HomeMy WebLinkAboutASPEN HEIGHTS STUDENT HOUSING - PDP - PDP110018 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT
Aspen Heights - Fort Collins
s.w. Corner, Conifer St. & Redwood St.
Fort Collins, Colorado
Prepared For:
Breckenridge Property Acquisition, LP
1301 S. Capital of TX Hwy
Building B, Suite 201
Austin, TX 78746
(512) 369-3030
-Ia B Prepared OWEN CONSULTING By:
GROUP, INC.
3715 Shallow Pond Drive,
Fort Collins, CO 80528
Phone: 970-226-0264
Fax: 970-226-3760
Revised March 26,2012
December 2011
Proj. No.: 11-358
ASPEN HEIGHTS - FORT COLLINS
PRELIMINARY DRAINAGE REPORT
Table of Contents
ENGINEER'S CERTIFICATION .... .. .... ..... ........ .. ........ .. ......... .. .. ... ......... .. ............... .... .... .. ...... 1
I. LOCATION AND DESCRIPTION OF PROPERTY AND PROPOSED DEVELOPMENT .. .... 2
A. Location .... ..... .... ... .... ........ ..... ..... ....... ... ....... ...... .... .... .. ..... .. .... ... ... ... .. .. ... ..... ...... ....... ... ..... 2
B. Description of Property .. ... ...... ... .... ... ...... ... ......... .... ...... .. ... ..... ... ........ .... ... .. ... ... .... ........ .. .. 2
C. Description of Proposed Development .... ... .... ............ ........ ... ........ ..... ..... .... ...... .... ..... ...... 3
II. DRAINAGE BASINS AND SUB-BASiNS...... .... ......... ............... .............. ....... .. .. ........ .. ........ .. . 3
A Major Basin Description ......... .. ..... ..... .............. .. ........ .. ............. ..... ........... .. .. ... ......... .... .... 3
B. Sub-Basin Description ... ... ........ .............. .. ...... .... .. ... ... ........ ........ .. ........... .. ............ ... ........ 4
III. DRAINAGE DESIGN CRITERIA .. ...... .................. ..... ...... ... ........ ...... .... ... .. ......... ... ... ......... ..... 4
A. Regulations ... ......... ... ........ .... ......... ... .. .............................. .. .. ........ .. ......... ........ .... ... .. ....... . 4
B. Development Criteria Reference and Constraints ..... ..... ........... ..... ............ ..... ..... ... .. ...... . 4
C. Hydrologic Criteria .... ................. .... ......... .... ....... ..... ..... .. .. .......... ............ .... .................. ... .. 5
D. Hydraulic Criteria .. .. .. ...... ... ...... ........ .. ... ...... .... ......... .......... .......... .. .... ......... .. .. .................. 5
E. Floodplain Impacts ........... ...... .... .. ... .......... .. ........ ......... .............................. .... ........ .. .... ... .. 6
F. Waiver I Variance from Criteria ........ ...... ... ... ..... .. .. .. .... .. ... .. ... ........ ..... .. ..... ..... .... .......... .. .. . 6
IV. WETLAND PRESERVATION AND MITIGATION ..... ... ....... .. .... ..... .. .. ... .. .......... .. .. ...... .... ........ 6
V. DRAINAGE FACILITY DESiGN ....... .. ........ .... ...... .. ... ....... ... ... ... ...... .. ... ...... .... ......... .. ......... ... .. 7
A. General Concept .... ...... .. ... ...... ........... .......... ........ .......... .. .. .. ... ... .......... .......... ....... ..... ...... . 7
B. Specific Details .. ...... ... ... .... .. ............... .. .......... ... .. ....... .......... .. ... ... ........... ...... ..... ..... ...... .. . 7
C. Storm Water Considerations .... ........... ........ ......... ... ....... ...... ..... .. .... ............. .... .. ... .. ... ..... 10
VI. CONCLUSiONS... .... .. ..... .... .. ........... .. ......... ............ .. ........ ..... ...... .... .. .. ... .... ... .. ...... .... ........ .. . 11
A Compliance with Standards .. .... .. .. ........ .... ...... ..... .. .. .. .......... ....... ... ........ ...... ... .. .... ...... .... 11
B. Drainage Concept ....... ... ..................... .. ................ ......... .............. ....... ... ..... .............. ...... 11
VII. REFERENCES ... ... ............ .......... .. ... ......... .......... .. ........ ... ...... ... ...... .... .. ......... ... ..... ........ ... ... 12
VIII. ATTACHMENTS
IX. DRAWINGS
ASPEN HEIGHTS - FORT COLLINS
PRELIMINARY DRAINAGE REPORT
ENGINEER'S CERTIFICATION
I hereby certify that this Preliminary Drainage Report for the design of stormwater management
facilities for the Aspen Heights student housing development was prepared by me, or under my
direct supervision, in accordance with the provisions of the City of Fort Collins Storm Drainage
Design Criteria and Construction Standards for the owners thereof.
Larry C. Owen, P.E.
Registered Professional Engineer
State of Colorado No. 29871
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ASPEN HEIGHTS - FORT COLLINS
PRELIMINARY DRAINAGE REPORT
I. LOCATION AND DESCRIPTION OF PROPERTY AND PROPOSED DEVELOPMENT
A. LOCATION
The proposed development is located in the Southwest Quarter of Section 1, Township 7
North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado. The site is bounded on the north by Conifer St., on the east by Redwood
St., on the south by the future realignment of Vine Dr., and on the west by vacant land.
Adjacent developments and land uses, beyond the abutting streets, include residential and
commercial to the north (Evergreen Park), residential to the east (Redwood Meadows),
residential to the south (Old Town North), and commercial beyond the vacant land to the
west. The site is entirely within the bounds of the City of Fort Collins.
B. DESCRIPTION OF PROPERTY
The site comprises a total area of 31 .0 acres, of which approximately 26.1 acres is
developable. The property is currently vacant, but has been used for agriculture in past.
The current ground cover is a mix of native grasses.
The site slopes relatively uniformly from northwest to southeast at an average approximate
gradient between 0.5% - 1.0%. A remnant of the Dry Creek channel lies within a tongue of
the site, southeast of the proposed right-of-way for the realignment of Vine Drive. This
portion of the site (approx. 1.84 ac) is effectively undevelopable, so the Dry Creek channel
will not be impacted by the proposed development, other than to a small extent by the
construction of Vine Drive. In addition to the remnant Dry Creek channel, there is a
drainage ditch that traverses the property from north to south, along an alignment that is
approximately 40% of the width of the property from the west boundary. This ditch is
approximately five to six feet deep and conveys runoff through the property from tributary
areas to the north. There is also a branch ditch that extends from the northwest corner of
the property to a confluence with the main north-south ditch, at a point approximately 30% of
the distance from the north property line to the south boundary of the site. The Lake Canal
Irrigation Company channel passes to the south of the site, and is closest to the site at a
point approximately 550 feet east of the south east corner of the property.
The native soils underlying the site are predominantly (89%) Nunn clay loams, with a small
band of Caruso clay loams in the northeast quadrant of the site. Both of these soils fall
within NRCS Hydrologic Soil Group C. The Preliminary Geotechnical Investigation that was
conducted at the site generally confirms this characterization. Ground water was
encountered at depths ranging from approximately six to nine feet, at the time of drilling.
After 19 days, the depth to the water table had stabilized at between six and seven feet,
throughout most of the site, with the exception of the southwest quadrant, where the depth
to water was approximately ten feet.
Flood plain mapping for the vicinity of the development site shows a FEMA-designated
floodplain and f100dway (the Dry Creek Floodplain) that extends into the southeast corner of
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the site. The floodway extends along a portion of the Dry Creek channel, with some
extension of the floodplain north along the alignment of the not-yet-constructed portion of
Redwood Street, north of the proposed realignment of Vine Drive. The floodplain and
floodway boundaries are delineated on FEMA FIRM Panel # 08069C0977G, dated June 17,
2008. This area is not designated as a floodplain on the City of Fort Collins mapping of
flood hazard areas in the vicinity of the site. A comparison of the design profiles for the
proposed streets relative to the Base Flood Elevation (BFE) information for the FEMA
designated floodplain indicates that the 100-yr flood water surface would be less than one
foot above the finished road surface at the intersection of Redwood Street and Vine Drive.
C. DESCRIPTION OF PROPOSED DEVELOPMENT
The proposed development for the site is a residential community devoted to students. The
build-out will include two-story, cottage-style residences; a clubhouse and recreation I
amenities area; off-street surface parking, accessed via a network of local public streets and
private driveways; and landscaped open areas and pedestrian I bicycle paths. Buildings will
account for approximately 21 % of the site area; paved roads, sidewalks and parking areas
will account for a further approximately 30% of the site; and landscaped areas will account
for approximately 49% of the developable area of the site. The balance of the site
(approximately 4.9 acres) will be either dedicated to the City for the construction of the
realigned Vine Drive (3.1 ac), or left in it's current natural state (1.8 ac).
Access to the development will be via existing and proposed perimeter streets, at three
locations; 1) from Conifer St., in the north, as an extension of Blue Spruce Dr.; 2) from
Redwood St., in the east, as an extension of Lupine Dr.; and 3) from realigned Vine Dr. in
the south, opposite Blondel St. The layout of the proposed development is shown as the
background to the Grading and Drainage Plan, which is included as an attachment to this
report.
Trunk infrastructure for supply of potable water and collection of sanitary sewage is
available in the perimeter streets and will be extended throughout the site to serve the
development. Electric power, natural gas, telephone, cablevision and fiber optics services
are also available to serve the development.
Stormwater runoff from the development will be directed via overland flow to appropriately
sized and located storm drain inlets and drainage piping, and conveyed either to the north
south channel and thence to the detention basin on the adjacent property to the south, or
piped directly to the detention basin. The detention basin will be an interim facility, sized to
attenuate storm flows and enhance stormwater quality emanating from this development,
but it will also be an initial phase of a larger, regional detention facility planned for the site.
Discharge from the interim detention facility will be piped to the nearby Lake Canal Irrigation
Channel. Discharge from the ultimate regional detention basin will be conveyed, via pipe
and open channel, to the Cache La Poudre River.
