Question of the Day - 30 June 2021

The Hoover Dam spillways only come into play when the lake is completely full and excess water needs to be released into the Colorado River, which last happened in 1983. Based on recent history, it will be a cold (and wet) day in you know where when that happens again.

What you seem to be asking about, however, are the penstocks. These are the 30-foot pipes that regulate normal river flow and power Hoover Dam’s hydroelectric plant. Those would become unusable if the surface level of Lake Mead ever dropped as low as 895 feet above sea level, at which point the largest reservoir in North America would become a dead pool.

Even then, however, Las Vegas would still be able to slake its thirst from the so-called “third straw,” a giant intake pipe that goes into the lake at the 875-foot level.

This doesn't mean that Vegas is in the clear when it comes to water-use restrictions. As of this writing (mid-June), Lake Mead is at 1,070 feet of water or about 35 percent full. If the reservoir doesn't rise above 1,075 feet by August, a determination will be made by the federal Bureau of Reclamation whereby southern Nevada’s current allocation of water (300,000 acre feet per year) is cut by 13,000 feet. Since Las Vegas gets by on 250,000 acre feet per year, the margin for error is definitely shrinking. 

Says Southern Nevada Water Authority spokesman Bronson Mack, “This is why conservation is so important.”

Even more severe cuts could be on their way if Lake Mead doesn’t meet “Tier 2” levels (1,030 feet) by 2023. “We need three to four consecutive years of above-average inflow, snowpack runoff and inflow into Lake Powell, to refill these reservoirs,” says one federal official. Or as John Wesley Powell prophesied in 1893, “I tell you, gentlemen, you are piling up a heritage of conflict and litigation over water rights, for there is not sufficient water to supply these lands.”

Lake Mead has not been this low since 1935, when then-Boulder Dam was brand new. Twenty-plus years of sustained drought have taken their toll, lowering Lake Mead’s surface by 140 feet. The reservoir is heavily affected by what happens upstream in Lake Powell, whose inflow is estimated to be just 26 percent of its long-term average. Nor is the Rocky Mountain snowpack much help: The Bureau of Reclamation’s Mike Bernardo told the Arizona Republic that the ground is so water-starved that “when the snowmelt starts to run off, it just gets sucked up into the ground like a sponge.”

It’s not just Nevada. Arizona and California are facing cutbacks in their water draw, and Mexico has already made some. A Hoover Dam that once threw off 2,074 megawatts of electrical power now generates only 1,567 megawatts (enough for a quarter of a million homes). That number goes to zero if Lake Mead hits the dead-pool level and Hoover Dam’s turbines cease to spin for lack of water. Warns Bernardo, “The way the reservoir is shaped, we call it a teacup, but it's more like a martini glass. And the lower the elevation goes, the faster the rate of decline.”

This has inspired some alarm, such as in the book Cadillac Desert, whose author Marc Reisner wrote in 1986 that Colorado River-dependent Southwesterners “will probably find themselves facing chronic shortages, if not some kind of catastrophe.”

More circumspectly, Eric Kuhn and John Fleck trace the problem back over a century. True, they write, climate change has played a role. But the present crises “are the inevitable result of critical decisions made by water managers and politicians who ignored the science” back in 1920s, penciling in allocations of Colorado River water so generous it would put the tributary into a deficit. 

This “set in motion decades of decisions that would end in the overuse seen today.” The two authors are not completely pessimistic, however, adding, “The river’s future is not all dark. Innovation, cooperation, and an expanded reliance on science are now the foundation for basin-wide solutions.”

Those solutions appear to be in process, although a fair amount of sacrifice is all but inevitable along the stream toward optimism.