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Adaptation option

Seawalls and jetties

A seawall is a structure made of concrete, masonry or sheet piles. It is built parallel to the shore at the transition between the beach and the mainland or dune, to protect the inland area against wave action and prevent coastal erosion. Seawalls can be combined with jetties in port areas, to stabilise the sides of navigation channels and tidal inlets and to avoid siltation. 

Seawalls are usually massive structures designed to resist storm surges. The height of a seawall will at least cover the difference between the beach level and the mainland, though commonly seawalls are built higher 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 covered part that may be used for a road, promenade or parking area (see for example the wave-damping” square in Ostend). The shape of the seawall face determines its capacity to reflect or to dissipate wave energy. Smooth, vertical sea walls mainly reflect wave energy seawards. They possibly create turbulence and suspending sediments, thus further increasing the risk of erosion. Vertical seawalls can also cause a scour hole at the foot of the structure leading to its instability. Slopes and irregular surface of the structure design of seawalls can improve their performance, allowing wave breaking, energy dissipation and scattering of the direction of wave reflection.  

Seawalls are often found in the case of narrow or steep beaches, where a typical breakwater is either too large or not economical. They are frequently used in locations where further shore erosion will result in excessive damage to coastal roads and settlements, providing a high degree of protection also from flooding. To be effective for flooding in the medium and long period, regional and local projections of sea level rise must be incorporated in the design specifications. Possible increase in wave heights and storminess due to climate change should also be considered to ensure durability and efficacy of the structure under more severe climatic conditions.  

While seawalls protect infrastructures and settlements in the hinterland, erosion in front of the seawall and in the adjacent coastal stretches will continue also at increasing rate, without solving the causes of erosion. To counteract disadvantages of seawalls and other grey protection measures, an increasing number of projects started to integrate seawall construction and strengthening with nature-based solutions in the framework of large coastal interventions (see for example Saltmarsh recreation by managed realignment in Hesketh Out Marsh). This integration needs coordination among different governance levels to ensure long-term sustainability of the adaptation interventions. 

A jetty is a structure built to protect a navigation channel or a tidal inlet, stabilising one or both sides. Jetties are also employed to avoid large volumes of sand filling the inlet. In this way, the navigability of the channel is improved or, for tidal channels of lagoon areas, a sufficient opening is ensured for an adequate water exchange. A wide variety of materials including rock armour, concrete, tetrapod, and steel piling can be employed for construction of jetties. Jetties (like groynes) are designed to interrupt long-shore sediment transport. In this way, they can cause sediment accumulation at the updrift side and erosion at the downdrift side, due to lack of transported sediments. Sand accumulation in the updrift side can create space for land-based activities, for example for tourism and ports. However, downdrift erosion can lead to major setback of the coastline.  


Additional Details
Reference information

Adaptation Details

IPCC categories

Structural and physical: Engineering and built environment options

Stakeholder participation

Seawalls and jetties are primary implemented to ensure protection against flooding and storms of valuable human settlements and activities, particularly at risk. However, they can negatively affect the coastal landscape and environment as well as the natural value of a beach and its use. At the same time, by exploiting sand accumulation in the updrift side of the structure, these structures can be used to artificially widen the beach and therefore create additional space for human activities. The decision to construct seawalls and jetties must therefore consider and balance different stakeholders’ perspectives and needs considering both the implementation and maintenance phase. Stakeholder consultations should include local authorities, tourism operators, coastal communities, NGOs and coastal research institutions. 

These defensive structures might be subject to Environmental Impact Assessment, depending on national laws and regulation. When they are implemented in sites with high ecological value, protected under the Birds and Habitat Directives (Natura 2000 sites), an appropriate assessment considering their potential impacts is usually required. Both processes must ensure the right to access information and formally consult the interested parties. Similarly, the EU Floods Directive, the EU Water Framework Directive and the Maritime Spatial Planning Directive call for public participation processes that may include this  typology of projects. 

Success and Limiting Factors

Seawall construction can be considered a useful adaption option when high valuable coastal areas cannot be protected in other ways (e.g. due to space constrains). Although the option locally provides a high level of protection from erosion and flooding, it poses high concern in the long-term sustainability of the approach due to possible environmental impacts. Main success and limiting factors of seawalls and jetties are discussed below. 

Success factors 

  • A seawall provides a high degree of protection against coastal flooding and erosion.  
  • Seawalls have a lower space requirement than other coastal defences such as dikes. Seawalls can be heightened to face sea level rise, which requires simultaneously a widening of the foundation. 
  • The high level of security provided by a seawall can favour the development of the hinterland. The crest of the seawall often extends into a stone covered part providing other functions, e.g. road, promenade or parking places. 
  • Sufficient long jetties limit siltation in an inlet or navigation channels, thereby keeping sufficient depth within the channel. They can be used to artificially widen the beach area in the updrift side, offering new opportunities for the development of land-based economic and social activities 
  • Seawalls and jetties are rather common and simple structures widely used in coastal areas. They have been applied around the world for many years. Consequently, a broad experience can support their correct design and construction, also to mitigate environmental impacts.  

