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Glen Canyon Dam’s evaporating hydropower

 

Updated 7/10/13

Ever since water levels in Lake Powell started dropping in 1999, the last time the reservoir was near full, I’d heard a lot about the infamous bathtub ring—the white band of minerals and salts that separates the current lake level from the high water mark. So I was looking forward to seeing it for myself when I headed out on a rafting trip down Cataract Canyon, below the confluence of the Green and Colorado rivers, two weeks ago. What stuck me most as I floated down the river was not the ring, but the inhospitality of those re-emerging shorelines. Oozing silty beaches that sucked you in up to your knees, eroding sandy cliffs and thickets of tumbleweeds were a staple of the lower third of the trip, where the river merged with the reservoir. At the takeout, what used to be a short, gravelley boat ramp has become a long slog up a sandy hill to a parking lot that was once on the shore. Perhaps the only upside of the lake’s recession was the widespread die-off of tamarisks stranded tens of feet above the new, lower waterline.

The government entities that manage Glen Canyon Dam and sell the power its turbines generate are also distressed at Lake Powell’s retreat, albeit for economic and political reasons. According to the Bureau of Reclamation, in May the reservoir was only 48 percent full, and is expected to drop 11 feet before September, ending the summer at 44 percent capacity. Severe to extreme drought in much of the Colorado River’s watershed, plus record heat, isn’t exactly helping.

Despite the dismal conditions, Glen Canyon Dam is still discharging 8.23 million acre-feet of water this year (measured from Oct. 1, 2012 to Sept. 30), as it does every year that lake levels stay above approximately 3,650 feet (the exact levels were decided in a 2007 environmental impact study designed to address water storage issues on the Colorado River in times of drought). But there’s a 50-50 chance that the lake will soon drop below that height, triggering a lower water release next year. If that happens, it would be the first time since Lake Powell’s creation that less than 8.23 million acre feet of water will pass from Glen Canyon Dam, according to Bureau of Reclamation spokesperson Lisa Iams. “It’s not a promising statement about the hydrology that all of us face,” she said. “The realities of drought and climate change are increasing.”

Glen Canyon Dam was constructed primarily to store Colorado River water, helping arid Western communities, industries and farms weather drought and dry seasons. But it plays a  role in the Western electrical grid, too: Its eight generators can produce up to 1,320 MW of electricity, and the dam helps supply power to 5.8 million customers. Although it’s a relatively minor player in the West’s energy supply, its generators can ramp up quickly, helping to match sudden surges in electricity demand or drops in production from renewable energy generation (for more on this, check out “Haywired,” Jonathan Thompson’s recent feature on the challenges of integrating renewables into the grid).

Drought is bad for electricity generation at Glen Canyon Dam for two primary reasons: One, when lake levels are low enough to merit a smaller release (like they could be this coming year), less water goes through the turbines, producing less energy. That hasn’t happened yet, but the dam has already seen a reduction in electricity generation. Here’s why: Lower water levels mean there is less pressure on the water as it passes through the turbines. “As our lake level drops, the same volume of water going through the dam generates less electricity,” explained Jason Tucker, facility manager for Glen Canyon Dam. “The deeper the water, the more energy there is for making electrical power.”

As lake levels have dropped (solid line), so has the amount of power being generated (dotted line). Courtesy Argonne National Laboratory.

The graph below shows the tight linkage between lake elevation (solid line) and power generation (dotted line).

Courtesy Argonne National Laboratory.

As a result of the reduction in power generation, Western Area Power Administration, the government body that sells Glen Canyon’s electricity, has told its buyers to expect less electricity from the dam, according to spokesman Randy Wilkerson.

Elsewhere in the West, drought has actually raised the price of hydropower. Decreased electricity generation from Missouri River dams has forced WAPA to buy power on the open market to fulfill its obligation to customers in eastern Montana, the Dakotas and eastern Colorado (WAPA’s contracts with buyers of Glen Canyon’s electricity don’t require the agency to do this). Customers in the Missouri River basin now see something called a “drought adder” on their electricity bills, which shows what percentage of the rate hike is due to drought.

Living in an increasingly warm, dry West, it’s good to keep in mind the connection between energy and water. Whether it’s the millions of gallons used to frack gas wells, cool nuclear power plants or drive turbines in dams, water is never too far behind the flick of a switch.

Emily Guerin is a correspondent at High Country News.