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Description of Alternatives turbidity and disrupt the aquatic food chain below Lees Ferry. Other potentially adverse impacts are unknown. A sediment slurry pipeline would require 15 to 20 years to implement, and a plan to operate the dam in the interim still would be needed. If sediment augmentation is desired in the future, this action would be the subject of a separate EIS. Without sediment augmentation, the flows under this alternative would cause more erosion to sediment deposits below Glen Canyon Dam than other alternatives, including no action. Historic Pattern Alternative Conclusion This alternative was a modification of the Run-of-the-River Alternative. It attempted to more closely follow predam water flow patterns, while still managing flows within current powerplant capacity. The Historic Pattern Alternative also included a sediment slurry pipeline and selective withdrawal. This alternative was eliminated from detailed study for most of the same reasons as the Run-of-the-River Alternative. A sediment slurry pipeline would require 15 to 20 years to implement, and a plan to operate the dam in the interim still would be needed. Without sediment augmentation, the flows under this alternative would cause more erosion to sediment deposits below Glen Canyon Dam than other alternatives, including no action. Mitigating these impacts by reducing seasonally high flows creates a flow regime incorporated into the -- Seasonally Adjusted Steady Flow Alternative. For these reasons, the Historic Pattern Alternative was not further considered. Reregulated Flow Alternative Conclusion The EIS team responded to scoping comments requesting full use of Glen Canyon Dam Powerplant's generating capacity by developing the Reregulated Flow Alternative. The objective of this alternative was to initiate operational changes to fully use the powerplant's generating capacity (flows of 33,200 cfs) while reducing, to the extent possible, existing adverse impacts on downstream resources by constructing a reregulation dam. Constructing a reregulation dam in Glen Canyon National Recreation Area would require changes in existing laws that protect the values for which the recreation area was established and prohibit construction of a dam within a national park or monument. While most downstream resources would experience improved conditions over the No Action Alternative, resources in the Glen Canyon reach would experience negative impacts. 34 Glen Canyon Dam EIS Summary