Are We Headed for the First Colorado River Compact Tripwire?

By Eric Kuhn and John Fleck

The Bureau of Reclamation’s January 2024 “Most Probable” 24-month study forecasts that annual releases from Glen Canyon Dam for both Water Years 2025 and 2026 will be 7.48 million acre-feet per year (maf). If this happens, the ten-year total flow at Lee Ferry for the 2017-2026 period will drop to about 83.0 maf, only about 500,000 acre-feet above 82.5 million acre-feet, the first 1922 Compact hydrology “tripwire.”

That line – 82.5 maf feet of Lee Ferry deliveries over a ten year period – has become a dividing line between two contending interpretations of the most important unresolved question in the century-old Colorado River Compact: How much water must the Upper Basin deliver to the Lower Basin? What happens if it doesn’t?

The consequences of triggering the tripwire, which might happen in 2027, are significant. In the worst case scenario, it could plunge the basin into Supreme Court litigation over the interpretation of the 1922 Compact, which could result in a forced curtailment of post-compact water uses in the Upper Basin. Or, alternately, if the Basin States are willing to settle their long-term disputed issues or implement basic changes to the Law of the River via the renegotiations of the post-2026 operating rules, it could be a “non-event.”  This is one of the fundamental issues facing the states as they meet to develop their basin-state alternative.

The 82.5 maf tripwire is based on the 1922 Compact’s two flow-related requirements at Lee Ferry; Article III(d) requires the four Upper Division States to not cause the progressive ten-year flow at Lee Ferry to be depleted below 75 maf. Additionally, Article III(c) provides that if there is not sufficient surplus water to meet the annual water delivery requirements of the 1944 Mexican Treaty, normally 1.5 maf, then each basin must provide half of the deficiency (the required annual delivery minus the available surplus). The Upper Division States must deliver their share of the deficiency at Lee Ferry in addition to their obligations under Article III(d).

The Upper Division and Lower Division States have never agreed on the meaning and interpretation of Article III(c). There have been numerous papers on the disputed issues by both compact scholars and practitioners and Article III(c) has never been interpreted by the U.S. Supreme Court. Suffice it to say that the Lower Division States believe that the Upper Division States must deliver at Lee Ferry a total of 82.5 maf every ten years (75 maf + 10 x 750,000), but the Upper Division States believe that they currently have no obligation to Mexico, so the number is at most 75 million. There are of course, nuances. The Lower Division States have suggested that the Upper Division States might also need to cover transit losses between Lee Ferry and Mexico and the Upper Division States have most recently suggested that if climate change, not Upper Basin depletions, is causing the ten-year flow to fall below 75 million, then their article III(d) non-depletion obligation must be appropriately adjusted. Further, if pursuant to either the extraordinary drought provision or a treaty minute, the required annual delivery to Mexico is less than 1.5 maf, then, even with no surplus, the Upper Division’s 50% share would be less than 750,000 acre-feet.

One should recognize that the annual releases from the Glen Canyon Dam and the annual flow at Lee Ferry (the compact point) are not the same.  Between the dam and Lee Ferry, the river gains flow from groundwater accretions (in part due to leakage around the dam) and from the Paria River. These gains can vary from about 30,000 acre-feet to over 300,000 acre-feet annually.  The ten-year Lee Ferry flow for 2014-2023 was approximately 86.1 maf.

That amount – 86.1 maf – might seem like a safe cushion. But because it is a ten-year moving total, we are about to drop out years with big releases (9 million acre feet) and replace them with years with just 7.48 maf. At the end of 2024, because both 2014 (the year that drops out) and 2024 (the year that is added in) are 7.48 maf years, the ten-year flow will stay about the same.  The way the ten-year flow calculation works is next year, 2015 will drop out and 2025 will be added in, and so on, but here is the problem; From 2015 through 2019, the 2007 Interim Guidelines dictated an annual release of 9 maf per year. With accretions, flows at Lee Ferry averaged about 9.18 maf per year (source: UCRC 74th Annual Report). Thus, if 2025 and 2026 are 7.48 maf years, the ten-year flow will lose about 1.5 maf/year making the total about 83 maf for the 2017-2026 period. Because the 2007 Interim Guidelines expire, we don’t know what the annual release will be in 2027, but if it’s less than about 8.5 maf, because 2017 was a 9 maf year, the ten-year Lee Ferry flow could drop below the tripwire – 82.5 maf (with two more 9 maf years, 2018 and 2019, in the pipeline).

