#Runoff in #ColoradoRiver basin likely below-average, @usbr official warns — @AspenJournalism #snowpack #COriver #aridification #cwcac2019

A big beach on the banks of the Green River in September 2018, one of the lowest months on record for inflow into Lake Powell. Runoff is 2019 is expected to be better than 2018, but still below average due to dry soil conditions in the area drained by the Green and Colorado river systems. Photo: Brent Gardner-Smith/Aspen Journalism

From Aspen Journalism (Brent Gardner-Smith):

The regional director of the Upper Colorado River Basin for the Bureau of Reclamation told water managers and users last week to expect below-average runoff this year, despite encouraging snowfall this winter.

Brent Rhees — who oversees the federal reservoirs in the upper basin for the Bureau of Reclamation, including Lake Powell, Flaming Gorge and Blue Mesa — said that although this winter’s snowfall, or “snow water equivalent,” in the upper basin above Lake Powell was now above average (109 percent on Feb. 7) the parched ground left in the wake of a hot, dry 2018 likely would soak up a lot of the resultant moisture in the spring.

As such, this year’s runoff is not expected to reach the average level, although storms in February and March could push it up to the 80 percent range.

“What we’re suffering from is last year’s dry year,” Rhees told the members of the Colorado Water Congress on Feb. 1. “And so, the runoff that is forecast is not that great. Last year, you all remember, it was the third-lowest on record inflow into Lake Powell. So, it’s not looking really good.”

Since Rhees’ remarks, it has been snowing a lot in Colorado, and the snowpack in the Roaring Fork River basin was at 115 percent of average on Feb. 6. But, again, Rhees was looking at future runoff over a thirsty landscape.

The inflow into Lake Powell during water year 2018 (Oct. 1 to Sept. 30) totaled about 4.5 million acre-feet, or MAF, while about 9 MAF was released from Glen Canyon Dam to run down the Colorado River and into Lake Mead, Rhees said.

“So, the math is pretty simple, isn’t it?” Rhees said. “More went out than came in. And so, we saw a significant drop in reservoir elevation.”

As of Jan. 1, the Bureau of Reclamation forecast that 6.98 MAF, or 64 percent of average, would most likely flow into Lake Powell, but releases from Lake Powell are expected to be about 8.6 MAF.

“We’re going to release a little bit more than comes in, likely this year,” Rhees said.

That means Lake Powell is expected to continue to shrink in 2019.

On Feb. 3, the elevation of the reservoir, as measured against the upstream face of Glen Canyon Dam, was 3,575 feet above sea level, or 39 percent full, and held 9.6 MAF.

A diagram showing the intake structures on the upstream face of the Glen Canyon Dam, which forms Lake Powell.

Three efforts

The first ongoing effort to bolster water levels in Lake Powell is weather modification in the form of cloud seeding.

Rhees said the federal government’s position on funding cloud seeding has moved from funding only research to funding active operations, too.

“That’s good news from my perspective,” he said.

The second effort is “drought-response operations,” which will begin if Lake Powell drops to the triggering elevation of 3,525 feet, or 35 feet above minimum power pool (which it is not yet forecasted to do in either 2019 or 2020).

But should the reservoir hit 3,525 feet, the drought-response operations will entail releasing up to 2 MAF of water from federal reservoirs in the upper basin, primarily from Flaming Gorge Reservoir on the Green River, which can hold 3.7 MAF; Blue Mesa Reservoir on the Gunnison River, which can hold 829,500 acre-feet; and Navajo Reservoir on the San Juan River, which can hold 1.69 MAF.

Rhees said Flaming Gorge is “the one that can have the biggest impact, (but) all (federal) reservoirs can participate in propping up that minimum power pool of 3,490 (feet).”

He also said the releases from the reservoirs would be “indiscernible” to river users and the water would not come down the river in a big wave of water, as some might imagine.

“You won’t know, if you are on the river, that it’s even happening,” he said.

The third effort to add more water to the river system is “demand management,” or a purposeful reduction in the amount of water diverted from rivers and put to a consumptive use, such as growing a crop or a lawn.

Voluntary demand-management programs are now being investigated in Colorado, Utah and Wyoming, and the water saved by irrigators fallowing fields — for money — is to be stored in a new regulatory pool of up to 500,000 acre-feet in Lake Powell.

Editor’s note: Aspen Journalism covers rivers and water in collaboration with The Aspen Times and other Swift Communications newspapers. The Times published this story on Thursday, Feb. 7, 2018.

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