliminary Drainage Report