HomeMy WebLinkAboutDrainage Reports - 04/22/1984STORM WATER DRAINAGE REPORT
FOR
STUART STREET MEDICAL PARK
A PLANNED MEDICAL PARK
IN THE
CITY OF FORT COLLINS, COLORADO
APRIL 1984
L
� TARANTO, STANTON & TAGGE
CONSULTING ENGINEERS
9::..i�iON FORT COLLINS, COLORADO
• TAGGF
1
April 5, 1984
Re: Stuart Street Medical Park
Drainage Report
Job No.: 84-175-005
1
City of Fort Collins
300 LaPorte Avenue
Fort Collins, CO 80521
Attn: Planning Department
Enclosed is the Drainage Report for Stuart Street Medical Park, for your
review and approval.
Exhibit "C" shows the routing for the 2-year and 100-year developed storm
which is in accordance with the City of Fort Collins "STORM DRAINAGE DESIGN
CRITERIA"
A variance of the storm water detention requirement has been applied for
' and approved for the previous P.U.D. in April of 1981, and November of
1983. Enclosed please find a letter re -applying for this variance. This
variance will allow us to direct storm water directly to Spring Creek.
If you have any questions concerning this report, please feel free to
contac our office.
Res tfully s 'tted,
ry �
•• STER •.
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Donald N. TaranyP•E•
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CONSULTING ING ' ;:
Enclosures
LLO/DNT:ses
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TARANTO, STANTON & TAGGE
Consulting Engineers
748 Whalers Way - Building D - Fort Collins, CO 80525
(303) 226,0557 - Metro Denver Number '3031 595-9103
' April 5, 1983
' Re: Request for Variance of Storm
Water Detention Requirements -
Stuart Street Medical Park
' Job No.: 84-175-005
City of Fort Collins
' Drainage Department
300 LaPorte Avenue
Fort Collins, CO 80521
Attn: Mr. Phil Waite
Dear Phil:
As requested by Mr. Mauri Rupel of the City of Fort Collins, we are
re -applying for a variance of the storm water detention requirement. As
outlined in the previous letter, dated April 3, 1981, and November 4, 1983,
due to the proximity of the site, we are requesting a variance for on -site
detention. We feel that due to the location of the release point to Spring
' Creek, as is shown by the enclosed storm water drainage report, the storm
runoff will peak ahead of the storm in Spring Creek.
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Stuart
stmmary, we are requesting a variance of the City of Fort Collins storm
detention requirements, thus allowing us to direct runoff frcan
Street Medical Park directly to Spring Creek. Your cooperation on
woulg be greatly appreciated.
__ 5467
Donald N. Tara$to•;AP.E. '. *'
TARANTO, STANTC .15r�'*GGE 6.'do O
CDNSULTING ENG"Wo�orvq�
Enclosure "Ooil11110t`
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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
TABLE OF CONTRh`TS
I. INTRODUCTION
II. AREA OF STUDY
III. DESIGN CRITERIA
IV. PROPOSED STORM DRAINAGE SYSTEM
V. CONCLUSIONS AND RECONIl`=ATIONS
LIST OF EXHIBITS
EXHIBIT "A" AREA OF STUDY
EXHIBIT "B" RAINFALL INMiSITY CURVE
EXHIBIT "C" PROPOSED STORM DRA-ILNAGE SYS11 4
DRAINAGE REPORT FOR STUART STREET MEDICAL PARK
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 Stuart Street Medical
Park, a Planned Medical Park.
The site is proposed for five (5) medical use buildings. The existing
building on the southwest corner of the project will be removed to
allow construction of the commercial building.
The site will include improvements to East Stuart Street for asphalt,
curb, gutter, and four -foot walk. LeMay Avenue, which borders the
site on the west, is complete at this time. However, we plan to
install a one-way exit from the site on to LeMay Avenue for doctors'
use only. The total developed area includes 4.25 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. Design Calculations
' II. AREA OF STUDY
Exhibit "A" shows the project under consideration. Stuart Street
Medical Park is bordered on the west by LeMay Avenue, on the south by
' East Stuart Street, and on the north and east by existing Santana
Apartments. More particularly, the site is located in the Northwest
' Quarter of Section 19, Township 7 North, Range 68 West of the Sixth
Principal Meridian, Fort Collins, Colorado.
