Transbasin Diversions in Colorado: How is this Even Possible?

This is the second post in a six-part series fulfilling requirements of ENVS 5000: Science, Policy and the Environment, at the University of Colorado Boulder.

If you read my post on the history and climatology driving transbasin diversions in Colorado, a few questions may have come to mind. For my part, when I first discovered that we dig enormous tunnels to take 600,000 acre-feet of water out of the perfectly good rivers it starts in and move it into other rivers that were perfectly good without it, I asked “How is this even possible?”

The answer to that question is twofold: there is a legal basis, and there is an physical basis, for how we undertake these highly unnatural projects. This post will first look at the legal framework underlying transbasin diversions in Colorado, and then we’ll look at the works of engineering that make it all possible, before I start looking at transbasin diversions’ impact on society in later posts.

Colorado Water Law and the Irrelevance of Geography

The foundational principle of Colorado water law, and to varying degrees water law in other Western states, is the principle of prior appropriation. In its inevitably over-simplified form, the principle states “First in Time, First in Right,” or, that entities that use a certain water source first have the first right to use it in times of shortage. In other words, if I have been diverting water from Generic Creek since 1870, and you have been diverting water from Generic Creek since 1890, only when I have received all of the water I usually get do you get any at all. In dry years, your diversions will be turned off (“curtailed”) before mine. The technical term is that my rights are senior rights, and yours are junior rights. My water rights trump yours no matter where you and I are located on (or off) the creek. This last point is essential, as we shall soon see.

This “Colorado Doctrine” differs fundamentally- though not necessarily irreconcilably- from the system of water rights present in the Eastern United States. This system is known as riparian rights, and provides the right to use water flowing across your own land, within restrictions that vary by state. The essential point is that water users must own land adjacent to a stream in order to divert from it. No such requirement exists in Colorado; the principle of absolute prior appropriation was settled in Coffin v Left Hand Ditch Co in 1882.

This point has extended to diversions under, over and through mountain ranges. Many Colorado water users on the wet Western Slope have called it sensible to allow appropriation to lands not immediately on river banks (otherwise, non-riparian lands would be essentially useless for agriculture and development, and all water would be in the hands of whatever monopoly happened to buy up the creek banks) but ludicrous to extend such a principle to diversions under the Continental Divide.

In 1939, the Colorado Supreme Court emphatically disagreed, stating that “geographical advantage does not apply to beneficial use,” in City and County of Denver v Sheriff et. al. The implication was well put by historian James Cox, who wrote “An appropriator on the eastern slope has just as much right to a priority on western slope water as a western slope appropriator to a priority on eastern slope water” (Cox, Metropolitan Water Supply: the Denver Experience, 1967, pp 68-71). Of course, this legal equivalence has not manifested itself in reality, to the benefit of the Front Range. To sum up: the right to use water in Colorado belongs to whomever can first appropriate it for beneficial use, regardless of their position on a stream, off the stream, or even outside of the entire river basin. This allows thirsty east slope interests to operate the many tunnels and ditches across basins that I described in my previous post in this series.

But there is another foundation to transbasin diversions: those tunnels, ditches and reservoirs themselves are massive, costly, and draw water a long way both horizontally and vertically. Surely, you might think, there was an easier way to find and store all that water without tunneling through miles and miles of granite…

Water is Heavy

This simple fact actually explains a lot about transbasin diversions. One gallon of water weighs a little more than eight pounds. Scale that up to, say, one acre-foot, roughly the amount of water used by two domestic households in a year: it weighs about 2.7 million pounds. Put another way, all the water in all of Denver’s reservoirs, if they were full, weighs about twice as much as the total weight of every human on earth, approximately 1.87 trillion pounds. This means that the cost of pumping water up a hill is pretty high, whereas the cost of letting it run downhill is zero. The implication is that finding and storing water high in elevation is advantageous. As we saw in the first post in this series, the most water in Colorado is found in high-altitude snowpack west of the Divide. Digging a tunnel at high elevation from west to east is a major investment, but suppose that the alternative was to continually pump water from below Denver on the South Platte River back up to the city (Denver and other cities actually do this on a small scale in addition to their transbasin diversions). On a large scale, the scale of hundreds of thousands of acre-feet per year, this would be enormously costly. The cost of tunneling, by contrast, starts to be recouped immediately.

