FLOOD11630 ‎(2)‎

• County: Statewide
• Basin: Arkansas
• Title: Post Flood Assessment Report - Arkansas River
• Date: 9/15/1999
• Floodplain - Doc Type: Flood Documentation Report

the Arkansas River. Between the time of the Phase I General Design Memorandum effort in the
area and the 1993 investigation, the drainage inlets to the Arkansas River which had been above
the normal water elevation of the river had become submerged.
Stormdrain backup is the primary cause of flooding in the south portion of La Junta and is
especially frequent along U.S. Highway 50 (First Street). Local afficials and residents have also
indicated that backwater effects from the John Martin Dam reservoir and percolation from the
Fort Lyons irrigation channel have surchazged groundwater levels and made some lands unusable
for agricultural use. Others contend that backwater effects on the groundwater from the dam
may he influencing river stage and flaod frequencies as well.
A pilot project to mine river sediments downstream of La 3unta is expected to start soon. It may
prove to have a beneficial effect on the channel aggradation problem upstream in La Junta. A
commercial river mining venture would provide the least cost alternative for the City of La Junta
to regain channel capacity lost over the years to aggradation in the river. However, a without a
comprehensive sediment transport study, it is difficult to determine the long-term benefits and
other effects of such a venture.
FLOOD MANAGEMENT SYSTEM DEFICIENCIES
Fountain Creek and Tributaries
Fountain Creek: ~'here are no flood managernent systems along Fountain Creek upstream of
Pueblo. The bankfull capacity of the creek near Colorado Springs was estimated to be 4,470
c.f.s. in April 1994. Furthez'downstream near the City of Fountain the bankfull capacity of the
creek was estimated to be only 2,450 c.f.s. Damages in Fountain aze estimated to begin at a flow
of 3,890 c.f.s. which is something less than a 10-year event. The Fountain Creek I,evees and
Channelization project in Pueblo provides flood pratection up to the 200-year event.
Templeton Gap Floodway Diversion Channel: This project was constructed in 1949 by the
Corps of Engineers on this left bank tributary to Monument Creek downstream of Colorado
Springs. The confluence enters from a much higher elevation than the Monument Creek channel
invert. As a result, a large plunge pool has formed. Although an exit channel cutoff wall was
included, the plunge pool has begun to undermine the e~t channel cutoff wall and invert.
Continued erosion could cause cantilever failure of the channel within the confluence area.
Large scale undermining could threaten commercial properties on the right overbank of
Templeton Gap and residential properties on the left overbank.
Manitou Springs: Fountain Creek is constricted through the city of Manitou Springs by
encroaching developments. The channel ca~acity is extremely low at about 1,000 c.f.s.
Damages begin to occur above this flow capacity which is about a 5-year flood event.
Recommendations have been pursued to enhance flaod warning systems; however, the speed at
which flood flows reach and exceed channel capacity is so fast that flood warning systems are
~ Chapter S- Flood Risk Assessment
Post Flood Assessment Report ~ 37 Draft Revised 09/09/99