FLOOD01785

• County: Larimer
• Community: Fort Collins
• Stream Name: South Platte Tributaries
• Title: Hazard Mitigation 404 Grant Application Floodproofing
• Date: 9/1/1999
• Prepared For: Larimer County
• Prepared By: Fort Collins
• Floodplain - Doc Type: Miscellaneous

City of Fort Collins

Hazard Mitigation 404 Grant Application

hydrology calculations, and flood hazard delineations associated with the 10, 100
and 500-year rainfall events. Flooded areas within the urban drainage basins are
generally associated with uncaptured runoff rather than a defined river or stream.
Local floodplains are administered by Fort Collins the same as FEMA floodplains
with regard to permitting and design requirements. The Old Town Master
Drainage Basin Plan (1993) identifies specific areas within Old Town with
particular flood problems such as the intersections of LaPorte and Shields, Mason
and Mulberry, Locust and Whitcomb, Locust and Whedbee, Plum and Bluebell,
and Magnolia and Washington Streets_ Average annual flood damages for the
Old Town drainage basin were determined to be $585,000_

Of the total 797 structures described above, there are approximately 220
structures (1995 inventory) in the Poudre River Floodplain that includes some
buildings located in the County jurisdiction. The Poudre River Master Plan
estimates $6 million of property damage that may occur along the River during
the I DO-year flood_

Spring Creek has approximately 34 structures (1995 inventory) in the regulated
floodplain. Following recent (1983-1993) channel, culvert, and bridge
improvements, and a revised FlS (1996), a substantial number of structures have
been removed from the regulatory floodplain including 41 structures that were
acquired by the City and removed.

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There are currently (1995) 542 structures in the Dry Creek 100-year floodplain
within the City limits_ Of the 542 structures, there are approximately 101
commercial and 441 residential structures_ In addition, there are 675 residential
and 254 commercial structures in the SOD-year floodplain. The estimated
damages resulting from the 100-year flood is $5,779,700 (1990 dollars). Because
of the network of irrigation canals which intercept small to moderate flood flows
and much of the excess drainage from entering the lower Dry Creek basin in Fort
Collins, a false perception of the flood hazard has prevailed resulting in
development of lower Dry Creek basin in the City before floodplains regulations,
design criteria, or basin master plans_ These canals, however, do not have the
capacity to intercept larger flood flows, such as the I DO-year event, and increased
drainage flows from new development in the lower basin of Dry Creek is already
increasing the magnitude and frequency ofthose flows.

Fossil Creek has no structures in the floodplain. "Erosion buffer limits" were
established to protect man-made structures from the instability of the river system.
The erosion buffer limits establish minimum setbacks for development near Fossil
Creek, thereby eliminating all development within the flood and erosion hazard
area.

Specific Causes of the Problem

Discussed below are reasons for frequent shallow flooding of buildings and
reasons why floodproofing may be an effective solutions.

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