HomeMy WebLinkAboutGrading Plans - 10/11/2016
Drainage Memo
Date: October 11, 2016
Project: 417 North Grant Avenue Project No. 376-006
Fort Collins, Colorado
Attn: Dan Mogen
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
Stormwater Staff:
This letter serves to document the proposed drainage impacts of a new home proposed at 417
North Grant Avenue in Fort Collins, Colorado.
Project Overview
The project proposes to completely remove the existing 1-story residential home and construct a
new home and garage with upstairs loft. The garage will be accessed from the alley on the west
side of the property.
Existing Site
The existing site was primarily a flat lot, draining towards the northeast corner, North Grant Avenue
towards the east, and the alley towards the west. Existing grades in the front yard range between
1%-5%, existing grades on the northern yard range from 0.7%- 4%, and existing grades in the rear
of the building vary between 0.7%-6%. In addition to the existing building, the lot consists of an
existing shed on the northwestern side of the building. The remainder of the site is Kentucky
Bluegrass lawn, dirt with sparse ground cover, and mature trees.
The total existing impervious area for the lot is 1,524 sf.
Proposed Site
The proposed site remains relatively flat, but features improved drainage away from the proposed
and existing structures. Drainage from the south side of the building, as well as the southern
portions of roof runoff of the new residence, is being directed via a concrete valley pan along the
south property line towards the front yard. A grass swale is proposed in the front yard to improve
infiltration and removal of contaminates from the south valley pan, and to direct drainage towards
North Grant Avenue. A proposed swale , in the rear yard, between the new residence and garage,
will collect runoff from the rear yard, eastern roof runoff from the garage, and western roof runoff
from the
yard and northeast corner of the site. Remaining roof runoff from the residence will follow existing
drainage patterns across the north yard and towards the northeast corner of the site. Roof runoff
from the proposed garage and western half of driveways will follow existing drainage patterns west
towards the alley. Grades outside of our existing improvements remained unchanged.
The total proposed impervious area for the lot is 2,928 sf. This is an increase of 1,404 sf. No
adverse impacts to adjacent properties is anticipated.
Detention
Since the increase of impervious area is less than 5,000 sf, no detention is required for the site.
Water Quality
Water Quality for the site is being provided by releasing concentrated flows from the roof into
landscaped areas allowing stormwater runoff to infiltrate into surrounding soils. Stormwater that is
unable to infiltrate is slowly passed through vegetated areas, further removing stormwater
contaminates, before leaving the property.
An exhibit has been provided to illustrate the existing and proposed impervious areas. Please feel
free to contact us if you have any questions.
Sincerely,
Frederick S. Wegert, PE
Design Engineer
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DESCRIPTION
EXISTING VS. PROPOSED
IMPERVIOUS AREA
DRAWN BY
DATE PROJECT SK-C1
SCALE
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