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Research on Flow Rates in Colorado River Fuels New Thinking for Future Agreements

A recent report from the Center for Colorado River Studies at Utah State University takes a deep dive into the history of water flow on the Colorado River to help water users assess the future of this high use, drought plagued resource. Professor Jack Schmidt is the Center's Director. Today we take a quantitative look at the future of a river that was once called the Nile of America. 



HOST (Lou Gum): I'm Lou Gum. This is Arizona Edition on KAWC. 


The topic today is the Colorado River - how it's measured, how it's managed, and why it matters. 


Our guest today is Professor Jack Schmidt, director of the Center for Colorado River Studies at Utah State University. 


The spark for our conversation was a recent report titled The Future Hydrology of the Colorado River Basin - a recent white paper. But it turns out that paper was just one of several that addressed the challenges facing the Colorado River. 


Still, the report highlights research on water flow in the River that leans heavily on the numbers. 


What struck me about this paper and if I could just read this line, “Although it is relatively easy to qualitatively describe scenarios of drought or water abundance, it's much harder to quantitatively estimate likely future conditions.” 


Why would it be important to have this quantitative understanding of River flow, and can you help our listeners understand that distinction, describing scenarios qualitatively versus quantitatively? 


JS: Thanks, and thanks for this opportunity to visit with you and your listeners. 


You know the Colorado River... We're managing the water supply today, right on the, right on the edge of using every drop that the water, that the River provides. And so, when the flows change, or if the flows get less, that matters because there's some user out there who has the potential to not get as much water as they've used. 


And of course, any listener in the Yuma area knows that probably better than anyone else, because you are at the far downstream end. You know, in most years, not a drop of water gets past Morellos Dam. 


And so, why do the numbers matter? 


Every drop of water in this River system is allocated and spoken for, and if the number of drops or the size of the pie, whatever metaphor you want to use, if the pie is getting smaller, if there are fewer drops available to be allocated, then there's somebody at risk. - Professor Jack Schmidt

The numbers matter because every drop of water in this River system is allocated and spoken for, and if the number of drops or the size of the pie, whatever metaphor you want to use, if the pie is getting smaller, if there are fewer drops available to be allocated, then there's somebody at risk, and so that's why these numbers matter because it really is all about getting these numbers right. 


LG:  This report, in particular, took out a wide view of these numbers, an if I'm understanding the goal properly, it was to sort of quantitatively figure out how dry the Colorado River watershed could become based on what has happened in the past and could happen again in the future. 


Before we get into that, though I have a question that I've always kind of had about Upper Basin versus Lower Basin. Are these hydrology terms or geographic classifications? How does that distinction help us understand usage of the Colorado River? 


JS: Well, those terms are physiographic and geographic, and they are immensely political. 


Of course, everyone who lives around Yuma knows that more than a century ago, the Colorado River began to be referred to as America's Nile. The Nile River of America. And that metaphor really says it all in the sense that., we once upon a time had an immense amount of water that flowed out of the distant upstream areas and came down to the lower Colorado River where it fueled agricultural development and economic development. First in the Imperial Valley and in the Yuma Irrigation District, and at other patches of water along the Lower Colorado River. And so, in that sense, the whole focus of managing the Colorado River is how much water arrived at Yuma, and what was the risk of floods, and how dry would the River get during the dry season? And oh, it sort of came from some distant place upstream. Meanwhile, upstream there were small areas of valleys in the late 1800s, being irrigated around Grand Junction and a few other places.  


And so, in the early 1900s the discussions began about who was going to develop the water where and for how much. And if one pursues water policy, and water development, water rights, in the same way that we pursue it within states, then we live by what's called the prior appropriation doctrine - first, in time, first in right. The earliest oldest users have the most senior rights to the water. And so, it was recognized early that the use of the water around Yuma, the use of the water by the state of California would preemptively have senior right on in the entire basin and the Upper Basin states who were economically growing much slower wanted to preserve their opportunity to develop water in the future. And so that sort of difference between upper and lower basin, of existing versus future use, is long embedded. So, then the decision was made, well, let's just carve the basin up in half politically and sort of begin to divide the pie, let's use that metaphor, of who's going to use, what, where.  


The decision to divide the River, at Lee’s Ferry is for a very precise physiographic reason -  

it's in the middle of nowhere, it's in the rocky, you know, majesty of the Colorado Plateau, and it’s also one of the few places that you could drive to and access the River so the River could be measured at that place. So, it just happens to be the place in the 1920s that you could get to, to make measurements, and all of the upstream users are somewhere upstream of that in Colorado, Utah, New Mexico and Wyoming, and all of the downstream users are somewhere far below the Grand Canyon in California and Arizona, and today also in Nevada. So Lees Ferry is just the place in the middle of nowhere that you could sort of say, well, we're downstream of all the upstream guys, were upstream of all the downstream guys, and that's how it got chosen. 


