HomeMy WebLinkAboutDrainage Reports - 04/14/20170
April 17, 2017
NORTHERN
ENGINEERING
Basil Hamdan
City of Fort Collins Utilities
700 Wood St.
Fort Collins, CO 80521
RE: Drainage Letter for 5608 College — Cultivation Facility
City of ft.. Collins ppr ed Plans
Approved By
Date-/ -17
This letter is in regards to 5608 South College Avenue, more specifically the historic drainage
patterns and any effects the proposed change of use may have on the current conditions. The
project site is Lot 1 of South 13 Subdivision located in the northwest quarter of Section 12,
Township 6 North, Range 69 West of the 6" Principal Meridian, City of Fort Collins, Larimer
County, Colorado. The site is currently bounded to the north by open space, to the east by a vacant
lot, to the south by a commercial building and to the west by U.S. 287 Frontage Road.
The site currently consists of a combination of concrete, gravel, and natural areas with one existing
structure located on the western portion of the lot. There are four concrete parking areas located at
the front of the building with a concrete area also located to the south of the building. An existing
gravel drive travels around the north and east of the existing building. The remaining area to the
east of the building is native vegetation. The site drainage is divided to the east and west by a ridge
line running north and south along the front of the building. The stormwater routed to the west is
conveyed overland from south to north through a concrete chase connecting the two existing parking
areas. The stormwater is discharged to the west undetained. The stormwater routed to the east is
conveyed via overland flow and discharged undetained at the northeast corner of the site. The site
is currently 46 percent impervious.
The proposed change of use will not alter the existing drainage patterns of the site. The area
draining to the east will route stormwater to the historic location. To improve the existing water
quality of the site, a bio-retention pond has been proposed east of the existing drive capturing the
stormwater from the existing parking area and the existing gravel drive. The size of the bio-retention
pond was determined by the amount of low sloping area between the existing gravel drive and the
existing water and sewer easement. The Bio-Retention pond has a 6 inch maximum water quality
depth and a capture volume of 178 cubic feet. The capture volume will treat over 100% of the
upstream drainage basin area, but only 73% of the entire area within Basin P2. The remaining
untreated area consist of natural vegetation and therefore does not require any water quality.
During high -flow events, overflow from the Bio-Retention Pond will sheet flow over the east
embankment of the pond at the 43 foot long level earth berm. Calculations for the bio-retention
FORT COLLINS: 301 North Howes Street, Suite 100, 80521 1970.221.4158
GREELEY; 820 8" Street, 80631 1 970.395.9880 1 WEB: www.northemengineering.com
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Kati{ k7c���i �; t•)d'=,
pond have been attached to this report. The majority of the proposed improvements are located
within the area draining to the west and consists of an additional bike parking, and Landscape
areas and the elimination of both the northern and southern parking areas in front of the building.
The existing concrete chase will be extended to the south and north to maintain the drainage
connectivity between the northern and southern concrete areas. Both discharge points will remain
at existing locations. The proposed site is calculated at 44 percent impervious, with a net loss of 2
percent from existing. By eliminating 2 percent of the impervious area and maintaining historic
drainage patterns, the site will have no adverse effects on any existing drainage systems or adjacent
properties and will decrease in overall runoff quantities.
If you should have any questions, please feel free to contact me at 970.221.4158, extension 115.
Sincerely,
c�uS.A l
27302
Cody Snowdon, El Roger Curtiss, PE A
Project Engineer Vice President %F1
NORTHERN
ADDRESS:
PHONE:970.221.4158
WEBSITE:
ENGINEERING
200 S. College Ave. Suite 10
Fort Collins, CO 80524
FAX: 970.221.4159
wNw nortt�nengimring co.n
August 11, 2015 City of Fort Collins roved Plans
Basil Harridan Approved by.
City of Fort Collins Utilities Date:
700 Wood St.
Fort Collins, CO 80521
RE: Drainage Letter for 5608 College — Cultivation Facility
This letter is in regards to 5608 South College Avenue, more specifically the historic drainage patterns
and any effects the proposed change of use may have on the current conditions. The project site is Lot 1
of South 13 Subdivision located in the northwest quarter of Section 12, Township 6 North, Range 69
West of the 6`h Principal Meridian, City of Fort Collins, Larimer County, Colorado. The site is currently
bounded to the north by open space, to the east by a vacant lot, to the south by a commercial building
and to the west by U.S. 287 Frontage Road.
The site currently consists of a combination of concrete, gravel, and natural areas with one existing
structure located on the western portion of the lot. There are four concrete parking areas located at the
front of the building with a concrete area also located to the south of the building. An existing gravel
drive travels around the north and east of the existing building. The remaining area to the east of the
building is native vegetation. The site drainage is divided to the east and west by a ridge line running
north and south along the front of the building. The stormwater routed to the west is conveyed
overland from south to north through a concrete chase connecting the two existing parking areas. The
stormwater is discharged to the west undetained. The stormwater routed to the east is conveyed via
overland flow and discharged undetained at the northeast corner of the site. The site is currently 46
percent impervious.
