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Unpacking the Colorado River Compact

            Studying and writing about the Colorado River Compact could easily be a full-time job for many people. I get it. It’s fascinating, and I’ve certainly spent time down its rabbit hole, where the river, history, politics, law, development, hydrology, and people are all in the mix.

One take on the compact is that it is simply a negotiated “carve out” of the prior appropriation system, agreed to in 1922 by representatives of the seven states under intense pressure to divvy up the water before a booming California used it all. A hundred years later, it can be argued the Compact has held up well, but it always seems to always be lurking in the corner of the room at water meetings in Colorado, in the form of a potential compact call coming up the river, made more likely by ongoing aridification.   

The Compact continues to shape water policy in the state, and the region, in a myriad of significant ways, to say nothing of how it shapes opinions among Coloradoans about the good people of California, Arizona, and Nevada, or how many water lawyers throughout the river basin relish pondering its implications. Before I delve into some of the Compact’s more nuanced aspects, let me first share some of my key takeaways about it.

·      Four Upper Basin states—Utah, Wyoming, New Mexico and Colorado—are obligated to deliver enough water to Lake Powell so that the Lower Basin states of California, Arizona and Nevada receive 7.5 million acre-feet each year, and Mexico another 750,000 acre-feet, 8.25 million acre-feet in all. Colorado is responsible for delivering most of that water.

·      To meet these obligations, the Upper Basin states must effectively deliver 82.5 million acre-feet into Lake Powell every ten years plus additional water to cover evaporation losses. Because this obligation extends ten years into the future, Upper Basin states cannot know today how much water will be available to them for further development.

·      From 1999 through 2009, the Upper Basin delivered 81 million acre-feet into Lake Powell, nearly 1.5 million short of its requirement. From 2011 through 2021, it again missed the required deliveries, as only 79 million acre feet was delivered to Lake Powell. Additional transmountain diversions to the Front Range, if approved, will reduce deliveries into Lake Powell and increase the likelihood of a Compact Call.

·      In September 2022 Lake Powell was 24 percent full and Lake Mead was 28 percent full. Reservoir levels have recovered since then, but not by much, and in September 2024 the combined reservoirs were still only 26% full.

·      If there is a Compact call, Colorado alone has to meet it, at least initially, since the state has been over-using its share of the river. Based on 2011-2020 records, Colorado must deliver the first 1,470,000 acre-feet of a call before the other Upper Basin states must pony up their share of a deficit.

·      If states refuse to honor the Colorado River Compact, the U.S. Supreme Court will likely decide the outcome. That leaves states at the mercy of the Supreme Court, whose previous water decisions have been based on diverging theories of law. We cannot predict what the court will decide.

And before proceeding any further down the Compact rabbit hole, let me recommend four good books that deal with different aspects of Compact: Silver Fox of the Rockies, Delphus E. Carpenter and Western Water Compacts, by Daniel Tyler; Dividing the Waters: Century of Controversy Between the United States and Mexico, by Norris Hundley, Jr.;  the previously mentioned Science Be Dammed, How Ignoring Inconvenient Science Drained the Colorado River, by Eric Kuhn and John Fleck; and of course, Cadillac Desert, the American West and Its Disappearing Water, by Marc Reisner.

I also suggest you read the Compact for yourself. It’s short, direct, and easy to find online. The transcriptions of the meeting of the Compact Commission themselves are also illuminating, as one can hear the representatives of the seven states working through potential solutions to the challenge in front of them. Someday the meeting transcripts will find their way to a skilled scriptwriter, who will fashion a compelling movie about the meetings, and the horse-trading that went on, especially among Arizona and the Upper Basin representatives.

“The simpler the plan the more perfectly it will work, and if we know the principle in simple terms, the details will work out automatically,” Delph Carpenter, the water attorney representing Colorado in the Compact negotiations, told Arizona’s representative, W.S. Norviel, during a lively meeting, the 17th, which was held in Santa Fe on November 15th, 1922, six weeks before the end-of-year deadline. “There is no need of injecting cumbersome machinery. In the final analysis, when time has passed, the river will automatically take care of itself, in the matter of supply and demand. There is no desire to see how much we may reduce you. The spirit of the whole meeting has been to provide a compact which we can fulfill.”

To which Norviel, who would get the most screen time in a Compact movie, responded, “I presume, inasmuch as I am older in years, I would suggest, our needs, in the upper and lower divisions, are practically the same.”

Trust me, that’s gripping stuff for full-on Compact nerds.

 In any event, with the above recommended sources, you’ll be in good hands as it relates to the Compact, and thus I feel better about elaborating below on what I think is most relevant about it to Colorado.

Three politically charged issues seemed ever-present behind Colorado’s 2015 and 2023 state water plans: preserving agriculture; sending more water through transmountain diversions to the Front Range; and dealing with the Compact. Farm irrigation rights are so politically charged, the 2015 and 2023 Colorado Water Plans mainly say they must be protected, taking the path of least resistance. And both versions tiptoe around the prospect of future transmountain diversions, other than adding the Conceptual Framework in the mix, the six-point plan to protect the Western Slope before another diversion to the Front Range takes place. And then there is the Compact, the big unknown, which was dealt with in both water plans in relatively light fashion, given the weight it carries in Colorado water policy.

One predictable thing, though, is this: any new transmountain diversions to the Front Range will increase the risk that California, Arizona, and Nevada will not get the water allocated to them in the Compact, and so they will call out post-1922 water rights holders in Colorado, Wyoming, Utah, and New Mexico. And this demand for water under the Compact will ripple through the priority system, even likely affecting senior pre-Compact water rights.

