WAPA navigates costs of countering smallmouth bass

Featured image:  Water is released from two of Glen Canyon Dam’s four bypass tubes, which the Bureau of Reclamation is using to cool the Colorado River and keep warm-water, non-native fish from reproducing below the dam. Photo by Craig Ellsworth.

Smallmouth bass invade Grand Canyon

Prolonged drought in the West has left Lake Powell both lower in elevation and warmer in recent years. Warm surface waters – where non-native fish thrive – are now at the level of Glen Canyon Dam’s intakes. This has allowed non-native fish, such as smallmouth bass, to get “entrained,” or pass through the dam, and access prime habitat in the Grand Canyon. These non-native fish pose a grave and growing threat to the recovery efforts for federally listed fish, like the humpback chub.

WAPA, the Bureau of Reclamation and other partners in the Glen Canyon Dam Adaptive Management Program have for years been exploring ways to control populations of invasive non-native fish in the Upper and Lower Colorado River Basins. These efforts primarily aim to protect four federally listed native fish that risk being preyed on or having to compete with non-native fish for resources.

Reclamation’s recent environmental impact study, in response to this non-native fish invasion, has required significant changes in operations at Glen Canyon Dam. As a result, WAPA’s Colorado River Storage Project regional office is coordinating weekly with Reclamation’s hydropower operators and technical staff to help mitigate how these new operations impact hydropower generation while trying to curtail smallmouth bass establishment in the Grand Canyon.

A cool mix of water

On May 30, Reclamation released the Glen Canyon Dam Long-Term Experimental and Management Plan Final Supplemental Environmental Impact Statement and signed the Record of Decision on July 3. This SEIS examines the use of bypass flows to attempt to slow the spread of non-native smallmouth bass in the river below the dam. Reclamation selected the “Cool Mix Alternative,” and implementation began on July 9.

The Cool Mix strategy blends the warm water from the hydropower generators with colder releases from the bypass tubes, in order to keep the river cooled to 15.5 degrees Celsius (60 degrees Fahrenheit) at the confluence with the Little Colorado River – about 76 miles downstream from the dam. However, waters released through the bypass tubes aren’t used to generate power, so CRSP must purchase that lost generation.

“Since we have contracts with our customers to deliver a certain amount of energy, if we cannot provide power through our own generation, we have to go out on the market and purchase replacement power to provide them,” said CRSP Regional Manager Rodney Bailey.

Sizing up the shift

Beginning last year, WAPA partnered with DOE’s National Renewable Energy Laboratory and Argonne National Laboratory to analyze the effects of bypass operations on hydropower generation at Glen Canyon Dam. CRSP estimated that the Cool Mix Alternative could result in up to $220 million of increased energy purchases over the next four years to meet WAPA’s contractual obligations with customers.

“The models suggest significant costs in some years due to higher purchase power costs during summer months when bypass flows are implemented,” CRSP Environmental Protection Specialist Jerry Wilhite said. “The increased energy needed from thermal generation sources would also increase emissions regionally and rely on more expensive energy than WAPA’s hydropower product.”

Summer brings higher energy prices

In July, WAPA spent around $1 million weekly from the Basin Fund – a pool of revolving funds maintained by hydropower revenues – to buy replacement power on the day-ahead and spot markets. After approximately three weeks under the new operational strategy, WAPA completed an off-peak and partial on-peak block purchase of 200 megawatts per hour, based on projected bypass patterns at the time of purchase, from August through October. CRSP sees this block purchase power as a good hedge that already appears to be paying off by avoiding volatile market prices.

A summer of bypass flows will significantly impact the Basin Fund, potentially jeopardizing its future solvency. Both WAPA and Reclamation use the Basin Fund to support the operation and maintenance of the Colorado River Storage Project, which primarily includes Glen Canyon Dam, Flaming Gorge Dam and the Aspinall units.

“Addressing the smallmouth bass problem with bypass flows has significant implications for the Colorado River Storage Project, as these same funds are used for operations, maintaining our transmission system and for similar expenses from Reclamation’s Upper Colorado Region,” CRSP Administrative and Technical Services Manager Brian Sadler said. “If the Basin Fund is depleted, this could result in the need to defer expenses such as maintenance of the hydropower plants or delay transmission infrastructure investments for grid upkeep.”

