2.4 ASSESSMENT OF TAILWATER PROCESSES
The assessment of water quality processes that suggest enhancement techniques may be
applicable in a reservoir tailwater, begins with a clear definition of the perceived problem(s) and
identification of the objectives to be accomplished. Once the problem(s) has been determined and
objectives defined, investigations of processes likely contributing to the problems can be conducted.
These processes may be occurring in the watershed, the reservoir, or the tailwater and may be
associated with reservoir operations, natural conditions, or existing conditions. Determination of the
contributing processes leads to identification of variables to measure (e.g., hydrology and other physical
features, water quality constituents, and biota). These processes occur over a variety of time scales
(e.g., microbial life cycles are measured at hourly or daily scales compared with years for fish, water
movement can be measured in seconds (velocity), days to months (flood attenuation), or years
(repetitive cycles or high/low annual flow)). These varied time scales are associated with data
collection needs for meeting objectives and, in part, determine the type of equipment necessary for
successful data collection.
The next step is the careful and thoughtful design of the sampling program with consideration
given to cost constraints, logistics, scientific soundness (including quality assurance and quality control),
and meeting stated objectives (if possible). Implementation almost always requires some trial and error
and readjustment so allowing for site visits, trial studies, and periodic review should be incorporated
into sample design. During and after sampling, data analysis (beginning with a good database
management plan) should be an ongoing activity. Attention should be given to equipment and analytical
calibrations, accuracy, and precision, accurate data entry and conversions, and the integrity of
databases during transport to graphic and analytical packages. The final step involves combining the
above activities with available tools, such as models, for developing an approach or technique for
enhancement. Knowledge of available tools and required inputs should be used in the previous steps.
Coordination with others should also be a component of the assessment and some ideas are presented
in a later section.
The objective of this section is to review the assessment process for identification of problems,
formulating solutions, and implementing enhancement techniques. Problem identification is presented in
a previous section and there are numerous references for sample design and data analysis (e.g.,
Montgomery 1997; Gilbert 1987; Green 1979). Emphasis will be placed on sampling considerations
and analytical tools.
2.4.2 SAMPLING CONSIDERATIONS
Problem identification in reservoir tailwaters usually occurs via a downstream user (e.g., water
supply, recreational users) or by personnel in close proximity to the project. For example, fish kills or