Hold the line

Based on kindly provided information by the Scottish Natural Heritage

Groynes are cross-shore structures designed to reduce longshore transport on open beaches or to deflect nearshore currents within an estuary. On an open beach they are normally built as a series to influence a long section of shoreline that has been nourished or is managed by recycling. In an estuary they may be single structures.

Groynes reduce longshore transport by trapping beach material and causing the beach orientation to change relative to the dominant wave directions. They mainly influence bedload transport and are most effective on shingle or gravel beaches. Sand is carried in temporary suspension during higher energy wave or current conditions and will therefore tend to be carried over or around any cross-shore structures. Groynes can also be used successfully in estuaries to alter nearshore tidal flow patterns.

Technical feasibility

Groynes can be made from different material. Rock is often favoured as the construction material, but timber or gabions can be used for temporary structures of varying life expectancies (timber: 10-25 years, gabions: 1-5 years). Rock groynes have the advantages of simple construction, long-term durability and ability to absorb some wave energy due to their semi-permeable nature. Wooden groynes are less durable and tend to reflect, rather than absorb energy.

Groynes along a duned beach must have at least a short “T” section of revetment at their landward end to prevent outflanking during storm events. The revetment will be less obtrusive if it is normally buried by the foredunes. Beach recycling or nourishment is normally required to maximise the effectiveness of groynes. On their own, they will cause downdrift erosion as beach material is held within the groyne bays.

Groynes can have a significant impact on the shoreline, and schemes should always be undertaken under the supervision of a competent coastal consultant. As with all rock structures on the shoreline the rock size, face slopes, crest elevation and crest width must be designed with care. Rock size is dependent on incident wave height, period and direction, structure slope, acceptance of risk, cross-sectional design, and the availability/cost of armour rock from quarries. In general 1-3 tonne rock will suffice for the landward parts of the groynes, provided that it is placed as at least a double layer, with a 1:1.5 to 1:2.5 face slope, and there is an acceptance of some risk of failure. Larger rock, probably 3-6 tonne, may be needed for the more exposed body and seaward head of each structure.

The groyne berm should be built to the anticipated crest level of the beach. The groyne berm length should equal the intended crest width of the updrift beach. The groyne should extend down the beach at a level of about 1m above the anticipated updrift shingle beach, normally at a slope of about 1:5 to 1:10. The groyne head should extend down into the sand beach, allowing for some future erosion.

As a general rule, groynes should not be built on an open beach unless construction is accompanied by a commitment to regular recycling or nourishment. Without this commitment the groynes are likely to cause downdrift erosion as the upper beach becomes starved of sediment. Where there is a plentiful sediment supply, or where downdrift erosion is not considered to be a significant issue, then recycling may not be required.

Timber groynes must be built from hardwood to endure the harsh shoreline environment. Much hardwood comes from tropical sources, making it both costly and potentially environmentally unacceptable. Timber groynes tend to reflect, rather than absorb, wave energy making them significantly less effective than rock on exposed coasts. They are also more likely to structural failure due to formation of scour channels around their seaward ends.

Political & social feasibility

Rock structures on recreational beaches should be built with a view to minimising the potential for accidents involving beach users slipping between rocks

Cost of implementation & maintenance

The costs of groynes are considered as moderate

Ecological feasibility

Implementing groynes disrupts natural processes. The effects must be properly monitored and if possible compensated.

Key lessons learnt

Provided that groynes are used in appropriate locations, they reduce dependency on regular recycling or nourishment, and therefore reduce future disturbance of the shoreline environment. Localised accumulations of beach material will encourage new dune growth. Recycling, fencing and transplanting will help to keep the revetment sections buried, thereby enhancing habitat regeneration.

Measure category

Mitigation

Breakwaters

nst — Wed, 22 Mar 2017 08:49:13 +0000

Breakwaters nst Wed, 03/22/2017 - 09:49

Riverine or slow rise floods

Estuarine floods

Based on the information available on the ClimateAdapt Platform

A breakwater is a coastal structure (usually a rock and rubble mound structure) projecting into the sea that shelters vessels from waves and currents, prevents siltation of a navigation channel, protects a shore area or prevents thermal mixing (e.g. cooling water intakes). A breakwater typically comprises various stone layers and is typically armoured with large armour stone or concrete armour units (an exception are e.g. vertical (caisson) breakwaters). A breakwater can be built at the shoreline or offshore (detached or reef breakwater). This measure is not directly addressed to protect the coast in flood events, but can indirectly stabilize the coast by preventing erosion.

