HomeMy WebLinkAboutAFFINITY AT FORT COLLINS - PDP - PDP150010 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPDP DRAINAGE REPORT
FOR
AFFINITY FORT COLLINS
Prepared For:
AFFINITY FORT COLLINS, LLC
1620 N Mamer Road, Bldg. B
Spokane Valley, WA 99216
July 1, 2015
Project No. 39704.00
Prepared By:
JR Engineering, LLC
2900 South College Avenue, Suite 3D
Fort Collins, CO 80525
Page i
TABLE OF CONTENTS
Table of Contents ............................................................................................................................................... i
Vicinity Map ......................................................................................................................................................... 1
General Description and Location .................................................................................................................. 2
Location And Existing Site Characteristics ................................................................................................. 2
Site Soils ........................................................................................................................................................... 2
Floodplain ........................................................................................................................................................ 2
Drainage Basins and Sub-Basins ....................................................................................................................... 3
Major Basin ...................................................................................................................................................... 3
Historic Sub-Basins ........................................................................................................................................ 3
Developed Sub-Basins.................................................................................................................................... 5
Drainage Design Criteria .................................................................................................................................. 7
Regulations ...................................................................................................................................................... 7
Low-Impact Developement .......................................................................................................................... 7
Hydrologic Criteria ........................................................................................................................................ 7
Hydraulic Criteria........................................................................................................................................... 7
Drainage Facility Design .................................................................................................................................... 9
General Concept ............................................................................................................................................ 9
Proposed Retention Facilities .....................................................................................................................10
Future Water Quality/ Detention Facilities .............................................................................................10
Stormwater Pollution Prevention ..................................................................................................................12
Temporary Erosion Control ......................................................................................................................12
Permanent Erosion Control .......................................................................................................................12
Summary & Conclusions .................................................................................................................................13
Existing & Proposed Conditions ................................................................................................................13
References .........................................................................................................................................................15
APPENDIX
Appendix A – Site & Soil Descriptions and Characteristics
Appendix B – Historic Basin Calculations
Appendix C - Proposed Rational & Detention Pond Calculations
Appendix D - Existing & Proposed Drainage Plans
Appendix E – LID Exhibits
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Engineer’s Certification Block
I hereby certify that this Project Development Plan Drainage Report for Affinity Fort Collins was
prepared by me (or under my direct supervision) for JR Engineering, LLC and the owners thereof
and meets or exceeds the criteria of the City of Fort Collins Stormwater Design Standards.
________________________________________
Timothy J. Halopoff, PE
Registered Professional Engineer
State of Colorado No. 37953
Page 1
VICINITY MAP
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GENERAL DESCRIPTION AND LOCATION
LOCATION AND EXISTING SITE CHARACTERISTICS
Affinity Fort Collins is located in the southeast quarter of Section 32, Township 7 North, Range 68
West of the 6th Principal Meridian in the City of Fort Collins, Larimer County, Colorado. More
specifically, the Affinity Fort Collins site is a 7.22 acre property that is currently undeveloped and is
being used for irrigated agricultural purposes. The site is zoned HC (Harmony Corridor District)
and will support apartments and associated amenities once developed.
The proposed use of the site is a three-story multi-family apartment complex and associated
amenities. The proposed concept includes one main apartment building with separate garden area,
pool building, and parking and garages around the perimeter of the site. The proposed main
building is 167,538 total square feet, with 153 dwelling units.
The existing site generally slopes from the southwest to the northeast with slopes ranging between
0.60% and 2.5%. The property is generally covered with sparse native grasses. The site currently
drains to the northeast and east. Runoff sheet flows off the east side of the property and a portion
of the runoff flows to a point in the north.
SITE SOILS
The Affinity Fort Collins site soils consist of loamy soil, predominately Nunn clay loam. Nunn clay
loam belongs to hydrologic soils Group C. Group C soils have a slow infiltration rate when
thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement
of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water
transmission. Nunn clay loam with 0-3 percent slopes generally has a combined surface layer
thickness of approx. 30 inches. Runoff is moderately high, and the hazards of wind erosion are
moderately low. Supporting figures can be found in the Appendix, page A-1.
FLOODPLAIN
The site is shown on FEMA FIRM panel 08069C0994F, dated December 19, 2006. The site lies
within Zone X, areas which are determined to be outside the 0.2% annual chance floodplain. The
“City of Fort Collins Floodplain Review Checklist for 50% Submittals” checklist is not applicable for
this PDP Drainage Report.
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DRAINAGE BASINS AND SUB-BASINS
MAJOR BASIN
The proposed Affinity Fort Collins site is located in the Fox Meadows major basin. The Fox
Meadows Basin encompasses approximately 2.4 square miles in southeast Fort Collins. The basin is
bounded by Horsetooth Road on the north, Lemay Avenue on the west, Harmony Road on the
south, and the Cache La Poudre River on the east. The Fox Meadows basin is primarily developed
with residential development, some commercial areas and the Collindale Golf Course. The basin
does not include a major drainageway for conveying flows through the basin, so no regulatory
floodplain has been mapped. Storm runoff flows through a network of storm sewers, local drainage
channels and detention ponds.
The Fox Meadows Basin was studied by two earlier reports: the “Fox Meadows Basin Drainage
Master Plan Update”, prepared by ICON Engineering, Inc., dated December 2002 and revised
February 2003; and the “Stormwater Quality and Stream Restoration Update to the Fox Meadows
Basin Stormwater Master Drainage Plan”, prepared by ICON Engineering, Inc., dated October 2012.
The site is located in the second reach, which is generally located between Ziegler Road and
Timberline Road. Proposed improvements identified in the Master Plan documents consist of
remedial improvements to existing ponds which overtop in the major storm event, and a new
detention facility, Ziegler Pond, located east of the mobile home park. The Ziegler Pond was
broken into six total detention ponds placed in series in the “Final Drainage and Erosion Control
Study for Front Range Village, Fort Collins, Colorado”, prepared by Stantec Consulting, dated
February 2007.
There are no major drainageways located within or immediately adjacent to the site. The site is
shown on FEMA FIRM panel 08069C0994F, dated December 19, 2006. The site lies within Zone X,
areas which are determined to be outside the 0.2% annual chance floodplain. An annotated FIRM
exhibit is included in Appendix A.
HISTORIC SUB-BASINS
Affinity Fort Collins is an infill development piece of property. It is governed by the City’s
Reasonable Use policy, in which the proposed drainage basins will need to follow the generally
accepted principle of releasing the 100-year developed condition flow rate at the same location and
magnitude as the 2-year pre-development condition flow rate. There are offsite areas that flow
across the proposed development site. Referring to the “Existing Drainage Plan”, included in the
Appendix, the following describes the existing condition drainage basins.
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Existing Offsite Drainage Basins (OS):
Sub-basin OS1 consists of 7.82 acres of the Harmony Mobile Home community that
drains in a northeasterly direction onto the subject property. In the existing condition,
runoff from this portion of the mobile home park (assumed 45% impervious based on
approximately 8 units per acre and Figure RO-3) is conveyed through the Affinity Fort
Collins site.
An existing 15” corrugated metal pipe with 2’x1’ square openings is located along the west
edge of the mobile home site. In the 100-year event, 15.25 cfs is captured in the pipe and
conveyed north, according to data provided by the City of Fort Collins. The flows are
taken north and west of the Affinity site to an existing pond. This reduction in flows is
assumed to only occur for the 100-year event.
Existing Onsite Sub-Basins:
The site has two existing onsite drainage basins approximately delineated by a diagonal line
stretching from the southwest corner of the site to the northeast corner of the site with
sub-basin EX1 on the north half and EX2 on the southern half.
Sub-basin EX1 consists of a 4.93 acre area of undeveloped open space with native grasses
and weeds covering the majority of the ground and is assumed to be 2% impervious. Runoff
from the Harmony Mobile Home community (Sub-basin OS-1) enters the site along the
western boundary and joins on-site flows. Runoff generally flows northeasterly across basin
EX-1, at slopes ranging from 0.70% to 2.0%, generally leaving the site at the northeast
corner near Kingsley Court.
Sub-basin EX2 consists of a 3.47 acre area of undeveloped open space with the same
ground cover and percentage imperviousness as sub-basin EX-1. Runoff from Pond 286, just
south of the site boundary, enters sub-basin EX-2 during the 100 year storm, heads north
before turning east and exits the site along the eastern boundary into the Sollenberger
property. Existing slopes range from 0.60% to 2.50%.
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DEVELOPED SUB-BASINS
The proposed developed condition sub-basins have been designed to mimic the historic basins’
runoff patterns, for both on- and off-site basins. The following describes the proposed conditions
on-site drainage basins. Refer to the “Proposed Drainage Plan” in the appendix for reference.
Proposed Onsite Sub-Basins:
Sub-basin A1 consists of 0.54 acres on the southwest corner of the subject property.
Runoff from the proposed building and parking lot travels north to a sump area inlet. Piped
flows are conveyed in the storm sewer around the north side of the property and are
discharged into the proposed retention pond at the east side of the property.
Sub-basin A2 consists of 0.64 acres on the west side of the subject property. Runoff from
the proposed building and parking lot is conveyed to a sump area inlet. Runoff from the
proposed garages discharges to a grass-lined bio-swale behind the garages, which discharges
to the parking lot and is captured in the inlet. Piped flows are conveyed in the storm sewer
around the north side of the property and are discharged into the proposed retention pond
at the east side of the property.
Sub-basin A3 consists of 0.41 acres near the northwest corner of the subject property.