 Limiting factors 

  • Seawalls are poorly flexible structures. In the design phase, sea level rise projections and possible increase in storminess need to be properly taken into consideration to ensure the life-time of such structures in the face of climate change. 
  • Due to their perpendicular-to-shore placement, jetties can disturb the longshore drift (sediment transport) and cause downdrift erosion. The longer the jetty is, the greater impact it has on adjacent areas. 
  • Seawalls often interfere with natural processes such as habitat migration, causing the impairment of intertidal habitats. However, these effects depend very much on the main wave and sediment transport direction and the design of the seawall. The choice of coastal defences must be made according to site-specific conditions and primary and secondary goals (such as wave protection, road stabilization, space conservation and mooring capabilities). Where sufficient space is available and no conflict with other primary or secondary goals exists, green measures (such as beach nourishments and dune restoration) are often preferred. 
  • Seawalls often do not stop erosion in front of the structure but prevent erosion of the dunes and hinterland. Vertical seawalls often reflect wave energy instead of dissipating it, which makes the shoreline more subject to erosion. Many seawalls have therefore been more recently conceived to integrate slopes. 
  • When seawalls are regularly overtopped, or when this occurs in major storms, the water can remove soil or sand behind the wall and weaken it. Overtopping water saturates the soil and increases pressures from the landward side, which can cause structural collapse. Sea rise level and potential overtopping must be taken into account in the construction of the seawall. In general, continued erosion can undermine the foot of the structure and threaten its stability. 
  • Seawalls and jetties can have negative impacts on the overall appearance of the landscape and can reduce its attractiveness. Consequently, it is very important that the design aspect is properly prioritized, also based on stakeholder consultation. 

Costs and Benefits

Construction costs of seawalls are high. However, these structures usually require low maintenance costs if properly designed. Construction costs vary according to the shape of the seawall structure: the volume of the seawall depends on the required crest level, on the foundation level, the wave loading, and acceptable overtopping rates. Costs for seawalls also vary according to the availability and proximity of construction materials and to the environmental condition on the site. If the design of the seawall includes additional facilities such as roads or promenades on the top of the sea wall, costs increase consequently. However, those costs can be compensated by a better integration into the landscape, an increased social acceptance and new recreational opportunities.  

According to the estimates reported by the UK Environmental Agency (2015), cost for sea walls (not including maintenance) range from 700 to 5000 £/m (820-6300 €/m, on 2007 cost base). High variation in costs is expected between projects as a result of the high number of above mentioned factors that affect different types of seawall projects. 

Jetties are generally rather simpler measures with expected lower cost of construction, similar to the cost of groynes and breakwaters. According to estimates reported in UNEP-DHI (2016), purchase and transport of rocks based on transport distance of about 50 km can cost about 25 USD/ton (about 21 euros per ton) while placing costs are about 40 USD/ton (about 34 euros per ton). 

Maintenance should be considered at both the design stage and throughout the operational life of the structure. Post-storm, seasonal or annual inspections and related repair work are also required for all coastal defense interventions. 

The construction of coastal works to mitigate erosion and hard sea defences ‘capable of altering the coast’, such as seawalls and jetties, fall into Annex II of the Environmental Impact Assessment (EIA  Directive) and successive amendments): Member States decide whether projects in Annex II should undergo an EIA procedure, either on a case-by-case basis or in terms of thresholds and criteria. However, this requirement does not affect the maintenance and reconstruction of these works. Any infrastructure project likely to have a significant impact on a Natura 2000 sites site must be subject to an ‘appropriate assessment of its implications for the site’ to determine whether the project will adversely affect the integrity of the site. 

The EU Water Framework Directive calls for the good status of Europe’s water bodies, including coastal waters. Coastal defences could alter the hydromorphological characteristics of coastal waters, for example, in terms of water flow, sediment composition and movement. They can thus lead to a deterioration of ecological status. Any projects that do so would need to meet criteria set out in Art. 4(7) of the Directive. The EU Floods Directive provides a legal framework for flood actions and defence. The construction and restoration of dikes could be part of measures under the flood risk management plan that Member States are asked to prepare to implement the Directive. The 2014 Maritime Spatial Planning Directive requires to consider the interactions between land and sea, along with maritime activities and adaptation to climate change. Seawalls and jetties could affect these land/sea interactions. 

Implementation Time

The simple placement of the material onsite can take short time (generally less than 1 year). However,  the whole process of selecting the best solution, collecting and analysing data on waves, currents and sediment transportation, properly designing the infrastructure and involving the stakeholders in a participated process certainly requires more time (more than 1 year for seawalls in particular). Implementation tTime also depends on the length of the coastal stretch to be protected and on the dimension of the structure (length and height of the structure) required to be effective. 

Life Time

Seawalls and jetties generally have a long life expectancy (typically, 20-50 years) before major repair is needed. Regular inspection of seawalls, to early identify the need of small repair action, can improve the lifetime of these structures. 

Reference information


UNEP-DHI (2016). Managing climate change hazards in coastal areas. The coastal hazard wheel decision-support system: Catalogue of hazard management options. United Nations Environment Programme & Lars Rosendahl Appelquist ISBN: 978-92-807-3593-2 

DHI (2017). Shorelines management guidelines

Published in Climate-ADAPT Jun 07 2016   -   Last Modified in Climate-ADAPT Dec 12 2023

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