FLOOD11630 ‎(2)‎

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

the breached levee and channel continued to enter North La Junta on May 4, 19~~9 while an
engineer team from the Corps of Engineers Albuquerque District office inspecte,d damage with
the local sponsor. The local sponsor requested rehabilitation of the Corps levee. The Corps of
Engineers is scheduled to restore the levee under authority of Public Law 8499, Emergency
Levee Restoration and Repair Program.
Local residents have indicated that the Fort Lyons Canal along the northern footlull of North La
Junta may be responsible for a higher ground water table, poor drai~age and basement seepage
problems. There have also been concerns expressed about the backwater effects of the John
Martin Reservoir creating a similaz problem. There has been no spe~ific quantit~~tive correlation
made between groundwater levels and water levels within the Fort Lyons Canal ~nd reservoir
levels at John Martin Dam. Seepage from the Fort Lyons Canal might have some localized
effects. Although the John Martin Reservoir would greatly affect groundwater lE;vels, given the
distance to La Junta, the effect would certainly be attenuated to some exten~
Las Ani~nas: The Arkansas River flood crest passed the town of Las Animas on May 3, 1999.
The USG5 measured the flow shortly after the crest. The peak flow was comput~ed to be 28,000
c.f.s. The Conservancy District and an engineer team from the Corps of Engineers Albuquerque
District office inspected the Corps constructed levee on May 5, 1999. The levee had performed
well, although some minor erosion occurred at the levee toe in a single location. The local
sponsors recalled that the levee had quickly eroded back to the centerline of the l~vee at this
same location during a past flood event. Just upstream of this portion of the Ievee, the Arkansas
River meanders to the right (south) and splits around a heavily vegetated sandbar in front of the
levee. In this reach, the right half of the river flow impinges directly on the levee at about a 60-
degree angle. In an attempt to push the flow away from the levee, the Conservan~cy District
constructed a stone-reinforced berm and road crossing a short distance upstreazn of the point of
attack. The April 29, 1999 flood washed out this embankment and re-established flow against
the levee face. The Conservancy District continued to make inspections and monitor the Las
Animas levee until the river receded. The Conservancy District also maintained ri.prap on hand to
annor the levee toe if it became necessary. The sponsor scheduled an inspection of the entue Las
Animas levee on May 12, 1999. The sponsor of the Corps constructed Las Animas levee project
then sent a request for Corps rehabilitation of the levee project. Repairs were sch~duled to be
completed undez authority of the Corps of Engineers Public Law 8499 Emergenry Levee
Restoration and Repair Program.
Trinidad Reservoir: Between Apri130, 1999 and May 1, 1999, the reservoir was below normal
elevation for the time of yeaz. At that time, flow was not expected to fill the conservation pool.
The dam was storing all inflows from the Upper Purgatoire River, which was appr.oximately
2,000 c.f.s. on May 3, 1999. Field observations were initiated by May 4, 1999 as a result of the
rapidly rising pool elevation. Surveillance and onsite inspections were conducted in accordance
ER 1110-2-100, Periodic Inspections and Continuing Ewiluation for Completed Givil Works
Structures. Seepage collected downstream of the dam in the Frisco Canyon azea vvas being
monitored daily. Frisco Canyon is located on the east end of the dam. Seepage fl~ws in the
Frisco Canyon are measured using a V-notch weir. Seepage on the right abutment of the main
Chapter 3- Flood ofApri119, 1999
Post Flood Assessment Report 22 Draft Revised 09/09/99