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Why your favorite beach might be eroding

In 2018, the San Francisco Public Utilities Commission is moving 50,000 cubic yards of sand around at Ocean Beach as a stopgap measure for the erosion along the south end of the shoreline.

Posted on August 14, 2023

While most people think of the beach as a place to relax, it has always served a more purposeful role: a buffer against storms. It’s a role that will become even more important as climate change continues to disrupt nature’s delicate balance, inciting sea level rise and stronger, more frequent storms on the coasts.

But those living right along the shore may soon find themselves without as much of a cushion, as coastal erosion diminishes or displaces major beaches. At least 13 miles of beaches have been lost on the Hawaiian islands of Kauai, Oahu, and Maui, and entire beachfront communities are collapsing on the Outer Banks in North Carolina. States like Texas and Alaska have seen their coastlines “retreat” by an average of five to 10 feet per year since 1900. Two-thirds of California beaches could disappear by 2100 all because of sea level rise.

Some forms of soft and hard engineering, like trapping sand with wooden fences, promise to keep erosion at bay, but scientists warn these shouldn’t be considered a permanent fix.

How does coastal erosion work?

When a beach shrinks or even disappears, it’s because coastal erosion removes sand, mud, pebbles, or other sediment along large bodies of water. This could include the saltmarshes in southern Louisiana, sandy strips in the Bay Area of California, and the Great Lakes.

It’s natural for the beach to be wider in northern summers, when waves are weaker and leave more sediment, and sparser in northern winters, when waves are stronger, according to Jennifer Miselis, who studies the effects of storms and sea level rise on coastal geology for the United States Geological Survey. This is because of many seasonal factors, including increased winds, storms, groundswell, and gravitational pull from the moon in winter.

The problem is when sand is taken from the shoreline and then not replenished, resulting in chronic erosion. In the US, this is usually because the pathways that bring sand from the ocean or river become blocked. For example, an inlet that forms naturally might prevent sediment from flowing alongside the coast. In other countries, especially in the Global South, companies are intentionally eroding beaches through sand mining. Sand, which is a key ingredient in concrete, is the second most used resource in the world after water, according to the United Nations Environment Programme.

Climate change could also mean less sand on shorelines. Stronger storms mean that more sand will be swept off beaches and into the water. Rising sea levels will cause more areas of beaches to be covered by water. “It’s what I call the bathtub model,” says Stephen Leatherman, a professor at Florida International University who researches beach erosion and sea level rise. “If you bring the water level up, it submerges things, but you’re not having any erosion. Your bathtub’s not falling apart.” However, when coupled with stronger storms, he explains, sea level rise can cause more of the beach to be washed away.

Where do people factor into all this?

Coastlines have always changed over time, says Mark Kulp, a professor of geology at the University of New Orleans. If you study the geologic record, you would find that sea levels have risen about 400 feet over the past 20,000 years or so. But climate change is causing sea levels to rise faster than before, and coastal infrastructure will make it harder for home and business owners to migrate.

Unlike many millennia ago, humans help drive erosion today. It’s often exacerbated by structures that were built to protect people from flooding, but block off sediment flow from bodies of water as a consequence.

Sandbags are one small measure for fighting coastal erosion on Lanikai Beach on Oahu, Hawaii.

Take Galveston, Texas, where a hurricane killed between 6,000 and 12,000 people in 1900, making it the deadliest natural disaster in American history. After that, the city built a 10-mile-long seawall along the coast. The seawall has kept residents and property safe for the past century, but it also decimated what was once a wide beach, causing the city to lose 100 yards of sand a year and hurting local ecosystems and the tourism industry. And in southern Louisiana, which has some of the fastest deteriorating coasts in the country, part of the problem is the levees built to protect communities from flooding, which also prevent sediment from flowing through and replenishing the marshes.

While people might think development along the coast is responsible for driving coastal erosion, Leatherman says this isn’t true—the reasons for coastal erosion and solutions vary significantly from place to place. But generally, he thinks jetties, which are rock structures built perpendicular to beaches to provide a safe passage for ships into harbors, and then seawalls cause the most erosion out of manmade structures.

What solutions are there?

Renourishment, which could mean dumping trucked-in sand on a beach, designing ways to trap sediment the tide washes in from flowing back into the ocean, or even dredging up sand from the ocean or lake floor to redistribute it on the beach, has been an increasingly popular method of slowing down the effects of erosion around the world. In the northeastern US in particular, “we’re doing a good job by nourishing beaches and keeping them in place,” Miselis says.

But renourishment, especially when it involves transporting new sand, is costly and only a Band-Aid for the problem. “Everybody wants beach nourishment,” Leatherman says. “But people don’t realize, you only set back the erosion clock. In other words, it’s like you’re treating the symptom, not curing the disease. You’re not stopping the sea level from coming up; you’re not stopping coastal storms from coming in.”

Other fixes might employ “soft engineering” techniques to trap sand on the beach, like fashioning wooden fences to build artificial sand dunes, and then planting native plant species to keep the dunes put. And in some cases, like in Louisiana, the levees that keep out flooding could be altered to allow some sediment to flow back into the Mississippi Delta, Kulp says.

But ultimately, people have to accept that some of their favorite beaches will wash away little by little. “If we’re gonna live in coastal environments, we just have to come up with creative and unique solutions to try to limit or reduce some of the erosion,” Kulp says. “But we also need to simultaneously recognize that there may be coastal sections on a global [level] that we can’t necessarily do anything about. We just have to accept that they’re going to disappear and change and that’s part of the process.”


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