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Reviving old canal to help water supply raises ecological concerns

In World
May 12, 2024

May 11—Amid the flocks of sandhill cranes blanketing the mountainous backdrop in a white spectacle, it’s easy to miss the old canal flowing past the Bosque del Apache’s ponds and savannas.

The canal is half-cloaked by cattails, willows, cottonwoods and other riparian flora that have taken root near its banks, allowing this human-made channel to blend with the wilder surroundings.

Known as the low-flow conveyance channel, it’s a mid-20th century relic, built alongside the Rio Grande to divert and funnel water to Elephant Butte Reservoir when the river stopped flowing to that destination and caused New Mexico to amass an immense water debt with Texas.

The canal became a second river, literally, diverting the entire Rio Grande from the old San Acacia Diversion Dam, north of Socorro, to about 70 miles south. The artificial conduit served its purpose, boosting deliveries enough for the state to pay off its massive debt by the early 1970s.

A decade later, the canal shut down after getting overrun with sediment.

Now water managers want to revive the defunct canal for the same reason it was built: to channel water more efficiently to the southern reservoir to pay a hefty debt owed to Texas, one that has proved difficult to whittle down, even in the recent wetter years.

The Middle Rio Grande Conservancy District, which oversees irrigation along a 178-mile stretch of the river, announced plans last year to conduct a five-year study on restoring the channel as a remedy to the river often failing to reach Elephant Butte and compounding the debt to Texas.

The prospect concerns environmentalists who view it as turning back the clock to serve commercial agriculture at the expense of ecosystems and wildlife, including endangered species. They worry the channel will siphon water from the river, creating miles of dry beds and sandbars, and from the bosque, which is seen as an oasis in an arid region.

A Santa Fe conservation group thinks district officials in proposing to resurrect the old channel are unwilling to take a holistic approach to managing the river.

“They have been saying that this water that’s not making it all the way down to Elephant Butte is water wasted, and to us that reflects an outdated mindset that the only purpose of a river is to convey water from point A to point B,” said Joanna Zhang, WildEarth Guardians wild rivers advocate.

The river, even when truncated, supplies water to riparian vegetation, birds and protected species such as the silvery minnow, she said. There’s also been no research showing how much the channel would boost water delivery to Texas to help meet obligations under the Rio Grande Compact, she said.

Zhang was referring to the 1938 water-sharing agreement between New Mexico, Colorado and Texas. The compact governs how much Rio Grande water a state must send downstream, based on the river flow measured at key points.

She said the apparent lack of analyses accompanying the district’s plans to explore bringing back the channel has raised concerns.

Officials have conducted no assessments — including hydrological studies — under the National Environmental Policy Act, and have had no public meetings beyond a listening session last year, Zhang said. They seem to have made up their minds to do the project, she said.

Jason Casuga, CEO of the conservancy district, said there are no immediate plans to restore the channel, though he foresees pursuing that in the near future because it’s essential for delivering sufficient water to Texas.

“We as are going to have to pursue looking at that in the next couple of years,” Casuga said. “I don’t think we can foreseeably manage the compact without it.”

As long as the compact is in place, New Mexico must send a certain volume to its southern neighbor every year, and meeting those requirements has become increasingly difficult with the river hitting a dead-end north of Elephant Butte, Casuga said.

Wet years in the 1940s created muddy, swampy areas north of the reservoir that blocked the river. As a result, New Mexico ended up owing Texas more than 500,000 acre-feet of water by 1953.

An acre-foot is roughly 326,000 gallons, enough to submerge a football field in a foot of water and supply two or three average U.S. households in a year.

The U.S. Bureau of Reclamation installed the rock-lined conveyance channel that sliced through the swamped stretch and bypass thick, water-sucking vegetation, enabling the state to pay off Texas by 1972.

The Rio Grande now is encountering a somewhat similar impediment that’s contributing to New Mexico owing Texas about 128,000 acre-feet.

The southern dam backs up the river for 40 miles, causing sediment carried in the water to build up and form an enormous, muddy delta.

The state engineer estimates about 30% of the river’s water in the summer is lost in this lower reach. The water trapped in the delta seeps into the muck or evaporates, especially during warmer weather.

The Reclamation Bureau dredges it regularly, but it muddies up again.

From this choke point, a portion of the water gets to the reservoir mainly through a narrow “delta channel,” Casuga said.

Water loss in the lower stretch has frustrated Casuga and other water managers who blame it for the district not making more headway in clearing the debt with Texas.

Wet periods, instead of being a blessing, have often been a curse.

The higher river flow measured at the Otowi Bridge in the northern section — which determines the amount that must be sent to Texas — is often depleted at the delta, reducing the volume that’s actually delivered. New Mexico then goes deeper in the hole.

Water managers want to avoid having the debt balloon to 200,000 acre-feet, a threshold that could trigger the U.S. Supreme Court intervening. Reestablishing the channel would be a way to prevent a loss of autonomy.

Casuga said the district will not fully divert water to the channel all growing season as was done 60 years ago. He would opt for intermittent diversions, perhaps during a heavy flow, which might add up to 20,000 acre-feet in a season, about a third of the volume diverted in the 1960s, he said.

The immediate plan, he said, is to clear vegetation and silt from the channel and maintain it as a drainage canal that catches groundwater seeping from the river.

He plans to use about $5 million of leftover money from the $15 million the Legislature approved for canal upkeep and to pay farmers not to plant crops for water conservation.

Zhang contends the conveyance channel would be a Band-Aid at best. Harder decisions must be made on how to manage the river and sustain water supply as the climate grows warmer and drier in an already arid state, she said.

The channel predates the Endangered Species Act and other environmental laws, she said. It contributed to the river being narrowed and straightened into a spillway to feed agriculture, disconnecting it from the flood plain, she said.

“Seeing money spent on restoring the natural river channel would seem like a better solution to me than going back to using this piece of infrastructure from the 1950s,” Zhang said.

In general, new thinking is required amid the challenges of a changing climate, Zhang said. That might include reducing agriculture that a decreasing water supply can’t support the way it did in the mid-20th century, she said.

But Casuga said it wasn’t constructive to dismiss viable options like the channel just because it was installed at an earlier time. The dams, channels and levees were built when people decided to live along waterways, and they’re the reason the beloved bosque exists, he said.

Paying off what’s owed to Texas and avoiding future debt is environmentally sound, he said, because then there’s more water to use to enhance habitat and help endangered species.

And at the same time, you’ll have ample water for farmers, while encouraging them to be more efficient, he said.

“We need every tool available,” Casuga said. “We will not be able to balance municipal, agricultural and environmental uses along the valley without operations of the low flow at some time.”

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