Limitations and Concerns
These techniques are limited by the availability of low-cost,
Outlet structures of the reservoir must be capable of han-
nutrient water.
dling the added discharge.
This may not always be the case, particularly with
smaller, older impoundments.
Also, the downstream impacts of significantly
increased discharge must be considered.
Finally, dilution/flushing water must
have acceptably low concentrations of contaminants such as heavy metals or
pesticides.
Summary
Dilution is a reservoir improvement technique wherein amounts of
nutrient water are added in quantities sufficient to promote cell washout and
to significantly lower in-lake nutrient concentration.
The amount of reduc-
tion in concentration can be estimated, with assumptions that may not hold
true for eutrophic reservoirs, from knowledge of nutrient loading, sedimenta-
tion, and flushing rate.
Flushing is a procedure to wash out algal cells and
does not imply dilution of nutrient concentration in the reservoir unless
water with low concentration is used.
Both techniques can produce large improvements in
state, as
illustrated by two case histories.
The primary drawback to their use is the
availability of the additional water and possible effects of increased reser-
voir discharge on downstream areas.
Table 4 summarizes this procedure.
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