HomeMy WebLinkAboutCOLLEGE EIGHT THIRTY - PDP - PDP150019 - SUBMITTAL DOCUMENTS - ROUND 1 - STORMWATER-RELATED DOCUMENTSLID Conformance Report
Date: September 9, 2015
Project: College Eight Thirty Project No. 574-006
Fort Collins, Colorado
Attn: Stormwater Staff
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
Stormwater Staff:
This letter serves to document conformance of the above referenced project with City of Fort Collins Low
Impact Development (LID) requirements. In particular, the project is meeting Section 3.1 of the Fort Collins
Stormwater Amendments to the Urban Drainage and Flood Control District Criteria Manual, including Section
3.1 (a)(1) requiring that no less than 50% of any newly added impervious area be treated using one or more
LID techniques and Section 3.1(a)(2) requiring that no less than 25% of all new paving use a permeable
pavement technology that is considered an LID technique.
Section 3.1(a)(1)
The project as a whole is proposing 0.307 acres of new impervious area. This results in a minimum required
LID treatment area of 0.154 acres. The project is providing 0.235 acres of impervious area treated by
pavers (directly or indirectly), and is treating 0.021 acres of impervious areas using rain gardens. The total
project area treated by LID techniques is 0.257 acres, which is 83.48% of the total new impervious area.
There is also a small area of roof (0.018 acres) that is being released into a landscaped area within the public
ROW that is not being counted towards the requirement but that does treat runoff, making the effective
treatment percentage even higher.
Section 3.1(a)(2)
The project as a whole is proposing 2,165 sf of new impervious paving that will be exposed. This results in a
minimum required permeable paving area of 541 sf. The project has evaluated various areas for pavers, and
has determined that the only appropriate location is the exposed area of paving. The total area of permeable
pavers provided by the project is 2,165 sf, which is 100.0% of the total new paving. This greatly exceeds
the requirement of 25%.
An exhibit has been provided to illustrate the topics outlined. Please feel free to contact me if you have any
questions.
Sincerely,
Andrew Reese
Project Engineer
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 434 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 14 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 0.0 cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = 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 = 10 sq ft
D) Actual Flat Surface Area AActual = 32 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 32 sq ft
F) Rain Garden Total Volume VT= 16 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 = 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
College Eight Thirty
North Rain Garden
Design Procedure Form: Rain Garden (RG)
Andy Reese
Northern Engineering
September 9, 2015
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
UD-BMP_v3.02_North Raingarden.xls, RG 9/8/2015, 12:52 PM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 434 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 14 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 0.0 cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = 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 = 10 sq ft
D) Actual Flat Surface Area AActual = 32 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 32 sq ft
F) Rain Garden Total Volume VT= 16 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 = 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)
Andy Reese
Northern Engineering
September 9, 2015
College Eight Thirty
South Rain Garden
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
UD-BMP_v3.02_South Raingarden.xls, RG 9/8/2015, 12:51 PM