Documenting beach loss in front of seawalls in Puerto Rico: Pitfalls of engineering a small island nation shore

The island of Puerto Rico is densely populated and heavily developed in some places, particularly along the shore and in coastal lowlands. Hard shoreline engineering is commonplace, even in low development density portions of the island. There are many examples of small trash revetments or cemented rock seawalls in front of individual buildings. In some cases, buildings themselves located within reach of waves and tides at the shoreline are behaving as seawalls too. Gabions have proliferated, even though they are decidedly not designed for either high-wave energy or salt-water usage. Along the island’s approximately 500-km long shoreline, and not counting major port city developments, 48 shoreline stretches were identified where segments of the shore contained a seawall and an immediately adjacent sandy stretch. A comparison between beach width in front of the walls and beach width of the adjacent sandy stretch showed that the ratios of natural (unstabilized) dry beach widths to those of beaches in front of seawalls is between 2:1 and over 4:1, respectively. These data corroborate findings of Wright (The effect of hard stabilization on the sediment transport system along the shoreline of Puerto Rico. Unpublished Master's thesis, Duke University, Durham, NC, 200 p, 1989) and lend credence to the claim that seawalls actively influence narrowing of beaches. The fate of beaches along developed stretches of the shoreline is grim if efforts continue to concentrate on hard structures to armor the coast.