SEDIMENT REMOVAL
Problem Addressed
External loading of silt and organic matter, along with the deposition
of partially decomposed plant biomass produced in the reservoir, can bring
about loss of reservoir volume.
As well, nutrient-rich sediments are sources
of nutrients to the water column and, in shallow areas, provide ideal condi-
Shoaling may interfere with boating, and loss of stor-
tions for macrophytes.
age capacity can have severe impacts in potable water supply and flood control
Dense macrophyte infestations interfere with recreation and,
reservoirs.
along with algae, contribute organic matter to the water column.
This pro-
motes loss of dissolved oxygen in deep water, and the organic matter may
interact with the chlorination step in potable water treatment to produce
organohalides such as trihalomethanes.
Some reservoir sediments can
significant levels of toxic substances (e.g., heavy metals,
from
upstream discharges.
Sediment removal is a highly effective method to deepen reservoirs and
o
shoals, and secondarily to remove nutrient-rich or toxic sediments
This procedure has been reviewed by Peterson
and to control rooted plants.
(1979, 1981, 1982) (see also Cooke et al. 1986).
Theory, Design, and Costs
The object of most sediment removal projects is to regain lost'storage
capacity, and secondarily to improve water quality by control of internal
nutrient release.
In the cases of shoaling, loss of volume, or toxic sub-
stance contamination, there is little choice except sediment removal.
Inter-
nal nutrient loading may also be controlled with other methods, and macrophyte
may be better and less expensively handled through harvesting, herbi-
cide treatments, water level drawdown, or biological controls.
Application of the method
are two means of removing reservoir sediments.
First, the reser-
voir may be drawn down and the sediments allowed to dewater.
This is followed
by the use of mechanical equipment to remove sediments.
Obviously the
is limited to those reservoirs where significant and long-term water
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