We recognize that the 24-month studies don’t predict the future. They are a planning and management tool. It’s plausible that by 2027, a series of wet years could result in a ten-year flow that is much higher than 82.5 maf, something that is, in our view, unlikely. But as we sit here in January 2024, the 24-month study is the only planning tool we’ve got. It would behoove us to pay attention to what it is telling us.

If a future 24-month study projects that ten-year flows will fall below 82.5 maf, it will be a big deal for the basin. What provision of the Law of the River will control annual releases from Glen Canyon Dam – the post-2026 Operating Guidelines, the Lower Division’s interpretation of the 1922 Compact (82.5 maf), or the Upper Division’s interpretation of the 1922 Compact (75 maf or less)?  If the Lower Division States agree to a ten-year flow target of less than 82.5 maf, are they effectively surrendering to the Upper Division States? If the Upper Division States agree to a flow target of 82.5 maf, are they effectively surrendering to the Lower Division States? If the Upper Basin states agree to either 82.5 maf or some smaller compromise delivery target and the hydrology remains bad, how will Wyoming, Colorado, New Mexico, and Utah – our states – approach the required water use reductions? What if there is not enough water in storage in Lake Powell (and the other CRSP reservoirs) to release sufficient water to bring the ten-year flows to 82.5 maf? Will the Lower Division insist that that the UCRC implement a curtailment of post-compact uses in the Upper Basin. If the UCRC refuses to do so, will that plunge the Basin into litigation?

At the recent 2023 CRWUA meeting, representatives of the Lower Division States stepped up and made it clear they own the “structural deficit,” and the conference was buzzing with talk of the innovative system approach the Lower Division has put on the table. This is great news, but as Colorado’s Royce Tipton concluded sixty years ago, the “structural deficit” is not a single number. It’s a range that depends on the interpretation of the Lee Ferry obligations of the Upper Division States under the 1922 Compact. If the average annual flow requirement is 8.25 maf/year, (which Tipton referred to as “fictional”) he calculated the deficit to be about 1.2 maf/year. Today we believe it’s about 1.4 -1.5 maf/year (Tipton’s assumptions about system losses were probably too low and perhaps his Lee Ferry to Lake Mead inflow assumptions too high). If, however, the average annual flow requirement is 7.5 maf/year, he calculated the deficit to be about 2 maf/year, today maybe 2.2 maf/year. This difference is huge, especially for the Central Arizona Project, the junior user on the Lower basin mainstem.

In the past decades, water managers in the Colorado River Basin have made accomplishments that even two decades ago were considered out of reach: The 2019 Drought Contingency Plans, the shortage sharing agreements with Mexico, the increased recognition of the rights of the Basin’s Native American communities are just a few. The Lower Division’s recent pronouncement that they own the structural deficit is another major step forward, but it has a fundamental flaw. Representatives of all seven Basin states continue to stubbornly insist that the Law of the River, and specifically, the 1922 Colorado River Compact, will serve as the “foundation” of the post-2026 operating guidelines. The flaw is that is that we don’t know if this foundation is based on a ten-year Lee Ferry flow of 82.5 maf, or 75 maf, or something different.

Put simply, the states agree that the Law of the River has to be the basis of what we do, but don’t agree on what the Law of the River actually says. Without an agreement on this fundamental issue, calling the 1922 Compact a foundation is nothing more than self-delusional wishful thinking. Now that the Lower Division States have agreed to own the structural deficit, is the next step for all seven states and the federal government to openly acknowledge that given the impacts of climate change on the river, the 1922 Compact’s overallocation of water and its disputed Lee Ferry flow provisions are core problems for the basin, not the foundation? Finding a sustainable future, without litigation, will require accepting and acknowledging the basic problems we face, not avoiding them.



  1. Follow the Laws. The Law of the River, and Sr. Water Rights. If the Lower Basin has to have water cuts, the Upper Basin must have water cuts as well. Everyone equal

  2. Appears to me that the basic problem to be faced is the “Law of the River.” It is a figment of hydrologic, legal and political illusion that can rarely be met in todays climate environment. A system based on mandated annual basin wide shortage sharing, while difficult and anathema to the CAP and Salt River Project attorneys, is technically attainable and could avoid these crisis events.

