Hoover Dam in the fading light of a hot summer evening

A water nerd friend and I made a pilgrimage yesterday evening to Hoover Dam, spanning the Colorado River on the Arizona-Nevada border.

We’d had dinner at one of the restaurants on the docks at Hemenway Harbor, and driven up to the old abandoned boat ramp at Boulder Harbor, two Lake Mead landmarks for me, places I often visit. It was late, and hot as hell, and we were tired, but it didn’t take much persuasion for my friend to say “yes” to a last stop at Hoover Dam.

I’m here in Southern Nevada to be part of a PBS Newshour livestream Wednesday: “Tipping Point: Colorado River Reckoning.” I came out a couple of days early to see some friends and do the sort of “place-based” stuff that’s at the heart of my Colorado River work. I’ve been coming to this place – Lake Mead and Hoover Dam – for the last 15 years, watching the reservoir rise and fall, using this place as a conceptual anchor as I write my books.

My best guess based on hazy childhood memory is that I first visited Hoover Dam 60 years ago. We were on our annual summer car-camping trip, and I remember five-year-old John being both awestruck and uneasy – a bit frightened? – at the scale of the thing. Many years later, on one of many return trips, I stumbled on the thing that I remember most vividly: off the side of an embankment, massive concrete plugs that had been removed from the turbine tubes, dumped off the old rail line, lying today in a ravine.

It was a vague thing, fuzzy and just out of reach, but seeing them again on a bike ride along the Hoover Dam rail trail, the memory jumped up out of the ravine at me. As my friend remarked when I told them the story last night, I got bitten early.

Deb Chachra and the social nature of infrastructure

In an interview published last week in Public Books, the engineer Deb Chachra said a kaching thing about Hoover Dam that captures why I keep coming here, why I anchor so much of my thinking in the dam itself:

To borrow an idea from Joan Didion, who used it to describe driving in Los Angeles, these older forms of infrastructure, especially charismatic megastructures like bridges and train stations, can be secular cathedrals. We recognize that these are things that we made for ourselves and for each other. People have been visiting the Hoover Dam in droves since it was brand-new, so I don’t think it’s nostalgia per se—I think it’s more about celebrating this idea of the collective, these collective or communal projects. If we’re nostalgic, I think it’s less about the physical structures and more about the idea of working collectively.

The Boulder Canyon Project Act, carved in stone

Five years ago, on my umpty-first tour of Hoover Dam, a friend steeped in the “law of the river” led me to the elevator tower on the dam’s Nevada side to look at the decorative frieze. It’s a stone carving (or maybe cast concrete), visualizing the statutory purposes embodied in the Boulder Canyon Project Act, the act of Congress that authorized construction of the dam.

Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That for the purpose of controlling the floods, improving navigation and regulating the flow of the Colorado River, providing for storage and for the delivery of the stored waters thereof for reclamation of public lands and other beneficial uses exclusively within the United States, and for the generation of electrical energy as a means of making the project herein authorized a self-supporting and financially solvent undertaking, the Secretary of the Interior, subject to the terms of the Colorado River compact hereinafter mentioned, is hereby authorized to construct, operate, and maintain a dam and incidental works in the main stream of the Colorado River at Black Canyon or Boulder Canyon…. (emphasis added)

This is what Chachra is talking about. We often view Hoover Dam as a remarkable achievement of physical engineering, and it is. But it is, more importantly, an act of collective will. We came together in the 1920s, in community, to envision a desired future – of cities and farms in a place with too little water for either without infrastructure. We wrote a set of rules – the Colorado River Compact, the Boulder Canyon Project Act – that instantiated that collective will in the construction of a physical object – Hoover Dam.

And then we did the same thing, again and again, across the West. This enabled the places that tens of millions of us now call home.

Yesterday evening it was 110F (43C) after sunset, the parking lots were closed, and the tourists still came. My friend, who may be more of a Hoover Dam/Lake Mead/Colorado River nerd than I am (this is saying a great deal) was talking about the dam’s aesthetics – the care paid to the art deco flourishes – like the Boulder Canyon Project Act frieze. It’s a testament to the understanding of the people who built it that it was more than physical infrastructure – that it was a monument to collective action, the point Chachra so eloquently made.

