From Florida to the Costa del Sol, costly sea defences are accelerating beach erosion and will ultimately fail to protect coastal towns and cities from rising tides, say experts
The world’s beaches are being washed away as coastal developments increase in size and engineers build ever higher sea walls to defend against fierce winter storms and rising sea levels, according to two of the worlds’ leading marine geologists.
The warning comes as violent Atlantic and Pacific storms this week sent massive 50ft waves crashing over sea defences, washed away beaches and destroyed concrete walls in Europe, north America and the Philippines.
“Most natural sand beaches are disappearing, due partly to rising sea levels and increased storm action, but also to massive erosion caused by the human development of the shore,” said Andrew Cooper, professor of coastal studies at the University of Ulster.
“The widespread damage on western Europe’s storm-battered shores, the devastation caused by hurricane Sandy along the northeastern US seaboard, the deaths brought on by typhoon Haiyan in the Philippines all exemplify the total inadequacy of [coastal] infrastructure and the vulnerability of cities built on the edge of coastlines”, said Orrin Pilkey, professor of earth and ocean sciences at Duke University in Durham, North Carolina.
Pilkey and Cooper say in a new book, The Last Beach, that sea walls, which are widely believed by many local authorities to protect developments from erosion and sea level rise, in fact lead to the destruction of beaches and sea defences and require constant rebuilding at increasing cost.
Dunes and wide beaches protect buildings from storms far better than sea walls, say the authors. “The beach is a wonderful, free natural defence against the forces of the ocean. Beaches absorb the power of the ocean waves reducing them to a gentle swash that laps on the shoreline. Storms do not destroy beaches. They change their shape and location, moving sand around to maximise the absorption of wave energy and then recover in the days, months and years to follow,” said Pilkey .
Beaches in nature are almost indestructible, but seawall construction disrupts the natural movement of sand and waves, hindering the process of sand deposition along the shorelines, said Cooper.
“The wall itself is the problem. If you build a sea wall to protect the shore, the inevitable consequence is that the beach will disappear. The wall cannot absorb the energy of the sea. All beaches with defences … are in danger. When you build the sea wall, that is the end of the beach,” he said.
“Beaches have become long, narrow engineering projects sustained only by constant maintenance and ongoing expenditures. Ugly seawalls have removed beaches altogether. Trying to hold the shoreline in position makes a flexible response to sea level rise more difficult,” said Pilkey.
Many of the world’s most famous beaches are now ecologically dead and dependent for their survival on being replenished with sand or gravel, they say. “The death knell has already sounded for large stretches of beaches along densely developed shorelines like those in Florida, Spain’s Costa del Sol, Australia’s Gold Coast and Brazil’s Rio de Janeiro,” says Pilkey.
But Jonathan Simm, technical director for flood management at HR Wallingford defended engineers. “We are but servants. There are some very difficult social and political decisions that have to be made about which frontages should be defended. Engineers get struck in the middle between different… political and technical arguments.
“The reality is that major urban conurbations are going to want to sustain their existing defences. But a lot of beaches are under stress so the engineering is going to become much more expensive.”
Sea level rise, which is expected to raise levels significantly over the next 100 years, will affect beaches in different ways, said Pilkey. “Although the sea has only risen a foot (0.3 meters) over the last 100 years or so, that amount can have a real impact on shoreline retreat on very gently sloping coasts. In theory, a one-foot sea-level rise should push the shoreline back 2,000 feet.”
As beaches disappear, countries are turning to increasingly expensive sand replenishment programmes which dump thousands of tonnes of dredged sand on existing, eroded beaches.
But these artificial beaches usually erode at least twice as fast as natural beaches and can only ever be a temporary solution, said Cooper. “As time goes on and as the sea level rises, the interval of re-replenishment will get shorter because the beach becomes less stable. Beach replenishment is only a plaster that must be applied again and again at great cost. It doesn’t remove the problem, it treats the symptoms. Eventually and inevitably beach replenishment will stop either as sand or money runs out”.
It also smothers all life on the beach. “The near shore food chain that originates with the tiny organisms living between grains of sands and surviving on occasional influxes of seaweed is now gone. The whole ecosystem is out of whack. Habitats for turtle and bird nesting are being destroyed,” said Cooper.
“We have a mentality to just rebuild everything after a storm. The simplest solution would be to move the infrastructure back. The problem is the obsession with building and defending property right next to the beach and to hold the beach in place. This process just destroys the beach.”
Source: The Guardian