SEATTLE - The U.S. Army Corps of Engineers others will conduct spill tests at Chief Joseph Dam near Bridgeport from April 28 to May 1.
     Purpose of the test is to evaluate the effectiveness of recently installed flow deflectors at reducing total dissolved gas concentrations downstream from the dam, a Corps announcement said.
     The Corps will perform a series of 12 tests lasting three hours each. Spill amounts will be as low as 18,000 cubic feet per second to as high as 145,000 cfs, and spread across all 19 spill bays.
     The maximum river flow during the tests is not expected exceed 235,000-240,000 cfs, about the same level seen during the spring melt in 2008.
     The reservoir above Chief Joseph Dam, Rufus Woods Lake, may be operated below the normal operating pool level of 950 feet above sea level, the Corps said.
     The lowest elevation the pool may reach would be 947 feet.
     People living, playing and working on or near the river are urged to be aware and be cautious for changing river conditions, the announcement continued.
     Spill is not a common event at Chief Joseph Dam. In the event more water is passed on to Chief Joseph Dam than can be used for power generation, the spillway gates are opened to pass the excess water.
     The flow rate in the Columbia River seldom exceeds the power plant capacity at Chief Joseph Dam.
     The Corps did a spill test in April 2007 and 2008 and also spilled intermittently from late May through early July 2008 during the spring melt when in-river flows reached a high of about 235,000 cfs.
     Chief Joseph is the Corps' largest hydropower-producing dam, and the nation's second largest. It is a run-of-the-river project that maintains a relatively constant level in Lake Rufus Woods throughout the year.
     High spring flows can trigger a need to use the spillway at Chief Joseph and the falling water can entrap gas, creating conditions that are not good for resident and Endangered Species Act-listed fish, the Corps said. With spillway deflectors, the flow stays on the surface and allows the gas to dissipate quickly.