HomeMy WebLinkAboutDrainage Reports - 05/28/1993r ''4
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Final Approved Report 'Rev'
Date
FINAL DRAINAGE REPORT
FOR
TIMBERLINE STORAGE P.U.D.
MAY 21, 1993..
STEWART & ASSOCIATES. INC.
103 SOUTH MELDRUM STREET
FORT COLLINS, COLORADO 80521
303/482-9331
FINAL DRAINAGE REPORT
TIMBERLINE STORAGE P.U.D.
SITE LOCATION:
The site is located in the Southeast 4 of Section 31, Township 7 North,
Range 68 West of the Sixth P.M., Fort Collins, Larimer County, Colorado. It
is bounded on the west by the Union Pacific Railroad, on the south by the
"Timberline Wetlands" and on the east by undeveloped land. The northeast corner
of the site abuts Automation Way and Caribou Road. The site area is 4.38 acres
more or less.
HISTORIC SITE DRAINAGE:
The site is located in the Fort Collins Fox Meadows Basin (Basin H)
Drainage Master Plan by Resource Consultants, Inc. dated February 25, 1981.
The South 3.38 acres of this site, referred to in the report as Sub —basin 1,
flow to the southeast at a slope of two percent (2%) more or less to the
"Timberline Wetlands" area. There is an old 12—inch outlet pipe flowing
northeast from this wetlands.area and a newly constructed 42" outlet under
Timberline Road. The historic runoffs from Sub —basin l are Q2 = 0.95 c.f.s.r
Q10 = 1.69 c.f.s. and Q100 = 3.38 c.f.s.
Sub —basin 2 is the north 1.0 acre of this site. Runoff is to the northeast
at about 1.25%. The historic discharges are Q = 0.32 c.f.s., Ql = 0.56 c.f.s.
and Q100 = 1.15 c.f.s. All runoff from this sh—basin drains to �he already
constructed detention pond at the northeast corner of Collindale Business Park.
This pond is at the location shown in Figure 5 of the Fox Meadows Basin (Basin
H). There is no offsite runoff across this site.
DEVELOPED SITE DRAINAGE:
The site will be developed as rental storage units. The developed site
will be divided into Sub —basin "A" and Sub —basin "B".
Sub —basin "A": Runoff from Sub —basin "A" will run off undetained to the
"Timberline Wetlands" causing a 0.02 foot rise in the pond's 100—year water
surface. Please see letter report by RCE dated 4/16/93. The sub —basin area
is 3.63 acres, and the discharge is Q2 = 10.35 c.f.s., Q 1 0 = 17.93 c.f.s. and
Q100 = 25.41 c.f.s. .
On behalf of Mr. William Vigor, the developer of the proposed Timberline
Storage P.U.D., I am requesting a variance for the requirement of onsite storm
water detention. A hydrologic analysis was made by Resource Consultants and
Engineers, Inc. to identify any adverse effects on the storage capacity of
the Timberline Wetlands. The rise in the water level in a 100—year storm was
found to be 0.02 feet. Due to this minimal rise, a variance to the requirement
seems prudent. Their SWMM model was modified to show the results of the runoff
from the P.U.D. Their results and their conclusions are a part of the storm
drainage report. Water quality measures were voluntarily included in the design
of the project to minimize adverse effects on the Wetlands.
Sub —basin "B": :Runoff from Sub=basin "B" will be to Automation Way, then
north along Automation Way, then east to the already developed Collindale
Business Park detention pond in the northeast corner of. -that development.
The area of Sub —basin "B" is 0.75 acres more or less.
Timberline Storage P.U.D.
Page 2
Runoff from this sub —basin will be required to be released at the 2—year
historic rate of Q = 0.32 c.T.s. because of the street capacity for Automation
Way per the ColliNale.Business Park Drainage Report. A detention pond is designed
along the north property line to store the difference between the developed
100—year flow and the historic 2—year released flow. The required storage is
5177 cubic feet. The capacity of the pond is 5366 cubic feet. The top of the
pond will be 0.3 feet above the 100—year high water line elevation for freeboard.
