Seawalls and Beach Protection: Myths Debunked

Building a seawall can provide some protection to a beach, but it comes with both benefits and drawbacks. This article delves into the pros and cons of protective seawalls, drawing from personal experiences and scientific insights. We will also explore how seawalls can fundamentally alter beach ecosystems and coastal processes.

The Benefits of Seawalls

Seawalls offer several tangible benefits in the realm of coastal protection:

Erosion Control

Seawalls can effectively reduce coastal erosion by acting as a physical barrier against waves and storm surges. This can help protect valuable infrastructure such as homes, roads, and businesses from flooding and damage.

Immediate Safety

Seawalls can provide immediate safety for beachgoers and local communities during extreme weather events, acting as a protective buffer zone.

Infrastructure Protection

They help safeguard coastal infrastructure from the destructive forces of storms, ensuring the safety and continuity of vital public services.

The Drawbacks of Seawalls

While seawalls offer short-term protection, their long-term effects are often detrimental to the beach and coastal ecosystem:

Beach Narrowing

Seawalls can lead to beach narrowing or loss as they disrupt natural sediment transport processes. Waves that hit the seawall can erode the beach, resulting in a narrower and potentially less stable shoreline.

Increased Erosion Down Coast

The disruption of sediment flow can cause increased erosion in adjacent areas, potentially harming other parts of the coastline. This can create a cascade effect, undermining the very protection initially intended by the seawall.

Cost and Maintenance

Seawalls are expensive to build and maintain. They may require ongoing repairs due to constant wear from the elements, ultimately leading to higher long-term costs.

Visual and Environmental Impact

Seawalls can alter the natural landscape, impacting local ecosystems. They can harm marine and coastal habitats by changing the normal action of nearshore processes and disrupting sediment transport.

A Case Study: The Seawall in Galveston, Texas

My transformation from an astrophysicist to a geophysicist involved geological field trips provided by my employer. One memorable trip led by Rufus J. Leblanc, a renowned sedimentologist, explored the seawall in front of Galveston, Texas.

Following a devastating hurricane in 1900, a seawall was constructed to protect the city. However, due to the high value of seafront real estate, the seawall's location was chosen seaward enough to avoid valuable properties. This strategic positioning, while intended to safeguard infrastructure, had unintended consequences:

Wave Action and Beach Erosion

Leblanc explained that high-energy waves could run up the beach far enough to reflect off the seawall, carrying sand away in the resulting turbulence. From over the seawall, he pointed out that the area we perceived as a beach was actually lagoonal muds that the waves couldn't carry away. This illustrates how seawalls can interfere with natural sediment transport processes.

The Impact of Jetties

The construction of Galveston Jetties had interrupted the longshore flow of sand from the east. To maintain the Galveston City beaches, sand needed to be dredged between the jetties and pumped onto the "beaches." This ongoing process highlights the additional costs and maintenance required for coastal protection.

Conclusion: Sustainable Coastal Management

While seawalls can provide short-term protection against erosion and flooding, they are not a long-term solution for beach preservation. Sustainable coastal management often involves a combination of strategies such as beach nourishment, dune restoration, and managed retreat. These approaches better address coastal erosion and protect beaches in the long run.