this procedure is species specific.
Some plants are eliminated, some
unaffected, and others may flourish when water levels are restored.
The sur-
vey will also identify the area of the plant infestation, thus giving the
depth to which water must be withdrawn to achieve partial or complete exposure
of macrophytes,
Procedures for conducting the
survey are outlined in
Forsberg (1959) and Nichols (1982).
As illustrated in the case histories, most drawdowns for the control of
macrophytes in northern states have taken place during winter months.
Many
plants (Table 10; refer to Cooke 1980 and Cooke et al. 1986 for list of
responses of 74 plants species) are susceptible to prolonged periods (3 to
4 weeks) of freezing and dewatering.
Soils that remain moist or that are not
frozen will protect roots and rhizomes, and regrowth will occur.
Water level
will provide access to areas in need of maintenance
and repair.
Shoreline erosion, a significant source of turbidity in some res-
ervoirs, is a problem that can be treated during water withdrawal.
Shoreline
erosion may be caused by one or several of these factors:
waves, abrupt water
level fluctuations, erodible and bare soils, ground-water seepage, bluff
slumping,
In one of the few studies of its kind,
and surface runoff erosion.
Wilson (1979) found that 82 percent of the total solids income to a small Ohio
reservoir was from shoreline erosion.
Shoreline stabilization may be brought
about through construction of protective structures, planting of vegetation,
development of drainage controls from the land, and by altering bluff slopes.
Details of these procedures are available through the Soil Conservation Ser-
vice (SCS) and in several reports (US Army Corps Engineers 1973; Clemens,
undated).
also provides access for the installation of sediment covers
Normally, these materials are applied during
areas such as beaches and docks.
A less expensive and more effective
summer months using SCUBA (see Part XII).
method is to fasten them to frozen reservoir soils.
With regard to eutrophic reservoirs and their improvement or restora-
tion, water level
is used primarily as a procedure to control rooted
macrophytes.
Further discussion of this procedure will be confined to this
purpose.
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