Accounting for Colorado River evaporation

Helpful piece by Luke Runyon on steps toward accounting for Lower Colorado River evaporation and riparian system losses.

During a September Colorado River symposium held in Santa Fe, both Interior Department Secretary Deb Haaland and Bureau of Reclamation Commissioner Camille Calimlim Touton told attendees that the issue of evaporation and transit loss in the Lower Colorado River Basin were short-term priorities for their respective agencies.

Key bit – timing:

They are giving states until the end of 2024 to prepare for what would amount to a significant cut in annual water allocations to users in Nevada, California and Arizona.

I have my talking points:

“It would be a huge change in how water is administered in the lower Colorado River,” Fleck said. “The states, especially California and Arizona, had come to depend on really big allotments that were only possible because we ignored the laws of physics and didn’t account for evaporation and system losses….”

“The underlying problem is that the water users in the Lower Basin have refused to step forward and save themselves by coming up with a plan to reduce their own use,” he said. “So we look for some tool that the federal government could use to force them to save themselves. And accounting for evaporation and system losses has always been hanging out there because it’s just nuts that we don’t do this.”


  1. I confess, I am still unclear on this evap thing.

    Do lower-basin users currently have a guarantee of x-AF at the point of use (after evap loses)? And the new allocation might be the same AF, but measured at Lake Havasu (before evap loses)?

  2. How about solar panels to shade the Central Arizona Project canals? That would also generate a bunch of renewable energy.

  3. I agree with your John. These dumb as water planners have completely ignored evaporation from our rivers wetlands and man made reservoirs. I applied to the OSE almost 25 years ago to salvage the evap water and store it underground. The OSE denied my applications and we fought it out in court for 10 years with no clear victor. I was denied due process at every turn. Never had a hearing. Never even went to trial Motioned to death. In the meanwhile we have lost more than about 6 million acre feet.

    As you may recall, back in the 1980’s I was pushing groundwater recharge projects in the arroyos that debouch from the Sangre de Cristo, Sandia, and Manzano.Mountains. There is no comfort in being 25 to 30 years ahead of his time.

    Then there was the San Juan Chama storage project fiasco that was swept under the rug. As the expert hydrologist for the Jicarilla Apaches in the 1979 federal court case in which we prevailed and voided the Albuquerque contract with the Reclamation service to store SJC water for Albuquerque in the B.M. Hall Reservoir, I pointed out that SCJ as not native Rio Grande water floats on top of the native RG water in the reservoir. I pointed out that if B.M. Hall spilled , it would be the SJC water over the spillway first. USBR laughed and tried to convince Judge Payne that it would never happen. Then in the mid-90s B.M. Hall spilled three times, I believe, and all of that SJC water went on down the river. I wonder how the hydro-accountants covered that up or, did the just ignore it. Probably and conveniently they probably ignored it. You’re the investigative guy. Why not find out.

  4. In response to Tres Engish. What is to understand about evaporation. It is the process whereby 540 calories of heat is added to a groam of fresh water whereupon it changes pahse to a gas and it blow away to Texas. It is one term in the mass balance equation known as Baldy’s Law: “Some of it plus the rest of it, generally equals all of it. Mathematically,

    Wa = Wr + We

    Wa = All of the wet water
    We = Evaporated water
    Wr = Remaining wet water..

    The units are volume in whatever measurement system you use. It could be in cubic fuds as long as you give conversion factors to common units as cubic meters, cubic feet, or gallon, liters etc. In colonial Cyprus, before they went to the “cgs” system, it could have been in “okes” where an oke is 2.8 lbs.
    My grand-daughter is in 2nd grade and she knocked me off my chair last week by solving this equation. I didn’t learn algebra until junior high school and I was in one of the smartest school districts in New York State at the time.

  5. 2024 to make cuts?

    By that Lake Powell will be at dead pool, and Lake Mead will hanging on by a thread. They won’t even have to take cuts by then because there will be no water left.

  6. So, cutting usage is the required answer: But how much? 20% is one thing, but 80% is another entirely.

  7. To Songbird: The All American Canal is completely lined. This was done by the San Diego Water district, and the savings were accrued to them. It was a significant amount as I recall. It also dried out the Colorado river delta in Mexico. The seep had kept the delta wetland wet until the lining.

    Covering the lower basin canals with solar panals: Research has been done on the California Aqueduct, with promising results. Worth it, in other words.

    Final thought: Understandable that Deb Haaland and Camille Calimlim Touton have a decidedly upper basin bias regarding water. The challenge is it is not the settled law that will cause judicial problems with the big reductions, it is the Un-settled law that will cause the biggest heartburn. Going back to pre-1922, the trans-basin diversions were treated as a State issue, and were never settled as part of the inter-state water rights. The State of Colorado was very quiet about this, but this detail might come back to light if everything is re-opened. This would be part of the can of worms that would come from a disregarding of the 1922 Compact with as huge reduction in rights.

  8. We didn’t suddenly discover LB evaporation in the last twenty years. California argued throughout the 50’s in AZ v. CA that there wasn’t sufficient water to meet the 4.4/2.8/0.3 allocations in the Lower Basin, but this argument wasn’t considered in the final Decree. That’s WHY California insisted on the junior priority for the CAP in 1968, because it was clear even then that the Lower Basin states would have an annual overrun when at full build-out, once evap/losses are taken into account. Research accompanying the ’68 Act made it abundantly clear that the long-term reliable yield of the CAP was somewhere around 0.400-0.600 MAFY. Arizona agreed to that provision, and since then has been singularly focused on shifting the burden of this commitment to someone else.

    There’s more than one way to deal with evaporative losses, and in the Lower Basin, for the last 50+ years, that has been to take the cuts via the priority system. Obviously those cuts haven’t been large or regular enough, but that is a problem with previous agreements, not the method itself. Absorbing evaporative losses by the priority system isn’t unique to the Lower Basin. As much as the UB claims that they’re “assessed” for evaporation, evaporative losses on their large reservoirs (CRSP) don’t affect water users unless there’s a compact call. In that instance, total state usage would be tabulated, and reductions would happen via each state’s priority system.

    For the past fifty years, California has been striking deals with all of its water users, moving hundreds of thousands of AF per year, and spending huge amounts to live within its limits on the River, with the understanding that previous commitments in the Law of the River meant something. All of these intra-California measures would be jeopardized if evaporative assessments to users are forced on its water users. Other states don’t have anything comparable to the complex set of interlocking transfers California does, so they don’t seem to understand (or maybe they just don’t care) how evaporative loss assessments would destabilize this framework. It would be a reversal of a key piece of the Law of the River that California has been relying upon in building all those decades of agreements. Others seems to think they can strike just one part of the Law of the River, and the rest will remain in place, but if this is pushed forward, it will be the first domino to fall of many. Be careful what you wish for.

    California will never accept an assessment of evaporative losses, and if it’s forced on California, to be blunt, it will be tantamount to a declaration of war. If that’s the goal, keep going. However, if the goal is to actually reduce uses in a way that compensates for evaporative losses, the existing agreed-to cuts in the Lower Basin are already greater than annual evaporative and system losses.

  9. Pingback: Wet winter won’t fix Colorado River woes » Yale Climate Connections - Cape Weather

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