Whether Colorado can continue to meet its water delivery obligation, or intent, under the Compact is a guessing game because it is based on the next ten years’ precipitation, which may fluctuate even more wildly going forward with climate change. On the other hand, one has to concede, so far, so good with the Compact, as the Upper Basin has yet to fail to meet its Compact obligations since it was adopted in 1922. And the Lower Basin has not made a call.

But if water users in Colorado move more water from the Colorado River through new appropriations and transmountain diversions, and the ensuing ten years continue in drought, the Lower Basin states may then be in a position, however reluctant they might be, to make a call and try to force more water flow to down the Colorado River system to Lake Powell and Lake Mead.

The Compact says diversions in both the upper and lower basin that were in place prior to 1922 “are unimpaired by this compact,” which that means post-1922 water rights in the Upper Basin and Colorado would be called out before the pre-Compact rights in the Upper Basin.

 With that in mind, consider the priority dates of the major transmountain diversion projects in Colorado.

The Fryingpan-Arkansas Project, managed by the Southeastern Colorado Water Conservancy District, has a 1956 right to divert about 50,000 acre-feet from the Roaring Fork and Fryingpan rivers to Pueblo and beyond.

Aurora and Colorado Springs have a 1952 right to divert about 25,000 acre-feet from the Eagle River basin via the Homestake project.

Denver Water has a 1946 priority date to divert about 60,000 acre-feet of water from the headwaters of the Colorado River through the Roberts Tunnel from Dillon Reservoir.

And the Northern Colorado Water Conservancy District has a 1935 right to divert about 225,000 acre-feet from the Colorado headwaters to the South Platte River basin via the Colorado-Big Thompson Project. (The acre-feet quoted are typical annual diversions, not absolute diversion rights).

There is little risk these esteemed water providers will just have their water cut off, as water providers are just too powerful, and popular. And that’s why the Western Slope is concerned it will somehow bear the brunt of a Compact call. Even though nearly all significant Western Slope agricultural water rights were established long before 1922, many expect those rights, mainly used to grow hay, will be curtailed before the state curtails transbasin diversions to the Front Range that hundreds of thousands of citizens rely upon.

Figure 17.1 Front Range diversions and a compact call

This forward-looking graph is my best attempt to illustrate how a call would work. The 4 transbasin diversion rights are on the left, put in inverse date order since the youngest rights, the lower blue rows, will get called out first. Suppose the Lower Basin States make a call for 450,000 acre feet in 2030. This would call out, in order, Fry-Ark’s 1956 right for 50,000 acre feet, then Aurora-Colorado Springs’ 1952 Homestake right for 25,000 acre feet, then Denver’s 1946 Dillon Reservoir right for 60,000 acre feet, and then 165,000 acre feet of Northern Water’s 1937 right for 225,000 acre feet in the Colorado Big Thompson project. The same thing would happen in 2031 if the call continued, this time for 400,000 acre feet, except that Northern Water’s right would only be curtailed 115,000 acre feet since the call was for 50,000 less acre feet.

Before we blow right past it, Aaron Million proposed a new pipeline in 2007 from Flaming Gorge Reservoir on the Utah-Wyoming border to the Front Range, the pink row at the bottom of the table. Practically no one in Utah, Wyoming, or in Colorado’s west slope likes it, and the CWCB turned down Million’s $330,000 grant request to study it in 2019. But if it were built, the table above illustrates the first point in the Conceptual Framework, that “Eastern slope water providers are not looking for firm yield from a new TMD and the project proponent would accept hydrological risk for that project.”[1]

The project is not dead, as Million brought in a Florida development company with $8 billion in annual revenues as a partner in 2022.[2] Suppose the Flaming Gorge pipeline had come online in 2015. It would have been entirely called out in both 2030 and 2031, meaning the Front Range cities that relied on it would have to scramble for other water supplies (that’s what is meant by “hydrological risk”). But, it would not cover the other water rights in blue being called out because the Flaming Gorge pipeline is a new diversion that is added on top of the other post-1922 diversions in the table above. So, the Flaming Gorge pipeline does not decrease the risk that the older water rights will be called out, it increases the risk because the 750,000 acre feet theoretically diverted into the Flaming Gorge Pipeline from 2025-2029 actually decreased water in Lake Powell, and that likely caused the 2030 and 2031 calls in the first place.

It’s not clear exactly how Colorado will meet a Compact call, mind you. The state does not have a public plan, outside of prior appropriation, to deal with a call. And while some say there is indeed a state plan, good luck getting a straight answer about it. The transmountain diverters have not broadcast their intentions, either, other than always promoting or building, new or expanded dams.

After over 100 years with the Compact in place, it’s fascinating to me that growth in Colorado is causing the agreement to be so obsessed over, as it was growth in California 100 years ago that compelled the Compact to be agreed upon in the first place. You see, California was growing so fast in the early 1900s that it could appropriate all remaining water in the Colorado River to the disadvantage of every other state in the Colorado River Basin, including Colorado. As Reisner put it in Cadillac Desert, “Los Angeles, growing like a gourd in the night, would soon overrun its Owens Valley supply; the next logical source of water – the only logical source – was the Colorado River. Under simple appropriative-rights doctrine, the water would belong to California as soon as it began its use.”

