FLOOD04472

• County: Statewide
• Community: Nemaha County Nebraska
• Stream Name: Missouri River Miles 532.4-528.9
• Basin: Statewide
• Title: Langdon Bend Habitat Restoration/Preservation Project Volume 1
• Date: 6/1/1995
• Prepared For: US Army Corps of Engineers
• Prepared By: Greenhorne & O'Mara, Inc.
• Floodplain - Doc Type: Project

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Alternative C, while it would diversify the functions of the site, does not enhance in a
significant manner either large-river fisheries or waterfowl habitat. Alternative D least meets the
project goals.

Concurrence with Alternative A as the preferred alternative has been received from the
Nebraska Game and Parks Commission (Brolunan 1995), Nebraska Department of Enviromnental
Quality (Bender 1995 and Rice 1995), and Nebraska Natural Resources Commission (Williamson
1995). Copies of correspondence are included in Appendix F.

8. SEI,ECTED PLAN WITH DET All ,ED DESCRIPTION

a. General Description: The following is a description of the selected plan,
Alternative A, with a pilot channel constructed through the right overbank of Langdon Bend.
Major features of the plan are listed below and are depicted on Plates 1 through 4 located at the
end of this volume.

b. Pilot Channel: A trapezoidal pilot channel would be constructed in the right
overbank area along the approximate aligmnent of the historic chute channel. The pilot channel
would be connected to the Missouri River by an inlet structure at River Mile 531.77 and by an
outlet structure at River Mile 529.30 The pilot channel would have a bottom width of 10 feet and
side slopes of 2H to I V and would have an approximate length of 10,600 feet. The overall slope
of the pilot channel would be about 0,00026 ft/ft. The pilot channel would eventually scour to
an estimated ultimate channel width of 200 feet. The channel depth and width would be stabilized
by the grade control structure described below.

Excavated material would be placed as f1ll within the overbank area at two locations. The
excavated spoil material from the upstream portion of the site (stations 46+00 to 105 +90) will
be placed as a wide, flat benn located approximately 250 feet to the east of the pilot channel.
Placing the benn at this distance will allow the chute channel to meander more freely. This benn
would have a top width of about 90 feet with side slopes of 3H to I V, with a maximum height of
about 6 feet. The second spoil configuration applies to the downstream portion of the site
(stations 0+00 to 46+00) and consists of sidecasting the excavated material on either side of the
pilot channel into the existing vegetated areas. The approximate excavation quantity for the
selected alternative is 195,000 cubic yards.

c. Inlet/Outlet Structures: The proposed inlet and outlet structures would provide
a hydraulic connection from the Missouri River to the pilot channel. The structures would consist
of riprap material with bedding, and would be constructed with a bottom width of 200 feet and
side slopes of 3H to 1 V. This width matches the configuration of the estimated ultimate chute
channel width. The constructed pilot channel would transition to a 10-foot width from the full
2oo-foot width at the downstream end of the inlet structure and vice versa at the outlet structure.
The approximate riprap and bedding material quantities for the inlet and outlet structures are
33,665 tons and 6,200 tons, respectively.

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