  3. John and Eric, A few finer points worth exploring:
    1. Article IIIc says nothing about a 10-year average, so any Mexico deficiency would seem to require delivery within the year of the shortfall. This is obviously a difficult proposition given that….
    2. The compact allots an additional 1 Maf of consumptive use to the lower basin, an amount which doesn’t come close to covering the consumptive use of Gila River water by Arizona. That consumption in excess of 1 Maf is part of the “surplus” mentioned in IIIc, and is a credit to the US, not just the lower basin states. After that surplus is delivered to Mexico, the two divisions would need to make up the deficit.
    3. If I were Arizona, I’d be very afraid of any proceedings that take a deep dive into this question, as it puts yet another large target on their back.

  4. John C. From a modern-day Upper Basin perspective, I agree – but, unfortunately, the Upper Basin’s history suggests some potential hiccups with your points 1 & 2.
    Point 1 Pre- Lake Powell, most Upper Basin officials took the position that the last sentence of Article III(c) means that the Upper Division’s obligation was based on the long-term average or possibly a 10-year rolling average and was not determined annually. Stone, Tipton, Breitenstein, and others argued that the 1922 Compact negotiators defined “surplus” as the average annual natural flow of the Colorado River at the border minus 16 million acre-feet. In Compact reports and testimony, both Carpenter and Hoover both referred the surplus (from which Mexico would get its water) was an average annual figure. They took this position for self-interest reasons. During the 40s when the 1944 Treaty and the 1948 were negotiated and ratified, the consensus was that the average natural flow below Yuma (including the Gila) was about 18 maf/year (17.8 maf/yr). Look at the math – 5 years of 20 maf/year plus 5 years of 15 maf/year equals an average of 17.5 maf/year – thus the surplus is (17.5-16) or 1.5 maf/year, so no deficiency. If the UD’s obligation is calculated on an annual basis, in the five 15 maf years, there would be deficiency and the UD States would owe additional water at Lee Ferry. As late as 1975, in Congressional testimony, Colorado’s Sparks and NM’s Reynolds took the position that the UD’s obligation to Mexico is based on average natural flows not calculated annually. Of course, those were the days of “stationarity.” (I won’t go into their math in this blog.)
    Further, there is the question of – if there is a “surplus” – where in the system is it located. Stone and Tipton conceded that the UD States had an obligation to deliver to Mexico the share of the surplus that was located above Lee Ferry. Suffice it to say these issues aren’t settled.
    As to your point 2 – it all depends on how compact apportionments are measured- again the UD’s history is not good. In the 40s Colorado and Arizona were aligned on the position that water made available by “salvage by use” did not count against either Basin’s compact apportionment – check out how depletions are measured under Article VI of the 48 Compact. UB official testified in Congress (and their lawyers wrote briefs) stating that the Lower Basin’s 8.5 maf compact apportionment is measured as the impacts of man-made depletions to the natural flow of the Colorado River at the border. Under this definition, because the Gila system naturally loses one maf + from Phoenix to Yuma, that extra one maf of III(b) water might go a long ways. Again – nothing is settled -so lets hope the basin states can reach a compromise settlement.

  5. The last paragraph sums it up. It has also been true since it became apparent that the CR flow was much less and getting worse. I’ve said here before that the first step is to agree to a flow quantity and to reset the allocations accordingly. I was hoping the Feds would get that done sooner than later. Alas, it is an election year.

  6. “Again – nothing is settled -so let’s hope the basin states can reach a compromise settlement.”

    Compromise on what? Unreality? Patrick, above, proposes a start, but it doesn’t go far enough. The Compact, originally based on inadequate data then modified by ignorant court interpretations, political agreements, and stitch-in-time minutes, is today an unworkable mess loved only by attorneys, politicians, some “activists”, and perhaps(?) accountants. Without a major rework of the Compact, it will never be able to avoid these recurring crises that occur when nature doesn’t provide the water everyone would like to have. Reality isn’t so kind. Shortages are the reality and absent a basin wide agreement on how inevitable shortages are shared the Compact is not adequate and we are left with inter basin squabbles and court cases. And how has that worked out? Crafting flexible, workable shortage sharing provisions is not difficult. Implementing and accepting them is, primarily because it’s difficult to sell the concept that no one can promise any certain amount of usable water. But that is reality.

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