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

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ARKANSAS RIVER FROM OTEROIPUEBLO COUNTY LINE
TO JOHN MARTIN RESERVOIR
CHANNEL CAPACITY AND RIPARIAN HABITAT PLANNING STUDY

4. DOCUMENTATION OF VEGETATI(j)N AND CHANNEL PROBLEMS

4.1 RESULTS OF AERIAL PHOTOGRAPH COMPARISONS OF VEGETATION

Previous studies conducted in the Arkansas River Valley that specifically discussed
phreatophytes and their effects include those reported by Bittinger and Stringham (1963),
Lindauer and Ward (1968), Lindauer (1970, 1983 1990), Nadler (1978), and Nadler and
Schumm (1981). These studies included areas that are specific to this planning study's problem
areas. Aerial photography from CWCB (1998), USQA (1999), (Otero County 1975), USACE
(1980), and several other sources was utilized during this planning study and are as referenced.
The aerial photography from CWCB (1998) and the USDA (1999) was color photography, all
other aerial photography reviewed was black and white. Aerial Photographs, that have been
numbered 1 - 6 and are incorporated into this report, are sequential from upstream near La Junta
to downstream at Las Animas. This report is a review of aerial photography and therefore, the
report is limited in the fact that no quantitative measurements of vegetation can be reported and
only qualitative descriptions are presented. The effeCt of riparian vegetation, which is primarily
salt cedar, on the Arkansas River in southeastern Colorado, is that salt cedar has encroached
upon and confines the river to the existing channel. The salt cedar in effect is armoring the
channel banks and therefore the position of the channel is maintained even during small flood
events. The salt cedar; however, does slow overbank flood flows and is causing significant
sediment deposition in the floodplain.

In Channel Problem Area No.1 (Figure 2), yisual comparisons between Otero County's
1975 aerial photographs and the 1998 aerial photogt1aphs provided by the Colorado Water
Conservation Board found that there is much more "egetation in 1998 that includes trees and
herbaceous growth. Vegetative composition in the area was similar to that previously
documented. Cottonwood and salt cedar had matured in the area and salt cedar stands were
much denser and more extensive in 1998. Dense, new salt cedar growth is very evident and has
encroached on reshaped sand bars and on the river channel banks. Although it is difficult to
compare the 1975 black and white photos with the ~998 color photographs that are also at
different scales, the river channel appears to be similar in width between the 1975 and 1998
photographs and the river has maintained a similar channel configuration. In 1998, salt cedar
appears to be much denser in the eastern half of Chrtnnel Problem Area No. 1. This denser
growth begins about 1.5 miles downstream of the Highway 109 bridge at La Junta and extends
for about 4 miles in length. Vegetation in the upper half of Channel Problem Area No. 1 (Aerial
Photograph 1) would cause some slowing of overbank flood flows but this would not be
significant. In the lower half of Channel Problem Area No.1, vegetation is dense enough that it
would cause flood flows to slow and could cause significant overbank sediment deposition.

Lindauer and Ward (1968:9, Appendix X, 38) selected an area located about 314-mile
east of Bent's Old Fort National Historic Site for their Transect Line No.4. Transect 4 is about 2