While the border wall between the United States and Mexico faces several political challenges, it has one key player that stands in its way: Mother Nature.
The White House issued an executive order within days of Trump's inauguration, calling for a "wall" along the southern border to prevent illegal immigration and drug- and human-trafficking by "transnational criminal organizations." The wall was a cornerstone of Trump's 2016 presidential campaign and a promise he followed up on early in his presidency.
However, building any kind of barrier of that length over varied terrain would require years of studying before construction can begin.
"The geological barriers along the way are of different types and different challenges," said Terry Engelder, a professor of geosciences at Penn State University. "You have to understand the terrain that the barrier is going to be built on."
The terrain along the U.S. and Mexican border consists of thousands of miles of extremely varied land lined with mountain ranges, desert sand dunes and rivers.
"A wall that might work in one area may not work in other areas, so it's not like you can just come up with a uniform plan," said Gary Clendenin, a senior hydrogeologist at ICF, a venture capital firm that invests in both private and public projects. "There'd be a number of different considerations that might constrain the use of one type of method."
The process to begin a project like this is comparable to a highway or an oil pipeline, involving years of environmental study and land surveying, experts said. Trump's executive order called for a full study of the border to be completed within 180 days.
"[Surveyors have to] very precisely delineate the path that the structure is proposed to take," said Clendenin. "You got to have boots on the ground... surveying something within a foot or five feet of accuracy."
"When you're talking about potentially 1,000 miles of wall, that's a very extensive undertaking."
For starters, waterways, like the Rio Grande and Colorado Rivers, can't be interfered with by any sort of barrier, said Engelder.
"Rivers particularly during flood stage tend to jump up their stream banks, and a barrier can't get in the way of that," he said.
Clendenin said any kind of barrier could upset the natural flow of not only the major rivers but any of their tributaries as well.
"The wall, if it's this fortresslike device that's being considered, potentially could upset the natural flow of ground water and surface water in the region," Clendenin said.
Sand dunes create their own concerns. Blowing sand would eventually build up along any sort of wall or fence, meaning it would have to be moved periodically. "That particular stretch of land just can't take a permanent wall," said Engelder.
Besides how to handle the terrain, there are other environmental problems to address.
"You have sort of migratory pathways of animals that live in that part of the world," said Clendenin, explaining a physical wall could disrupt species' natural migrations.
The White House released its proposed budget last week, asking for $1 billion in 2017 to work on the project. Recent Department of Homeland Security documents leaked to CNN say that money would go to adding 48 miles of new fence and repairing fence that's already there.
This is a fraction of what experts have said the total cost of building a wall the length of the border would be, which could be up to $21 billion.
The order states that the wall shall mean a contiguous physical wall or other similarly secure, contiguous and impassible physical barrier. This means the barrier could end up being more fencing as opposed to a concrete wall.
The DHS is currently accepting proposals from contractors for a design of the barrier. The chosen company will allegedly be selected as soon as mid-April.
While a fence would be less expensive and invasive to the environment, one that went the length of the border would still take a number of years to complete.
More than 650 miles of fencing were already built following the 2006 Secure Fence Act. Whether the new barrier will be additional fencing or a full-fledged wall remains to be seen.
"It is feasible," said Engelder. "This is a very standard civil engineering job. Because of the rugged terrain, it makes it a heck of a lot more expensive than it might be other places, but there’s nothing in terms of a technological challenge that will slow this down."
"It’s just a very, very expensive project."
Customs and Border Patrol did not respond to AccuWeather for comment.