After Friday’s blog post and some intemperate tweeting about whether the Colorado River Drought Contingency plan cuts about to go into effect were voluntary or mandatory, a friend involved in the negotiations explained that they actually came up with a word for this: “vandatory”.

The idea was that everything they all agreed to in DCP was voluntary to enter into. But once signed, fulfilling its terms then becomes mandatory (i.e. contractually binding and now mandated by congressional directive to the Secretary).

I’m gonna get my “CLOSE IS NOT DONE” tattoo lasered off and replaced with one that says “VANDATORY”.

a screenshot of the actual historic text message

Walking across the University of New Mexico campus yesterday afternoon on my way to orientation for our incoming UNM Water Resources Program students, at precisely 3:10 pm MDT, a friend sent me a historic text message: “1089.4”.

Translated from the native language of the Colorado River Water Nerd, “1089.4” means “The surface of Lake Mead in the Bureau of Reclamation’s August 24-month study is forecast to end the year at less than 1090 feet above sea level, triggering the first mandatory cuts in the long history of the Law of the Colorado River.”

Below we will discuss quibbles with two of the words in that sentence: “first” and “mandatory”. But in my struggle to distill the complex into overly simple messaging that I can bang home in the style of the newspaper writer I once was – yes, this is historic.

This almost didn’t happen. When the DCP was signed in May, the Bureau of Reclamation was forecasting that Mead would end the year at elevation 1084.9, more than five feet below the trigger for mandatory cutbacks. Yesterday’s forecast was nearly five feet higher, just barely below the cutback trigger. But we’ve had a really wet year, haven’t we?

But 2019’s been really, really wet, right?

Not exactly. Some really helpful back-and-forths by email and telephone the last few days with Colorado State’s Brad Udall and my coauthor Eric Kuhn (buy our book, soon) has convinced me that a lot of the rhetoric about a giant snowpack and booming runoff, including some of my own, has not held up terribly well. Here’s a super helpful graph Brad made showing elevations in Lake Powell:

Elevation of Lake Powell, courtesy of Brad Udall

Yes, Powell is up this year, but it’s just a 22 percent above the long term average, nothing like 2011 and not all that much higher than 2017. I guess it seemed to me like a lot of water because the 21st century has been so dry.

Long term Colorado River flow

The main reason Mead is ending the year so much higher than the May forecast is a) a reduction in Lower Basin use as compared to the May forecast, and b) an increase in tributary inflow below Glen Canyon Dam. That combination came within half a foot of Lake Mead elevation of saving me the need to write this tangled blog post.

I prefer to call the DCP cuts “mandatory”

There’s been a weird linguistic thing going on in the news coverage of 1089.4, with some writers characterizing the coming reductions of water use as “voluntary”. It’s easy to get sidetracked in a twisted binary linguistic argument about whether the cuts are “mandatory” or “voluntary”, which is best sidestepped by being explicit about the actual characteristics of the thing that is happening here.

In recent years, including this one, the states of the Lower Colorado River Basin have been doing a bangup job of using less water. No one is forcing them to, so the term “voluntary” seems to pretty clearly apply. Importantly, this means that they are not required to do this, and there are no guarantees that in coming years they would.

In May, all the states signed an agreement explicitly laying out rules that would cut their water use when Lake Mead is below 1090.  Lake Mead will be below 1090. So the rules now require Arizona, Nevada, and Mexico to reduce their water use. Rather than hope for voluntary reductions in 2020, we can all count on the cuts because the rules require them. This carries an important characteristic of “mandatoriness” to me.

Did the states agree to the rules? Yes. Does that make them voluntary? Sure, whatever, I guess this has some characteristic of voluntariness too. But by this linguistic argument, we’d have to call Interior Secretary Gale Norton slashing California’s deliveries to L.A. through the Colorado River Aqueduct Jan. 1, 2003 “voluntary” because California had agreed in 1928 to the rules Norton was invoking. All the mandatory cuts we can see out there in the future of the Law of the River – an Upper Basin Compact call being the most obvious – would under this linguistic interpretation count as “voluntary” because they grow out of enforcement of rules to which the states had previously agreed.

It is the case that the states did come together to agree to these cuts, and there is voluntariness about that process that matters. Still, the fact that we now have enforceable rules that create requirements seems the salient point here, whatever words we use to describe them.

But is this really the first time we’ve had mandatory cuts?

So I guess now that I think it through, that “first time” thing was a bunch of crap designed to sell newspapers. As I acknowledge above, Gale Norton forced California to reduce its Colorado River water use from more than 5 million acre feet to 4.4 million acre feet back in 2003.

In thinking it through to write this post (folks this is why I blog) I’ve clarified my own thinking from the bombastic “OF COURSE IT’S MANDATORY” thinking of intemperate afternoon tweets. The voluntariness of what is happening now, as compared to what happened with California in 2003, seems relevant.

Maybe we could call it the first time the states have voluntarily agreed to mandatory cuts?

