August 18, 2016

Drought like 2000-2006 could empty Lake Powell

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The “bathtub ring” in Lake Powell in the fall of 2014. Today, Powell is half-full, and an ongoing study suggests that the water levels in the lake could drop further during a severe drought. In order to keep the reservoir at operational levels, water users in the upper basin may need at to cut back on their water use by 300,000 to 1.5 million acre feet, depending on the severity of a drought.

The “bathtub ring” in Lake Powell in the fall of 2014. Today, Powell is half-full, and an ongoing study suggests that the water levels in the lake could drop further during a severe drought. In order to keep the reservoir at operational levels, water users in the upper basin may need at to cut back on their water use by 300,000 to 1.5 million acre feet, depending on the severity of a drought.

The “bathtub ring” in Lake Powell in the fall of 2014. Today, Powell is half-full, and an ongoing study suggests that the water levels in the lake could drop further during a severe drought. In order to keep the reservoir at operational levels, water users in the upper basin may need at to cut back on their water use by 300,000 to 1.5 million acre feet, depending on the severity of a drought.

Brent Gardner-Smith/Aspen Journalism

The “bathtub ring” in Lake Powell in the fall of 2014. Today, Powell is half-full, and an ongoing study suggests that the water levels in the lake could drop further during a severe drought. In order to keep the reservoir at operational levels, water users in the upper basin may need to cut back on their water use by 300,000 to 1.5 million acre-feet, depending on the severity of a drought.

GLENWOOD SPRINGS – From his office along the Colorado River in Glenwood Springs, Eric Kuhn can see the bottom of Lake Powell.

Kuhn, the general manager of the Colorado River District, has been working for months on a study asking if future droughts will drop water levels in Lake Powell so low that Glen Canyon Dam won’t be able to produce hydropower or release enough water to meet downstream demands.

“If we were to have another 2000-2006 drought, with where our starting conditions are today, we would basically empty Lake Powell,” Kuhn told the board of directors of the river district last month in an update on the study. “Now, we’re not going to do that. No one will allow Lake Powell to become empty.”

But today, Lake Powell is already half-full after one of the driest 15-year periods on record in the upper basin.

And Kuhn said no one wants to see a “compact call” triggered because Colorado, Wyoming, and Utah fail to deliver enough water through the Glen Canyon Dam to California and Arizona.

Such a call could prevent those who own post-1922 water rights from diverting water from the river. And that includes most of the transmountain diversions in Colorado.

“As long as you keep water in Powell above minimum power [pool], you’ll never have a compact problem,” Kuhn told the board.

So the $52,000 risk study Kuhn is working on with Hydros Consulting of Boulder is looking at how much water the upper basin states may have to send to keep Lake Powell above two key elevations.

The first important elevation is 3,525 feet, which triggers an operational guideline for how the reservoir is managed. The second is 3,490 feet, which is the “minimum power pool” below which hydropower cannot be produced at Glen Canyon Dam.

Failure to meet the operational guideline could require, ironically, that the upper basin states release even more water, depending on the level of Lake Mead, thus dropping the water level in Powell even faster toward minimum power pool.

And failure to stay above minimum power pool could prevent the eight turbines inside Glen Canyon Dam from producing about $120 million worth of electricity a year.

Buyers of that electricity include the cities of Aspen, Glenwood Springs, Delta, Gunnison, and Colorado Springs and utilities including Holy Cross Electric Association and Public Service Co. of Colorado.

Once minimum power pool is reached, it may also be difficult to physically move enough water through the dam’s infrastructure to meet the terms of the Colorado Compact.

On Saturday, Aug. 13, the surface of Lake Powell was at 3,617 feet and was 52 percent full.

The reservoir can hold 26,215,000 acre-feet of water at full elevation of 3,700 feet, according to the Bureau of Reclamation.

Although the past three years have yielded average precipitation in Colorado, the period from 2000 to 2015 brought the lowest flows over any 16-year period since Glen Canyon Dam was completed in 1963, according to Reclamation.

The current operational guidelines provide that the upper basin now needs to release 8.23 million acre-feet (maf) of water a year to the lower basin, which Kuhn said has made significant progress on reducing its water usage and has set ambitious goals to use even less.