To build breakwaters, rock size, face slopes, crest elevation and crest width and toe protections and aprons should be designed according to the natural characteristics of the sites as these factors have an important impact on the shoreline. Sand may build up behind breakwaters to form salients. Sand can accumulate enough to connect with the breakwater and form a tombolo (a stretch of sand developed by wave refraction, diffraction and longshore drift forming a ‘neck’ connecting the structure to the shore). Considering the significant impact these structures have on the coastal environment, they should only be considered as part of a global adaptive management policy, taking into account the characteristics of the specific site and the potential effects on the whole coast. The construction of breakwaters could also be linked to a beach nourishment programme, and breakwaters can be used in a protected beach nourishment approach.

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. If a project creates a significant impact on a Natura 2000 site, the ‘appropriate assessment’ of the infrastructure project could include a public participation process, but this is not mandatory. Similarly, the Floods Directive, the Water Framework Directive and the Maritime Spatial Planning Directive establish public participation processes that may include these projects.

A range of stakeholders could be affected by the construction of breakwaters: for local communities and landowners, hard defences could negatively impact their property. Hard defences can visually disrupt the landscape, affecting tourism interests, recreational users and other sectors. Waterborne activities can also be adversely affected if the installation of hard structures goes wrong.

Success and Limiting Factors

Artificial structures such as breakwaters tend to modify longshore drift, and have adverse effects on adjacent beaches by causing downdrift erosion. In general, 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.

Breakwaters provide safe mooring and berthing procedures for vessels in ports. They enhance workability and provide thus higher efficiency in loading and unloading vessels.

Costs and Benefits

Construction costs depend significantly on structure dimensions. Costs can be highly influenced by availability of suitable rocks, transport costs to the construction sites and associated costs of beach nourishment.

In the Netherlands, breakwaters are estimated to cost about EUR 10,000 to 50,000 per running meter (Deltares, 2014).

According to Scottish Natural Heritage, in 2000 construction costs of breakwaters are high – GBP 40,000 to 100000 (50,000-125,000€) – but they require low maintenance; for these structures in particular, beach nourishment costs should be added.

Legal Aspects

The construction of coastal works to mitigate erosion and hard sea defences ‘capable of altering the coast’ fall into Annex II of the EIA Directive (codified as Directive 2011/92/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 a Natura 2000 site must be subjected to an ‘appropriate assessment of its implications for the site’ to determine whether the project will adversely affect the integrity of the site.

The Water Framework Directive calls for the Good Environmental 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, and thus to a deterioration of ecological status. Any projects that do so 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 dikes could be part of measures under flood risk management plans. The 2014 Maritime Spatial Planning Directive requires the consideration of the interactions between land and sea, along with maritime activities and adaptation to climate change. Breakwaters could affect these land/sea interactions.

Life Time

Breakwaters have a typical design lifetime of 30-50 years. This is the case for most rock structures.

Further Readings

Scottish Natural Heritage: A guide to managing coastal erosion in beach/dune sy…

VLAAMS INSTITUUT VOOR DE ZEE: Detached Breakwaters

Measure category

Mitigation

EXAMPLE: MOSE system of mobile flood barriers, Venice (IT)

nst — Tue, 07 Feb 2017 08:35:19 +0000

EXAMPLE: MOSE system of mobile flood barriers, Venice (IT) nst Tue, 02/07/2017 - 09:35

Flash floods

Reduction

Water flow regulation

Flood and storm surge barrier

Venice, Italy, is a city famous around the world for not only its stunning canals and historic buildings, but also for its high vulnerability to flooding. The MOSE system of mobile flood barriers is a bold initiative intended reduce risk, preserve the cherished cityscape, and protect the entire Venice Lagoon from flooding.

Based on information from the project website

General description

The MOSE (short for “Modulo Sperimentale Elettromeccanico” in Italian) system consists of four mobile barriers closing off three inlets in the Venice Lagoon. The barriers themselves are made up of 78 flap gates that are installed at the bottom of the inlets to separate the lagoon from the sea when raised. The system takes approximately 30 minutes to open and can be closed in 15 minutes, but takes on average five hours to close. Once raised, the barriers are able to withstand three meters of high tide. The barrier at the Malamocco inlet even has a lock system installed to allow merchant and industrial ships to cross while the MOSE system is in operation to reduce interference on port activities.

