HomeMy WebLinkAboutDrainage Reports - 10/09/1984STORM WATER DRAINAGE REPORT
FOR
COURTNEY PARK P.U.D.
FOR
JLB CONSTRUCTION
IN THE
CITY OF FORT COLLINS, COLORADO
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OCTOBER 1984
TARANTO, STANTON $c TAGGE
CONSULTING ENGINEERS
FORT COLI. INS , C O L O H A D O
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' October 5, 1984
Re: Courtney Park P.U.D. Drainage
■ Report
' Job No. 84-310-054
City of Fort Collins
' 300 LaPorte Avenue
Ft. Collins, CO 80521
' Attn: Planning Department
Enclosed is the Final Drainage Report for Courtney Park, P.U.D., for
' your review and approval.
Exhibit "C" shows the proposed routing for the 2-year and 100-year
developed storm which is in accordance with the City of Fort Collins "STORM
' DRAINAGE DESIGN CRITERIA".
This Final Storm Water Drainage Study is in accordance with the
' over-all Drainage Study prepared for the Master Plan entitled Golden
Meadows a Planned Unit Development. If you have any questions concerning
this report please do not hesitate to contact our office.
' Sincerely�1111111IItplIjU�i
�N 0 REG, V//
' Rick TMYO 00
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TARANTO ° °
' CONSULT Il IINEERRS o 4
Enclosures �oi���r��®��`�•
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TARANTO, STANTON & TAGGE
Consulting Engineers
748 Whalers Way • Building D • Fort Collins, CO 80525
' (303) 226-0557 • Metro Denver Number (303) 595-9103
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I. INTRODUCTION
II. AREA OF STUDY
III. DESIGN CRITERIA
IV. PROPOSED STORM DRAINAGE SYSTEM
V. CONCLUSIONS AND RECOMMENDATIONS
LIST OF EXHIBITS
EXHIBIT "A" AREA OF STUDY
EXHIBIT "B" RAINFALL INTENSITY CURVE
IMTJ3IT "C" PROPOSED STORM DRAINAGE SYSTEM
FINAL DRAINAGE REPORT FOR COURTNEY PARK P.U.D.
FORT COLLINS, COLORADO
I. INTRODUCTION
The purpose of this report is to outline the method of conveyance and
disposal of storm water runoff for the proposed Courtney Park P.U.D.,
a Multi -Family Planned Unit Development.
The site is planned for thirteen apartment buildings comprising;248
units. As amenities the site offers, pool and club house facilities
located approximately in the center of the proposed development.
As part of an agreement between the developer and the original owner
of the site LeMay Avenue will be improved. This will not be a part of
the subdivision agreement between the City of Fort Collins and the
Developer. In addition, improvements to Wheaton Drive, to the North
will be completed prior to construction of any units on this project.
The total developed area includes 14.07 acres.
Items to be covered in this report are as follows:
1. Area of Study
2. Design Criteria
3. Proposed Storm Drainage System
4. Conclusions and Recommendations
5. Preliminary Design Calculations
II. AREA OF STUDY
Exhibit "A" shows the project under consideration. Courtney Park
P.U.D. is bordered on the north by Wheaton Drive, on the east by
Golden Meadows fifth filing on the south by East Harmony Road and on
the west by South LeMay Avenue. An adjacent development to Courtney
Park are Wood Brother's Homes to the west and Medema's third and forth
filings to the north. The developer is J.L.B. Construction.
Off -site historic drainage contributory to Courtney Park is
negligible. The improvements to LeMay Avenue and Wheaton Drive
intercept flows coming from the north and the west and route them away
from the site.
The site historically breaks in approximately the northern third of
the acreage and drains to the northeast and the southeast
respectfully. Flows going to the northeast will eventually dump onto
Wheaton Drive and became part of the Golden Meadows storm sewer which
outlets into a 100 year storm reservoir on the south side of Harmony
Road. The runoff exiting from the southeast will traverse easterly to
the same release point through a system of drainage swales and culvert
encompassed in an 80 foot drainage easement platted throughout Golden
Meadows Master Plan. The site is generally lower than the adjacent
street (South Le4ay Avenue, East Harmony Road) and should require some
earthwork to drain the site in the developed condition.
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III. DESIGN CRITERIA
The design criteria for this study was based upon the Denver Regional
Council of Government's "Urban Storm Drainage Manual". Because the
overall drainage basin area of the site was less than 200 acres, the
Rational Method can be used to evaluate flows from the site for the
two (2) year and one hundred (100) year storm for both developed and
undeveloped conditions. The Rational Method relates runoff to
rainfall intensities by the following formula:
Q = CiACf
Where:
Q = Maximum peak runoff in cubic feet per second (c.f.s.).
C = Runoff coefficient in inches per hour. "C" is the ratio
between the maximum rate of runoff from the area and the
average rate of rainfall intensities for the period of
maximum rainfall of given frequency of occurrence having
a duration equal to the time of concentration (Tc).
i = Average rainfall intensities in inches per hour for a
duration equal to the time of concentration. The time
of concentration is the time required for water to flow
from the most remote point of the basin to the point of
interest.
Cf = Frequency factor which is used to account for
antecedent precipitation conditions. To be used when
determining runoff from storms that occur less
frequently than once in ten (10) years.
Recurrence Interval Cf
(Years)
2 to 10
1.00
25
1.10
50
1.20
100
1.25
The runoff coefficients used in these calculations were an adjusted
value which reflects the degree of imperviousness or perviousness.
