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A Colorado River glossary: Jargon explained
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A Colorado River glossary: Jargon explained

  • Lake Powell at sunrise.
    Brigitte Werner/PixabayLake Powell at sunrise.

These are perilous times in the troubled Colorado River basin, a make-or-break moment in which some of the nation’s fastest growing and most arid states begin to reckon with a drier future.

The next month will be especially intense.

Several weeks ago, in the face of another paltry runoff forecast, the Bureau of Reclamation issued an ultimatum to the basin’s seven states: to keep key reservoirs Mead and Powell from crashing, develop a plan by mid-August to conserve 2 million to 4 million acre-feet of water in the next year — or the Bureau would make the cuts as it sees fit.

Those are astounding figures. On the higher end, that amount of conservation is one-third of the Colorado’s recent annual flow. It’s also about as much water as California is allocated from the river.

The plan’s due date coincides with the publication of a highly anticipated and consequential Bureau of Reclamation report. The so-called 24-month study — tentatively scheduled for August 15 — determines how much water Mead and Powell will release in 2023. It also determines how much water Arizona, California, Nevada, and Mexico, which shares the basin, will be required to forgo next year.

Discussions about the Colorado River can resemble a doctor’s visit: filled with technical jargon, unfamiliar acronyms, and the anxiety that comes from incomplete understanding.

This glossary is an attempt to demystify the language. It outlines key terms and phrases and their context — so as the basin chatter heats up you can keep your DCP and DROA actions straight and know who’s taking ICS.

Upper/lower Basin

In terms of law and management, the Colorado River basin is split in two.

The upper basin states are Colorado, New Mexico, Utah, and Wyoming (plus a tiny sliver of Arizona that is essentially Navajo Nation land). The lower basin is Arizona, California, and Nevada. Separate agreements bring Mexico into the mix.

Dead pool

All reservoirs have limits. Dead pool, an evocative term, is the ultimate limit. It’s the point at which water can no longer be released downstream because a reservoir falls below its lowest outlet pipe.

For Lake Mead, dead pool is elevation 895 feet. For Powell, 3,370 feet.

Today, the reservoirs are at 1,040 feet and 3,536 feet, both at about 27 percent of full capacity.

Even at dead pool some water might remain in the reservoir, but it can’t flow without extraordinary assistance. Las Vegas, in a proactive step, invested $1.3 billion in an intake pipe and low-elevation pumping station that allow the city to draw water from Mead when the reservoir is at dead pool.

Minimum power pool

A second limit for a reservoir, minimum power pool refers to the water level required to generate hydropower.

This is the level near the location of the penstocks. Penstocks are the pipes that move water from the reservoir to the power-generating turbines.

For Powell, minimum power pool is 3,490 feet. The Bureau of Reclamation is attempting to prevent Powell from dropping below this level.

For Mead, minimum power pool is 950 feet.

Operational neutrality

The Bureau of Reclamation took an unprecedented step in May, announcing that it would reduce releases from Powell to Mead this year by 480,000 acre-feet.

The move helped keep Powell above minimum power pool. But it came with a worrisome side effect for the lower basin states: less water sent downstream to Mead.

They have good reason to worry. Depriving Mead of that water meant a greater likelihood of a more severe shortage tier for the lower basin next year. Mead, in fact, has plummeted this year, falling 21 feet since April.

The states and the feds agreed to a work-around. To maintain “operational neutrality” the shortage tiers for next year would be calculated as if the 480,000 acre-feet had been released to Mead. In other words, on paper the water is in Mead…but in reality it sits upstream in Powell.

Every bit of water matters these days. Currently one foot of elevation change in Mead is equal to about 70,000 acre-feet. So the 480,000 acre-feet held back in Powell corresponds to roughly 6.8 feet in Mead.

How long will this shadow accounting be in place? Becki Bryant, a Reclamation spokesperson, told Circle of Blue that the agency is discussing that matter with the states. They hope to reach an agreement by the publication of the August 24-month study.

