WSP06131

• File Number: 8149.911
• Description: Miscellaneous Small Projects and Project Studies - SE Needs Assessment and PSOP
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 8/1/2001
• Author: US Army Corps of Eng
• Title: Arkansas River From John Martin Dam To The Colorado-Kansas State Line Channel Capacity and Riparian Habitat Planning Study
• Water Supply Pro - Doc Type: Report/Study

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1. · John Martin Reservoir. Since that time the elevation of the top of thiB sandstone has
controlled a temporary base level that has slowed down cutting upstream from the
arch. This slowing of downcutting has caused the river to meander widely along the
section between Adobe Creek and the arch" (ShllIps 1969:C68-C69).
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Sharps (1969:C70) attributed the lateral migration of the river to the disproportionate deposition
of large volumes of finer sediments from the river's tributaries. Recent studies indicate that
these geologic sedimentation processes, that involve the deposition oflarge amounts of sediment
to the main channel, are still active today (USACE 1965:23, 1970:B65-B66, 1973:50-53,
1985:15; Nadler 1978:89, 113, 126; Nadler and Schumm 1981:104.109,113).

The Las Animas arch may also be responsible for the location of what has been described
as the famous "Big Timbers" (Grinnell 1923:82-85: iWolf 1932:207; West 1995:26-27,
frontpiece map). Big Timbers, located downstream of John Martin Dam and the arch, extended
to the vicinity of Lamar and was the location of a large concentration of cottonwood trees, many
of which grew to huge sizes (Grinnell 1923:82-85: Wolf 1932:207). The Big Timbers was a
noted resting stop on the Santa Fe Trail and was also extensively used by Native American
during the winter months. The valley area below the arch widened and flood flows constricted
by the arch most likely rushed through the Las Aninias Arch flowing out of the channel to
overbank areas and spread over the widening valley.: Thia annual event would have replenished
the soil nutrients in thiB area and afforded the contin\led growth of a healthy and extensive
cottonwood forest.

Another interesting feature of the valley, located on the south side of the river, beginning
east of La Junta and reaching into central Kansas, is :"the most striking sand-dune area of
Colorado" (Fenneman 1931:34). Eolian processes cbllllisting of hard northwest winds blew the
lighter sands out of the river'B floodplain to fonn th~ dunes (Elkin 1972:72: Fenneman 1931:34;
Holliday 1982:394-396). These "lighter sands" are ~so indicative of the sediments that are
being transported by strew flows and deposited in the Arkansas River channel today.

The Arkansas River iB an alluvial, sand-bed river with a "Btream course [that] is
characterized by low banks and a broad sandy bed, which shifts frequently (USACE 1983a:411-
4/2,4/8-4/10; 1985:3: Watts and Lindner-Lunsford 1992:4). Hiatorically the river, in the study
area, was a straight braided stream; however the ri ver has undergone significant changes over the
last 150 years and most significantly since 1926 (Nadler 1978: 117; Nadler and Schumm
1981: Ill). Nadler (1978) conducted an extensive st\1dy on the Arkansas River that included
analysis of channel morphology such as width, depth, width-depth ratio, meander wavelengths
and amplitude, and gradients along with hydrology, yegetation, and sediments. Nadler (1978)
and Nadler and Schumm (1981:95) indicate that the Arkansas and the South Platte Rivers
"... have undergone dramatic historic changes that are so extensive that they can be tenned a
metamorphosis. "

Nadler (1978:58-60) and Nadler and Schumm (1981 :95-97) use the 150-year time period
which began with the 1849 California and 1859 Colorado gold rushes to pin-point a historical
reference point from which to reflect upon the signifJcance of the introduction of intensive
agriculture and the subBequent development of irrigation systems in the Arkansas and South

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