We can build a concrete, vinyl and composite, or wood seawall to protect your property and other structures. Before construction, our knowledgeable team can take a look at the area and recommend the best option for your situation. If you have any questions about our seawalls, we can walk you through the process to help you better understand this structure. What Is a Seawall? Vertical Walls Vertical seawalls are fairly easy to construct, and they can adequately deflect wave energy to protect the coastline.
Why Might Seawalls Be Necessary? What Are Seawalls Made Of? Do Seawalls Need to Be Maintained? The problems of wave reflection and scour can be reduced to some degree by incorporating slopes and irregular surfaces into the structure design. Slopes encourage wave breaking and therefore energy dissipation while irregular surfaces scatter the direction of wave reflection French, Pilarczyk a recommends the use of maximum seawall slopes of to minimise scour due to wave reflection. Sediment availability is also affected by seawall construction.
The problem is caused by replacing soft, erodible shorelines with hard, non-erodible ones. While this protects the valuable hinterland, it causes problems in terms of sediment starvation; erosion in front of the seawall will continue at historic or faster rates but the sediment is not replaced through the erosion of the hinterland French, This can cause beach lowering, which reduces beach amenity value and increases wave loadings on the seawall by allowing larger waves close to the shore.
In the absence of a seawall, natural shoreline erosion would supply adjacent stretches of coastline with sediment, through a process known as longshore drift.
Once a seawall is constructed however, the shoreline is protected from erosion and the supply of sediment is halted. This causes sediment starvation at sites located alongshore, in the direction of longshore drift and this has the capacity to induce erosion at these sites. Although seawalls prevent erosion of protected shorelines, where the seawall ends, the coast remains free to respond to natural conditions.
This means that undefended areas adjacent to the wall could move inland causing a stepped appearance to the coast French, The downdrift end of the seawall is also typically subjected to increased erosion as a result of natural processes see Figure 3.
This flanking effect can cause undermining and instability of the wall in extreme cases. Figure 3: A seawall as viewed from above, showing typical end effects associated with the structure Source: Adapted from McDougal et al. Because seawalls are immovable defences, they can also interfere with natural processes such as habitat migration which is naturally induced by sea level change. Seawalls obstruct the natural inland migration of coastal systems in response to SLR, therefore causing coastal squeeze.
This process causes a reduction in the area of intertidal habitats such as sandy beaches and saltmarshes because these environments are trapped between a rising sea level and unmoving, hard defences. In estuaries, seawalls also cause changes to the area inundated by the tides thus, reducing the available area for occupation by water on a high tide. With the same volume of water flowing into the estuary, the level of the water after seawall construction will be higher. This may mean areas in front of the defence remain submerged longer and by greater depths.
In turn, this is likely to affect the distribution of vegetation and could increase tidal range upstream of the defence French, Another potential problem is overtopping. This occurs when water levels exceed the height of the seawall, resulting in water flow into areas behind the structure. Overtopping is not a continuous process but usually occurs when individual high waves attack the seawall, causing a temporary increase in water level which exceeds the structure height Goda, If the structure is too low, excessive overtopping can remove considerable amounts of soil or sand from behind the wall, thus weakening it.
Overtopping will become increasingly problematic with SLR, increased wave heights and increased storminess. As mentioned in the advantages section, seawalls increase security by reducing the risk of flooding and erosion. However, the coastal zone remains a high risk location not least due to the presence of residual risk. To combat unwise development of the coastal zone, future developments need to be carefully planned. Additionally, by encouraging development, hard defences necessitate continued investment in maintenance and upgrades, effectively limiting future coastal management options.
Although authorities may not have a responsibility to continue providing protection, the removal of defences is likely to be both costly and politically controversial Nicholls et al. Seawalls also reduce beach access for handicapped people and for emergency services.
This can be problematic if the beach fronting such structures is to be used for recreation. The appearance of seawalls can be aesthetically displeasing which can further negatively affect beaches dependent upon a tourist economy. A study by Linham et al. The study found seawall costs for around ten countries. Most were developed country examples, although a number of newly developed and developing countries, such as Egypt, Singapore and South Africa were also found.
Problems arise in the reporting of unit costs for vertical seawalls as the effect of height on unit costs is rarely considered. As such, these costs are likely to relate to seawalls of various heights; this explains some of the significant variation in costs between projects. Some of the best unit cost information is given by the English Environment Agency , for unit costs relevant to the UK. This cost includes direct construction costs, direct overheads, costs of associated construction works, minor associated work, temporary works, compensation events and delay costs.
Maintenance costs are another significant and ongoing expense when a hard defence is selected. Continued investment in maintenance is highly recommended to ensure defences continue to provide design levels of protection Linham et al. Stakeholder participation. If an EIA is undertaken, the EU Directive provides for the right to access information and to participate in the environmental decision-making procedures to the public concerned by the project.
Similarly, the Floods Directive, the Water Framework Directives and the Maritime Spatial Planning Directive establish public participation processes that may be relevant for these projects. Several categories of stakeholders can be affected by strengthening seawalls or jetties. A seawall as well as a jetty can negatively affect the landscape and the use of the beach, or can be used to artificially widen the beach to create recreational space.
Tourists and tourism industry as well as other recreational users will therefore be affected. However, the protection against flooding offered by the seawall can benefit settlements and economic activities. Success and Limiting Factors. Costs and Benefits. Construction costs are high but these structures usually require low maintenance. Construction costs vary according to the shape of seawall structures: the volume of the seawall depends on the required crest level, the foundation level, the wave loading, and acceptable overtopping rates.
No indication on the length of the seawall was provided. These and other sources note that costs for seawalls vary according to the type of construction, dimensions, availability and proximity of construction materials, anticipated rates of future erosion and wave loadings, facilities such as walkways and steps or slipways. Legal Aspects. However, this requirement does not affect the maintenance and reconstruction of these works. Coastal defences could alter the hydromorphological characteristics of coastal waters — for example in terms of water flow, sediment composition and movement— and thus to a deterioration of ecological status.
Any projects that do so would need to meet criteria set out in Art. The construction and restoration of dikes could be part of measures under flood risk management plan. The Maritime Spatial Planning Directive requires consideration of the interactions between land and sea, along with maritime activities and adaptation to climate change. Such adhoc methods can be used to not only protect long sections of foreshore, but also individual private properties.
The substantial and solid appearance of rock walls can provide owners of foreshore assets with a sense of security — which unfortunately is frequently misguided given the often inadequate design and construction of these structures. Their subsequent failure or damage can not only lead to the re-establishment of the original erosion problem, but the scattering of removed rocks can adversely affect foreshore use and visual amenity.
Seawalls — blight or remedy? You may need a coastal engineer to assist you in that evaluation. Facebook Facebook. About the Author: Paul O'Brien. His particular expertise is the practical application of state-of-the-art techniques and systems of foreshore protection and maritime engineering design in tropical and sub-tropical regions.
Since many of these applications are in coastal areas having significant environmental, cultural, social and commercial values, Mr. Popular Recent. Groynes — for what purpose?
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