May 22, 2014: The water supply forecast at The Dalles Dam is for 107 percent of normal. 

In high flow conditions, it may be necessary to spill more than is required for fish passage. While spill of water past dams helps juvenile salmon and steelhead migrate downstream, very high amounts can harm fish and other aquatic life by raising dissolved gas levels. Read more here.  

To use the water supply forecast from NOAA's Northwest River Forecast Center, refer to the 5-day forecast January to July typically used (highlighted with arrow).

Dissolved gas levels would likely be higher without recent investments in flow deflectors and other improvements at FCRPS dams. Since 2000, the U.S. Army Corps of Engineers has installed spillway flow deflectors at Bonneville Dam, John Day Dam, Lower Monumental Dam, Little Goose Dam and Chief Joseph Dam.

A spill management plan also helps control gas levels while assisting juvenile fish migration through the hydrosystem. 

At the right is spill at Chief Joseph Dam in 2011. This chart compares TDG levels in 2011 at the tailrace of Chief Joseph Dam with 1997 (another very high flow year), before the Corps installed flow deflectors.

To see daily Total Dissolved Gas percentages at the Columbia River Basin dams, go this U.S. Army Corps of Engineers' webpage.  As shown in this screen shot, click on "Dissolved Gas Percent" and click on any dam you want to view.  Then hit "Begin Run."