II. DRAINAGE BASINS AND SUB-BASINS
A. MAJOR BASIN DESCRIPTION
The development site is located in the lower Dry Creek Drainage Basin, as delineated in the
City of Fort Collins Drainage Basin Master Plan (City of Fort Collins, June 2004).
Historically, runoff from this portion of the Dry Creek Drainage Basin has flowed overland to
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the southeast and into Dry Creek, which drained, historically, to the Poudre River. More
recently, however, the Dry Creek channel has been largely impounded at Redwood St.,
such that flows in the channel pond behind the embankment and eventually overflows,
through a culvert and shallow ditch, and drains into the Lake Canal Irrigation Channel.
The existing north-south drainage ditch through the development site, along with the lesser
branch ditch flowing from the northwest corner of the site to the main ditch, convey runoff
from the area north of Conifer St. south to Dry Creek. These flows will ultimately all be
conveyed to the regional detention facility in large diameter pipes, then through the
detention facility and on to a confluence with the Poudre River at a point near Mulberry St.
and Timberline Rd.
B. SUB-BASIN DESCRIPTION
For purposes of analyzing the drainage regime for the proposed development, the project
site has been subdivided into 27 on-site drainage sub-basins, reflective of the anticipated
final topography of the site. These drainage sub-basins range in size from 0.14 acres to
3.36 acres. In addition to the on-site sub-basins, five off-site sub-basins, plus the detention
basin, have also been delineated, ranging in size from 0.36 acres to 1.04 acres. These on
site and off-site sub-basins comprise the drainage regime for the project and are accounted
for in the stormwater management analysis and the design of stormwater management
improvements for the development project.
While final grading of the development site will result in localized ridges and depressions,
the overall direction of storm flow will continue to be from northwest to southeast, consistent
with the existing predevelopment drainage pattern of the site.
III. DRAINAGE DESIGN CRITERIA
A. REGULATIONS
The proposed stormwater management improvements for the Aspen Heights development
are designed in compliance with the requirements of the City of Fort Collins Storm Drainage
Design Criteria and Construction Standards (City of Fort Collins, May 1984, March 1991 and
January 1997). The design of stormwater management improvements for the project also
takes into account the previously developed designs for the North East College Corridor
Outfall (NECCO) Preliminary Design Report, prepared by Ayers Associates (January 2008).
Reference was also made to the Urban Storm Drainage Criteria Manual (Urban Drainage
and Flood Control District, April 2008).
B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
The criteria used as the basis for analysis and design of stormwater management
improvements for this site are those found in the references cited in the section immediately
above.
To the knowledge of the author, there are no other capital drainage improvements planned
for this portion of the Dry Creek Drainage Basin, aside from those referred to above, that
would constrain or otherwise influence the design of the stormwater improvements for this
site.
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C. HYDROLOGIC CRITERIA
Stormwater runoff from the respective sub-basins of the Aspen Heights site is analyzed for
storms with 2-year and 1 DO-year return frequencies.
Due to the relatively small area of the developable portion of the site (less than 30 acres)
and the fact that the off-site tributary flows are quantified in the NECCO Report, the Rational
Method was chosen for use in the design of the on-site stormwater management system.
The Rational Method provides that:
Q =CIA, where:
Q =Design flow in cubic feet per second (cfs)
C =Coefficient of runoff for the area under consideration
I =Rainfall intensity for the design storm duration (in/hr)
A = Area of the drainage sUb-basin under consideration (ac)
Composite coefficients of runoff were calculated for the two design storm events, based on
the applicable percent imperviousness of the respective surfaces (roof, pavement,
landscaped areas, etc.) within the various SUb-basins. Rainfall intensities were determined
using information presented in the City of Fort Collins Storm Drainage Design Criteria and
Construction Standards.
For this Preliminary Drainage Report the required detention capacity to accommodate the
design 100-yr storm event was calculated using the Modified FAA Method, and a depth
capacity curve has been generated for the detention basin. As the design evolves, the final
sizing of the detention basin will be determined using the SWMM model. In the interim, an
adjustment factor of 1.25 has been applied to the volume determined through the Modified
FAA Method, in order to ensure the adequacy of the preliminary analysis.
The required Water Quality Capture Volume for the interim detention basin was calculated
using the methodology set out in the Urban Storm Drainage Criteria Manual.
The design worksheets included in the Attachments to this Preliminary Drainage Report
present documentation of the hydrologic calculations for the on-site storm drainage system.
D. HYDRAULIC CRITERIA
Within the development, a significant portion of the runoff will be conveyed on the surface,
initially as sheet flow and subsequently as concentrated flow in shallow pans and gutters. In
order to minimize surface accumUlations of runoff, the assessment of required capacity and
the sizing of the respective components of the drainage system are based on the anticipated
runoff from the 1 ~O-year storm event. No detention is planned within any of the parking
areas, and it is the intent of the design that there be minimal, if any, accumUlation of runoff
in paved parking or travel areas. Inevitably, however, some accumulation will occur under
extreme storm events, due to the constriction presented by inlet openings upstream of the
detention basin. In all cases, it is the intent of the design that the maximum depth of
accumUlation be less than one foot and that the duration of localized impoundment be short.
Where the site grading design in localized areas precludes continuous surface migration of
runoff to the detention basin, appropriately sized inlets and storm drain piping are included,
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to convey the accumulated runoff from these localized collection points to the detention
basins.
The calculation spreadsheets included in the Attachments to this Preliminary Drainage
Report reflect this design approach.
E. FLOODPLAIN IMPACTS
As stated in Section I B (Description of Property) above, the existing Dry Creek floodplain
and floodway will be impacted by the proposed construction of Redwood Street and Vine
Drive. The impacts will be somewhat mitigated by the construction of the Interim Detention
Basin to serve the Aspen Heights development, but a CLOMR will be necessary to quantify
the impacts and demonstrate compliance with FEMA regulations. Upon completion of
construction of the road improvements, a LOMR will also be required. Documentation of the
CLOMR and LOMR will be submitted to the City for review and approval.
Regardless of any impacts to the Dry Creek floodplain due construction of the road
improvements, neither the interim detention basin nor any of the proposed structures within
the development will be in jeopardy of flooding. The crest elevation of the interim detention
basin perimeter berm is a minimum of 1.0 foot above the maximum BFE at the upstream
end of the floodway, and the lowest building in the development is approximately 6.5 feet
above the maximum BFE in the floodplain.
All designs for improvements that may impact the floodplain will be in compliance with
applicable floodplain regulations (Chapter 10 of the Fort Collins Municipal Code), and a
Floodplain Use Permit will be obtained prior to commencing any construction within the
floodplain.
F. WAIVER I VARIANCE FROM CRITERIA
There are no waivers or variances from the City of Fort Collins Storm Drainage Design
Criteria and Construction Standards requested in connection with the design of the
stormwater management facilities for the Aspen Heights development.
IV. WETLAND PRESERVATION AND MITIGATION
There are currently wetlands within the main north-south drainage ditch and within the
branch ditch, traversing the developable portion of the site. There are also wetlands within
the area that will be developed as the detention basin. These wetlands have been
delineated and mapped, and are the subject of a Wetland Delineation Report (Wildland
Consultants, Inc., Nov. 2011). The total area of delineated wetlands amounts to 0.297
acres. A copy of this report has been submitted to the City, as part of the submittal package
for this project.
All of the existing wetlands will be impacted by the construction of the proposed
development, and it is proposed that the impacted wetlands be mitigated as part of the
development of the site. Discussions with City staff lead to the conclusion that it would be
preferable to implement the wetlands mitigation in a portion of the proposed detention basin,
in order to maximize the opportunity for successful re-establishment of a suitable habitat in
an area that is somewhat removed from the occupied portion of the development. Details of
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the wetland mitigation will be developed in consultation with City staff, and will be presented
on project drawings as they evolve.
The existing north-south drainage channel will be reshaped as part of the development
project, and will be revegetated with native grasses and shrubs, but not necessarily wetland
species. The branch drainage channel will be eliminated, as part of the development
program.
v. DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
The design of the stormwater management systems for the Aspen Heights development is
based on the premise that runoff generated within the site should be managed within the
site, to the greatest extent practicable, such that there is no adverse impact to either the
development or to adjacent or downstream properties, drainage facilities and waterways.
The grading plan for the site has been designed to promote positive drainage away from all
building envelopes, and to direct collectable runoff flow to the detention basin.
Within the bounds of the site, the proposed drainage patterns for the development will
generally follow the historic patterns of the predevelopment site, with minor, localized
exceptions to encourage flow away from building envelopes and to the collection points and
then to the detention basin. Discharge of storm water from the developed site, however, will
differ, in the short term, from the historic experience, in that the collected runoff will be
discharged to the Lake Canal Irrigation Channel, rather than to Dry Creek and ultimately to
the Poudre River. As stated earlier in this report, under current conditions, flows that enter
the Dry Creek channel from the vicinity of the site, and upstream tributary areas, do in fact
discharge to the Lake Canal Irrigation Channel, but that is not the historic condition. Dry
Creek historically discharged to the Poudre River, and the discharge from the Regional
Detention Pond will be conveyed to the Poudre River. However, in the interim, no facilities
exist to convey the stormwater discharge to the Poudre River, so the Lake Canal has been
chosen as an interim receiving waterway.
The design worksheets included in the Attachments to this Preliminary Drainage Report
present details of the hydrologic and hydraulic calculations pertinent to the design of the on
site storm drainage system. A Preliminary Drainage Plan, showing the Concept Plan for
development of the site and proposed developed drainage patterns is included in the map
pocket following the attachments.
B. SPECIFIC DETAILS
There are five collection and conveyance scenarios within the drainage regime associated
with this development. The respective scenarios are described below.
Runoff from the portions of the site within reasonable proximity (both east and west) of the
north-south drainage channel will be conveyed via overland and shallow channel flow to
appropriately located inlets at the low points of the sub-basins, and thence, via short lengths
of pipe, to the reconfigured north-south channel and to the detention basin. There are 14
drainage sub-basins that fit within this category, with individual and cumulative runoff values
calculated at 14 design points. The reconfigured north-south channel will also convey the
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collected tributary flows from areas north of the site that are currently conveyed in the north
south ditch and the branch ditch.
