HomeMy WebLinkAboutDrainage Reports - 04/14/1995RMINC.
Engineering Consultants
209 S. Meldrum
Fort Collins, Colorado 80521
303/482-5922
FAX: 303/482-6368
April 13, 1995
Mr. Basil Hamdan
City of Fort Collins
Utility Services, Stormwater
235 Matthews Street
Fort Collins, Colorado 80522
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RE: Addition of a Storage Shed
Oakridge Business Park, Sixteenth Filing (a.k.a Simpson Sheet Metal)
Dear Basil:
This letter and the attached memorandum and blueline copies are intended to satisfy
the City of Fort Collins requirements for Drainage and Erosion Control regarding the
addition of a storage shed at the Simpson Sheet Metal Site. Computations in this
report comply with those in the City of Fort Collins Storm Drainage Design Criteria.
Included here is also an erosion control plan and erosion control security obligation.
The Final Drainage and Erosion Control Study for the Simpson Sheet Metal Site was
approved by the Stormwater Utility in March of 1993. This report shows that the
building addition will have no effect on the existing conveyance system.
We appreciate your time and consideration in reviewing this submitted document.
Please feel free to call us if you have any questions.
RBD Inc. Engineering Consultants
Prepared by:
FM �.. Om
.•
ineer
cc: Bob Ross, Simpson Sheet Metal
Greg Fisher, Architect
Reviewed by:
Roger �. Curtiss
Project Manager
Denver 303/458-5526
DRAINAGE STUDY FOR STORAGE SHED
ADDITION AT THE SIMPSON SHEET METAL SITE
I. GENERAL LOCATION AND DESCRIPTION
A. Location
The Simpson Sheet Metal site is located within the Oakridge Business
Park and is adjacent to and east of Innovation Drive, south of the WYCO
Mechanical and Industrial Park (Oakridge Business Park, Seventeenth
Filing), currently under construction, and west of the Union Pacific
Railroad Right of Way. More particularly, the site can be described as
being located in the Northeast Quarter of Section 6, Township 7 North,
Range 68 West of the 6th Principal Meridian, City of Fort Collins, County
of Larimer, State of Colorado.
B. Description of Property
The Simpson Sheet Metal site is presently developed. The proposed
improvements include the addition of a 9000 square foot.storage shed
directly to the east of the existing Simpson .Sheet Metal building. The
addition is to be phased,with 4500 square feet being added upon.
approval of these revisions, and the remaining 4500 square feet to be
added in the future. There is also an existing open channel running along
the east line of the property.
II. DRAINAGE BASINS
A. Major Basin Description
The proposed additions lie entirely within Basin 200 of the Oakridge
Business Park Master Drainage Plan, as prepared by RBD Inc. Engineering
Consultants dated June 22, 1990. An open channel (Conveyance
Element 20) runs from north to south along the easterly boundary of
Basin 200, and conveys flows from Basin 200 to the Regional Detention
Pond located in the southeast corner of Oakridge Village 7th Filing. Per
the Master Drainage Study, developed flows from Basin 200 will be free
release and detained in the Regional Detention Pond. A copy of a portion
of the Overall Drainage Plan is included with this report.
1
Ill. DRAINAGE FACILITY DESIGN
A. Regulations
The City of Fort Collins Storm Drainage Design Criteria is being used for
the subject site. Specifically, the Final Drainage and Erosion Control
Study for the Simpson Sheet Metal Site and the one for Oakridge
Business Park, Seventeenth Filing will be used in conjunction with the
calculations in this report.
B. Development Criteria Reference, Constraints, and Comparison
As taken from the Simpson Report, the. 10 and 100 year developed
storm runoff from the site will be routed to an open channel running
along the east property line to the Regional Detention Pond.