24-month study

The name explains its purpose. Published every month, this Bureau of Reclamation study projects reservoir elevations in the Colorado River basin for following 24 months.

The pivotal edition is the August study, which sets the operating conditions for the reservoirs for the next year. Here’s how it works:

Reclamation looks at the projected elevations of Mead and Powell at the beginning of the upcoming year. Their elevations determine how much water flows from Powell to Mead. There are complex charts that describe the scenarios and dictate the decision.

In turn, Mead’s elevation determines if the lower basin states are in a shortage tier, which requires water supply cuts from the river.

Shortage tiers

When Mead drops below certain elevations, the lower basin states and Mexico must reduce their withdrawals from the river.

The shortage tiers have evolved as the basin’s water supply imbalance has become more pronounced.

The initial tiers were set in 2007, in what are known as the interim guidelines. The tiers were updated in 2019 in the DCP. What’s that, you ask?

DCP

Short for drought contingency plan, the DCP was approved by the basin states and the federal government in 2019.

The DCP updated the shortage tiers by increasing the amount of water cuts that lower basin states would take as Mead drops. For the first time, California agreed to take cuts, but not until Mead drops below 1,045.

In 2022, the lower basin is in a Tier 1 shortage. Arizona is taking most of the cuts.

What about the upper basin? Those states signed DROA…

DROA

Short for drought response operations agreement, this is the upper basin’s portion of the DCP. It outlines actions that the upper basin will take to preserve water levels in Powell.

One of those actions this year was for Reclamation to release 500,000 acre-feet into Powell from upstream reservoirs.

Shortage tier 2A

One of two possible shortage tiers for 2023. This tier occurs when the August 24-month study projects that Mead will be between 1,050 feet and 1,045 feet on January 1 of the following year.

Mead is on the cusp right now. Alan Butler, a Reclamation hydraulic engineer, said on July 13 that Mead is projected to be at elevation 1,045.9 feet in January, after accounting for operational neutrality.

If a 2A tier is declared, Arizona continues to take the largest cut. It would forgo 592,000 acre-feet, about four-fifths of the total cuts shared by the lower basin and Mexico.

Shortage tier 2B

This is the other possible outcome, which would take place if Mead is projected to be between 1,045 feet and 1,040 feet.

In this tier, California takes its first shortage cuts. Though Arizona, having to cut 640,000 acre-feet, would still feel the most pain, California would be required to cut 200,000 acre-feet.

These shortage tier numbers do not include Reclamation’s mandate for 2 million to 4 million acre-feet of additional savings, nor do they include the 500-plus plan.

500-plus plan

An agreement from lower basin states to conserve an additional 500,000 acre-feet in 2022 and 2023 beyond what was required in the Tier 1 shortage declaration for 2022. The states and federal government contributed $200 million combined, money that will pay water users to leave their allocations in Mead.

Protection volumes

When Reclamation ordered the basin states to plan for 2 million to 4 million acre-feet in additional conservation, Camille Touton, the agency’s leader, said it was to protect “critical levels” in Mead and Powell.

What are those critical levels? Reclamation analyzed two scenarios. But the conservation mandate was derived from the scenario that keeps more water in the reservoirs.

That scenario is Mead above 1,020 feet and Powell above 3,525 feet. The “protection volumes” are the 2 million to 4 million acre-feet needed to preserve the reservoirs above those thresholds.

ICS

An acronym that stands for intentionally created surplus, which acts like a savings account in Mead.

Lower basin water users can accrue ICS when they undertake conservation projects that permanently reduce consumption. Combined, the lower basin states have just accumulated shy of 3 million acre-feet of ICS credits stored in Mead.

Some of that water will be drawn this year. Metropolitan Water District of Southern California, a large wholesale agency, anticipates taking 175,000 acre-feet of ICS, according to spokesperson Bob Muir. This is to offset reduced allocations from the State Water Project, a canal system that moves water from north to south in California.

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