HomeMy WebLinkAboutU-4 ODP & MODIFICATION OF STANDARDS - 37-00 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT3�3
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U-4 LLC. Project #v1961
Preliminary Detention Calculations
9/13/00
C
Cf
COMPOSITE
C
T�
INTENSITY
100-year
Storm
(in./hr.)
AREA
(Ac.)
INFLOW
(cfs)
POND
VOLUME
(ft')
ALLOWABLE
OUTFLOW
(cfs)
ALLOWABLE
VOLUME
RELEASE
(ft)
REQUIRED
DETENTION
VOLUME
(Ac-ft)
0.70
1.25
0.88
5
9.95
2.7
23.5069
7052.063
2.34
702
0.146
0.70
1.25
0.88
10
7.72
2.7
18.2385
10943.1
2.34
1404
0.219
0.70
1.25
0.88
15
6.52
2.7
15.4035
13863.15
2.34
2106
0.270
0.70
1.25
0.88
20
5.6
2.7
13.23
15876
2.34
2808
0.300
0.70
1.25
0.88
25
4.98
2.7
11.7653
17647.88
2.34
3510
0.325
0.701
1.251
0.88 1
30 1
4.52 1
2.7 1
10.6785 1
19221.3 1
2.34 1
4212 1
0.345
0.70
1.25
0.88
35
4.08
2.7
9.639
20241.9
2.34
4914
0.352
0.70
1.25
0.88
40
3.74
2.7
8.83575
21205.8
2.34
5616
0.358
0.70
1.25
0.88
45
3.46
2.7
8.17425
22070.48
2.34
6318
0.362
0.70
1.25
0.88
50
3.23
2.7
7.63088
22892.63
2.34
7020
0.364
0.70
1.25
0.88
55
3.03
2.7
7.15838
23622.64
2.34
7722
0.365
0.70
1.25
0.88
60
2.86
2.7
6.75675
24324.3
2.34
8424
0.365
0.70
1.25
0.88
65
2.78
2.7
6.56775
25614.23
2.34
9126
0.379
0.70
1.25
0.88
70
2.6
2.7
6.1425
25798.5
2.34
9828
0.367
0.70
1.25
0.88
75
2.42
2.7
5.71725
25727.63
2.34
10530
0.349
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use = D 70
Q = 6 bq _ (0. 70) (1- 2 42. 70) = 2,3 c
13
EXHIBIT C
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EXHIBIT B
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EXHIBIT A
jIntroduction
This report is the result of a conceptual drainage evaluation for the proposed U-4 LLC
development. Preliminary drainage calculations were performed to determine the
project site's required detention pond volume for the 100-year storm event, releasing at
the historic 2-year storm discharge.
Proiect Location and Description
The U-4 LLC project proposes construction of 4 multi -family residences, comprised of 12
units each, located at the Northeast corner of North Shields Street and West Vine Drive.
The project parcel consists of 2 lots, Lot 1 is 83,492 ft2 and Lot 2 is 34,230 ft2. Lot 1 will
be the site of the apartments; Lot 2 will serve as a location of ingress and egress.
This site is located in Section 2, Township 7 North, Range 69 West of the West Principal
Meridian, Larimer County, Fort Collins, Colorado. This site is bounded on the north by
Arthur Ditch, on the west by North Shields Street and a gas station, on the south by
West Vine Drive and a gas station, on the east by Larimer County single-family
residences. A location map is provided in Exhibit A.
Existing Conditions and Proposed Drainage Improvements
The site has been investigated to analyze the existing drainage patterns. The property
currently slopes to Arthur Ditch, however at the request of the City of Fort Collins, storm
water shall be diverted elsewhere, as to reduce discharge to the ditch. Two options
have been developed to reroute the storm water. Option #1 involves draining the site
northward to the Cache La Poudre River, bypassing the Arthur Ditch. Option #2
considers directing discharge easterly from the site, down West Vine Drive to the swale
along Wood Street.
West Vine's 100-year floodplain encroaches on the U-4 LLC site. Compensatory
storage, if deemed necessary, will be provided at the rate of 150% of the fill volume
placed below the 100-year floodplain elevation. This will ensure that there will be no
increase in the established floodplain elevation. As requested by the City of Fort Collins,
a HEC-2 analysis shall be performed to illustrate the stability of the recorded floodplain
elevation post -construction. A floodplain map is illustrated in Exhibit B.
Detention Pond Analysis
Utilizing the Rational Method, post -construction storm water conditions were determined.
Calculations generated the anticipated detention volume required, based upon a 100-
year storm event, releasing at the existing 2-year storm event discharge. It has beeri
concluded that approximately 0.38 Ac.-ft of storage will have to been provided for this
development. The calculations and tables are included in Exhibit C.
September 13, 2000
Mr. Troy W. Jones; City Planner
City of Fort Collins
Community Planning. and Environmental Services
281 North College Avenue
Fort Collins, Colorado'80522 r`
Re: U-4 LLC Development
Affordable Housing Apartments
Our Project No. 1961
Dear Mr. Jones:
As requested,, enclosed are four. copies of the Conceptual Overall Drainage
Report for the proposed .U-4 LLC development. This report details the project
location, existing and proposed drainage conditions, -detention pond analysis and
supplemental exhibits:
If you have any questions or comments concerning our conceptual study, please
feel free to contact our office at your convenience.
Very truly yours,
JIM SELL DESIGN
Melinda E. Fadz Lester Crawford, P.E.
Enclosure
MEF/mf -
153 WEST MOUNTAIN AVENUE FORT COLLINS. COLORA00 80524 970 484 1921 FAX: 970 484 2443 E-MAIL: JIMSELLCFRII.COM