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Lake Mead, the vital Colorado River reservoir outside Las Vegas, hit a record low Sunday, The New York Times reports. The reservoir is the lowest it’s been since being filled in the late 1930s, just 39 percent full.

Millions of people — San Diegans included — rely on the reservoir’s water. So what does its drop mean here?

In the short term, nothing. It doesn’t have any impact on San Diego’s supply even though we relied on the river for 61 percent of our water in 2009. But it does send a bad signal that the river supplying the Southwest’s lifeblood is continuing to face pressure — a pressure that scientists say is growing as the climate warms.

If the lake continues dropping, it will first cause problems for cities in Arizona and Nevada before San Diego. Those states hold lower-priority rights to Colorado River water than California does.

Right now, Lake Mead is filled to 1,083 feet above sea level. If it drops to 1,075 feet, the U.S. Bureau of Reclamation will declare a shortage and implement cuts the seven Colorado River states agreed to in 2007. Those cuts hit Arizona and Nevada — not California.

The cuts would stay in place until the reservoir hits 1,025 feet. Then the shortage is renegotiated and becomes an issue that could affect California.

I asked Maureen Stapleton, the San Diego County Water Authority’s general manager, about that trigger in a 2009 question-and-answer. She responded:

Ultimately, you’re right, California gets pulled into those renegotiations when you’re talking about extremely severe drought. That’s where you get to issues of health and safety. You’re not talking about increasing your economy. You’re talking about moving to a fairly severe level. Of course it’s a concern. It’s something we hope we never have to deal with, but we have to plan for these things. We think we have a good agreement among states to have a thoughtful process to address those shortages if they come.

Thoughtful means non-litigious?

You can never be guaranteed that you won’t have an agency or state take something to court. But if you look at the history over the last 10 years you have an excellent track record of the seven basin states working together to find something fair and equitable.

The Bureau of Reclamation expects those negotiations will be difficult. “Certainly, there will be some views in the basin that if we’re at that position in the reservoir, it’ll have to be sharing of the pain among the shareholders,” Terry Fulp, a U.S. Bureau of Reclamation official, told me last year. “There will be disagreement in your state — that’s why it won’t be an easy negotiation.”

So will Lake Mead hit 1,025 feet anytime soon?

Scientists say it will drop in the long-term as climate change cuts the amount of precipitation in the West. Water agencies are preparing for Lake Mead to continue falling. The Southern Nevada Water Authority, which supplies Las Vegas, is spending $817 million to build new intake pumps in Lake Mead.

The authority currently has two pumps drawing water out of the reservoir. The first goes inoperable when Lake Mead hits 1,050 feet. The second is lost at 1,000 feet. The new intake can draw until the reservoir hits 900 feet.

In the last decade, the reservoir’s peak has dropped as much as 24 feet in a year. But a shortage declaration could be avoided in the near term, the Times’ story notes:

The Bureau of Reclamation’s current plan for the coming year calls for an increase of up to 40 percent in the amount of water delivered to Lake Mead from Lake Powell, the big reservoir upstream, a step that could help equalize the amount of water in each reservoir and possibly avoid triggering the shortage declaration.

Please contact Rob Davis directly at rob.davis@voiceofsandiego.org or 619.325.0529 and follow him on Twitter: twitter.com/robwdavis.

Rob Davis

Rob Davis was formerly a senior reporter for Voice of San Diego.

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