In 2011, A devastating tsunami crashed into the northeast coast of Japan, destroying entire villages, killing thousands and causing a meltdown at the Fukushima Daiichi nuclear power plant. In the wake of the disaster, the Japanese government implemented a number of reforms, including relocating coastal villages to higher land and forbidding further development along the northeast coastline.

The most controversial of these tsunami prevention measures was the construction of hundreds of miles of concrete seawalls and breakers along the most vulnerable stretches of the coast. So far, Japan has spent approximately $12 billion building towering concrete walls, some as high as 41 feet...