This is why I’m confident, despite the current conflicts over how to share the shortages we face as a result of climate change, that we’ll figure things out. Collective action is at the heart of what we’ve been doing, it’s often hard, but we do it.

A note on Chachra’s book

Chachra’s book, How Infrastructure Works, is a terrific look at the social nature of infrastructure. Highly recommended.

By Jack Schmidt, Utah State University Center for Colorado River Studies

How did we do in the continuing effort to recover reservoir storage? How much reservoir storage accumulated from this year’s snowpack, and how does that accumulation compare to other years?

In Summary:

Total basin-wide reservoir storage is an appropriate metric to describe the status of the regional water supply and its year-to-year changes. Reclamation provides data on the storage contents of 46 reservoirs in the basin that are primarily managed by the Bureau of Reclamation but also by municipal water agencies and water conservancy districts. Whether destined for within-basin use or for trans-basin diversion, the total amount of water in these reservoirs is the carryover storage available to sustain use during dry times.

Accumulation of storage in those reservoirs occurred between mid-April and early July 2024, and basin-wide storage increased by 2.5 million acre feet. This amount is only 30% of the increase in storage that occurred during the same period in 2023. Nevertheless, basin-wide reservoir storage increased by 300,000 af when the summer peak of 2024 is compared with the summer peak of 2023, because consumptive uses and losses in the intervening time between the two runoff years was only 2.2 million acre feet. Despite the modest runoff of 2024, water managers were able to increase reservoir storage, because they had done such a good job of limiting consumptive uses following the 2023 runoff season.

Today, 62% of the total basin-wide storage is in Lake Mead and Lake Powell. The combined contents of these two largest reservoirs in the United States peaked on 8 July at 18.5 million af. Most of 2024’s snowmelt runoff was stored in Lake Powell, and storage in Lake Mead declined during spring and early summer 2024. Now that the runoff season has ended, some of the contents of Lake Powell will be gradually transferred to Lake Mead.

The Details:

On 6 July, storage in the Colorado River basin peaked for the year at 30.0 million acre feet (af), approximately 50% of capacity of the reservoir system¹ (Fig. 1). The combined contents of Lake Mead and Lake Powell peaked on 8 July at 18.5 million af, approximately 37% of the capacity of those two reservoirs. The last time total basin reservoir storage was as much as this was in early January 2021, and the combined storage of Lake Mead and Lake Powell had last been at its present volume in very late April 2021. Thus, reservoir storage has not yet recovered to the average conditions between 2005 and 2020.

Figure 1. Graph showing reservoir storage in the Colorado River watershed between 1 January 1999 and 15 July 2024.

The season of water accumulation, when inflow to reservoirs exceeds outflow, that began in mid-April has now ended. How did we do in the continuing effort to recover reservoir storage? How much reservoir storage accumulated from this year’s snowpack, and how does that accumulation compare to other years?

The snowpack of the Upper Basin peaked on 3 April at 16.8 in of snow water equivalent (SWE)². For comparison, the median peak SWE for the past 30 years, as computed by the Natural Resource Conservation Service, was 16.0 in., so 2024 was a pretty good year. Nevertheless, 2024 was not nearly as good a year as 2023 when the peak SWE was 23.9 in. Preliminary estimates of natural flow at Lees Ferry for Water Year 2024 are that this year’s natural flow³ will be 12.1 million af, although that estimate may change slightly by the end of the water year.

The relation between peak estimated SWE in the Upper Basin and natural flow at Lees Ferry has a reasonably good correlation for data from 2000 and the years of the 21^st century (Fig. 2). There is year-to-year variation in this relation caused by springtime weather that affects the rate of melting and the amount of sublimation. Variation is also caused by the intensity of the summer North American monsoon that augments the natural flow but is unrelated to snowmelt. Estimated natural runoff in 2024 was well predicted by the general relation.

Figure 2. Graph showing the relation between peak annual snow water equivalent for the Upper Colorado River basin and natural flow at Lees Ferry, estimated by Reclamation. The solid line is an exponential relation fit to these data.⁴

The amount of water added to reservoir storage is very well predicted by the natural flow at Lees Ferry (Fig. 3), and this relation shows that much more of the natural runoff is captured by reservoirs in wet years than in dry years. In 2024, approximately 20% of the estimated natural flow was stored, consistent with comparable years (2010, 2014, 2015, and 2016) (Fig. 3). A higher proportion of the natural runoff was stored in the wet years of 2005, 2011, 2019, and 2023, when more than 40% of the natural runoff was captured in reservoirs. More than 30% of the natural runoff was stored in 2008, 2009, and 2017.

