FLOOD03889

• County: Statewide
• Community: Harrison County, Iowa
• Stream Name: Missouri River Miles 651-64905
• Basin: Statewide
• Title: California Bend Habitat Restoration/Preservation Project Volume 1
• Date: 10/1/1994
• Prepared For: US Army Corps of Engineers
• Prepared By: Greenhorne & O'Mara, Inc.
• Floodplain - Doc Type: Project

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b. Selection Process: The California Bend area was selected as a development project
in the State of Iowa after on-site evaluations and review of existing aerial photography and site
plans. After preliminary investigations and studies were conducted, the Iowa Department of
Natural Resources (DNR) nominated the site as a candidate for planning, design, and
construction. The site is owned by the State of Iowa.

3. AFFECTED ENVIRONMENT

The Missouri River Bank Stabilization and Navigation Project authorized channelization
of the Missouri River from Sioux City, Iowa to its confluence with the Mississippi River in
1935. The majority of the work was completed between 1945 and 1965. Rock revetments and
pile dikes were used to reduce the wide cross-section of the river by cutting off side channels
and shallow sand-bar complexes. Previously wet areas aggraded with sediment, and the channel
was eventually stabilized into a narrow corridor about 600 feet (183 meters) wide.
Channelization has altered overbank flooding patterns, isolated the floodplain from the river, and
increased water velocities in the channel (Fredrickson and Reid 1990).

Prior to channelization, the Missouri River was uncontrolled and meandered across the
river valley causing erosion, deposition, and accretion. The channel "consisted of numerous
islands, channels, chutes, sandbars, and back-water areas supporting vegetation in various stages
of succession. The meander belt consisted of a 606,ooo-acre area adjacent to the natural
channel. This area consisted of successional wetlands and various types of herbaceous and
woody habitats, as well as some fonn of agricultural use. It is estimated that over 500,000 acres
of aquatic and terrestrial habitat will have been eliminated from the natural channel and meander
belt by the year 2003." (U.S. Anny Corps of Engineers 1990).

The Missouri River system in its natural state provided a diversity of habitats for fish and
wildlife. Historically, it contained large populations of fishes and a diversity of species. These
have been affected by the loss of water surface area and habitat. The Missouri River and
associated habitats supported many mammals, reptiles, amphibians, songbirds, shorebirds, and
waterfowl. Channelization has resulted in a general reduction in wildlife numbers due to
changes in habitats.

An assessment of the existing environment has been completed for this DPR. This
assessment included research of existing reports, maps, and aerial photographs, as well as field
investigations of current site conditions. Results of the various investigations are summarized
below.

a. Physiography and Topography: The California Bend site is located in Iowa which
is part of the Dissected Till Plains Section of the Central Lowland physiographic province.
Terraces, sloughs, and abandoned channel meanders are found in the nearly flat bottomlands
adjacent to the Missouri River. The area is relatively flat with an approximate average
elevation of 996 to 997 feet above mean sea level. There is a small upland hill in the southwest
comer of the site which reaches an elevation of 1017.5 feet above mean sea level. Historical

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