Runoff from areas that are further east of the north-south channel, and that are at elevations
that are either too low to flow overland to the north-south channel or that are separated by
localized ridges from the north-south channel, will be directed to appropriately located inlets
and then conveyed via a central pipe run to the detention basin. There are seven sub
basins that fit within this category, with runoff values calculated at four design points.
There is one on-site sub-basin and one adjacent off-site basin from which runoff cannot be
captured to the on-site drainage system and conveyed to the new detention basin. These
areas include the narrow strip of land along the north and northeast perimeters of the site
(Sub-basin 4) and the adjacent south half of Conifer St and the west half of Redwood St,
north of the existing high point. Runoff from these sub-basins will flow along the street
gutter to the existing inlet at the southwest corner of the intersection of Conifer and
Redwood, and from there into the Redwood Pond. Runoff from the street sub-basin and a
significant portion of what will be on-site Sub-basin 4 currently flow to this inlet, so runoff
entering Redwood Pond will not change substantially from current conditions. However, the
proposed interim detention basin will be sized as if runoff from Sub-basin 4 were being
captured by the on-site drainage system and detained in the proposed interim detention
basin.
There are several other sub-basins from which runoff is not captured directly by the on-site
drainage system, but which drains first to the perimeter street gutters, which flow to
proposed new street inlets, which will drain to the interim detention basin. There are four
on-site and two off-site SUb-basins that fall into this category, with runoff flows being
calculated at four design points. The piped storm drain system conveying the collected
runoff from the west side of Redwood St. also picks up runoff from one additional on-site
SUb-basin (Sub-basin 22) enroute to the detention basin.
Finally, there are two on-site sub-basins that shed runoff directly into the detention basin via
overland flow. The aggregate runoff from all the on-site and directly tributary off-site sub
basins is accounted for at the design point in the detention basin (D.P. 22)
Following is a summary of the calculated storm runoff for the proposed Aspen Heights
development.
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DRAINAGE DATA SUMMARY TABLE
SUB-BASIN DESIGN BASIN COMPo RUNOFF COEFF. DESIGN RUNOFF (cfs)
I.D. POINT AREA (ac) C 2 C100 (.h Q 100
Off-Site Basins
OS-1 2 1.020 0.78 0.98 1.44 6.31
OS-2 3 0.359 0.77 0.97 0.65 3.06
OS-3 16 1.044 0.74 0.93 1.57 7.24
OS-4 17 0.475 0.68 0.84 0.71 3.24
OS-5 21 0.598 0.77 0.96 1.10 5.27
DET'N BASIN 22 4.917 0.25 0.31 2.31 10.08
On-Site Basins
1 1 0.297 0.43 0.53 0.29 1.28
2 2 0.688 0.60 0.75 0.98 4.62
3 3 0.303 0.53 0.66 0.37 1.69
4 16 1.170 0.42 0.52 0.95 4.26
5 17 0.840 0.44 0.54 0.72 3.14
6 5a 0.583 0.68 0.85 1.13 4.95
7 6a 2.287 0.70 0.88 3.86 18.55
8 7 0.851 0.38 0.48 0.80 3.59
9 8 1.076 0.62 0.77 1.43 6.69
10 8 0.379 0.68 0.85 0.64 3.15
11 9 1.159 0.62 0.78 1.53 7.10
12 9 0.290 0.70 0.87 0.50 2.51
13 10 3.361 0.70 0.87 5.51 26.23
14 11 0.824 0.39 0.48 0.82 3.64
15 12 1.124 0.66 0.82 1.94 9.19
16 13 0.858 0.67 0.84 1.50 7.15
17 13 1.163 0.73 0.92 1.90 9.03
18 13 1.092 0.41 0.51 0.94 4.25
19 14 0.994 0.62 0.77 1.42 6.88
20 14 0.754 0.66 0.83 1.24 6.19
21 15 1.975 0.68 0.85 2.94 13.78
22 18 1.786 0.68 0.85 3.05 14.89
23 22 0.240 0.25 0.31 0.15 0.68
24 19 0.385 0.45 0.56 0.36 1.62
25 20 0.990 0.64 0.80 1.49 6.99
26 21 0.457 0.46 0.57 0.08 0.35
27 22 0.137 0.25 0.31 0.09 0.42
As stated earlier in Section III C of this report, design of the detention basin was conducted
using the Modified FAA Method, and an adjustment factor of 1.25 was applied to the
calculated required volume, pending confirmation of sizing using the SWMM model as the
design evolves. A design worksheet entitled "Required Detention Volume" is included in the
Attachments to this Report, presenting tabulations of the input data and the detention
capacity requirements analysis to accommodate the 100-yr storm event in the detention
basin.
The analysis indicates that the detention capacity required to attenuate the 100-yr storm,
assuming an allowable release rate equivalent to the rate of runoff due to a 2-yr storm event
impacting the undeveloped site, is 4.85 ac-ft. The additional detention capacity required to
provide for enhancement of water quality, the Water Quality Capture Volume (WQCV) is
calculated to be 0.53 ac-ft. Therefore, the aggregate detention capacity required for the
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interim detention basin to serve this development is calculated to be 5.38 ac-ft. A depth
capacity curve for the proposed interim detention basin is included in the Attachments to this
Report.
The low point of the floor of the interim detention basin has been set at an elevation of
4954.75 ft so that the detention basin will be above the groundwater table, and to allow
conveyance of the allowable discharge volume to the Lake Canal Irrigation Channel by
gravity. The worksheet entitled "Detention Basin Depth-Capacity Analysis" provides
tabulated and graphical representations of the detention capacity provided in the proposed
interim detention basin, as well as the water surface elevations at which each of the required
capacities is achieved. This worksheet indicates that the WQCV will be achieved at a water
surface elevation of 4956.40 ft, and that the water surface elevation for the attenuated 100
yr storm event will be 4958.89 ft. The minimum elevation of the crest of the impounding
berm along the south perimeter of the proposed interim detention basin is shown as 4960.0
ft, which provides a freeboard allowance in excess of the required 1.0 ft minimum.
The detention basin will include an Outlet Control Structure with appropriately sized orifices
to regulate the release of accumulated storm water from the facility. The maximum
allowable release rate from the detention basin was established by applying the calculated
historic equivalent runoff rate due to the impact of a 2-yr storm event on the undeveloped
site, multiplied by the developed area of the site. The maximum allowable unit rate of
release for the 100-yr storm event is calculated to be 0.33 cfs/ac. Multiplying this unit rate
by the developed area of the site yields a maximum allowable release rate from the interim
detention basin of 8.50 cfs.
The following table presents a summary of the detention capacities and water surface
elevations for the proposed interim detention basin.
DETENTION BASIN DATA SUMMARY
Required Water Quality Capture Volume (WQCV) 0.53 ac-ft
Required 1 OO-yr Storm Attenuation Volume 4.85 ac-ft
Required Aggregate Detention Volume 5.38 ac-ft
WQCV Water Surface Elevation 4,956.40 ft
Aggregate Water Surface Elevation 4,958.89 ft
The proposed configuration of the detention basin is presented on the drawings included in
the map pocket at the conclusion of this report.
While the primary functions of the detention facility will be the attenuation of storm flows and
improvement of storm water quality, prior to discharge from the site, the detention area will
be graded and landscaped such that it also serves as attractive site amenity area and
possible passive recreation area. No secondary use of the detention basin, however, will be
allowed to impede or impair the primary functions of storm water attenuation and water
quality enhancement.
C. STORM WATER QUALITY CONSIDERATIONS
Permanent water quality enhancement will be provided through the design of the outlet
control structure components of the detention facility, as addressed above.
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In addition, storm water quality and erosion control during construction will be addressed
through the application of Best Management Practices (BMPs), as recommended in Volume
III of the Urban Storm Drainage Criteria Manual (UDFCD, April 2008).
Throughout the course of construction and until such time as permanent drainage surfaces
and/or vegetation are established throughout the development, appropriate measures will be
implemented and maintained to minimize erosion and limit the transport and migration of
sediment. Silt fencing will be installed along the downstream perimeter of the site (south
and east), as well as around sub-sites or work areas within the site, as appropriate.
Temporary drainage swales will be established throughout the site, as necessary, to collect
and convey storm runoff from the work areas, and temporary sediment barriers (hay bales,
wattles, etc.) will be installed at regular intervals along the lengths of these swales to slow
the runoff flows and promote deposition of sediment and other suspended solids. The
anticipated locations of the temporary swales, as well as details of erosion control Best
Management Practices (BMP's) will be shown on the Erosion Control Plan, submitted as
part of the Final Compliance drawing set.
The permanent detention basin, which will have capacity to detain flows from the fully
developed site due to the 100-yr storm event, will be constructed at the outset of the project
and an interim construction sediment trap will be established in the detention basin.
Additional temporary sediment traps will also be established, as necessary, at appropriate
locations within the development site, to limit sediment transport from disturbed areas of the
site during construction.
All runoff from the disturbed portions of the site will be intercepted and directed to one of the
temporary sediment traps or the permanent detention basin, and discharge from these
facilities will be controlled. Accumulated sediments will be periodically removed from these
facilities and properly disposed of.
Permanent landscaping will be installed within the developed area, as soon as practicable,
and temporary revegetation or mulching will be implemented if there are any areas disturbed
by construction activities, but not scheduled for immediate implementation of development
improvements.
VI. CONCLUSIONS
A. COMPLIANCE WITH STANDARDS
The design of the storm water management improvements to serve the Aspen Heights
development is in compliance with the City of Fort Collins Storm Drainage Design Criteria
and Construction Standards, as well as Chapter 10 of the City of Fort Collins Municipal
Code. The criteria and recommendations of the Urban Storm Drainage Criteria Manual are
also reflected in the design of the drainage systems.
B. DRAINAGE CONCEPT
The proposed drainage improvements for the Aspen Heights development, including the
detention basin and outlet control works, will effectively protect the proposed development,
as well as downstream properties, from storm runoff, resulting in no adverse impacts from
the improvements proposed for this site. Development of the site, as proposed, should have
11
a beneficial impact on water quality in downstream drainage facilities and drainage ways by
reducing the rate of runoff from the site, compared to that from the existing previously
undeveloped property and by significantly delaying the initial discharge of runoff from the
site such that sediments and other potential pollutants typically carried by this first flush are
removed from the flow.
