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Shallow Water Habitat (SWH)
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The restoration of SWH comes from one element of the reasonable and prudent alternative (RPA) outlined
in the 2003 Biological Opinion (BiOp) which requires the restoration of 20% of the SWH which existed
prior to construction of the Bank Stabilization and Navigation Project (BSNP). To meet
this requirement, which only applies to the river below Gavins Point, 20 to 30
acres of SWH per river mile must be in place by 2020. The BiOp identifies the
difference between the target condition of 20-30 acres of SWH per mile and the
2003 river condition as a deficit of 12,035 to 19,656 acres. This SWH may be
restored through flow management, channel widening, side channel chutes, manipulation
of existing aquatic habitat, manipulation of summer flows, or combinations thereof.
A major component of the Missouri River Recovery Program is meeting this element of the RPA.
Both the Omaha and Kansas City Districts are involved in this effort. Almost all
of the required SWH acres will need to be created by channel widening and the
restoration of chutes and side channels. Channel widening is accomplished by
modifying the configuration of some of the roughly 7,000 rock and piling structures
that comprise the BSNP. Modifications include notching, extending, raising and
lowering the structures to effect changes to the existing aquatic habitat and/or
erosion of the high bank. The result is the creation of SWH acres within the current
top-width of the river and the creation of SWH by the conversion of terrestrial acres
into new aquatic habitat. At some locations, new structures, such as chevrons, are
built in combination with structure modifications to create the desired habitat. Side
channel chutes, in contrast, are constructed by excavation of a pilot channel through
the overbank. The side channel is allowed to erode, widen and meander in a controlled
manner resulting in a dynamic aquatic environment. Flows through the chute are
controlled by new rock structures placed within the chute.
A challenge of the SWH effort is the prevalence of private property adjacent to the
river. Channel widening and chutes can only be accomplished where the Corps or a
cooperating government agency owns the adjacent property. Private landowners can
also participate by selling the government a sloughing easement where the landowner
retains ownership of the land, but the government has the right to intentionally erode
the land. The landowner can benefit by receiving payment for the land and continued
use until it erodes.
Channel widening and chute construction result in the displacement of large amounts
of overbank material. The displacement is the result of the excavation required
during construction and planned erosion of the bank after construction. Recently,
the Missouri Clean Water Commission (Commission) raised concerns about the effect on water
quality from the planned erosion and the construction practice of placing excavated
material directly into the river. The U.S. Army Corps of Engineers is currently addressing those concerns
by contaminant and nutrient testing of bank material and study of the effect of the
material on the river morphology and ecology. In addition, the Corps is contracting
with the National Academy of Sciences to obtain an independent assessment of the
Commission's concerns.
As the Commission's concerns are being addressed, both Districts are continuing
with design work on future projects and the engineering and biological assessment
of existing projects. In addition, to meet the deadlines specified in the BiOp
and stay in compliance with the Endangered Species Act, construction activities are continuing upstream
of Missouri on numerous chute and river structure modification projects.
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| Reverse Sill under construction near River Mile (RM) 656, Oct 2006. |
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2-D Modeling Data - Lower Decatur
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Council Bend Chute, Summer 2007, near RM 616.8.
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