The runoff from the Simpson Sheet Metal site was conservatively
calculated using a runoff coefficient of 0.8 for the 10 year condition (1.0
for the 100 year), to be consistent with the Oakridge Business Park
Master Drainage Plan. As figured through composite 'c' value
calculations, the actual runoff coefficient for the site was 0.58, thereby
making any increase to this value still acceptable as far as the channel
size is concerned, as long as it would not exceed 0.8. With the addition
of the aforementioned 9000 square feet of building area, the runoff
coefficient increases to 0.61. The design capacity of the Regional
Channel is 133 cfs and the runoff from the Simpson Sheet Metal site
was calculated to be 51.92 cfs. This regional channel received
certification in September, 1993. With the proposed additions, runoff
values from the site still fall under 51.92 cfs, since this figure was
calculated using the conservative 'c' value.
Runoff from the roof of the Phase 2A , portion will be conveyed by
downspouts and overland flow to a Swale running along the north
property line. This swale, being constructed with the Oakridge Business
Park, Seventeenth Filing, has a depth of 1.4' and lies entirely within an
easement on.the Oakridge Seventeenth property. The roof of this shed
will contribute an additional 0.9 cfs to this swale. Per the approved Final
Drainage and Erosion Control Study for the Oakridge Business Park,
Seventeenth Filing, this swale was sized with enough freeboard to
accommodate this additional runoff. Calculations are, included in the
back of this report. Runoff, from the roof of Phase 2B will sheet flow
across the gravel storage yard to the regional channel.
2
IV. EROSION CONTROL
A. General Concept
The erosion control plan for this addition assumes that the building will
constructed within 3 months of grading the area. If this does not
happen, then the area will be covered once again with gravel similar to
that already in place at this site. It will also be necessary to place straw
bales in the Regional Channel and near construction activity to control
any sediment movement induced by grading. Since the development is
to be phased, the erosion control escrow amount listed below applies
only to Phase 2A. Upon application for a the Phase 2B building permit,
it will be necessary to supply a second erosion control security deposit
in the amount of the one used for Phase 2A. The erosion control plan for
Phase 2B will be identical to that for Phase 2A.
The performance standard for this erosion control plan is greater than
that for the site, as computed in the Final Simpson Report. There will be
approximately 0.25 acres disturbed, including the future Phase 2B.
Using the city criteria of $1300 per acre for construction sites less than
10 acres, and using a 150% contingency, the total obligation of Simpson
Sheet Metal for a security deposit would be:
(0.25 acres) x ($1300.00 per acre) x 1.5 = $487.50
A cost breakdown of these erosion control measures is listed below:
Gravel Mulch to be applied at 135 tons per acre (10.00 per ton)
= $330.00
Straw Bale check dams
(6 @ $150 apiece) = $900.00
TOTAL x 1.5 = $1845.00
Therefore, the larger amount, or the amount of security deposit
obligation should be in the amount of $1845.00
CONCLUSIONS
A. Compliance with Standards
All computations that have been completed in this report are in
compliance with the City of Fort Collins Storm Drainage Design Criteria
Manual. In addition, all figures are in conjunction with the Final Drainage
and Erosion Control Studies for the Oakridge Business Park, Sixteenth
and Seventeenth Filings.
3
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RBD INC. ENGINEERING CONSULTANTS
CHANNEL RATING INFORMATION
SECTION F OAKRIDGE 17
DRAINAGE
Bonn cn.�et - c a.P• ,_I��l-1 . _
GHPiJt•�E7� GA-I.GS r�'C_ 6\\�1L�
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0.00
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20.00
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15.00
41.00
20.00 .
IN' VALUE SLOPE (ft/ft)
0.035 0.0050
ELEVATION
AREA
VELOCITY
DISCHARGE
FROZE
(feet)
(sq ft)
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(fps)
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(cfs)
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15.50
1.5
1.3
1.99
0.43�_
16.00
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2.0
9.99
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3.5
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0.54
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4.0
154.83
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230.12
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4.8
324.98
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19.50
85.5
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440.86
0.60
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105.0
5.5
579.74'
0.61
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•
EROSION CONTROL ` _/7
EFFECTIVENESS CALCULATIONS
PROJECT: STANDARD FORM B
COMPLETED BY: DATE: 03.00, 95
Erosion Control' C-Factor P-Factor
Method Value Value Comment
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