The Impact of Seawalls on Rincón’s Beaches

Passive Erosion
From Bush, D.M., et al., 1995, Living with the Puerto Rico Shore: Pilkey, O.H. and Neal, W.J. (eds), Duke Univ. Press, Durham, NC, 193 pp.

Beaches are an incredibly dynamic system that are affected both by watershed processes such as natural erosion of the hills that supply sand to the beach and also by oceanic conditions such as wave climate and sea level rise. Beaches are a precious resource for many reasons; they are an extremely popular form of recreation, they provide a natural buffer against storm surf and they are also an important habitat for birds, turtles and many other species. Due to impacts in watersheds and sea level rise many beaches in the world are eroding, including many of the beaches in Rincón. Natural beach erosion doesn’t reduce the size of the beach. Instead the beach tends to march towards the land. There is no problem with the health of the beach unless the beach erosion begins to encroach man-made development. Responding to beach erosion by the creation of seawalls can temporarily protect development, but ultimately results in the loss of the beach.

For example, the excellent scientific book regarding the health of Puerto Rico’s shorelines entitled “Living with the Puerto Rico Shore” published in 1995 has a picture of the first rock and wire “seawall” constructed along the Balneario. This wall was an effort to maintain the seaward edge of the park, unfortunately that seawall has fallen apart and created a beach hazard. Directly south, a more substantial seawall was built which has all but destroyed the beach (see photos). This is a predictable and common result of building seawalls along the beach. To maintain wide sandy beaches for everyone’s enjoyment and a healthy marine environment it is important to build far enough back from the beach that the slow erosion of approximately one foot per year can take place naturally.

How Seawalls Impact the Beach

1. Passive erosion -”Wherever a hard structure is built along a shoreline undergoing long-term net erosion, the shoreline will eventually migrate landward beyond the structure. The effect of this migration will be the gradual loss of beach in front of the seawall or revetment as the water deepens and the shoreface moves landward…. While private structures may be temporarily saved, the public beach is lost. This process of passive erosion appears to be a generally agreed upon result of fixing the position of the shoreline on an otherwise eroding stretch of coast, and is independent of the type of seawall constructed.”

It is evident that passive erosion will eventually destroy the recreational beach area unless this area is continually replenished. Excessive passive erosion may impact the beach profile such that shallow areas required to create breaking waves for surfing are lost.

2. Placement loss – Seawalls are placed on the beach. In many cases, construction of seawalls is on the beach, which is public property. This is a taking of extremely valuable public property.

3. Active Erosion – Refers to the interrelationship between wall and beach whereby due to wave reflection, storm surf zone narrowing and a thousand other processes the wall may actually increase the rate of loss of beach. This is site specific and dependent on sand input. There are varying opinions on if this effect actually exists. However, as watchdogs of the coast, until there is overwhelming evidence that this effect is not significant, this represents yet another reason to avoid constructing seawalls.

4. Public access impacts – these can be a result of passive erosion, placement loss or active erosion. Seawalls built on eroding beaches, will lead to the loss of access. Most beaches in Rincón are undergoing erosion.

5. Visual/aesthetic impacts – Seawalls are ugly and detract from simple pleasures as a walk on the beach.

6. Economic issues – local, state or federal subsidies or construction to protect private property, or insurance coverage. Construction is performed on State or Municipal land. The public has never been compensated for this loss of valuable property.

7. Loss of sand supplied by the eroding coastline that is armored. This is sand that is lost from the system because seawalls prevent the naturally occurring erosion to supply additional sand to beaches. This natural erosion also creates additional space for the beach to stay wide.

8. The most important thing to remember is that a seawall is never built to protect the beach. Rather, it is built to protect property, structures or a cliff from erosion.

Click below for more information

Surfrider Foundation Beachscape Info and Tools for Puerto Rico

Surfrider Foundation’s State of the Beach report