Seawalls - Types

Types

A seawall works by reflecting incident wave energy back into the sea, thereby reducing the energy and erosion which the coastline would otherwise be subjected to. In addition to their unsightly visual appearance, two specific weaknesses of seawalls exist. Firstly, wave reflection induced by the wall may result in scour and subsequent lowering of the sand level of the fronting beach. Secondly, seawalls may accelerate erosion of adjacent, unprotected coastal areas because they affect the littoral drift process. The design and type of seawall that is appropriate depends on aspects specific to the location, including the surrounding erosion processes. There are three main types of seawalls: vertical, curved or stepped, and mounds, as set out in the table:

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 sea wall. 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 sea walls deflect wave energy away from the coast.
  • Loose rubble can absorb wave energy.
  • These are partial to 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.
  • Less durable.
  • Shorter life expectancy.
  • Cannot withstand or protect from high-energy conditions effectively.

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