A variance is requested from the City standard of 1.0 freeboard. The 35—foot
wide driveway entrance is used for the pond's emergency spillway. The outlet
from the pond is an 8" PVC pipe to a curb chase on Automation Way. A 2.9" X 2.9"
restriction plate is.required to reduce the outlet rate to the historic flow.
A variance is also requested to not require a concrete pan in Pond "B" due
to a bottom of pond slope of less than 2%. The pond will be maintained by the
owner and not the City of Fort Collins. The grass flow line will filter out
sedimentation and oils that the concrete pan would pass through, thereby improving
the water quality of the storm runoff.
Design and calculation -in this report are in accordance with the City of
Fort Collins Storm Drainage Manual.
EROSION CONTROL
The detention pond in Sub —basin "B" will have a rock filter placed over the
outlet pipe which will create a sediment trap. The pond will be graded.as the
first step of construction. The sediment trap will be in use until the north
building and the north driveway are completed and the pond is seeded.
The grading of Sub —basin "A" will also be the first step of construction.
The silt fence along the south property line of the project will be erected prior
to beginning any dirt work, and it will remain in place until all of the buildings
have their slabs poured and all of the driveways have been paved. The driveways
will have their base material placed immediately after grading so that construction
work on the storage buildings will have an all—weather surface and erosion will
be minimized.
WATER QUALITY:
In order to improve the quality of the storm water runoff from the site into
the Timberline Wetlands, a raised asphalt ridge will be constructed along the
south edge of the asphalt to contain any spills that may occur. The top of the
ridge is level at elevation 55.5, and the flow line along the north side of the
ridge is level at elevation 55.3. The ridge not only provides the containment
desired but will spread the storm water out to sheet flow from the inverted
driveways. A varying width strip of irrigated blue grass will be provided between
the asphalt edge and the new security fence to filter out sedimentation. The
15—foot wide landscape buffer will have native grasses that also act as a filter.
There also is a strip. of native grass cover offsite before the runoff en,s1,the
wetlands. Although this minimizing of pollutants is not required b��1J 5st,
of Fort Collins, the developer has agreed to the above measures. �•``�.Q�:•G%s7eq Fgfp�:
Richard A. Rutherford, P.E. & L.S.
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STEWART&ASSOCIATES 103 S. ME9331 LDRUM, FORT COLLINS, CO 80521
PH. 482-FAX 482-9382
Consulting Engineers and Surveyors
By: Date: Client: Sheet No. of
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Date: Client: jr-4/-�W- Sheet No. A- of
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OLLINS, CO 805212
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Scale [ in feet I
1000 500 0 12007=
Legend:
drainage divides
_ __ open channel with
direction of flow
stormsewers and drains
with direction of flow
general direction of flow
of. surface drainage
Qponding areas,
detention ponds, etc.
Odrainage concentration points
1 see Table 31
FOX MEADOWS BASIN ( BASIN
Existing Drainage Patterns
Figure 2
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RESOURCE CONSULTANTS, INC. • Fort Collins, Colorado
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RAINFALL
PERFORMANCE STANDARD
EVALUATION'
PROJECT:
T/M0EPl-1/U6 SrORArCo
f?U.D
STANDARD
FORM A
COMPLETED
BY: ,¢p
DATE: MAC uj
(DEVELOPED
ERODIBILITY
Asb
Lsb
I
Ssb
Lb
Sb I
PS
SUBBASIN
ZONE ,
(ac)
(ft)'
(%)
(feet)
(%) I
10
()
------By-
MODERATE
I
0•734..
4Z0 '-!