VII. REFERENCES
"City of Fort Collins Storm Drainage Design Criteria and Construction Standards" City of Fort
Collins, May 1984, March 1991 and January 1997
"City of Fort Collins Municipal Code", Chapter 10 - Flood Protection and Prevention City of
Fort Collins, 1987
"Urban Storm Drainage Criteria Manual", Volumes 1 & 2, UDFCD, April 2008
"Urban Storm Drainage Criteria Manual", Volume 3, UDFCD, April 2008
12
ATTACHMENTS
Hydrologic Soil Group-Larimer County Area, Colorado
(Aspen Heights Subdivision - Fort Collins, CO)
:'0
a
400 36'13" 400 36' 13"
400 35' SO" 400 35' SO"
Map Scale: 1:3,380 if printed on A size (8 .5" x 11") sheet.
A N o ~___"'!_30 ="====60 ~_-_________120 I1:-==:=:=:=========~Meters ~Feet 180
o 100 200 400 600
1?/14/?(111
Hydrologic Soil Group-Larimer County Area, Colorado
(Aspen Heights Subdivision - Fort Collins, CO)
MAP LEGEND MAP INFORMATION
Area o of Interest Area (AOI) of Interest (AOI) The Map soil Scale: surveys 1 :3,380 that if comprise printed on your A size AOI (8.were 5" x mapped 11") sheet. at 1 :24,000.
Solis
Soil Map Units Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil line
Soil o Ratings A
placement. The maps do not show the small areas of contrasting
o AJD soils that could have been shown at a more detailed scale.
OB o BID measurements. Please rely on the bar scale on each map sheet for accurate map
o C Source of Map: Natural Resources Conservation Service
o C/O Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov
o D This Coordinate product System: is generated UTM from Zone the 13N USDA-NAD83 NRCS certified data as of
Not rated or not available the version date(s) listed below.
Political Features Soil Survey Area: Larimer County Area, Colorado
o Cities Survey Area Data: Version 7, May 1, 2009
Water Features Date(s) aerial images were photographed: 8/6/2005
Streams and Canals The orthophoto or other base map on which the soil lines were
Transportation compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor shifting
+++ Rails
of map unit boundaries may be evident.
"...,. Interstate Highways
/'V' US Routes
Major Roads
.-'V Local Roads
USDA Natural Resources Web Soil Survey
'1iE Conservation Service National Cooperative Soil Survey Page 2 of4
12/14/2011
Hydrologic Soil Group-Larimer County Area, Colorado Aspen Heights Subdivision - Fort Collins, CO
Hydrologic Soil Group
Hydrologic Soil Group- Summary by Map Unit - Larimer County Area, Colorado (C0644)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
22 Caruso clay loam, 0 to 1
percent slope
C 3.5 8.2%
73 Nunn clay loam, 0 to 1
percent slope
C 39.0 91.8%
Totals for Area of Interest 42.4 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive precipitation
from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (ND, BID, and C/O). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly
wet. These consist mainly of deep, well drained to excessively drained sands or
gravelly sands. These soils have a high rate of water transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well drained
soils that have moderately fine texture to moderately coarse texture. These soils
have a moderate rate of water transmission.
Group C. Soils having 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.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a clay pan or clay layer
at or near the surface, and soils that are shallow over nearly impervious material.
These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (ND, BID, or C/O) , the first letter is
for drained areas and the second is for undrained areas. Only the soils that in their
natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
USDA Natural Resources Web Soil Survey 12/14/2011
=-=
Conservation Service National Cooperative Soil Survey Page 30f4
Hydrologic Soil Group-Larimer County Area, Colorado Aspen Heights Subdivision - Fort Collins, CO
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
= USDA Natural Conservation Resources Service National Web Cooperative Soil Survey Soil Survey Page 12/14/40f4 2011
s
EX CON IFER
« 0::
§I ZONE X
STREET
Z EX
1
DEVELOPMENT SITE
(Including NECCO
Detention Basin Site)
MAP SCALE 1" =500'
250 a 500 1000
I H H I I I FEET
:L E:i_ E3 - ~-I -
"';IIII !!!! II III! II!!IIL PANEL 0977G J
ili l ililill!i! il iilllil{ i
FIRM
FLOOD INSURANCE RATE MAP
LARIMER COUNTY,
COLORADO
AND I NCORPORATED AREAS
PANEL 977 OF 1420
(SEE MAP INDEX FOR FIRM PAN EL LAYOUT)
CONTAINS
COMMUNITY
lARIMER COUNTY
FORT COUINS, cnv OF
Nl.!M!!lli ~ ~
060101 09n G
080102 09n
Notice to U$sr: Th e Map Number shown below should be
used when ple.d~ mep orders; the Comm unity Number shown
above should be used on Insuf1!.nCl!! app ~ callons foT the subjec1
community.
MAP NUMBER
08069C0977G
MAP REVISED
JUNE 17,2008
Federal Em ergency Management Agency
This is an offici al copy of a portion
was extracted using F·M IT On·Une. This map does not reflect c hanges
or amendm ents w hic h m ay have been m ade s ubsequent to the date on the
title block. For the latest product information about N ati onal Fl ood Insurance
fl ood maDS c heck the FEMA Fl ood Map Store at WWN.
ASPEN HEIGHTS - FORT COLLINS
DRAINAGE BASIN COMPONENT AREA DATA
11/30/11
Basin I.D. Total Area Pavement Buildinqs Landscaped
(s.f. ) (ac) (s.f. ) (ac) (s.f.) (ac) (s.f.) (ac)
OS1 44,440 1.020 33822 0.776 0 0.000 10,618 0.244
OS2 15,619 0.359 11 658 0.268 0 0.000 3,961 0.091
OS3 45,465 1.044 31980 0.734 0 0.000 13,485 0.310
OS4 20,696 0.475 12576 0.289 0 0.000 8,120 0.186
OS5 26,034 0.598 19367 0.445 0 0.000 6,667 0.153
Det'n Basin 214185 4.917 0 0.000 0 0.000 214185 4.917
Off-Site Subtotal 366439 8.412 109403 2.512 0 0.000 257036 5.901
1 12,940 0.297 763 0.018 2,518 0.058 9,659 0.222
2 29,959 0.688 12012 0.276 3126 0.072 14,821 0.340
3 13,188 0.303 0 0.000 5,305 0.122 7,884 0.181
4 50,977 1.170 0 0.000 12252 0.281 38725 0.889
5 36598 0.840 2513 0.058 7210 0.166 26,875 0.617
6 25408 0.583 9,377 0.215 6299 0.145 9,732 0.223
7 99,629 2.287 37907 0.870 26225 0.602 35,497 0.815
8 37,083 0.851 0 0.000 7079 0.163 30,004 0.689
9 46,880 1.076 17764 0.408 6964 0.160 22,152 0.509
10 16,499 0.379 7496 0.172 2,676 0.061 6327 0.145
11 50,496 1.159 18247 0.419 8,583 0.197 23,666 0.543
12 12626 0.290 6528 0.150 1,531 0.035 4568 0.105
13 146,389 3.361 55,906 1.283 37690 0.865 52,793 1.212
14 35,904 0.824 0 0.000 6,969 0.160 28,935 0.664
15 48,961 1.124 19536 0.448 8,952 0.205 20,474 0.470
16 37,392 0.858 13483 0.310 8,942 0.205 14,968 0.344
17 50,649 1.163 24,225 0.556 10816 0.248 15,608 0.358
18 47,580 1.092 3,891 0.089 7,097 0.163 36593 0.840
19 43,301 0.994 11208 0.257 11,371 0.261 20,723 0.476
20 32,840 0.754 13096 0.301 6,316 0.145 13,428 0.308
21 86019 1.975 33011 0.758 19,853 0.456 33155 0.761
22 77,798 1.786 31 831 0.731 16,351 0.375 29,616 0.680
23 10468 0.240 0 0.000 0 0.000 10,468 0.240
24 16774 0.385 748 0.017 3,989 0.092 12038 0.276
25 43134 0.990 19390 0.445 4551 0.104 19,193 0.441
26 19,890 0.457 0 0.000 5,890 0.135 14,000 0.321
27 5974 0.137 0 0.000 0 0.000 5974 0.137
On-Site Subtotal 1 135356 26.064 338932 7.781 238551 5.476 557873 12.807
Trib Area Total 1,501,795 34.476 448,335 10.292 238,551 5.476 814,909 18.708
ASPEN HEIGHTS - FORT COLLINS
RUNOFF COEFFICIENTS & PERCENT IMPERVIOUSNESS
Rational Method Runoff Coefficients & % Imperviousness
Runoff Coeff % Imprerv.
Roof 0.95 90
Pavement 0.95 100
Landscaped 0.25 0
Basin I.D. Total Basin Bldg Footprint Pavement Landscaped Composite Composite
Area Area Area Area Runoff Coeff. % Imperv.
