Sediment removal
will create at least a temporary problem with
turbidity, nutrient release, and transport of contaminated particles.
Normally,
settle rapidly.
In some situations, turbidity or the
transmission of particulate matter to other reservoir areas is undesirable.
In these cases, specialized dredges are available (Cooke et al.
or a
silt curtain can be installed (Barnard 1978).
Montgomery (1984) describes
specialized dredging equipment and procedures that can be used to minimize
of sediment resuspension while removing contaminated sediments.
Disturbance of nutrient-rich sediments may release significant amounts of
nutrients, leading to algal blooms.
Nutrient levels should return to normal
or even lowered concentrations after dredging.
Gibbons and Funk (1983) point
that can produce reservoir problems.
out errors in hydraulic dredge
In the case of Liberty Lake, Washington, the paths of the cutterhead did not
overlap, resulting in mounds and trenches that later merged through slumping.
As a result, nutrient-rich sediments still covered the lake
and
neither nutrient release nor macrophyte coverage was improved.
Disposal methods and sites are a very important part of the process of
minimizing the environmental impacts of sediment removal, and guidelines for
their construction for this purpose are available (US Army Corps of Engineers
1987).
Upland containment areas are commonly used.
Sediment removal for a
reservoir improvement project would be defeated by in-reservoir disposal
unless the sediments could be placed in very deep water (25 to 30
where
currents are minimal, or unless the sediments are placed in a containment area
used to create an island acceptable to reservoir users.
Unconfined disposal
in shallow water means that problems may simply be displaced (i.e., creation
of new shoals or creation of another site of nutrient release or macrophyte
infestation) or that the undesired sediments will be dispersed by'currents.
Prior to selection of a disposal method, some preliminary data must be
obtained.
The short-term pollution potential of nutrients, heavy metals, and
should
estimated with an elutriate test (Palermo
1988).
While most dredged material poses little risk from release of toxic contami-
In the event that the
target sediments are contaminated, environmental risks can be minimized.
The
reader is referred to the reports referenced above for guidelines and methods
to
these factors and risks.
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