I just read about new front range reservoir drawing water from the western slope. So, a question for WW’s water wizard, JFR. How is the water diverted from the Colorado watershed to the front range and beyond accounted for in the 7 state divvy?
Great question. Trans-basin diversions are included in the math that divides the water from the Colorado River among the seven states. It's a substantial amount of water. In 2024, Colorado transferred about 0.51 maf across the divide to the Front Range, and Utah sent another 0.25 maf out of the system to the SLC metro area. And then don't forget New Mexico--about 0.07 maf headed out of the basin for its use. That means that in total, about 0.83 maf was diverted out of the Colorado River watershed before it ever reached one of the major USBR reservoirs downstream. That's roughly 20% of the upper basin states total use (4.1 maf) that year.
Those diversions, by the way, are allowed under the Compact and subsequent laws because those laws define use by the states, and such use is not restricted to being contained in the Colorado River watershed. Colorado has been diverting water across the front range for more than a century. The Big Thompson project ramped that up, mostly constructed in the 1940s and 50s.
All that of course is a big issue when it comes to accounting for total water use in the system going forward.
Say all the bad things you want about the lower basin states, but by the time they get any water, the upper basin states have already taken what they want, and a lot of that water is forever lost to the system. In 2024, that was 0.83 maf. At least Las Vegas returns something like 90% of what it uses right back to Lake Mead.
That's one reason USBR's hands are tied with respect to limiting upper basin use in the latest management proposal--they don't have any leverage over upper basin water supply, since that water is diverted before any major federal impoundments...
