FLOOD11630 ‎(2)‎

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

TABLE 3-3
CHANGE IN CE[~~NNEL C(~]V]EYANCE CAPAC`I7CY
ARKANSAS RIVER AT LA JUN'~'A
Period Covered Gauge Heig ht = 5.5 feet Gauge Heig ht = 7.0 feet
Q(C•F•S•) Chan e in Q(C•F•S•) Chan e in
10/1163 - 9/30/64 1,200 (est) N/A 3,700 N/A
10/1/64 - 6/14/65 1,200 0 3,700 . 0
6/14/65 - 9/30/65 1,230 30 3,700 0.
11/1/67 - 9/30/71 895 -305 3,700 0.
10/1/71- 9/30/80 660 -540 3,190 -510
10/1/80 - 2/28/91 320 -880 1,860 -1,840
3!1/91 -11/1997 98 -1,102 730 -2,970
The elevation of incorporated La Junta on the south overbank area of the Arkansas River is about
twenty feet higher in elevation than North La Junta. Nevertheless, the City of La Junta is still
subject to frequent IIooding along U.S. Highway 50 (First Street) neag Brandish A,venue as a
result of stormdrain backup. Drainage from the Anderson Arroyo on the west andl King Arroyo
on the east have begun to face near adverse northwazd gradients into the Arkansas River as a
result of aggradation in the streambed. The First Street Stormdrain running eastward also backs
up to pond along the highway when the flap gates shut as a result of Arkansas River flow and
aggradation related ponding. The Fifth Street Stormdrain, further south of First Slreet, also runs
eastwazd and enters King Arroyo; however surface flows northward a~ong the streets by pass the
stormdrain and contribute to flooding along the highway. The Santa Fe Street Stormdrain runs
northward into the First Street Stormdrain and further contributes to interior floodi~ng along the
highway. Commercial and residential properties are oftem affected by this interior drainage
problem. Fortunately the arroyos and local drainage supplied little flow during this event Flood
water depths still exceeded three to four feet along First Street and Second Street n~ear their
intersections with Brandish and Harriet Streets just west of King Arro~o.
'The Arkansas River crested on May 2, 1999. According go a USGS estimate, the peak flow was
approximately 40,000 c.f.s. just downstream of La Junta. The spoil bank levee performed well
until the levee was overtopped. The overtopping flows created breaches at four points along the
levee. The county worked around the clock to repair the breaches and cutoffthe floodwaters.
The entire levee upstream of the State Route 109 (Main Street) Bridge was overto~rped. Over
200 homes and commercial properties were flooded. As many as 300 a~esidents were evacuated
from their homes. Floodwaters from the Arkansas River had also ente~ed the Fort .Lyons
irrigation channel in North La Junta. The channel subsequendy breached and floocied North La
Junta. It was unclear whether the irrigation channel breached prior to the Corps le~~ee being
overtopped; however, a local newspaper account did indicate that this ~,vas the case. Water from
Chapter 3 -Flood ofApri12~9, 1999
Post Flood Assessment Report~~ 21 1~raft Revised ~~9/09/99