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Other Views: Glen Canyon Dam structurally sound, no underachiever

Glen Canyon Dam is a National Resource. Last Friday’s editorial ("Lots to unwind if Glen Canyon Dam shuttered too soon") discussed the newly signed management plan for Glen Canyon Dam, but incorrectly attributed its 20-year focus to a possible end to federal management by 2036. Glen Canyon Dam is a crucial national resource, and the federal government remains fully committed to its long-term successful management well into the future. This new plan enhances certainty and

predictability for water and power users while protecting downstream environmental and cultural resources. The plan’s 20-year focus simply provides a timeline for regularly adjusting dam operations as ongoing science and other factors inform future planning. Several other assertions merit correction as well. There are no mounting bills for dredging or structural upkeep. Silt buildup hasn’t yet reached the dam and sediment deltas are more than 100 miles upstream in the reservoir. Estimates predict silt won’t fill behind the dam for 700 to 1,000 years. Sediment buildup poses no threat to the dam’s integrity--it is completely structurally sound. Claims of lost water through seepage are also overstated. Some groups advocate decommissioning the dam based in part on outdated water loss studies. However, a recent assessment by the Center for Colorado River Studies at Utah State University found seepage rates are much lower than those groups claim and that rates are actually declining over time. Seepage water enters the ground water system and eventually returns to the reservoir or river channel.

 

Without both Lake Powell and Lake Mead, basin-wide drought impacts would have been even more severe. In fact, seven of the past 17 drought years saw less than 8 million acre feet (maf) of unregulated inflow into Lake Powell—that’s the amount that would flow to Lake Mead without Glen Canyon Dam. Four years saw less than 6 maf and 2002’s inflow was only 2.64 maf. However, during even the driest years, storage in Lake Powell allowed full water deliveries with average annual releases of 8.71 maf throughout the drought. Examining total water storage and use further highlights Lake Powell’s continued importance. Storage capacity at Lakes Mead and Powell is finite—Lake Mead’s maximum capacity is 28.9 maf and Lake Powell’s is 26.2 maf, for a total combined capacity of 55.1 maf. Both reservoirs were at or near full when the drought began in 2000. By the end of water year 2016, regular water deliveries had depleted combined reservoir storage by 30.7 maf—more than either Lake Mead or Lake Powell could support on its own. Without Lake Powell’s storage, those obligated water deliveries would have completely drained Lake Mead before 2016. Far from being an underachiever, Glen Canyon Dam is doing precisely what is was intended to do — storing water in wet years to ensure predictable, full deliveries across the basin every year. Populations in Arizona and the west continue to grow, as do the challenges and complexities of efficiently managing limited water resources. Glen Canyon Dam has been integral to meeting those challenges for more than 50 years and will continue its role for many decades to come.

 

Thank you Ron