How Do Seawalls Work

Sea Walls has been around for Centuries and were popular in Ancient times. Sea Walls today protect cities and towns on coastlines and keep oceans from damaging businesses from flooding along with saving lives. They are massive structures that are constructed to resist the energy built up from the Ocean. How Do Seawalls work?

A Seawall effectively acts as a form of coastal defense by redirecting the energy of a wave made by a storm surge back to the ocean water, protecting the coastline from flooding and reducing erosion of the beach front.

A seawall is a passive structure, which protects the coast against erosion and flooding. Seawalls are often used at locations off exposed city fronts, where good protection are needed and where space is scarce. In the coming years Seawalls will be used on coastlines worldwide in the defense of rising sea levels from Global Warming.


Advantages Of a Seawall


The primary purpose of a seawall is protecting residential shorelines from upland erosion and surge flooding. A seawall acts as an important coastal defense to these types of events. When a wave crashes onto the shore, the seawall redirects a lot of that energy back to the water, protecting the coastline and reduces erosion of the beach front. It also protects residential areas from flooding. There are many advantages to using retaining walls along coastal beaches and inland shorelines.

The environment can be protected keeping the soil and sand from being eroded and destroyed. There are many businesses that thrive along the coastline that couldn’t exist without the help of a Seawall and the protection it provides. They ensure the natural beauty of the coastline and prevent the alternatives that are prevalent like coastal storm surges and when Hurricanes and Tsunamis rear their ugly heads. Other advantages of Seawalls are:

  • They reassure the public
  •  Relatively Cheap They use cheap material like Rocks
  • They have a long life span.

Studies suggest that flooding from rising sea levels will prove more costly than building barriers to protect coastlines. The storms on the East Coast alone in the last few decades have created a need for Seawalls and other protective construction projects near the shoreline that prevent disasters and huge Insurance rates that businesses and homeowners just can’t afford to pay. Insurance Companies predict Seawalls will be built all around the world.

In previous years, lots of low lying communities have been allowed to build on properties that were well under sea level. Add the fact that ocean levels have been rising for decades because of Global Warming and the risk is obvious.

The high insurance rates that are already unbearable in places where people like I’m from. A bad storm can create flooding in the coastal areas of New Jersey or New York.  Then after the cleanup, comes the higher rates tacked on to premiums before your house is even livable.  That’s just New Jersey. 

This is a growing global problem with projections saying that 5% of the world’s populations live in coastal regions that are below sea levels.

Seawall Disadvantages

A well constructed Sea Wall will have some negative factors attached to it too. Mainly, because the wave action’s energy that tends to spread out from the area that it’s built around to the neighboring areas with no protecting structures. Quickly eroding property and reducing the sand supply to their beaches.

Seawalls can cause increased damage to adjacent areas of the beach that do not have seawalls. This so-called “flanking erosion” takes place at the ends of seawalls. Wave energy can be reflected from a seawall sideways along the shore, causing coastal bluffs without protection to erode faster. Some other disadvantages of a Seawall are:

  • They can make it harder to enter the beach
  • Interfers with sediment flow along the coast
  • Environmentally ugly
  • Recurved sea walls cause greater erosion at the base of the wall

Another negative factor in building a Seawall is the maintenance cost. Even well-constructed Seawalls have a maintenance cost. Some maintenance cost will include:

  • If no weep holes are installed in the seawall, groundwater and rain percolating through the soil will build up pressure behind it, pushing over the wall.
  • Scouring at the toe of the wall may tip the wall if there is not any toe protection.
  • Wave energy deflects down the wall, eventually destroying the ends of the wall.
  • Storms and high tides carrying debris can severely damage the seawall.

Seawalls, according to scientist have affected ecosystems along the coastline with creating losses to habitats and changes in biodiversity. When natural beaches were compared to beaches with man-made structures there were large differences in the Ecology of both systems.

