Global Warming Shreds Colorado River Compact As Glen Canyon Dam Nears End Of Hydropower Generation, Possible Deadpool

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Western water law is based on the prior appropriation doctrine, which gives the first entity to make “beneficial use” of water the right to keep on using that amount, even if that means that upstream “junior” users’ spigots will get shut off. By the early 1900s, a rapidly growing California was enthusiastically diverting the Colorado River, with huge irrigation districts gobbling up the senior water rights. Less-populous Colorado, Wyoming and Utah were forced to watch in increasing dismay as downstream users gained control over larger and larger shares of “their” river. To appease these headwaters states — and to garner their support for huge dams and other water projects on the lower river — the seven Colorado River Basin states hammered out the Colorado River Compact of 1922. It divided the states into an Upper Basin (Colorado, Wyoming, Utah and New Mexico) and a Lower Basin (Arizona, California and Nevada), with the dividing line at Lees Ferry, Arizona. It aimed to share the river’s water equally between them, giving each basin the exclusive use of 7.5 million acre-feet (MAF) of water per year.

The compact was far from perfect, but the concept of dividing the water equally generally held up, even if the reality didn’t always follow suit: The Upper Basin states have always used far less than their allotted amount (around 4 MAF), while the Lower Basin for years has consumed far more than its share (as much as 11 million MAF). That wasn’t a problem as long as the river had enough water to go around. But for the last 26 years, it hasn’t. Since around the turn of the century, warming temperatures and abnormally dry years have severely diminished the headwaters states’ snowpack, thereby shrinking the river. The annual “natural flow” at Lees Ferry, or the estimated amount of water the river would hold without any upstream diversions or human consumption, has been about 12 MAF on average since 2000, dropping below 6 MAF in 2002, or just over half of what the Lower Basin alone consumed at the time.

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Glen Canyon Dam and Lake Powell were supposed to make things easier by acting as an Upper Basin savings account that could be drawn from during dry years. But withdrawals have greatly exceeded deposits more often than not in recent decades, leaving Lake Powell at about one-third of its full storage capacity and bringing its surface level critically close to hitting minimum power pool, the point at which water can no longer be released through the hydroelectric turbines. When this happens — possibly as early as this fall, according to current federal forecasts — the dam will stop generating hydropower for Southwestern utilities. It will also force all releases to go through the outlets lower in the dam, which were not engineered for such sustained use. This would compromise the outlets and possibly the dam itself, and Bureau of Reclamation engineers have strongly warned against it, meaning that minimum power pool becomes the de facto deadpool.

If current climate trends continue, the only way to avoid reaching minimum power pool — aside from re-engineering the dam on a very short timeframe — is either to substantially increase flows into Lake Powell by curtailing Upper Basin water use and draining upstream reservoirs, or else significantly reduce releases from Glen Canyon Dam, forcing the Lower Basin — and the river through the Grand Canyon and its endangered native fish — to take major cuts.

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Exposed sand is seen on a northern side of a depleted Lake Powell in 2022, when historically low water levels led to closures of many popular recreational areas.

https://www.hcn.org/articles/the-colorado-river-rift-abides/