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I 1\ I I I I I I I I I I I I j I I I, I SECTION VI: IMPACTS OF CURRENT OPERATIONS Current Operations Are Characterized By Flood Releases And Fluctuating Releases Two aspects of current operations have substantial impacts on downstream resources: flood releases and fluctuating releases. This chapter describes the effect of these releases on the critical environmental and recreational resources. Flood releases are defined as releases greater than the designated powerplant capacity of 31,500 cfs which are discharged through the river outlet works and spill- ways. The river outlet works are generally operated at or near the full capacity of 15~000 cfs, or not at all. Therefore, releases above powerplant capacity are usually in the range of 40,000-50,000 cfs. Flood releases generally occur for four to six weeks in May or June in years when runoff is well above average or the forecast of runoff is too low. These kinds of releases were very rare prior to the filling of Lake Powell in 1980. Since then, flood releases have oc- curred in five of seven years. Under current op- erations, flood releases are expected to occur in one out of four years (Appendix D, section III). A typical flood release pattern (Figure VI-la) for the 1986 water year shows the high releases in May and June. Fluctuating releases are made when the dam is being operated to produce peaking power. A typical daily re- lease pattern for peaking power operations is shown in Figure VI-lb. For the purposes of the GCES, fluctuations are defined as a change in dam release greater than 10,000 cfs during a day. This cut-off point, although somewhat arbitrary, is based on changes in flow that appear significant for recreation and the environment. For example, when daily fluctuations are greater than 10,000 cfs, they are noticed by a substantial majority of white-water boaters. Also, in practice, when releases are' fluctuating, the fluctuations are almost always greater than 10,000 cfs. Lake Powell has the necessary to provide releases of 8.23 maf drought (Appendix D). water storage capacity the required m~n~mum annual even during a long period of Therefore, steady flows lower 43