Runoff from the proposed building and parking lot is conveyed to a sump area inlet. Piped
flows are conveyed in the storm sewer around the north side of the property and are
discharged into the proposed retention pond at the east side of the property.
Sub-basin A4 consists of 0.31 acres on the north side of the subject property and includes
part of the proposed building, courtyard, and garden areas. Runoff is captured in a
proposed area inlet, surrounded by a grass buffer in the center of the sub-basin. Piped
flows are conveyed in the storm sewer around the north side of the property and are
discharged into the proposed retention pond at the east side of the property.
Sub-basin A5 consists of 0.91 acres in the center north portion of the subject property
and includes the proposed building, garden area, and recreational area. Runoff is conveyed
to a proposed sump area inlet in the parking lot. Piped flows are conveyed in the storm
sewer on the north side of the property and are discharged into the proposed retention
pond at the east side of the property.
Sub-basin A6 consists of 0.17 acres on the east side of the subject property and consists
of parking lot area. Flows are captured in a sump inlet and are conveyed to the proposed
retention pond at the east side of the property.
Sub-basin A7 consists of 0.74 acres in the center-east portion of the site and includes a
portion of the proposed building and the upper pond of the two onsite retention ponds.
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Runoff enters the upper pond and is conveyed to the proposed retention pond at the east
side of the property.
Sub-basin A8 consists of 0.89 acres on the north side of the subject property. Runoff
from the proposed garages discharges to a grass-lined bio-swale behind the garages, which
discharges to the parking lot and is captured in the inlet. Piped flows are conveyed in the
storm sewer around the north side of the property and are discharged into the proposed
retention pond at the east side of the property.
Sub-basin B1 is comprised of 0.16 acres at the southwest side of the proposed building.
Flows are captured in an area inlet and are conveyed in the proposed storm sewer around
the south side of the building to the proposed retention pond at the east side of the
property.
Sub-basin B2 is comprised of 0.60 acres at the south side of the site. Flows are captured
in an area inlet and are conveyed in the proposed storm sewer around the south side of the
building to the proposed retention pond at the east side of the property.
Sub-basin B3 is comprised of 0.27 acres of parking lot at the south side of the proposed
building. Flows are captured in an area inlet in the parking lot and are conveyed in the
proposed storm sewer around the south side of the building to the proposed retention
pond at the east side of the property.
Sub-basin B4 is comprised of 0.22 acres of parking lot at the south side of the site. Flows
are captured in an area inlet in the parking lot and are conveyed in the proposed storm
sewer to the proposed retention pond at the east side of the property.
Sub-basin B5 is comprised of 0.81 acres of parking lot at the south side of the proposed
building. Flows are captured in an area inlet in the parking lot and are conveyed in the
proposed storm sewer around the south side of the building to the proposed retention
pond at the east side of the property.
Sub-basin C is comprised of 0.87 acres of drive aisle on the east side of the subject
property. Flows are captured in an area inlet in the street and are conveyed directly to the
proposed retention pond at the east side of the property.
Sub-basin D is a portion of the east side of the building and the proposed retention pond
at the east side of the property. The 0.67-acre sub-basin drains directly to the proposed
retention pond.
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DRAINAGE DESIGN CRITERIA
REGULATIONS
This report was prepared to meet or exceed the City of Fort Collins stormwater criteria. The City
of Fort Collins Storm Drainage Design Criteria and Construction Manual (with all current 2011
Revisions)(FCSDDCCM) and the Urban Drainage Flood Control District’s (UDFCD) Drainage
Criteria Manual (USDCM) Volumes 1, 2 and 3 were referenced as guidelines for this design.
LOW-IMPACT DEVELOPMENT
Volume reduction is an important part of the Four Step Process and is fundamental to effective
stormwater management. Per City criteria, a minimum of 50 percent of new impervious surface
area must be treated by a Low-Impact Development (LID) best management practice (BMP). The
proposed LID BMPs will have the effect of slowing runoff through the site lot and increasing
infiltration and rainfall interception by encouraging infiltration and careful selection of vegetative
cover. The improvements will decrease the runoff coefficient from the site and are expected to
have no adverse impact on the timing, quantity, or quality of stormwater runoff. Site-specific LID
BMPs are discussed in the following sections of this report and an illustrative LID/Surface Map is
provided in Appendix E.
HYDROLOGIC CRITERIA
The rational method was performed to calculate the peak runoff rates for each basin. Weighted
percent imperviousness and weighted runoff coefficients were calculated for each basin using
USDCM Tables RO-3 and RO-5 based on Natural Resources Conservation Service (NRCS) Type C
hydrologic soil classification and surface characteristics of each basin. The time of concentration
was calculated using USDCM Equation RO-3 and the intensity was calculated using the
corresponding storm rainfall depth and USDCM Equation RA-3. To more closely match the City of
Fort Collins IDF Curve, Coefficient 3 of the UDFCD’s intensity formula was adjusted to 0.7867.
The City of Fort Collins area has 2-year, 1-hour rainfall depth of 0.82 inches and a 100-year, 1- hour
rainfall depth of 2.86 inches. These depths do account for the 1997 adjusted rainfall depths. The 2-
hour 100-year rainfall total is 3.67 inches, based on the rainfall frequencies adopted by the City of
Fort Collins.
HYDRAULIC CRITERIA
This report demonstrates that the proposed stormwater retention and future detention concept is
able to reduce the 100-year developed condition flows to the 2-year historical release rates;
thereby satisfying the City’s Reasonable Use requirements. The Rational Formula-based Federal
Aviation Administration (FAA) method is used to preliminarily size the detention ponds in
accordance with City criteria, as the tributary area is less than 20 acres in size. The resulting
storage volume is increased by a factor of twenty five (25) percent to better match the result that
would be obtained from SWMM modeling, per City criteria.
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In the interim condition, retention ponds will be used to capture the developed conditions runoff
from the site until ultimately, an outfall is constructed to convey flows east to the storm drainage
system in Ziegler Road. The City requires that retention facilities are sized to capture, at a
minimum, the runoff equal to two times the two hour, 100-year storm over the entire site area,
plus one foot of freeboard. No credit is taken for infiltration.
The ultimate Affinity Fort Collins storm drainage system will be designed to convey the minor and
major storm events through the property with the proposed inlets, storm sewer pipes, and swales
for the flows being calculated by this report. Per the requirements provided by the City of Fort
Collins Storm Drainage Design Criteria and Construction Manual, all inlets and storm pipes will be
designed to convey the 100-year storm flows. During the major storm event, the developed
condition 100-year storm, the accumulated water depth in the ponds will be held to a maximum
level of one-foot below all building finished floor elevations. Additionally, this report summarizes if
any, the expected changes to offsite conditions or flows. This drainage report will eventually show
that the flow rate released downstream is less than would historically be experienced, and that the
sedimentation is lessened through increased infiltration.
All swale and pipe outlets will be protected with turf mat or riprap; whichever is most appropriate.
Storm sewer pipe outlets will be protected using the requirements set by the USDCM for the
protection of downstream conveyance channels and culverts. LID measures have been integrated
into this design, which exceeds the requirements set by the City of Fort Collins. In all, 55% of this
project’s impervious areas pass through and are treated in LID’s prior to reaching the
retention/detention ponds.
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DRAINAGE FACILITY DESIGN
GENERAL CONCEPT
The proposed improvements to the Affinity site will result in developed condition runoff being
conveyed around the proposed building and to the east via storm sewer and surface flow. Low-
impact development best management practices are proposed to improve the quality of runoff and
aid in reducing peak flows. Specifically, permeable pavement systems are proposed for portions of
the parking lot and drive aisle, rain gardens in areas around the proposed building to treat roof
drainage, and grass lined bio-swales are proposed behind the garages on the north and west sides of
the site to improve water quality.
Runoff from the site is captured in inlets located in the parking lot and in open areas adjacent to the
building. Runoff is conveyed in storm sewers in an easterly direction to the proposed ponds at the
east end of the site. Secondly, surface overflow paths have been provided, such that the 100-year
storm flows remain at least 1 foot below the finished floor elevation, in a fully clogged sub-basin
condition.
With the introduction of a detention pond concept to the site design, there currently exists no
storm drain daylight or release outfall that allows Affinity’s flows to reach the storm drain system in
Ziegler; where it is allocated to pass the HP channel. Outfall concepts are currently being
investigated in collaboration with adjacent landowners, although a specific concept has not been
advanced. As a result, the proposed interim drainage concept for the Affinity Fort Collins site
utilizes onsite retention until a drainage outfall is in place.
In the current design, offsite flows from the Harmony Mobile Home community cross the western
boundary of the development site and enter into basin A2. The flows are collected in the grass
lined bio-retention (soft-swale) along the western site boundary and conveyed to the north where
they are collected by sump inlets. These offsite flows are then routed east through the proposed
onsite storm sewer and into the proposed retention pond. In the interim retention condition,
offsite runoff during the minor storm will be discharged into the retention pond. In the ultimate
detention configuration, minor flows will be routed through the outlet structure of the pond at
existing rates. In the interim and ultimate conditions, the 100-year offsite flows will be passed over
two weirs, the retention pond weir and the level spreading weir, and will exit the site on its east
boundary in the same quantity, character and quality as the historic condition. The future detention
system is anticipated to convey the offsite flows through the site, but not to detain or treat them.
