Life on the Edge - Coastal Development and Erosion

People love living near waterways – in the United States, for example, 55% of the population lives within 808 miles of a major coastline. According to the National Oceanic and Atmospheric Administration (NOAA) by the year 2025, that number will be up to about 75%. So what’s the problem?

The problem is that we don’t think like geologists. Geologists know that coastlines are mobile features, constantly shifting in response to wave and storm action. Geologists know that the coast is in a delicate balance, and building in a particular area often accelerates erosion, even when the structures we are building were supposed to prevent the erosion. Geologists know that fragile bits of land like spits can be completely washed away during a major storm. And geologists – at least some of us – wonder why people keep building on the beaches.

Beaches are not stable structures, but dynamic ones. They are often reshaped, diminished, or completely washed away by winter storms. Local economies which depend on beaches for tourism dollars often rely on dredging operations to rebuild the beaches. The dredges scrape sand from the ocean floor and spray it back on the beaches. This kind of artificial beach replenishment, often required every 3 to 5 years, isn’t cheap. One popular resort beach in Ocean City, Md. has been replenished several times over a decade, costing taxpayers $80 million in the process. And that’s nothing compared to the money paid out in federally-funded grants, loans, and insurance payments to hurricane victims, such as the billion dollars paid to North Carolina coastal residents in a single year.

Sea walls are another attempt to conquer the natural world through engineering. Sea walls are meant to prevent erosion – however, the walls are actually a barrier to natural beach replenishment. As a result, the beach is narrowed and the offshore slope is increased. This leads to more powerful wave action, which increases erosion – eventually the sea wall will fail, but by then the beach will likely be completely gone.

Groins are protrusions built out into the water designed to catch beach sand as it drifts down-current. Groins do catch sand, which is often built-up on the up-current side. But that means the water below the groin is sand-starved, which leads to increased erosion on the down-current side. When the lower beach begins to disappear, the answer is often to build another groin farther down the beach. Eventually that groin, too, causes increased erosion below it -–and the process continues.

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