Lawmakers will seek $500,000 to study water lost from canals in the Green and Little Snake River basins to ensure Wyoming is accurately credited for conservation when it chooses or is forced to close irrigation systems in the troubled Colorado River Basin.
The study could help Wyoming limit reductions in water diversion as seven Western states and Mexico wrangle with an over-allocated and dwindling supply in the drainage. Members of the Legislature’s Joint Select Water Committee voted to draft a measure to seek the money from the general fund when the legislative session commences early next year.
“I could see [a conveyance loss study] very easily reaching $500,000,” Jason Mead, interim director of the Wyoming Water Development Office told lawmakers Wednesday. State Engineer Brandon Gebhart said his “mind was right at $500,000 for this,” but that “it could be a lot more.
“I do think that this is a really good start,” he said.
One hundred years after the signing of the Colorado River Compact, water managers cannot accurately measure what’s used and have not agreed on how to resolve conflicting views on rights to use what water there is.
The amount of incidental seepage and phreatophytic losses — canal-side, plant-used water — associated with irrigation is an “area of agriculture data collection that need[s] to be updated and verified,” the U.S. Bureau of Reclamation states in its 2022 Upper Colorado River Basin Consumptive Uses and Losses report.
The proposed Wyoming study could help the state claim that when it shuts off water to a field of crops, it is saving that crop’s consumption plus what’s lost in the conveyance system of canals and ditches that carry the flow from river to field.
By showing it saves more, Wyoming would cut off fewer users in a “curtailment” situation where water managers require conservation. The data could also better inform the purchase of temporary water rights transfers from one user to another.
“Understanding what that conveyance loss is,” Gebhart said, “could benefit the water users in our state.”
Conveyance loss is significant in Wyoming’s Green River Basin, one lawmaker told the committee.
“We know in Sublette County that we have some canals that are over 20 miles long that go through a glacial till and alluvium that, anecdotally we’ve heard, they lose up to 80%,” Sen. Larry Hicks (R-Baggs) told the committee. Irrigators estimated losses in a survey conducted by the Water Development Office, but none has reported losses as high as 80%; the statewide average is 24%.
A contractor would lay out the groundwork for the study starting next spring, identifying perhaps eight sites and 50 miles of canals in the Green and Little Snake River drainages that could be monitored. Investigators would install water-pressure sensors in canals to record water-level fluctuations through a season.
Once in place, consultants would measure and record flows and pressures in the 2024 irrigation season. Mead of the WWDO described how the survey would work.
Investigators would be “going out there four or five, six times to actually get measurements on the canal at four or five or six different spots down, say, a 15-mile section,” he said.
The results would show, for example, the difference in canal seepage at the beginning of an irrigation season when the ground is drier compared to seepage in mid-summer when the canal has been flowing and “things are wetted up and primed,” Mead said.
Engineer Gebhart distinguished between two categories of conveyance losses — consumptive loss and seepage — and whether Wyoming could claim credit for staunching either.
Consumptive loss is the amount consumed by ditch-side plants and trees, the amount lost to evaporation, plus that which leaks into an aquifer “that does not return back to the [Colorado River] system,” he said.
Gebhart defined the second category — seepage loss — as leakage that returns to the system. “It may be delayed, but it does return back to a stream,” he said.
As Wyoming calculates what’s consumptively used — and what it can save if that consumptive use is taken off-line — it might not be credited for reducing some associated seepage.
“Seepage [that] returns to the system … that is not considered a consumptive use,” Gebhart said. “I would say a majority of ditch loss is lost to seepage.”
Results from the study would be ready in late 2024 or in 2025, according to a scenario painted by Mead.
Wyoming doesn’t expect to face curtailment — when it might be forced to shut down users — until 2028, if drought continues. Wyoming and its sister states in the Upper Division or upper basin — Colorado, Utah and New Mexico — would face mandatory cuts if the Lee Ferry gauging station just below Lake Powell shows a flow of less than 75 million acre-feet in the previous 10 years.
Under the 1922 Colorado River Compact, “[t]he States of the Upper Division will not cause the flow of the river at Lee Ferry to be depleted” below that level. The upper basin encompasses about 45% of the drainage area but produces 92% of the runoff.
Colorado River laws apportion Wyoming rights to 14% of the upper basin’s water, officials say. They believe upper basin states are not yet at the critical “75/10” metric where reductions are necessary.
“We’re currently about 85 million acre-feet,” Gebhart said, referring to the previous 10 years. “So we’ve got a little buffer.”
“We’ve blown through the hydrology, we’ve used most of the storage in the Colorado River Basin,” Hicks said. “And now … the director of the Bureau of Reclamation, [is] looking for somewhere between 2 [million] and 4 million acre-feet of reductions in the Colorado.”
The original estimate was 15 million acre-feet were in the system annually, but that water, “it doesn’t exist,” Hicks said. In the last decade, it’s averaged 12 million acre-feet or less, he said. One water administrator in Colorado has said experts tell water managers to plan for 9 million acre-feet a year as a worst-case scenario.
Municipalities and industry — usually holding inferior, junior water rights and so the first to face curtailment — could be looking for water. In Wyoming, agriculture holds 80% of the water rights, Hicks said, and could be approached to sell through a temporary-transfer system or some other arrangement.
“That’s the water bank that you’re looking at,” Hicks said of agriculture.
“At some point in time, we’re gonna have to recognize that there’s not 15 million acre-feet to be divided up,” he said. “That’s really the issue. This is why all the states are lawyering up.”
Wyoming is preparing for negotiations, measurements, debates and possibly fights over water rights. In the last year, the state has added a Colorado-River staffer to the state engineer’s office and also the attorney general’s office, Hicks told the committee.