Why a wall won't work.
Legal Obstacles
-More than 2/3rds of the land along the border do not belong to the federal government. Private parties own the vast majorit of the border land in Texas, and for that reason, 70% of the existing fencing is located in Califonia, Arizona, and New Mexico on federally controlled land.
-The government would have to use eminent domain to seize the property of land owners along the border that do not voluntarily hand over their land for a border wall. Lawsuits challenging the compensation the government offers for eminent domain could impose serious delays in construction. Plus I'm sure it will piss off quite a few people who don't want to see a 35 ft wall in their back yard.
-Native American tribes, such as the Tohono O'odham Nation own land on both sides of the border, and have pledged to fight construction of a wall on their lands
-Land management laws delay or limit access to portions of federal lands along the border. This would pose a problem when it comes to maintaining or repairing the wall in a timely fashion.
-A 1970 treaty requires that the floodplain of the Rio Grande remain open to both sides of the border. The Obama administration attempted to build fences along the river, but due to the treaty, the fence had to be relocated so far into the interior of the USA that many US residents found themselves living between the fence and the Rio Grande River. Many holes in the fence had to be made to allow US residents access to their property.
Practical Considerations
-Fences and walls can be damaged by natural considerations. Erosion of the soils around a fence or a wall can cause segments to collapse.
-Walls can be easily climbed with the use of a ladder. Mats can be placed over concertina wire. Tunnels can be dug underneath walls, even to depths of 20 feet below grade. Between 2007 and 2010, the Border Patrol discovered more than one tunnel per month under current physical borders. Building a wall that has a sub-grade foundation deep enough to prevent tunneling would add significantly to the total cost of the construction. No such "tunnel technology" exists to all the Border Patrol to practically identify tunneling activity.
-A border wall would have to allow water to pass through at some locations, otherwise the force of raging water could damage its integrity
-A solid wall would reduce sight lines, reducing border patrol agents ability to anticipate and react to illegal immigrants from climbing the wall.
The Efficacy of a Wall
-When the San Diego sector of the border was reinforced with walls, illegal crossings at that location did slow, but it appears that it simply pushed migrants further east to locations where a barrier did not exist. There will always be areas along the US/Mexican border with no barrier. It's impractical to build walls in some of the rougher terrain along the border, as well as along many segments of the winding sections of the Rio Grande.
-More than a third of all unauthorized immigrants entered the US lawfully and the overstayed their visas. A wall does nothing to combat this. In 1992, only one in three border crosses overstayed their welcome. And this was before most of the current fencing was created along the border. By 2012, visa overstays accounted for 58% of all new unauthorized immigrants. A wall does very little to prevent these people from entering, but may actually incentives more people to stick around without authorization.
-Border walls increase the cost to cross the border, from $500 in 1995 to $3000 in 2009. While yes, this does serve to prevent some migrants from crossing. But it also makes it more lucrative for illegal elements to get involved with aiding would be border crossers to get to the US.
The Price Tag
-Congress allocated $1.2 billion for the 700-mile border fence back in 2006, and it ended up costing $3 billion. That's more than double the intended price tag. The 700-mile fence consisted little more of a combination of pedestrian fences and vehicle impediments. In 2009, the Border Patrol estimated that it would cost on average $325 million per year to maintain these barriers.
By 2015, the Congressional Research Service found that by 2015, Congress had already spent $7 billion on the fencing project, or more than $10 million per mile. For fencing. A border wall would cost much more than this.
-Assuming Trump decides a fence along the remaining un-fenced locations would be acceptable, Congress will still need to front at least $10 billion over 10 years. The entire fence would price out at $18 billion counting for inflation. This does not count the costs associated with acquiring private land and building in less than accessible areas.
Again, a wall would cost much more.
-Existing fences were relatively inexpensive to build because we already had a lot of material for it laying around. Much of the wall was constructed using old helicopter pads left over from the Vietnam War.
-If made from concrete, the wall would require almost 1.5 times the amount of concrete used during the construction of the Hoover Dam. This would require a large amount of the United States' concrete production capacity to be diverted to the wall construction. Concrete that could be used for the foundations for new homes or new businesses would go to the wall instead. The price of concrete would likely increase due to the increased demand resulting in high construction costs for Americans.
https://www.cato.org/publications/commen...-wont-work
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