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I I I I I I I I I I I I I I I I I I I SECTION VIII: CONCLOSIONS AND MANAGEMENT OPTIONS ~ Conclusions ~ (1) Flood releases and fluctuating releases from Glen Canyon Dam have a significant effect on many of the downstream environmental and recreational resources. Adverse downstream consequences are caused primarily by sustained flood releases significantly greater than powerplant capacity and by fluctuating releases. The most critical impacts are the erosive effect of floods on sand deposits and vegetation and the impact of fluc- tuations on white-water recreation. Continued flood releases will substantially reduce sand deposits in Grand Canyon, which are essential to vegetation and wildlife and are highly valued by white-water boaters. Replenishment of sand in beaches is now dependent on sand delivered by tributaries within Grand Canyon. Because the amount of sand for resupply is much less than before dam construction and is highly variable from year to year, these erosive effects are probably permanent. For white-water recre- ation alone, loss of a substantial number of beaches could reduce recreation benefits by $5.2 million per year. Flood releases also double the risk of white-water boating accidents at major rapids, compared to flows below powerplant capacity. Even infrequent floods cause loss of camping beaches and vegetation substrate, and it appears that this loss is irreversible. Even though infrequent flooding may benefit some resources, the magnitude, duration, and frequency needed to provide those benefits are unknown. Loss of resources could be prevented by avoiding floods until the response of resources to floods is better understood. spring flood releases have no negative impact on humpback chub, or trout. In fact, these high benefit chub. apparent long-term common native fish, flows may actually Daily fluctuations substantially reduce the value of white-water recreation and trout fishing by degrading the natural character of the environment and making the management of white-water and fishing trips more 81