Harden shorelines (that are developed areas) that are beaches that have Bulkheads or Seawalls built to protect Erosion, had losses in or sand or land, Some areas causing damage somewhere else along the beachfront areas.


Seawall Construction Methods

Although there are several different ways of constructing a seawall, there are three main methods used.

  • the first is thin, interlocking sheet piles driven deeply into the ground.
  • The second method of seawall construction is individual piles used to support an above-ground structure.
  • The third method is a massive gravity construction resting on the shore bottom or embedded slightly in it. This construction is supported by its own weight rather than by piling

A Large Seawall is built from concrete masonry or sheet piles and runs parallel to the shore at the transition between the beach and the mainland or dune in order to protect the inland area from wave action. They usually are massive structures that can resist storm surges for long periods of time.

The height of a seawall will at least cover the difference between the beach level and the mainland, though commonly seawalls are built higher and can be straight or curved walls to protect the land against wave overtopping. Seawalls are also used to stabilize eroding cliffs and protect coastal roads and settlements.

The crest of the wall often extends into a stone area part that could be used for a road, promenade or parking area. A seawall creates a distinct separation between the beach and the mainland. Seawalls are often found in cases of narrow or steep beaches, where a typical breakwater is just too large.

A jetty platform on wooden or concrete piles built into the sea to protect a navigation channel and it allows the berthing of ships. It usually does not have a shore protective function which instead breakwaters do. Parallel jetties are frequently built to delimit a navigation channel.

Jetties will affect the longshore transport of sediment and ecological processes. Jetties can be constructed with concrete, stone, timber or steel. Jetties are not usually adaptation measures but may be connected with seawalls or other hard coastal defense structures. the life Expectancy of these types of Seawalls is between 35 years without doing major repairs. The average price of a Seawall in the United States is $2.6 million dollars per/meter


Wall & Stone Jetty From Atlantic City Seawall                            Steel Panels laid between Concrete and Stone Jetty

Large Seawalls like this one close to where I lived in Atlantic City NJ are very expensive to build. A very good friend of mine was contracted out by the Army Corp of Engineers to work on surveying for this enormous project. Federal monies were granted to the city for the project that was done in as little 2 years.

The northern area of the city was destroyed during Superstorm Sandy and this project was used to revitalize that area and will finally open it back up since it was closed downed 2012. Massive stones were shipped in from a Pennsylvania stone quarry to be used on the ocean side of the Seawall.

How Long Do Seawalls Last

Large Seawalls and other man-made structures that provide protection against the damaging effects from the waves of the ocean are called man-made landscaping that is mostly caused by urbanization and infrastructure expansion.

Nowadays lots of structures are being built along the coast because of rising sea levels that are being brought on by Global Warming. More and more people live by the sea or have businesses there.

Dykes, Rock fills Seawalls are used to hold back nature to prevent the danger to populations on coastline so the building can go on. Faced with erosion and rising sea levels sustainable development are needed to keep from Mother Nature reclaiming coastlines that used to belong to her.

New types of Seawalls are expected to last up to 100 years depending on materials used to make them or 50 years without major repair done to them. Researchers believe that every country around the world within 90 years, will be building structures much like Seawalls to defend itself from the rising tides and wave heights caused by warming temperatures because the cost of flooding will be more expensive than the cost of these protective projects.

 JimGalloway Author/Editor


Related Questions:


 How do seawalls prevent erosion?

A structure separating land and water areas. It is designed to prevent coastal erosion and other damage due to wave action and storm surge, such as flooding. Seawalls are normally very massive structures.

Why are seawalls 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.

 Are sea walls sustainable?

Sea walls are exactly that. Giant walls that span entire coastlines and attempt to reduce erosion and prevent flooding in the process. They also produce a strong backwash in waves which undercuts the sea wall making their long term sustainability questionable


referencesSeawalls May be Cheaper than Rising Waters

 Jim has over 30 years in Water/Wastewater& Water Filtration Business. He has written over 300 articles on the Worldwide Water Situation


Author/Editor, MyWaterEarth&Sky

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