Seawall

A seawall (or sea wall) is a special wall built along the coast to protect land from the sea. It helps keep towns, nature areas, and places where people like to spend time safe from strong waves, high tides, and big waves caused by events like earthquakes under the ocean.

Seawalls are made from strong materials such as reinforced concrete, big rocks, steel, or special boxes filled with rocks called gabions. Sometimes they are even made from wood, metal, or special sandbags. Building a seawall can change how sand moves along the shore, which may cause other problems for the environment.

Even though seawalls are very strong, they can be expensive to build. Because of this, people are sometimes looking for other ways to protect the coast that are easier on nature, like adding more sand to beaches. Seawalls are an important part of keeping coastal areas safe, but they need to be planned carefully to balance protection with caring for the environment.

Types

A seawall helps protect land by pushing wave energy back into the sea, which reduces erosion. However, seawalls can have weaknesses. They might cause the sand in front of them to wash away, and they can also speed up erosion in nearby areas without protection.

There are special barriers built to protect against big waves, like those from underwater earthquakes. After a big disaster in January 2005, India started planting trees and plants along its coast as a natural way to protect against future waves. Some studies show that walls placed far out in the water can lower big wave heights by up to 83%.

The best kind of seawall depends on where it is built. There are mainly three types: straight walls, curved or stepped walls, and mound-shaped walls.

Natural barriers

A report from the United Nations Environment Programme (UNEP) found that areas with natural protections, like mangroves and coral reefs, experienced less damage during a big wave event in December 2004. These natural features help stop big waves and reduce flooding.

Seawall types

Type	Illustration	Advantages	Disadvantages	Example
Vertical	Vertical seawalls are built in particularly exposed situations. These reflect wave energy. Under storm conditions a non-breaking standing wave pattern can form, resulting in a stationary clapotic wave which moves up and down but does not travel horizontally. These waves promote erosion at the toe of the wall and can cause severe damage to the seawall. In some cases, piles are placed in front of the wall to lessen wave energy slightly.
		The first implemented, most easily designed and constructed type of seawall. Vertical seawalls deflect wave energy away from the coast. Loose rubble can absorb wave energy.	These can suffer a lot of expensive damage in a short period of time. Vertical design can be undercut by high-wave energy environments over a long period of time.
Curved	Curved or stepped seawalls are designed to enable waves to break to dissipate wave energy and to repel waves back to the sea. The curve can also prevent the wave overtopping the wall and provides additional protection for the toe of the wall.
		Concave structure introduces a dissipative element. The curve can prevent waves from overtopping the wall and provides extra protection for the toe of the wall Curved seawalls aim to re-direct most of the incident energy, resulting in low reflected waves and much reduced turbulence.	More complex engineering and design process. The deflected waves can scour material at the base of the wall causing them to become undermined.
Mound	Mound type seawalls, using revetments or riprap, are used in less demanding settings where lower energy erosional processes operate. The least exposed sites involve the lowest-cost bulkheads and revetments of sand bags or geotextiles. These serve to armour the shore and minimise erosion and may be either watertight or porous, which allows water to filter through after the wave energy has been dissipated.
		Current designs use porous designs of rock, concrete armour. Slope and loose material ensure maximum dissipation of wave energy. Lower cost option.	Shorter life expectancy. Cannot withstand or protect from high-energy conditions effectively.

Trade-offs

A good way to decide if a seawall is useful is to think about whether its benefits are worth the cost. Besides stopping erosion, we need to think about how building a wall changes the natural coastal ecosystems and what it might do to homes or activities near the water.

Seawalls are fixed structures, and this can create problems because the coast is always changing. They can stop the natural movement of sand and other materials between the land and the sea. The table below shows some good and bad things about seawalls that can help us compare them to other ways to manage the coast, like beach nourishment.

In general, seawalls can be a good way to control coastal erosion if they are built well and made from strong materials. They can last a long time and offer protection during big storms as well as everyday wear from waves. However, big natural events can show where seawalls are weak, and studying these events can help us make better seawalls in the future.

Issues

Sea level rise makes seawalls harder to use because it makes the water level higher and waves stronger. This means some seawalls might not be tall enough to protect the land. Big storms, like Superstorm Sandy in 2012, can cause a lot of damage when the sea level is higher.

Seawalls also need to deal with water pressure from groundwater and waves. If water gets trapped behind a seawall, it can push the wall and make it crack or move. Extreme storms can create waves much stronger than usual, which can damage seawalls that were not built to handle such force.

Putting seawalls near ocean life can change the light and space that sea creatures need. Projects like Living Seawalls in Sydney, Australia try to help sea life by designing special tiles on seawalls that look more like natural rocks.

Finally, seawalls need regular care to stay strong. Old seawalls can break down and become costly to fix if they are not maintained.

History and examples

Seawall construction has existed since ancient times. In the first century BCE, Romans built a seawall or breakwater at Caesarea Maritima to create an artificial harbor called Sebastos Harbor. They used a special kind of concrete called Pozzolana that hardens in seawater. Barges filled with this concrete were floated into place and sunk, and the harbor still stands today after more than 2000 years.

The oldest known coastal defense is a row of large rocks off the coast of Israel in the Mediterranean Sea. These rocks were placed to protect a coastal settlement from rising sea levels. They were discovered in 1960 during an underwater search for shipwrecks and were uncovered in 2012 when storms moved away covering sand.

More recently, seawalls were built in 1623 in Canvey Island, UK, after big floods happened there. Since then, seawall designs have become more advanced with better materials and understanding of how coastlines work.

The Vancouver Seawall in British Columbia was built to protect the area from waves caused by passing ships. Construction began in 1917, and today it is a popular 22 km path for walking and biking. It also helped provide jobs during tough economic times.

In 2004, a huge tsunami caused by an earthquake in the Indian Ocean hit India's coast, but the city of Pondicherry stayed safe thanks to a strong stone seawall built by French engineers hundreds of years ago. This wall, kept in good condition over time, protected the city even when water levels rose very high.

In Japan, many coastlines have seawalls to protect against big waves and tsunamis. During a major tsunami in 2011, some seawalls were not enough to stop the waves, showing that even strong protections have limits. This event made people think about better ways to protect coastlines.

After Hurricane Sandy in 2012, New York City planned to spend money on new seawalls and other protections. In Florida, special dams called tiger dams are used to shield homes near the water.