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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 keep 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.


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 in the Figure below runs parallel to the coast like a barrier island.

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


Longshore drift can erode the sediment from a beach. To keep this from happening, people may build a series of groins. A groin 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. You can see how groins work in Figure below .

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


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

This seawall protects a beach 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.

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 Tohoku 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.


  • breakwater : Structure built in the water parallel to the shore to protect from strong incoming waves.
  • groin : Long, narrow piles of stone or timbers built perpendicular to the shore. A groin will trap sand.
  • seawall : Structure built parallel to the shore on the beach to protect against strong waves.


  • 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.


Use this resource to answer the questions that follow.

Methods Used to Slow Down Coastal Erosion at http://www.youtube.com/watch?v=nujYG_b8lI8 (1:52)

  1. What are the two methods to stop coastal erosion?
  2. What is a sea wall?
  3. What is a jetty?
  4. What is a groin?
  5. What are breakwaters?
  6. Why don't people like most of the methods to prevent coastal erosion?
  7. What is beach nourishment?
  8. What problems does beach nourishment cause?


  1. How does a groin protect a beach?
  2. How does a seawall protect a beach?
  3. How does a breakwater protect a beach?

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Difficulty Level:



6 , 7

Date Created:

Jan 04, 2013

Last Modified:

Oct 27, 2014

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