by Jeniffer Solis, Nevada Current
Rising water temperatures across the Colorado River and its reservoirs are creating new challenges for water treatment operations in Lake Mead and hydropower production at Hoover Dam.
Extended drought and climate change has steadily increased surface temperatures in Lake Mead. In the past, the Nevada reservoir could depend on cooler water being delivered from upstream Lake Powell, but as Lake Powell shrinks, warmer surface water is moving through Glen Canyon Dam and into Lake Mead.
Water in the Colorado River generally warms 1.8 degrees F for every 30 miles traveled downstream during warmer months of the year, meaning by the time water reaches Lake Mead its several degrees higher than when it started.
This year, water flowing into Lake Mead is projected to be at least 10.8 degrees F warmer than usual by the end of fall, said Todd Tietjen, the regional water quality manager for the Southern Nevada Water Authority.
“We’ve seen this once or twice before,” Tietjen said. “But if it’s sustained, we don’t quite know what will happen.”
During the annual Nevada Water Resources Association Conference Wednesday, a panel of water quality experts raised the alarm about the potential impacts of warmer water surface temperatures on the Colorado River and its reservoirs.
The good news is that despite a steady decline in Lake Mead water levels, the lake’s depth and size has helped buffer the impacts of drought and climate change on water quality. But preliminary data suggests there’s a potential for risk.
Water treatment plants in Southern Nevada were designed and optimized to treat the deepest and coldest layer of water in Lake Mead. While warmer water can be treated, it’s often more expensive and difficult.
“We really rely on the cold water being present for our treatment process. Our treatment process was designed around cooler, colder waters. Our buildings on site are cooled by this water,” Tietjen said.
Water treatment plants in Southern Nevada also need cool water to operate vital ozone water treatment systems, which purify water by breaking down contaminants like bacteria, dissolved metals, and pesticides.
“The ozone is used as a disinfectant. The generators that produce it are cooled by this water and lose efficiency rapidly if they don’t have cold water for cooling,” Tietjen said.
Warmer water temperatures also have the potential to impact operations at Hoover Dam. Hydropower turbines and generators at Hoover Dam are cooled using water sourced directly from Lake Mead. Those cooling water systems are crucial for preventing overheating and maintaining full operational capacity at the dam.
If water pulled in through the turbines reaches a temperature of at least 78.8 degrees F for three or more consecutive days, it has the potential to disrupt operations, according to the Bureau of Reclamation.
“Most of the turbines are cooled by Lake Mead water, so they run into problems if they have hot water, and if we lose power at Glen Canyon and Hoover Dam, that’s a big problem for the West,” Tietjen said.
“The system is so clearly designed for the lakes to be full,” Tietjen continued. “There was no thought that the lake would not be full most of the time.”
Another concern is that warmer inflow from Lake Powell could increase the chance of harmful algal blooms in Lake Mead and other downstream reservoirs, including Lake Mohave.
Warmer water “cascades down to Lake Mohave as Lake Mead drops,” Tietjen said. “Eventually Lake Mead will stop releasing as much cold water, and will release more warmer water, totally shifting the dynamic down to the next lake.”
The four warmest years on record for Lake Mead coincide with toxic algae blooms, indicating a potential link between water temperature and the strain of algae that produce toxins, said U.S. Bureau of Reclamation hydrologist Thomas Ashley.
“The thing that is a little concerning is that the frequency of detections has gone up in the last 10 years,” Ashley said, adding that the abundance of toxic algae increases in reservoirs with even warmer surface temperatures further downstream, like Lake Mohave.
Toxic algae blooms can be difficult to manage. Not all algae blooms are toxic, a single species of algae can have both toxic and non-toxic strains, and a bloom that tests non-toxic one day can be toxic the next.
Lake Mead does have an advantage that natural lakes facing climate change challenges don’t. Unlike natural lakes, water storage and outflow are actively managed.
Water quality in Lake Mead has remained high due to the movement of water in and out of the lake. Low water age is generally associated with high water quality due to shortened exposure time to the nutrients that feed algae and bacteria.
“We’re not seeing large degradations in water quality in Lake Mead, because the withdrawals from Lake Mead have not changed that much as we’ve gone through this drought,” Tietjen said. “It’s simply passing through the lake a lot faster, allowing us to maintain relatively high water or extremely high water quality.”
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