Current work in wildlife, rivers, public lands, and climate

A conservation group working in the American West has proposed a dramatic solution to water woes in the Rio Grande basin. In a report published in February, WildEarth Guardians suggest that federal water managers decommission the largest reservoir in the basin and store its water in other artificial lakes farther upstream.The problem, according the report, titled “The Rio Grande: Rethinking Rivers in the 21st Century,” is that Elephant Butte Reservoir’s large size combined with its shallow depth make its water exceptionally vulnerable to evaporation. In fact, the fuller the reservoir is, the more its water sprawls outward under the sun and the less efficient it becomes at containing the precious resource, Jen Pelz, who compiled the report, tells Water Deeply. And every drop of Rio Grande water is needed.

In her report, Pelz explains how 19th-century water law, 20th-century water infrastructure and 21st-century changes in climate and human population are converging on a collision course in the Rio Grande basin. The 1,900-mile (3,000km)-long river is born in the snows of Colorado’s San Juan Mountains and, between the United States and Mexico, supplies water to more than 2 million acres (809,000 hectares) of farmland before reaching the Gulf of Mexico.

But the river’s flows are too fickle to support the demands for its water. In fact, so little water remains in the heavily tapped system that the Rio Grande runs dry for months of the year in some stretches. Several fish – including the Rio Grande silvery minnow and the shovelnose sturgeon – have dwindled or vanished from the basin.

Changing the way water is stored in the basin could help stretch water supplies further. When filled to its capacity of 2.2 million acre-feet (2.7 billion cubic meters), Elephant Butte Reservoir releases roughly 250,000 acre-feet of water vapor in a year. What Pelz suggests is storing more water in several reservoirs upstream and at higher elevation, where greater lake depth, less surface area and cooler ambient temperatures will mean less evaporative water loss.

“Heron Reservoir evaporates 46 percent of the water that Elephant Butte evaporates at capacity,” she says, citing the lake that she sees as the best option for relocating most of Elephant Butte’s water.

Employees give tours of the Elephant Butte Dam during the centennial celebration on Wednesday, Oct. 19, 2016, at Elephant Butte, N.M. A conservation group has proposed storing Rio Grande water farther upstream from Elephant Butte to reduce water lost to evaporation at the reservoir. (Josh Bachman/The Las Cruces Sun-News via AP)

This strategy could ultimately save as much as 85,000 acre-feet of water per year, Pelz has calculated, and through improved water supply create enough wiggle room to protect and even partially restore the watershed’s ailing ecosystem, home to a variety of endangered species.

Unless strident action is taken, water supply problems are almost certainly only going to get worse in the future. Climate change, Pelz explains, is going to make the Southwest desert region drier and hotter. It already has, in fact, with temperatures in the basin climbing almost twice as rapidly as the global average. In the next 80 years, scientists expect the region’s average temperature to increase by 5–7F (2.7–3.9C) due to human-caused climate change.

A warmer, drier climate will have a manifold impact on the Rio Grande’s water supply.

“Temperature increase is going to intensify all these problems,” Pelz says. “Crops will need more water, cities will need more water, evaporation will increase.”

Water supply in the Rio Grande basin has been a problem for centuries. As long ago as the 1600s, Euro-Americans established unsustainable water laws and allocation policies, according to Pelz. By the 1800s, a system had been established by which settlers followed a first-come-first-served basis of portioning out the river.

“The problem is the whole point of the system was to divert the river without any consideration of what would happen if there was no water left in the river,” Pelz says.

Settlers of the region had no inkling that the river’s flows might diminish 200 years into the future. By the early years of the 20th century, the river’s flows had been over-allocated, with people along its banks depending on more water than actually flowed through the basin.

To address this problem, which is common in watersheds throughout the West – and is especially prominent today in California’s Sacramento-San Joaquin river system – the government began building dams to increase water storage space. Elephant Butte Reservoir, which has 2.2 million acre-feet storage capacity, was filling behind its namesake dam by 1916. More reservoirs would follow. Eventually, eight artificial lakes in the middle stretches of the Rio Grande created 5 million acre-feet of storage space. There are more than a dozen smaller reservoirs in the basin.

Collectively, these reservoirs still do not solve the water supply issue. Pelz says it may never be possible to completely correct the shortcomings of the existing water supply infrastructure and restore the river basin’s biodiversity to something resembling its unimpaired state.

The river is pumped completely dry in places, and Pelz says many farmers routinely argue that the river never ran year-round anyway – which, she says, is a false ploy to throw off conservation efforts.

“There’s no doubt – it was absolutely a perennial river,” she says.

She hopes her research will prompt the U.S. Bureau of Reclamation to take a close and serious look at relocating Elephant Butte Reservoir’s water to a location less impacted by evaporation. Ultimately, she hopes, more water will be available to help keep the Rio Grande itself alive.

“My hope is that my kids will see the river running from its headwaters to the Gulf of Mexico,” she says.