Existing conditions offsite flows also enter the site from the south, from Pond 286 during the 100-
year storm event. At the 100-year level, Pond 286 located immediately south of the site, discharges
at 116 cfs over a concrete control weir located at the northeast end of the pond. These flows
currently sheet flow onto the Affinity Fort Collins site and they continue to do so with the
proposed design. The existing 100-year flows are then routed north into the parking lot and drive
Page 10
aisle, and flow into the proposed private at the east end of the Affinity site. When the enlarged
retention pond fills, combined 100-year flows will then overtop the proposed weir on the east side
of the proposed pond and will sheet flow over the drive aisle to the east, to be conveyed offsite
across a level spreading concrete control weir onto the Sollenberger property.
PROPOSED RETENTION FACILITIES
Because no outfall exists from the site to the east, onsite retention is proposed until a drainage
outfall is gained and constructed, at which time the retention ponds will be converted to detention
ponds by retrofitting the ponds to drain to the outfall in accordance with City criteria. The onsite
retention is designed to hold twice the 100-year volume generated by a 100-year two-hour storm
(3.67”) across the entire site with no credit for infiltration.
The main proposed retention pond, Pond A, is located on the east side of the proposed building.
This pond receives flows directly from the onsite bio-retention swales and storm sewer.
Pond B is a secondary retention facility that works in tandem with Pond A. Pond B receives flows
from Basin A7 only, and is not connected to Pond A or with the proposed storm sewer system.
Pond B has no proposed restriction on the outlet, and drains into Pond A freely. In the event that
the water surface elevation in Pond A causes the north storm sewer system to back up, Pond B will
act as additional storage for Pond A, essentially acting as one retention facility. The entire Pond A
and Pond B retention system provides 5.04 acre-feet of storage with a minimum of 1’ below the
finished floor elevations.
The total minimum combined retention volume for Ponds A and B is 5.04 acre-feet. Retention
calculations are provided in the appendix.
FUTURE WATER QUALITY/ DETENTION FACILITIES
In addition to the site’s LID’s, the future water quality and detention system will be provided by
retrofitting Pond A and eliminating Pond B when the future outfall to Ziegler Road is constructed.
Converting Pond A to a detention pond will require raising the bottom of the pond to a minimum
elevation in order to permit the pond to drain to the outfall, and providing the pond with adequate
cross-slope and longitudinal slope to allow the pond to drain to a center swale leading to the outlet
structure. Because the required retention volume is in excess of the required detention volume,
Pond B can be eliminated altogether once the outfall is constructed.
The City’s Reasonable Use principle limits the rate of flow from developing properties to their 2-
year pre-development condition flow rate during the 100-year storm event. The future detention
pond release rates were calculated using the onsite 2-year historic flows and allowing the historic
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offsite 100-year flows to pass through the outlet. See Appendix A3 for maps showing the on-site 2-
year historic flows and offsite 100-year historic flows.
Two potential future outfall alignments are currently being investigated. One involves routing flows
directly through the Sollenberger property to the east, with direct conveyance from the Affinity site
to Ziegler Road. The second outfall option involves routing developed conditions detained runoff
south, around the Sollenberger property and through a series of existing detention ponds. These
outfall concepts are currently being investigated and should not impact the ability of the Affinity site
to provide onsite retention in the interim condition.
The most recent version of the UD-Detention software (Version 2.35, January 2015) was used to
determine the ultimate detention volume requirements. Per City of Fort Collins requirements, the
calculated detention volume using the FAA method was increased by a factor of 1.25. The
calculated water quality capture volume (WQCV) was added to the total factored FAA detention
volume, and one-foot of freeboard was planned for in the ultimate detention configuration as well
as in the initial retention phase. The outlet structure was also preliminarily designed in the UD-
Detention spreadsheet and is based on releasing the 2-year event at historic rates (onsite and
offsite) and the 100-year event (onsite only; calculated release based on 2-year historic flows)
through the outlet structure, while the 100-year offsite flows are discharged over the weir in
addition to the 116 cfs from Pond 286. The weir also serves as an emergency overflow in the event
that the outlet structure becomes blocked. See Table 1, below, for future pond sizing and release
rates.
Table 1: Detention Pond Values
Future
Detention
Pond
Storage
Volume
Required
(acre-ft)
WQCV
Volume
Required
(acre-ft)
Total
Volume
Required
(acre-ft)
Storage
Volume
Provided
(acre-ft)
100-yr Max
Inflow Rate
(cfs)
100-yr Max
Release Rate
(cfs)
A 2.06 0.252 2.313 2.76 35.45 134.46
Future Water Quality/Detention Facilities:
Pond A is a future onsite water quality and detention pond located on the east side of the
site and collects flows from all onsite basins and from the offsite basin. The pond detains
the 100-year developed onsite flows and releases the offsite flows at existing rates over the
weir. The future pond will detain the 100-year onsite developed conditions runoff, and
release at a rate of the site’s 2-year historic or 0.2 cfs/ acre, whichever is less. The 2-year
developed onsite and offsite flows will be released through the outlet structure. In addition
to the constructed LID measures, water quality will be provided and will be released via a
perforated orifice plate to accomplish a 40-hour release of the WQCV.
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STORMWATER POLLUTION PREVENTION
TEMPORARY EROSION CONTROL
A temporary erosion control plan is to be implemented for the site during construction.
Temporary erosion control measures include, but are not limited to, slope and swale protection,
silt fence placed around downstream areas of disturbance, construction vehicle tracking pad at
entrances, a designated concrete truck washout basin, designated vehicle fueling areas, inlet
protection, and others. All temporary erosion control measures are to be removed after they are
deemed unnecessary.
PERMANENT EROSION CONTROL
Permanent erosion control measures include, but are not limited to, the constructed
detention/water quality ponds, riprap pads placed for culvert outlet protection, seeding and mulch
placed to enable and established vegetative growth, etc. Long-term maintenance of these erosion
control measures shall be the responsibility of the owner of the property. Ultimately before
construction is permitted to begin, a more detailed Storm Water Management Plan (SWMP) will
need to be performed per the storm drainage criteria requirements of the City of Fort Collins.
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SUMMARY & CONCLUSIONS
The proposed concept for the development of the Affinity Fort Collins site involves surface flows
and piping of developed conditions flows to a proposed adequately sized onsite retention pond.
LID site enhancements will treat the site runoff at the source before allowing the runoff to be
conveyed to the proposed retention pond. Offsite flows from the west will be conveyed through
the site and directly released. Offsite flows from Pond 286 to the south (100-year flows only) will
enter the site from the south and will be bypassed through the Affinity site. Both off-site 100-year
flow rates will pass through the site and over the level spreading concrete weir, across its 150 foot
length during a major event; in the same character, quality and rate as historically passed through
the site.
EXISTING & PROPOSED CONDITIONS
The existing conditions drainage has two onsite sub-basins with different outfall points on the east
side of the subject property. The major differences between the existing condition and the
proposed condition are as follows:
1. In the existing condition, Design Point 1 (Basins OS-1 and EX1) discharges near Kingsley
Court. In the proposed condition, this offsite and onsite runoff is collected in the proposed
storm sewer and retention pond system. In the future condition, these flows will be
conveyed to the ultimate Ziegler Road outfall with the remaining onsite flows.
2. The existing condition, flows from Basin EX2 and the 100-year offsite flows from Pond 286
(116 cfs) are both discharged across the east side of the subject property over the level
spreading concrete weir. The onsite basin EX2 has a variable concentrated flow path
through the site and the offsite flows from Pond 286 enter the Affinity site after being level-
spread over the Pond 286 weir. In the proposed condition, the onsite flows will be retained
in the proposed retention pond and the 100-year offsite flows from Pond 286 will be
allowed to pass over the proposed retention pond’s weir, thus providing no additional
detention for the Pond 286 overflows. In the future condition, all onsite flows will be
discharged from the future onsite detention pond at allowable historic rates, while the Pond
286 overflows that enter the site will be allowed to pass over the detention pond’s weir.
In both proposed and future conditions, all flows that pass over the onsite pond’s weir will
be level-spread over a proposed weir as the flows leave the Affinity site on its eastern
boundary.
The existing conditions drainage patterns are maintained in the proposed and future conditions.
The proposed improvements will have no adverse impacts on the flow rate, character, or quality of
runoff leaving the site.
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The hydrologic and retention/detention calculations were performed using the required methods as
outlined in the City of Fort Collins Amendments to the Urban Drainage and Flood Control District
Criteria Manual. The proposed drainage improvements meet or exceed the City’s requirements.
This PDP Drainage Report and the complimenting drainage plans and LID plans propose
appropriate grading, permanent landscaping, LID BMPs, and onsite facilities (e.g. storm sewer, inlets,
retention/detention facilities) that are shown in their preliminary configuration and will be designed
in the Final Drainage Report for Affinity Fort Collins with supporting calculations. This report
exhibits that both the retention and future detention storm water systems meet or exceed the
requirements set forth in the City of Fort Collins “Storm Drainage Criteria Manual and
Construction Standards”, along with all its addendums.
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REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood
Control District, June 2001.
2. Storm Drainage Criteria Manual and Construction Standards, City of Fort Collins Storm Water
Utility, City of Fort Collins, Colorado, Updated January, 1997.
3. “Hydrologic Group Rating for Larimer County Area, Colorado”, USDA-Natural Resources
Conservation Service, National Cooperative Soil Survey. Web Soil Survey URL:
http://websoilsurvey.nrcs.usda.gov. [July 21, 2010]
SITE & SOIL DESCRIPTIONS AND CHARACTERISTICS (A)
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HISTORIC BASIN CALCULATIONS (B)
Subdivision: Affinity Fort Collins Project Name: Affinity Fort Collins
Location: Fort Collins Project No.:
Calculated By: TAB
Checked By: 0
Date: 6/18/15
EX1 4.930 2 4.930 2.00 2.00
EX2 3.470 2 3.470 2.00 2.00
TOTAL 8.400 2.00
Weighted %
Imp.
