Significant Findings
The U.S. Geological Survey (USGS), in cooperation with the U.S. Army Corps of Engineers, collected total-dissolved-gas and water-temperature data at eight sites near dams on the lower Columbia River in 2002. When water is released through the spillways of dams, air is entrained in the water, increasing the concentration of total dissolved gas to levels that can have adverse effects on freshwater aquatic life. Significant findings include:
- For the eight monitoring sites in water year 2002, an average of 99.6% of the total-dissolved gas data were received in real time by the USGS satellite downlink and were within 1% saturation of the expected value, based on calibration data and ambient river conditions at adjacent sites.
- Most field checks of total-dissolved-gas sensors with a secondary standard were within 1% saturation. Field checks of barometric pressure and water temperature were usually within 1 millimeter of mercury and 0.05 degrees Celsius, respectively.
- In June and July 2002, spills exceeded 140,000 cubic feet per second at the John Day, The Dalles, and Bonneville Dams. These spills resulted in levels of total dissolved gas that exceeded 120% saturation downstream of the dams.
- The variance to the State of Oregon water-quality standard for total dissolved gas of 110% saturation was exceeded at seven of the eight monitoring sites. The sites at Camas and Bonneville are considered forebay sites and had the most days exceeding the variance of 115% saturation. The forebay exceedances may have been the result of the cumulative effects of significant spill throughout the lower Columbia River. Apparently, the levels of total dissolved gas did not dissipate rapidly enough downstream of the dams before reaching the next site.
- From mid-July to mid-September, water temperatures were usually above 20 degrees Celsius at each of the seven lower Columbia River sites in operation. According to the Oregon water-quality standard, when the temperature of the lower Columbia River exceeds 20 degrees Celsius, no measurable temperature increase resulting from anthropogenic activities is allowed.
