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Show CEA Report Water Supply ONE OF THE PRIMARY PURPOSES of building Glen Canyon Dam was to store water for delivery to downstream users, and to protect the upper basin's water interests. Virtually all lower basin water users, however, take water from downstream sources, thereby making Powell reservoir unnecessary for water storage. Water for the town of Page and the coal- burning Navajo Generating Station, the only direct users of water from Powell reservoir, could be piped directly from the river or from a small, off- channel reservoir without the need to store 27 million acre- feet ( MAP) of water. • If Powell reservoir were drained, annual delivery of water to the lower basin would fall short of 7.5 million AF 27% of the time, versus 20% of the time under current operating conditions. 17 However, there is only a 1.3 in one million chance that water delivery would fall short of the requirements specified in the Colorado River Compact ( 75 million AF over 10 years) if Powell reservoir were drained. 33 Water shortfalls can be compensated for through conservation and better management of resources. 6 Without Powell reservoir, water delivery to the upper basin states would not change from current levels. 17 Without Powell reservoir, average annual flows into the Colorado River Delta would increase by 444,000 AF per year due to reduced evaporative loss. 6 Without Powell reservoir, average water delivery to the lower basin states would be reduced by 91,000 AF per year. 17 This is due to inter- annual variability of river flow. In high- flow years, excess water runs to the Sea of Cortez, rather than being stored for consumptive use. In low- flow years, there is a shortfall ( less than 7.5 million AF) to the lower basin. This variability averages out to a 91,000 AF per year shortfall. Comparative Average Annual Water Volumes • Current Operations f Drain Powell Reservoir 1 Figure 10 Predicted annual average water volumes with and without Powell reservoir. Much of the evaporative losses saved by draining the reservoir end up in Mexico and are available for replenishment of the Colorado River Delta ( after Rosekrans, 1997). page 13 |
