Significant Findings

When water is released through the spillways of dams, air is entrained in the water, increasing the downstream concentration of dissolved gases. Excess dissolved-gas concentrations can have adverse effects on freshwater aquatic life. The U.S. Geological Survey (USGS), in cooperation with the U.S. Army Corps of Engineers, collected dissolved-gas and water-temperature data at eight monitoring stations on the lower Columbia River in Oregon and Washington in 2010. Significant findings from the data include:

• During the spill season of April through August 2010, hourly values of total dissolved gas (TDG) were occasionally larger than 115-percent saturation for the forebay stations (John Day navigation lock, The Dalles forebay, Bonneville forebay, and Camas). Hourly values of total dissolved gas were occasionally larger than 120-percent saturation for four tailwater stations (John Day Dam tailwater, The Dalles tailwater, Cascade Island, and Warrendale).
• From late July to late August or early September 2010, hourly water temperatures were greater than 20°C (degrees Celsius) at the eight stations on the lower Columbia River. According to the State of Oregon temperature standard, the 7-day average maximum temperature of the lower Columbia River should not exceed 20°C; Washington regulations state that the 1-day maximum should not exceed 20°C as a result of human activities.
• All 105 laboratory checks of the TDG sensors (without the membrane attached) with a certified pressure gage were within ± (plus or minus) 0.5 percent saturation after 3 to 4 weeks of deployment in the river.
• All but 1 of the 85 in situ field checks of TDG sensors with a secondary standard were within ± 2.0-percent saturation after 3–4 weeks of deployment in the river. All 88 of the field checks of barometric pressure were within ±1 millimeter of mercury of a primary standard, and all 87 water-temperature field checks were within ±0.2°C of a secondary standard.
• For the eight monitoring stations in water year 2010, a total of 99.7 percent of the TDG data were received in real time and were within 1-percent saturation of the expected value on the basis of cali-bration data, replicate quality-control measurements in the river, and comparison to ambient river conditions at adjacent stations. Data received from the individual stations ranged from 98.4 to 100.0 percent complete.

First posted March 10, 2011