Figure 17.2 Growth in Colorado River Basin states 1900 to 1950

The reality of the prior appropriation system motivated the Upper Basin states to divvy up the Colorado River by compact, which is simply a form of a binding agreement or contract. The legal significance of a water compact is that it trumps state prior appropriation regimes. It is essentially a giant exception to the prior appropriation system, where a senior water right holder makes concessions for the sake of “comity” on a river and a certain level of security. The Colorado River Compact’s opening sentence says “The major purposes of this compact are to provide for the equitable division and apportionment of the use of the waters of the Colorado River System . . .”  And when the Lower Basin states signed the Compact, they ensured they would receive 8.5 million acre-feet a year—7.5 million acre feet in Article III(a) and another 1 million acre feet in Article III(b) from the Gila River, although the Gila remains unnamed in the document itself. And the Upper Basin would be secure in its ability to use up to 7.5 million acre feet per year, from which it was also expected to cover 50 percent of Mexico’s share if a treaty with Mexico was ever established.

During the time that representatives of the seven basin states were negotiating the Compact, the Supreme Court issued a ruling in Wyoming v. Colorado, which caused the Upper Basin states much hand wringing. In that case, Colorado wanted to divert 100,000 acre-feet a year from the Laramie River and move it through a tunnel beneath the Never Summer Range to the Poudre River to irrigate farms in Greeley. (The Laramie River flows north out of Colorado into Wyoming, and its headwaters at Cameron Pass are close to the headwaters of the Poudre River). Wyoming objected to Colorado’s diversion plan, arguing its farmers needed the water to irrigate 325,000 acres in Wheatland, about 70 miles north of Cheyenne. Wyoming claimed that it had a superior right under prior appropriation, and that Colorado’s right to divert the Laramie River should only date to 1909, when excavation on the Laramie-Poudre tunnel began. Justice Willis Devanter, the only Wyoming justice ever appointed to the U.S. Supreme Court, wrote the Wyoming v. Colorado decision in 1922. Justice Devanter’s brother-in-law was Wyoming’s lead attorney in the case. Not surprisingly, Devanter ruled in favor of Wyoming, holding that Colorado was entitled to only 37,750 acre-feet and Wyoming to 272,500 acre-feet of the Laramie River. Crucially, Justice Devanter held that the Laramie-Poudre tunnel irrigation right had a priority date of 1909, junior to the Wheatland irrigation district in Wyoming.

Wyoming v. Colorado affirmed the prior appropriation system, holding that it applies across state lines as Wyoming argued, which meant California had a solid claim to the water it would put to use before the Upper Basin states could.

Delph Carpenter, the attorney who represented the Greeley-Poudre Irrigation District and Colorado in Wyoming v. Colorado, suddenly had a lot to think about. “Colorado lost the priority battle, but Carpenter learned certain lessons from his work on the Laramie and Republican rivers,” Daniel Tyler writes in Silver Fox of the Rockies. “Headwater states, such as Colorado, would not fare well in interstate stream conflicts if the Supreme Court decided the outcome. If he could affect the apportionment of water among states through negotiations leading to compact agreements prior to a trial, the impact of a Supreme Court decree could be minimized or altogether avoided.” Before arriving at Bishops Lodge, Carpenter proposed quietly to R.E. Caldwell, the Utah representative to the Compact Commission, that the Upper Basin states should be able to divert half the river flow, with the other half available to the Lower Basin states. The idea of a 50/50 split of the flows in the Colorado River proved tenable. The commission members also agreed to give Arizona something of a 1 million acre-foot bonus by conceding the flow of the Gila River in the lower basin to Arizona.

The Gila River has its headwaters in New Mexico. It joins the Colorado River at Yuma in the southwestern corner of Arizona, barely fifty miles above the Gulf of California, essentially capturing every major river in Arizona including the Salt and Verde rivers flowing into Phoenix. Norviel was such a tenacious negotiator for Arizona, and so insistent about the Gila, that Herbert Hoover, then U.S. Commerce Secretary and chair of the Compact Commission, described him as "the best fighter on the Commission." Hoover told him, "Arizona should erect a monument to you and entitle it 'One million acre-feet.' " Arizona fared well in the Compact, even though it proved contentious throughout the long approval process.

Mexico fared less well in the Compact, and the clause related to their share of the river continues to shape water deliveries from the Upper Basin today. Article III(c) makes the only reference to Mexico in the Compact. It says, “if, as a matter of international comity, the United States of America shall hereafter recognize in the United States of Mexico any right to the use of any waters of the Colorado River System …” then Mexico’s share shall be from surplus waters that exceed the 15 million acre-feet already allocated to the Upper Basin and Lower Basin. If Mexico fails to receive its share, “… the burden of such deficiency shall be equally borne by the Upper Basin and the Lower Basin, and whenever necessary the States of the Upper Division shall deliver at Lee Ferry water to supply one-half of the deficiency.” Twenty-two years after signing the Compact, the United States finally signed a treaty with Mexico in 1944, giving Mexico 1.5 million acre-feet, plus 200,000 acre-feet in high flow years when surplus flows were available.

As is so often true of legal documents (and what makes them so hard to review), what is not said is often more significant than what’s been written. The Compact says the Upper Basin states are allotted 7.5 million acre-feet each year. But since the Upper Basin states must deliver at least 75 million acre-feet every 10 years, that means the Lower Basin states have priority—the Upper Basin states are relegated to using what’s left. But the Compact does not come out and say the Lower Basin has priority. As pressure has mounted on the Compact since 2000, given the severe drought, it’s come to light that the formula of splitting the river based on certain assumptions about the amount of water flowing downstream may have been skewed. Put another way, if you’re having trouble splitting a theoretical pie, maybe it is easier if the pie just gets bigger.