% Imp. Area (ac)
39704.00
COMPOSITE % IMPERVIOUS CALCULATIONS
Weighted
% Imp.
Basins Total
Basin ID Total Area (ac) % Imp. Area (ac) Weighted % Imp.
Roofs
% Imp. Area (ac)
Weighted
% Imp.
Paved Roads Lawns
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs - Historic.xlsm Page 1 of 1 6/30/2015
Subdivision: Affinity Fort Collins Project Name: Affinity Fort Collins
Location: Fort Collins Project No.:
Calculated By: TAB
Checked By: 0
Date:
FINAL
BASIN D.A. Hydrologic Impervious C100 C2 L S Ti L S Cv VEL. Tt COMP. Tc TOTAL Urbanized Tc Tc
ID (AC) Soils Group (%) (FT) (%) (MIN) (FT) (%) (FPS) (MIN) (MIN) LENGTH (FT) (MIN) (MIN)
EX1 4.93 C 2.00 0.51 0.06 300 1.6 28.2 233 0.9 7.0 0.7 5.8 34.0 533.0 13.0 13.0
EX2 3.47 C 2.00 0.51 0.06 300 1.0 33.0 251 1.1 7.0 0.7 5.6 38.6 551.0 13.1 13.1
NOTES:
Ti = (0.395*(1.1 - C5)*(L)^0.5)/((S)^0.33), S in ft/ft
Tt=L/60V (Velocity From Fig. 501)
Velocity V=Cv*S^0.5, S in ft/ft
Tc Check = 10+L/180
For Urbanized basins a minimum Tc of 5.0 minutes is required.
For non-urbanized basins a minimum Tc of 10.0 minutes is required
Cv
2.5
5
7
10
15
20
DATA (URBANIZED BASINS)
INITIAL/OVERLAND
(Ti)
TRAVEL TIME
(Tt)
STANDARD FORM SF-2
TIME OF CONCENTRATION
SUB-BASIN Tc CHECK
39704.00
6/18/15
Nearly bare ground
Grassed waterway
Paved areas and shallow paved swales
Type of Land Surface
Heavy Meadow
Tillage/field
Short pasture and lawns
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs - Historic.xlsm Page 1 of 1 6/30/2015
Project Name: Affinity Fort Collins
Subdivision: Affinity Fort Collins Project No.:
Location: Fort Collins Calculated By: TAB
Design Storm: Checked By: 0
Date:
TRAVEL TIME
STREET
Design Point
Basin ID
Area (Ac)
Runoff Coeff.
Tc (min)
C*A (Ac)
I (in/hr)
Q (cfs)
Tc (min)
C*A (Ac)
I (in/hr)
Q (cfs)
Slope (%)
Street Flow (cfs)
Design Flow (cfs)
Slope (%)
Pipe Size (inches)
Length (ft)
Velocity (fps)
Tt (min)
REMARKS
1 EX1 4.93 0.06 13.0 0.30 2.24 0.7
2 EX2 3.47 0.06 13.1 0.21 2.24 0.5
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE
STANDARD FORM SF-3
STORM DRAINAGE SYSTEM DESIGN
(RATIONAL METHOD PROCEDURE)
2-Year
39704.00
6/18/15
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs - Historic.xlsm Page 1 of 1 6/30/2015
PROPOSED RATIONAL & DETENTION POND CALCULATIONS (C)
Subdivision: Affinity Fort Collins Project Name: Affinity Fort Collins
Location: Fort Collins Project No.:
Calculated By: TAB
Checked By: 0
Date: 6/18/15
A1 0.540 100 0.276 51.10 5 0.087 0.80 90 0.177 29.50 81.40
A2 0.635 100 0.159 25.10 5 0.245 1.90 90 0.231 32.70 59.70
A3 0.411 100 0.173 42.10 5 0.115 1.40 90 0.123 26.90 70.40
A4 0.311 100 0.027 8.70 5 0.215 3.50 90 0.069 20.10 32.30
A5 0.914 100 0.481 52.70 5 0.265 1.40 90 0.168 16.50 70.60
A6 0.168 100 0.104 61.90 5 0.022 0.70 90 0.041 22.20 84.80
A7 0.743 100 0.054 7.30 5 0.492 3.30 90 0.197 23.90 34.50
A8 0.894 100 0.000 0.00 5 0.547 3.10 90 0.347 34.90 38.00
B1 0.159 100 0.019 11.80 5 0.056 1.80 90 0.084 47.60 61.20
B2 0.624 100 0.240 38.40 5 0.170 1.40 90 0.214 30.90 70.70
B3 0.269 100 0.232 86.30 5 0.037 0.70 90 0.000 0.00 87.00
B4 0.218 100 0.189 86.60 5 0.029 0.70 90 0.000 0.00 87.30
B5 0.809 100 0.257 31.80 5 0.210 1.30 90 0.342 38.00 71.10
C 0.868 100 0.639 73.70 5 0.219 1.30 90 0.010 1.00 76.00
D 0.673 100 0.034 5.10 5 0.516 3.80 90 0.122 16.30 25.20
OS1 7.820 --- --- --- 45.00
TOTAL 8.234 60.22
Weighted %
Imp.
% Imp. Area (ac)
39704.00
COMPOSITE % IMPERVIOUS CALCULATIONS
Weighted
% Imp.
Basins Total
Basin ID Total Area (ac) % Imp. Area (ac) Weighted % Imp.
Roofs
% Imp. Area (ac)
Weighted
% Imp.
Paved Roads Lawns
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs.xlsm Page 1 of 1 6/30/2015
Subdivision: Affinity Fort Collins Project Name: Affinity Fort Collins
Location: Fort Collins Project No.:
Calculated By: TAB
Checked By: 0
Date:
FINAL
BASIN D.A. Hydrologic Impervious C100 C2 L S Ti L S Cv VEL. Tt COMP. Tc TOTAL Urbanized Tc Tc
ID (AC) Soils Group (%) (FT) (%) (MIN) (FT) (%) (FPS) (MIN) (MIN) LENGTH (FT) (MIN) (MIN)
A1 0.54 C 81.40 0.75 0.61 61 7.6 3.6 119 2.2 20.0 3.0 0.7 4.2 180.0 11.0 5.0
A2 0.63 C 59.70 0.63 0.40 39 1.4 7.2 381 0.3 15.0 0.8 7.7 14.9 420.0 12.3 12.3
A3 0.41 C 70.40 0.68 0.49 35 1.7 5.5 144 1.1 20.0 2.1 1.2 6.7 179.0 11.0 6.7
A4 0.31 C 32.30 0.57 0.24 20 8.3 3.5 108 0.5 20.0 1.4 1.3 4.7 128.0 10.7 5.0
A5 0.91 C 70.60 0.68 0.50 20 8.3 2.4 228 0.5 20.0 1.4 2.7 5.1 248.0 11.4 5.1
A6 0.17 C 84.80 0.78 0.65 20 2.0 2.9 80 1.0 20.0 2.0 0.7 3.6 100.0 10.6 5.0
A7 0.74 C 34.50 0.57 0.25 20 8.3 3.4 230 1.0 20.0 2.0 1.9 5.4 250.0 11.4 5.4
A8 0.89 C 38.00 0.58 0.27 30 1.3 7.7 732 0.2 15.0 0.7 17.0 24.7 762.0 14.2 14.2
B1 0.16 C 61.20 0.64 0.42 20 8.3 2.8 30 0.5 20.0 1.4 0.4 3.1 50.0 10.3 5.0
B2 0.62 C 70.70 0.68 0.50 20 8.3 2.4 188 2.0 20.0 2.8 1.1 3.5 208.0 11.2 5.0
B3 0.27 C 87.00 0.80 0.68 20 2.0 2.7 157 2.0 20.0 2.8 0.9 3.7 177.0 11.0 5.0
B4 0.22 C 87.30 0.81 0.69 20 2.0 2.7 155 2.0 20.0 2.8 0.9 3.6 175.0 11.0 5.0
B5 0.81 C 71.10 0.68 0.50 20 8.3 2.4 206 2.0 20.0 2.8 1.2 3.6 226.0 11.3 5.0
C 0.87 C 76.00 0.71 0.55 20 2.0 3.6 306 3.0 20.0 3.5 1.5 5.0 326.0 11.8 5.0
D 0.67 C 25.20 0.56 0.20 20 2.0 5.8 262 0.5 20.0 1.4 3.1 8.9 282.0 11.6 8.9
OS1 7.82 C 45.00 0.59 0.31 112 1.5 13.4 990 1.1 20.0 2.1 7.7 21.1 1102.0 16.1 16.1
NOTES:
Ti = (0.395*(1.1 - C5)*(L)^0.5)/((S)^0.33), S in ft/ft
Tt=L/60V (Velocity From Fig. 501)
Velocity V=Cv*S^0.5, S in ft/ft
Tc Check = 10+L/180
For Urbanized basins a minimum Tc of 5.0 minutes is required.
