Riprap consists of boulders used to armor a riverbank, shoreline, roadcut, etc., and is not recommended if you want to preserve the beach as a beach.   

 

Offshore barriers are still in the experimental stage and I can't speak authoritatively about them. So far, they seem to cause more problems than they solve, for reasons that have little to do with any particular design. The barriers are hazardous to swimmers and boaters. Aesthetically, they are discordant and ugly. Biologically, they add hard substrates to shores that had none. But worst, they either don't work as advertised, or they do work and make sand accrete onto the protected beach while unprotected beaches down-drift are starved of sand and therefore undergo erosion. Now that this is a predictable effect, landowners sometimes succeed in suing up-drift landowners. The ultimate culprit in such cases is most often engineering works that cut off the supply of sand at the source for a whole stretch of coastline.

 

Another culprit is building too close to the shoreline. If a storm wave hits a wall, then part of the energy reflects back onto the sand, which is then transported seaward. If a condo, for instance, is built too close to the sea, then it can increase erosion on its own beach. This is a predictable, common-sense effect that you can test for yourself by planting a board vertically in the sand parallel to the beach where the waves can hit it. Watch what happens to the sand on the seaward side of the board. In your imagination, scale that up to the size of a seawall or a condo. You don't even have to imagine a storm of the scale of Hurricane Ivan to be convinced that building too close to the sea is a bad idea.

 

Global sea-level rise. Hm. It's been pretty slow so far; on some coasts (such as the northern Gulf of Mexico, especially Louisiana), subsidence is more rapid and therefore more important, if equally inexorable. Cut off the source of sand and a shoreline may be severely eroded in only a few years, not decades.

 

I hate to say it, but I have to agree with Orrin Pilkey: If the decision has been made to protect houses on a beach, then the most effective and least offensive way to do it is by beach renourishment. But I also agree with him that it's better to build farther inland to begin with. In the long run, you get either an armored coastline or ruined houses, neither of which is very attractive.

 

Andrew K. Rindsberg