Nature Notes; Spring-Fed Gem of the Borderlands: The Hydrology of the Lower Canyons

The writer Edward Abbey, no stranger to Western rivers and canyons, described it as “the most primitive country to be found along the Rio Grande, a harsh and lonely land of spectacular beauty.”

The Lower Canyons of the Rio Grande are legendary for their beauty, and their inaccessibility. The canyons run for 140 miles between La Linda, in Brewster County, and Langtry, and there’s no access by paved road. It requires a boat, and at least a week, to see this country.

But the Lower Canyons are more than a wilderness destination. They’re also a unique ecosystem. In recent years, scientists have begun to better understand the ecology of this remote part of West Texas.

A soak in the riverside hot springs near Rio Grande Village is a must for many visitors to Big Bend National Park. The Langford Hot Springs were one of the region’s first tourist attractions.

Downstream, thermal springs flow into the Rio Grande from Black Gap to the edge of Amistad Reservoir.

Scientists knew those springs existed. But only recently they’ve taken their measure.

Jeff Bennett is a scientist at Big Bend National Park. With help from staff and students at Sul Ross State University in Alpine, he began mapping the springs in 2006.

The springs’ output is truly impressive.

“We’ve got pretty good estimations there that it’s somewhere between 160,000 to 200,000 acre-feet a year – which is significant,” Bennett said. “That’s a lot of water.”

Two hundred thousand acre-feet – that’s more than 65 billion gallons. That’s more water than all the tap water used each year by the people of the Trans-Pecos – El Paso included.

Bennett and his colleagues have identified four sets of springs. There are springs near Rio Grande Village, in the Black Gap area, at Lower Madison Falls, and at Foster’s Weir, near the Terrell/ Val Verde county line.

In the Big Bend, the condition of the Rio Grande can be bleak. Not much water reaches the region from the north. The Rio Conchos joins the Rio Grande at Ojinaga, and a treaty requires Mexico to deliver 350,000 acre-feet of water a year from the Conchos.

But that’s averaged out over a five-year cycle. Flows in the Big Bend are often low, and parts of the river can even run dry.

But in the Lower Canyons, the springs provide a consistent “base flow.” And they also improve water quality.

For fish and other river wildlife, the conditions are a boon.

Freshwater mussels are declining rapidly in North America. Their presence is a sign of river health. A 2005 park service study found only a single mussel between Lajitas and Rio Grande Village. But the researchers found 45 in the Lower Canyons. And the canyons support fish that are scarce elsewhere: the blue sucker, the Tamaulipas shiner and the longnose dace.

Bennett said the Lower Canyons are a special habitat.

“I was sort of encouraged that we had so much left – because in some systems, it’s much more stark, the loss,” he said. “What we have left there is really a gem, and not everybody is that lucky to have a river close by that still has most of the fish and most of the turtles and most of the mussels.”

The springs that feed the Lower Canyons emerge from the Edwards-Trinity Aquifer. It’s the largest aquifer in Texas – stretching from the Permian Basin to San Antonio. As Texas grows, pumping from the Edwards-Trinity Aquifer is likely to increase.

And the habitat of the Lower Canyons could hang in the balance.

“The reality is that the flows from the upstream tributaries, the Rio Conchos being one of those, aren’t coming anymore,” Bennett said, “and that means that groundwater is that much more important. It’s no longer a system depending upon the monsoonal runoff, for instance – it’s depending on groundwater. Now the Big Bend reach of the Rio Grande, especially downstream of Big Bend National Park, is dependent upon groundwater – that’s what’s keeping it alive.”

The Lower Canyons are a gem of the borderlands. Understanding their hydrology is critical if they’re to be preserved.

Nature Notes is underwritten by the Dixon Water Foundation and is produced by Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Andrew Stuart.