As we lumber toward a renegotiation of the operating rules on the Colorado River, one of the challenges folks in basin management face is the differing understandings of the Law of the River. There’s stuff we all know, or think we know, or stuff Lower Basin folks think they know that Upper Basin people may disagree with, and stuff Upper Basin folks think they know that Lower Basin people may disagree with.

Larry MacDonnell, one of the Law of the River’s great legal minds, has written a terrific treatise to help us untangle this. It’s clearly written from an Upper Basin perspective (“Yay!” said the guy – me – who drinks Upper Basin water!), so Lower Basin folks may disagree with some of what Larry is saying. That’s OK, the important thing is to understand that the answers to these questions are not given – that there are genuine disagreements on this stuff, and the negotiations to come need to wrestle with these questions.

A few of Larry’s key questions:

Uncertainties Concerning Mainstream Water Use Entitlements in the Lower Basin

The traditional understanding of fixed allocations to the three mainstream states in the Lower Basin must yield to the reality of a declining water supply.

In some sense, this is a “duh”. If the water isn’t there, it doesn’t matter how much water the Compact or the Boulder Canyon Project Act or whatever says you’re entitled to. But Larry is making a more nuanced argument about what the rules themselves say.

Uncertainties Respecting Uses of Water from Lower Basin Tributaries

This is an argument I’m increasingly hearing from Upper Basin folks. Andy Mueller, general manager of the Colorado River District, made it forcefully in a webinar last week (starts around minute 12 in this recording). The current Colorado River accounting norms tend to ignore Arizona’s in-state use of the water from its Colorado River tributaries, but there’s a lot of water involved here. A million acre feet a year? Two million acre feet a year? We don’t know, because it’s not being accounted for right now.

Here’s Larry:

All beneficial consumptive uses of tributary water in the Lower Basin are
included within the Articles III (a) and (b) apportionment and need to be fully identified and accounted for annually. The effect of these uses on water availability in the main Colorado must be taken into account. Uses exceeding 8.5 maf/year may constitute a violation of the Law of the  River under certain circumstances such as if their existence causes a failure to meet treaty obligations with Mexico.

Uncertainties Respecting the Meaning of Article III (d) in an Era of Climate Change–Induced Water Shortages

Does the Upper Basin have a legal obligation to deliver 7.5 million acre feet a year past Lee Ferry? Or it, as my Upper Basin friends like to say “a non-depletion” obligation. What if it’s climate change that’s depleting the water rather than the diversions to my tap to bring me all that sweet, sweet San Juan-Chama drinking water?

How much is the Upper Basin on the hook for meeting our delivery obligations to Mexico?

The traditional view that the Upper Basin has an obligation to provide 750,000 acre–feet per year to meet the Treaty obligation to Mexico needs to be reconsidered when Lower Basin uses exceed 8.5 maf/year, when Mexico adjusts its delivery requirements to reflect shortages, and in view of the fact that, in some manner, the treaty water is a national obligation.

There’s a lot more, river nerds should really read the whole thing, and as I said there will be smart Lower Basin people who will be happy to explain “Nothing to see here, move along.” But these ambiguities in the Law of the River have to be part of what we sort out in the upcoming negotiations.