This is not about whether a wall is desirable. That is a political question, to be solved by the political process.

Democracy is well suited to maintaining an equitable and stable social order. As questionable  as the recent record  of American government has been, democracy still has a strong association with maximum realization of human potential. But when  a construction project or anything technical  is mandated by politics, it is vulnerable to failure.  Democracy has a fundamental weakness  in dealing with technical issues.

With technical issues, the shortfall of the body politic, and elected officials, in dealing with the boundary between human affairs and the physical world is acute, and getting worse. In the case of the wall, the reasons are a mix of generalities and specifics:

• Natural reluctance of persons of authority to admit limits of competence, or to subjugate the political will to the limits of the achievable. This is a cousin of the Peter Principle.
• Ballooning complexity of the questions themselves. A wall used to be a pile of rocks. Not any more; all devices, including walls, are required to be smart.  Brains replace mass.
• There are no walls, except in our imaginations, There are only barriers. Maintaining the  integrity of a barrier is a dynamic process.

Amy Patrick, eminent  licensed structural engineer, assesses the proposed wall, with (Facebook) negative conclusions. Her comments deserve the amplification of historical perspective. History would be much different if there were such a thing as an impenetrable barrier.

By the first century B.C. the Romans had perfected siege engines that could easily breach the proposed wall. In a hypothetical match up, the Great Wall of China might have withstood Caesar, because it had a road on top, and was heavily manned. The proposed wall would compare poorly in mass with the Great Wall, because we don’t have millions of slaves and generations to build it.

But the advent of gunpowder, and later, of high explosives, renders the above argument obsolete. Gunpowder made fixed fortifications obsolete. With every advance in the technology of warfare, concentration of force has become greater. In recognition of  this,  Hitler’s Atlantic Wall was not a wall-with-ramparts. It was an agglomeration of obstacles and strong points. Ramparts were obsolete by the late Middle Ages, replaced by the increasingly futile efforts to create fortresses along the principles of military science .

Any kind of wall can stop an unaided migrant. But on the other side of the border, we face rogue forces with capabilities that approach those of a modern military – submarines, planes, drones, and more. These forces have the capability to mount sapper attacks with modern  shaped charge explosives, employing the (Army Research Laboratory) Munroe Effect. These forces have enormous revenue streams,  smuggle drugs into the U.S. with about 75% efficiency, and can respond to the human-smuggling challenge of a wall with well-funded agility. Hence any wall construction which relies on a fixed concept of the adversary is in error.

If it is your inclination to discount the above, with arguments like

• A hole can be patched.
• One shaped charge can’t collapse the wall.
• Attempts would be interdicted.

you may suffer from mental rigidity. It is unfortunately necessary to consider all possible combinations of threats.  What if the adversary decides to spend $5K on a rock drill and an air compressor, with a Mariachi band for company? In  the technique developed for hard rock mining, the holes thus made are filled with explosive, vastly increasing the destructive power. And compared to granite, concrete is not very hard.

What if the adversary chooses to degrade the wall over time, gradually knocking hundreds of holes in it, turning it, eventually, into a heap of gravel? This scenario challenges the idea of rushing border control officers to plug a single breach.

The concept of a wall as a static obstacle, like an ocean or mountain range, is not valid. Protection of the border becomes a problem for Operations Research, with cost/logistical/functional study of:

• Static resistance  – the ability of the wall to resist short term intrusion.
• Maintainability; the cost of repairing damage inflicted by the adversary.
• Optimal trade-off between the fixed asset, the wall, and dynamic assets, human patrol and interdiction.
• Relative cost allocation of the dumb and smart attributes: the quality of static resistance, and the ability of the wall to detect and report challenges.

A smart wall is simply an extension of battlefield technology. The modern battlefield is alive with sensors, enabling rapid, accurate response. While military use centers on lethal force, the smart wall is compatible with minimized lethality. In Israel, border barriers comprise mainly (AZ Central) steel fences, augmented by sensor fusion to provide detailed information about who is doing what to the barrier, and where.

Any damage to a steel fence, even a truck bomb, can be repaired in a few hours, versus months for a concrete wall.

And certainly in less time than a typical government shutdown.