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 Figure 4.6.2 Schematic of localized mixing application
a. The specific objective of the localized mixing application must be determined, such as
improvement of release water quality. This will involve determination of release temperature, dissolved
oxygen, and/or trace constituents such as iron, manganese, and hydrogen sulfide in the existing release
water. The desired release quality and the vertical profile of the water quality in front of the intake must
then be determined. This involves the parameter(s) defined above as the specific objective. If the
desired release quality does not exist in the profile taken in the reservoir, localized mixing will not meet
the objectives.
b. Assuming that the desired release quality exists in the reservoir, the next task is the
determination of the withdrawal zone characteristics of the intake structure. This determination is
formulated through the use of the SELECT model (Davis et al. 1987). This model requires input of the
thermal and quality profile of concern, release quantity, and structure intake configuration for
computation of the vertical withdrawal profile and predicted release quality. Verification of the
prediction is made through comparison with observed releases. The results of this model will indicate
the relative proportions of water in the release coming from a given layer, as well as the limits of the
withdrawal zone.
c. With the withdrawal description, the volume of the desired quality water needed to achieve
the release quality goal should be determined. This can be determined using a simple mass balance
criterion by diluting the release with epilimnetic water. The dilution factor, which is the ratio of
epilimnetic volume to release volume, can be used in this determination. However, there are some
limitations to the amount of dilution that can be achieved. According to Moon, McLaughlin, and
Moretti (1979), the maximum dilution that can be achieved is approximately 75 percent. This means
that for a total release volume of 1,000 cfs, only 750 cfs could be replaced by epilimnetic water.
4.6-8
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