To avoid further impacts, CRSP is seeking alternative, non-reimbursable funding to recover losses to the Basin Fund incurred by this operation. WAPA estimates a total cost between $15 million and $20 million for this year’s bypass flows.

Partnering to ease the strain

WAPA and Reclamation have been working since the bypass flows started to optimize the hours of bypass to mitigate some of the impacts.

“Our staff are coordinating with our partners at Reclamation every week, making sure we can meet the requirements of the experiment while maintaining the highest value of power, especially during critical peak hours in the afternoon,” Wilhite said. “By working directly with Reclamation, we’re able to dial up or down the bypass flows in order to meet daily average temperature targets, and this allows us to prioritize afternoon and early evening generation during the super peak.”

For example, CRSP has been able to turn off bypass during the daily peak hours from 3 p.m. – 10 p.m., allowing power generation to increase from 210 MW to 552 MW when power is needed the most. Timing the bypass flows during off-peak hours, when energy prices are lower, has saved 12-15% on WAPA purchases while providing critical power to the grid during afternoon and evening peaks.

Over the four-year experiment, WAPA will continue to collaborate with Reclamation in the interest of power customers across the West to maintain the value of CRSP hydropower.

“We have at least four years to work through this, so it’s not a fleeting problem,” Bailey said. “It’s an ongoing problem that we will deal with until other solutions are figured out. Raising the reservoir elevation could be a good start.”

Arid adaptations

WAPA actively participates in the Glen Canyon Dam Adaptive Management Program, which provides the Secretary of the Interior with recommendations on dam operations, downstream resource protection and management, and monitoring and research needs.

“WAPA takes our commitment to environmental stewardship and working with others in the Adaptive Management Working Group very seriously while advocating for our nearly 700 hydropower customers, mainly in rural areas across the West,” Bailey said. “WAPA remains committed to providing low-cost, reliable hydropower to our customers and seeks collaborative solutions to ensure we can deliver on that promise, and this experiment shows that we can find ways to mitigate impacts to power.”

WAPA continues to work closely with its federal partners at Reclamation, as well as state, local and tribal stakeholders, to address the ongoing challenges posed by drought. For example, WAPA and Reclamation jointly funded a review of smallmouth bass management options below Glen Canyon Dam published by the Center for Colorado River Studies at Utah State University. The report identifies several key uncertainties and research needs to better understand the risks and probabilities of smallmouth bass establishment below Glen Canyon Dam.

Running its course

After the four-year experiment, additional approaches might be developed to address the smallmouth bass problem. According to Wilhite, modeling suggests that maintaining an end-of-water-year elevation at Lake Powell above 3,570 feet would lower the probability of needing bypass flows to cool Glen Canyon Dam releases. Aided by two years of good hydrology, Lake Powell’s elevation rose from an all-time low of 3,519 feet during the winter of 2023 to 3,587 feet in the summer of 2024.

“The higher you keep the reservoir, the more you reduce smallmouth bass entrainment through the dam, and the colder your water releases are likely to be,” he continued. “In other words, the deeper you can keep the penstock intakes, the less bypass you need to keep release temperatures low.” However, maintaining higher elevations in Lake Powell during periods of drought remains challenging because of water delivery requirements both above and below Lake Powell.

Another approach being investigated involves the installation of a thermal curtain in the forebay just upstream of the dam. “Thermal curtains block the warm surface water from entering the penstocks and allow deeper, cooler water to be released downstream. They are being used with success at other Reclamation reservoirs,” said CRSP Fishery Biologist Craig Ellsworth.

These strategies would also reduce entrainment through the dam – something the current bypass regimen does not address. “Preventing the establishment of a fish like smallmouth bass below Glen Canyon Dam will require a multi-faceted, coordinated approach that not only addresses warm-water releases, but also reduces entrainment and modifies the downstream habitats that these fish could establish in,” Ellsworth added.

As drought persists, arid conditions will continue to test the federal agencies tasked with managing the CRSP system.

“In spite of two good water years, we are still amid a megadrought across the West,” Bailey said. “WAPA continues to work closely with our partners to find creative solutions that preserve the valuable hydropower resource for our customers and, at the same time, respect the environment – one of our core organizational values.”