Seasonal high water is a constant threat to Venice, and the city has adapted with raised walkways, waterproofed buildings, and power outlets installed halfway up the wall in businesses and homes. Flooded scenes of a usually picturesque St Mark’s Square can be explained due to the fact that it is the city’s lowest point. However, more extreme high tides that occur roughly every three years and can raise water levels by over a meter present a much greater risk to Venice’s cultural heritage and justify a system such as MOSE.

Governance aspects

Venice and its Lagoon is a UNESCO World Heritage Site, which makes its protection even more important. The MOSE project was implemented by the Italian Ministry of Infrastructure and Transport and managed by the Consorzio Venezia Nuova for the purposes safeguarding Venice and the lagoon. The decision to construct the mobile flood barriers was made after collaboration between all levels of government and consideration of various other coastal defence measures.

Innovative aspects

The MOSE system in its entirety is an impressive and innovation response to the threat of coastal flooding and erosion, both from a construction and coordination standpoint. The hydrological and geophysical profile of the Venice Lagoon needed to be fully considered when designing the barriers and their final locations.

While the MOSE Control Centre uses advanced technology to predict flooding, model the effects of gate manoeuvres, predict port traffic, determine warning levels, and so on, the MOSE project also employs other smaller scale measures to optimise the overall goal of flood risk reduction in the lagoon. These local defences consist of raising quaysides, roads, walkways, and installing smaller gates in the urban canals in the lagoon settlements, known as the “Baby MOSE” gates. This holistic and comprehensive approach to encouraging protection for the entire lagoon, aside from that which is provided by MOSE, is also innovative.

Key lessons learnt

It is not easy to construct such large-scale defences in fragile environments, but, as the MOSE system illustrates, sometimes this approach is necessary to provide significant long-term protection. Venice represents an especially vulnerable coastal city with globally significant heritage sites and a very active tourism industry. With so much at risk, the MOSE system will ensure businesses, residents, and visitors will be able to enjoy the fabled canals, palaces, and plazas without the threat of flooding and building damage. The implementation of local defences diversifies the resilience of the settlements in the lagoon and increases the rate of success for the MOSE project.

Relevant case studies and examples

Further Readings

CityLab: Venice's Vast New Flood Barrier Is Almost Here

Measure category

EXAMPLE: Seawall at Skara Brae, Scotland (UK)

nst — Tue, 24 Jan 2017 08:37:41 +0000

EXAMPLE: Seawall at Skara Brae, Scotland (UK) nst Tue, 01/24/2017 - 09:37

Skara Brae is one of Scotland’s most significant and famous UNESCO World Heritage Sites and it has been under constant threat of damage due to coastal erosion for decades. Fortunately, a seawall protects the base of this archaeological site from the erosive power of waves and storm events.

Based on information from Historic Environment Scotland and UNESCO World Heritage Centre.

General description

The 5000 year old settlement of Skara Brae is one of the four monuments that make up the Heart of Neolithic Orkney, a UNESCO World Heritage Site. It is also quite possibly one of Scotland’s most at-risk historic sites due to coastal erosion. Ironically, Skara Brae was only discovered as a result of coastal erosion from major storm events since the 1800’s.

The risk of coastal erosion to Skara Brae was addressed in the early days of its heritage management. The first seawall was constructed in the late 1920’s, and has been refortified several times since then. Like all seawalls, this 4-meter high wall serves as a protective barrier that is able to absorb the brunt of wave action and thereby shield vulnerable infrastructure, or in this case archaeological structures, from eroding.

Historic Environment Scotland, the public body responsible for managing Scotland’s heritage sites, has been over the years maintaining the integrity of the wall, with the support of other organizations. There has also been extensive monitoring of the entire bay area to determine the rate and location of erosion so that additional fortification can be made. Skara Brae is a cherished piece of Scotland’s history and therefore has much public support for protection from coastal erosion.

Innovative aspects

Considering the early adoption of a seawall protection measure for Skara Brae, Scottish authorities have been quite proactive in ensuring the long term reduction of coastal erosion at this heritage site. With the first wall erected in the late 1920’s, this measure was a relatively pioneering tactic for heritage conservation. Today, Historic Environment Scotland has also employed the latest technologies of 3D and 4D digital surveying to monitor the state of erosion along the coast and measure the ongoing effectiveness of the sea wall.