The two largest Front Range water providers, Denver Water and Northern Water, operate largely pump-free systems. In fact, both systems generate revenue by using the weight of water tumbling down the east slope of the Rockies to power hydroelectric turbines. Water leaving the Adams Tunnel from the headwaters of the Colorado River to the Big Thompson River watershed falls 2900 vertical feet on its way down and east, passing through the turbines of six power plants that generate enough power for 68,000 homes. One of those six plants provides revenue directly to Northern Water, the rest benefit the federal government, which built the Adams Tunnel.

A cross-section of the Colorado-Big Thompson Project

A simplified cross-section of the Colorado-Big Thompson Project. Water exiting the Adams Tunnel falls 2900 vertical feet, through four power plants, before being pumped into Carter Lake. Image courtesy Northern Water.

The Colorado-Big Thompson Project cost $162 million in 1944 dollars, very expensive (about $2 billion today), but a bargain for supplemental irrigation on 640,000 acres of Northeastern Colorado for the last sixty-nine years. I’ll cover economic impacts in a later post. The Windy Gap Project, which uses C-BT infrastructure, cost $120 million (about $300 million today) to provide water for nine cities and two water districts on the Northern Front Range. But those costs are upfront, and are recouped by water deliveries and power sales for every year of the projects’ operation.

In summary: water is heavy, and that means the easiest way to move it is to allow it to flow downhill, including through tunnels, canals, and pipelines. The easy water for Front Range cities and farmers to get at, then, was not the small amount of water directly above and below them on their own rivers- much of which had already been appropriated anyway- but, remarkably, the vast amounts of water reachable through one or two dozen miles of tunnel, on the western slope of the Continental Divide. Cities had every right to that water if they could develop it first, and the foresight of Front Range leaders and the skill of Front Range engineers means that so much precious water no longer flows west from the Colorado River headwaters, it flows east.


2 thoughts on “Transbasin Diversions in Colorado: How is this Even Possible?

  1. Nicely written amigo. I knew water was heavy, but to weigh in in the trillions verges on absurdity. I suppose in relative scales–say, the weight of the rocks blasted and dug through to create the tunnel systems to transport said water–it’s probably comparable, but numbers like that are difficult to conceptualize. Something like deep time, i.e. billions of years when discussing the evolution of life in Earth’s history, is discussable, but possibly an insurmountable challenge for us to relate to in much of a meaningful way–so maybe something similar holds for such vast weights, or “deep weight” if we can call it that. Even the weight of 600,000 acre-feet is hard to imagine in meaningful terms. Nevertheless–and here’s my rub (it’s a nit-picky point)–inconceivable or relationally meaningless in every day life, to say that the feat of such water weight’s transport or the projects undertaken to enable its transport are “unnatural,” strictly speaking, is either rhetorical or moral/aesthetic. These projects–indeed everything humans do–are “natural” and part of the natural order of things. Humans are part of the natural condition of the planet, and in turn, so too are our alterations of its functioning. Beavers build dams, ant life ultimately consumes more NPP than humanity, and humans in the American West reroute huge amounts of water. Moreover these projects–especially these projects–are distinctly natural in that they use natural physical laws to human advantage. To say they are unnatural implies a supernatural status, and we are certain not that. Unnaturalness seems to me a value-laden rhetorical tool, which is okay, but it’s interesting to note (I’m guilty of this too, no doubt). However, if it’s not rhetorical, then–as Sagoff points out in a few places in “Price, Principle, and the Environment”–it’s moral/aesthetic in the sense of an elevated human obligation of non-interference over and above the rest of the “natural” world, closer to, perhaps, the divine (no pun intended) or to preserve certain aesthetics out in the world, even at cost to ourselves.

    • Good points all around, my friend. I think a farmer on the West Slope would use it in the rhetorical sense to motivate opposition to the tunnels- but of course his irrigation practices are profoundly “unnatural” as well, and the question would be if there’s a morally relevant difference between the two (I’ve consistently argued that there is not). I wonder if people’s perceptions of water projects are bound up with the moral/aesthetic sense, though, on some level like this: Denver is the 300-pound gorilla in the room, throwing its weight around, taking all the water that (nature/God) clearly placed on our side of the mountains. In that sense, while still a tool of rhetoric, it seems to display a concern for not “remaking” the earth to suit our own purposes.

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