'
Due Historic layout there is
to the topographic of the project site,
no offsite drainage considered contributary to the project. The
'
improvements to East Stuart Street and improved LEVay Avenue intercept
flows and directs them to the east and north, respectively.
Historic drainage for the site, as is illustrated by Exhibit "C",
'
travels north and northeasterly into the existing Santanna Apartments
development. Due to the proposed improvements to the site, storm
runoff will be collected in the parking areas and drives using curb
'
and gutter and transported to the Northwest Corner of the site. A
storm sewer will then transport these flows to Spring Creek. Due to
'
landscape improvements along Stuart Street and Lemay Avenue, some.
runoff cannot be caught by the site and will be transported by
existing drainage facilities in Stuart Street, LeMay Avenue, and
Santanna Apartments.
'
The existing topographical layout of the site shows the flat, slightly
rolling portion of the property in the Southwest Corner of the
'
property with the remainder of the property averaging between 5 and 8%
in slope.
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EXHIBIT A
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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, (4.23
ac. ) 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 = Ma;:imum peak runoff in cubic feet per second. (c.f.s.).
C = Runoff coefficient in inches per hour. "C" is the
ratio between the maximLmi 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 r_
Planned Business
0.75 uJ�
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 times of concentration
'
for runoff, each surface was
evaluated. For example, when flows
were overland (lawns), a "C"
value of 0.20 was used. When flows
t
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 0.75 was used in the Rational Method
'
formula.
Q = CiACf
Rainfall intensities were based on the intensity curves as shown in
Exhibit "B".
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C
' IV. PROPOSED STORM DRAINAGE SYSTEM
' The proposed drainage plan for the site is shown on Exhibit "C".
The entire site has been reduced to major drainage basins "A" through
'
D . Due to the development of the site, Basins "A", B , and C
will not transport drainage flows to the point of release in the
northwest corner of the project. Basin "D" will contribute flows to
' the inlet in the Northwest Corner of the site. The impact of
directing flows from basin "B" onto Stuart Street will be minimal.
Two year and 100 year runoff figures are shown in the attached
' calculations.
The 2-year and 100-year storm water flays are shown by the flow
arrows. Both 100-year and 2-year developed flows will pass through
' the storm water inlet. These flows will be transported by a storm
sewer to Spring Creek.
' Anticipating approval of the storm water detention variance, the site
does not provide detention facilities. we feel the storm water can be
' conveyed this small distance without causing problems with existing
drainage facilities or posing a threat to adjacent property owners. .
' As can be seen by the flow arrows, the parking and drives have been
' overlotted to channel water in the direction the site can most
adequately handle them. Construction of vertical curb and gutter will
transport flows to the point of release in the Northwest Corner of the
site.
' As previously mentioned, there is no offsite drainage to be
considered. LeMay Avenue and East Stuart Street act as interceptors
to channel any storm flows.
1
' As can be seen in reviewing Exhibit "C", the overall grading and
drainage plan uses the historic layout of the property as its
fundamental concept. All flows generated by the developed site are
collected along the north property line and transported to the west.
UI
we feel the additional flows generated by the developed conditions
should not impact any adjacent property owner or Spring Creek, should
the 100-year storm occur. .
Attached as part of this storm water drainage report are the drainage
calculations necessary to develop the 100-year and 2-year flows. In
addition, any storm water appurtenances which were necessary to carry
these flows will be sized to adequately handle the flows intended to
pass through than. This sizing has been included as part of the
calculations in Appendix "A".
V.
CONCLUSIONS AND RECOHVEENDATIONS
Due to the proposed use of the area, an abundant amount of driving and
parking areas have been provided. By using these items for drainage
conveyance, we are able to provide a safe and efficient means of
transporting storm water flows from the project. To prevent any
.excessive erosion due to overland flow and to better control runoff,
curbing has been provided.
We feel the drainage questions of this project, both on -site and
off -site, have beer. answered. By providing the vertical curb and
gutter sections along East Stuart Street, we have met City standards
for continuity in improvements between existing and proposed
developments and have filled in an inccn plete portion of the Citys'
storm drainage system.
If there are any questions regarding the storm water drainage report
prepared for Stuart Street Medical Park, please feel free to contact
our office.
We will await vour review and caTunents.
APPE xTDTk "till
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