For non-urbanized basins a minimum Tc of 10.0 minutes is required
Cv
2.5
5
7
10
15
20
DATA (URBANIZED BASINS)
INITIAL/OVERLAND
(Ti)
TRAVEL TIME
(Tt)
STANDARD FORM SF-2
TIME OF CONCENTRATION
SUB-BASIN Tc CHECK
39704.00
6/18/15
Nearly bare ground
Grassed waterway
Paved areas and shallow paved swales
Type of Land Surface
Heavy Meadow
Tillage/field
Short pasture and lawns
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs.xlsm Page 1 of 1 6/30/2015
Project Name: Affinity Fort Collins
Subdivision: Affinity Fort Collins Project No.:
Location: Fort Collins Calculated By: TAB
Design Storm: Checked By: 0
Date:
TRAVEL TIME
STREET
Design Point
Basin ID
Area (Ac)
Runoff Coeff.
Tc (min)
C*A (Ac)
I (in/hr)
Q (cfs)
Tc (min)
C*A (Ac)
I (in/hr)
Q (cfs)
Slope (%)
Street Flow (cfs)
Design Flow (cfs)
Slope (%)
Pipe Size (inches)
Length (ft)
Velocity (fps)
Tt (min)
REMARKS
1 OS1 7.82 0.31 16.1 2.42 2.03 4.9 Offsite flows enter site at DP1
A1 0.54 0.61 5.0 0.33 3.14 1.0 Sump Inlet A1
2A A2 0.63 0.40 12.3 0.25 2.29 0.6 16.1 2.67 2.03 5.4 Surface flows at inlet A2
2 A2 16.1 3.00 2.03 6.1 Flow in the Pipe at inlet A2
3 A3 0.41 0.49 6.7 0.20 2.88 0.6 16.1 3.20 2.03 6.5 Sump Inlet A3
4 A4 0.31 0.24 5.0 0.07 3.14 0.2 16.1 3.27 2.03 6.6 Sump Inlet A4
5 A5 0.91 0.50 5.1 0.46 3.12 1.4 16.1 3.73 2.03 7.6 Sump Inlet A5
6 A6 0.17 0.65 5.0 0.11 3.14 0.3 16.1 3.84 2.03 7.8 Sump Inlet A6
7 A7 0.74 0.25 5.4 0.19 3.08 0.6 16.1 4.03 2.03 8.2 Pond B
A8 0.89 0.27 14.2 0.24 2.15 0.5 Sump Inlet A8
B1 0.16 0.42 5.0 0.07 3.14 0.2 Sump Inlet B1
8 B2 0.62 0.50 5.0 0.31 3.14 1.0 5.0 0.38 3.14 1.2 Sump Inlet B2
9 B3 0.27 0.68 5.0 0.18 3.14 0.6 5.0 0.56 3.14 1.8 Sump Inlet B3
10 B4 0.22 0.69 5.0 0.15 3.14 0.5 5.0 0.71 3.14 2.2 Sump Inlet B4
11 B5 0.81 0.50 5.0 0.40 3.14 1.3 5.0 1.11 3.14 3.5 Sump Inlet B5
C 0.87 0.55 5.0 0.48 3.13 1.5 Sump Inlet C
D 0.67 0.20 8.9 0.13 2.61 0.3
12 16.1 5.99 2.03 12.2 Pond A
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE
STANDARD FORM SF-3
STORM DRAINAGE SYSTEM DESIGN (MINOR STORM)
(RATIONAL METHOD PROCEDURE)
2-Year
39704.00
6/18/15
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs.xlsm Page 1 of 1 6/30/2015
STANDARD FORM SF-3
STORM DRAINAGE SYSTEM DESIGN (MAJOR STORM)
(RATIONAL METHOD PROCEDURE)
Project Name: Affinity Fort Collins
Subdivision: Affinity Fort Collins Project No.:
Location: Fort Collins Calculated By: TAB
Design Storm: Checked By: 0
Date:
TRAVEL TIME
STREET
Design Point
Basin ID
Area (Ac)
Runoff Coeff.
Tc (min)
C*A (Ac)
I (in/hr)
Q (cfs)
Tc (min)
C*A (Ac)
I (in/hr)
Q (cfs)
Slope (%)
Street Flow (cfs)
Design Flow (cfs)
Slope (%)
Pipe Size (inches)
Length (ft)
Velocity (fps)
Tt (min)
REMARKS
OS1 7.82 0.59 16.1 4.61 7.07 32.6 Offsite flows enter site at DP1
Reduction in flows from Exsting 15" CMP
1 16.1 2.45 7.07 17.3 DP1 Flows to DP2A
A1 0.54 0.75 5.0 0.40 10.94 4.4 Sump Inlet A1
2A A2 0.63 0.63 12.3 0.40 8.00 3.2 16.1 2.85 7.07 20.2 Surface flows at inlet A2
2 16.1 3.25 7.07 23.0 Flow in the Pipe at inlet A2
3 A3 0.41 0.68 6.7 0.28 10.05 2.8 16.1 5.69 7.07 40.2 Sump Inlet A3
4 A4 0.31 0.57 5.0 0.18 10.94 2.0 16.1 5.87 7.07 41.5 Sump Inlet A4
5 A5 0.91 0.68 5.1 0.62 10.88 6.7 16.1 6.49 7.07 45.9 Sump Inlet A5
6 A6 0.17 0.78 5.0 0.13 10.94 1.4 16.1 6.62 7.07 46.8 Sump Inlet A6
7 A7 0.74 0.57 5.4 0.42 10.74 4.5 16.1 7.04 7.07 49.8 Pond B
A8 0.89 0.58 14.2 0.52 7.50 3.9 Sump Inlet A8
B1 0.16 0.64 5.0 0.10 10.94 1.1 Sump Inlet B1
8 B2 0.62 0.68 5.0 0.42 10.94 4.6 5.0 0.52 10.94 5.7 Sump Inlet B2
9 B3 0.27 0.80 5.0 0.22 10.94 2.4 5.0 0.74 10.94 8.1 Sump Inlet B3
10 B4 0.22 0.81 5.0 0.18 10.94 2.0 5.0 0.92 10.94 10.1 Sump Inlet B4
11 B5 0.81 0.68 5.0 0.55 10.94 6.0 5.0 1.47 10.94 16.1 Sump Inlet B5
C 0.87 0.71 5.0 0.62 10.91 6.8 Sump Inlet C
D 0.67 0.56 8.9 0.38 9.11 3.5
12 16.1 10.03 7.07 70.9 Pond A
39704.00
PIPE
100-Year
DIRECT RUNOFF TOTAL RUNOFF STREET
6/18/15
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs.xlsm Page 1 of 1 6/30/2015
Tributary Area tc Q5 Q100
Sub-basin (acres) C5 C100 (min) (cfs) (cfs)
A1 0.54 0.61 0.75 5.00 1.0 4.4
A2 0.63 0.40 0.63 12.33 0.6 3.2
A3 0.41 0.49 0.68 6.70 0.6 2.8
A4 0.31 0.24 0.57 5.00 0.2 1.9
A5 0.91 0.50 0.68 5.11 1.4 6.8
A6 0.17 0.65 0.78 5.00 0.3 1.4
A7 0.74 0.25 0.57 5.36 0.6 4.5
A8 0.89 0.27 0.58 14.23 0.5 3.9
B1 0.16 0.42 0.64 5.00 0.2 1.1
B2 0.62 0.50 0.68 5.00 1.0 4.6
B3 0.27 0.68 0.80 5.00 0.6 2.4
B4 0.22 0.69 0.81 5.00 0.5 1.9
B5 0.81 0.50 0.68 5.00 1.3 6.0
C 0.87 0.55 0.71 5.05 1.5 6.7
D 0.67 0.20 0.56 8.94 0.4 3.4
OS1 7.82 0.31 0.59 16.12 4.9 32.6
BASIN SUMMARY TABLE
X:\3970000.all\3970400\Excel\_Denver Files\3970400 Drainage_Calcs.xlsm Page 1 of 1 6/30/2015
Subdivision: Affinity Fort Collins Project Name: Affinity Fort Collins
Location: Fort Collins Project No.: 39704.00
Calculated By: TAB
Checked By:
Date: 6/22/2015
Area (ac): 8.23
100-yr 2-hr (in): 3.67
Runoff Volume (ac-in): 30.22 (no credit taken for infiltration)
Minimum Design Volume (ac-ft): 5.04 (2 times the two times the two hour, 100-year storm)
RETENTION CALCULATIONS
POND A
Subdivision Affinity Fort Collins Project Name: Affinity Fort Collins
Location Fort Collins Project No. 39704.00
By: TAB
Checked By:
Date: 6/22/2015
Elevation Surface Area Surface Area Lower Surface + Average Depth Volume Cumulative Volume Cumulative Volume
(square feet) (acres) Upper Surface Surface Area (feet) (cubic feet) (cubic feet) (acre feet)
4930.00 14,890 0.34 14,890 7,445 0.00 0 0 0.00
4931.00 14,892 0.34 29,782 14,891 1.00 14,891 14,891 0.34
4932.00 14,893 0.34 29,785 14,893 1.00 14,893 29,784 0.68
4933.00 14,895 0.34 29,788 14,894 1.00 14,894 44,678 1.03
4934.00 14,896 0.34 29,791 14,896 1.00 14,896 59,573 1.37
4935.00 15,532 0.36 30,428 15,214 1.00 15,214 74,787 1.72
4936.00 18,166 0.42 33,698 16,849 1.00 16,849 91,636 2.10
4937.00 18,167 0.42 36,333 18,167 1.00 18,167 109,803 2.52
4938.00 18,169 0.42 36,336 18,168 1.00 18,168 127,971 2.94
4939.00 18,170 0.42 36,339 18,170 1.00 18,170 146,140 3.35
4940.00 18,171 0.42 36,341 18,171 1.00 18,171 164,311 3.77
4941.00 18,172 0.42 36,343 18,172 1.00 18,172 182,482 4.19
Pond Volume
POND A - RETENTION
POND A - RETENTION
PREPARED BY JR ENGINEERING, 6/30/2015
POND B
Subdivision Affinity Fort Collins Project Name: Affinity Fort Collins
Location Fort Collins Project No. 39704.00
By: TAB
Checked By:
Date: 6/22/2015
Elevation Surface Area Surface Area Lower Surface + Average Depth Volume Cumulative Volume Cumulative Volume
(square feet) (acres) Upper Surface Surface Area (feet) (cubic feet) (cubic feet) (acre feet)
4933.22 0 0.00 0 0 0.00 0 0 0.00
4934.00 1,932 0.04 1,932 966 0.78 753 753 0.02