The proposed change of use will not alter the existing drainage patterns of the site. The area draining to
the east will route stormwater to the historic location. To improve the existing water quality of the site,
a bio-retention pond has been proposed east of the existing drive capturing the stormwater from the
existing parking area and the existing gravel drive. The size of the bio-retention pond was determined
by the amount of low sloping area between the existing gravel drive and the existing water and sewer
easement. The Bio-Retention pond has a 6 inch maximum water quality depth and a capture volume of
178 cubic feet. The capture volume will treat over 100% of the upstream drainage basin area, but only
73% of the entire area within Basin P2. The remaining untreated area consist of natural vegetation and
therefore does not require any water quality. During high -flow events, overflow from the Bio-Retention
Pond will sheet flow over the east embankment of the pond at the 43 foot long level earth berm.
Calculations for the bio-retention pond have been attached to this report. The majority of the proposed
improvements are located within the area draining to the west and consists of an additional bike
parking, and Landscape areas and the elimination of both the northern and southern parking areas in
front of the building. The existing concrete chase will be extended to the south and north to maintain
the drainage connectivity between the northern and southern concrete areas. Both discharge points
will remain at existing locations. The proposed site is calculated at 44 percent impervious, with a net
loss of 2 percent from existing. By eliminating 2 percent of the impervious area and maintaining historic
drainage patterns, the site will have no adverse effects on any existing drainage systems or adjacent .
properties and will decrease in overall runoff quantities.
If you should have any questions, please feel free to contact me at 970.221.4158, extension 115.
Sincerely,
\1UU1lllll111llp//
\\��OP�� � DEN`�G.F9�O
Cody Snowdon, El Roger Curtiss, PE = S 27362 �S
Project Engineer Vice President
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Design Procedure Form: Rain Garden (RG)
Sheet 1 of 2
Designer
A. Morse
Company:
Northern Engineering
Date:
June 29, 2015
Project:
5608 College Cultivation Facility
Location:
Fort Collins, CO
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, I,
1„ =
560
'%
(100 % If all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = 1,1100)
=
0.560
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time
WQCV =
0,18
watershed inches
(WQCV= 0.8' (0.91' i3 - 1.19 - i?- 0.78 - i)
D) Contributing Watershed Area (including rain garden area)
Area =
10,950
sq If
E) Water Quality Capture Volume (WOCV) Design Volume
VWocv =
tuft
Vol = (WQCV 112)' Area
F) For Watersheds Outside of the Denver Region, Depth of
d,, =
0.43
In
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region,
Vwocv oT+isR =
cu fl
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume
VWQCV USER =
178.0
cu ft
(Orgy if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)
D,,,,-, =
6
in
B) Rain Garden Side Slopes (Z = 4 min., honz. dist per unit vertical)
Z =
4.00
ft / ft
(Use "0" t rain garden has vertical walls)
C) Mimimum Flat Surface Area
Am,. =
119
sq ft
D) Actual Flat Surface Area
A,va„ =
256
sq It
E) Area at Design Depth (Top Surface Area)
A,. =
385
sq it
F) Rain Garden Tolal Volume
V,=
160
cu ft
(Vr((A,m+Ax )/2)'Depth)
3. Growing Media
Dose
Q IB" Rain Garden Growing Media
Q Other (Explain):
City Required Media
4. Underdmin System
Choose One
A) Are underdrains provided?
Ir
L
O YES
® NO
B) Underdmin system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage
y=
N/A
it
Volume to the Center of the Orifice
ill Volume to Drain in 12 Hours
Vol,, =
NIA
cu ft
iii) Onfice Diameter, 3/8' Minimum
Du =
NIA
in
609-001 UD-BMP v3.02.xls, RG 6/29/2015, 4:12 PM
Design Procedure form: Rain Garden (RG)
Sheet 2 of 2
Designer: A. Morse
Company: Northern Engineering
Date. June 29, 2015
Project: 5608 College Cultivation Facility
Location: Fort Collins, CO
Choose One
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
Q yB
A) Is an impermeable liner provided due to proximity
Q NO
of structures or groundwaler contamination?
choose One
6. IMet / Outiel Control
Sheet How- No Energy Dissipation Required
A) Inlet Control
Q Concentrated Flow- Energy Dissipation Provided
7. Vegetation
Q Seed (Plan for frequent weed Control))
Plantings
p Sand Grown or Other High InflltratlonSod
6. Irrigation
Q YES
T0
A) Will the rain garden be irrigated?
NO
I
Notes:
609-001 UD-BMP v3.02.x1s, RG 6/2912015, 4:12 PM
water Quality volume.txt
Project: Cultivation Facility
Basin Description: P2 (Bio-Retention Pond)
Contour
Contour
Depth
incremental
Cumulative
incremental
Cumulative
Elevation
Area
(ft)
volume
volume
volume
volume
(sq. ft)
Avg. End
Avg. End
Conic
Conic
(cu. ft)
(cu. ft)
ft) (cu.
ft)
4,990.290
216.15
N/A
N/A
0.00
N/A
0.00
4,990.400
357.24
0.110
31.54
31.54 .
31.21
31.21
4,990.600
548.86
0.200
90.61
122.15
89.93
121.14
4,990.789
112.11
0.189
62.46
184.61
57.27
178.41
Page 1
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