We live by what's called the prior appropriation doctrine - first in time, first in right. The earliest, oldest users have the most senior rights to the water. - Professor Jack Schmidt

LG: And Lee’s Ferry is interesting, because flow records and observations there are mentioned in the White Paper we're talking about as a historic source of information. 


JS: So, the U.S. Geological Survey operates gauging stations, and gauging stations have been operated in the Colorado River basin since the late 1800s. The first gauging station in the Colorado River basin was established, I think in 1885, something like that, on the Gila River where it emerges out of the Mogollon Rim near a place called Buttes, Arizona. Gauging near Yuma began about 1905, as I recall, plus or minus a year. Lee’s Ferry was viewed as the most accurate place to measure how much water came out of the upper basin states and was sort of available for distribution amongst Nevada, Arizona, California, and now of course Mexico. 


LG: One of the things this paper seems to point out, though, is that, that data was sort of inadequate, in terms of maybe just the time that it covers, to really understand the impacts that something like a drought can have on the Colorado River system. 


Talk about what it took to understand that at a deeper level, and I guess I'm asking more about that tree ring drought data and how that informed the understanding. 


JS: Yeah. So, in the early 1900s. The U.S. Geological Survey, a scientist hydrologist by the name of EC LaRue, a made estimates. And the gauging record at Yuma in the early 1900s was a record of substantial stream flow - 15, 17, 20-million acre-feet of water a year. And LaRue offered the observation that, you know, this period in the early 1900s that we're living in might actually be unusually wet. And what he did is, he looked at the only long-term historical record that was available of hydrology in the West, and that was the ebbs and flows of the Great Salt Lake. Because the elevations of the Great Salt Lake were known and recorded by the Mormon settlers of the Salt Lake Valley. 


LG: Our guest today is Professor Jack Schmidt, director of the Center for Colorado River Studies at Utah State University. We're talking about the early days of water flow management on the Colorado River. When we come back, we'll hear how tree data contributes. 


I'm Lou Gum. This is Arizona Edition on KAWC. We'll be right back. 




LG: Welcome back to Arizona Edition on KAWC. I'm Lou Gum.  


Our guest today is Professor Jack Schmidt, director of the Center for Colorado River Studies at Utah State University.  


We've been hearing about how a young hydrologist named Eugene Clyde LaRue planted a seed of doubt about incredibly high flow rates in the Colorado River in the 1910s and 20s. Flow rates that, despite his warnings, were used as the basis for water negotiations at the time, including the historic Colorado River Compact of the early 1920s. 


JS: Negotiations went forward, assuming the pie, the available amount of water, was quite large. We went into the drought of the 1930s and 1940s, and so we came out of a wet period into a dry period.  


And at the same time in the 1940s, scientists in California and Arizona realized that long-lived trees on hill slopes in the mountains of the West had different thicknesses of tree rings, based on wet and dry years and that began the study of what we call tree ring hydrology. And today it's a well-developed science, much of it led by scientists at the University of Arizona in Tucson, in which we estimate what was the flow hundreds of years into the past by looking at the tree rings of long-lived trees, establishing a correlation for the period in which we have overlapping records of tree rings and amount of water in the River and then you look back in time, apply those correlations and say, well, in the past we have records of extreme droughts, wet years, and what we know is this.  


In the 1940s, scientists in California and Arizona realized that long-lived trees on hill slopes in the mountains of the West had different thicknesses of tree rings based on wet and dry years, and that began the study of what we call tree ring hydrology. - Professor Jack Schmidt

We know that the period in the early 20th century was amongst the very wettest in the last 1000 years. So, we know that the agreements to divide the River were in a very unusually wet year. The long-term average between 1906 and 1929 is a number like 18 million acre-feet of water as a natural run-off. And we know that we've never had that since. And the long-term average since 1906 to today is a number like 15-million-acre feet of water and the estimated average annual natural flow of the River since the year 2000 has been 12-million-acre feet. And in a River in which every drop of water is allocated, 12 is a much smaller number than 18. 


LG: And understanding that longer period of time helps you know that the original baseline was a little off. 


JS: Yes, yeah, that's correct. 


But of course, the challenge going forward is that none of us has a time machine. If we had a time machine, we wouldn't have to do any of these studies, we would just get into time machine and fly off 50 years in the future and know exactly what happens, right? 


We can sort of describe the worst-case scenarios in the basin of it getting drier or getting, or maybe it gets wet for just enough years to give us a false sense of security and then it turns dry. But we can talk about all that in words. But at the end of the day, river engineers, river negotiators, everybody who represents a state, or an irrigation district, cares exactly how much water there is going to be available to distribute. That's why we need numbers. 


One of our efforts in our work has been to try to estimate what might be plausible future hydrology, that's what we've sought to do in some of our work. And then we've also sought to look at, given those hydrology's, what are the implications for, you know, how much water can be used in the basin? 


LG: What are the implications though, for how we're managing the River? A lot of the Law of the River has been established just in the last 50 to 75 years, so if it's been based on assumptions that are now different, how does that affect how we move forward? 


