Click the link to read the article on the InkStain website (John Fleck):

It is agonizing to watch this, but here we are.

With efforts by the Colorado River Basin states to craft an agreement to share the river’s water skidding, brakes screeching, toward a cliff, we appear on the brink of repeating the disastrous mistake the authors of the Colorado River Compact made a century ago: ignoring inconvenient truths about the risks we face, washing away genuine uncertainties with convenient talking points.

As Eric Kuhn carefully documented in a post here [February 22, 2024], there is once again a genuine risk that we will ignore inconvenient truths about a huge uncertainty in our understanding of how much water the river can offer us, and for whom. We are pretending that an uncertainty literally at the scale of millions of acre feet in how we measure and manage water does not exist.

Resource: A freight train of thoughts about the Colorado River — Allen Best (Big Pivots)

A masterful Upper Colorado River Basin public relations blitz, led by the Colorado Water Conservation Board, would have us believe one set of numbers about the river’s future, a set of numbers that has given Upper Basin water users comfort that they can sit tight and blame others for the river’s woes.

But as Eric’s analysis showed, there are hidden assumptions behind the Upper Basin’s numbers – assumptions that hide a genuine and irreducible uncertainty. The uncertainty is irreducible because more than a century after the adoption of the Colorado River Compact, there is still no agreed upon definition of how to measure the use of water. As Eric wrote, these are questions “with enormous potential impacts on the allocation and distribution of the shrinking Colorado River – questions we have avoided dealing with by draining the Basin’s reservoirs. We no longer have that option.”

ARITHMETIC AND LAW

Eric is a master of the arcane and wonky details of the interface between Colorado River law and hydrology, and I commend you to his analysis – it rewards a careful read. But Eric once described my role in our collaboration as “dewonkifying”, so let me try to put this in simpler terms.

The 1922 Colorado River Compact based its allocations on “beneficial consumptive use”. But the phrase was never defined, and the definitions ended up bitterly contested in the decades that followed. It remains undefined to this day. Or rather, there are two competing definitions that yield very different results.

Each definition makes intuitive sense, and at first glance they look puzzlingly similar. But at the scale of the Colorado River Basin they yield very different results that have become a critical piece of the current basin management debate.

Method A is based on the collective amount of water communities take from the river, minus the amount they return – “diversions less return flows.”

Method B is based on the ultimate impact of that use on the Colorado River downstream of the use – for the Upper Basin, for example, at Lee Ferry, or for Arizona at the confluence of the Gila and the Colorado near Yuma. This is the “stream depletion theory”.

Those might sound so similar that the differences are trivial. And at localized scales they are. But, as Eric explained in yesterday’s post, with a classically Eric Kuhn working out of the mathematical details (I love collaborating with this guy – he shows his work!) at the scale of the Lower Colorado River Basin the differences amount to nearly 2 million acre feet of water.

Under Method A, Lower Basin use is more than 10.1 million acre feet per year, well above its Colorado River Compact allocation of 8.5 million acre feet. This is the methodology the Colorado Water Conservation Board staff used in its now-famous PowerPoint slide purporting to demonstrate that the  Lower Basin is using more than its legally allotted share of the Colorado.

But under Method B, Lower Basin use is some 8.3 million acre feet – less than its Compact allocation. Importantly, Method B is the method adopted by the Upper Basin Compact, and therefore the method used in the Upper Basin’s management of its share of the river.

LET’S BE HONEST ABOUT THE UNCERTAINTIES

To be clear, Eric and I are not arguing in favor of A or B. We are arguing, as we did in our book Science be Dammed(we spent chunks of three chapters on this question), that the lack of an agreement over the definition of “beneficial consumptive use” remains a genuine and important unresolved uncertainty in the Law of the River, and our discussions of the future management of the Colorado River need to acknowledge that uncertainty, not pretend that it does not exist.

This is what I, as a stakeholder whose community depends on the Colorado River, expect of those leading the interstate effort – public honesty about the genuine risks and uncertainties we face.