The Beaches Are Shrinking! How Coastal Squeeze Causes Beach Erosion

Beaches made of sand can change shape over time as the grains of sand move in the wind and waves. They may shrink during storms as sand erodes away, and then grow larger as calmer waves bring new sand to the beach. 

But around the world, many beaches have been eroding for years or decades without growing again. About one-third of the world’s coasts have sandy beaches, but 20% to 24% of those beaches are eroding rapidly, according to scientists who studied coasts with satellite images to explore how beaches worldwide have changed. It’s likely that even more beaches will erode as sea level rise speeds up this century, although, as we will see, sea level rise is not the only reason that beaches are shrinking.

Beaches have important roles as coastal protection during storms and habitat for wildlife like shorebirds, crabs, clams, and sea turtles that lay eggs in sand. People, of course, also flock to beaches for fun. Shrinking beaches affect the lives of people in coastal cities and towns and wildlife that needs beaches.

Along a coast without roads or buildings (which is called an undeveloped coast), a beach will typically move landward over many years as sea level rises. Its sand will also be tossed landward by waves from storms like hurricanes, which are growing stronger as the climate warms and changes.

But along a developed coast with cities, towns, roads, and other human-built infrastructure, a beach can’t move landward as it is pummeled by waves and as sea level rises. Instead, the sand erodes away and the beach shrinks. This phenomenon is called coastal squeeze because the beach is squeezed between communities and the ocean.

Along coasts lined with long, narrow barrier islands made of sand (like most of the U.S. East Coast) sea level rise and strengthening storms also cause coastal squeeze, although sometimes it’s not the beaches that shrink. When undeveloped barrier islands move landward, they take space from the calm water lagoons and salt marshes between islands and the mainland. This causes lagoons and marshes to shrink. A developed barrier island with cities and towns, unable to move landward, is prone to erode and may disappear entirely over time. 

Beaches also shrink along coasts with seawalls. These human-made walls of rock or concrete are built to protect cities and towns from flooding and waves, but seawalls also typically destroy the beaches next to them. As waves crash on a seawall, their energy scours sand away from the beach, sending it out to sea; it eventually settles down on the ocean floor. For example, a seawall was built in 1900 on Galveston Island, a barrier island on the Texas coast, to protect the city during hurricanes. The beach next to the seawall eroded away in about two decades. That was before beaches were shrinking as the impacts of warming climate were causing coastal squeeze. Today the combination of seawalls, sea level rise, and strengthening storms is even more of a threat to beaches.
 

What can we do to save beaches?

To reverse erosion, huge amounts of sand are added to beaches, a process called beach nourishment or sand replenishment. The sand is often pumped up from the seafloor in a giant hose and then spread by bulldozers. Beach nourishment can rebuild a beach — the Galveston beach that eroded along a seawall was later recreated this way — but it is expensive and temporary. Erosion continues, so sand that is added will eventually be gone. In addition, moving massive amounts of sand can disrupt wildlife, both on the beach where sand is added and on the seafloor where sand is removed. 

Dunes are a natural source of sand for beaches and help protect coastal communities, but they are often destroyed when buildings and roads are built. Sand dunes can be restored, often by adding native grasses and other plants at the landward edge of a beach. The plants’ roots hold sand in place, and more sand, carried by wind and waves, naturally collects around the plants. 

Because undeveloped coasts are not as affected by coastal squeeze, coastal nature preserves can help protect beaches. Another way to let beaches move instead of eroding is to design buildings that allow sands to shift. And if buildings near beaches are needed, designing structures that allow sands to shift over time, and that are movable, can help keep beaches from shrinking. Developed coasts can avoid coastal squeeze by moving buildings, roads, and other structures away from the shore, which is called managed retreat. When people in a coastal community disagree about what needs to be done, it can be challenging to make a plan for managed retreat. But a plan can have big benefits: saving beaches and protecting homes and roads from flooding and other damage. In the city of Ventura, California, roads, a bike path, and parking lots were moved away from the coast at Surfers Point, where the beach had been eroding for decades. Areas on Surfers Point that used to be paved are now part of the beach and sand dunes. 

According to recent modeling, half the world’s beaches could be lost by the end of the century. But the number of beaches that are actually lost depends on our actions. People who live near coasts can take action by moving structures, including seawalls, from beaches and by restoring beach sand and dunes. And all of us can help beaches, even if we don’t live near one, by releasing less heat- trapping greenhouse gases into the atmosphere to slow warming and sea level rise.