HomeMy WebLinkAboutDrainage Reports - 02/21/1996i
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December 21, 191
Mr. Ward Stanford
City of Fort Collins
Engineering Department
28 l, North College Avenue
P.O. Box 580
Fort Collins, CO 80522-0580
Re: Paragon Point P. U.D. - Phase Five, Stormwater Drainage Supplemental
Project No. 10-695-025
Dear Ward:
During the final review of the Paragon Point P.U.D. - Phase Five construction plans, concerns
were brought to my attention regarding the storm drainage runoff from Trilby Road impacting
the Phase Five project. TST, Inc. Consulting Engineers has evaluated the possible effects of the
storm drainage flow from Trilby Road onto the Phase Five property in the present condition and
also in the future condition (widening of Trilby Road).
TST, Inc. performed a hydrologic analyses of the two conditions. Included in this analysis was
the following:
1. Existing storm drainage runoff from the centerline of Trilby Road to the proposed
drainage swale on the south side of the project.
2. Future storm drainage runoff from the widening and improved Trilby Road. Verifying
that the flow will not overtop the curb and encroach onto the project site.
3. Future storm drainage runoff from the right of way (back of sidewalk) to the proposed
drainage swale.
The following are results of the analyses and supporting documentation is attached at the end of
this report.
The storm drainage runoff from Trilby Road for the existing condition was not included as part
of the Final Drainage Report for Paragon Point P.U.D. - Phase Five due to a proposed retaining
wall which prevented the flow from encroaching onto the property. Final revisions were made
to the design and the retaining wall was removed. As a result of the removal of the retaining
wall, it was overlooked that the drainage from Trilby Road would now encroach onto the
property. An analyses was performed determining what the 100-year flow would be onto the
site.
TST INC. 748 Whalers Way - Building D
102 Inverness Terrace East
Fart Collins,80525
suitelo5
Consulting En
$ Engineers (303) 226-055757
Englewood CO 80112
Metro Denver (303) 595-9103
(303)792-0557
Fax (303) 226-0204
Fax (303) 792-9489
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TST, INC.
December 21, 1995
Mr. Ward Stanford
Page Two of Two
Using information from the Final Drainage Report and using the Rational Method to calculate
the volume of runoff from Trilby Road, it was determined that an additional 1.96 cfs would be
added to the drainage swale to the south. Calculations were performed to determine if the
proposed drainage swale would carry the additional flow. The additional flow raised the 100-
year water surface of the swale from 0.9 feet to 1.16 feet. The 133-year water surface was
calculated to be 1.29 feet, to determine the required freeboard of 0.13 feet. The total depth of
the proposed swale is 2.0 feet, providing a freeboard of 0.84 feet. Thus, the proposed Swale is
designed sufficiently to carry the additional runoff from Trilby Road.
Future storm drainage runoff from the widening of Trilby Road was also analyzed. The peak
runoff for the 100-year storm was calculated to be 2.60 cfs. The 100-year theoretical street
capacity (flow limited to top of curb) was determined to be 12.20 cfs. Therefore, the 100-year
runoff from the widening of Trilby Road will not overtop the curb and will not encroach onto
the Phase Five property.
Additionally, the future storm drainage runoff from a narrow strip between the north right of way
of Trilby Road and the proposed swale was also analyzed to determine what impact it would have
on the proposed swale. The 100-year peak runoff was calculated to be 0.11 cfs. The proposed
swale is designed adequately to carry this minimal amount of additional runoff.
In summary, the storm drainage flow from Trilby Road (existing and future conditions) flowing
onto the Phase Five property will be carried by the proposed swale without any adverse affects.
Thank you for your time in reviewing this report. Please contact me should you have any
questions or require further information.
Respectfully Submitted,
TST, INC. CONSULTING ENGINEERS
Sharlene A. adowen, P.E.
SAS/lg
Enclosures
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INPUT DATA:
DISCHARGE _
BOTTOM WIDTH =
BED SLOPE _
SIDE SLOPE _
MANNINGS N =
RESULTS:
NORMAL DEPTH =
FLOW VELOCITY =
HYDR. DEPTH =
TOP WIDTH =
FROUDE NUMBER =
SPECIFIC ENERGY=
INPUT DATA:
DISCHARGE _
BOTTOM WIDTH =
BED SLOPE _
SIDE SLOPE _
MANNINGS N =
RESULTS:
NORMAL DEPTH =
FLOW VELOCITY =
HYDR. DEPTH =
TOP WIDTH =
FROUDE NUMBER =
SPECIFIC ENERGY=
4.760000 CFS ------ 100-year
0.000000E+00 FT
5.000000E-03 FT/FT
3.000000
6.000000E-02
1.161168 FT
1.176630 FPS
5.806583E-01 FT
6.967010 FT
2.721145E-01
1.182666 FT
6.330000 CFS
0.000000E+00 FT
5.000000E-03 FT/FT
3.000000
6.000000E-02
1.292174 FT
1.263574 FPS
6.461462E-01 FT
7.753042 FT
2.770176E-01
1.316966 FT
133-year
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