is
possible and where sediments will dewater to the degree needed
heavy equipment. Born et al. (1973) describe the use of this pro-
cedure in a small reservoir, and Snow et al. (1979) describe a case history.
The more common method of sediment removal is the use of dredges.
The two basic categories of dredges are mechanical and hydraulic, plus
some special-purpose designs for the removal of toxic or fine-grained sedi-
These are reviewed by Barnard
Peterson
and Cooke
ments.
The most common mechanical dredges are the clamshell or
et al. (1986).
bucket designs.
Dredges of this type are limited by the requirement that dis-
charge is either in the immediate vicinity of the dredge or into a barge or
truck.
The bucket types have low.productivity rates, can create uneven bottom
produce significant sediment resuspension.
They are highly
contours,
mobile and can work in small areas.
The hydraulic cutterhead dredge is the
Cutterhead dredges are faster than the grab-buckets, may
most common type.
produce less turbidity, and are able to dredge over large distance> due to
However, up to 80 percent of the
their floating pipeline discharge system.
removed material is water; therefore, confined disposal areas must have
adequate volumes to permit the settling of suspended materials.
In small
there
be some
due to the hydraulic dredging
reservoirs,
process.
There are also specialized and portable hydraulic dredges.
Barnard
and Clark (1983) has reviewed the operating fea-
(1978) has described
tures of 46 models of portable hydraulic dredges.
Also, the Oozer and
Clean-up dredges (see review in Cooke et al. 1986) have been developed for
removal of contaminated sediments, though it appears that these dredges are
unavailable in the United States.
Several of these dredges produce very
little turbidity and thus little dispersion of toxic materials.
Herbich and
Brahme (1983) report an average suspended solids concentration of 4.0 and
mg
at 3 and 7 m above the bottom for Clean-up and Pneuma-type dredges,
-1
versus 40 to 80 mg
for conventional hydraulic cutterhead dredges. How-
ever, unless the lake sediments are contaminated, the conventional cutterhead
dredges may be used with good results.
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