The goal of the monitoring program dictates the deployment design. If the goal of the
program were to measure critical total dissolved gas concentrations, then a single monitor near
the area of highest total dissolved gas concentrations may be sufficient (point A, Figure 3). If
concerns were for the mean total dissolved gas concentrations for the area, a single monitor
located near midchannel may be appropriate (point B). However, if the program's goal were to
map the total dissolved gas concentrations for the tailwater, a single fixed monitor would be
inappropriate, and an alternate plan would have to be developed, involving numerous fixed
positions (for example, points C, D, and E in Figure 3). This example highlights the need for
good planning and preinstallation sampling in the early stages of developing a monitoring
program.
Monitor Equipment
Hardware
Data requirements and available funding will dictate the hardware selected for the monitor
installation. Water quality instruments equipped to measure most parameters of concern are
commercially available. However, these instruments vary with respect to accuracy, precision, data
presentation, and expense.
Consideration should be given to the design limitations of the instrument when selecting water
quality equipment. For example, if the purpose of the monitor were to record dam release
dissolved oxygen (DO) concentrations for mitigation and the requirement was to remain within
0.5 mg/L of a target DO concentration of 5.0 mg/L, then oxygen probes with an accuracy of less
than 0.5 mg/L would be inadequate.
Deployment/retrieval monitoring is used for thermal monitoring and special studies at Richard
B. Russell Reservoir on the Savannah River. For this application, water quality instruments with
data logging capabilities are deployed, and the data are retrieved later. If data are needed real
time, a computer/modem system can be used. Relatively inexpensive, reliable water quality
sondes interfaced with a personal computer/modem can be obtained for less than ,000 (1996).
Commercially built data collection platforms are available, and most can be tailored to fulfill the
design requirements of the site. With computers and other data platforms, the operator achieves
greater flexibility with respect to how the data are stored and accessed.
As a general rule, equipment should be selected based on the following factors:
! Instrument accuracy, precision, and resolution desired.
! Instrument deployment requirements.
! Deployment method (deploy/retrieval, computer/modem, incorporation with existing equip-
ment, etc.).
! Fouling concerns and required calibration and maintenance regimens.
! Instrument expense and monitoring program budget constraints.
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Water Quality Technical Note AM-02 (January 1998)
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