I
O SQ-
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-------
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kale
3.G5/k.j
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DI/SF-A:1989
EFFECTIVENESS CALCULATIONS
--------- ---------------- - -----------------------------------
PROJECT: T/m5ecz /NE J-ro9 Ar.e^ p U. D. STANDARD FORM B
COMPLETED BY: p,.A,p. DATE: At -Ale- /,,,gq
Erosion Control-
-C-Factor
P-Factor
Method
Value
Value Comment
------------- ---------------------------------------------
BaeE Ge-ovN�
/.av
boo
BUILD/AI
0,01
A00
A.rp.Hq LT �Co,vc,
SILT Fe vc-c
0, 01
00
1.00
6,50
JED1M£d/T 7-9Av
-----------------------------------------------------
/• 00
+ 6,5-[7
----------------
MAJOR PS. SUB AREA
BASIN (Iwo) BASIN {Ac) CALCULATIONS
----- ------ ----- ------ --------------------------------------
AB, 073Ac, 84QcGP-ov.vb = U,.Z4 4c.
. BvIC.D/.v6.
As P H A LT• e CO NC . = 0, 31 Ac,
A* 13 %sA' r
VJ'r'D G = (o•a4x/.00.)+(0./8X 0,0)+(6-3/x&a1)
O.34-
w,-p P = G•so
EFF •_ (I— 0.34xo.s�/Oo — 83.0
BARE GeOv vD _ 0,1$ Ac.,
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TOTAL EFF. _ (a,83x o•73� t �0.`J7x3•Gs�
¢•38
94.a% 77.3% 0k
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CONSTRUCTION SEQUENCE
PROJECT: -rim _f-ro, .4 rp i?U.D.
STANDARD FORM C
SEQUENCE. FOR 19 -73 ONLY COMPLETED BY: p .4 4 DATE: M.0 ecH
Indicate by use of a bar line or symbols when erosion control measures will be installed.
Major modifications to an approved schedule may require submitting a new schedule for
approval by the City Engineer.
YEAR
MONTH ,
I I IMI- IMiIJ !.1 1--1s to IN DI
�I I
OVERLOT GRADING I T I I I i ! )
WIND EROSION CONTROL
Soil Roughing
Perimeter Barrier
Additional Barriers
Vegetative Methods
Soil Sealant
Other
5UILD1/V& FDU.VPAT/DA)
RAINFALL EROSION CONTROL
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters
Straw Barriers
Silt Fence Barriers
Sand Bags
Bare Soil Preparation
Contour Furrows
Terracing
Asphalt/Concrete Paving
Other
VEGETATIVE:
Permanent Seed Planting
Mulching/Sealant
Temporary Seed Planting
Sod Installation
Nettings/Mats/Blankets
Other I
STRUCTURES: INSTALLED BY MAINTAINED BY
VEGETATION/MULCHING CONTRACTOR
DATE SUBMITTED -.;..,APPROVED BY CITY OF FORT COLLINS ON
HOI/SF-C:1989
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RCERESOURCE CONSULTANTS & ENGINEERS, INC.
A KLH Engineering Group Company
April 16, 1993
Mr. Dick Rutherford
James H. Stewart & Associates
103 S. Meldrum
Fort Collins, Colorado 80521
Re: (RCE Project Number 93-130)
Dear Dick:
As per your request, I have completed a hydrologic analysis of the Timberline sump for the proposed
Timberline Storage, P.U.D. We have analyzed the Impact of the increased drainage area and greater
percentage impervious on the floodwater levels in the sump. Based on our analysis the impact of the
proposed development is minimal.
We utilized the Storm Water Management Model (SWMM) that was developed for the Fox Meadows Basin
(Ref: Fox Meadows Basin Drainage Master Plan, Resource Consultants, 1981). This model was used for
drainage planning for the entire basin. This model was revised in .1987 (ref: Updated Hydrology For the Fox
Meadows'Basin Drainage Master Plan, October 1987) to reflect changes in originally planned detention
ponds in,the basin. The model .was further refined in 1990 (ref: Letter to Mr. Glen Schlueter, January 17,
1990 from David Frick) to reflect the new outlet structure for the Timberline sump. These changes reflected
a revised storage discharge curve for the sump based upon field surveys and plans for the proposed outlet.
