Because it is unlikely that the normal spill program for passing out-migrating juvenile salmonids will be implemented in 2001 due to expected low runoff, the ISAB encourages the judicious use of surface spill at dams in the Columbia-Snake River system. Spill, in whatever form, facilitates in-river passage, which spreads the risk (or benefit) of different routes of passage among members of populations of smolts to help maintain biological diversity, and also retains fish in the river for important monitoring. Relative to normal spill, most studies have shown that surface spill can be effective in passing large numbers of downstream migrants in small amounts of water. Surface spill can be implemented fairly quickly by using existing surface spillways at some dams and by installation of stop logs in conventional spillways at dams to create surface spill where there are no existing surface spillways. We justify our recommendation with the information that follows.
Several articles in the Columbia Basin Bulletin of Friday, March 16, 2001, (for example) described the angst over low river flows anticipated in the Columbia River basin this year and, to meet energy needs, the likely elimination of the normal spill program. At its February 21 meeting, the ISAB heard John Fazio of the Council staff describe the potential costs of maintaining the normal spill program in 2001; several ISAB members also heard an update of the situation at the ISRP briefing on March 14. We recognize that the cost of spill this spring and summer, if it were to go ahead normally, is now estimated to be $1.6 billion for purchase of replacement power. Nonetheless, CRITFC and others are still recommending some spill for fish, and many others, ourselves included, lament the inevitable loss of fish if spill is eliminated completely.Previous work of the ISAB (and predecessor groups) and its members offers an alternative to complete cessation of spill, in the form of "skim spill" or surface spill (ISG 1996; Whitney et al. 1997; Coutant and Whitney 2000).
