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 Figure 4.3.2 Nutrient reduction through hypolimnetic withdrawal
thermal stability may be reduced, depending upon the lake's morphology and inflow water quality
characteristics.
This technique does not necessarily lead to destratification in the traditional sense, since it
involves removing the hypolimnetic water and not mixing it with the epilimnetic waters. Traditional
destratification would enhance nutrient transport from the hypolimnion to the epilimnion and accelerate
eutrophication. A possible consequence of this technique is the release of poor-quality (low dissolved
oxygen and high dissolved solid) hypolimnetic water downstream.
4.3.2.3 Evaluation Methodology
General design guidance was given by Nurnberg (1987) for hypolimnetic withdrawal in lakes.
The design approach given below is that of Nurnberg with additional criteria for large reservoirs.
The design of a hypolimnetic withdrawal system should begin with a clear definition of the
existing stratification structure and nutrient budget of the lake. The analysis of the thermal structure
requires temperature and DO profiles during the stratified period. These should be at sufficient intervals
to describe the stratification process, the development of anoxic conditions in the hypolimnion, and the
4.3-6
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