With just a few days left, it looks like Lake Mead will end 2014 down 19 feet, which would be the second biggest one-year drop of the “modern era” (the years since completion of Glen Canyon Dam upstream damped down the river’s ups and downs).

Lake Mead annual elevation change

With inflow largely regulated by Glen Canyon Dam and outflow largely determined by downstream use, Mead is plumbing. Climate plays a role here, but climate is heavily buffered by management decisions, so to understand what’s happening we need to look at institutions as much as the weather upstream.

Here are the key factors responsible for this year’s big drop:

• Less inflow than usual – a release of only 7.48 million acre feet from Lake Powell, rather than the usual 8.23 maf, in conformance with rules aimed at keeping levels in the two reservoirs balanced (background here)
• More outflow than usual – the Metropolitan Water District of Southern California has been cashing out some of the credits it had built up under the water banking scheme known as “Intentionally Created Surplus”, so water left in Mead in previous years as a hedge against drought is being used. Also, Mexico took out some of its banked water for last spring’s Minute 319 environmental pulse flow.

The previous pre-Glen Canyon Dam record for biggest one-year drop came in 2002, the last year in which California was allowed to use excess supplies before it had to curtail its usage to stay within its legal 4.4 million acre feet per year allocation.

All this is very orderly, and was expected, but that makes it no less unsettling if you’re Las Vegas or Arizona, looking at threats to long term water supply as Mead continues to drop.

Annie Snider left an excellent summary in our Christmas stocking of the state of play on the Colorado River. Lake Mead approaches the end of the Calendar year at elevation 1,087 feet above sea level, which is nearly 20 feet below last year at this time, as basin water managers scramble to build new institutional widgets aimed at propping up the lake’s level against looming shortage declarations. A deal signed this month takes the next step:

All sides agree that the deal, signed during the users’ conference here, won’t begin to solve the basin’s overarching problems. For one thing, users have only mapped out the path to 750,000 acre-feet of those reductions and are back-weighting the targets.

But it does suggest states are prepared to share the pain rather than battle over the remaining water in court.

It also follows an earlier agreement among water users in the Lower Basin this summer to conduct an $11 million conservation pilot program (Greenwire, Aug. 1).

“I think the significance of the system conservation agreement isn’t the volume of water; it isn’t the amount of money; it’s not even the parties who are there,” said John Entsminger, general manager of the Southern Nevada Water Authority.

“It’s the fact that for the first time on the river, we see major water users acting with the basin as a whole in mind and getting to that equilibrium and treating the system as the beneficiary rather than acting in their own local best interest and trying to put water in their bank accounts.”

Deputy Interior Secretary Mike Connor at the San Luis Bridge, March 28, 2014, watching the delta pulse flow

Michael Connor, the Interior Department’s second in command, who helmed Reclamation for more than four years, had tough words for his former colleagues in the basin.

If conditions worsen without consensus from the states on what to do, the federal government will have to step in, he told them at the conference.

“We need more urgency, more definitive commitments and more collaborative agreements,” he said. “Without proactive agreements, I fear the Colorado River Basin will return to its past and replicate what still goes on in many basins, which is conflict, litigation and gridlock.”

The entire piece, which seems to be out from behind the E&E paywall, is worth reading.

Even with the release of extra water from upstream reservoirs, Lake Mead outside Las Vegas is forecast to continue dropping in 2015 and into 2016, according to the U.S. Bureau of Reclamation’s latest monthly “24-Month Study” (pdf). At this point, as Lake Mead drifts deeper into record emptiness, it goes without saying that the big reservoir, the key to supply water for urban-suburban Nevada, Arizona and Southern California, along with the vast agricultural empires of the southwestern deserts, is heading into record territories.

Storage in Lakes Mead and Powell. Data source: USBR, graph by John Fleck

But for the record, the current forecast end-of-water-year level for Sept. 30, 2015, is 1,075.32 feet above sea level, which would be a record low for the end of a water year. Forecasting into 2016 should be taken as little more than median flow arm-waving, but for the record, 2016’s 1,070.64 would be, yup, another record. The forecasted drops would happen even with an anticipated release of surplus water from upstream, according to the Bureau’s analysis.

Faced with serious risks if dropping reservoir levels continue, the board of the Southern Nevada Water Authority last week voted in favor of spending another $650 million to build a new pumping plant capable of sucking water out of the reservoir at very low levels. Brett Walton reported the details:

The water authority’s two existing intakes will be exposed to desert air if the lake’s elevation drops below 1,000 feet above sea level. A third intake is currently under construction, but it would require a separate pumping station — like the one that the committee recommended — to operate at the lowest water levels, those below the 1,000-foot mark.

This is not Las Vegas expecting Lake Mead to drop that far, but rather buying some extremely expensive insurance against an enormous downside risk. To senior managers at SNWA, that risk has to appear in the realm of possibility. Since 1998, Mead’s elevation has dropped 133 feet. The 1,000-foot mark – the point at which a major U.S. city’s water supply is gone – is just another 81 feet away.

Source data