Groynes, breakwaters and artificial reefs

Stakeholder participation generally does not play a major role in the technical design and construction of groynes, breakwaters, and artificial reefs, unless they are part of a larger coastal defence plan. However, these measures can raise concern about possible environmental impacts on the marine ecosystem and about the visual impacts on the coastal landscape. Conflicts can arise between coastal communities and economic sectors: the tourism sector generally benefits from protected beaches or safer touristic moorings, while local communities can be worried about the modification of the coastal landscape, habitat and biodiversity loss and environmental impacts in general. Such conflicts call for an active involvement of all potentially affected actors, including local authorities, coastal communities, tourism operators, research institutions and/or NGOs.

These defence structures might be the subject of Environmental Impact Assessments, depending on national laws and regulation. When they are implemented in sites, protected under the EU Natura 2000 network, 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 EU Maritime Spatial Planning Directive call for public participation processes that may include this typology of projects.

In general, groynes are efficient to protect certain parts of the coast and maintain upper beach stability. They are effective on sand and shingle beaches, and in rivers and estuaries to reduce water flows. By contributing to the widening of beaches they can provide co-benefits for recreation and tourism. Breakwaters provide additional co-benefits, such as safe mooring and berthing procedures for vessels in ports. They enhance workability and provide thus higher efficiency in loading and unloading vessels. Submerged reefs, in addition to counteracting the wave strength, can provide substrates for benthic species (flora and fauna), attracting fish and thus improving biodiversity. Submerged reefs can even become attractive for snorkelling, creating new tourism opportunities.

Groynes, breakwaters and artificial reefs can be combined with a number of other approaches, including green measures as beach nourishment and dune construction and strengthening. They have been applied around the world for many years. Consequently,  broad experience can support their correct design and construction. 

Artificial defence structures also have negative impacts that suggest a careful evaluation before their implementation. Groynes, breakwaters, or reefs tend to modify longshore drift, and have adverse effects on adjacent beaches by causing downdrift erosion. To avoid these effects on the coastline, artificial nourishments and/or dune development are often preferable over hard structures unless there are other needs, such as the safe berthing of ships. However, the extent of the blocking of longshore drift, disturbance of adjacent beaches and degradation of landscape values depends very much on the design, orientation of the structure and the main wave/sediment transport direction at the specific site.

Artificial structures can also have negative impacts on landscape values affecting the appearance of beach areas and thus the beach users. Breakwaters can cause side deposition of mud, can retain algae and capture litter or debris from ships, making the beach area both unpleasant and unsafe. Currents around the ends of breakwaters and reefs can be strong and dangerous for swimmers. Submerged reefs are offshore, away from beach users. If they don't function as intended, they can be a hazard for navigation and water sports, such as surfing with potential impacts on tourism.

Construction costs depend significantly on the structure dimensions. Costs can be highly influenced by the selected construction material, local availability of suitable material, amount of the material needed, transport costs to the construction sites, environmental conditions on site and associated costs of beach nourishment. The latter are frequently required to enhance grey measures’ efficacy. Cost assessment should also include the analysis of wave conditions and sea currents as well as sediment transport dynamics. The assessment should be performed by specialized staff in order to properly design the structures.

According to the 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 EUR per ton) while placing costs are about 40 USD/ton (about 34 EUR per ton). Additional costs, though rarely considered, are related to the maintenance of these measures in the long-term perspective.

Indirect benefits of the stabilization and enhancement of beaches can lead to increased tourist attractiveness. Apart from situations where local strong currents may be generated, by stabilizing the shoreline and reducing wave action, groynes generally create also safer beach environments. This can lead to a more pleasant and secure experience for swimmers and families with children, thus increasing the appeal of the beach to a broader range of tourists with positive impacts on the local economy.  

The construction of coastal works to mitigate erosion and of hard sea defences ‘capable of altering the coast’ fall into Annex II of the EU Environmental Impact Assessment (EIA) Directive (2014/52/EU): 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 sites protected under the Natura 2000 network (Birds Directive and Habitat Directive) site, must be subjected to an ‘appropriate assessment of its implications for the site’ to determine whether the project will adversely affect the environmental integrity of the site.

The EU Water Framework Directive calls for the ‘Good Environmental Status’ of Europe’s water bodies, including coastal waters. Coastal defences could alter the hydro-morphological characteristics of coastal waters, for example in terms of water flow, sediment composition and movement. This could lead to a deterioration of the ecological status. Any projects that is expected to generate the above effects, would need to meet criteria set out in Art. 4 of the Directive. The EU Floods Directive (2007/60/EC) provides a legal framework for flood actions and defence. The construction and restoration of coastal defence structures could be part of measures under flood risk management plans. The 2014 Maritime Spatial Planning Directive requires the consideration of interactions between land and sea, along with maritime activities and adaptation to climate change. Groynes, breakwaters and artificial reefs systems could affect these land/sea interactions.

Groynes, breakwaters and artificial reefs are rather simple, small-scale interventions, which are implemented at the local scale (stretch of a coast in erosion). The simple placement of the material on-site can take short time (from weeks to months). 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 (about 1 year). 

When constructed, the protective function of breakwaters, groynes and artificial reefs can be maintained for many years, requiring only basic monitoring and maintenance. Breakwaters have a typical design lifetime of 30-50 years. This is the case for most rock structures. Wooden groynes have a lifetime of about 10-25 years; and groynes made of gabions have a lifetime of only 1-5years.