(ac) (acL (acl (ac)
OS-1 1.020 0.776 0.244 0.78 76.11
OS-2 0.359 0.268 0.091 0.77 74.64
OS-3 1.044 0.734 0.310 0.74 70.34
OS-4 0.475 0.289 0.186 0.68 60.77
OS-5 0.598 0.445 0.153 0.77 74.39
Det'n Basin 4.917 4.917 0.25 0.00
1 0.297 0.058 0.018 0.222 0.43 23.41
2 0.688 0.072 0.276 0.340 0.60 49.48
3 0.303 0.122 0.000 0.181 0.53 36.20
4 1.170 0.281 0.000 0.889 0.42 21 .63
5 0.840 0.166 0.058 0.617 0.44 24.60
6 0.583 0.145 0.215 0.223 0.68 59.22
7 2.287 0.602 0.870 0.815 0.70 61 .74
8 0.851 0.163 0.000 0.689 0.38 17.18
9 1.076 0.160 0.408 0.509 0.62 51 .26
10 0.379 0.061 0.172 0.145 0.68 60.03
11 1.159 0.197 0.419 0.543 0.62 51.43
12 0.290 0.035 0.150 0.105 0.70 62.61
13 3.361 0.865 1.283 1.212 0.70 61 .36
14 0.824 0.160 0.000 0.664 0.39 17.47
15 1.124 0.205 0.448 0.470 0.66 56.36
16 0.858 0.205 0.310 0.344 0.67 57.58
17 1.163 0.248 0.556 0.358 0.73 67.05
18 1.092 0.163 0.089 0.840 0.41 21 .60
19 0.994 0.261 0.257 0.476 0.62 49.52
20 0.754 0.145 0.301 0.308 0.66 57.19
21 1.975 0.456 0.758 0.761 0.68 59.15
22 1.786 0.375 0.731 0.680 0.68 59.83
23 0.240 0.000 0.000 0.240 0.25 0.00
24 0.385 0.092 0.017 0.276 0.45 25.86
25 0.990 0.104 0.445 0.441 0.64 54.45
26 0.457 0.135 0.000 0.321 0.46 26.65
27 0.137 0.000 0.000 0.137 0.25 0.00
On-site Tot. 26.064 5.476 7.781 12.807 0.61 48.76
Off-site Tot. 8.412 0.000 2.512 5.901 0.46 29.86
Trib Area Tot. 34.47e 5.476 10.292 18.708 0.57 44.15
ASPEN HEIGHTS - FORT COLLINS
Developable Portion of Site
Prepared by: ~
TImes of Concentration
2-yr Stonn Event
Date: 11/30/11
Frequency Adjustment Factoc 1.00
Sub-Basin Data
Basin Area Runoff Coeff LenQth
I.D. ae It
OS-1 1.020 0.78 30
OS-2 0.359 0.77 30
OS-3 1.044 0.74 30
OS-4 0.475 0.68 20
OS-5 0.598 0.77 40
1 0.297 0,43 15
2 0.688 0.60 41
3 0.303 0.53 48
4 1.170 0,42 60
5 0.840 0.44 76
6 0.583 0.68 45
7 2.287 0.70 48
8 0.851 0.38 67
9 1.076 0.62 52
10 0.379 0.68 72
11 1.159 0.62 50
12 0.290 0.70 75
13 3.361 0.70 48
14 0.824 0.39 30
15 1.124 0.66 48
16 0.858 0.67 48
17 1.163 0.73 51
18 1.092 0.41 56
19 0.994 0.62 98
20 0.754 0.66 78
21 1.975 0.68 46
22 1.786 0.68 52
23 0.240 0.25 30
24 0.385 0.45 15
25 0.990 0.64 50
26 0.457 0.46 70
27 0.137 0.25 20
Det'n Basin 4.917 0.25 55
Total 16.78
Initial I Over1and lime
Slope li
% min
2.0% 2.59
2.0% 2.67
2.0% 2.91
2.0% 2.83
2.0% 3.10
2.0% 3.87
2.0% 4.73
7.2% 3.84
5.8% 5.53
2.6% 7.90
2.0% 4.17
2.0% 4.12
25.0% 3.79
ASPEN HEIGHTS - FORT COLLINS
Developable Portion of Site
Prepared by: ~
Times of Concentration
1OO-yr Storm Event
Date: 11 /30/11
Frequency Adjustment Factor. 1.25
Sub·8asin Data Initiall Overland TIme Channel Travel TIme Te Check Final Te Remarks
Basin Area Ru noffCoeff Lenath Siooe TI Lenath Siooe Veloeitv Tt Como Te Tot. Lenath Te = U 180 .10
1.0. ae It % min It % fos min min It min min
OS-1 1.020 0.78 30 2.0% 0.99 1075 OAO% 1.20 14.93 15.92 1105 16.1 15.9
OS-2 0.359 0.77 30 2.0% 1.10 386 0.30% 1.10 5.85 6.94 416 12.3 6.9
OS-3 1.044 0.74 30 2.0% 1.40 790 0.50% 1.40 9.40 10.81 820 14.6 10.8
OS-4 OA75 0.68 20 2.0% 1.70 520 0.40% 1.20 7.22 8.92 540 13.0 8.9
OS-5 0.598 0.77 40 2.0% 1.29 470 0.60% 1.55 5.05 6.34 510 12.8 6.3
1 0.297 0.43 15 2.0% 3.26 370 0.30% 1.10 5.61 8.87 385 12.1 B.9
2 0.688 0.60 41 2.0% 3.29 254 0.40% 1.20 3.53 6.82 295 11.6 6.8
3 0.303 0.53 48 7.2% 2.94 324 0.30% 1.10 4.91 7.85 372 12.1 7.9
4 1.170 0.42 60 5.8% 4.68 680 0.50% 1.40 8.10 12.78 740 14.1 12.8
5 0.840 0.44 76 2.6% 6.60 520 0.40% 1.20 7.22 13.82 596 13.3 13.3
6 0.583 0.68 45 2.0% 2.47 97 2.00% 2.80 0.58 3.05 142 10.8 3.0
7 2.287 0.70 48 2.0% 2.31 382 0.70% 1.70 3.75 6.06 430 12.4 6.1
8 0.851 0.38 67 25.0% 3.28 265 0.40% 1.20 3.68 6.96 332 11.8 7.0
9 1.076 0.62 52 2.0% 3.50 595 0.80% 1.80 5.51 9.01 647 13.6 9.0
10 0.379 0.68 72 2.0% 3.13 255 1.00% 2.00 2.13 5.26 327 11.8 5.3
11 1.159 0.62 50 2.0% 3.39 623 0.70% 1.70 6.11 9.50 673 13.7 9.5
12 0.290 0.70 75 2.0% 2.95 236 1.00% 2.00 1.97 4.92 311 11.7 4.9
13 3.361 0.70 48 2.0% 2.35 495 0.83% 1.90 4.34 6.69 543 13.0 6.7
14 0.824 0.39 30 25.0% 2.19 282 0.35% 1.15 4.09 6.27 312 11 .7 6.3
15 1.124 0.66 48 2.0% 2.87 220 1.20% 2.10 1.75 4.62 268 11.5 4.6
16 0.858 0.67 48 2.0% 2.71 283 1.57% 2.40 1.97 4.67 331 11.8 4.7
17 1.163 0.73 51 2.0% 1.94 617 0.74% 1.75 5.88 7.81 668 13.7 7.8
18 1.092 0.41 56 2.0% 6.52 358 0.56% 1.50 3.98 10.50 414 12.3 10.5
19 0.994 0.62 98 2.0% 4.88 242 1.54% 2.40 1.68 6.56 340 11.9 6.6
20 0.754 0.66 78 2.0% 3.55 207 1.35% 2.20 1.57 5.12 285 11 .6 5.1
21 1.975 0.68 46 2.0% 2.52 611 0.70% 1.70 5.99 8.51 657 13.7 8.5
22 1.786 0.68 52 2.0% 2.63 306 0.84% 1.90 2.68 5.32 358 12.0 5.3
23 0.240 0.25 30 2.0% 6.42 0 0.00% 0.00 6.42 30 10.2 6,4
24 0.385 0,45 15 2.0% 3.11 538 0.37% 1.20 7.47 10.59 553 13.1 10.6
25 0.990 0.64 50 2.0% 3.18 420 0.83% 1.90 3.68 6.86 470 12.6 6.9
26 0.457 0.46 70 2.0% 6.58 320 0.60% 1.55 3.44 10.02 390 12.2 10.0
27 0.137 0.25 20 2.0% 5.24 0 0.00% 0.00 5.24 20 10.1 5.2
De!'n Basin 4.917 0.25 55 2.0% 8.69 815 0.40% 1.20 11 .32 20.01 870 14.8 14.8
Total 16.78
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City of Fort Collins
Rainfall Intensity~Duration-Frequency Table
for using the Rational Method
(5 minutes - 30 minutes)
Figure 3-1a
Duration
(minutes)
2-year
Intensity
(in/hr)
10-year
Intensity
(in/hr)
100-year
Intensity
(in/hr)
5.00 2.85 4.87 9.95
6.00 2.67 4 .56 9.31
7.00 2.52 4.31 8.80
8.00 2.40 4.10 8.38
9.00 2.30 3.93 8.03
10.00 2.21 3.78 7.72
11.00 2.13 3.63 7.42
12.00 2.05 3.50 7.16
13.00 1.98 3.39 6.92
14.00 1.92 3.29 6.71
15.00 1.87 3.19 6.52
16.00 1.81 3.08 6.30
17.00 1.75 2.99 6.10
18.00 1.70 2.90 5.92
19.00 1.65 2.82 5.75
20.00 1.61 2.74 5.60
21.00 1.56 2.67 5.46
22.00 1.53 2.61 5.32
23.00 1.49 2.55 5.20
24.00 1.46 2.49 5.09
25.00 1.43 2.44 4.98
26.00 1.40 2.39 4.87
27.00 1.37 2.34 4.78
28.00 1.34 2.29 4.69
29.00 1.32 2.25 4.60
30.00 1.30 2.21 4.52
ASPEN HEIGHTS - FORT COLLINS
Developable Portion of Site
ON-SITE STORM DRAINAGE SYSTEM DESIGN
(Rational Method Procedure)
2-YR STORM EVENT
Prepared by: ~ Dale --1.1GQ!1l
BaSin Desl n
1.0. Poi I
Conifer Inlets
1 1
OS-1
2 2
OS-2
3 3
Conifer Culv.
4
6 5a
5b
7 6a
6b
8 7
9
10 8
11
12 9a
9b
13 10
14 11
15 12
16
17
18 13
19
20 14
21 15
OS-3
4 16
OS-4
5 17
22 18
24 19
25 20
OS-5
26 21
23
27
DlrectRunoff
Sub-Basin Runoff Time of C-A Rainfall Design
"'ea Coeffic Concentr Intens Runoff
ao min ac inthr ct.
22.50
0.297 0.43 9.5 0.13 2.25 0.29
1.020 0.78 16.1 0.80 1.80 1.44
0.688 0.60 8.3 0.42 2.37 0.98
0.359 0.77 8.5 0.28 2.35 0.65
0.303 0.53 8.7 0.16 2.33 0.37
Cummulativ e Runo1'l' Channell Gutter Flow
Total Time Cumm. Rainfall Cumm. Channel FI...
of Conc. C' A lotens Runoff Slo Oe th
min ac inlhr '" % ft
ASPEN HEIGHTS - FORT COLLINS
Developable Portion of Site
ON-SITE STORM DRAINAGE SYSTEM DESIGN
(Rational Method Procedure)
100-YR STORM EVENT
Prepared by. ..bf.:2:...- Date: ~
Basin Desi n
I. Poinl
Con~er Inlets
1 1
OS-1
2 2
OS-2
3 3
CoMerCulv.
