Beach Erosion (Water Science)

Erosion is the removal of soil and sand by the forces of wind and water and it has occurred for as long as land has met water. Erosion is a continual natural process; material is constantly being shifted around to change the shape of a stream, river-bank, or beach. Today, when much available land bordering the ocean (coastlines) is developed for housing, the erosion of beaches is an important concern. Wave action can cause erosion that can remove the support for a house, causing it to tumble into the ocean. Along the 80,000 miles (128,748 kilometers) of coastline in the United States, beach erosion has become a big problem. While erosion is a natural process, humans have caused the rate of erosion to increase. The main factor causing the increased erosion damage is development.

Waves continually change a beach's shape by moving sand, small rocks, and debris.

Waves continually change a beach’s shape by moving sand, small rocks, and debris.

How beach erosion occurs

A beach is the rocky or, most often, sandy zone where the land meets the lake or ocean. This wind also moves the water towards the land, pushing the water to form waves. As the depth of the water decreases towards the beach, the waves change shape. Eventually, the top of the wave crashes over and down onto the beach. Then the water is pulled back out as the next wave makes its way towards the coastline.


This constant movement of water in and out across the sand or rocks is similar to the action of sandpaper on wood. Each wave can wash away or as least slightly move a tiny portion of the beach. Over a very long period of time, all these tiny events add up to the rearrangement of the beach. Sometimes, beach erosion occurs at a faster rate, as storms bring larger waves that crash more forcefully onto the beach. Storm waves carry more energy than calm waves, and can quickly wear away beach material.

For all the sand lost from a beach, the action of the waves also brings an equal amount of sand ashore. Thus, although the shape of a beach will change, the beach itself will remain.

Problems caused by erosion

Although erosion is a natural process and does not completely remove a beach, scientists are concerned about beach erosion because human activities have altered the way erosion occurs. Coastlines are attractive places and many people want to live or visit there. Many beaches are now completely lined by buildings, parking lots, and roads. The beachfront areas of Miami Beach, Atlantic City, and Honolulu, are three examples of heavily developed beaches in the United States. The large area of land covered by concrete does not allow rainwater to soak into the ground and gently trickle out over the beach at many different points. Instead, the water empties onto the beach at only a few streams. The streams wear away selected portions of the beach, which can make erosion more severe.


Carolina Outer Banks

Beach erosion makes seaside homes more vulnerable to storm surges. Families must often evacuate when hurricanes threaten.

Beach erosion makes seaside homes more vulnerable to storm surges. Families must often evacuate when hurricanes threaten.

The Outer Banks are series of dunes that stretch for 130 miles (209 kilometers) in the sea off the coast of North Carolina. Among the well-known attractions of the Outer Banks is Kitty Hawk, site of Orville and Wilbur Wright’s famous 1903 flight, and a series of distinctive lighthouses.

The Cape Hatteras lighthouse is also an example of the power of erosion. When the lighthouse was built in 1870 it stood about 1,500 feet (457 meters) back from the waves crashing on the beach. By 1999 erosion had brought the waves to within 150 feet (46 meters) of the lighthouse. To preserve the structure, engineers picked up the lighthouse, put it on a movable treadmill similar to the ones used to transport Apollo spacecraft to the launch pad in the 1970s, and moved the lighthouse further inland.

One of the reasons that erosion claimed so much land was a manmade attempt to stop the process. In the 1970s the United States Navy built two groynes just north of the lighthouse. The groynes were put there to protect a building. Unfortunately, they accelerated the erosion downstream to the point where moving the lighthouse was necessary to save it.

Development and erosion

The desire for a home right on the ocean has lead many people to literally build their houses on top of sand dunes, which are hills of sand heaped up by the wind. Dunes are not permanent structures; they naturally wear away. To attempt to reduce erosion, people have built structures like seawalls and narrow strips that jut out into the water (a groyne). These structures break the pattern of the waves in a small area. The United States government spends over $150 million each year to build beach-protective structures. Homeowners also spend a great deal of money.

While a small section of a beach may be protected by these structures, other areas of the beach are often more affected by the resulting interrupted wave action. To compensate, sand must often be added to a beach if the beach is to be preserved. In parts of Florida, beach repair of this type averages about $1 million per mile of beach every year.

The use of seawalls, in some areas, especially where they are built by homeowners intermittently along a coast, has proven to be unwise. Rather than allowing the incoming energy of a wave to disappear over the area of a beach, a seawall can actually accelerate the speed of incoming water flowing around or over it. This speeds up the removal of material from the beach. In some areas where seawalls have been in place for many years, the beach has often completely disappeared and the waves lap the base of the wall. Where seawalls are built along a large, continuous area such as in Galveston, Texas, and are constructed high enough that waves do not crash over them, they cause less slow beach erosion. The Galveston seawall also protects against the rapid beach erosion that occurs during hurricanes.

Coastal Development Laws and Acts

The need to protect coastlines from erosion and overdevelopment has lead the United States to enact various rules and regulations.

In 1972 the federal government created the Coastal Zone Management Act. This voluntary program helped encourage coastal states to make changes that would help protect beaches by sharing the cost of some of this development. In the years since then, the act has been revised to make money available to projects that seek to restore coastal areas to a more natural state and to keep beaches from being bought by private owners.

The state of California has a series of regulations that together make up the California Coastal Act. The rules help control what type of development can occur along the coast and how much of the coast is available to the general public. A similar coastal management program exists in Atlantic coast states including Maine and New Jersey.

Reducing beach erosion

Many areas have passed laws to prevent the destruction of sand dunes, which serve as a natural protective barrier against erosion during storms. Where sand dunes are destroyed by humans or erosion, artificial barriers of wire or tree limbs secured in dune-forming areas help to speed their formation. Protected dunes along seashores are rich in plant life, which serves to further strengthen the dunes because of the root networks of the tall grass-like plants. Although dunes provide little protection for narrow beaches, they help decrease erosion in broad beaches, such as those in Florida and Texas.

A strategy that scientists are evaluating to reduce erosion is to build up the bottom of the ocean farther out from the beach, creating an off-shore ridge with sand and materials such as steel from aircraft and ships, or stone. Incoming waves break over the ridge of piled up material instead of breaking on the beach. Researchers are examining whether this disrupts the natural environment in a negative manner.

The most popular method to keep the sandy beaches that are so desirable to homeowners and recreational beachgoers is to bring sand to the beach. Often sand will be taken from the ocean bottom further away from shore and sent through a pipe to the beach. This temporary measure only delays the effects of erosion, and is often repeated.

WORDS TO KNOW

Coastline: The land that lies next to the sea.

Erosion: Wearing away of the land that occurs by natural forces such as wind and waves.

Groyne: A wall-like structure that sticks out into the water from the beach, which is intended to trap material.

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