Silt, Sand and Sediment on the Rio Grande

Silt, sand and sediment are choking the Rio Grande, creating islands and broad banks of exotic vegetation that are slowing the water flow of the river. Bill Wellman, superintendent of the Big Bend National Park is working to implement natural methods to clear the intrusions and help claim what is left of this once great river.

Projecting Power Point slides on the screen during his lecture to the Sierra Club last week, Wellman compared a 1955 photograph of a vegetation free and clearly channeled Rio Grande at the mouth of the Santa Helena Canyon to a recent shot of the same place, where a small green forest of non-native Salt Cedar and Giant Cane grew over and around an easy sloped, slightly trickling Rio Grande.

“The Rio Grande is flowing at 1/6th of historical levels,” Wellman said. “The river is unable to move the silt, sand and sediment.”

“We’ve had an 8 1/2 foot build up of silt since 1991,” Wellman said.

Salt Cedar also known as Tamarisk and the Giant Cane, are non-native exotic plants that act as sediment traps.

“The river banks have become extremely stabilized by the exotic vegetation,” Wellman said.

The clogging of the river essentially slows the flow, eliminating the braided nature of the old river, sometimes creating a myriad of channels that eventually end stagnate, sometimes a single deeper channel, and sometimes forcing it underground. There are places between Fort Quitman and the Rio Conchos where the river does not flow at all.

As the population in the west boomed both in the USA and Mexico the demand for hydro-electric power and water also increased. Two major dams were completed in 1916: Elephant Butte in New Mexico on the Rio Grande and La Boquilla in Chihuahua on the Rio Conchos, a river that flows into the Rio Grande at Ojinaga. Today the dams are a major part of the slow-flowing Rio Grande problem, each taking billions of gallons of water out of the confluence each year.

The domestic and industrial water needs of the booming two million plus population of the El Paso-Juarez metropolitan area is another factor endangering the river.

A third problem is the farming below El Paso-Juarez in the Juarez Valley where water thirsty Pecan groves and onion farms stay wet with flood irrigation systems. The Rio Grande at this point looks more like one of the many skinny irrigation canals zig-zagging through-out the area.

“The question is, what can we do with what’s left of the river?” Wellman asked.

“Dam operators like steady flows,” Wellman said. “We’re having conversations with people who control the river’s flow, trying to get them to mimic something closer to the natural flow of the river. We need major releases to coincide with the monsoons – so we can move silt. Not the steady trickle they’re giving us now.”

“Our compacts with Mexico specify a certain quantity of water but give no time constraints,” Wellman said.

Doing what he can politically upriver is one thing but closer to home at the Big Bend, Wellman is focusing on the water-guzzling, sediment-trapping intruders; Salt Cedar and the Giant Cane.

“We can chop down the Salt Cedar and the Giant Cane but its expensive and takes a long time,” Wellman said.

The new attack plan for the Salt Cedar is to release the Salt Cedar Beetle, an insect found in Kazakhstan and the surrounding Central Asian region.

They hope to obtain an 85 per cent control factor on the tree utilizing the beetle’s healthy appetite for the tree’s leaves.

“These beetles grow exponentially and once they eat most of the trees, most will die,” Wellman said. “They will almost starve to death before they’ll eat anything else.”

The Parks Service presently have the beetles in cages along release sites on the river. They expect to release them into the wild in early fall.

“It may take five or ten years for the beetles to do their job,” Wellman said.

Controlling the Giant Cane is almost a bigger problem according to Wellman.

In the past, burning the Giant Cane and then treating the reduced biomass with herbicide was one way of getting rid of the cane. An old fashion method, recently done at a national heritage site near Yuma, AZ., produced “excellent results,” according to Wellman, but the labor-intensive, shovel-dig operation was very expensive.

Bulldozing is another option, however, Wellman explained, “Bulldozing is more manipulative than we like to do in a national park.”

“Ideally, we want to use the river as our bulldozer,” Wellman said.

“Giant Reed doesn’t have the roots that the Tamarisk has,” Wellman said. “If we can get the flow higher, cave in the banks, we can get it down river.”

The Rio Grande like most rivers in the western USA are puny compared to their former size, before the mass migration toward the Pacific that all started shortly after the Civil War when the telegraph and railroad lines connected east with west. Today we are left with remnants. Restoration to former glories, except in certain places, is almost impossible. What do we do with what we have left is key, and people like Bill Wellman will continue to seek the answers.