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748 Whalers Way
Suite 200
Fort Collins, CO 80525
970.226.0557 main
970.226.0204 fax
ideas@tstinc.com
www.tstinc.com
February 26, 2025
City of Fort Collins
700 Wood Street
Fort Collins, CO 80521
Re: Drainage Letter – 5408 South Timberline Road
Project No. 9000.0126.00
TST, Inc. Consulting Engineers (TST) are pleased to submit this drainage letter for
5408 South Timberline Road property. The purpose of this letter is to evaluate the
addition of a shed to an existing property.
The 5408 South Timberline Road project is located in the southwest quarter of
Section 5, Township 6 North, Range 68 West of the 6th Principal Meridian, within
Fort Collins, Larimer County, Colorado. The project is located in the McClelland’s
Creek Basin, according to Fort Collins Master Drainage Plan. The existing lot
contains approximately 2.13 acres that consists of an existing house, sheds, stable,
and open space. A proposed shed, 30 feet by 40 feet with an 8-foot covered porch,
is being proposed within the open space on the east side of the lot. The existing
drainage patterns remained unchanged in the proposed condition. The runoff from
the site sheet flows to the northeast corner of the lot which is collected in an existing
channel that runs north to the southern border of the Stetson Creek Subdivision.
The runoff is then directed east via a channel and directly into McClelland’s Creek
(Muskrat Ditch). See Appendix A for a drainage map showing existing drainage
patterns.
According to Fort Collins criteria, detention requirements can be waived if the
impervious percentage is less than what was used for the City’s Master Drainage
plan for the basin. The project is in subbasin 305, within the McClelland’s Creek
master basin, which assumes a percent imperviousness of 35% based on the
zoning designation of Estate Residential (ER). A land use area calculation was
conducted to ensure our compliance with the requirement. See Appendix B for the
land use calculation showing the difference between the proposed condition and the
existing. The lot was analyzed with half of Timberline Road adjacent to the property
making the total area analyzed approximately 2.29 Acres. The calculation shows
that the new imperviousness is 34.06% which does not require detention within the
project area. Water quality will be handled by directing all the roof drains onto the
open space around the proposed shed that will sheet flow across established
vegetation. No detention or water quality pond will be necessary for the proposed
shed.
City of Fort Collins Approved Plans
Approved by:
Date:
Wes Lamarque
06/13/2025
Appendix A:
Drainage Plan
Appendix B:
Land Use Calculation
5408 South Timberline Road Drainage Letter
Composite
C C2 C10 C100
Open Lands, Transition 1.87 0.20 20
Streets: Paved 0.31 0.95 100
Roofs 0.11 0.95 90
Open Lands, Transition 1.91 0.20 20
Streets: Paved 0.31 0.95 100
Roofs 0.07 0.95 90
Basin 1 2.29 34.06%
Attribute Area
(ac)
Composite Runoff CoefficientsRunoff
Coefficient, C Percent ImperviousImpervious
0.34 0.34 0.420.34
Onsite Basin Composite Runoff Coefficients
Basin/ Sub-Basin Area (ac) Attribute
0.41Exisitng Basin 1 2.29 32.99% 0.32 0.32 0.32