Seawalls - Trade-offs

Trade-offs

A cost benefit approach is an effective way to determine whether a seawall is appropriate and whether the benefits are worth the expense. Besides controlling erosion, consideration must be given to the effects of hardening a shoreline on natural coastal ecosystems and human property or activities. A seawall is a static feature which can conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The table below summarises some positive and negative effects of seawalls which can be used when comparing their effectiveness with other coastal management options, such as beach nourishment.

Advantages and disadvantages of seawalls according to Short (1999)
Advantages Disadvantages
  • Long term solution in comparison to soft beach nourishment.
  • Effectively minimizes loss of life in extreme events and damage to property caused by erosion.
  • Can exist longer in high energy environments in comparison to ‘soft’ engineering methods.
  • Can be used for recreation and sightseeing.
  • Forms a hard and strong coastal defence.
  • Very expensive to construct.
  • Can cause beaches to dissipate rendering them useless for beach goers.
  • Scars the very landscape that they are trying to save and provides an ‘eyesore.’
  • Reflected energy of waves leading to scour at base.
  • Can disrupt natural shoreline processes and destroy shoreline habitats such as wetlands and intertidal beaches.
  • Altered sediment transport processes can disrupt sand movement that can lead to increased erosion down drift from the structure.

Generally seawalls can be a successful way to control coastal erosion, but only if they are constructed well and out of materials which can withstand the force of ongoing wave energy. Some understanding is needed of the coastal processes and morphodynamics specific to the seawall location. Seawalls can be very helpful; they can offer a more long term solution than soft engineering options, additionally providing recreation opportunities and protection from extreme events as well as everyday erosion. Extreme natural events expose weaknesses in the performance of seawalls, and analyses of these can lead to future improvements and reassessment.

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