4
6 Sa
5b
7 6a
6b
8 7
9
10 8
11
12 9a
9b
13 10
14 11
15 12
16 ·
17
18 13
19
20 14
21 15
OS-3
4 16
OS-4
5 17
22 18
24 19
25 20
OS-5
26 21
23
27
Dern Basin 22
Direct R noff
ub-Basin Runoff Time 01 C -A Rainfall esl n
Area <>effie Concentr. Inlensi unoff
" "',
" inlhr ofs
78.99
0.297 0.43 8.9 0.13 8.07 1.28
1.020 0.78 15.9 0.80 6.32 6.31
0.688 0.60 6.8 0.42 8.90 4.62
0.359 077 6.9 0.28 8.85 3.06
0.303 0.53 7.9 0.16 8.42 1.69
ummulative Run ff Channel l
Total n mm. Rainfall C, Channel
N£a".o ?.a=L/A1/";,4~y ~'-~N ~P4er - E;P,eT StJl//f Ou77.::tcrr.
J 1.
Carryover_TO_B9A JUNCTION 50.56 50.56
-re;7~1
11ffe"-/
{ij'$k)
0.121
EG_Outlet_3 JUNCTION 0.00 72.06 o 01:09 0.000 2.683
EG Outlet 4 JUNCTION 0.00 72 . 07 o 01:09 0.000 2 . 683
EX_IN_205 JUNCTION 0.00 41.11 o 00 : 35 0.000 0.396
EX_IN_304 JUNCTION 0.00 24.73 o 00:35 0 . 000 0.230
EX IN 305 JUNCTION 0.00 54.43 o 00:35 0.000 0 . 545
EX_MH_112 JUNCTION 0.00 203.98 o 00:36 0.000 1.983
IN 803 JUNCTION 0.00 82 . 61 o 00 : 35 0.000 0.985
IN 804 JUNCTION 0.00 272.95 o 00:35 0.000 2.779
IN_80S JUNCTION 0.00 205.06 o 00:35 0 . 000 3 . 483
IN 810 JUNCTION 0.00 88.53 o 00:35 0 . 000 0.860
INLET_A5A JUNCTION 0 . 00 20.60 o 00 : 32 0.000 0.187
INLET A5B JUNCTION 0.00 44.32 o 00:32 0.000 0.410
INLET A6 JUNCTION 0.00 72.65 o 00:35 0 . 000 0.671
INLET_A7A JUNCTION 0 . 00 14.78 o 00 : 35 0 . 000 0.140
INLET_A7B JUNCTION 0.00 14 . 68 o 00;35 0.000 0.140
INLET_A8A JUNCTION 0.00 24.39 o 00:35 0.000 0 . 234
INLET_A8B JUNCTION 0.00 11.89 o 00:35 0 . 000 0.112
INLET_A9A JUNCTION o . 00 50.13 o 00:35 0.000 0.486
INLET_A9B JUNCTION 0.00 23 . 74 o 00:35 0.000 0.233
INLET_B10A JUNCTION 0.00 44.00 o 00:33 0 . 000 0 . 771
INLET_BlOB JUNCTION 0.00 25.85 o 00:34 0 . 000 0.243
INLET_B4A JUNCTION o .00 61. 34 o 00:34 0.000 0.360
INLET_B4B JUNCTION 0 . 00 33.51 o 00:35 0.000 0 . 313
INLET_B5A JUNCTION 0.00 38.14 o 00 : 35 0.000 0.367
INLET_B6A JUNCTION 0.00 18.71 000:35 0.000 0.201
INLET_B7A JUNCTION 0.00 25.67 o 00:34 0 . 000 0.239
INLET B8A
INLET B9A
INLET B9B
INLET C3A
JUNCTION
JUNCTION
JUNCTION
JUNCTION
0 . 00
0 . 00
0.00
0.00
11.77
~
~
59.74
o 00:34
o 00:35
o 00:34
o 00:35
0.000
0.000
0.000
0.000
0.110 /,.,;'L.er-:s,Q7 ,;kJLJT# £A!C;;
0.212L Of'? ~U£. S'?R(jc£ ;p,e.
0.201/ ;;Jo."<7'"H Or t:o,vlr£:e 'ST
OWEN
CONSULTING
GROUP, INC.
DESIGN WORKSHEET
Client:
Project:
Task:
Breckenridge Land Acquisition, LP
As~en Heights - Fort Collins
Detention Requirements Analysis
Job No.:
By:
Checked:
Page:
11-358
LCO
1
Date:
Date:
of:
11/30/11
3
For purposes of this Preliminary Design Report, the required capacity of the Interim
Detention Basin will be determined using the Modified FAA Method. The capacity derived via
the Modified FAA Method is based upon the area tributary to the basin, the composite runoff
coefficient of the tributary area, the time of concentration of tributary flow, the one-hour 100-yr
rainfall depth for the area, and the maximum allowable rate of release from the basin. For this
project, the detention basin is to be designed to capture and detain runoff from the 1 OO-yr storm
event and the maximum allowable release rate is to be equivalent to the runoff from the
undeveloped tributary area due to the 2-yr storm event.
Historic Runoff Analysis
For purposes of determining the allowable rate of release from the detention basin, the
historic rate of runoff will be calculated based on the area of the development site that would
currently be tributary to the proposed Interim Detention Basin. This tributary area excludes the
off-site street areas, since they do not currently drain to the location of the Interim Detention
Basin, as well as the portion of the site that is south of the proposed location of Vine Drive and
at a lower elevation than the proposed Interim Detention Basin.
• Tributary area:
• A = 26.06 acres
• Average slope of the development site:
• Swest = 0.4% +1- (west of the N-S drainage ditch)
• Seast = 0.6% +1- (east fo the N-S drainage ditch)
• Time of Concentration:
• Assuming overland flow on nearly bare ground and using Fig. RO-1 from the Urban
Drainage Criteria Manual:
• Tc (west) =665' 10.6 (60) =18.5 mins
• Tc (east) =945' 10.75 (60) =20.9 mins
• Rainfall Intensity:
• Based on T c (west) = 1.68 inlhr
• Based on Tc (east) =1.57 inlhr
• Average 2-yr rainfall intensity 12 =1.63 in/hr.
DRAINAGE CRITERIA MANUAL (V. 1)
50
30
~ 20
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Client: Breckenridge Land Acquisition, LP Job No.: 11-358
Project: Aspen Heights - Fort Collins Date: 11/30/11
Task: Detention Requirements Analysis Page: 2 of 3
• Design 2-yr Runoff:
• Q2= CI2A = 0.2(1.63)(26.06) = 8.50 cfs
=0.33 cfs/ac
Required Detention Capacity
The capacity required for attenuation of runoff due to the 100-yr storm event, is based on
the Modified FAA Method.
• Basic required detention volume V100 = 3.88 ac-ft (See spreadsheet following)
• Adjustment factor for Modified FAA Method = 1.25
• Adjusted attenuation volume = 4.85 ac-ft
Water Quality Capture Volume
In addition to attenuation of storm flows, the detention basin is also designed to provide
water quality enhancement, particularly of the initial runoff flows. Per the UDFCD criteria, the
detention capacity that is required for water quality enhancement (the water quality capture
volume or "WQCV') is calculated as follows:
• WQCV = A*R /12, where R is a function of the composite % imperviousness of the site.
• I = 48.76% i = 0.4876
• R =0.91 i3-1.19i2+0.78i
=0.203 in
• WQCV = 26.06 * 0.203/ 12
= 0.44 ac-ft
• Allowing 20% increase for sedimentation, results in total required volume =0.53 ac-ft
Aggregate Detention Capacity
The aggregate required detention capacity is the sum of the storm attenuation volume and
the water quality capture volume. In this case, the aggregate required detention volume
amounts to 4.85 + 0.53 = 5.38 ac-ft.
Available Detention Capacity
The interim detention basin is sized to provide the required aggregate detention volume,
plus provide a freeboard allowance of a minimum of 1.0 feet above the 100-yr water surface
elevation. The following worksheet presents a tabular and graphic demonstration of the depth
capacity relationship of the proposed interim detention basin.
Outlet Control Structure and Discharge Piping
An outlet control structure will be constructed within the detention basin to regulate the rate
of release of accumulated stormwater runoff to the Lake Canal Irrigation Channel. The outlet
control structure will be designed in the Final Compliance phase of the project, in accordance
Client: Breckenridge Land Acquisition, LP Job No.: 11-358
Project: Aspen Heights - Fort Collins Date: 11/30/11
Task: Detention Requirements Analysis Page: 30f3
with the requirements of the City of Fort Collins Storm Drainage Design Criteria and
Construction Standards.
Basin Designation 11/30/11
Tributary Area (acres)
Composite Runoff Coefficient
Time of Concentration (mins)
Max. Allowable Release Rate (cfs/ac)
One-hour rainfall depth (inches)
ASPEN HEIGHTS - FORT COLLINS
Required Detention Volume
Modified FAA Method
Preliminary Basin Sizing
Interim Basin
26.06
0.61
13.80
0.33
2.86
Storm Rainfall Cum. Inflow Outflow AverClg"e Cum. Outflow Required Required
Duration Intensity Volume Adi . Factor Outflow Rate Volume Storaqe Vol. Storaqe Vol.
