Trump s Border Wall Would Be the World s Longest Dam

Even a fence as open as this vehicle barrier in Organ Pipe Cactus National Monument can trap debris, worsening flooding during monsoon season. | Photo: Chris Clarke

Californias border with Baja California is a complex region with unique environmental issues. Our Borderlands series takes a deeper look at this region unified by shared landscapes and friendship, and divided by international politics.

As it becomes seemingly inevitable that Donald Trump will be the Republican Party's candidate in the 2016 Presidential race, it's a fitting time to take a look at he environmental effects of his signature campaign proposal - building a massive wall to seal off the U.S. border with Mexico.

As we saw in the first article in this series, building a concrete wall to Trump's vague, hand-wavy specifications would dump a massive amount of greenhouse gases into the atmosphere. But that's not the only way Trump's border wall would wreak weather-related havoc. Building the wall would also heighten the danger from existing weather. Simply put, a solid concrete wall would cause catastrophic flooding in the desert. And to explain how, there's no better place to start than the border community of Lukeville, Arizona.

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Lukeville isn't much more than a wide spot in the road at the south end of Arizona State Route 85, best known to Arizonans as the road between Gila Bend and the Sonoran beach town of Puerto Pe asco. Lukeville's population tops out at about 30 year-round residents. That can more than quadruple during the tourist season when Gringo Pass's trailer campground fills up with tourists visiting Organ Pipe Cactus National Monument, which surrounds Lukeville on three sides.

On the fourth side, southwest across the border, lies the town of Sonoyta, Sonora, home to about 18,000 people. East of Organ Pipe is the Tohono O'odham nation's 4,400-square-mile reservation, and westward lies the Cabeza Prieta National Wildlife Refuge, 1,344 square miles of some of the most rugged desert to be found in the Lower 48.

The Southwest's deserts are home to some of the most unpredictable flooding on the planet, and Arizona's borderlands are no exception. Some floods happen during the days-long winter storms that soak the desert in El Ni o years. But the most violent floods come in the summer monsoon season, when superheated air rises from the desert, drawing in moisture from the nearby Sea of Cortez.

A monsoonal storm drops heavy rain on the Sonoyta Plain, Organ Pipe Cactus National Monument | Photo: Chris Clarke

The monsoon storms that result can be highly localized and hard to anticipate. On one triple-digit temperature day in July, 2006 I was walking the long, cactus-studded Sonoyta Plain south of Organ Pipe's Kris Eggle Visitor Center, trying for some good photos of the Monument's eponymous column cacti. Off toward the border, I watched a storm cell develop and darken, the ground beneath it suddenly obscured by a column of heavy rain. Within four minutes the storm front had reached me. I was startled by its violence, rain and hail pelting my exposed skin painfully. Then the lightning started to strike, several bolts in a few seconds a few hundred feet away from me, and I sprinted the mile back to my pickup truck. By the time I caught my breath, the storm had passed.

Such storms can dump an inch of rain in just a few minutes. Two- or three-inch rainstorms spanning just an hour and fifteen minutes aren't at all uncommon in monsoon season. They fall on land that may not have seen a drop of rain in months or years. The desert's mineral soils can only absorb so much water at a time. The rest runs off, one tributary after another filling the main washes, filling them. The resulting flash floods can scour trees out of the earth. They gather up three, four years' worth of accumulated leaves and branches; the skeletons of cholla cacti and coyotes, plastic bags and beer cans, driftwood the size of fireplace logs, driftwood the size of railroad ties. All of it goes downstream in an advancing front that is as much debris flow as watercourse.

Whether such a flood constitutes a disaster or a boon depends on how you work with the desert landscape. Farmers of the Tohono O'odham traditionally follow the floods, choosing recently flooded washes and arroyos as that season's field. They plant crops in the newly fertilized soil, often tepary beans, a drought-tolerant native legume. O'odham farmers using this method don't force the water to come to them: they see where the water chooses to go and follow it. I write in the present tense, not the past: there are still O'odham farmers who plant this way, though it's harder nowadays to find access to appropriate washes. There's a wisdom in yielding to the demands of nature rather than demanding nature bend to human whims. And beans grown this way seem to be more nutritious than those grown on conventional farms.

But the same floods that offer deep watering and organic matter to traditional Oodham fields can serve as battering rams if anyone is lacking enough in that traditional wisdom that they try to put rigid structures in the course of the flood.

The best defense isn't always a fence

There hasn't always been a lot of development near Lukeville, at least on the U.S. side of the line. Until the 1990s, the whole area north of the border - especially the Cabeza Prieta - was considered a desert naturalist's paradise, a beautiful and dangerous landscape that could kill you as easily as it could inspire you. Author Ed Abbey referred to Cabeza Prieta in particular as the best desert wilderness left in the United States. Outside of Sonoyta and its outlying communities, the desert south of the border was even wilder, with the Pinacate Mountains usually considered th

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