Published: 1996-09-01
Total Pages: 282
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River flows passed through the spillways of the dams located on the lower Columbia and lower Snake Rivers produce water that is supersaturated with dissolved gases. These high levels of dissolved gases are detrimental to aquatic life. In the 1970's, spillway deflectors were installed on the spillways of several U.S. Army Corps of Engineers' projects (Bonneville, McNary, Lower Monumental, Little Goose, and Lower Granite Dams) to reduce the high levels of total dissolved gas (TDG) produced. However, in 1976, it was decided to postpone the construction of deflectors at Ice Harbor Dam. Key fishery researchers of that time judged that spillway deflectors at Ice Harbor Dam would cause poor hydraulic conditions in the tailrace that would likely delay or block adult fish passage. Also, the severity and frequency of TDG supersaturation downstream of Ice Harbor Dam was expected to be reduced significantly in the near future because of several factors. These factors included: (1) the recent completion of all six powerhouse turbines at Ice Harbor Dam, which would significantly reduce the amount of spill discharge required during periods of high flow; (2) the recently completed Dworshak Dam, having 3 million acre feet of active flood control storage, which would also reduce the amount of spill required at Ice Harbor Dam due to high flows; and (3) the installation of spillway deflectors and the accelerated schedule for turbine installation at the three lower Snake River dams upstream of Ice Harbor Dam, which would reduce the frequency and level of TDG entering the forebay of Ice Harbor Dam in the near future. This reduction of TDG in the forebay was expected to reduce, to some extent, the level of TDG downstream of Ice Harbor Dam as well. Operation of Ice Harbor Dam has changedh-IS)GT*GD,G9>G-* (DES(
