In a recent bombshell letter to newly appointed Interior Secretary Doug Burgum, the Lower Colorado River Basin states of California, Nevada, and Arizona sounded the alarm: any realistic plan for managing the Colorado River must address the plumbing problem at Glen Canyon Dam. The outdated plumbing at the dam and its threat to the water supply of downstream users is a problem that GCI and other environmental groups have been vocal about for years. Now it appears that some of the most influential decision makers in the basin agree.

The Lower Basin letter was prompted by the ongoing Post-2026 Colorado River Operations Environmental Impact Statement (EIS), a process required for major federal actions that will impact the environment under the National Environmental Protection Act (NEPA). This EIS is a renegotiation of guidelines laid out in 2007, and aims to stabilize a river management system in freefall. To bring water demand into balance with dwindling supply, the years-long heated negotiations between the Upper Basin and Lower Basin have focused primarily on which states will cut water consumption, and by how much.

But the heart of the letter penned by the Lower Basin states gets at a much deeper and more fundamental problem: Glen Canyon Dam itself poses a serious threat to the water security of 25 million people downstream.

As GCI told the LA Times, “The writing is on the wall that something has to be done sooner than later. If we want to actually fix this river system for the long term, we have to have a thorough debate about how to reengineer Glen Canyon Dam.”

The Glen Canyon Dam Plumbing Problem

When Glen Canyon Dam was designed in the 1950’s, the Colorado River still flowed to the Sea of Cortez. The dam was designed in an era of “excess” available water, but the river’s flows have declined by 20% over the last century. It never crossed the minds of its designers that one day the reservoir behind the concrete impoundment might fall to the low levels we see today.

Most of the time, water passes through the dam’s eight hydropower penstocks at an elevation of 3,470 feet, about 340 feet above the original riverbed. Below the penstocks, the only way for water to be released is through four smaller “river outlet works” (ROWs). These steel tubes are only 96” in diameter, and sit at elevation 3,374, about 244 feet above river elevation. This level is also known as “dead pool” because unlike many modern dams, there is no “drain plug” at the bottom of the reservoir to release water or sediment.

The ROWs were designed for occasional releases, not for round-the-clock operation. But if the reservoir drops below elevation 3,490, or minimum power pool, the only way to release water downstream to the Grand Canyon and the majority of Colorado River water users is through the ROWs. This is extremely problematic, as their release capacity is less than one half of what the higher elevation penstocks can release. As the reservoir drops from minimum power pool to dead pool, the pressure behind the dam to push water out through the ROWs shrinks. Well before reaching dead pool, at a certain elevation, the dam is physically incapable of delivering enough water to meet downstream delivery obligations required by the Colorado River Compact.

The designers of the dam assumed the reservoir would never drop to such low levels, but in 2023, it came within 30 feet of minimum power pool. Compounding the problems of the ROWs, it was revealed that they sustained serious damage in 2023 during use in an environmental flood for the Grand Canyon. When the ROWs were opened at low reservoir levels, sediment and air made their way into the tubes creating a hydrologic effect known as cavitation. Cavitation can lead to rapid erosion of structural material—in 1983, it was cavitation that led to the extreme damage of the two spillways at Glen Canyon Dam. In 2024, the Bureau painted an epoxy coating in the ROWs as a temporary measure to minimize, but not stop, cavitation.

The bottom line is this: not only do the ROWs hinder releases based on their sheer size limitation, but we now know that the hydrologic dynamics of low water operations have the potential to render them completely unusable. In a worst case scenario, future damage to the outlets could mean that there is no way to release water downstream.

For years, GCI and a coalition of environmental groups have been outspoken about this problem at conferences, in the media, and in direct communications to the Bureau of Reclamation. We have stressed that any process that seeks to maintain durability in this system must address the infrastructure limitations at Glen Canyon Dam. The response from Reclamation, however, has been that the Post-2026 EIS is “not an infrastructure EIS,” and they will not consider any modifications to the dam. Meanwhile, the agency has been quietly assessing options to alter the dam behind closed doors without releasing much information to the public aside from a brief webinar in 2023.

With a future certain to include low flow years due to a warming climate, it is almost inevitable that the reservoir will drop to levels where using the ROWs will be required. Not including at least one alternative in the EIS that looks at the engineering restrictions at the dam is not only short sighted, but negligent in presenting the public with a complete picture of the risk involved in future operations at Glen Canyon Dam. The government owes it to the public to give the full picture of the potential impacts and the solutions.

What’s in the letter

There is a lot to unpack in the Lower Basin’s 26-page letter to Interior. The states are making an argument that the Post-2026 EIS didn’t properly consider their alternative proposal, based on the “preview of alternatives” that was released last November. In and of itself, this argument is not too different from what they’ve been saying for years: the Lower Basin states have taken cuts and will continue to do so, but the Upper Basin must make bigger sacrifices with their use of the river. What sets this letter apart is its insistence that Bureau of Reclamation has thus far failed to (a) properly consider the implications of a Compact Call; or (b) propose an alternative which addresses the infrastructure problems at Glen Canyon Dam.

