The Misunderstood Impact of Seawalls and Jetties on Beach Erosion

Seawalls and jetties are artificial shoreline stabilization structures often built to protect inland human constructions from erosion. Despite their intentions, these structures have a significant impact on beach erosion.

Introduction to Seawalls and Jetties

Seawalls and jetties are widespread along coastal regions worldwide. They are typically constructed by the U.S. Army Corps of Engineers and local authorities to provide flood protection, enhance navigation, and protect valuable beachfront properties. However, their role in erosion is often not well understood.

Seawalls and Beach Erosion

Seawalls are built to protect against wave erosion and storm damage. However, they can also contribute to beach erosion. This is often due to the redirection of wave energy. If a seawall is built too close to the shoreline, it can cause waves to reflect off the structure and carry sand away from the beach, ultimately leading to erosion (see the example of Galveston, TX).

For instance, after the 1900 Galveston hurricane, the city constructed a seawall. However, the wall was built too close to the surf line. As a result, storm waves reflected off the seawall, carrying sand from the beach out to sea. If you observe today, you’ll likely see dense lagoonal muds instead of sand from the reflecting waves. To counteract this, the U.S. Army Corps of Engineers has had to dredge sand and deposit it on the beach.

Jetties and Coastal Stabilization

Jetties, on the other hand, are built to stabilize the shipping channel entrances. They help in maintaining a navigable channel by preventing sand from moving into the channel. However, by doing so, they can also cause erosion on one side of the jetty and deposition on the other side.

For example, pairs of breakwaters were built between the west end of Galveston Island and the Bolivar Peninsula to protect the shipping entrance into the Port of Galveston and the Houston Ship Canal. The longshore current moves from the east, bringing sand that would normally deposit on the beach. However, since sand is now deposited against the Bolivar breakwater and into the ship channel, man must expend significant energy to pump sand onto the Galveston Beach to maintain a sandy shoreline.

Other examples of how interfering with natural processes can lead to unintended consequences are numerous. This further highlights the need for a more holistic approach to coastal management.

Conclusion

In conclusion, while seawalls and jetties serve important functions, they can also have adverse effects on beach erosion. It is crucial to carefully consider the consequences of such interventions and develop strategies that do not disrupt natural coastal processes. Understanding these impacts can help in making more informed decisions that balance human needs with the need to preserve our coastal environments.