HomeMy WebLinkAboutDrainage Reports - 06/15/2023September 15th, 2021
City of Fort Collins City of Fort Collins Approved Plans
Community Development and Neighborhood Services Approved by: Dan Mogen
281 North College Avenue Date: 06/15/2023
Fort Colfins, CO 80522
RE: DRAINAGE MEMORANDUM FOR NUMERICA MINOR AMENDMENT PROJECT
FORT COLLINS, COLORADO
NE PROJECT #: 1857-001
Dear Staff:
Northern Engineering Services is pleased to submit this Drainage Memorandum for the Numerica Minor
Amendment application for your review. The site occupies the parking lot and public parkway of 4450 Denrose
Court in Fort Collins, C0. The subject site is located in the Northwest quarter of Section 15, Township 7 North,
Range 69 of the 6th P.M. Fort Collins, Larimer County, Colorado. The site is bounded to the south by Denrose
Court, to the west by McDonald's, to the north by East Mulberry Street, and to the east by a business building.
This Drainage Memorandum has been prepared in accordance with the Fort Collins Stormwater Criteria Manual
(FCSCM) and Mile High Flood District (MHFD) standards.
The intent of this project is to amend the current parking lot with one continuous island containing a new
garage, employee pavilion, access walkways, and landscaping that preserves as much of the existing foliage as
possible. There will also be an additional garage instalfed to the north replacing an area of asphalt parking
spaces, as well as a paved observation area with a small structure at the southeast corner of the building to
replace a small hardscaped area. There will also be an extension of the public walk along the north edge of
Denrose Court. The intention is to construct these improvements in a manner that maintains historic drainage
patterns without installation of new LID or drainage infrastructure. The bulk of historic runoff at this site is
directed to an existing area inlet that directs water to the existing drainage swale to the north, the remainder is
channeled to the same location via curb cutout directed to a section of rip-rap along the north edge of the lot.
Our calculated net change in impervious surface area demonstrates a decrease in impervious area by over 3000
square feet, as such we believe that provided all runoff of the developed site is directed to the same existing
outlets at the same proportions, no downstream improvements or new onsite LID treatments will be required.
Upon completion of the amendment, the disturbed areas will maintain historic drainage patterns and
contribute to a net decrease in impermeable space.
If you have any questions, please feel free to contact us at your earliest convenience.
Sincerely,
NORTH ERN ENGINEERING SERVICES, INC.
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Sterling Hallauer
Project Engineer
NORTHERfdENGINEERING.COM � 970.221.4158
FORT COLLINS � GREELEY
Danny Weber, PE
Project Manager
PRELIMINARY DRAINAGE MEMO: Numerica MinorAmendment
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Project: 1857-001 Numerica Minor Amendment
Calc. By: S. Hallauer
Date: September 15th, 2021
. .- .
Surface Area Percent Impervious
Description
(sq ft) Impervious Area (sq ft)
Rooftop 0.00 90% 0.00
Concrete 1822.37 100% 1822.37
Asphalt 8596.60 100% 8596.60
Pavers 0.00 40% 0.00
Gravel 0.00 40% 0.00
Landscaping 3404.26 2% 68.09
Total 13823.22 10487.05
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Surface Area Percent Impervious
Description
s ft Im ervious Area s ft
Rooftop 2775.69 90% 2498.12
Concrete 3696.83 100% 3696.83
Asphalt 795.35 100% 795.35
Pavers 0.00 40% 0.00
Gravel 0.00 40% 0.00
Landscaping 6281.21 2% 125.62
Total 13549.07 7115.92
Difference in Impervious Area (ft2) -3371.13
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