In the seventeen years before the 1922 Compact, the average runoff on the Colorado River was 18 million acre-feet, the highest sustained flows over the past 1,250 years, and 22 percent higher than the 1906-2020 average.[3] And so the pie looked pretty big. But E.C. LaRue, a hydraulic engineer with the U.S. Geological Survey, had studied flows in the river and he had doubts by 1920 about the river’s capacity to meet the visions of the seven states in the basin. “Based on his understanding of the relatively few available gauge measurements, the limited period of record, and his concern with the uncertainties concerning past droughts, he [LaRue] concluded that, without a basin-wide plan, there would not be enough water to the meet the aspirations of the seven states,” write Kuhn and Fleck in Science Be Dammed. The authors are critical of the members of the Compact Commission for not listening harder to LaRue and embracing larger estimates of water. By avoiding LaRue’s concerns about the sufficiency of the water supply – ignoring reservoir evaporation, failing to correct their flow data for development that had already happened on the river, and other sins – they had conjured up a larger Colorado River than nature could actually provide,” Kuhn and Fleck write. (Need page cites to Kuhn/Fleck[BG1] .)

Today, it’s possible to lose several days, or weeks, trying to figure out who knew what when about water in the Colorado, but in the end the Colorado River Compact of 1922 is a negotiated agreement between parties, and the pie was split as it was split. Except, of course, that the 7.5 MAF a year that the Upper Basin owes the Lower Basin has been increased by 750,000 AF to 8.23 MAF a year to meet the 1948 Mexican Treaty obligation, minus the 20,000 acre-feet of average inflow from the Paria River, which comes in just below Lake Powell. This explains why the Lower Basin states see the total delivery obligation from the Upper Basin as being 82.3 MAF on a ten-year basis.

“The Lower Basin states, especially California, however, continue to contend that the Upper Basin’s non-depletion obligation kicks in at 82.5 MAF,” Andy Mueller, the general manager of the Colorado River District, wrote in a report to the district’s board on July 2, 2024. “The anticipated continued dry hydrology in the Basin seems to indicate that unless this issue is addressed through a cooperative set of operating guidelines, it is likely that that there is a major flash point for dispute and even Supreme Court litigation over this issue as soon as 2026. It is important for this board and our water users to understand the economic, social, political and hydrologic implications of such a dispute.”  (Need to cite Mueller’s quote)[BG2]  Reclamation reconstructs flows past Lee’s Ferry from 1906 to 2020 as if the river was free-flowing and no water had been held back by any dams or diversions (also described as the “unregulated inflow”). The average reconstructed flow past Lee Ferry in 2000-2020 was just over 12.66 MAF, only two-thirds of the average 19 MAF annual flow past Lee Ferry from 1914-1923 when the Compact was negotiated.[4] Colorado River runoff has likely changed since 1922 but the terms of the 1922 Compact agreement have not.

One way to reform a contract is to claim it was based on mistake of fact—if the contract signers believed X million acre feet flowed down the river, but only Y million acre feet actually does under a hotter earth, the contract can be reformed to reflect actual conditions because the states were mistaken as to the amount of water the river typically had. But the Lower Basin states can claim there was no mistake—the Upper Basin states are required to deliver 7.5 MAF a year, based on a ten-year rolling average, and the Upper Basin must simply suffer the consequences of a lower river with less water. The doctrine of mistake is problematic, especially with a Supreme Court that places so much importance on history and what the drafters believed at the time they wrote the document.

There is also a later Compact, between the Upper Basin states, that shapes how Colorado will fare under a Compact Call.  Recognizing the vagaries of climate and weather, the 1948 Upper Colorado River Basin Compact did not guarantee a firm-yield to any Upper Basin state. Instead, each state receives a percentage of the available flow. The percentage allocations recognize that the Upper Basin states had to adapt their beneficial use to the hydrological cycle, and not the other way around. It tacitly affirms that no state had the upper hand in the negotiations, in contrast to the power California wielded in the 1922 Compact and later Colorado River negotiations. Colorado is allocated the lion’s share in this program, at 51.75 percent, although its snowpack likely contributes 70 percent or more to Lake Powell’s inflow each year. Notably, the 1948 Upper Colorado River Basin Compact starts with the same language as the 1922 Colorado River Compact: “The major purposes of this Compact are to provide for the equitable division and apportionment of the use of the water of the Colorado River System.”

But it’s important to note that two different legal doctrines govern the two river compacts that divvy up the Colorado River—prior appropriation law underpins the 1922 Compact since the Lower Basin receives its share first, while equitable apportionment law guides the 1948 Upper Colorado River Basin Compact. Under equitable apportionment (also known as sharing), all four Upper Basin states know the pleasure of high-water years and the pain of drought-reduced flows.

In the 1922 Compact negotiations, the Upper Basin states took what they could get. They had little choice in light of Wyoming v. Colorado. This serves as a parable for how Colorado divides up water for its future growth. The Front Range has eighty percent of the population, wealth, and legislative clout. The Western Slope will have to take whatever the Front Range offers, unless voters across the state decide otherwise. No compact or agreement within Colorado guarantees water to the Western Slope, outside of the prior appropriation system, which, as the Compact itself illustrates, can be worked around.

The contrast in the approaches between the 1922 Colorado Compact and the 1948 Upper Basin Compact is illustrated in the table below.

Table 17.1 Consumption in the upper and lower Colorado River basins

The above table also helps illustrate the concept in the Upper Basin Compact that if any Upper Basin state uses more than its share over a ten-year period, it lands in a “ten-year penalty box,” meaning that it alone must meet a Compact call until its use is brought back into balance.[5] While Colorado is entitled to 51.75 percent of the Upper Basin states’ total share, Colorado consumed 55.47 percent from 2011 through 2020 (highlighted in yellow in the table above.[6] Reclamation records indicate that Colorado consumed 1,470,000 more acre-feet than its 51.75 percent Upper Basin share. If a Compact call is made, Colorado alone must alone reduce its Colorado River consumption by 1,470,000 acre-feet or until the call is met, whichever occurs first.                                     

