How Do Seawalls Work

Sea Walls have 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 beachfront.

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 is needed and where space is scarce. In the coming years, Seawalls will be used on coastlines worldwide in defense against rising sea levels from Global Warming.


Advantages Of a Seawall


The primary purpose of a seawall is to protect residential shorelines from upland erosion and surge flooding. A seawall acts as an important coastal defense against 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 reducing erosion of the beachfront. 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 by 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 materials 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 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 are 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 population 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 tends to spread out from the area that it’s built around to the neighboring areas with no protective 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
  • Interferes 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 costs 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 scientists have affected ecosystems along the coastline 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) are beaches that have Bulkheads or Seawalls built to protect against Erosion and losses in sand or land, Some areas cause damage somewhere else along with 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 that were driven deep 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’s 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 is built into the sea to protect a navigation channel and it allows for 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 major repairs. The average price of a Seawall in the United States is $2.6 million dollars per/meter

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 which was done in as little as 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 of the waves of the ocean are called man-made landscaping which 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 the coastline so the building can go on. Faced with erosion and rising sea levels sustainable development is needed to keep Mother Nature reclaiming coastlines that used to belong to her.

New types of Seawalls are expected to last up to 100 years depending on the materials used to make them or 50 years without major repairs 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.



For more information on Oceans and anything Water like this article stay here on MyWaterEarth&Sky-In the last couple of decades, Tsunamis have killed hundreds of thousands of people using a series of giant waves called “wave trains” that also happen in what’s called a ………………. Continue reading



JimGalloway Author/Editor

References:  Seawalls May be Cheaper than Rising Waters



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