HomeMy WebLinkAboutREPLAT OF PARAGON POINT PUD PHASE FIVE - 48 91M - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTTST
Mr. Basil Hamden
City of Fort Collins
Stormwater Department
PO Box 850
Fort Collins, CO 80522
Re: Paragon Point P. U.D. - Phase Five
Project No. 10-891-000
Dear Mr. Hamden,
January 26, 1999
We are pleased to submit this letter summarizing our evaluation of the hydrological analysis of Paragon
Point P.U.D. - Phase Five. Phase Five is bounded by Paragon Point Phase Four to the North, Lemay
Avenue to the West, Trilby Road to the South and open space to the East.
The proposed site was analyzed by Lidstone and Anderson, Inc. in the "Final Drainage Report for the
Paragon Point P.U.D. - Phase Five". Due to the fact that building pad footprints have changed slightly
since the Drainage Report was approved on November 11, 1995, we have readjusted the basin delineation
to accurately match the new building pad footprint. The revised basin delineation can be found on the
Grading, Drainage and Erosion Control Plan accompanying this letter.
The rational method was used to reevaluate peak runoff from the revised subbasins, which is consistent
with the methodology used in the L/A report. Flow lengths, slopes and the composite runoff coefficients
did not change from L/A analysis. However, due to the building pad footprints changing the basin areas
changed slightly. These areas were not estimated but were calculated based on the proposed footprints
using the area routine in AutoCAD 14. The revised hydrologic calculations are submitted in Table I
accompanying this letter for your review.
Though the basin areas changed slightly, the overall area of the project did not, Thus, not increasing the
overall stormwater runoff for the site or the direction of the stormwater to the stormwater conveyance
systems. For this reason we feel that a revised analysis of the detention facilities is unnecessary and should
not be required.
Accompanying this letter are L/A hydrologic calculations, TST, Inc. hydrologic calculations, revised basin
delineations on the Grading, Drainage and Erosion Control Plan. We believe this evaluation should satisfy
your requirements. We look forward to your review and comments. If you have any questions please feel
free to contact us.
Sincerely,
TST, INC. CONSULTING ENGINEERS
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Enclosures
TST, INC.
Consulting Engineers
748 Whalers Way — Building D
Fort Collins, CO 80525
(970) 226-0557
Metro Denver (303) 595-9103
Fax (970) 226.0204
102 Inverness Terrace East
Suite 105
Englewood, CO 80112
(303) 792-0557
Fax (303) 792-9489
TABLE 1. HYDROLOGIC CALCULATIONS WORKSHEET
BASIN
SUB
BASIN
DESIGN
POINT
AREA
(Ac.)
COMPOSITE
12UNOFF COEFF.
C
OVERLAND:
FLOW
LENGTH
(ft)
AVERAGE
OVERLAND
SLOPE
(%)
OVERLAND
TRAVEL TINIE
Ti
2-yr (min)
OVERLAND
TRAVEL TINIE
Ti
100-yr (min)
GUTTER
FLOW
LENGTH
(ft)
AVERAGE
GUTTER
SLOPE
(%)
A
A
1
0.75
0.69
35
2.00
3.60
2.10
475
0.50
B
B
2
1.08
0.41
50
2.00
5.30
4.50
700
0.50
C
Gl
3
0.84
0.80
50
2.00
3.10
0.60
350
0.50
C2
3
0.33
0.77
50
2.00
3.50
1.40
150
0.50
D
D
4
0.76
0.46
100
10.00
5.60
4.60
0
0.00
TST, INC.
CONSULTING 1/22/98
ENGINEERS 101hydro.als
TABLE 1. HYDROLOGIC CALCULATIONS WORKSHEET
BASIN
SUB
BASIN
DESIGN
POINT
GUTTER
FLOW
VELOCITY
(fps)
GUTTER
TRAVELTINIE
Tt
(min)
TIME OF
CONCENTRATION
Tc
2-yr (min)
TIME OF
CONCENTRATION
Tc
100-Vr (min)
RAINFALL INTENSITY
I I
2-yr 100-yr
(in/hr) (irt/hr)
PEAK DISCHARGE
Q Q
2-yr 100-yr
(cfs) (cfs)
A
A
1
1.50
5.28
8.90
7.40
2.6
7.0
1.3
4.5
B
B
2
1.10
10.61
15.90
15.10
2.1
6.0
0.9
3.3
C
C l
3
1.50
3.90
7.00
5.00
2.9
7.0
1.9
5.9
C2
3
1.50
1.70
5.20
5.00
3.2
7.0
0.8
2.2
D
D
4
0.00
0.00
5.60
4.60
3.2
7.0
1.1
3.1
TST, INC.
CONSULTING 1 /22/98
ENGINEERS 101 hydro.als
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