The answers to questions such as those listed above help managers determine if automated
monitoring is needed to attain the goal of the program. Grab sampling may be better suited to a
temporary monitoring program or one having a long sampling interval. In a lengthy or
permanent installation or one requiring a short sampling interval, grab sampling quickly becomes
cost prohibitive, and automated, remote monitors are both more appropriate and effective.
After the decision to install an automated monitor has been made and the water quality
parameters to be measured have been identified, the next step in the preinstallation process is to
characterize the study area. This may be accomplished with short-term manual sampling. A
working knowledge of the parameter(s) to be measured is essential to identify the most
representative deployment site. In addition, the hydrology, morphometry, flow patterns, climate,
chemistry, and biology of the site determine the optimum monitoring location. Characterization
of the area should include identifying any lateral, longitudinal, and vertical heterogeneities.
Sampling should be conducted under the conditions that will be experienced by the monitor; that
is, if the monitor is to measure hydropower release water quality, then preinstallation sampling
should be conducted during release periods.
Four general areas need to be considered in deploying hydroproject monitors: the forebay, the
area within the hydroproject's physical structure, the tailrace, and the tailwater. Preliminary areas
of study would depend on the monitoring objective. For example, the preliminary study area for
a release water quality monitor for a hydropower dam may be the tailrace. An installation for
monitoring the effectiveness of water quality improvement measures may be located upstream for
pretreatment conditions and downstream for posttreatment conditions. A monitor for evaluating
hydroproject operation on downstream habitat may be located in the tailwater some distance
downstream of the project.
Regardless of the monitoring program's goal, certain locations will probably be apparent as
logical starting points for consideration. Secondary consideration may focus on accessibility for
calibration and maintenance; however, the most convenient location is not always the most
representative one, and greatest emphasis should be placed on data quality.
Many relatively inexpensive water quality instruments that are capable of internally storing
data are commercially available. These instruments allow project planners to experiment with
various site locations via short-term deployments. These data can then be combined with grab
data to provide temporal and spatial representations of the daily and seasonal variations for the
area. Careful analysis of the available data is crucial during the preliminary stages of developing
a monitoring program, to prevent future problems regarding data validity and defensibility. Often,
a logical location for the monitor may be apparent; however, peculiarities of the site, particularly
with respect to flow patterns, may preclude installation of the monitor in this area. The logical
location provides a starting point for the validation stage of the preinstallation process.
Conservative water quality measures (such as temperature or specific conductance), which are
not easily affected by biota, may be used as "tracers" to track parcels of water. Comparing
conservative parameters cannot conclusively validate the representativeness of a potential location
but can eliminate a nonrepresentative one. Several case studies will be presented to further
develop these ideas.
Water Quality Technical Note AM-02 (January 1998)