Why Do We Build Sea Walls?

Sea walls are used for many purposes, including protecting beaches from storm surges, preventing flooding, and creating landfills. They also provide protection from coastal erosion.

Seawalls are hard engineered structures with a primary function to prevent further erosion of the shoreline. They are built parallel to the shore and aim to hold or prevent the sliding of the soil, while providing protection from wave action (UNFCCC, 1999).

Seawalls are exposed to all sorts of coastal processes, like erosion. They conflicts with the active nature of the sea, and comes in between the interaction between land and sea. Hence, seawall structures needs regular maintenance and frequent replacement to function properly.

Seawalls can be constructed using rubble stones, concrete, steel, aluminum, timber, and vinyl. Rubble mound seawall is the most common type of seawall constructed, given the rubble stones are easily available and cheap.

Features of Seawalls

  • Seawalls are engineering structures that are located near the beach to prevent beach erosion.
  • These structures are modes through which the energy of the waves are either absorbed, dissipated or diverter before the waves approach the beach. 
  • Seawalls can be large structures to small ones based on the harbor type.
  • Seawalls not only reduce erosion, but also protect any structure near the beach.

Variation in Different Design of Seawalls
Image Courtesy: Xianli Zhu Technical University of Denmark
Technologies for Climate Change Adaptation – Coastal Erosion and Flooding
  • As shown in figure above, revetment are engineering structures similar to seawalls, that are used to protect the coastline.

Types of Seawall Construction

Three main types of seawalls constructed are:
  1. Vertical Seawall Construction
  2. Curved Seawall Construction
  3. Mound Seawall Construction

1. Vertical Seawall Construction

  • These seawalls are stick straight wall into the air like a fence that is made of steel or concrete.
  • Vertical seawalls are easy to design and construct.
  • It is a tried and true method used to block any high powered wave.
  • Vertical walls stay perpendicular to the water and take full brunt of wave. The waves slow down only after hitting these walls. Hence, vertical walls wear off very easily. 
  • Vertical walls are hence best for areas where the waves are calm and the coastline are protected. So that waves do not require repairs after a couple of years.

Vertical and Curved Seawalls

2. Curved Seawalls

Curved Seawall Construction
Image Courtesy: Mammoth Memory

  • Curved seawalls are also called as steeped seawalls.
  • These structures redirect the waves without causing much disturbances as vertical seawalls.
  • It resembles the shape of a wave and it is one of popular type.
  • Curved seawalls drifts the waves upwards thus reducing the impact.
  • These walls are normally built using poured concrete.
  • These structures helps undercutting at the base of the wall.
  • Best option used to dissipate energy of the waves and helps protect the structure.
  • Good option for construction of seal walls close to the coast.
  • Greater defense against natural disasters and tide.
  • Are highly durable and can stay for years without retouching.
Concrete Curved Seawalls

3. Mound Seawalls

  • Common seawall constructed using concrete blocks and stones
  • Less expensive than previous options.
  • Formed by rubble and rocks
  • Slope shape reduces the forces with which the waves hit

Construction Details of Rubble Mound Seawalls

The rubble mound seawall is generally designed to consist of three layers. Viz. core, secondary layer and an amour layer (Fig.1). A minimum of two layers of stones (units) in the amour and secondary layer is always necessary.

Typical Section of a Rubble Mounded Sea Wall

While the thicknesses of these layers are determined by the size of stones used, including that of the core are determined based on maximum water level, design wave height, wave run-up, permissible overtopping and method of construction.

The typical construction steps for rubble mound seawalls are:
  1. Determination of the water level range for the site
  2. Determination the wave heights
  3. Determination of the beach profile after the storm condition / monsoon
  4. Selection of suitable location and configuration of the seawall
  5. Selection of suitable armor to resist the design wave
  6. Selection of size of the armor unit
  7. Determination of potential run-up to set the crest elevation
  8. Determination of amount of overtopping expected for low structures
  9. Design of under-drainage features as per the requirement
  10. Provide for local surface runoff and overtopping runoff and make any required provisions for other drainage facilities such as culverts and ditches
  11. Always consider end condition to avoid failure due to flanking
  12. Design toe protection, filter and under layers
  13. Provide for firm compaction of all fill and back-fill materials. This requirement should be included on the plans and in the specifications. 
  14. Develop cost estimate for each alternative
  15. Provision for regular maintenance and repairs of the structure

Factors Affecting Seawall Construction

The type of seawall constructed is dependent on the:

  1. Nature of the forces they have to resist
  2. The climatic conditions
  3. The type and strength of waves (wave height, wave period, direction)
  4. Nature of the bed and material
  5. Availability of materials for seawalls
  6. Availability of equipment
  7. The purpose of seawall structure

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