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 CEQUAL. The computational nature of these approaches makes them very precise. Consequently,
their general application is difficult and each application must ensure that all assumptions and demands
such as boundary conditions are thoroughly addressed. A precise, realistic result is not undesirable and
the ability to achieve such results is a function of the proper choice of a tool for a particular question as
well as proper application.
Computational tools such as SELECT are useful and can be applied to specific unsophisticated
situations to answer basic questions. SELECT, for example, is capable of making predictions regarding
the withdrawal zone in a lake and the quality of the water being released. It employs lake profile data
and knowledge of the release structure to calculate the mix, if any, and the characteristics of release
water to be expected. It is not a dynamic model, however, and makes no use of inflows, dynamic lake
processes, or other factors that may prevent steady-state conditions. In this sense, this tool lacks
elements of realism necessary for more sophisticated predictions.
More sophisticated tools such as PROFILE allow even further derivations from field data.
PROFILE, for example, employs time series of lake profile data to calculate, among other things,
oxygen depletion rates for depth ranges of interest. BATHTUB can provide much insight to loading
trends with relative ease. However, it does not include detail on specific limnological processes that
control or influence loading or which determine the sources or fates of loaded materials.
For such detail, numerical methods include very sophisticated models that do include such
processes. However, models such as CEQUAL are far from trivial to use and the many types of input
necessary for the best predictions are also sources of potential error. They do work, however, and
when applied in a robust manner (results confirmation from several sources) they are powerful
predictive and investigative tools.
2.3.5.2 Other Specialized Assessment Methods
There are numerous other ways to address lake issues. These are often related to specific
questions and involve detailed specific studies. The assessment of dissolved oxygen dynamics and
contributing factors is one example of these. A basic approach to field or laboratory measurement may
be modified to fit the study needs in such cases. Long-term BOD measurements, sediment exchange
measurements, etc. are techniques that cannot easily be applied in a routine manner. However, it is
very informative to have the results, say, of long-term sediment oxygen demand if other methods have
not provided needed understanding of the oxygen dynamics.
In each of these cases, the critical element is trained personnel with good understanding of the
aquatic system. This facilitates understanding of the results and allows identification of additional needs
when conventional assessment methods fail.
2.3-10
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