(min) (in/hr) (cu.ft1 (cfSL (cu.ftl (cu.ft.) (ac-ft)
5 9.70 46,262 1.00 8.60 2580 43683 1.003
10 7.74 73,800 1.00 8.60 5,160 68640 1.576
15 6.49 92892 0.96 8.26 7,430 85,461 1.962
20 5.63 107320 0.85 7.27 8720 98,599 2.264
25 4.98 118842 0.78 6.67 10,010 108832 2.498
30 4.49 128,401 0.73 6.28 11300 117 101 2.688
35 4.09 136556 0.70 6.00 12590 123965 2.846
40 3.77 143660 0.67 5.78 13,880 129780 2.979
45 3.49 149,953 0.65 5.62 15,170 134 782 3.094
50 3.26 155600 0.64 5.49 16460 139,140 3.194
55 3.06 160723 0.63 5.38 17,750 142,973 3.282
60 2.89 165413 0.62 5.29 19040 146373 3.360
65 2.74 169739 0.61 5.21 20,330 149409 3.430
70 2.60 173,754 0.60 5.15 21620 152,134 3.493
75 2.48 177,502 0.59 5.09 22,910 154593 3.549
80 2.37 181018 0.59 5.04 24,200 156818 3.600
85 2.27 184329 0.58 5.00 25490 158,840 3.646
90 2.18 187460 0.58 4.96 26,780 160680 3.689
95 2.10 190430 0.57 4.92 28,070 162360 3.727
100 2.03 193255 0.57 4.89 29360 163,896 3.763
105 1.96 195951 0.57 4.87 30650 165,301 3."795
110 1.89 198,528 0.56 4.84 31940 166589 3.824
115 1.83 200999 0.56 4.82 33,230 167769 3.851
120 1.78 203,371 0.56 4.79 34,520 168,851 3.876
DETENTION BASIN DEPTH-CAPACITY ANALYSIS
Project No.:
Project Name:
Basin 1.0.:
11-358
Aspen Heights - Fort Collins
Interim Detention Basin
Date: 11/30/11
Contour Plan Depth Volume Cummulative
Elevation Area Interval Increment Volume
(amsl) (s.f.) (ft) (c.f. ) (c.f.) (ac-ft)
4954.75 10 0.00 0.00 0.00 0.000
4955.00 512 0.25 49.46 49.46 0.001
4956.00 20349 1.00 8029.60 8079.06 0.185
4957.00 58573 1.00 37815.31 45894.37 1.054
4958.00 101 114 1.00 78881 .70 124776.08 2.864
4959.00 147131 1.00 123405.44 248181 .52 5.697
4960.00 166810 1.00 156867.60 405049.12 9.299
" ,...,...
g
o s:::
:;:::;
> nI
..!!!
w ...
o ~
-o s:::
o
2.000 4.000 6.000 8.000 10.000
"Ti:.. lV " I . VV
~vvv I,....'''... ,vv ...,....
,...,..,... ,...,...
,&>JV.vv
,..... ,.." ,...,...
',h.JU.VV
,......... ""7,...,...
"Tvv 11"\1:"1"I ' .,vv ...,... /
'vvv. vv If
..... ,..,.. ,...,...
'V>J>J . vv
, ..... ,... A ,...,...
"Ti:lv"T. VV
-2.000 0.000
---~ ----~
~
~~
Detention Volume (ac-ft)
- The required aggregate detention volume of 5.38 ac-ft for the 1 OO-yr storm attenuation plus WQCV
is satisfied at a water surface elev'n of: 4958.89
- The required detention volume of 0.53 ac-ft for the WQCV is satified at a water
surface elev'n of: 4956.40
DRAWINGS
, 'I )J, 'j i, I
? j--- -I ' \;~ I SEeO!D
FIGURE RO-1
Estimate of Average Overland Flow Velocity for Use With the Rational Formula
RUNOFF
06/2001 RO-13
Urban Drainage and Flood Control District
0.659
INLET C4A JUNCTION 0 . 00 12.48 o 00:33 0.000 0.094
INLET_C4B JUNCTION 0.00 26.71 o 00:35 0.000 0 . 325
INLET C6A JUNCTION 0.00 14.50 o 00:32 0.000 0.103
INLET_C6B JUNCTION 0.00 10.68 o 00:35 0 . 000 0.103
I~
\. . ', )
.~
INLET E21
INLET_E2A
INLET E2B
{ J_912 1
J10
JUNCTION
JUNCTION
JUNCTION
JUNCTION
JUNCTION
0 . 00
0.00
0.00
0.00
0 . 00
48.03
17.84
35 . 93
\132 . 14)
107.44
o 00:35
o 00 : 34
o 00 : 35
o 00:55
o 00:36
0 . 000
0.000
0.000
0 . 000
0.000
0.478
0 . 165
0.385
9.910- /,JPCoW 7"'0 ",1-5 CH,Qrlfl/l£
3 . 480 ,C',et::I"f C:::.rJ,PEte sr.
J11 JUNCTION 0 . 00 25.65 o 00 : 36 0.000 2.714 c2dL- VtEP?7=S·
J2 JUNCTION 0.00 5.01 o 03 : 06 0.000 1.440
J3 JUNCTION 0.00 5.01 o 03:14 0 . 000 1. 438
J4 JUNCTION 0 . 00 10.73 o 00:36 0.000 1.515
J5 JUNCTION 0.00 62.48 o 00:35 0.000 2 . 078
J6 JUNCTION 0 . 00 9 . 71 o 00:22 0.000 1 . 745
J7 JUNCTION 0 . 00 62.15 o 00:35 0.000 2.635
J8 JUNCTION 0.00 78.50 o 00:36 0 . 000 3.048
J9 JUNCTION 0 . 00 25.22 o 00:38 0 . 000 2 . 700
JUNCTION C2C JUNCTION 0.00 46.39 o 00:34 0.000 1.139
JUNCTION C2E JUNCTION 0.00 39.35 o 00 : 32 0.000 1 . 036
Link_209+280 JUNCTION 0.00 23.05 o 02:01 0.000 3 . 238
MH 101 JUNCTION 0 . 00 135.24 o 00:35 0 . 000 1.449
MH 112 JUNCTION 0.00 175.54 o 00:36 0.000 0.932
MH 400 JUNCTION 0.00 78.52 o 00 : 33 0.000 1 . 018
MH 401 JUNCTION 0.00 165 .. 03 o 00:33 0.000 1.437
MH 500 · JUNCTION 0.00 20.30 o 00:58 0.000 3.620
MH 501 JUNCTION 0 . 00 20.30 o 00:58 0.000 3.620
MH 502 JUNCTION 0.00 20 . 29 o 00:59 0.000 3 .620
. MH 503 JUNCTION 0.00 20.29 o 01:12 0 . 000 3.620
MH 600 JUNCTION 0.00 11.35 o 07:26 0 . 000 3.438
MH 604 JUNCTION 0 . 00 309.07 o 00:35 0.000 7.046
MH 700 JUNCTION 0.00 1 2 7 . 74 o 00:51 0.000 9.540
MH_701 JUNCTION 0.00 132 . 88 o 00 : 51 0 . 000 9.840
MH_913a JUNCTION 0.00 124.58 o 00:35 0.000 1.363
MH 914b JUNCTION 0 . 00 98.25 o 00:35 0.000 1 . 162
MH Al JUNCTION 0.00 379 . 67 o 00:59 0 . 000 48 . 359
·MH AID JUNCTION 0.00 130 . 21 o 02 : 15 0.000 20 . 906
MH A2 JUNCTION 0.00 375.73 o 00:56 0.000 48.056
MH A2A JUNCTION 0.00 12.05 o 05:19 0.000 3.338
MH A2B JUNCTION 0.00 80. 4 7 o 00:34 0.000 4.008
f (Cone. "", C-so A Intansi inlhr ds , ff Sio % e
8.9 0.13 8.07 80.27
15.9 1.21 8.90 13.50 0.30%
18.2 1.65 5.89 12.16
Design Flow into Surface Channel at Con~er SI. (NECCO Report) 132 .14
144.30 0.30%
0.583 0.68 3.0 OAO 9.95 4.95 3.0 0.40 9.95 4.95
18.3 2.05 5.87 226.17 0.30%
2.287 0.70 6.1 160 9.26 18.55 6.1 1.60 9.26 18.55
18.7 3.65 5.80 237 .61 0.30%
0.851 0.38 7.0 0.33 8.80 3.59 19.1 3.98 5.74 239.67
1.076 0.62 9.0 0.67 8.03 6.69
0.379 0.68 5.3 0.26 9.76 3.15 9.0 0.92 8.03 9.28
1.159 0.62 9.5 0.72 7.88 7.10
0.290 0.70 4.9 0.20 9.95 2.51 9.1 1.85 8.00 18,47
19.4 5.83 5.69 252.57 0.30%
3.361 0.70 6.7 2.34 8.95 26.23 6.7 2.34 8.95 26.23
0.824 0.39 6.3 0.32 9.16 3.64 20.6 8.49 5.28 267.15
1.124 0.66 4.6 0.74 9.95 9.19 4.6 0.74 9.95 9.19
0.858 0.67 4.7 0.57 9.95 7.15
1.163 0.73 7.8 0.85 8.46 9.03
1.092 0.41 10.5 0,45 7.57 4.25 10.5 2.62 7.57 24.76
0.994 0.62 6.6 0.61 9.00 6.88
0.754 0.66 5.1 0.50 9.89 6.19 10.6 3.73 7.54 35.15
1.975 0.68 8.5 1.34 8.21 13.78 11 .6 5.07 7.26 46.03
1044 0.74 10.8 0.77 7.46 7.24
1.170 0.42 12.8 0.49 6.97 4.26 12.8 1.26 6.97 11 .02
0,475 0.68 8.9 0.32 8.07 3.24
0.840 0.44 13.3 0.37 6.86 3.14 13.3 0.69 6.86 5.89
1.786 0.68 5.3 122 9.76 14.89 13.8 1.91 6.75 16.10
0.385 0.45 10.6 0.17 7.54 1.62 10.6 0.17 7.54 1.62 0.67%
0.990 0.84 6.9 0.63 8.85 6.99 11.2 0.80 7.37 7.41 0.67%
0.598 0.77 6.3 0,46 9.16 5.27
0.457 0.08 10.0 0.04 7.72 0.35 13.1 1.30 7.72 12.56 0.67%
0.240 0.25 6.4 0.06 9.11 0.68
0.137 0.25 5.2 0.03 9.82 0.42
4.917 0.25 14.8 1.23 6.56 10.08 20.6 19.36 5.28 338.89
Max allowable release rate from detention basin 8.50
I I I I
r Flow Pioe Flow Trovel Time
F ow si n ,eipe Pi e i L.. Velocity Tim
D. • th Flow ofs Slo % Si m C•• lofsl • Ifps mm
80.27 0.38 38 x60 89.08 525 8.08 108
0.59 388 2.82 2.29
12.16 2.00 18 14.85 44 9.41 0.08
1.88 92 3.38 0.45
4.95 0.90 18 9.96 102 5.64 0.30
2.39 108 3.85 0,47
18.55 2.80 24 37.82 80 12 .04 0.11
2A5 95 3.90 0.41
239.67 0.30 3@34x53 140 9.00 0.26
9.28 1.00 18 10.50 30 6.18 0.08
18,47 6.50 18 26.77 34 16.21 0.03
2.53 287 3.97 1.20
26.23 2.09 24 32.67 95 20.71 0.08
Discharge from channel into detention basin
9.19 0.50 24 15.98 300 9.22 0.54
24.76 0.50 30 28.99 30 4.63 0.11
35.15 0.30 36 36.48 348 5.93 0.98
46.03 0.50 36 47 .09 56 5.63 0.17
11 .02 1.50 18 12.86 112 8.22 0.23
5.89 0.40 18 6.84 126 4.25 0,49
1610 0.70 24 18.91 34 11.99 0.05
0.29 100 2.57 0.66
0.44 372 3,40 1.82
0.51 12.56 1.00 30 41 .00 75 11 .35 0.11
Total design runoff tributary to the Interim Detention Basin
I I I
8.50 0.31 I 18 PVC I 7.63 976 I 0.52 31.41
I I I
Notes:
~design runoff entenng the system via the Conifer St. inlets (Inlets S9A and 898 on Blue Spruce Dr. Just north of Conifer st.) Is derived from the 10o..yr design runoff attributed to
these inlets In the EPA SWMM Hydraulic
Modeling output data Included in the NECCO Preliminary Design Report. Copies of the applicable output data pages from the NECCO Report are aHached for reference.
