HomeMy WebLinkAbout210-212 W. MAGNOLIA ST., URBAN LIVING LOFTS - PDP - 24-05 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTNorth Star Design, Inc.
700 Automation Drive, Unit I
Windsor, CO 80550 i
RUNOFF COEFFICIENTS 8 % IMPERVIOUS
LOCATION: Urban Living Lofts at Magnolia
PROJECT NO: 247-01
COMPUTATIONS BY: PPK
DATE: 5/11/05
Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria
Recommended % Impervious from Urban Storm Drainage Criteria Manual
Streets, parking lots (asphalt)
Sidewalks (concrete)
Roofs.
Lawns (flat <2%, heavy soil),
Runoff
%
coefficient
Impervious
C
0.95
100
0.95
96
0.95
90
0.20
0
SUBBASIN
DESIGNATION
TOTAL
AREA
(ac.)
TOTAL
AREA
(sq.ft)
ROOF
AREA
(sq.ft)
PAVED
AREA
(sq•h)
SIDEWALK
AREA
(sq.ft)
LANDSCAPE
AREA
(sq.ft)
RUNOFF
COEFF.
(C)
%
Impervious
REMARKS
EXISTING
0.36
15,750
3029
6332
320
1 6,069
0.66
59
PROPOSED
0.36
15.750
12500
1390
131
1,729
0.87 1
81
'i
PROPOSED WI HALF
0.46
E19,
12500
3690
733
2,991
0.84
79
OF MAGNOLIA
'
Equations
- Calculated C coefficients & % Impervious are area weighted
C=E(Ci Ai) /At
Ci = runoff coefficient for specific area, Ai a
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At =total area over which C is applicable; the sum of all Ai's
Flow-prelim.xls Cval
I
this is not a residential living space, this encroachment into the floodplain should be
allowed and the new structure will be floodproofed to 18" above the flood plain elevation
as required.
-nts or need additional information, please call me.
North Star
�`, design, inc.
May 11, 2005
Glen Schlueter
City of Fort Collins Stormwatcr
700 Wood Street
Fort Collins, CO 80522
Re: Stormwater Requirements for 210 Magnolia
Project No: 247-01
Dear Glen,.
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
building will be floodproofed to 18" above the flood plain elevation as required. The
proposed garage floor is set at 4993.7 which is below the floodplain elevation. Because
700 Automation Drive, Unit I Windsor, Colorado 80550
970-686-6939 Phone • 970-686-1 188 Fax