Click the link to read the article on the Sibley’s Rivers website (George Sibley):

Yes, that diagram again. I was chastised by readers last week for using it – partly for the ‘Antique’ in the diagram’s title, but also for not adequately explaining what the diagram shows. I apologize for the latter. These posts tend to run long and demand a lot more of readers than the 15-second attention span for which Americans are derided. But just to keep them down to a couple thousand words or so, I find myself having to go through some things too quickly in order to get to whatever point I was aiming for. Brevity unfortunately is not the soul of my wit.

But having a sense of the structure and infrastructure of our big dams is critical to understanding what is going on along the Colorado River these days, where it is easy to confuse the river itself (which is experiencing chronic low flows but is not ‘drying up’) with the ‘river management system’ (which really could dry up critical stretches of the river under the current management regime). The ‘river management system’ is the integrated set of physical structures along the river for storing the river’s water and distributing it to users – and the operating systems whereby those structures are managed.

The ‘Supplemental Environmental Impact Study’ the Bureau of Reclamation is doing now is basically an analysis of its own operating systems for the big structures on the Colorado River, and how those systems might be radically changed with an equitable distribution of impacts on humans – systems that could have been changed gradually over the past several decades, the past century even, to reflect undeniable evolving realities, both natural and cultural, but now must be done with radical surgery – the call for an almost-immediate reduction in Lower Basin uses of two million acre-feet.

This might be what life in the Anthropocene will mostly be on many fronts: learning how to live well enough with the world we have imposed on the world we found here. A recreated world where some cultural works were done naively and maybe profligately, under assumptions now needing correction – which one might hope we will learn to begin sooner rather than later – or too late, period.

So it is fitting to look critically at what we’ve done along the ‘First River of the Anthropocene’ – trying not to fall into hypocritical analysis, gnawing on the hands that feed us. And on that spectrum of critical analysis, I do need to explain, if not defend, using a diagram that calls the ‘plumbing’ of a major element in the management system we’ve imposed on the Colorado River ‘antique.’

I will say first that I do not necessarily think of ‘antique’ as a derogatory term (although that was probably intended by the creators of this diagram). If an automobile is fifty years old and still running, it qualifies for an ‘antique’ license plate; that’s cool, an achievement for those who kept the car functional. I think of the word as more descriptive than judgmental: an antique is an artifact whose time is past but which reflects that time, something old but with an element of class, something that summons memories of a previous time, a time we want to remember but not necessarily carry forward.

So, being more than 50 years old at this point – is Glen Canyon Dam an antique? We can start with an examination of its ‘plumbing,’ which says something about its life and times. (My doctor uses colonoscopies for a similar analysis.)

One piece of plumbing not shown on the diagram is the dam’s spillways – two huge ‘drains’ up at the 3,700-foot elevation, near the dam’s 3,715-foot crest (for context, 583 feet above the original streambed). The purpose of the spillways is to keep the reservoir from filling to the point where it would go over the crest. Glen Canyon’s spillways have only been used once, in 1983, when a very wet May and hot June caught the dam managers unaware, with the reservoir already too full to perform its flood-control function. The spillways proved to be not up to the task of getting the flood waters past the dam; the water pouring down them caused a cavitation problem – a million tiny ‘air-hammers’ beating on the concrete with enough cumulative force to break it up. The managers knew there was a problem when large chunks of concrete, then sandstone, started washing out the bottom of the spillway outlets. That threatened the integrity of the dam itself; it was necessary to close off the spillways, lining the top of them with sheets of plywood four feet high and praying that the water would stop rising before it topped the plywood. It did stop in time, and the dam was saved. The spillways were rebuilt, hopefully resolving the cavitation problem, and have not been used since – and at this point, given the projections about climate change, it is hard to imagine the reservoir ever being that full again. The spillways alone might qualify as ‘antiques,’ built for a river that needed them (once) but may no longer exist. (Oh great river gods, please make me eat my words!)

For the dam managers, however, to ‘spill’ water at all is a mark of bad management; their ideal is for every gallon of water contained by the dam to be released through openings 210 feet below the spillways, at hydropower generation level, the 3,490-foot elevation (see diagram). Those openings into the dam drop the water through pentstocks a couple hundred vertical feet to turbines in generators the size of small houses; on its way to its designated use downstream, the water generates electricity. The higher the reservoir level, the more pressure the water’s weight exerts in pushing the water through the turbines; with the reservoir at high levels, the Glen Canyon generators can produce annually up to five billion kilowatt-hours of electricity. In 2022, however, with the reservoir level only around 35 feet above the pentstock inlets, it only produced 2.6 kilowatt-hours. (Bureau figures)

The Bureau’s semi-panicky call in 2022 for massive reductions in use basin-wide was based on projections forward of another couple water years like the 2020-22 period; under the current river management regime, the level of the reservoir would have dropped below the level of the pentstock intakes in a couple years, and year-round power generation would have been impossible.

