Lake Mead: drought empties lake and puts third intake into action

It had once been unthinkable.

But after years of severe drought, it has become inevitable: the original infrastructure that provides water to Las Vegas can no longer perform this crucial role because its intake valve stands above the surface of a shrinking Lake Mead, the largest artificial body of water in the United States.

Created by the Hoover Dam that blocks the flow of the Colorado River, the lake is the source of nearly 90 percent of southern Nevada’s water, but its surface level has reached a historic low, leaving the intake valve to draw air for the first time since it came into service in 1971.

“It’s official,” read an April 26 post on the Twitter feed of the Southern Nevada Water Authority (SNWA), the public entity responsible for providing water to millions of homes and businesses, including the casinos. “The top of Intake No. 1 is now visible.”

The photos accompanying the tweet show the grate of the uppermost of three intake valves facing the sky in the open air at 1,050 feet above sea level.

Although this moment might have been unthinkable years – if not decades – ago, the SNWA had nevertheless planned for it as the consequences of a warming climate became apparent.

As a result, it has been able to guarantee the supply of water from the lake by putting into service a new pumping station connected to a third intake valve that it had installed by Webuild. Nicknamed the “third straw”, this intake valve is situated at the bottom of the lake so as to ensure access to water at very low levels – levels that the lake’s surface has yet to reach. “Southern Nevada would have lost half of its capacity to bring water into our community (if it was not for this intake valve),” SNWA spokesman Bronson Mack told 12 News at 6, a news programme of a local affiliate of NBC. “We had the low lake level pumping station built …and ready to go (so) we were able to make a seamless transition.”

Completed in 2020, the pumping station can deliver up to 900 million gallons a day to the water treatment facilities. It draws the water from the intake valve through a four-kilometre-long tunnel that Webuild excavated under the lake, a record-breaking project. It saw the Italian civil engineering group overcome serious geological challenges, such as a theoretical water pressure above the heads of the workers steering the TBM of up to 15 bars – five times the usual one to three bars

In an interview with the Associated Press, Pat Mulroy, the former head of the SNWA, was more emphatic in describing the importance of the tunnel and intake valve. He said the entity would have lost its reason for being if it were not for this latest piece of infrastructure being able to guarantee access to water from the lake.  “Without the third intake, Southern Nevada would be shutting its doors,” he said. “That’s pretty obvious, since the first straw is out of the water.”

The SNWA has nevertheless managed to improve dramatically water conservation in the area, with consumption of water from the Colorado River down by 26% despite a population increase of nearly 50%, according to AP.