Data Collection Methods, Quality Assurance Data, and Site Considerations for Total Dissolved Gas Monitoring, Lower Columbia River, Oregon and Washington, 2000.

Excessive total dissolved gas pressure can cause gas-bubble trauma in fish
downstream from dams on the Columbia River. In cooperation with the U.S. Army
Corps of Engineers, the U.S. Geological Survey collected data on total
dissolved gas pressure, barometric pressure, water temperature, and probe depth
at eight stations on the lower Columbia River from the John Day forebay (river
mile 215.6) to Camas (river mile 121.7) in water year 2000 (October 1, 1999, to
September 30, 2000). These data are in the databases of the U.S. Geological
Survey and the U.S. Army Corps of Engineers. Methods of data collection,
review, and processing, and quality-assurance data are presented in this
report.

The purpose of TDG monitoring is to provide USACE with (1) real-time data for
managing streamflows and TDG levels upstream and downstream from its project
dams in the lower Columbia River and (2) reviewed and corrected TDG data to
evaluate conditions in relation to water-quality criteria and to develop a TDG
data base model for modeling the effect of various management scenarios of
stream flow and spill on TDG levels.

Instrumentation at each fixed station consisted of a TDG probe, an electronic
barometer, a data-collection platform (DCP), and a power supply. The TDG probe
was manufactured by Hydrolab Corporation. The probe had individual sensors for
TDG, temperature, and probe depth (unvented sensor). The TDG sensor consisted
of a cylindrical framework wound with a length of Silastic (dimethyl silicon)
tubing. The tubing was tied off at one end and the other end was connected to a
pressure transducer. After the TDG pressure in the river equilibrated with the
gas pressure inside the tubing (about 15 to 20 minutes), the pressure
transducer produced a measure of the TDG presure in the River. The
water-temperature sensor was a thermocouple. The barometer was contained in
the display unit of the Model TBO-L, a total dissolved gas meter manufactured
by Common Sensing, Inc. More information abou the TDG probe is provided by
Tanner, D. Q. And Johnston and M.W. 2001.

The fixed station monitors were calibrated every 2 weeks from March 10 to
September 15, 2000, and every three weeks for the remainder of the year, at
which time Warrendale and Bonneville forebay were the only sites in operation.
The general procedure was to check the operation of the TDG probe in the field
without disturbing it, replace the field probe with one that had just been
calibrated in the laboratory, and then check the operation of the newly
deployed field probe. The details of the laboratory calibration procedure are
outlined in Tanner and Johnston, 2001.

Information for this metadata was obtained from the Technical Reports of the
Oregon District available at http://oregon.usgs.gov/pubs_dir/online_list.html .