HomeMy WebLinkAboutCULTIVATION FACILITY (5608 S. COLLEGE AVE.) - FDP - FDP150016 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTApril 22, 2015
Basil Hamdan
City of Fort Collins Utilities
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 6th 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 retail 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 concrete area also located to the south of the building. An existing gravel
drive travels around the north and east of the current 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. The stormwater routed to the west is conveyed overland from south to north through
a concrete chase connecting the two current 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 remain as existing with no proposed improvements other than a bio retention pond located
at the northeast corner of the site. A drainage swale east of the existing gravel drive directs flow from
the vegetated area to the Bio-Retention pond. The size of the bio-retention pond was determined by
the amount of low sloping area within that corner. The Bio-Retention pond has a 6 inch maximum water
quality depth and a capture volume of 158.0 cubic feet. The capture volume will treat over 85% of Basin
P2 watershed tributary area. During high-flow events, overflow from the Bio-Retention Pond will sheet
flow over the north-east embankment of the pond at the 18.5 foot long level edge. 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. By
eliminating 2 percent of the impervious area, 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,
Cody Snowdon, EI Roger Curtiss, PE
Project Engineer Vice President
Character of Surface
Percent
Impervious*
Streets, Parking Lots, Roofs, Alleys, and Drives:
Asphalt ……....……...…...…...………………………………………….. 100.00%
Concrete …….......…….……………….………………………………… 90.00%
Gravel ……….………….………………………………………………….. 40%
Roofs …….…….………………………………………………………….. 90%
Lawns and Landscaping
Sandy Soil ……..………………………………………………………….. 0%
Clayey Soil ….….……….…………………………………………………. 0%
Basin ID Basin Area
(sq. ft.)
Basin Area
(acres) Area of Concrete
Streets, Sidewalks
(sf)
Area of Roofs
(sf)
Area of
Gravel
(sf)
Area of Vegetated
Surfaces
(sf)
Percent
Impervious
H1 3,664 0.084 2,538 0 15 1,111 63%
H2 14,962 0.343 2,106 3,600 2,767 6,489 42%
Total: 18,626 0.428 4,644 3,600 2,782 7,600 46%
P1 3,664 0.084 2,169 0 15 1,480 53%
P2 14,962 0.343 2,041 3,600 2,767 6,554 41%
Total: 18,626 0.428 4,210 3,600 2,782 8,034 44%
Runoff Coefficients are taken from Table RO-5 of the Urban Drainage and Flood Control District Drainage Criteria Manual (06/2001)
HISTORIC RUNOFF COEFFICENTS
* Percent Impervious
values are taken from
Table RO-3 of the
UDFCD Drainage Criteria
Manual (06/2001)
Page 1 of 1
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 42.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.420
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.15 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 14,958 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = 0.43 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = 158.0 cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 6 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 105 sq ft
D) Actual Flat Surface Area AActual = 256 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 385 sq ft
F) Rain Garden Total Volume VT= 160 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = N/A ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
A. Morse
Northern Engineering
April 22, 2015
5608 College Cultivation Facility
Fort Collins, CO
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
609-001 UD-BMP_v3.02.xls, RG 4/22/2015, 12:25 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes: 85.6% of the watershed tributary area of Basin P2 is captured in the Water Quality Volume of 158 cu ft. and treated in the Bio-retention Pond.
Design Procedure Form: Rain Garden (RG)
A. Morse
Northern Engineering
April 22, 2015
5608 College Cultivation Facility
Fort Collins, CO
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
609-001 UD-BMP_v3.02.xls, RG 4/22/2015, 12:25 PM