A honeycomb sea wall (also known as a "Seabee") is a coastal defense structure that protects against strong waves and tides.
[1] During strong storms, surging sea water loses energy as it travels down the holes and through the underlayer.
The water returns to the sea by upward flow through holes at levels below the transient phreatic surface in the underlayer, causing the downslope disturbing drag force to be reduced.
Water that does not go through the holes is redirected by the concrete wall back into the path of oncoming waves, creating more turbulence.
Cost comparisons between various seawalls are always site specific, but Seabees use approximately 22% the mass of rock for the same exposure.