But Kuhn, and many other regional water managers, still want to know what will happen if drought returns while Lake Powell is half-full, as it is today.

Upper Lake Powell in the fall of 2014.

Brent Gardner-Smith/Aspen Journalism

Upper Lake Powell in the fall of 2014.

What the study shows

The first phase of the study is now about three-quarters complete, Kuhn told the Colorado River District board in July.

The study’s methodology assumes only modest future water-supply development and then applies data from three different droughts in the last 25 years: the drought of 1988 to 1993, the drought of 2000 to 2006, and the drought of 2013 to 2014.

Kuhn said the model is showing, even with little new growth, that the upper basin can expect shortages ranging from 300,000 to 500,000 acre-feet in a relatively moderate drought.

In a severe drought Kuhn said the shortages could range from 500,000 to 1 million acre-feet, and in a drastic drought, some years could bring shortages of 1 million to 1.5 million acre-feet.

“This is what I call the ‘sticker shock,’” Kuhn said of those figures. “Basically, what we’re saying is if we were to have, under today’s conditions, one of these three droughts, we would go below our target of 3,525 feet.”

Another potential conclusion from the risk study is that any new transmountain diversion would only make it more likely that Powell would go below target levels.

“What we’re suggesting is that a new transmountain diversion could still divert, but only if there’s enough water in Lake Powell,” Kuhn told the board.

Kuhn put it another way during a presentation to the Gunnison River basin roundtable on Aug. 1.

“It is going to be a very high burden to show that a new transmountain diversion won’t impact system usages,” he said.

In fact, Kuhn said the model is showing that there has only been one year since 2000 that a new transmountain diversion wouldn’t have had a negative impact.

“So are you going to build a multi-billion dollar project that is going to operate once in 20 years?” Kuhn said in Gunnison. “I don’t think so.”

That’s if the operator of such a system agrees not to divert in years that would hurt levels in Lake Powell, which is not a legal obligation under Colorado water law.

If there was no agreement to limit diversions, Kuhn said a new transmountain diversion that lowers levels in Lake Powell would mean that other water users in Colorado would have to cut back on their water use, and do so more frequently, perhaps as much as half of the years in the study’s 25-year forecast period.

“That’s a fairly important message,” Kuhn told the River District board.

And, he said, that’s without the increasing heat of climate change factored in.

“I haven’t shown the climate change hydrology because it just scares everybody,” Kuhn said. “This is the recent hydrology.”

A graphic illustrating the findings of the "risk study" about levels in Lake Powell.

Source: Metro Roundtable

A graphic illustrating the findings of the “risk study” about levels in Lake Powell.

Several options

Kuhn says water users in the upper basin have three main levers they can pull to keep Powell operational.

One is to continue cloud seeding 
efforts, which are underway but only marginally helpful.

A second is to release water from three big upstream reservoirs: Flaming Gorge Reservoir on the Green River; Navajo Reservoir on the San Juan River; and Blue Mesa Reservoir on the Gunnison River.

Those reservoirs “have the same purpose as Powell, which is to allow the upper basin to manage for the upper basin’s obligations,” Kuhn said.

Those three reservoirs can together release about 2 maf if needed, but they would be hard pressed to do that several years in a row, Kuhn said.

A third lever is to pay ranchers and farmers to fallow fields and leave the water in the river to run downstream to Lake Powell, often called “water banking” or “demand management.”

Demand management means using less water, or curtailing the amount of water put to a consumptive use.

In a severe multi-year drought, the system will need the releases from the three big reservoirs above Lake Powell and a lot of demand management, Kuhn said.

So what’s the tolerance for the risk that water levels will drop far enough in Powell to make significant levels of “demand management” necessary?

Kuhn said if we assumed a severe drought comes only twice in a 50-year period, we might just say, “we can live with it.”

And if drastic droughts occur three or four times in a 50-year period, Kuhn said, “we can probably, with the tools that we have and can reasonably implement, be able to address” the challenge.

But if there is a severe drought like 2000-to-2006, he said, “it will take the system beyond what we can do and then you’re going to have some big problems. That’s the message that the study suggests. The other message is, future demand matters.”

Editor’s note: Aspen Journalism and the Aspen Daily News are collaborating on coverage of rivers and water. The Daily News published this story on Monday, August 15, 2016.

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