HomeMy WebLinkAboutDrainage Reports - 09/10/1988Engineering Consultants
2900 South College Avenue
Fort Collins, Colorado 80525
303/226-4955
September 9, 1988
Ms. Susan Hayes
City of Fort Collins
P.O. Box 580
Fort Collins, Colorado 80522
RE: FINAL DRAINAGE REPORT FOR THE SEVENTH FILING OF
OAKRIDGE VILLAGE P.U.D., REVISED
Dear Susan:
This Seventh Filing of Oakridge Village P.U.D. is located north of
Keenland Drive and east of McMurray Drive in southeast Fort Collins,
Colorado. The 7th Filing is bordered on the north, east and south by
the regional pond for the area. More specifically this site is lo-
cated in Section 6, Township 6 North, Range 68 West of the 6th Prin-
cipal Meridian.
This site exists as a cultivated field with some graded areas as-
sociated with the construction of the Oakridge regional pond. Drainage
study references for this site include; the McClellands Basin Master
Plan, June 20, 1986 by Greenhorn and O'Mara, Inc.; the Final Drainage
Report for Oakridge Village P.U.D., Filing 2, July 3, 1986, by RBD,
Inc. Engineering Consultants; Drainage Report for the Oakridge Village
P.U.D. Filings 3,4 and 5, April 1987 by RBD Inc. Engineering
Consultants; and the draft Final Drainage Investigation for Oakridge
Business Park, May 17, 1987, by James H. Stewart and Associates, Inc.
The report by Stewart and Associates covered the Business Park or ap-
proximately the north half of the Oakridge Development. The report
identified areas with onsite detention and the release rate that could
drain from the areas during a 100-year storm, shown on the following
key map. The report also created two additional regional detention
ponds for drainage of the business park area. These ponds are.
referred to as the west pond and middle pond by the above report and
are shown on the following key map.
The reports by RBD, Inc. covered the Oakridge Village Filings, the
Com hear Site, and a limited portion of the Oakridge Business Park.
Other Offices: Vail, Colorado 303/476-6340 • Colorado Springs, Colorado 303/574-3504
This area is comprised of some filings which were not required to
detain (ie. Oakridge Village Filings 1&2) and areas which are detained
principally in the Oakridge Regional Pond.
This report proposes two changes to the approach taken in the above
reports. The first change concerns the proposed recreation center for
the Seventh Filing. (See key map) This area was to have onsite deten-
tion and release at 0.5 cfs/acre into the regional pond. The area
will now flow directly into the regional .pond without onsite
detention. The attached volume calculations for this recreation
center, using a 0.2 cfs/acre release rate, show the required volume to
be 0.29 ac-ft. The 100 year pond water surface of the regional pond
will be raised to create additional storage volume for these flows.
The second change proposed in the previous reports' approach involves
elimination of the middle pond that was proposed by the James H.
Stewart and Associates Report. Again, the water surface elevation of
the regional pond will be raised to accommodate the increased volume
of 4.43 ac. ft. Apart from these two changes the approach taken in
this report conforms to previous drainage reports. The Seventh Filing
itself will drain directly into the regional pond with no offsite
flows being routed through the development. All nearby offsite flows
drain directly into the regional pond. In order to accommodate the
two changes in approach the pond volume will be increased by raising
its maximum 100 year storm surface elevation from 50.5 to 51.0. This
increases the storage volume from 21.22 ac.-ft. to 28.05+ ac.-ft. The
required volume increases to 25.94 ac.-ft. when the two additional
volumes (0.29 ac.-ft. and 4.43 ac.-ft.) are added to the previous
required volume (21.22 ac.-ft.). This volume is less than the avail-
able 28.05+ ac.-ft. suggesting that more than enough storage volume is
available.
Calculations for street capacities, based on the basins shown on the
grading and drainage plan, are shown on the following calculations to
be at acceptable limits. The three sidewalk culverts were sized for
the two year storm, if these inlets became plugged, or more than a two
year storm occured, the flows would safely spill over the curb and
into either the regional pond or a swale which has calculations which
follow.
This drainage report, when fully implemented,
veyance of storm drainage for this single family
current City of Fort Collins criteria.
Sincerely,
RBD, Inc.
Stan A. Myers, P.E.
Project Manager Nk��
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will provide safe con -
subdivision based on
Brian H. Cole, P.E.
Project Engineer
• KEY MAP �
uu
THE LANDINGS PUD
ONSITE DETENTION
WITH 0.2 cfs /AC.
RELEASE RATE
j
f
0 IT QETE
s WI0
RELEASRATE
11
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L
l r
l..
--- I I FUTURE
INEIGHBORHOOD
CENTER
/ I
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/I
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\. \l cam, _.'•
\�EE"N'D AKINt A_TION
J:
GOLDEN MEADOWS PUD
HARMONY ROAD ••
(\Q� M S 0NSITE DETENTI N.�
WITH .0.5 cfs /A(-
RELEASE
RATE
. 1
WEST POND
��`
SITE DETfigTION
KITH. 0.f cfs /AC.
RgL SE RATE
MLiNEAR
i- TCH•Eb AREAS DRAIN
D\MTHQ`UT NSIT 4
\-T\OX RIDGE ANt-&IX�TI_O�
SOUTiiRIDGE GREENS PUD
)[� y KNOB HILL \\
CA
TO MAI EAS
ENT.
Ee
ONSITE DETENTION /
WITH 0.5 cfs /AC.
RELEASE RATE /
EARLIER REPOR
MIDDLE POND T
BE ELIMINATE
BY THIS REPO T
AND ADDED T
MAIN (EAST) PO
PROPOSED
RECREATIO
CENTE
MAIN (EAST)
POND
RIDGE
AREA
o eoo
DATE: 7-27-8E
PROJECT: OAKRIDGE VILLAGE P.U.D. FILING 7 RECREATIONXENTER AREA
JOB NUMBER, 035-066 '
DESIGN EHGINEER:. BC
BASIN DESIGNATION = REC. CENTER
DETERMINE EXISTING Q FOR 2 YEARSTORM
HISTORIC RUNOFF (7f.}EFFICIENT .2
BASIN SLOPE: 1 pFRCENT
BASIN LEN'TH 250 FEET
AREA: 1.38 ACRES _
HIST TC,= 1.87*(1.1-( 1 * � .2
))*SQRROOT 250 >>/ 1
26.61057 MINUTES
HISTORIC OUTFLOW IS SUPERCEDED BY: .28 CUBIC FEET PER SECOND
DETERMINATION OF DETENTION POND VOLUME FOR DEVELOPED CONDITIONS
-' —
DEVELOPED STORM:
100
YEAR STORM
DEVELOPED RUNOFF COEFFICIENT
1
- '
CCFAC = 1
*
1.25
*
1.38 =
1.725
_
DURATION
GROSS VOL.
OUTFLOW VOL.
DETENTION VOL.
MIN
CU. FT.
CU. FT,,
CU. FT
5
3775.68
84
3691.68 .
10
5812.56
168
5644.56
15
7402.32
252
7150.32
30
10234.08
504 _
9730.08 �
45
12295.8
756
11539.8
60
12966.48
1008
11958.48
90
14009.76
1512
12497.76
120
14307.84
2016
12291.84
180
15500.16
3024
12476.16
360
17288.64
6048
11240~64
REQUIRED DETENTION
VOLUME IS
12497'76
CU. FT. OR
.2869091
ACRE FEET
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