FLOOD07093

• County: Otero
• County: Pueblo
• Community: Otero, Pueblo Counties
• Stream Name: Arkansas River
• Basin: Arkansas
• Title: Arkansas River Channel Capacity and Riparian Habitat Planning Study
• Date: 8/1/2001
• Prepared For: CWCB
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

found that the area is primarily a huge wetlands area with extensive areas of surface water. The
CWCB 1998 and USDA 1999 aerial photography also show the areas of standing and slowly
flowing surface water in the floodplain. The surface water covers an area that extends from
upstream of the U.S. Highway 50 Bridge north of Las Animas, downstream through Channel
Problem Area No.3, to John Martin Reservoir (Aerial Photographs 5 and 6). This surface water
slowly flows through extensive areas of wetland vegetation such as cattails and in some places it
is deep enough to form small areas of open surface water (Photographs 1 and 2). Salt cedar
growth in the area is also extensive and extremely dense. Small stands of willow were observed,
and upstream of Channel Problem Area No.3 near the U.S. Highway 50 Bridge north of Las
Animas, Russian olive is invading the floodplain. Cottonwoods in the area are maturing but
generally, they remain to be rather sparse. There is some new cottonwood growth and currently
there are more cottonwoods in the area than were visible in 1965 and 1980 aerial photographs;
however, the increase in surface water is causing much of the new cottonwood growth to die out
due to inundation (Photograph 2). Field observation also found that a significimt amount of this
surface water is now flowing to the Las Animas levee's interior drain outfall ditch.

Lindauer and Ward's (1968:9-10, 18, Table I, 39) Transect Line No.5 measured 1,690
feet in length and their sampling and analysis indicated that salt cedar cover was 31 percent and
cottonwood cover was 9 percent for a 40 percent total foliage cover along the transect. Although
a true comparison cannot really be accomplished between their actual field samples and the 1998
CWCB aerial photography, it is estimated that the vegetative cover seen in the 1998 photograph
is about twice as dense as their 1968 description and that the majority of that growth is salt cedar.
Vegetation in Channel Problem Area No.3 has encroached on the river channel and is extensive
across the floodplain. This dense vegetation is having significant effects on flood flow
conveyance, conveyance capacity, and on overbank sediment deposition.

4.2 INTERPRETATION OF CHANNEL PROBLEMS AS SEEN IN AERIAL
PHOTOGRAPHS

The increasing ground water problems in the La Junta area (see Ground Water Problem
Areas No.1 and No.2, Figure 2), have been attributed to the local application of surface water
for irrigation, seepage of irrigation water from the Fort Lyon Canal, seepage of surface water
from the Arkanslls River to the ground water aquifer, and to decreased ground-water pumpage
for irrigation (Watts and Lindner-Lunsford 1992:51; Bossong 2000). Other irrigation water
transport and storage facilities, all located within 15 miles of the Arkansas River, may also be
affecting the local ground water table. These facilities include the Ft. Lyon Storage Canal, the
Lake (Holbrook) Canal, Lake Henry, Lake Meredith, Horse Creek & Black Draw Reservoir, Dye
Reservoir, Holbrook Reservoir, Manby Lake, Taylor Lake, Cheraw Lake, Horse Creek
Reservoir, and Adobe Creek Reservoir. Watts and Lindner-Lunsford (1992:1) evaluated "Five
water-management alternatives that were proposed as methods of lowering the water table in the
valley [that include]: (1) Deepening the channel of the Arkansas River, (2) lining the Fort Lyon
Canal, (3) increasing municipal pumpage, (4) installing relief wells, and (5) installing a drainage
system." Each of these five alternatives would have local effects of varying effectiveness (Watts
and Lindner-Lunsford 1992:51-52).

The aerial photography provided visual evidence of historic encroachment on the

49