The mighty San Pedro River in Southeastern Arizona and Northern Mexico has survived droughts, floods, fires and wars, but will the Trump administration’s proposal to build a wall on the U.S.-Mexican border threaten one of the last undammed rivers in the United States?
The river flows north out of Mexico and across the border into the United States near Hereford. The river has a rich cultural, ecological and historical record, and is the lifeblood to the small communities that have sprouted up along its banks. It also impacts a riparian area that is home to more than 250 migratory birds and more than 100 species of breeding birds, including the yellow-billed cuckoo. The riparian area of the San Pedro is also home to 84 species of mammals such as jaguars, coatimundi, beavers and bats.
It is here in Southern Arizona where concerns about the environmental impacts of a possible “wall” on the river are mounting.
Jacob Petersen-Perlman, research analyst for the Transboundary Aquifer Assessment Program at the University of Arizona’s Water Research Center said building a wall on the river “could be a big issue.”
“But I think the bigger thing would be the wildlife, more so than the water itself,” he said. “I think that is what is seen as a more serious impact.”
Petersen-Perlman is not alone in his concerns for the wildlife in the area assuming a wall is built on the border. Robert Weissler, president of the Friends of the San Pedro, said the existing fence already prevents larger wildlife from crossing the border in some areas, so an actual wall would make it difficult for wildlife to migrate across the border.
“There are at least three flavors of the border fence around here,” Weissleer said.“One is the 20-foot-tall sort of posts that are sunk in with a pile driver. Those have a gap not wide enough for a person to squeeze through, but for small wildlife, they can fit through it. So whether we need to have a ‘wall’ as opposed to that is questionable.”
Over the past few years, jaguar sightings have become more common in the Southern Arizona, as their habitat that stretches from Northern Mexico into Southern Arizona. Just last week a third jaguar sighting was reported in the area.
“How did it get there? It could have come up the San Pedro River and then taken one of the washes and followed it up into the mountains,” Weissler said. “So you build a wall and obviously large critters like jaguars are going to be excluded.”
Petersen-Perlman pointed to the Red River in Minnesota, where he grew up, to illustrate the power of water to make its own path. Recalling the large levees and walls built along the Red River to hold back the spring floods. Petersen-Perlman said the barriers worked for some time, but eventually gave way to massive flooding in the area of Grand Forks, North Dakota, and East Grand Forks, Minnesota, when the water overtopped the walls built to protect the cities. He said, “anytime you build infrastructure, particularly around water, there is just going to be times when nature will win.”
Petersen-Perlman also referred to the flooding disaster in New Orleans when Hurricane Katrina hit in 2005, another example of water finding a way over and through levees, walls and barriers built to hold the water out of an area. Petersen-Perlman said the key to keeping these structures from being overpowered by nature is regular maintenance. “That’s one thing that will be interesting to hear if this wall does get built is, what are the plans for maintenance?”
Although the wall may create a physical barrier to the river’s flow and wildlife migration, Petersen-Perlman said the political aspect of the wall may be the greater threat to the river for agencies on both sides of the border that collaborate on efforts to protect the waterway.
“This wall and the politics make our job harder,” he said. “It’s not like the upper level people in Mexico are all that enthusiastic to cooperate with the United States when something like this is proposed. So it is definitely something we are watching closely to see how this impacts our own work down there.”
Petersen-Perlman is not alone in his concerns in preserving the San Pedro’s perennial flow and riparian habitat that has been shrinking over the last few decades due to a number of factors. Said Weissler: “We don’t want this river to have happen to it what happened to the Santa Cruz River in Tucson.”
Weissler said the Santa Cruz was once a perennial river that had year-round flowing water and riparian areas like the San Pedro. But excessive groundwater pumping and a lowering water table caused the Santa Cruz to become a dry wash bed, he said, only flowing after heavy monsoon or winter rains.
To prevent this from happening to the San Pedro, Weissler and the Friends of the San Pedro River organization have focused their efforts on two issues: the surface condition of the landscape in the San Pedro Riparian National Conservation Area (SPRNCA) and the aquifer that feeds base flows of the river in the absence of precipitation events.
Weissler said the surface condition of the river has improved dramatically since cattle were removed from most areas of the conservation area in the late 1980s. He also said the breeding success of birds has improved dramatically in the riparian area. “Most of this surface restoration is simply letting nature heal the river over the decades since,” Weissler said.
Although the surface of the river is in fairly good shape, there are always issues to deal with that impact the future of the river.
“Battles over groundwater dominate the headlines locally in recent years,” Weissler said. “Planned residential developments that would increase groundwater pumping in the watershed threaten the aquifer that supports the river, not to mention the wells of existing residents.”
The possibility of a border wall over the San Pedro would just be one of many roadblocks the river would inevitably find a way to overcome.
“Of course, you can’t put a wall directly in the river,” Weissler said. “The existing border wall/fence is roughly 20 feet tall, but ends before it meets the river and is replaced by a Normandy-style vehicle barrier up to the river channel. The channel itself is open, because any obstruction in the river will simply be washed away during the monsoon rains of summer.”
Even great engineering marvels such as the Great Wall of China and the Berlin Wall never actually crossed any rivers. The Great Wall of China was constructed parallel to the Yellow River in some areas, and at times there was no wall at all, just the Yellow River marking the border. If the wall became perpendicular to the river, the wall would simply stop at the river, and then start again on other side of the river.
So how do you build a wall over a river? According to Weissler, “the answer is you don’t actually. The water has got to go somewhere unless you’re planning to build a dam which has a whole lot of other consequences.”
Taylor Dayton is a reporter for Arizona Sonora News, a service from the School of Journalism with the University of Arizona. Contact him at firstname.lastname@example.org