4935.00 7,087 0.16 9,019 4,510 1.00 4,510 5,263 0.12
4936.00 9,119 0.21 16,206 8,103 1.00 8,103 13,366 0.31
4937.00 9,947 0.23 19,066 9,533 1.00 9,533 22,899 0.53
4938.00 10,711 0.25 20,658 10,329 1.00 10,329 33,228 0.76
4939.00 13,286 0.31 23,997 11,999 1.00 11,999 45,226 1.04
4940.00 14,139 0.32 27,425 13,713 1.00 13,713 58,939 1.35
4941.00 14,907 0.34 29,046 14,523 1.00 14,523 73,462 1.69
4942.00 15,363 0.35 30,270 15,135 1.00 15,135 88,597 2.03
Pond Volume
POND B - RETENTION
POND B - RETENTION
PREPARED BY JR ENGINEERING, 6/30/2015
Project:
Basin ID:
Design Information (Input): Design Information (Input):
Catchment Drainage Imperviousness Ia = 60.36 percent Catchment Drainage Imperviousness I
a = 60.36 percent
Catchment Drainage Area A = 8.210 acres Catchment Drainage Area A = 8.210 acres
Predevelopment NRCS Soil Group Type = C A, B, C, or D Predevelopment NRCS Soil Group Type = C A, B, C, or D
Return Period for Detention Control T = 2 years (2, 5, 10, 25, 50, or 100) Return Period for Detention Control T = 100 years (2, 5, 10, 25, 50, or 100)
Time of Concentration of Watershed Tc = 13 minutes Time of Concentration of Watershed Tc = 13 minutes
Allowable Unit Release Rate q = 0.14 cfs/acre Allowable Unit Release Rate q = 0.14 cfs/acre
One-hour Precipitation P1 = 0.82 inches One-hour Precipitation P
1 = 2.86 inches
Design Rainfall IDF Formula i = C1
* P1
/(C2
+Tc
)^C3
Design Rainfall IDF Formula i = C1
* P1
/(C2
+Tc
)^C3
Coefficient One C1 = 28.50 Coefficient One C
1 = 28.50
Coefficient Two C2 = 10 Coefficient Two C
2 = 10
Coefficient Three C3 = 0.789 Coefficient Three C
3 = 0.789
Determination of Average Outflow from the Basin (Calculated): Determination of Average Outflow from the Basin (Calculated):
Runoff Coefficient C = 0.41 Runoff Coefficient C = 0.63
Inflow Peak Runoff Qp-in = 6.61 cfs Inflow Peak Runoff Qp-in = 35.45 cfs
Allowable Peak Outflow Rate Qp-out = 1.11 cfs Allowable Peak Outflow Rate Qp-out = 1.11 cfs
Mod. FAA Minor Storage Volume = 7,794 cubic feet Mod. FAA Major Storage Volume = 71,828 cubic feet
Mod. FAA Minor Storage Volume = 0.179 acre-ft Mod. FAA Major Storage Volume = 1.649 acre-ft
5 <- Enter Rainfall Duration Incremental Increase Value Here (e.g. 5 for 5-Minutes)
Rainfall Rainfall Inflow Adjustment Average Outflow Storage Rainfall Rainfall Inflow Adjustment Average Outflow Storage
Duration Intensity Volume Factor Outflow Volume Volume Duration Intensity Volume Factor Outflow Volume Volume
minutes inches / hr acre-feet "m" cfs acre-feet acre-feet minutes inches / hr acre-feet "m" cfs acre-feet acre-feet
(input) (output) (output) (output) (output) (output) (output) (input) (output) (output) (output) (output) (output) (output)
5 2.76 0.064 1.00 1.11 0.008 0.056 5 9.62 0.343 1.00 1.11 0.008 0.335
10 2.20 0.102 1.00 1.11 0.015 0.087 10 7.67 0.546 1.00 1.11 0.015 0.531
15 1.84 0.128 0.94 1.04 0.022 0.107 15 6.43 0.687 0.94 1.04 0.022 0.666
20 1.60 0.148 0.83 0.92 0.025 0.123 20 5.57 0.793 0.83 0.92 0.025 0.768
25 1.41 0.164 0.76 0.85 0.029 0.135 25 4.93 0.878 0.76 0.85 0.029 0.849
30 1.27 0.177 0.72 0.80 0.033 0.144 30 4.44 0.949 0.72 0.80 0.033 0.916
35 1.16 0.188 0.69 0.76 0.037 0.151 35 4.04 1.008 0.69 0.76 0.037 0.972
40 1.07 0.198 0.66 0.74 0.041 0.157 40 3.72 1.061 0.66 0.74 0.041 1.020
45 0.99 0.206 0.65 0.72 0.045 0.162 45 3.45 1.107 0.65 0.72 0.045 1.062
50 0.92 0.214 0.63 0.70 0.048 0.166 50 3.22 1.148 0.63 0.70 0.048 1.100
55 0.87 0.221 0.62 0.69 0.052 0.169 55 3.03 1.186 0.62 0.69 0.052 1.133
60 0.82 0.228 0.61 0.68 0.056 0.172 60 2.85 1.220 0.61 0.68 0.056 1.164
65 0.77 0.234 0.60 0.67 0.060 0.174 65 2.70 1.252 0.60 0.67 0.060 1.192
70 0.74 0.239 0.59 0.66 0.064 0.175 70 2.57 1.281 0.59 0.66 0.064 1.217
75 0.70 0.244 0.59 0.65 0.067 0.177 75 2.45 1.308 0.59 0.65 0.067 1.241
80 0.67 0.249 0.58 0.65 0.071 0.178 80 2.34 1.334 0.58 0.65 0.071 1.263
85 0.64 0.253 0.58 0.64 0.075 0.178 85 2.24 1.358 0.58 0.64 0.075 1.283
90 0.62 0.258 0.57 0.64 0.079 0.179 90 2.15 1.381 0.57 0.64 0.079 1.302
95 0.59 0.262 0.57 0.63 0.083 0.179 95 2.07 1.403 0.57 0.63 0.083 1.320
100 0.57 0.266 0.57 0.63 0.087 0.179 100 2.00 1.423 0.57 0.63 0.087 1.337
105 0.55 0.269 0.56 0.63 0.090 0.179 105 1.93 1.443 0.56 0.63 0.090 1.352
Project:
Basin ID:
UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.35, Released January 2015
DETENTION VOLUME BY THE MODIFIED FAA METHOD
Affinity Fort Collins PDP
EX1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 50 100 150 200 250 300 350
Volume (acre-feet)
Duration (Minutes)
Inflow and Outflow Volumes vs. Rainfall Duration
Minor Storm Inflow Volume Minor Storm Outflow Volume Minor Storm Storage Volume Major Storm Inflow Volume Major Storm Outflow Volume Major Storm Storage Volume
Copy of UD-Detention_v2.35 - DETENTION POND.xls, Modified FAA 6/30/2015, 4:16 PM
Project:
Basin ID:
Design Information (Input):
Width of Basin Bottom, W = ft Right Triangle OR…
Length of Basin Bottom, L = ft Isosceles Triangle OR…
Dam Side-slope (H:V), Zd
= ft/ft Rectangle OR…
Circle / Ellipse OR…
Irregular (Use Overide values in cells G32:G52)
New Minor Volume: 0.431
MINOR MAJOR
Storage Requirement from Sheet 'Modified FAA': 0.18 1.65 acre-ft.
Stage-Storage Relationship: Storage Requirement from Sheet 'Hydrograph': acre-ft.
Storage Requirement from Sheet 'Full-Spectrum': acre-ft.
New Major Volume: 2.313
Labels Water Side Basin Basin Surface Surface Volume Surface Volume Target Volumes
for WQCV, Minor, Surface Slope Width at Length at Area at Area at Below Area at Below for WQCV, Minor,
& Major Storage Elevation (H:V) Stage Stage Stage Stage Stage Stage Stage & Major Storage
Stages ft ft/ft ft ft ft
2
ft
2
User ft
3
acres acre-ft Volumes
(input) (input) Below El. (output) (output) (output) Overide (output) (output) (output) (for goal seek)
4929.50 (input) 0 0.000 0.000
4930.00 0.00 0.00 457 114 0.010 0.003
4931.00 0.00 0.00 8,466 4,576 0.194 0.105
4932.00 0.00 0.00 14,900 16,259 0.342 0.373
4933.00 0.00 0.00 14,900 31,159 0.342 0.715
4934.00 0.00 0.00 18,166 47,692 0.417 1.095
4935.00 0.00 0.00 18,166 65,858 0.417 1.512
4936.00 0.00 0.00 18,166 84,024 0.417 1.929
4937.00 0.00 0.00 18,166 102,190 0.417 2.346
4938.00 0.00 0.00 18,166 120,356 0.417 2.763 100 YR WSEL
4939.00 0.00 0.00 18,166 138,522 0.417 3.180
4940.00 0.00 0.00 18,166 156,688 0.417 3.597
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Project:
Basin ID:
STAGE-STORAGE SIZING FOR DETENTION BASINS
4929.50
4931.50
4933.50
4935.50
4937.50
4939.50
4941.50
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00
Stage (ft. elev.)
