HomeMy WebLinkAboutGrading Plans - 01/12/2024FRONT RANGE
Stormwater & Floodplain
Consulting
Fort Collins Stormwater Utility
Attn: Stephen Agenbroad
Development Review Engineer
222 Laporte Avenue
Fort Collins, CO 80522
December 22, 2023
Grading/Stormwater Plan Accepted
(Building Permit Released)
Accepted by: sagenbroad
Date: 01/12/2024
B2308593
RE: 416 N. Grant Avenue Drainage and Imperviousness Summary
Stephen,
Thank you for your time in review of the 416 N. Grant Avenue project. Based on our discussions with
you we are providing a summary of developed versus proposed imperviousness for the site, along with a
Historic Drainage Exhibit and a Developed Drainage Exhibit (Attached). The project site is located just
north of the intersection of North Grant Avenue and Cherry Street. General drainage patterns direct
historic surface flows primarily to the west and to the east.
The site has historically drained into the rear alleyway just to the east of the development site, with a
portion of the site draining into N. Grant Ave Right of Way. Drainage enters both conveyances as sheet
flow, and both flow paths ultimately which direct flow into Cherry Street Right of Way, just south of the
development site. We understand that there is concern regarding any increase in storm runoff entering
the existing rear alleyway and that if there is an increase in impervious area of over 350 square feet
draining from the site into the alleyway, analysis showing capacity or mitigation may be necessary.
Below is a summary of historic versus developed conditions impervious areas.
Historic versus Developed Conditions Impervious Areas:
BASIN ID BASIN AREA BASIN CONCRETE ASPHALT ROOFTOP GRAVEL
(SF) AREA (AC) AREA (AC) AREA (AC) AREA (AC) AREA (AC)
H 1 2744.28 0.06300 0.00165 0.00000 0.00270 0.00000
H2 8537.76 0.19600 0.00317 0.00000 0.04640 0.00000
Overall Total Historic 0.00482 0.00000 0.04910 0.00000
D1 3179.88 0.07300 0.03250 0.00000 0.03193 0.00000
DZ 8102.16 0.18600 0.00157 0.00000 0.03193 0.00000
Overall Total Developed 0.03407 0.00000 0.06387 0.00000
H2 vs. D2 (Drng to AlleyJ -435.6 -0.01 -0.001603 0.00000 -0.01447172 0.00000
P.O. Box 1561 � Cheyem�e, WY K2003 �(970)690-0493
www. frstorm flood. com
As shown above the proposed development will cause a net decrease in impervious area draining to the
rear alleyway. Based on this, there will be no net increase in runoff volume or discharge into the rear
alleyway and the project will meet the 350 square foot criteria discussed above.
Please feel free to contact me with any questions you may have.
Sincerely,
Front Range Stormwater & Floodplain Consulting, LLC
C�
Aaron Cvar, Ph.D., P.E.
President
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GRADING PLAN FOR
416 N. GRANT AVENUE
LOT 21 AND 22, BLOCK 284, WEST SIDE ADDITION TO THE CITY OF FORT COLLINS, LOCATED IN
NORTHWEST QUARTER OF SECTION 11, TOWNSHIP 7 NORTH, RANGE 69 WEST OF THE 6TH P.M.,
CITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADO
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ROOFTOP ORAINAGE FROM FRONT HALF OF
PROPOSED HOtJSE TO BE DIRECTE�VIA
DOWNSPOUT DRAIN SYSTEM TO N. GRANT
AVENUE RIGHT OF WAY.
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NOTES:
1. PROPERTY LMES SHOWN FROM
LARIMER COUNTY GIS DATA AND ARE
SHOWN fOR REFERENCE PURPOSES ONLY
- NOT FOR DESIGN.
2. ANY AERIAL IMAGERY SHOWN IS FROM
CNES (2020� DISTRIBUTION AIRBUS DS.
3.OFFSRE TOPOGRAPHIC CONTOURS (1-FT
INTERVAL) PER LIDAR �ATA fROM LARIMER
COUNTY GIS DATA. CONTOURS SHOWN
FORREFERENCEPURPOSES ONLY-NOT
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