Seawalls, from Ocean Beach in California to Uluwatu in Bali and Narrabeen in Australia, are often touted as a solution to coastal erosion. Yet, these structures may actually be exacerbating the very problems they are designed to solve.
The story of King Canute, who famously attempted to command the tide to halt, has endured for over a thousand years. His lesson, delivered in the 11th century, still resonates today: nature’s forces cannot be stopped by human will. Despite this, modern society continues to erect seawalls in an effort to stave off beach erosion, with little success.
In 1999, Cornelia Dean, science editor at The New York Times, wrote in her book Against the Tide that “seawalls damage virtually every beach they are built on.” She argued that, when placed on eroding shores — as they often are — seawalls eventually destroy the very beaches they are meant to protect. This idea has been repeatedly proven true. Seawalls harden the coastline, preventing natural adjustment and reflecting wave energy back toward the shore, which accelerates erosion. This cycle worsens when structures like groynes prevent sand from moving downdrift, further exacerbating the loss of sand. Ultimately, the result is coastal backwash — a term familiar to surfers, but disastrous for coastal ecosystems and properties.
Despite this evidence, the California Coastal Commission recently approved a $175-million seawall project at the southern end of San Francisco’s Ocean Beach, where a 3,200-foot-long, 55-foot-deep buried seawall will be built to protect a local wastewater treatment plant and sewage tunnel from erosion and rising sea levels.
Such projects are becoming increasingly common around the world, particularly in areas where infrastructure or private property was built long before the threats of erosion and rising sea levels were fully understood. Seawalls are often seen as the first line of defense against these growing threats. However, many experts argue that this is a “19th-century response to a 21st-century problem.”
Angus Gordon, a renowned Australian coastal engineer, criticized such approaches in The Guardian in response to the erection of a large concrete seawall in Collaroy-Narrabeen, Sydney. The seawall, measuring 7.5 meters high and extending 10 meters underground, was intended to protect beachfront properties that have long been at risk from storms and erosion. Gordon described this method as a throwback to outdated, non-environmental engineering practices that fail to address the root causes of coastal erosion.
In Collaroy-Narrabeen, where coastal erosion is well-documented, Professor Andrew Short from the University of Sydney has studied the issue since 1976. Short, who is considered one of the world’s foremost experts on coastal geomorphology, has criticized recent seawall construction in the region. “What we have now with this seawall is a total disaster,” Short said at a protest meeting, adding that only private landowners benefit from such measures. He suggested alternative, albeit more expensive, solutions, such as land buybacks or beach nourishment. The cheapest option, he noted, is often to take no action at all.
The buyback approach, though politically challenging due to the initial financial cost, could ultimately save money by transforming properties into parkland and restoring the natural state of the beach. This approach could buy time for properties further inland. Alternatively, beach nourishment, which involves replenishing the sand supply, could offer up to a century of protection. This method, while expensive, has been successfully implemented in other regions, such as the Gold Coast in Australia. There, a sand bypass project has significantly reduced erosion by pumping sand from the Tweed River to the beaches of southern Queensland.
At Ocean Beach, environmental groups like the Surfrider Foundation are advocating for a more sustainable approach, urging the California Coastal Commission to scale back the seawall project. They suggest constructing a smaller wall further from the coast, restoring dunes, and exploring alternative locations for critical infrastructure like the sewage tunnel.
Ultimately, research consistently shows that seawalls are not the panacea they are often made out to be. In fact, they frequently make the erosion problem worse. Experts argue that a more sustainable, long-term approach is needed — one that incorporates natural, “soft” shoreline stabilization techniques, such as vegetation, to allow coastlines to adjust to changing conditions over time.
King Canute’s lesson about the futility of resisting nature’s forces may have been lost on his courtiers, but it remains as relevant today as ever. As coastal communities continue to face the challenges of erosion and rising seas, it is time to heed his wisdom and adopt solutions that work with — rather than against — nature.
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