Even if that were to happen, however, it would still be possible to move water downstream from Powell Reservoir, through river outlet works with intakes 120 feet lower down in the dam, at the 3,370-foot elevation. The river outlets there are four big pipes, each eight feet in diameter, with a total flow capacity of 15,000 cubic feet per second – when there’s a lot of water in the reservoir to push water through them. If the water pressure stayed at that level, and all four tubes worked 24/7/365, it would be possible to move around 10 million acre-feet (maf) through the dam annually and down to Mead Reservoir, roughly the amount the Bureau has been releasing from Mead for Lower Basin and Mexican use – plus the system losses for which no one has wanted to claim responsibility.

That 10 maf leaving the system at the lower end obviously becomes problematic if only 6-8 maf are flowing into the system at the upper end, as has been the recent situation. For one thing, the Bureau is not sure the outlet works can stand that kind of constant use; they are getting old, and may not have been built for constant use anyway. So if the Bureau were able to keep only three tubes running all the time, with one in maintenance mode, the amount of water that could be moved at full pressure would drop to just about the Upper Basin’s Colorado River Compact commitment – 7.5 maf plus the Upper Basin’s share of the Mexican obligation (750,000 af).

But as the water level in the reservoir dropped closer to the outlet works intakes – 6-7 maf inflow minus 8 maf outflow equals a storage decrease of 1-2 maf/year – the water pressure through the tubes would also drop, and below the 3,430-foot elevation, it would no longer be possible to push the full Upper Basin commitment to the Lower Basin and Mexico through the tubes.

Worst case – if the reservoir level dropped below the 3,370-foot elevation, it would no longer be possible to move any water at all past the dam, even though there would still be just under two million acre-feet left in storage – the ‘dead pool.’ At that point, the Lower Basin states would either have to do something completely nonconstructive like sue somebody (Upper Basin states? Interior Department? The Bureau?), or argue about which states should pay how much to Upper Basin water users to let their water (not federally controlled) flow to Powell to try to raise the level back above the 3,370-foot elevation. And most of the Upper Basin water rights junior to the Compact are not a bunch of rugged individualist farmers and ranchers; they are the big transmountain diverters – Colorado’s Front Range cities, the Santa Fe-Albuquerque corridor, the Salt Lake basin, who are already ‘lawyered up.’

The ramshackle ‘Law of the River,’ grounded in appropriation law and followed to the letter of the laws, would have nothing to offer to relieve that situation; it is easier to imagine Paolo Bacigalupi’s ‘Water Knife’ war commencing.

That is an overview of Glen Canyon Dam’s plumbing – pretty standard for a big 20^th century dam, designed to operate optimally when the reservoir is more than two-thirds full and able to maintain a full power head in releasing water through the turbines for – oh yeah, not primarily power generation, but the dam’s main job of providing dependable water for agricultural and domestic users downstream. A specific warning in the Colorado River Compact (IV(b)).

Now to the question: is Glen Canyon Dam an ‘antique’? I think, at this point, given the prognostications for the future of the regional water supply, we could truly say that the dam was built for a different era, a different river – some of which river may have existed only in the minds of the dam builders. The ‘Hassayampa romance,’ carried along, like Deacon Holmes’ wonderful one-hoss shay, ‘for a century to the day’ – the day the Bureau finally abandoned its paper surplus calculations and called a shortage.

In addition to working on new river operation protocols, the Bureau now has a team working on ways to possibly modify the dam, undoubtedly at considerable cost, maybe enlarging the outlet works, maybe generating some flow of electricity through openings lower in the dam, and maybe constructing tunnels to bypass the dam entirely, leaving Mead Reservoir as the river’s major storage.

The latter concept could relieve a problem that the dam has created for ‘today’s river’ through the Grand Canyon: the beaches and sandbars that are essential as night stops for the billion-dollar Grand Canyon recreational boating industry are eroding away, with no replacement sand and silt getting past the dam. This is being dealt with now by occasional staged ‘floods’ like the one just recently: pouring 200,000-plus acre feet of water over 2-3 days down through the Grand Canyon to stir up sediment that has slumped from the beaches down into the riverbed, in hopes that it will be redeposited on a beach downstream. Ultimately this mostly just escalates the passage downstream of all the beach material with only irregular and inadequate deposits of new material from side streams. That this ultimate losing effort was done in April 2023, with Powell Reservoir under 30 percent full, but anticipating a runoff that might get it all the way up to half-full or only half-empty, depending on your psychological inclination…. There’s an underlying desperation there that is not goimng to let us look back on this period with any pleasant sense of nostalgia. But we might look back on antiquities like Glen Canyon Dam as a reminder of the consequences of operating on assumptions and standards not fully grounded in demonstrable reality.

A problem with this analysis, however, is that for better or worse, it evaluates Glen Canyon Dam out of context. To really understand why we have Glen Canyon Dam at all, it is necessary to see our river’s physical structures in the larger context of the less visible political and legal infrastructure that led us to pile five million yards of concrete (with internal plumbing) in the river’s path in that particular place. That is another great story in the evolution of this mixed bag we call America. Up next in a couple weeks; stay tuned.