2. The design runoff entering the system via Conifer St. culverts (3 - 30" dla. RCP culverts crossing Conifer St. and discharging inlo the north-south drainage ditch traversing the development
site) is derived from the 10Q..yr runon
attributed to these culverts (Node J.912) In the EPA SVVMM Hydraulic Modeling output data included In the NECCO Preliminary Design Report
9.5 0.13 2.25 22.79
16.1 1.21 1.80 2.18 0.30% 0.35
19.4 1.65 1.64 2.71
Design Flow into Surface Channel at Conifer SI. (NECCO Report) 34.71
37.42 0.30% 0.90
0.583 0.68 4.8 0.40 2.85 1.13 4.8 0.40 2.85 1.13
19.5 2.05 1.63 60.55 0.30% 1.18
2.287 0.70 7.9 1.60 2.41 3.86 7.9 1.60 2.41 3.86
20.2 3.65 1.60 63.05 0.30% 1.21
0.851 0.38 7.5 0.33 2.46 0.80 20.8 3.98 1.57 63.46
1.076 0.62 10.7 0.67 2.15 1.43
0.379 0.68 7.4 0.26 2.47 0.64 10.7 0.92 2.15 1.99
1.159 0.62 11.1 0.72 2.12 1.53
0.290 0.70 7.2 0.20 2.50 0.50 11 .1 1.85 1.53 2.83
21 .1 5.83 1.56 66.30 0.30% 1.24
3.361 0.70 8.5 2.34 2.35 5.51 8.5 2.34 2.35 5.51
0.824 0.39 6.6 0.32 2.58 0.82 22.9 8.49 1.49 69.86
1.124 0.66 6.3 0.74 2.63 1.94 6.3 0.74 2.63 1.94
0.858 0.67 6.4 0.57 2.61 1.50
1.163 0.73 9.8 0.85 2.23 1.90
1.092 0.41 11 .6 0.45 2.08 0.94 11 .6 2.62 2.08 5.44
0.994 0.62 8.8 0.61 2.32 1.42
0.754 0.66 7.3 0.50 2.48 1.24 11 .8 3.73 2.07 7.72
1.975 0.68 10.2 1.34 2.19 2.94 13.2 5.07 1.97 9.99
1.044 0.74 12.3 0.77 2.03 1.57
1.170 0.42 13.6 0.49 1.94 0.95 13.6 1.26 1.94 2.45
0.475 0.68 10.0 0.32 2.21 0.71
0.840 0.44 13.3 0.37 1.96 0.72 13.3 0.69 1.96 1.35
1.786 0.68 7.2 1.22 2.50 3.05 14.0 1.91 1.92 3.66
0.385 0.45 11.2 0.17 211 0.36 11 .2 0.17 2.11 0.36 0.67% 0.17
0.990 0.64 8.5 0.63 2.35 1.49 12.0 0.80 2.05 1.65 0.67% 0.29
0.598 0.77 8.2 0.46 2.38 1.10
0.457 0.08 11.4 0.04 2.10 0.08 14.3 1.30 1.91 2.49 0.67% 0.29
0.240 0.25 6.9 0.06 2.54 0.15
0.137 0.25 5.7 0.03 2.72 0.09
p; Fk>w TravelTime
Desl n p; Pipe
p; Len Veloci Time
Flow Sio Size Ca ,;
cis % in '" ft fool min
22 .79 0.38 38 x 60 89.08 525 5.59 1.56
388 1.97 3.28
2.71 2.00 18 14.85 44 6.39 0.11
92 2.23 0.69
1.13 0.90 18 9.96 102 3.72 0.46
108 2.60 0.69
3.86 2.80 24 37.82 80 7.82 0.17
95 2.64 0.60
63.46 0.30 3@34x53 140 7.14 0.33
1.99 1.00 18 10.50 30 4.58 0.11
2.83 6.50 18 26.77 34 9.70 0.06
287 2.68 1.78
5.51 2.09 24 32.67 95 13.87 0.11
Discharge from channel into detention basin
1.94 0.50 24 15.98 300 6.15 0.81
5.44 0.50 30 28.99 30 3.16 0.16
7.72 0.30 36 36.48 348 4.08 1.42
9.99 0.50 36 47.09 56 3.82 0.24
2.45 1.50 18 12.86 112 5.53 0.34
1.35 0.40 1S 6.84 126 2.97 0.71
3.66 0.70 24 18.91 34 8.35 0.07
100 2.13 0.78
372 2.71 2.29
2.49 1.00 30 41.00 75 7.05 0.18
Dern Basin 22 4.917 0.25 14.8 1.23 1.88 2.31 22.9 19.36 1.49 86.05 Total design runoff tributary to the Interim Detention Basin
I
I
Notes:
1. The design runoff entering the system via the Conifer St. inlets (Inlets BgA and 89B on Blue Spruce Dr. just north of Conifer St.) is an estimate derived as a representative percentage
of the 100-yr design runoff attributed to the
same inlets in the EPASWMM Hydraulic Modeling output data included in the NECCO Preliminary Design Report. Copies of the applicable output data pages from the NECCO Report are attached
for reference.
2. The design runoff entering the system viaConifer St. culverts (3 . 30" dia. RCP culverts crossing Conifer St. and discharging into the north·south drainage ditch traversing the development
Site) is an estimate derived as a
represnlative percentage olthe 100-yr runoff attributed to these culverts (Node J.912) in the EPA SVYMM Hydraulic Modeling output data included in the NECCO Preliminary Design Report.
2.0% 5.16
2.0% 5.28
2.0% 5.03
2.0% 5.19
2.0% 4.15
25.0% 2.53
2.0% 4.56
2.0% 4.43
2.0% 3.89
2.0% 7.66
2.0% 7.14
2.0% 5.73
2.0% 4.24
2.0% 4.47
2.0% 6.93
2.0% 3.76
2.0% 4.85
2.0% 8.00
2.0% 5.66
2.0% 9.38
Channel T ravel lime
LenQth Slope VeiociIY
It % Ips
1075 0.40% 1.20
386 0.30% 1.10
790 0.50% 1,40
520 0,40% 1.20
470 0.60% 1.55
370 0.30% 1.10
254 0,40% 1.20
324 0.30% 1.10
680 0.50% 1,40
520 0.40% 1.20
97 2.00% 2.80
382 0.70% 1.70
265 0.40% 1.20
595 0.80% 1.80
255 1.00% 2.00
623 0.70% 1.70
236 1.00% 2.00
495 0.83% 1.90
282 0.35% 1.15
220 1.20% 2.10
283 1.57% 2.40
617 0.74% 1.75
358 0.56% 1.50
242 1.54% 2.40
207 1.35% 2.20
611 0.70% 1.70
306 0.84% 1.90
0 0.00% 0.00
538 0.37% 1.20
420 0.83% 1.90
320 0.60% 1.55
0 0.00% 0.00
815 0.40% 1.20
-
TeCheck Final Te Remarks
Tt CompTe Toi. Length Te - U180}+1D
min min It min min
14.93 17.52 1105 16.1 16.1
5.85 8.52 416 12.3 8.5
9,40 12.32 820 14.6 12.3
7.22 10.05 540 13.0 10.0
5.05 8.15 510 12.8 8.2
5.61 9,48 385 12.1 9.5
3.53 8.26 295 11.6 8.3
4.91 8.75 372 12.1 8.7
8.10 13.62 740 14.1 13.6
7.22 15.12 596 13.3 13.3
0.58 4.75 142 10.8 4.8
3.75 7.86 430 12.4 7.9
3.68 7,47 332 11 .8 7.5
5.51 10.67 647 13.6 10.7
2.13 7.41 327 11.8 7,4
6.11 11 .14 673 13.7 11.1
1.97 7.16 311 11.7 7.2
4.34 8,49 543 13.0 8.5
4.09 6.62 312 11.7 6.6
1.75 6.31 268 11.5 6.3
1.97 6,40 331 11.8 6,4
5.88 9.76 668 13.7 9.8
3.98 11.64 414 12.3 11 .6
1.68 8.82 340 11 .9 8.8
1.57 7.30 285 11.6 7.3
5.99 10.23 657 13.7 10.2
2.68 7.15 358 12.0 7.2
6.93 30 10.2 6.9
7.47 11.23 553 13.1 11.2
3.68 8.54 470 12.6 8.5
3.44 11,44 390 12.2 11.4
5.66 20 10.1 5.7
11.32 20.70 870 14.8 14.8