Figure 17.3 The state of Colorado’s “penalty box” in the Compact

In the chart above, the blue bars represent each Upper Basin state’s average yearly consumption of Colorado River water from 2011-2020. The red bar shows Colorado’s cumulative overuse during the decade—it amounts to nearly a full year’s consumption. Only Colorado is currently in the ten-year penalty box.[7] When I think about this, this has, at least, the following implications … one, the other Upper Basin states may want Colorado to stay in the ten-year penalty box so that Colorado alone must initially meet a Compact call. And two, if Colorado consumes more of the Colorado River, the other Upper Basin states will probably increase their consumption in lockstep, knowing they may have Colorado’s use as a buffer before they have to cut back. Colorado can get out of the penalty box either by decreasing our use, or if the other Upper Basin states increase their use, so our share drops back down to 51.75 percent.

True to form, neither the 2015 nor the 2023 Colorado Water Plans discuss the ten-year penalty box. The closest the 2015 Plan comes, buried 352 pages into the document, is when it says, “new development planning should be focused on avoiding . . . development in excess of Colorado’s allocation under the Upper Colorado River Basin Compact.” That just doesn’t carry the same punch as saying, “If there’s a Compact call, Colorado must first reduce consumption by 1.5 million acre-feet before any other Upper Basin states need to reduce their use.”[8]

 All this leads us to a constantly nagging question in Colorado: Is there more water in the state to develop without triggering a Compact call from the Lower Basin? In 2016 John Carron, a hydrologist with a PhD, was retained by the Colorado River District to prepare a model indicating the risk of a Compact call under different water-development scenarios. Dubbed the Western Slope Water Risk Study, it immediately raised eyebrows on the Front Range. Carron determined that if the Upper Basin states increase consumption by 400,000 acre-feet over current use, there was a 50 percent risk of a Compact call by 2036 based on 1988-2012 precipitation records! If the states instead adopt a slow-growth strategy, the risk drops to about 20 percent, still unacceptably high. Carron’s conclusions did not sit well with the Front Range Water Council, the informal but powerful confederation of big Front Range water providers that favor more dams. In Carron’s model, Lake Powell never drops below an elevation of 3,525 feet, a level that is 35 feet and 2 million acre-feet above the dead pool level of elevation 3,490 feet, where no power will be generated because the water is below the level of the penstocks. It’s the difference between Lake Powell being 24 percent full and 16 percent full. The Front Range Water Council believes that selecting this elevation was arbitrary, but 3,490 feet is a level that Reclamation very much wants to avoid.

On March 17, 2022, Lake Powell dropped below 3,525’ for the first time since it began filling in 1963.[9] Once Lake Powell drops below 3,525 feet, Reclamation must release more water from the smaller reservoirs including Flaming Gorge, Blue Mesa, and others, once the spring snow melt dwindles toward the end of the summer, as part of the 2019 Colorado River Drought-Contingency Plan, to keep it afloat.[10]

Kuhn has talked about “risk” since at least 2005 when the roundtables started. Risk is the concern that if someone builds a reservoir and water users come to rely on it, they are at risk if the reservoir doesn’t fill. It’s a classic situation where “might makes right,” as powerful players could convince the legislature that it is pure conjecture the reservoir won’t fill in the future. Kuhn’s constant refrain is that we must develop supply based on the worst-case scenario—water users need to know there will be water in the lowest water years, not during the average or high years. The Front Range’s real objection to the Western Slope Water Risk Study seemed to be that it was a water supply study in disguise. In a letter dated November 9, 2016, to Front Range Water Council members, then Denver Water CEO Jim Lochhead said, “We are also concerned that the assumptions used in the Phase I modeling study may be creating biased impressions regarding the amount of the remaining developable water under the compacts.” If you can only base water projects on dependable supplies, which no water manager can dispute, the only way to justify additional water projects is to feign ignorance, to not know the supply (or to over-estimate the supply, which is what Reclamation and the seven Basin states did when they crafted the Colorado River Compact in 1922, a fiction they failed to acknowledge for the next 90 years).[11]

Early in the roundtable process, the state legislature awarded $500,000 to the CWCB in 2007 to determine how much water was available in the Colorado River for further development.[12] The engineers hired by the CWCB concluded that 0 to 800,000 acre-feet was available, a range so large that it was initially discounted as meaningless. Kuhn thinks the range was actually reasonable, since it reflected the wide variation in annual precipitation. It was billed as Phase 1 of the Colorado River Water Availability Study, and its conclusions were dire—while crop irrigation requirements were projected to increase 8 to 45 percent, more than 80 percent of the rivers they studied were expected to have lower flows by 2070.[13] Phase 2, designed to determine where the new water for “new supply” projects would come from, was never funded or completed. That means the state has no idea how much more water is available to develop without precipitating a Compact call.

