HomeMy WebLinkAboutDrainage Reports - 02/03/2006 (2)North Star
�`w design, inc.
December 9, 2005
Glen Schlueter
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522
Re: Stormwater Requirements for 210 Magnolia
Project No: 247-01
Dear Glen,
ad Repoq
Date
This letter is in reference to the proposed improvements associated with the Urban Living
Lofts at Magnolia located north of Magnolia Street and west of Mason Street in Fort
Collins. The site is located in the Old Town Drainage Basin. The site encompasses
approximately 0.33 acres (including half of the vacated alley) and currently has a
building and parking lot on the site. It is proposed that the existing building will remain
and be expanded into additional living units and a parking garage. The parking lot will
be removed.
The imperviousness for the calculated site was calculated and found to have
approximately 9360 square feet of imperviousness and a percent impervious of 59. The
proposed condition was also calculated and found to have 13,890 square feet of
imperviousness and a percent impervious of 81. When the adjacent street was included in
this calculation, the percent impervious went down to 79.
These analyses were completed based on the conceptual review comments which
indicated that no drainage and erosion control report is necessary if the increase in
imperviousness is less than 5000 square feet ,(this project will increase by 4530 square
feet) and if it can be shown that the total imperviousness, including on -half of any
adjacent streets or alley, is equal to or less than the master planned imperviousness of
90%, the report and detention requirements are waived.
The building currently exists in the 100 year flood plain. The flood plain elevation at this
location is 4994.7 and the existing building finished floor is at elevation 4994.4. The new
portions of the building will be floodproofed to 18" above the flood plain elevation as
required. The existing building will be upgraded and will be floodproofed to 6" above
700 Automation Drive, Unit I Windsor, Colorado 80550
970-686-6939 Phone 0 970-686-1 188 Fax
the BFE. The lowest elevation proposed at grade garage floor will not be below 4992.5
which is below the floodplain elevation. Because this is only parking and not a
residential living space, this encroachment into the floodplain is allowed and does not
have to elevated or floodproofed.
Also attached are the erosion control calculations for the site including the erosion
control escrow amount required.
If you have any questions or comments or need additional information, please call me.
'Sincerely,
P*iaoetch,
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North Star Design
700 Automation Drive, Unit I
Windsor, CO 80550
EFFECTIVENESS CALCULATIONS
PROJECT: Magnolia Lofts STANDARD FORM B
COMPLETED BY: PPK DATE: 09-Dec-05
EROSION CONTROL
C-FACTOR
P-FACTOR
METHOD
VALUE
VALUE
COMMENT
BARE SOIL
1.00
1.00
SMOOTH CONDITION
ROUGHENED GROUND
L00
0.90
SEDIMENT BASIN
1.00
0.50
-
ROADS/WALKS
0.01
1.00
GRAVEL FILTERS
1.00
0.80
PLACED AT INLETS
SILT FENCE
1.00
0.50
STRAW MULCH
0.06
1.00
ESTABLISHED GRASS
0.08
1.00
STRAW BARRIERS
I.00
0.80
EFF = (I -C'P)* 100
MAJOR
SUB
BASIN AREA
EROSION CONTROL METHODS
BASIN
BASIN
(Ac)
1
0.36
BARE SOIL 0.02 Ac.
ROADSIWALKS 0.29 Ac.
SILT FENCE 0.03 Ac.
ROUGHENED GROUND 0.00 Ac.
ESTABLISHED GRASS 0.02 Ac.
NET C-FACTOR 0.15
NET P-FACTOR 0.40
EFF = (I-C*P)• 100 = 93.9%
TOTAL AREA = 0.36 ac
TOTAL EFF = 93.9%
REQUIRED PS = 71.0%
Erosion.xls 2 of 4
CONSTRUCTION SEQUENCE
Project: Magnolia Lofts
Date: December 9, 2005
Indicate with bar line when constructions will occurr and when BMP's will be installed/removed in relation to the construction ohase
Grading (include Offsite)
DetentionMQ Ponds
Pipeline Installation (include Offsite)
Sanitary Sewer
•
'Concrete Installation (include Offsite)
Pond Outlet StructuresCurb
and Gutter
Box Culverts, Bridges
Street Installation (include OffsIte)
Miscellaneous (include OffsIte)
Irop Structures
Other (List)
:BEST MANAGEMENT PRACTICES
Silt Fence Barriers
Sediment Trap/Filter
Vehicle Tracking Pads
Flow Barriers (Bales, Wattles, Etc)
Stream Flow Diversion
Permanent Seed Planting
Cost Est
EROSION CONTROL COST ESTIMATE
Project: Magnolia Lofts
Prepared by: PPK
ITEM
IQUANTITY
UNIT
COST/UNIT
ITOTAL COST
Silt Fence
150
LF
$3
$450
Wattle Filters
2
EA
$150
$300
Gravel Inlet Filter
0
EA
$150
$0
Construction Entrance
0
EA
$550
$0
Subtotal
Contingency (50%)
Total
$750
$375
$1,125
CITY RESEEDING COST
Reseed/Mulch
0.36
ACRE 1
$775
$279
Subtotal
Contingency (50%)
Total
$279
$140
$419
EROSION CONTROL ESCROW AMOUNT $1,125
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