Storage (acre-feet)
STAGE-STORAGE CURVE FOR THE POND
Copy of UD-Detention_v2.35 - DETENTION POND.xls, Basin 6/30/2015, 4:16 PM
Project:
Basin ID:
WQCV Design Volume (Input):
Catchment Imperviousness, Ia = 60.4 percent
Catchment Area, A = 8.21 acres Diameter of holes, D = 0.960 inches
Depth at WQCV outlet above lowest perforation, H = 1.3 feet Number of holes per row, N = 1
Vertical distance between rows, h = 4.00 inches OR
Number of rows, NL = 3.00
Orifice discharge coefficient, Co = 0.63 Height of slot, H = inches
Slope of Basin Trickle Channel, S = 0.005 ft / ft Width of slot, W = inches
Time to Drain the Pond = 40 hours
Watershed Design Information (Input): 1.3
Percent Soil Type A = 0 %
Percent Soil Type B = 0 %
Percent Soil Type C/D = 100 % DI
Outlet Design Information (Output):
Water Quality Capture Volume, WQCV = 0.307 watershed inches
Water Quality Capture Volume (WQCV) = 0.210 acre-feet 0.00
Design Volume (WQCV / 12 * Area * 1.2) Vol = 0.252 acre-feet
Outlet area per row, Ao = 0.72 square inches
Total opening area at each row based on user-input above, Ao = 0.72 square inches
Total opening area at each row based on user-input above, Ao = 0.005 square feet
3
Row 1 Row 2 Row 3 Row 4 Row 5 Row 6 Row 7 Row 8 Row 9 Row 10 Row 11 Row 12 Row 13 Row 14 Row 15 Row 16 Row 17 Row 18 Row 19 Row 20 Row 21 Row 22 Row 23 Row 23 ΣΣΣΣ
4932.04 4932.37 4932.71 Flow
4929.50 0.0000 0.0000 0.0000 0.00
4930.00 0.0000 0.0000 0.0000 0.00
4931.00 0.0000 0.0000 0.0000 0.00
4932.00 0.0000 0.0000 0.0000 0.00
4933.00 0.0249 0.0202 0.0137 0.06
4934.00 0.0356 0.0324 0.0289 0.10
4935.00 0.0437 0.0412 0.0384 0.12
4936.00 0.0506 0.0484 0.0461 0.15
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Worksheet Protected
Project:
Basin ID:
STAGE-DISCHARGE SIZING OF THE WATER QUALITY CAPTURE VOLUME (WQCV) OUTLET
Affinity Fort Collins PDP
EX1
4929.00
4930.00
4931.00
4932.00
4933.00
4934.00
4935.00
4936.00
4937.00
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
Stage (feet, elev.)
Discharge (cfs)
STAGE-DISCHARGE CURVE FOR THE WQCV OUTLET STRUCTURE
Copy of UD-Detention_v2.35 - DETENTION POND.xls, WQCV 6/30/2015, 4:16 PM
Project:
Basin ID:
X
1
#1 Vertical #2 Vertical
Sizing the Restrictor Plate for Circular Vertical Orifices or Pipes (Input) Orifice Orifice
Water Surface Elevation at Design Depth Elev: WS = 4,938.50 feet
Pipe/Vertical Orifice Entrance Invert Elevation Elev: Invert = 4,929.10 feet
Required Peak Flow through Orifice at Design Depth Q = 1.11 cfs
Pipe/Vertical Orifice Diameter (inches) Dia = 18.0 inches
Orifice Coefficient Co
= 0.63
Full-flow Capacity (Calculated)
Full-flow area Af = 1.77 sq ft
Half Central Angle in Radians Theta = 3.14 rad
Full-flow capacity Qf = 26.3 cfs
Percent of Design Flow = 2361%
Calculation of Orifice Flow Condition
Half Central Angle (0<Theta<3.1416) Theta = 0.59 rad
Flow area Ao
= 0.07 sq ft
Top width of Orifice (inches) To
= 10.03 inches
Height from Invert of Orifice to Bottom of Plate (feet) Yo
= 0.13 feet
Elevation of Bottom of Plate Elev Plate Bottom Edge = 4,929.23 feet
Resultant Peak Flow Through Orifice at Design Depth Qo
= 1.1 cfs
Width of Equivalent Rectangular Vertical Orifice Equivalent Width = 0.54 feet
Centroid Elevation of Equivalent Rectangular Vertical Orifice Equiv. Centroid El. = 4,929.17 feet
RESTRICTOR PLATE SIZING FOR CIRCULAR VERTICAL ORIFICES
Copy of UD-Detention_v2.35 - DETENTION POND.xls, Restrictor Plate 6/30/2015, 4:16 PM
Project:
Basin ID:
Design Information (Input): #1 Horiz. #2 Horiz. #1 Vert. #2 Vert.
Circular Opening: Diameter in Inches Dia. = inches
OR
Rectangular Opening: Width in Feet W = 5.47 1.00 0.54 ft.
Length (Height for Vertical) L or H = 5.47 0.50 0.13 ft.
Percentage of Open Area After Trash Rack Reduction % open = 65 100 100 %
Orifice Coefficient Co = 0.63 0.63 0.63
Weir Coefficient Cw = 3.00
Orifice Elevation (Bottom for Vertical) Eo = 4933.50 4,932.60 4,929.10 ft.
Calculation of Collection Capacity:
Net Opening Area (after Trash Rack Reduction) Ao = 19.45 0.50 0.07 sq. ft.
OPTIONAL: User-Overide Net Opening Area Ao = sq. ft.
Perimeter as Weir Length Lw = 18.05 ft.
OPTIONAL: User-Overide Weir Length Lw = ft.
Top Elevation of Vertical Orifice Opening, Top = 4933.10 4929.23 ft.
Center Elevation of Vertical Orifice Opening, Cen = 4932.85 4929.17 ft.
Horizontal Orifices Vertical Orifices
Labels Water WQCV #1 Horiz. #1 Horiz. #2 Horiz. #2 Horiz. #1 Vert. #2 Vert. Total Target Volumes
for WQCV, Minor, Surface Plate/Riser Weir Orifice Weir Orifice Collection Collection Collection for WQCV, Minor,
& Major Storage Elevation Flow Flow Flow Flow Flow Capacity Capacity Capacity & Major Storage
W.S. Elevations ft cfs cfs cfs cfs cfs cfs cfs cfs Volumes
(input) (linked) (User-linked) (output) (output) (output) (output) (output) (output) (output) (link for goal seek)
4929.50 0.00 0.00 0.00 0.00 0.00 0.00 0.20 0.00
4930.00 0.00 0.00 0.00 0.00 0.00 0.00 0.32 0.00
4931.00 0.00 0.00 0.00 0.00 0.00 0.00 0.48 0.00
4932.00 0.00 0.00 0.00 0.00 0.00 0.00 0.60 0.00
4933.00 0.06 0.00 0.00 0.00 0.00 0.90 0.69 0.69
4934.00 0.10 19.15 69.53 0.00 0.00 2.71 0.78 0.78
4935.00 0.12 99.49 120.43 0.00 0.00 3.71 0.85 0.85
4936.00 0.15 214.06 155.47 0.00 0.00 4.49 0.93 0.93
4937.00 #N/A 354.59 183.95 0.00 0.00 5.15 0.99 #N/A
4938.00 #N/A 516.94 208.58 0.00 0.00 5.74 1.05 #N/A
4939.00 #N/A 698.50 230.60 0.00 0.00 6.27 1.11 #N/A
4940.00 #N/A 897.41 250.68 0.00 0.00 6.76 1.16 #N/A
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Project:
Basin ID:
Affinity Fort Collins PDP
EX1
STAGE-DISCHARGE SIZING OF THE WEIRS AND ORIFICES (INLET CONTROL)
4929.5
4931.5
4933.5
4935.5
4937.5
4939.5
4941.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Stage (feet, elev.)