Colorado water managers have about 200,000 acre-feet of additional Colorado River basin diversions in various stages of planning or development: 18,000 acre-feet Moffat Tunnel expansion, 30,000 acre-feet Windy Gap expansion, 20,000 acre-feet Homestake II reservoir, 60,000 acre-feet in the Blue River Decree, and 70,000 acre-feet for the Pueblo and Turquoise reservoir expansions.[14] So, if the risk of a Compact call is rising, what will happen if one actually comes? That remains a big unknown in Colorado River planning today. In 2015, Kuhn felt that the likelihood of a Compact call was remote. By tweaking how we release water from other reservoirs in the Colorado River Storage Project such as Flaming Gorge and Blue Mesa reservoirs, Kuhn said we could reduce the risk of a Compact call to almost zero.[15] But by 2016 as the drought that began in 2000 dragged on, which Kuhn now calls the “new normal,” he believed the risk of a Compact call was significantly greater, perhaps as high as 20 percent to 40 percent. In the 2016 River District annual report, Kuhn wrote, “If we look at inflows to Lake Powell over the last sixteen years, they’ve been below the long-term average. However, if we look to our local conditions in Colorado, we are certainly not in a drought. In fact, since the flooding rains in the fall of 2013, I believe we’ve been in a time of relative plenty or “pluvial” (the opposite of drought). If Colorado has not been in a drought, and Colorado’s mountains produce about two-thirds of the total runoff of the Colorado River system, then why is total storage in Lake Powell and Lake Mead continuing to decline?”

Kuhn continues, “it’s looking more and more likely that warming regional temperatures have turned above-average or abundant precipitation into just average runoff. Recently published scientific papers have zeroed in on this problem, and the consequences of warming on the Colorado River basin are very serious. Warming is reducing runoff.”[16] Kuhn’s consistent message was that the future is uncertain. The Upper Basin states plan to increase their consumption by 10 percent on average, an increase of about 300,000 acre-feet.[17] This will increase the risk of a Compact call. If Upper Basin consumption had been 300,000 acre-feet greater from 2001 to 2010, deliveries into Lake Powell would have been under 80 million acre-feet and the Lower Basin would have been that much closer to making a call.

All lawyers caution against underestimating the risks of litigation. The Supreme Court will likely require the Upper Basin states to meet a Compact call since the Compact is a contract that was freely negotiated. Taking more water out of the river and increasing water consumption increases risk. Unless an alternate agreement is reached, Colorado may be forced to initially meet a call since it alone sits in the 10-year penalty box. If precipitation decreases, as most climate projections suggest, we are closing in on a call. The blue bars in the graph below represent cumulative deliveries into Lake Powell by the Upper Basin states over 10 years, and the red bars represent total deliveries to the Lower Basin states over rolling 10-year periods.

Figure 17.4 Water input and output at Lake Powell 1999 to 2024

Some water providers point to the extra water being deposited into Lake Powell in the peak 10-year periods ending in 2000 and 2017 as evidence that Colorado can use more of the Colorado River. Others look at the bottoms in 2009 and 2021-2022 as evidence that the Upper Basin can claim no more water, reasoning that you plan for the lowest water years, not the highest.

The IBCC, the uber-roundtable managed by the CWCB, claims it reached a “breakthrough” in 2014 in the Conceptual Framework that would allow the Front Range to take more water from the Western Slope in high water years. But is there really more Colorado River water available as Front Range water providers believe?

Below is a depiction of what storage levels would look like if Mead and Powell reservoirs had operated the past 1,250 years.

David Meko and other scientists reconstructed flows at Lee Ferry between the years 762 and 1904 based on tree-ring studies, and Reclamation has maintained actual gage records since 1905.[18] They calculate the average yearly runoff was 14.6 million acre-feet past Lee Ferry between 762 and 1904. It was 14.8 million acre-feet between 1905 and 2014, 200,000 acre-feet more per year. The last 110 years were indeed wetter than average.

Figure 17.5 Projected levels in Lake Powell back to the year 762

This graph shows that if Powell and Mead reservoirs had been operating since the year 762, there would have been enough Colorado River water to support existing uses and for New Mexico, Utah, and Wyoming to increase their consumption by 297,000 acre-feet.[19] But like the mutual fund disclaimer, the past may not be a good predictor of future flows. Reclamation came up with its own estimate of future Colorado River flows in 2012, a study it has not yet updated. It concluded the Colorado River basin is likely to get hotter and that Colorado River flows could decline 7.5 percent by 2025, and 12.4 percent by 2080.[20]

Table 17.2 Temperature increase and runoff decrease

Midpoint of projected future period

2025

2055

2080

Projection period

2011-2040

2041-2070

2071-2090

Temperature increase since 2012

1.0 to 1.5 ⁰C

2.0 to 2.5 ⁰C

3.0 to 3.5 ⁰C

Evapotranspiration increase

ET is expected to increase by up to 30 percent

Expected average annual flow in million acre-feet

13.9

13.4

13.1

Decreased runoff at Lee’s Ferry compared to 1906-2007 average flow

-7.5 percent

-10.9 percent

-12.4 percent

Peak runoff month

June

May

May

What perhaps scares irrigators the most is the row in the above table that predicts that evapotranspiration will increase up to 30 percent.[21] That’s equivalent to a 30 percent decline in available water, since it means that plants need 30 percent more water to produce the same crop. Also concerning is the earlier peak runoff periods, since it means that water will be running past farms and hayfields before crops start growing and the water can be put to beneficial use. Dust on snow is expected to alone cause a 5 percent decrease in runoff because plants will come out and start consuming water earlier than in the past when they were dormant beneath the snow. It is tempting to call this river flow prediction alarmist, but “radical” is a not a word that comes to mind when describing Reclamation. Climate scientists predict flows could decrease this much because less water will reach the earth if the atmosphere is hotter. The recent low flows into Lake Powell coupled with the hot temperatures should be telling us to watch out—any other conclusion seems reckless. What happens if we plug Reclamation’s declining runoffs into the graph of historic runoffs past Lee Ferry? If Colorado River flow drops 7.5 percent, the low-end of the decline that Reclamation predicts to occur over the next few decades, Mead and Powell reservoirs will generate power less than 40 percent of the time, and a Compact call would occur every sixteen years on average. It’s bad news any time reservoir levels, depicted in blue, fall below the red line.