Threat of a Compact Call

Under the rules of the 1922 Colorado River Compact, if at any point the Upper Basin States are unable to deliver their legal water obligation to the Lower Basin States, a “Compact Call” could ensue. Under these circumstances, Lower Basin states could “call” on the Upper Basin to comply with the Compact’s terms and fulfill water deliveries by mandating upstream curtailments. This “tripwire” has long been considered a nuclear option in Colorado River politics, but with the declining hydrology in the basin, some experts suggest it could happen in the near future. In fact, in this letter, the Lower Basin states refer to a Compact Call as “likely” and “reasonably foreseeable.” The letter asserts that Reclamation is not properly modeling for the impact of a Compact Call in the EIS alternatives.

Time to Fix Glen Canyon Dam

The real bombshell in the letter is the argument that “Reclamation’s failure to consider an Alternative that addresses the Long-term Infrastructure Limitations from Glen Canyon Dam violates NEPA.” In essence, the Lower Basin States are claiming that by failing to address or model for engineering solutions to Glen Canyon Dam’s plumbing problem, Reclamation has nullified this entire EIS. “By not including an action alternative that resolves Glen Canyon infrastructure limitations,” the letter reads, “Reclamation impermissibly limits the range of reasonable alternatives.”

The letter references Reclamation’s secretive “value planning study” that is currently looking at modifications to the dam, including “overhauling or replacing the hollow-jet valves and other possible solutions (which may also include reengineering the dam or routing water through bypass tunnels).” The states take issue with the fact that this study is occurring outside the mechanism of the EIS despite such modifications being a “major federal action” clearly subject to the EIS process. They go on to argue that without including Glen Canyon Dam reengineering proposals into the Post-2026 EIS, the whole process is self-limiting, and in violation of NEPA. According to Reclamation, the value planning study will likely not be completed and released until 2026.

According to this letter, the Lower Basin States believe that  “Addressing the infrastructure limitations may be the one long-term measure that would best achieve operation and management improvements to the Glen Canyon Dam. Accordingly, Reclamation in this NEPA process must evaluate the impacts of infrastructure repairs, modifications and enhancements at Glen Canyon Dam.” This directly echoes what GCI and our partners have been saying for years.

What happens next?

After news of this letter broke through outlets like KUNC and the LA Times, there has been a lot of speculation about what this could mean for the Post-2026 EIS process and the future of Glen Canyon Dam. Will the administration step in to take drastic action? Wil Reclamation choose to overhaul the alternatives? Will “dam modifications” be included in this EIS? Will this become wrapped up in ongoing attempts to dismantle the bedrock environmental protections of NEPA?

It’s impossible to predict what the future holds. The states could come to an agreement on their own, the Interior Department could step in and take a more authoritative role, or it could end up being decided in the courts.

Most stakeholders in the Basin agree on one thing: they don’t want Colorado River policy to be decided by the courts. As a result, this EIS could play out similarly to the short-term Supplemental EIS completed in 2023—the states couldn’t come to a consensus until the Interior Department stepped in with its own vision which ultimately pushed the states back to the negotiating table to come to their own agreement. It stands to reason that the Post-2026 EIS would follow a similar track, with an expected Draft EIS to be released later this year.

As it currently stands, the Post-2026 EIS won’t address the looming problem of Glen Canyon Dam and its impacts to water supply and the environment. With less than a year to go, it’s logistically difficult to see how this EIS can or would include a proper analysis of dam modifications. This EIS will likely kick the can down the road long enough to slow the bleeding of water supply imbalance. But from a legal perspective, the legitimacy of the whole process is put into question by ignoring a major engineering problem at the center of Colorado River infrastructure and assuming water management alone will fulfill all future legal Compact requirements. 

The key takeaway is this: Glen Canyon Dam will be reengineered. It’s just a matter of time. Environmentalists have been saying this for years, and now some Basin states and agency officials agree. The big question is how it will be done, what problems will be solved, and to what degree the public and stakeholders will be involved. Reclamation is already assessing options to modify the dam with a focus on hydropower and water delivery, but apparently without any environmental considerations for Glen Canyon or Grand Canyon.

As the conversation around reengineering Glen Canyon Dam gravitates to the forefront of Colorado River management, it’s critical that every option be considered, including a full bypass of the dam to restore the river corridor to the greatest extent possible. Given the increasing likelihood of low water years, full bypass may prove to be the best option for both water delivery and the environment. We need to plan for a far drier hydrologic future in the Colorado River Basin and an ability to bypass water around the dam provides the most flexibility to all 40 million people who rely on it.

A 2023 paper by Schmidt et al. states that “Another option for reservoir management is to entirely abandon reservoir storage in Lake Powell by drilling river-level diversion tunnels around Glen Canyon Dam… Such an action would restore a natural streamflow and sediment regime to the Grand Canyon and might benefit some pre-dam elements of the Colorado River ecosystem, although there would likely be a multi-decadal period of ecosystem adjustment to the new flow and sediment conditions.” For 15 years, GCI has advocated for this option under our Fill Mead First proposal, but the time for decision makers to fully analyze this option is now.

When the dam is modified, it will take a lot of time and money, meaning we will probably only get one shot to do it right. We need to solve more problems than salvaging hydropower and water delivery. We need to think bigger about how to create system flexibility and reliability on the Colorado River of the 21st century. We need to acknowledge that our nation’s values have evolved since the 1950s and that ecosystems below and above Glen Canyon Dam are critically important. We need to let science drive the conversation, and foster transparency and open dialogue with Colorado River Basin residents. Right now, Glen Canyon Dam is the elephant in the room. Until it is addressed, we will never achieve sustainability on the Colorado River.