BOULDER CITY, Nev. — Drought and rising temperatures are forcing water managers across the country to scramble for ways to produce the same amount of power from the hydroelectric grid with less water, including from behemoths such as the Hoover Dam.
Hydropower is not the only part of the nation’s energy system that appears increasingly vulnerable to the impact of climate change, as low water levels affect coal-fired and nuclear power plants’ operations and impede the passage of coal barges along the Mississippi River.
“We’re trying to manage a changing climate, its impact on water supplies and our ability to generate power, all at once,” said Michael Connor, commissioner of the Bureau of Reclamation, the Interior Department’s water-management agency. Producing electricity accounts for at least 40 percent of water use in the United States.
Warmer and drier summers mean less water is available to cool nuclear and fossil-fuel power plants. The Millstone nuclear plant in Waterford, Conn., had to shut down one of its reactors in mid-August because the water it drew from the Long Island Sound was too warm to cool critical equipment outside the core. A twin-unit nuclear plant in Braidwood, Ill., needed to get special permission to continue operating this summer because the temperature in its cooling-water pond rose to 102 degrees, four degrees above its normal limit.
Scott Burnell, a spokesman for the Nuclear Regulatory Commission, said the safety of America’s nuclear plants “is not in jeopardy,” because the sources of water cooling the core are self-contained and might have to shut down in some instances if water is either too warm or unavailable.
“If water levels dropped to the point where you can’t draw water into the condenser, you’d have to shut down the plant,” he said. The commission’s new chairman, Allison Macfarlane, has asked her staff to look at “a broad array of natural events that could affect nuclear plant operations” in the future, such as climate change, Burnell added.
For more than three-quarters of a century, the Hoover Dam has represented an engineering triumph, harnessing the power of the mighty Colorado River to generate electricity for customers in not just nearby Las Vegas but as far away as Southern California and Mexico.
But the bleached volcanic rock ringing Black Canyon above Lake Mead, the reservoir created by the dam, speak to the limits of human engineering. Higher temperatures and less snowpack have reduced the river’s flow and left the reservoir 103 feet below elevation for its full targeted storage capacity, which it last came close to reaching in 1999.
In the Colorado River’s 100-year recorded history, 1999 to 2010 ranks as the second-driest 12-year period, yielding an average of 16 percent less energy.
Scientists have just begun to study some key questions, such as the rate of evaporation off dams’ storage facilities. Predicting river flows — which can flood one year and dry up the next — is even harder.
“Because of the variability of river systems, it’s a lot more difficult in modeling how climate change will affect them,” said Jenny Kehl, who directs the Center for Water Policy at the University of Wisconsin at Madison.
Rising temperatures have started to affect U.S. coal plants as well. This summer’s drought disrupted the transport of coal delivered by barges on the Mississippi, and the U.S. Army Corps of Engineers had to use dredges to deepen the navigation channel.
The Illinois Environmental Protection Agency granted special exceptions to four coal-fired plants and four nuclear plants this summer, allowing them to discharge water into local waterways that was hotter than the federal clean water permits allowed. Normally the discharge water cannot exceed 90 degrees, but the waiver allowed utilities to release water as hot as 97 degrees.
And the reduced flow on the Colorado River has raised questions about whether new power plants should be built. In August 2011, the Lower Colorado River Authority postponed indefinitely its decision to provide 8 billion gallons of water to cool the proposed White Stallion Energy Center in Texas, which the Sierra Club had fought on the grounds it would use too much water and emit harmful air pollution.
At the Hoover Dam, which hasn’t run at capacity since 1983 because of lower river flows and other water demands, the Bureau of Reclamation has had to compensate for the decline in water availability. The dam loses between 5 and 6 megawatts of capacity for every foot in elevation Lake Mead loses, meaning this year it lost the equivalent of a medium-size power plant.
The bureau’s most recent projections suggest that in the next 50 years, the lower Colorado River’s flow will decline between 9 and 10 percent because of climate change, with demand exceeding supply by more than a third. At the same time, it estimates it will take between 3 and 10 percent more water to meet agriculture demands.
In the past, the agency has compensated for a gap in water supplies with sufficient storage, said Terry Fulp, the bureau’s acting regional director for the lower Colorado basin. “Now, the question with the projections we have now is, is storage going to be enough? Probably not,” he said. “We need to start thinking of not just relying on this river system,” he said.