Figure 17.6 Levels in Lake Powell under another scenario

The message from these graphs is that we are likely already consuming more of the Colorado River as it can provide under a warmer climate. If Reclamation’s dire 2080 prediction proves correct—river flows are 12.4 percent lower—Mead and Powell reservoirs would have generated power only one out of every eight years, and a call would have been in place nearly a third of the time. There would be a lot less blue in the second graph above. Reclamation released the following graph in 2012. It shows that demands on the Colorado River outpaced supply in for the first time in 2002, 80 years after the Compact was signed. It also shows that demand is only expected to increase in the future despite dwindling supplies.

Figure 17.7 Projected supply and demand on the Colorado River

This graph shows up periodically at water meetings since it was released in 2012, but speakers rarely make the obvious conclusion that we should be talking about using less, not more. And I think if Colorado took a fresh look at the realities surrounding the Compact, it would now aim to minimize beneficial use and discard its old goal of trying to maximize it because it felt entitled to X amount of water under the Compact.

Figures

Figure 17.1 Front Range diversions and a compact call

Figure 17.2 Growth in Colorado River Basin states 1900 to 1950

Figure 17.3 The state of Colorado’s “penalty box” in the Compact

Figure 17.4 Water input and output at Lake Powell 1990 to 2014

Figure 17.5 Projected levels in Lake Powell back to the year 762

Figure 17.6 Levels in Lake Powell under another scenario

Figure 17.7 Projected supply and demand on the Colorado River

Notes

[1] CWCB, Colorado Water Plan 2023, pg. 75.

[2] Wood C., “Developer secures infrastructure partner for 338-mile pipeline to bring water from Utah to Front Range,” Loveland Reporter Herald, May 25, 2022, https://www.reporterherald.com/2022/05/25/developer-secures-infrastructure-partner-for-338-mile-pipeline-to-bring-water-from-utah-to-front-range/.

[3] The U.S. Reclamation tracks water flows at numerous rivers and dams in the Colorado River Storage Project. See, http://www.usbr.gov/lc/region/g4000/NaturalFlow/current.html. Select “CURRENT natural flow data 1906-2014 (Excel file, 1.4 MB) - Updated 9/20/16,” go to the spreadsheet titled NaturalFlows1906-2014_withExtensions_9.20.16, open tab AnnualWYTotal Natural Flow. Simulated runoff at Lee Ferry is in Column W.

[4] U.S. Reclamation reconstructed flows at Lee Ferry are from: Bureau of Reclamation, Colorado River Basin Natural Flow and Salt Data, 1906, “CURRENT natural flow data 1906-2020 (Excel file, 1.5 MB) - Updated 12/15/22,” downloaded 11-30-2024, https://www.usbr.gov/lc/region/g4000/NaturalFlow/current.html.

[5] Upper Colorado River Basin Compact of 1948, Article IV.

[6] Eric Kuhn said Colorado is using even more, up to 58 percent of total Upper Basin use. In a letter to the Colorado River District board dated Sep. 13, 2016, Kuhn stated “Colorado’s share of the total consumptive use in the four states ranges between 55-58 percent. It would be reasonable to assume Colorado’s share of demand management (i.e., the amount Colorado would have to cut back) would be in this range.” Colorado River Basin Roundtable minutes Sep. 26, 2016.

[7] "Colorado River System Consumptive Uses and Losses Reports, 2001-2005, 2006-2010 (Provisional), and 2011-2015 (Provisional),” Reclamation, downloaded 9-30-2015, http://www.usbr.gov/uc/library/envdocs/reports/crs/crsul.html.

[8] Colorado’s Water Plan,” Dec. 2015, Table 8.1 Colorado River Development - Discussion in the Basin Implementation Plans, pg. 8-19.

[9] Maneshni A., “Drop in Lake Powell could threaten power production as well as water supplies,” Cronkite News, March 17, 2022, https://cronkitenews.azpbs.org/2022/03/17/lake-powell-water-levels-drop-historically-low-level/.

[10] Ramirez R., “Lake Powell is about to drop below a critical level never reached before, as drought rages on,” CNN, March 3, 2022, https://www.cnn.com/2022/03/03/us/lake-powell-water-colorado-river-climate/index.html.

[11] The Bureau of Reclamation kept overestimating the Colorado River supply until  2013 when Colby Pelligrino, an engineer-hydrologist who was director of water resources at the Southern Nevada Water Authority, finally convinced the Bureau of Reclamation and the Basin States that the drought hydrology prepared by the Bureau of Reclamation was overestimating supply. That year the Basin States met with Department of Interior Secretary Jewell and agreed it was time to prepare drought contingency plans. Thus, for 90 years the Bureau of Reclamation was effectively fudging the numbers, a tact that may have convinced Congress to build the Central Arizona Project (CAP). By estimating Colorado River flows based on average flow from 1906 to 1965 (which averaged 15.3 maf per year), BuRec was able to show there was sufficient water for CAP to deliver 1,045,000 acre-feet each year on average to Phoenix and Tucson. If BuRec had used 1922-1965 hydrology to determine average Colorado River flows (which averaged 14.2 maf per year), a time period that is more in line with average river flows over the past 500 years, there would have been only 622,000 acre-feet available for Phoenix and Tucson. That may have dissuaded Congress from authorizing CAP. See, Kuhn E. and Fleck J., Science be Dammed, 2019, pgs. 174. 205-209.

