14.8: Protecting Shorelines

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Why do you see man-made structures on some beaches?

When you go to a beach, you may see man-made structures like these. Most attempt to keep the sand where people want the sand to be. A smaller number keeps the sand from coming into an area where it is not wanted.

Protecting Shorelines

Shores are attractive places to live and vacation. But development at the shore is at risk of damage from waves. Wave erosion threatens many homes and beaches on the ocean. This is especially true during storms, when waves may be much larger than normal. People build several types of structures to protect beaches.

Breakwaters

Barrier islands provide natural protection to shorelines. Storm waves strike the barrier island before they reach the shore. People also build artificial barriers, called breakwaters. Breakwaters also protect the shoreline from incoming waves. The breakwater pictured below (Figure below) runs parallel to the coast like a barrier island.

A breakwater protecting a beach

This rocky breakwater protects the beach at Tenerife in the Canary Islands, Spain.

Groins

Longshore drift can erode the sediment from a beach. To keep this from happening, people may build a series of groins. A groin (Figure below) is wall of rocks or concrete. The structure juts out into the ocean perpendicular to the shore. A groin stops the longshore movement of sand. Sand collects on the up-current side of the groin. Sand on opposite of side of the groin erodes. This reduces beach erosion.

A groin slows sand on the up-current side

This groin slows sand on the up-current side. Can you determine which way the water is moving based on where the sand is collecting?

Seawalls

A seawall is also parallel to the shore. However, a seawall is built onshore. Seawalls (Figure below) protect the shore from incoming waves.

A seawall protecting a shore

This seawall protects a shore in Vancouver.

Does Protection Work?

People do not always want to choose safe building practices, and instead choose to build a beach house right on the beach. Protecting development from wave erosion is difficult and expensive. The only foolproof way to prevent damage from erosion is to build away from shorelines.

Protection does not always work. The northeastern coast of Japan was protected by anti-tsunami seawalls. Yet waves from the 2011 tsunami that resulted from the Tōhoku earthquake washed over the top of some seawalls and caused others to collapse. Japan is now planning to build even higher seawalls to prepare for any future (and inevitable) tsunami.

Summary

People love the shore, so they develop these regions and then must protect them.
Seawalls and breakwaters are built parallel to the shore.
Groins are built perpendicular to the shore. They trap sand.