Geoscience Reference
In-Depth Information
portion of the raft was cleared by Captain Shreve by AD 1838. The final removal
of the raft occurred in AD 1893.
The Red River Raft was essentially a log jam that caused a complete change in
the geomorphic character of the Red River, from numerous anastomosing channels
when the raft was at its maximum extent to a single channel after removal of the
raft. The original formation of the raft is believed to have been the result of
extensive precipitation resulting from a long term period of climate change,
causing wetter conditions, rapid lateral migration, and copious rapid growing
riparian vegetation, thus exceeding a geomorphic threshold that resulted in an
avulsion, a flashy hydrograph, and a very heavy sediment load.
At its full extent, the Raft split the river into numerous anastomosing channels;
these channels were consolidated into a single, faster flowing channel as a result of
the Raft's removal. As the flow was increased, scouring caused by bank failure and
degradation also increased. The dominant modes of bank failure were rotational
slips and slab failures. These mechanisms also contributed significantly during the
formation of the Raft and continue to present challenges to anthropogenic modi-
fications to the river. The excess sediment produced from bank failure coupled
with failure to remove vegetation inland during the first attempts to remove the raft
allowed for reformation of the raft.
The Red River Waterway project involved a series of five locks and dams and
was authorized in AD 1968 with the purpose of providing a 9-feet deep by 200-
feet-wide navigation channel from the Mississippi River to Shreveport, Louisiana.
Because the Red River has one of the largest sediment loads of all major rivers in
the United States, intensive channel realignment and bank stabilization was nec-
essary to maintain navigability of the channel and meet the requirements of the
project. Further, because a large portion of the sediment load is fine grained
materials, large amounts of maintenance dredging are necessary to keep the locks
and dams functioning and the navigation channel open.
After the construction of the first two locks and dams, sediment maintenance
became a major concern. The problem of very large sediment load was solved with
a combination of revetments, which maintain higher river velocities and a jetting
system within the lock and dam itself. These fixes were designed to keep the
river's sediment load in suspension and have it drop in areas that could be reached
by maintenance dredges.
The first two locks and dams were modified after construction to reduce the
sediment maintenance problems, and the other three were subsequently modified
in design for the same objective. Today, the five Locks and Dams (Fig. 11 ) control
the flow of the lower Red River, raising it a total of 141 feet and maintaining a 9-
foot navigation channel from it confluence with the Mississippi River to Shreve-
port Louisiana. The Locks can accommodate a total of six barges (two across by
three lengthwise) with tug and are 84 feet wide by 685 feet of usable length.
Acknowledgments We want to thank to the many scientists and authors that provided the
original research and publications on which this document is based. Special thanks to Lawson
Smith, Paul Albertson, Ken Jones, and the USACE Vicksburg District for their vision and
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