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FLOOD11630 (2)
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FLOOD11630 (2)
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Last modified
1/26/2010 10:25:17 AM
Creation date
1/5/2009 12:18:27 PM
Metadata
Fields
Template:
Floodplain Documents
County
Statewide
Basin
Arkansas
Title
Post Flood Assessment Report - Arkansas River
Date
9/15/1999
Floodplain - Doc Type
Flood Documentation Report
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Rocky Ford: Although located well above the Arkansas River flood plain, on th~e south bank, <br />Rocky Ford is typically subject to flooding from irrigation canals that intercept n~umerous small <br />arroyos in the vicinity. The canals do not have by-pass structures so floodflows &om the arroyos <br />combine with irrigation flows to breach the canals. The overflow gQes through F~ocky Ford to <br />pond in low-lying azeas. <br />During the Apri129, 1999 flood the head gate of the canal on the Arkansas River was <br />overwhelmed and allowed unrestricted inflow from the river. This caused the canal to fail and <br />flooding in Rocky Ford. Dikes around sewage treatment lagoons were threatened, but never <br />breached. On May 2, 1999 tl2e town requested a loan of sandbags from the Corp~. The same <br />afternoon, approximately 7,500 sandbags were sent from John Martin Dam. Alttiough <br />recommendations were made for residents to evacuate, it was not an enforced ev~icuation. Most <br />residents chose not to evacuate. Some homes experienced flooding of yards and basements. <br />Sewer lines also backed up as a result of the flooding. <br />La Junta: The local levees and Corps of Engineers consgructed levee are only able to provide <br />minimal protection for the unincorporated azea known as North La Junta. North ]La Junta is <br />subject to tlie highest risk for flooding due to its location within the relatively low southern <br />overbank area of the Arkansas River. The Local Flood Protection Project Phase 1 General <br />Design Memorandum study by the Corps in 1986 showed the entire North La Jun.ta azea to be <br />within the 10-year floodplain. <br />Aggradation of the riverbed in this reach compounds the problem. Since constn~ction of the <br />Corps of Engineers spoil bank levee in 1956, Otero County officials have estimat~d that channel <br />capacity has been reduced down to a third from 15,000 c.f.s. to about 3,000 c.f.s. Residents <br />claimed that areas unaffected by the major flood of 1921 and 1965 had flood wate~rs reach them <br />during the 1999 flood. <br />In November 1997, the Colorado State Water Division 2 evaluated aggradation in the Arkansas <br />River at La Junta between 1963 and 1997. They found that aggradation had occwTed, but the <br />corresponding loss in channel conveyance capacity was much more significant. Some of this <br />reduction was attributed to increased channel vegetation and debris. ~e State W~~ter Division 2 <br />evaluation indicated that the aggradation within the low point of the river channel ranged from <br />1.45 feet to 4.94 feet. The 1965 flood scoured the channel and briefly improved c:hannel <br />conveyance; however, the rate of aggradation appears to have increased dramatically in the yeazs <br />that follow. The increased base flow of Fountain Creek from the discYzarge of trar~,s-mountain <br />water from Colorado Springs may be a contributing factor to erosion within Fountain Creek and <br />subsequent aggradation in the Arkansas River. These diversions from the western face of the <br />Continental Divide started with the Hoosier Tunnel project in 1952 and increased with the <br />completion of the Homestake Water Development Program by the cities of Aurora and Colorado <br />Springs in 1965. The Fryingpan-Arkansas Project by the BuRec further increased this potential <br />in June 1981; however, the City of Colorado Springs does not currently use its allotment of trans- <br />mountain water from the BuRec project. The dramatic change in channel conveyance capacity is <br />summarized in Table 3-3. <br />Chupter 3- Flood of April 19, 1999 <br />Post Flood Assessment Report 20 Dralr Revised 09/09/99 <br />
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