Discharge (cfs)
STAGE-DISCHARGE CURVE FOR THE OUTLET STRUCTURE
Copy of UD-Detention_v2.35 - DETENTION POND.xls, Outlet 6/30/2015, 4:16 PM
EXISTING & PROPOSED DRAINAGE PLANS (D)
A Westrian Company
AFFINITY FORT COLLINS
EXISTING CONDITIONS DRAINAGE PLAN
HARMONY
MOBILE HOME
COMMUNITY
SOLLENBERGER
PROPERTY
X:\3970000.all\3970400\Drawings\_Denver Files\3970400DRH01-PDP.dwg, EX Conditions, 6/30/2015 2:01:51 PM, BurnsR
A Westrian Company
AFFINITY FORT COLLINS
PROPOSED CONDITIONS DRAINAGE MAP
R
R R R
R
R
R
R
R
R
R R R
R
R R
R
R
R
R
R
R
R
R R
X:\3970000.all\3970400\Drawings\_Denver Files\3970400DRF01-PDP.dwg, 24x36 Title Landscape, 6/30/2015 4:42:58 PM, BurnsR
LID EXHIBITS (E)
A Westrian Company
AFFINITY FORT COLLINS
PROPOSED LID IMPLEMENTATION PLAN
AREA DESCRIPTION
AREA
(SF)
% OF
TOTAL
NEW IMPERVIOUS
AREA AFFLUENT TO
L.I.D. BMP'S
97,192 44%
PICP AREA 25,390 11%
TOTAL TREATED AREA 122,582 55%
NEW IMPERVIOUS
AREA NOT TREATED
99,394 45%
TOTAL IMPERVIOUS
AREA
221,976 100%
IMPERVIOUS AREA TREATMENT RATIO
R
R R R
R
R
R
R
R
R
R R R
R
R R
R
R
R
R
R
R
R
R R
X:\3970000.all\3970400\Drawings\_Denver Files\2015-06-26 NEW IMPERVIOUS AREA.dwg, 24x36 Title Landscape, 6/29/2015 5:19:38 PM, BurnsR
A Westrian Company
AFFINITY FORT COLLINS
PERMEABLE PAVEMENT AREA EXHIBIT
LID IMPLEMENTATION PLAN
SURFACE MATERIAL AREA (SF)
% OF
TOTAL
PERMEABLE
INTERLOCKING
CONCRETE PAVERS
(PICP)
25,390 71%
IMPERVIOUS
ASPHALT PARKING
10,395 29%
TOTAL 35,785 100%
PARKING AREAS
R
R R R
R
R
R
R
R
R
R R R
R
R R
R
R
R
R
R
R
R
R R
X:\3970000.all\3970400\Drawings\_Denver Files\2015-06-26 - PICP Exhibit.dwg, 24x36 Title Landscape, 6/29/2015 3:25:07 PM, BurnsR
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Routing 2: Water flows through WQCV plate and #1 vertical opening and #1 horizontal opening into #2 vertical opening (#2 horizontal
opening is not used).
STAGE-DISCHARGE SIZING OF THE WEIRS AND ORIFICES (INLET CONTROL)
Affinity Fort Collins PDP
EX1
Current Routing Order is #2
W.S. EL. WQ
W.S. EL. Minor
W.S. EL. Major
WQ
H1
H2
V1 V2
Routing Order #1 (Standard)
V1
W.S. EL. WQ
W.S. EL. Design Storm
WQ
H1
Routing Order #3 (Single Stage) Routing Order #4
V2
V1
H1
WQ
W.S. EL. Major
W.S. EL. Minor
W.S. EL. WQ
W.S. EL. Emergency Spillway
Emergency Overflow into Pipe- H2
V2
H1
WQ
W.S. EL. Major
W.S. EL. Minor
W.S. EL. WQ V1
Routing Order #2
Copy of UD-Detention_v2.35 - DETENTION POND.xls, Outlet 6/30/2015, 4:16 PM
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Central Elevations of Rows of Holes in feet
Collection Capacity for Each Row of Holes in cfs
STAGE-DISCHARGE SIZING OF THE WATER QUALITY CAPTURE VOLUME (WQCV) OUTLET
Affinity Fort Collins PDP
EX1
Copy of UD-Detention_v2.35 - DETENTION POND.xls, WQCV 6/30/2015, 4:16 PM
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STAGE-STORAGE SIZING FOR DETENTION BASINS
Affinity Fort Collins PDP
Check Basin Shape
EX1
Copy of UD-Detention_v2.35 - DETENTION POND.xls, Basin 6/30/2015, 4:16 PM
110 0.53 0.273 0.56 0.62 0.094 0.178 110 1.87 1.462 0.56 0.62 0.094 1.367
115 0.52 0.276 0.56 0.62 0.098 0.178 115 1.81 1.480 0.56 0.62 0.098 1.382
120 0.50 0.279 0.55 0.62 0.102 0.177 120 1.75 1.497 0.55 0.62 0.102 1.395
125 0.49 0.282 0.55 0.61 0.106 0.177 125 1.70 1.514 0.55 0.61 0.106 1.408
130 0.47 0.285 0.55 0.61 0.110 0.176 130 1.65 1.530 0.55 0.61 0.110 1.420
135 0.46 0.288 0.55 0.61 0.113 0.175 135 1.61 1.545 0.55 0.61 0.113 1.432
140 0.45 0.291 0.55 0.61 0.117 0.174 140 1.56 1.560 0.55 0.61 0.117 1.443
145 0.44 0.294 0.55 0.61 0.121 0.173 145 1.52 1.575 0.55 0.61 0.121 1.453
150 0.43 0.296 0.54 0.60 0.125 0.171 150 1.49 1.589 0.54 0.60 0.125 1.464
155 0.42 0.299 0.54 0.60 0.129 0.170 155 1.45 1.602 0.54 0.60 0.129 1.473
160 0.41 0.301 0.54 0.60 0.133 0.169 160 1.42 1.615 0.54 0.60 0.133 1.483
165 0.40 0.304 0.54 0.60 0.136 0.167 165 1.39 1.628 0.54 0.60 0.136 1.492
170 0.39 0.306 0.54 0.60 0.140 0.166 170 1.35 1.641 0.54 0.60 0.140 1.500
175 0.38 0.308 0.54 0.60 0.144 0.164 175 1.33 1.653 0.54 0.60 0.144 1.509
180 0.37 0.311 0.54 0.60 0.148 0.163 180 1.30 1.665 0.54 0.60 0.148 1.517
185 0.36 0.313 0.54 0.60 0.152 0.161 185 1.27 1.676 0.54 0.60 0.152 1.524
190 0.36 0.315 0.53 0.59 0.156 0.159 190 1.25 1.687 0.53 0.59 0.156 1.532
195 0.35 0.317 0.53 0.59 0.159 0.157 195 1.22 1.698 0.53 0.59 0.159 1.539
200 0.34 0.319 0.53 0.59 0.163 0.156 200 1.20 1.709 0.53 0.59 0.163 1.546
205 0.34 0.321 0.53 0.59 0.167 0.154 205 1.18 1.720 0.53 0.59 0.167 1.552
210 0.33 0.323 0.53 0.59 0.171 0.152 210 1.16 1.730 0.53 0.59 0.171 1.559
215 0.33 0.325 0.53 0.59 0.175 0.150 215 1.14 1.740 0.53 0.59 0.175 1.565
220 0.32 0.326 0.53 0.59 0.179 0.148 220 1.12 1.750 0.53 0.59 0.179 1.571
225 0.31 0.328 0.53 0.59 0.182 0.146 225 1.10 1.759 0.53 0.59 0.182 1.577
230 0.31 0.330 0.53 0.59 0.186 0.144 230 1.08 1.769 0.53 0.59 0.186 1.583
235 0.30 0.332 0.53 0.59 0.190 0.142 235 1.06 1.778 0.53 0.59 0.190 1.588
240 0.30 0.333 0.53 0.59 0.194 0.140 240 1.05 1.787 0.53 0.59 0.194 1.593
245 0.30 0.335 0.53 0.59 0.198 0.137 245 1.03 1.796 0.53 0.59 0.198 1.598
250 0.29 0.337 0.53 0.59 0.202 0.135 250 1.01 1.805 0.53 0.59 0.202 1.603
255 0.29 0.338 0.53 0.58 0.205 0.133 255 1.00 1.814 0.53 0.58 0.205 1.608
260 0.28 0.340 0.53 0.58 0.209 0.131 260 0.98 1.822 0.53 0.58 0.209 1.613
265 0.28 0.342 0.52 0.58 0.213 0.128 265 0.97 1.831 0.52 0.58 0.213 1.617
270 0.27 0.343 0.52 0.58 0.217 0.126 270 0.96 1.839 0.52 0.58 0.217 1.622
275 0.27 0.345 0.52 0.58 0.221 0.124 275 0.94 1.847 0.52 0.58 0.221 1.626
280 0.27 0.346 0.52 0.58 0.225 0.121 280 0.93 1.855 0.52 0.58 0.225 1.630
285 0.26 0.348 0.52 0.58 0.228 0.119 285 0.92 1.863 0.52 0.58 0.228 1.634
290 0.26 0.349 0.52 0.58 0.232 0.117 290 0.91 1.870 0.52 0.58 0.232 1.638
295 0.26 0.350 0.52 0.58 0.236 0.114 295 0.89 1.878 0.52 0.58 0.236 1.642
300 0.25 0.352 0.52 0.58 0.240 0.112 300 0.88 1.885 0.52 0.58 0.240 1.645
305 0.25 0.353 0.52 0.58 0.244 0.109 305 0.87 1.893 0.52 0.58 0.244 1.649
Mod. FAA Minor Storage Volume (cubic ft.) = 7,794 Mod. FAA Major Storage Volume (cubic ft.) = 71,828
Mod. FAA Minor Storage Volume (acre-ft.) = 0.1789 Mod. FAA Major Storage Volume (acre-ft.) = 1.6489
Determination of MAJOR Detention Volume Using Modified FAA Method
(For catchments less than 160 acres only. For larger catchments, use hydrograph routing method)
(NOTE: for catchments larger than 90 acres, CUHP hydrograph and routing are recommended)
UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.35, Released January 2015
Determination of MINOR Detention Volume Using Modified FAA Method
DETENTION VOLUME BY THE MODIFIED FAA METHOD
Affinity Fort Collins PDP
EX1
Copy of UD-Detention_v2.35 - DETENTION POND.xls, Modified FAA 6/30/2015, 4:16 PM
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