HomeMy WebLinkAboutGrading Plans - 08/11/2025Eric Lessard, PE
304 Smith St.
Fort Collins, CO 80524
8/7/25
City of Fort Collins – Development Review
281 N. College Ave.
Fort Collins, CO 80524
RE: 705 Stover St. Residential Detached Garage Drainage Memorandum
Fort Collins, CO – Old Town Drainage Basin
Dear Staff:
I am pleased to submit this Drainage Memorandum for the property of 705 Stover St. in the Old
Town Basin of Fort Collins, CO. In general, this memorandum serves to document the
stormwater impacts associated with the proposed project on this 9500 square foot property.
Site Location and Project Description
The 705 Stover St. property site (referred herein as ”the site”) is located in Fort Collins, at Block 177,
Parcel Number 9713119013, Subdivision 10177 - FTC BLK 177, Neighborhood 19711, Larimer County,
Colorado. The site has a platted area of 0.22 acres and is bounded by a north-south alley to the west
and then residential houses on Smith Street, Stover Street to the east, and existing residential buildings
to the north and south, eventually East Laurel Street to the North and East Plum to the south. The legal
description is COM 50 FT S OF NE COR BLK 177, FTC, S 50 FT, W 190 FT, N 50 FT, E 190 FT TO BEG.
The planned development for the site will consist of the following:
• The construction of 2 car 24’x25’ detached garage at the property alley, with a 15’x24’
concrete apron. The net increase in impervious area will be 960 sf.
• The building will have a garage door facing the alley (west) and an access door facing east.
• The building will have gutters running east – west on both the south and north side. The
north gutter will discharge at the northeast corner into the lawn in the backyard and the south
Grading/Stormwater Plan Accepted
(Building Permit Released)
Accepted by:
Date:
Derek Lutz
08/11/2025
No Certification of Lot Grading Required
gutter will discharge at the southwest corner and into the alley. The concrete apron will be
sloped to the west towards the alley.
Existing Conditions
Hydrology
The site, which is located within the Old Town Basin, is approximately 0.22-
acres in size and is currently developed as a residential property. The yard behind the house is
graded from east to west with a consistent slope. Storm runoff behind the house currently
drains towards the west, to the 20’ alley where it partially flows north to East Laurel Street and
also partially south to East Plum Street, and is intercepted by curb and gutter. There is a break
in the alley grading to the north and south at the approximate midpoint of the lot. The runoff
travelling north enters the curb and gutter on Laurel and travels east to Stover St. At Stover it
turns south and travels to the inlets at the northwest corner of Stover and Plum St. The runoff
that breaks south in the alley travels to East Plum and turns east within the curb and gutter. It
then enters the stormsewer inlets at the northwest corner of Stover and Plum St. The existing
yard where the garage and apron will be constructed discharge .004 cfs in the 100-year storm.
Existing backyard footprint runoff Rational Method Calculations:
C coefficient: .02 (backyard)
Intensity: 9.95 in/hr (100-year rain intensity for 5min TOC)
Area: 960 sf (.022 acres)
Runoff = .02*9.95*.022=.004cfs
Table of Suface Types Percent Impervious Values
Lawn, Clayey Soil (Yard) 2%
Garage Roof 90%
Concrete Apron 100%
Alley (Gravel) 40%
The above photos show the backyard of 705 Stover St.
The above photos show the opposite side of the alley adjacent to 705 Stover St. and the
existing garage. The floor elevation of the neighboring garage is above the alley elevation.
The above photos show the flow path of runoff from the proposed garage. The 1st photo is
facing south toward Plum. The 2nd photo is the south side of the alley at Plum. The 3rd photo is
the Plum Street north side curb & gutter. The 4th photo shows the bank of inlets at the
northwest corner of Plum and Laurel.
Floodplain
The site is not located within a FEMA or City-regulatory floodway or floodplain.
Constructed Conditions
Hydrology
The addition of the garage will increase the runoff from the property. The increase in runoff
will be .202 cfs. Runoff will be intercepted by two roof gutters and directed to downspouts
facing the backyard (at the northeast corner) and west towards the alley (at the southwest
corner). Runoff from the concrete apron will flow east to the alley.
Rational Method Calculations:
Garage and apron runoff:
C coefficient: .90 (roof top) & 1.00 (concrete apron), combined: .94
Intensity: 9.95 in/hr
Area: 960 sf (.022 acres)
Runoff = .94*9.95*.022=.206cfs
Net increase in runoff: .206-.004=.202cfs
The attached drawing shows the existing house outline and the proposed detached garage and
apron outline. In addition, it shows the flowpath (sheet flow) of precipitation runoff and the 2
downspout locatons. A level survey was completed and elevation differences are shown. The
zero elevation was set at the back of the existing house (between the existing house and the
proposed garage). A second figure downloaded from the City of Fort Collins GIS System shows
2’ contours and demonstrates the ability of the alley to convey drainage to the south. The
alley also has a 40% impervious value, further reducing the effects of the additional discharge
associated with the new garage.
Detention and Water Quality
Per City code, detention and water quality improvements are not required for this
development. It is less than 5000 sf.
Erosion Control
All runoff from the proposed travels across a mildly sloped vegetated yard. The existing
vegetation will prevent erosion from occurring.
P
/
L
P
/
L
P / L P / L P / L P / L P / L P / L P / L P / L
P
/
L
P
/
L
P / L P / L P / L P / L P / L P / L P / L P / L
SB
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L
SB / L SB / L SB / L SB / L
SB
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L
SB / L SB / L SB / L SB / L
PROPOSED 24X25
GARAGE
EXISTING HOUSE
EXISTING
DECK
ST
O
V
E
R
S
T
AL
L
E
Y
0
-1/2"
-1"
-2"
-2"
-5"-5"
-5 1/2"
-6 1/2"-7 1/2"
-3 1/2"
-5 1/2"-5"
-6 1/2"-6"
-7 1/2"-7 1/2"
The lot slopes toward the alley.
The high point in the Alley is the Northside of the garage
The garage across the way is higher in elevation than the alley
The Alley tips away from the house to the Northand has a strong downwards pitch
The Alley has a strong downward pitch to the South
-6"
DS
DS
Downspout
Locations
4978
4978
4976
4974
4972