HomeMy WebLinkAboutDrainage Reports - 09/03/2013[ik E
NORTHERN
ENGINEERING
Drainage Letter Report
Date: July 3, 2013
City of Ft. Collins A roved tans
Approved By
Date
ADDRESS: PNDNE:970.221,4158 WEBSITE:
200 S. College Ave. Suite 10 www.northernengineering.eom
Fort Collins, CO80524 FAX-970.221.4159
Project: Stoner Subdivision
Project Development Plan
Fort Collins, Colorado
Attn: Mr. Glen Schlueter
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
Dear Glen:
Project No. 358-002
This letter serves to address the stormwater impacts of the Stoner Subdivision Project Development Plan.'
The existing site contains an existing residence that is situated towards the western side of the existing lot,
as well as an existing garage located along the alley. In addition to the rooftops of those two structures,
there are also existing concrete walks, turf, trees, and other vegetation. It presently functions as a 'B' lot,
with historic drainage being split towards Wayne Street to the west and towards the alley to the east. The
total impervious area of the existing site is approximately 4,189 square -feet. The existing percent
impervious for the entire site is 23.6%.
The proposed project will subdivide the existing lot to create a new lot on the eastern half of the property.
The project intends to leave the existing building footprints unchanged, while adding a single family home
on the newly created lot. For the most part, existing paving will remain unchanged, although there will be
small areas of concrete removed. Also, there will be small areas of concrete walk added to serve the new
home. While minor grading changes will occur, existing drainage patterns will be maintained. The total
impervious area of the proposed redevelopment is roughly 5,513 square -feet. This is a slight increase from
the existing condition. The proposed percent impervious for the entire site is 31.0%.
The site is located in the Old Town master drainage basin, and therefore, on -site detention is not required
so long as the increase in impervious area is less than 5,000 square -feet. The total increase in impervious
area proposed with this development is approximately 1324 square -feet (5,513 — 4,189). A detailed
breakdown of the existing and proposed impervious areas is attached to this letter.
This proposed building is located within a City regulatory moderate risk floodplain in the Old Town Basin.
There are no elevation requirements associated with this type of floodplain, however efforts will be made to
elevate the proposed home 12" above the BFE to provide additional protection from flooding.
Page 1 of 2
D:\Projects\358-002\Drainage\Reports\Drainage Report\358-002 Drainage-Letter.dou
W (NORTHERN
ENGINEERING
Although regional stormwater quantity detention is provided by the Udall Natural Area for this property,
onsite stormwater quality mitigation will still be addressed by both temporary and permanent Best
Management Practices (BMPs). During construction, the Contractor will follow the appropriate and
applicable City of Fort Collins standards for erosion and sediment control. Since the approximately 6,467
sf area of disturbance for the project is less than one acre, a comprehensive Stormwater Management Plan
will not be prepared for this project. Post construction water quality and erosion control will be achieved
by a fully established and stabilized site. All areas disturbed during construction will receive permanent
hardscape, landscape, or building structure.
There are no existing stormwater BMP's currently on -site. Since the percent of site imperviousness is
increasing only slightly from the existing condition, formal water quality treatment is not required. While
formal water quality treatment is not required for this site, an effort has been made to employ low -impact
development strategies to treat the majority of stormwater runoff from the site. This treatment occurs
through a variety of methods. The first method is the use of earth lined swales to collect runoff from the
new residence, which allows for the filtering and settling of particulates to occur prior to drainage leaving
the site. Another method that is being utilized is to discharge roof drains into landscaped areas where
available.
To summarize, the proposed grading concept very closely matches existing elevations and drainage
patterns. On -site detention is proven to be unnecessary. Stormwater quality is not required, but has been
provided anyways. Therefore, it is my professional opinion that the Stoner Subdivision satisfies all
applicable stormwater criteria.
Please do not hesitate to contact me if you have questions or require additional information.
Sincerely,
P J'a�
Andrew Reese
Project Engineer
enc.
N&&t'
Nicholas W. Haws, PE LEED
Project Manager AP
Page 2 of 2
D:\Prolects\358-002\Drainage\Reports\Drainage Report\358-002 Drainage-Letter.docx
EXISTING IPROPOSED
200 South College Avenue, Suite 10
Fort Collins, Colotatlo 80524
MAGNOLIA STREET
(100' ROW)
NORTHERN
ENGINEERING
PHONE: 970.221,4158 FAX: 970.221.4159
w .northemengltearing.com
SURFACE
AREA (SF)
%IMPERV -
IMPERV.
AREA (SF)
ROOFTOP
2,878
100%
2,878
CONCRETE
1,311
100%
1,311
ASPHALT
0
100%
0
LANDSCAPE
11.798
0%
0
TOTALS 15,987 TOTAL= 4.189
EXISTING & PROPOSED
IMPERVIOUS AREAS
MAGNOLIA STREET
(100' ROW)
SURFACE
AREA (SF)
%IMPERV.
IMPERV.
AREA (SF)
ROOFTOP
4,330
100%
4,330
CONCRETE
1.183
100%
1.183
ASPHALT
0
100%
0
LANDSCAPE
10,473
0%
0
TOTALS 15,986 TOTAL= 5,513
STONER SUBDIVISION
DRAWN BY: A. Boese EXHIBIT
SCALE: tin=30ft
ISSUED: July 3, 2013
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