Total dissolved gas and water temperature in the Lower Columbia River, Oregon and Washington, 2003: quality-assurance data and comparison to water-quality standards

INTRODUCTION The U.S. Army Corps of Engineers (USACE) operates several dams in the Columbia River Basin, which encompasses 259,000 square miles of the Pacific Northwest. These dams are multipurpose facilities that fill regional needs for flood control, navigation, irrigation, recreation, hydropower production, fish and wildlife habitat, water-quality maintenance, and municipal and industrial water supply. When water is released through the spillways of these dams (instead of being routed through the turbines to generate electricity), ambient air is entrained in the water, increasing the concentration of total dissolved gas (TDG) downstream from the spillways. TDG conditions above 110% saturation have been shown to cause gas-bubble trauma in fish and adversely affect other aquatic organisms (U.S. Environmental Protection Agency, 1986). The USACE regulates spill and streamflow to minimize the production of excess TDG downstream from its dams, but there is also the goal of providing for fish passage with spilled water (rather than passage through the turbines). Consequently, the States of Oregon and Washington issue variances to the TDG water-quality standards during the summer months. In order to monitor compliance with these variances, the USACE oversees the collection of near real-time TDG and water-temperature data upstream and downstream from the Columbia River Basin dams in a network of fixed-station monitors. Data from these sites are available within about 4 hours of current time. Background Real-time TDG and water-temperature data are vital to the USACE for dam operation and for monitoring compliance with environmental regulations. The data are used by water managers to maintain water-quality conditions that facilitate fish passage and survival in the lower Columbia River. The U.S. Geological Survey (USGS), in cooperation with the Portland District of the USACE, has collected TDG and related data in the lower Columbia River every year beginning in 1996. Current and historical TDG and water-temperature data can be found on the USGS Website at http://oregon.usgs.gov/ projs_dir/pn307.tdg/. Reports that were published in 1996, 2001, and 2002 contained TDG data, quality- assurance data, and descriptions of the methods of data collection for water years 1996, 2000, 2001, and 2002 (Tanner and others, 1996; Tanner and Johnston, 2001; Tanner and Bragg, 2001; and Tanner and others, 2002, respectively). To provide suitable data for managing and modeling TDG in the lower Columbia River, real-time hourly data for 2003 were reviewed relative to laboratory and field measurements made during instrument calibration and daily intersite comparison. Some TDG data were deleted because they were not of suitable quality. The hourly data were stored in a USGS data base (Automated Data Processing System-ADAPS); and in a USACE data base (at http://www.nwd-wc. usace.army.mil/tmt/wcd/tdg/ months). The USACE database also includes discharge and spill data. Purpose and Scope The purpose of TDG monitoring in the lower Columbia River is to provide the USACE with (1) real-time data for managing streamflow and spill at its project dams and (2) reviewed TDG data to evaluate conditions in relation to water-quality standards and to provide a data base for modeling the effect of various management scenarios of streamflow and spill on TDG levels. This report describes the TDG data and related quality-assurance data from the lower Columbia River at seven sites from the forebay of the John Day Dam (river mile [RM] 215.6) to Camas, Washington (RM 121.7), (fig. 1, table 1). It is similar in format and content to the previous reports presenting TDG data for the lower Columbia River, mentioned above. Data for water year 2003 (October 1, 2002, to September 30, 2003) included hourly measurements of TDG pressure, barometric pressure, water temperature, and probe depth. Five of the sites were operated from March to September 2003, which is the usual time of spill from the dams. The sites at the forebay and tailwater of The Dalles Dam also were operated during October and part of November 2002 to evaluate the effects of spill tests during those times. Two sites (Bonneville forebay and Warrendale) were operated year-round.