JS: In the earliest part of the 21st century, as society began to come to terms with this very dry hydrology, we were beginning to realize what's happening. It began, ironically, right around the year 2000. We would continue to use lots of water in the basin for the next several years, and the reservoir elevations, especially in Lake Mead, were rapidly depleted because there was much water, more water, going out than there was coming in. And yet every year it just kept getting drier, or it never got wet again. And so, where that left us was with a reservoir storage that was going down. and so. 


The states got together and said well we need to tweak our agreements because we're going to lose the major reservoirs. An agreement was reached and signed in 2007 called the Interim Shortage Guideline. And they said, well, if it stays dry, then we're going to all have to begin to take some cuts because we can't have the reservoirs go dry. So essentially the 2007 agreement was an agreement of how to share the pain of drought. 


That is the great crossroads that the basin is at right now. The basin has to reach a new agreement about how to deal with shortage and drought. - Professor Jack Schmidt

And in another decade, it was like, oh my goodness, the interim shortage agreements are still not sufficiently restrictive in use, and we've got to take even bigger cuts, because the drought is continuing. And those agreements which were signed two years ago, in the last administration, were called the Drought Contingency Plan. That was an extremely contentious debate, especially in the state of Arizona about how those cuts would be distributed within the state of Arizona. 

Both of those agreements are over. They end in the year 2026. 


So, what we've now begun in the basin, and this is a negotiation that goes on amongst the main governmental entities, is a new agreement to deal with shortage and drought must be negotiated and must be in place by 2026. And that is the great crossroads that the basin is on right now. The basin has to reach a new agreement about how to deal with shortage and drought. 


And our paper is merely one contribution to try to push the discussion. To say if we're going to reach a new agreement then we'd better realistically, eyes wide open, appreciate how bad it might get, how dry it might get. But we are at a great crossroads and the states and the federal government are beginning to negotiate on these issues now and it’s all got to be finished in a couple years. 


LG: Basically, running out of time, but I know that this white paper that we're talking about has already informed further research and we will definitely link to that on our web posting.


But, just given the massive threats to the River and its importance to the lives of so many people, how are you not prone to doomsday thinking in your work? What brings you hope? 


JS: (laughter) Right? Yeah.  


I'm...  I've lived a lucky life. I began to work as a River scientist in the mid 1980s, in Grand Canyon, trying to understand how Glen Canyon Dam operations affected sandbars and the ecosystem of the Grand Canyon. I've worked in the Colorado River my whole life. I'm at the end of my career.  

The challenges are immense. I have hope because the people trying to find and seek solutions for the River all share a goal of understanding we have to find a solution. People can talk to each other. People respect and appreciate the roles of science and engineering. People are willing to roll their sleeves up and dive into the details and say, well, we're all in this together, we've got to share this River and we're going to have to deal with this somehow and people will talk and listen to each other.  


That doesn't, that is not to say that we don't disagree publicly. Behind the scenes, people are willing to talk and listen to each other. That's a very hopeful. 


It might get very dry. The societal dependence on the Colorado River is immense, I will tell you that. 

Because there are large users of water in the downstream end of the base, including at the far downstream and near where your listeners live, that guarantees that a whole lot of water comes through the basin and comes through Grand Canyon and there's a whole lot of water that stays in the River for a long time. 


The challenges of rehabilitating environments in the delta downstream from Morellos Dam along the limitrophe? Those are exceedingly difficult, challenging, hard, almost seemingly impossible challenges. But everybody wants to try to find a way to find a solution, even though it's hard to find one. 


We will have to take cuts. We will have to use less water. But we will find a way because we have to, and because we all have the willingness to. - Professor Jack Schmidt

We will have to take cuts. We will have to use less water. But we will find a way because we have to, and because we all have the willingness to.  


So ,I think that's probably it. I mean, if this were the Nile River, you know one country, you know, people threatening to blow up dams in another country, or you know, people threaten going to war? I mean, that's not going on in the Colorado River. I think we work together. It's a tough hand we're dealt. But there's a commitment to deal with what we've got in front of us. 


LG: Professor Jack Smith, director of the Center for Colorado River Studies at Utah State University. 

I know we've only scratched the surface, but hopefully in opening of dialogue between you and this station, hopefully we can reach out to you in the future. 


JS: Thank you very much. Thanks for the opportunity. 


LG: Will post an extended cut of my conversation with Professor Schmidt along with a transcript of today's show on our website, We’ll also provide links so you can scan for yourself the research of Utah State's Center for Colorado River Studies


Arizona Edition is a production of KAWC, Colorado River Public Media. Reach out via email to news@  


I'm Lou Gum. This is Arizona Edition. Thanks for listening. 

Lou grew up in Tucson and has a long family history in the state of Arizona. He began his public radio career in 1988 at KNAU in Flagstaff as a classical music DJ and has been hooked on public radio since, transitioning to news after trying his hand at several other careers in publishing and commercial broadcasting. Lou has a degree in American Studies from Arizona State University and was KAWC's Morning Edition host for two and half years before becoming News and Operations Director.
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