Figure 3. Graph showing increase in basin-wide reservoir storage as a function of natural flow at Lees Ferry. The solid line is linear relation fit to these data⁵.

The combined contents of Lake Mead and Lake Powell peaked on 8 July, but storage in each reservoir followed very different trajectories (Fig. 4). Lake Powell, which is upstream from Lake Mead, captured the inflowing snowmelt runoff and increased in storage by 2.2 million af between mid-April and early July while Lake Mead lost approximately 900,000 af.  Now that the inflow season has ended, storage will gradually decline in Lake Powell and increase in Lake Mead.

Figure 4.  Graph showing the distribution of reservoir storage in different parts of the Colorado River basin between 1 January 2021 and 15 July 2024.

The storage gains resulting from the 2024 runoff compensated for the consumption of reservoir storage that had occurred after the 2023 runoff season (Fig. 5). This year’s peak of 30.0 million af is slightly more than the peak storage in summer 2023 that was 29.7 million af. This small increase in storage occurred despite a modest 2024 runoff season, because the basin’s water managers had done a good job in conserving the gains of last year (see blog post of 21 May 2024). Only 2.2 million af was consumed or lost following the 2023 runoff season, and the gain of 2.5 million af in 2024 exceeded the preceding loss. Thus, basin-wide storage is ever so slightly better than last year, because we used so little water last year. We now begin a 9-month period when the job in front of us is to continue to reduce consumptive uses and losses until the onset of the 2025 snowmelt season.  Let’s not lose focus. We’re all in this together.

Figure 5. Graph showing changes in reservoir storage between 1 January 2023 and 15 July 2024.

Lower Basin U.S. use

Preparing for A Thing I’m doing next week, I updated the Crazy Fleck Spreadsheet this morning of data from Reclamation’s annual Lower Basin decree accounting reports.

Amid all the angst and rhetoric, it is easy to miss the salient fact made clear by this graph: Lower Basin water users have reduced their take on the Colorado River substantially since the early 2000s.

• Nevada’s use was the lowest since 1992.
• Arizona’s use was the lowest since 1991.
• Records that far back in time are tricky*, but California’s take on the river in 2023 was appears to have been the lowest since the late 1940s.

To be clear, the use in the late 1990s and early 2000s was unsustainably large. Praise is due for shrinking Lower Basin use, but the praise should be tempered by the fact that that they didn’t do it until the reservoirs had dropped to scary low levels.

But – crucially – everyone’s economy is doing fine. We’ve absorbed dramatic water use reductions without harming the basic structure and function of the Lower Colorado River Basin communities that depend on the river.

Upper Basin Data

Upper Basin water use

Working with Upper Basin data is trickier*. There’s a new dataset from Reclamation that uses remote sensing to estimate consumptive use from 1971 to 2023. There’s been a good deal of back-and-forth among Colorado River data nerds because of some confusing aspects of the data, which we hope to sort out soon to enable a more useful analysis. But the top line numbers tell a different but also ultimately an optimistic story.

The curve appears (see data nerd confusion caveat above) to show an upward trend since the 1970s with a huge amount of interannual variability. So we haven’t hit the conservation brakes yet, at least at the basin scale. But it also is clear that the Upper Basin is using far less than the 7.5 million acre feet tagged for us in the 1922 Colorado River Compact.

We Can Do This

It is easy to get tangled these days in the anger and finger pointing about who should cut, and by how much, about who has already cut and how and why, about questions that are both technical but more importantly deeply emotional about equity and fairness. We need to remember and learn from our successes.

* A Note on Data

The Lower Basin data from 1964 to the present is contained in the decree accounting reports, prepared by the Bureau of Reclamation since the Supreme Court ruling in the Arizona v. California case back in the 1960s. Prior to that, I have stitched in a dataset created by the numbers wizards at the Metropolitan Water District of Southern California.

The Upper Basin data comes from the new Upper Basin Consumptive Uses and Losses reports published by the Bureau of Reclamation. The were originally published in May, then a revised set was published in June, I’m cautious in my analysis and citation because there are still some things I don’t understand about them.