This model utilized assumed full developed conditions for the subbasins. For the area that included the site
of the Timberline Storage P.U.D., the assumed full developed impervious area was 40 percent. The
proposed Timberline Storage P.U.D. contains greater impervious area than originally planned for in the
model.
The purpose of this study was to analyze the impact of the increased impervious area and slightly increased
drainage area on the water levels in the sump and the outflows from the sump. The proposed development
in located in subbasin No. 7 of the SWMM basin model. The total area of the subbasin area is 55.8 acres.
The Timberline Storage P.U.D. drains 3.63 acres into the sump. The site historically drained 3.38 acres into
the sump. Therefore, the proposed development will Increase the drainage area of subbasin No. 7 from 55.8
acres to 56.1 acres. In addition the 3.63 acre area is 95 percent impervious and would increase the overall
imperviousness of the subbasin by approximately 2 acres. This equates to an increase in impervious area
of 4 percent from 40 percent to 44 percent overall.
Changes were made in the model to reflect this increase in drainage area and increased imperviousness.
The model was run for the 2, 10 and 100 year events. The changes in high water elevation and outflows
from the ponds are summarized in Table 1. As can be noted in Table 1 the effects on the storage, elevation
and outflow is very small. - Elevation changes are less than 0.1 fL and outflow rate changes are less than
1 cfs. Attached are copies of. computer.output for the runs and a disk containing the model data files.
3665 JFK Parkway, Building 2, Suite 300 • P.O. Box 270460 • Fort Collins, CO 80527
(303) 223-5556 •. Denver Metro (303) 572-1806 • FAX (303) 223-5578
Fort Collins, CO • Davis, CA • Laramie, WY
Mr. Dick Rutherford
2
April 16, 1993
Table 1.
in'. Event :.
YVflhout
With
Deference
.........
.:PU:D
AUD ..::.
2-Year Storage (AF)
0.4
0.5
0.1
Elevation (MSL)
4948.68
4948.73
0.05
(Outflow) (cfs)
21.0
21.0
0.0
10-Year Storage (AF)
10.6
10.8.
0.2
Elevation (MSL)
4950.97
4951.0
0.03
Outflow (cfs)
33.0
33.0
0.0
100-Year Storage (AF)
30.8'
31.0
0.2
Elevation (MSL) ..
4953.35
4953.37
0.02
Outflow (cfs)
41.0 1
41.0.
0.0
Construction of onsite detention for the southern portion of the site would not provide any significant benefit
for the overall drainage in the basin. Since the site is located adjacent to the sump there would be no
intervening areas impacted from increased site runoff. The sump will mitigate the increased flows so that
downstream properties are not effected.
In conclusion, the site development at a higher impervious area than included in the master plan would not
significantly effect the pond elevations or discharge.
DMF:sp
Enclosures
cc: Mr. Glen Schlueter
C:\DATA\VVP51\RUTHER4.LTR
Sincerely,
RESOURCE CONSULTANTS & ENGINEERS, INC.
David M. Frick, Ph.D., P.E.
Vice President
RCE
STEWART&ASSOCIATES
Consulting Engineers and Surveyors
April 26, 1993
Mr. Glen Schlueter
Storm Water Utility
City of Fort Collins
P. 0. Box 580
Fort Collins, CO 80522-'
Dear Glen,
The following is the cost estimate for erosion control facilities for
the Timberline Storage. P..U.D.
Costs Option 1:
1. Rock Filter $100
2. 220 L.F. of Silt Fence 550
Total $650
Costs Option 2: -
1• Reseeding 190,793 S.F. @ 0.0294/S.F. _ $5533.00
City required collateral is 150% of $5533 = $8299.50
The reseeding costs are used for the City required collateral. If you
have any questions regarding this cost estimate, please call.
Sincerely,
Richard A. Rutherford, P. E. & L.S.
President
P,AR/im
James H. Stewart
and Associates, Inc.
103 S. Meldrum Street
P.O. Box 429
Ft. Collins, CO 80522
303/482-9331
Fax 303/482-9382
*• 5023 -
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