Report: Lake Mead dropping 12 feet per year |

Report: Lake Mead dropping 12 feet per year

The white ring "around the tub" shows how much elevation the surface of Lake Mead has lost with drought stress on the Colorado River.
Rose Davis / Bureau of Reclamation |

The math is simple.

So states a disarming truism in a new report from the Colorado River Research Group, formed of water scholars in four states, “an independent, scientific voice for the future of the Colorado River.”

In 2007, the U.S. secretary of the interior adopted interim guidelines for a period of 20 years that sought peace among the seven Colorado River basin states and Mexico, most of which are always ready to grapple over one of the Southwest’s most precious resources: Colorado River water.

The guidelines set out how the river’s two giant reservoirs, upstream Powell and downstream Mead, would be managed during the period, and who would get shorted if the water was insufficient to meet basic entitlements. This month’s new report from the research group assesses just how those interim guidelines are faring.

Not so well, it turns out.

The math is simple.

Lake Mead, backed up by iconic Hoover Dam just outside Las Vegas, receives about 9 million acre-feet of water annually from Lake Powell, a small percentage of which also comes from downstream tributaries. But after sending water to Arizona, Nevada, California and Mexico, after evaporation and other subtractions, Lake Mead loses 10.2 million acre-feet each year.

During the ongoing 15-year period of drought in the river basin, the annual shortfall of 1.2 million acre-feet of water in Lake Mead has come to be known as the “structural deficit.” Everyone who has seen the ring-around-the-tub photos of Lake Mead in recent years knows what that means. Each year the deficit drops the surface level of Mead by 12 feet, according to the research group.

If the surface falls to 1,075 feet above sea level as measured on Jan. 1 of any year, the interim guidelines state that the secretary of the interior can declare a shortage on the river. And the lake briefly dropped below that level this past June, before record-breaking spring precipitation in the Rockies boosted it back.

Should a shortage be declared, water deliveries could be curtailed — with the size of the delivery reduction depending on just how far the lake level falls. Should Mead’s surface reach 1,025 feet, for example, deliveries of consumptive water to Arizona, Nevada and California would be curtailed by 500,000 acre-feet.

“It’s worth noting that 500,000 acre-feet is not even half of the structural deficit,” said Doug Kenney, director of the Western Water Policy Program at the University of Colorado, and a member of the research group. “It’s not enough to stop the problem.”

Lake Mead’s water level has dropped 135 feet since 2000.

In other words, even with the prescribed curtailment in deliveries, if the structural deficit remains the same, the lake level would continue to plummet.

“At 1,000 feet, the interim agreement calls for a ‘re-consult,’” Kenney said.

That would be an interesting meeting, because at an elevation of 1,000 feet, or thereabouts, Lake Mead would hit “dead pool” status, meaning that Hoover Dam could no longer generate electricity or deliver water to Las Vegas (the city is currently engaged in a massive construction project to place pipes closer to the bottom of the lake).

“The parties (to the interim guidelines) hoped that a shortage declaration would not actually be needed,” the research group report observes, “and only provided for reductions up to 500,000 acre feet. (But) as evidence grows of a warming-induced, long-term reduction in basin water supplies, the likelihood of shortages greater than 500,000 acre-feet increases.”

Indeed, the latest national climate assessment states that the nation’s hottest and driest region, the Southwest, will only become more so in the years ahead.

To say that there are immense legal and political challenges in dealing with water shortage issues on the river is to understate. Since the original pact between the seven states in 1922, there have been countless lawsuits, treaties, acts of Congress and Supreme Court decisions. And now it looks like the interim guidelines may not cut it.

The Colorado River Research Group’s new report calls first and foremost for enacting strategies to deal with the structural deficit in Lake Mead.

“There’s no way to solve the overall issues of the river without resolving the structural deficit,” Kinney said in an interview with Rocky Mountain PBS News. “This particular aspect is primarily a lower basin issue. But the faster the structural deficit pulls down Lake Mead, the more pressure, political pressure and legal pressure, will be on the upper basin.”

The research group proposes numerous tacks for diminishing the deficit, including developing alternative supply sources such as desalination, reducing existing losses — including ways to account for unavoidable losses such as reservoir evaporation in consumptive use decisions — conservation, voluntarily purchasing and retiring some water rights, and ensuring “continued flows from the upper basin at adequate levels.”

Arizona, for example, has proposed subtracting evaporation losses at Mead, about 600,000 acre-feet annually, on a proportionate basis from the consumptive allotments of the three lower basin states. Each state would get less, but that could cut the deficit in half.

Ultimately, the research group said, all of this “requires a redefinition of normal — one that is based on a realistic, and likely changing, basin water budget.”

The reality of drought in the last 15 years could become the new normal, Kinney said.

“Any little increment in warming has a huge impact on the basin,” he said. “A little more surface evaporation and evapotranspiration by plants make a huge difference. Those are huge users of water and are temperature dependent. During the drought, precipitation is down 4 percent, but stream flows are down 19 percent. It messes up every phase of the hydrological cycle.”

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