DOCUMENTING BEACH LOSS IN FRONT OF SEAWALLS IN PUERTO RICO

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 portions of the island with low development density. 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. Gabions have proliferated, even though they are designated by the coastal-regulating Federal agency (U.S. Army Corps of Engineers) as inappropriate structures 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 seawalls exist with 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 walled dry beach width ranges from 2:1 to over 4:1. These data corroborate a previous study and lend credence to the claim that seawalls actively influence narrowing of beaches. There are many more seawalls in Puerto Rico not included in this study because they did not satisfy the criterion of having an adjacent sandy shoreline stretch for comparison. However, a snapshot of beach width along the San Juan metropolitan area showed dry-beach width of sandy beaches to average around 18 meters, while dry-beach width of beaches in front of seawalls and in front of natural rocky shores to average 1 meter or less. The fate of beaches along developed stretches of the shoreline is grim if efforts continue to concentrate on hard structures to armor the coast.