[12] SB 2007-122, Section 15, pg. 9, http://www.leg.state.co.us/clics/clics2007a/csl.nsf/fsbillcont3/C1A03A4B43CB7CA187257251007C4512?Open&file=122_enr.pdf.

[13] The Colorado River Water Availability Study (CRWAS) was designed to be completed in phases. Phase 1, estimated to cost $1 million, would determine how much water was available, and Phase 2, estimated at $1-2 million, would determine where the additional developable water, if any, would come from; see, Colo. Basin roundtable minutes Sep. 24, 2007. The legislature’s 2007 appropriation of $500,000 was the only appropriation made to conduct the study. The study was released in 2012 to little fanfare. We heard at the May 24, 2010, and June 11, 2011, Colorado River basin roundtable meetings that 0 to 1 million acre feet was available to develop, but 200,000 acre-feet was subtracted from that to account for reservoir evaporation, resulting in a range of 0 to 800,000 acre-feet. The report was conducted by looking at 112 different climate scenarios. It concludes that Colorado temperatures are likely to rise 1.8 to 5.2o F by 2040, and 4.8 to 8.1o F by 2070; that crop irrigation requirements are likely to increase 1.9 to 7.4 inches by 2040 and 5.1 to 10.9” by 2070 (compared to 24” estimated to grow hay, this projects crop irrigation requirements will increase 8 to 45 percent—ed.); that the majority of climate scenarios indicate decreased annual river flow for both 2040 and 2070 at over 80 percent of the site locations studied in the report; that annual runoff shifted 8 days earlier by 2040 and 14 days earlier by 2070; and that most locations show less water availability in both 2040 and 2070. “Colorado River Water Availability Study,” Mar. 2012, CWCB, Table ES-2, pgs. ES-12 to ES-15, pdf pgs. 24-27.

[14] The 2015 Colorado Water Plan notes the Arkansas Basin Roundtable plans to “Increase surface storage available within the basin by 70,000 acre-feet by the year 2020.” Chap. 6 – Water Supply Management, pgs. 6-21, 22, and 6-34, 35. The Arkansas Roundtable does not mention PSOP, the Preferred Storage Option Plan, which would increase the height of the dams holding back Turquoise and Pueblo Reservoirs, instead obliquely referring to it as the need to “Implement a critical IPP.”

[15] Minutes from a meeting of the four Western Slope roundtables on December 18, 2014, Grand Junction.

[16] Kuhn, E., “The Colorado River Basin’s Uncertain Water Future,” 2016 Colorado River District Annual Report, pg. 4.

[17] Colorado plans to increase consumption 4 percent, Utah by 10 percent, and Wyoming and New Mexico by 13 percent, according to the Colorado River Research Group, an organization started by professors from western U.S. universities in 2014. See, “The First Step In Repairing The Colorado River’s Broken Water Budget: Summary Report,” Dec. 2014, Colorado River Research Group, pg. 3, https://www.colorado.edu/center/gwc/sites/default/files/attached-files/crrg_summary_report_1_updated1.pdf

[18] Meko, D.M., et al, “Medieval drought in the upper Colorado River Basin,” 2007, Geophysical Research Letters, Vol. 34, L10705, http://onlinelibrary.wiley.com/doi/10.1029/2007GL029988/pdf. For additional information, see http://www.ncdc.noaa.gov/paleo/pubs/meko2007/meko2007.html. Contributing author Jeff Lukas works for NOAA in Boulder and is a frequent speaker at Colorado water conferences.

[19] Either Colorado must decrease its annual consumption by 153,400 acre-feet, or New Mexico, Utah, and Wyoming must increase their use by 297,000 acre-feet to get Colorado out of the penalty box. The graph indicates the combined capacity of Lakes Mead and Powell (where 100 percent is full and 0 percent is empty, meaning water below the dead pool level is pumped out). The graphs in the text assume that Colorado gets out of the penalty box but does not reduce its consumptive use. Thus, each graph assumes that consumptive use of the Upper Basin goes up 250,000 acre-feet, from 3.91 million acre-feet (average consumptive use by Upper Basin states from 2001 to 2010) to 4.16 million acre-feet). The record of Upper Basin consumptive use for 2001-2010 is from 2 sources: 1971-2005 consumption - Table 2-4, Annual consumptive Use in the Upper Basin for the States of Arizona, Colorado, New Mexico, Utah, and Wyoming, 1971-2008, The Colorado River Documents 2008, Reclamation; 2006-10 consumption: Provisional Upper Colorado Basin Consumptive Uses and Losses Report 2006-10.

[20] “U.S. Reclamation Colorado River Basin Water Supply and Demand Study, Technical Report B – Water Supply Assessment,” February 2012 Update, pages B-51, 56-57, 86, available at http://www.usbr.gov/lc/region/programs/crbstudy/Report1/Updates/TechRptB.pdf.

[21] Id, page B-57. This figure is susceptible to misinterpretation, since Reclamation projects that ET will increase more in the fall and winter and less in the hot summer months when less water will be available. It is also projected to increase more in the Upper Basin in the Spring while declining in the Lower Basin in the Spring. Snow water equivalent (SWE) is expected to decrease 30 percent throughout the Basin by 2025. Soil moisture in July is expected to decline 5-10 percent throughout the Basin in all three time periods.

 [BG1]Add page cites re Science Be Dammed.

 [BG2]Page 5, General Manager’s Report, dated July 2, 2024, for the District’s third quarterly meeting, held on July 16, 2024.