' The coefficient reflects the effects of infiltration, detention,
' storage, evaporation, retention, flow routing and interception.
Recommended values of "C" values for various descriptions of land use
were provided by the City of Fort Collins Storm Drainage Design
Criteria. Those used are as follows:
' Description of Area Runoff Coefficients
Multi -Family Use 0.60
Asphalt Paving 0.95
' Unimproved Areas 0.20
Lawns (slope greater
than or equal to 2%) 0.25
' NOTE: For the "C" value to be used to determine the time of concentration
' for runoff, each surface was evaluated. For example, when flaws
were overland (lawns), a "C" value of 0.20 was used. When flows
were routed through streets, a "C" value of 0.95 was used. To
' evaluate the peak rate of runoff for the developed conditions, a
composite "C" factor of 0.55 was used in the Rational Method
formula.
4 = CiACf
' Rainfall intensities were based on the intensity curves as shown in
Exhibit "B".
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IV. PROPOSED STORM DRAINAGE SYSTEM
The drainage plan for the site is shown on Exhibit "C"in the folders
at the back of this report.
The entire site has been reduced to drainage basins "A", "B", "C",
' "D", and "E". Basins "A" and "E" will not contribute to the detention
volume required for the site. Due to the landscaping or to the
' natural layout of the site these flows cannot be caught by the
proprosed storm drainage system. These flows will flow to either the
' east, north or west emptying onto South IelAay Avenue or Wheaton Drive
or offsite, respectfully. This basin area equals 2.0 acres for basin
"A" and 0.40 acres for basin "E". Flows generated in the developed
' condition equal 2.55 cfs and 0.64 cfs for basins A and E respectively.
Basin "D", area equal to 6.00 acres drains to detention pond C in the
southeast corner of the site. Basin "B", area equal to 4.5 acres
' drains to detention pond A of the site and basin "C" area equal to
1.10 acres drains to detention pond "B" in the northeast part of the
' site.
The two year and 100 year storm flows are shown by the flow arrows.
Both the 100 year and two year developed flows will pass through the
same system of collection co plete with curb and gutter to direct
' flows to the detention areas. The criteria to be used to size the
ponds and the outlets will be to detain the difference between the 100
' year developed storm and the two year historic storm. As can be seen
in the reviewing exhibit "C", the overall grading and drainage plan
uses the historic layout of the property as the fundamental grading
concept. All flows generated by the developed basin will be collected
and transported to the detention ponds in the respective areas.
' Culverts then pass these flows to the curbs of which have sufficient
capacity to adequately handle the additional amount.
' Attached as part of this final storm water drainage report are the
' supporting drainage I calculations necessary to develop the 100 year
' and 2 year flows. Any storm water appurtenances including storm
sewers, drainage channels, and detention ponds will be adequately
sized to handle the flows intended to pass through them. This
exercise will be done as part of the final development drawings
' submitted as part of this final storm water drainage report.
V. CONCLUSIONS AND RDC0b2MMATIONS
Due to the proposed use of the area, adequate asphalt and curb and
gutter sections have been provided. By using these appurtenances for
' drainage conveyance, we are able to provide a safe and efficient means
of transporting storm water flows from the developed areas on site
' through the project into the detention areas. Eventually, these flows
will join flows previously considered by other developments as part of
' the master plan of Golden Meadows.
' We feel the drainage questions of this site, both on -site and
off -site, have been considered. We have met or exceeded City
standards for continuity in improvements between existing and proposed
' storm water drainage systems.
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DETENTION POND C
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HARMONY ROAD
1. BENCH MARK CITY OF FORT COLLINS BLACK BOLT SURVEY, HYDRANT NO. P-9-M,
LOCATED NORTHWEST CORNER OF HARMONY K LEMAY, NORTH BOMET ELEVATION • 499O.5O
2. INTERIOR WALKS SHOWN ON THIS DRAWING ARE FOR CONCEPTUAL 115E ONLY, FOR EXACT
DETAIL, DIMENSIONS, AND LOCATION OF WALKS SEE ARCHITECTUAL SITE PLAN.
SIDEWALKS ON ADJACENT STREETS SHALL CONFORM TO CURRENT CITY OF FORT COLLINS
STANDARDS.
3. SYM01 F.F. REPRESENTS FINISHED FLUOR ELEVATIONS.
A. REFER TO ARCNITECTUAL LANDSCAPE PLAN FOR COORDINATION OF SITE GRADING WITH
PROJECT BENMING AND LANDSCAPE.
5. THE DEVELOPER OR COURTNEY PARK APT. ASSOCIATION SHALL BE RESPONSIBLE FOR
MAINTENANCE OF THE DRAINAGE FACILITIES: UNLESS NOTED OTHERWISE.
SPECIAL NOTE:
'cMnrAe/ Section See
Rvvn9 Lb lei/ Shf.
Or in P.' a 1CF0"e
e SeOfti're Gooding
sht.
C
REVISIONS
_ GESCR. _
BY__OATE -
DRAWN RPw__ _ DESIGNED QW O(LE OCrS /9_!H
STANTON & TAGGE
7p
DESCRTARANTO
Br_onrE
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CONSULTING ENGINEERS
COURTNEY PARK P_U.D.
EXHIBIT C
rE3
BY_ OATE_-DescR. ___. _._
SCALE ART RRP vxolBCT xo.B[9/ooS9
g� FORT COLLIN9 COLO. HOLDREGE. NEER.
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