Will Hoover Dam go Bust?
May 29, 2016
As the Southwest continues in historic drought, Hoover Dam’s reservoir, Lake Mead, is at historic low water levels. What are the ramifications?
The last time Lake Mead was this low—in 1937—water managers were still filling the reservoir and putting finishing touches on the Hoover Dam. According to data from the U.S. Bureau of Reclamation, the water level has now reached a record low for the second year in a row.
On May 25, 2016, the surface level of Lake Mead at the Hoover Dam stood at 1,074.03 feet (327.36 meters) above sea level. The previous low of 1,075.08 feet (327.68 meters) was set in late June 2015. The lowest water levels each year are usually reached in late June or July, after water managers have released the yearly allotment of water for farmers and cities farther down the Colorado River watershed. That means water levels are likely to continue to fall in 2016 to roughly 1,070 feet (326 meters), according to the Bureau of Reclamation.
The pair of Landsat images above show the lake near its highest and lowest points over the past 32 years. The top image was acquired on May 15, 1984, by the Thematic Mapper on the Landsat 5 satellite. The lake last approached full capacity in the summer of 1983. The second image was acquired on May 23, 2016, by the Operational Land Imager (OLI) on Landsat 8. Turn on the image comparison tool to see the changes in the shoreline after lake water levels dropped 135 feet (41 meters). Notice the white-tan “bathtub ring” around the edges of the water; this is exposed sand and minerals that would normally be under water.
Lake Mead is now roughly 37 percent full. At maximum capacity, the reservoir would hold 9.3 trillion gallons (36 trillion liters) of water, reaching an elevation 1,220 feet (372 meters) near the dam. Most of the water in this great reservoir comes from snowmelt in the Rocky Mountain range and travels through Lake Powell, the Grand Canyon, and into Lake Mead. Farmers and some cities in Arizona, Nevada, California, and northern Mexico all rely on water from Lake Mead.
According to the Bureau of Reclamation, the lake will be refilled enough by the end of 2016 to avoid cuts in water deliveries in 2017. Lake Mead National Recreation Area continues to operate water sports, sightseeing, and hiking facilities in the area, despite ongoing drought.
Six years ago, at the end of the summer of 2010, federal Bureau of Reclamation officials worried that Hoover Dam, the biggest hydropower enterprise in the Southwest, might soon go dark. Water levels in Lake Mead, the dam’s energy source, were falling, and Hoover was moving “into uncharted territory,” the facility manager told Circle of Blue.
Today, the story has a twist. Lake Mead is 10 feet lower, a new record set on May 18 that is re-broken every day now. Yet though water levels continue to decline, Hoover’s hydropower is in a much better spot. Thanks to investment in efficient equipment, managers are confident that they can still wring electricity from the Colorado River even as the surface elevation of Lake Mead drops below 1,050 feet, the uncharted territory that was assumed to be Hoover’s operating limit.
“As far as power goes, we can still operate below 1,050 feet,” Rose Davis, Bureau of Reclamation spokeswoman, told Circle of Blue. Dam operators are revising the lower limit to 950 feet, a boundary that will be confirmed in October once the fifth and final more-efficient turbine is installed, Davis said.
Electricity from Hoover is some of the cheapest in the country, at 1.83 cents per kilowatt-hour. Constructions costs for the dam were paid off years ago and the energy source, the water, comes from Mother Nature free of charge.
Customers in Arizona, California, and Nevada, the destination for Hoover’s output, would like to keep the cheap power flowing. That is why they spent $US 14.9 million since 2011 on the turbines and wicket gates.
The problem with Mead’s low water level for power generation is physics. Pressure differences in the water coming into the generators produce air bubbles on the turbine blades. As the water flows across the blades, the bubbles collapse and burst, which causes vibrations that can damage the generating unit. If the vibrations worsen, the unit must be shut down.
Wide-head turbines are designed to avoid these “rough zones” and operate smoothly at low reservoir levels. Four of Hoover’s 17 turbines have been fitted with wide-head models, and a fifth will be installed by October.
The wicket gates, on the other hand, allow for more precise control of water flowing through the turbines. They also reduce water leakage so that every drop that passes through Hoover can generate as much power as possible. Digital controls, which allow for more precise positioning of the wicket gates, have been installed at Hoover as well as at Davis and Parker dams, downstream on the Colorado.
“Any efficiency in hydropower means more power for our customers,” Kara Lamb told Circle of Blue. Lamb is the spokeswoman for the Western Area Power Administration, which markets Hoover’s power.
Though Hoover will not shut down any time soon, low water levels still reduce its output.
Generating capacity — the maximum amount of power that the dam is capable of producing — is down 30 percent from when Mead was full. For every foot that Mead drops, generating capacity decreases by five to six megawatts. Money is power, the old saying goes. So is water.