* “Ill-named” because this isn’t about drought. This is about us using too much water.

By Eric Kuhn

The University of Arizona’s Vic Baker on paleofloods of the Colorado River. Photo by Eric Kuhn

Last week I had the pleasure of exploring the banks the Colorado River near Moab, Utah with two of our most accomplished river scientists, Jack Schmidt (Utah State) and Vic Baker (U of Arizona), and hear a presentation by Dr. Baker on the science of studying past floods on the Colorado River system.  When a flood occurs, the river leaves evidence of the flood by depositing materials that are carried by the river high on the banks of the river or in caves adjacent to the river. His basic message is “if it has happened in the past, it can happen,” therefore, if we can use the evidence nature has provided to estimate the peak discharge of past floods, we can use that knowledge to be better prepared for future floods.

With the recent focus by the basin’s water management agencies on drought contingency plans, flooding has been given little attention.  In fact, there are now only very few of us around who were actively involved in river operations during the last major flooding event on the river; the high flows of 1983 and ’84.  By now the story of 1983 is well known. The large runoff caused by a wet winter and spring combined with higher than normal carry-over storage in Lake Powell caught the Bureau of Reclamation by surprise.  The resulting inflow quickly filled the reservoir and far exceeded the capacity of Glen Canyon Dam’s power plants and outlet tubes (44,000 cfs) requiring a large amount of water to be released through the emergency spillways.  Cavitating flow through the spillways caused considerable damage carving out a small building-sized hole in soft sandstone that surrounds the dam. Further damage was avoided by the installation of 8’ plywood panels on the top of the dam (they were quickly replaced by steel panels).  In theory, the emergency spillways have now been repaired and redesigned to reduce cavitation (and successfully tested with a short duration high flow), but clearly the reoccurrence of a large uncontrolled spill at a dam anchored in relatively soft sandstone (Glen Canyon) is an event we want to avoid.

The remarkable aspect of the 1983 and ’84 high flows is just how unremarkable and modest the peak flow levels were. The inflow to Lake Powell peaked at about 116,000 cfs in ’83 and 125,000 cfs in ’84.  Before Glen Canyon Dam the largest peak flow we’ve experienced and documented at Lee’s Ferry is about 250,000 cfs in 1884, twice the peak flow of 1984. We know 1884 was a very big year based on newspaper reports and the diaries of settlers, but the flow estimate is somewhat crude. It was made based on the memory of one of the ferry employees whose cat became stranded in a tree by the flood and had to be rescued. Based on Dr. Baker’s science, even this 250,000 cfs flow at Lee’s Ferry is far from the largest flow that has happened in the past 2000 years.  Based the field work of Baker and his students, evidence of flood flows on the Colorado River just upstream of Moab, Utah and the nearby Green River point to a flow as high as 300,000 cfs (each). The estimated past peak flow at Lee’s Ferry is about 500,000 cfs, four timed the 1984 peak!

But wait you say, don’t we believe that climate change is reducing, not increasing, the natural flow at Lee’s Ferry? The answer is yes, the best available science suggests that the long-term average annual natural flow at Lee’s Ferry is likely declining.  That does not mean, however, that future large flood flows will be less. In fact, because a warmer atmosphere can hold more moisture, science points to the possibility of much larger future peak flows. I can envision an above average runoff year (like 2011 or 2019) that makes a reasonable dent in the filling of Lake Powell (enough that because of our concern with drought, the Upper Basin would want to keep every drop of it in storage) followed by a super-wet year. Perhaps a year where the track of a series of warm and very moist atmospheric rivers comes in off the Pacific through Southern California with the bullseye on the Colorado and Utah Rockies for an extended period of time. The resulting runoff peaks with an inflow to Lake Powell of over 400,000 cfs and a total volume of near 50 million acre-feet (the climate models suggest it’s possible).  The potential impacts of such an event could be very serious. Even if Lake Powell was only half full, such flows would quickly fill the available vacant space, then possibly exceed the capacity of Glen Canyon Dam’s emergency spillways and over-top the dam. In theory, the dam might survive an over-topping event, but remember how a little imperfection in the service spillway at Oroville Dam resulted in huge damage to the structure (because of the immense erosive power of high velocity water).

Ultimately the flood waters would work their way down through the Grand Canyon, scouring the canyon and causing major environmental damage, into Lake Mead and the Lower Basin main stem reservoirs. The highest flows would be dampened by the lower river facilities, but still high enough to potentially cause major damage to communities along the river From the Mojave-Parker strip to Mexico. This stretch has seen considerable growth, but no high flows since the mid-1980s.  In the worst-case scenario, the flooding impacts might cause a dam failure. The results of which would be catastrophic. I’m not predicting such an event will happen any time soon. I’m only suggesting that with the dominant focus on managing the impacts of aridification, we would also be derelict for not considering and being prepared for future large high-flow events. Given the uncertainties of climate change, the basin’s water agencies would be wise to fund additional studies on the high-flow side of hydrograph while they continue their plans to live with reduced average flows.