242 



and moving them downstream to safety '" The real issue in judging the effectiveness of such spill 

 programs is to ask the question whether the chances for survival are better in the turbines or with a 

 slight chance of GBT In most cases, turbine mortality would be much greater 



Recently NMFS designed and implemented (with other agencies) an emergency spill program to 

 help increase outmigrant smolt survival That program was able to keep nitrogen supersaturation 

 levels to 12W^o or below - not only well below the range of serious side eflfects, and also well below 

 the average of supersaturation levels resulting from incidental spills just the year before by random 

 chance. Spills of water over the dams occur all the time — whenever there is less power being drawn 

 by consumers than produced by the turbines (as for instance during summer months), or when rains 

 bring higher levels of inflow than can be stored In fact, levels of^ill which occurred in 1994 

 during this program were of considerably less volume than those that occurred in 1993 because of 

 naturally high runo^ levels. No signs of impacts from GBT are generally observed until levels of 

 supersaturation reached levels far in excess of the 120% cap for the 1994 emergency spill program 

 Even at these maximum allowed levels any observable eflFects were minor Extensive studies at 

 mainstem dams throughout the basin document that juvenile mortality from spills ranges from 0-3% — 

 far less impact than the 10-20% immediate mortality observed from letting the fish go through the 

 turbines instead " Spilling programs are neither new nor radical - spilling water over the dams is 

 done every year Why not do it at a better time and use these spills to benefit the fish? 



" 10. Snns.C W , aiKiF.JOssuiider(I981). Migrations of juvenile chinook salmon and suelhead trout in 

 the Snake Riverfront 1973 lo 1979, a research summary Report dated June 1 98 1 CoasUl Zone and Estnanne 

 Studies Division. Northwest and Alaska Fisbenes Center, NMFS, Seattle, WA [SS/UI A.2] 



1 1 See Northwest Power Planning Council (1986). ibid [see note 5). Ra>Tnond. HL (1988) " Effects of 

 hvdroelectnc devekipiDent and fisitenes enhanoement on spring and snmmer chmook sahnon and steelbead m the Cohimbia 

 RivCT BasBi" NorOt .American Journal of Fisheries Managemem. Vol 8 (1-24). Hohnes. H B ( 1 952) " Loss of sahnoo 

 fingerbngs m passmg Bonneville Dam as detenmnedby markmg expenments " Unpublished manuscript. US Fish & 

 Wildhfe Service 62 pages Ledgerwood. RD.et al (1990) "Relative somval of subyearling chinook which have passed 

 BoanevtUe Dan via the spillway or the Second Powerhouse turbines or bypass system m 1989.with compaiisoos to 1987 

 and 1988 " Unpublished mannscnpt; Iwamoto. Robert N . et al ( 1993) "Survival estnnates for the passage of juvenile 

 chinook sahnon through Snake River dams and reservoffs. 1993 " Annual report to Bonneville Power Administration. 

 Coastal Zone & Estuanne Studies Division. Northwest Marine Science Center, NMFS. Seattle. WA Draft report 140 



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