HomeMy WebLinkAboutOTTER BOX CORPORATE HEADQUARTERS (209 S. MELDRUM ST.) - PDP - 35-09 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT11/4/2008 Northam Engineenng Services Inc. 110 046 Rational Method Fin alxls
By: CNS Gunnison Ranch C-Values
Prof. No. 380-010
Page 2 of 2
11/4/2009 Northern Engineering Services Inc. 110-046_Rational _Method - Final.xls
By: CNS Gunnison Ranch H-C
Proj. No. 380-010
Character of Surface
v
Percent
Impervious'
5treet5, ParkIng Lots, Roofs, Alleys, and Drrve5:
As halt.................................................................................
1 00.00%
Percent Impervious
values are taken from
Table PO-3 of the
UDPCD Drainage Criteria
Manual (06/2001)
Concrete......................................................................... I....
90.00%
Gravel .........................................
40%
Roofs..................................................................................
00%
Lawns and L.?nd5capny
SandySoil............................................................................
0%
ClayeySoil............................................................................
0%
Runoff Coefficients are taken from Table R0-5 of the Urban Dramage and Flood Control District Drainage Criteria Manual (06/2001 )
Balm it)
Balm Area
(sa. ft.)
Basin Area
(acres)
Area of Concrete
Streets, Sidewalks
(sf)
Area of Roofs
(sf)
Area of
Asphalt
(sf)
Area of Vegetated
Surfaces
(acres)
Percent
Impervious
MI
3601(5,06
0.673
3040.040
836G.000
1 2 1 G42.000
4055.240
64I
Page 1 of 2
A
NORTHERN
ENGINEERING
ADDRESS: PHONE: 970.221.4158
200 S. College Ave. Suite 100 Northe
rn
E
Fort Collins, CO 80524 FAX: 970.221.4159 orthernEngineering.com
Wes Lamarque
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
November 4, 2009
Re: Drainage Report — OtterBox — New Headquarters
Dear Wes,
This letter is to summarize the drainage concepts for the proposed OtterBox
Building project located at 209 South Meldrum. More technically described as Lots 2 &
3 of Block 82 of the City of Fort Collins, County of Latimer, State of Colorado. The
project is located within the Old Town Master Drainage Basin.
The project will involve renovation and addition of the existing building located
at 209 S. Meldrum. Due to the current site conditions, a reconfiguration of the site has
been proposed. With the proposed construction, impervious area will be removed from
the site. Based on the Old Town Master Drainage Basin, and discussions that we have
had with you, as long as the additional imperviousness is less than 500 square feet,
detention is not required.
Existing and future percent imperviousness values for this basin are 84 percent
and 65 percent, respectively (please see Attachment #1). Based on our calculations, the
existing percent imperviousness for the overall property is 19 percent less than the
proposed site. These calculations do not include the planned proposal of a green roof.
Since the proposed percent imperviousness with the project is less than the existing
imperviousness, we conclude that detention is not required. Additionally, this site is
located in the Udall Natural Area which provides water quality treatment.
Historically, drainage from the site was divided to directed flows east and west.
As can be seen on the grading plan for the site, this drainage pattern is maintained with
the proposed construction. To achieve onsite water quality, both temporary and
permanent water quality measures have been included. The drainage entering the alley
has been routed through a vegetated swale and into an infiltration galley. This will lower
the amount of pollutants entering the existing storm system.
If you have any questions regarding drainage for this site, please do not hesitate to
contact me at 221-4158 ext. 133.
Sincerely,
NOR E=G SERVICES, INC.
Bud Curtiss, P.E.
Senior Engineer
"pi At G (AL
