Water levels are sufficiently low that by July, the water level could drop below the intakes for the turbines. At the point, the dam becomes a big concrete plug in the river, and essentially no water can flow downstream. Many things happen at that point, none of them good.
If (the water level drops below the openings), the massive turbines that generate electricity for 4.5 million people would have to shut down — after nearly 60 years of use — or risk destruction from air bubbles. The only outlet for Colorado River water from the dam would then be a set of smaller, deeper and rarely used bypass tubes with a far more limited ability to pass water downstream to the Grand Canyon and the cities and farms in Arizona, Nevada and California.
Such an outcome — known as a “minimum power pool” — was once unfathomable here. Now, the federal government projects that day could come as soon as July.
Worse, officials warn, is the possibility of an even more catastrophic event. That is if the water level falls all the way to the lowest holes, so only small amounts could pass through the dam. Such a scenario — called “dead pool” — would transform Glen Canyon Dam from something that regulates an artery of national importance into a hulking concrete plug corking the Colorado River.