Quality-assurance data, comparison to water-quality standards, and site considerations for total dissolved gas and water temperature, Lower Columbia River, Oregon and Washington, 2001

The U.S. Army Corps of Engineers (USACE) operates 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 over the spillways of these dams, air is entrained in the water, increasing the concentration of total dissolved gas (TDG) downstream from the spillways. Consequently, TDG may exceed Oregon and Washington water-quality standards for the protection of freshwater aquatic life. Concentrations 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 minimizes spill and regulates streamflow in the region to minimize the production of excess TDG downstream from its dams. The USACE also oversees the collection of real-time TDG and water-temperature data (data available within about 4 hours of current time) upstream and downstream from the dams in a network of fixed-station monitors. 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 waterquality 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 USACE, has collected TDG and related data in the lower Columbia River every year since 1996. Current 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 and 2001 contained descriptions of the methods of data collection and quality-assurance data for water years (WY) 1996 and 2000, respectively (Tanner and others, 1996; Tanner and Johnston, 2001). To provide a suitable data set for managing and modeling TDG in the lower Columbia River, real-time hourly data for WY 2001 were reviewed in relation to measurements made during instrument calibration. Some TDG data were deleted because they were not of suitable quality. The reviewed hourly data are stored in a USGS data base (Automated Data Processing System -ADAPS), and in the USACE data base (Columbia River Operation Hydromet Management System- CROHMS), which also provides discharge and spill data at http://www.nwd-wc.usace.army.mil/TMT/tdg _data. Purpose and Scope The purpose of TDG monitoring in the lower Columbia River is to provide the USACE with (1) realtime data for managing streamflows and TDG levels upstream and downstream from its project dams and (2) reviewed TDG data to evaluate conditions in relation to water-quality standards and to develop a TDG 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 for the monitoring program on the lower Columbia River, from the forebay of the John Day Dam (river mile [RM] 215.6) to Camas, Washington (RM 121.7). Data for WY 2001 (October 1, 2000 through September 30, 2001) included TDG pressure, barometric pressure, water temperature, and probe depth at eight fixed stations on the lower Columbia River (fig. 1, table 1).