Key lessons learnt

When it comes to vulnerable heritages sites along eroding coastlines, time is of the essence. While powerful storms throughout history revealed the existence of Skara Brae to the world, these same storm events and constant wave action threaten the longevity of the site as a place for future generations to enjoy. The prompt action of Scottish authorities to construct a seawall to protect the archaeological site decades ago has since been proven to have been a wise decision. Knowing what we know about the possibility of more hidden archaeological sites in the area, it is important to continue the monitoring efforts to not only assess the stability of Skara Brae, but also the impacts of the seawall as an element of the natural environment. The Bay of Skaill is a dynamic and ever changing system, and it is possible that the seawall might increase erosion from intensified wave action on the unprotected sand dunes on either side of Skara Brea.

Relevant case studies and examples

Seawall or Revetment

Further Readings

BBC report on Skara Brae

Measure category

Combination of groynes and beach nourishment, Clacton (UK)

nst — Mon, 16 Jan 2017 12:30:37 +0000

Combination of groynes and beach nourishment, Clacton (UK) nst Mon, 01/16/2017 - 13:30

Article about the measure in the East Anglian Daily Times

The Clacton to Holland-on-Sea (UK) stretch of coastline has suffered from significant sediment loss, which negatively impacts the local community and economy. Collectively, five kilometres of beach are at risk of washing away including nearby tourism promenades and over 3000 homes and businesses. In response, a major sea defence project is underway to fortify the coast through construction of new rock groynes and beach nourishment activities. It is expected that this project will reduce coastal erosion for the next 100 years.

Based on information from the Tendring Destrict Council.

General description

The beach area at risk is five kilometers long and runs from Clacton Pier to Holland Haven in Essex on the east coast of England. The project involves using 23 fishtail rock groynes, each 90 meters long and 220 meters apart, and adding roughly 950 000 cubic meters of sand and shingle beach material to the coastline

The project is the biggest of its kind to ever be undertaken by the Tendring District Council. It was approved by the UK Environmental Agency in 2013 and costs roughly 36 million pounds, with support from several funding organizations.

The groyne and beach recharge activities were effective, on time, and on budget. The materials for the rock groynes were made up of the crushed materials from the existing structures and new smaller rocks from a quarry, and were covered by a geotextile once in place in the sea. Larger rocks were placed on the geotextile and the groynes were designed in a fishtail style. The fishtail design of the groynes was chosen to allow dual protection, with the bigger arm blocking waves from the North Sea and the little arm blocking waves from Kent. The materials for beach recharge came from a licensed dredge site and was made up of sand and shingle (a mix of sand, gravel and cobbles, mimicking the natural beach material of the area. During high tide, a dredging ship would pump this mix through a pipe onto the beach, forming an 18 metre wide crest about one metre below the promenade walking level.

Key lessons learnt

Pumping the sand and shingle mix early in the project towards the shore created a platform to help construct the many fishtail rock groynes and support the heavy construction machinery used on the beach during construction. Even with all the groynes, periodic beach re-profiling will be necessary in the future due to coastal processes.

Relevant case studies and examples

Groynes

Further Readings

Scale

Local

Measure category

EXAMPLE: Beach drainage in Quend-Plage (FR)

nst — Fri, 13 Jan 2017 08:44:16 +0000

EXAMPLE: Beach drainage in Quend-Plage (FR) nst Fri, 01/13/2017 - 09:44

In the face of increasing beach and dune erosion, the community of Quend-Plage, located on the Picardy coast of northern France, installed a beach drainage system in 2008. As a result of this, the macrotidal beach of Quend-Plage has been stabilized, preserving both natural habitats and recreational spaces.

Based on: Bain, Olivier, Renaud Toulec, Anne Combaud, Guillaume Villemagne, and Pascal Barrier. "Five Years of Beach Drainage Survey on a Macrotidal Beach (Quend-Plage, Northern France)." Comptes Rendus Geoscience 348.6 (2016): 411-21. Web.

General description

The Quend-Plage beach is characterized by a mix of transverse bars and troughs along the tidal flat. The wider coastal region is subject to the influence of both waves and tides, and by contrasting temperate and oceanic climates.

The implementation of a beach drainage system had never been used in the north of France, despite being tested elsewhere in Europe and overseas. The system was placed in the upper tidal flat of the beach, and consists of a drainage pathway 5 m wide, 900 m long, and 1.5 m deep. The system is susceptible to damage from storms and can malfunction over time, requiring maintenance.

Tourism plays a large role in the local economy of the Picardy coast. With hundreds of thousands of visitors per year, much of the coast is dominated by the tourism industry including Quend-Plage beach. Mussel farming and sea animal harvesting are also important to the local fishing economy.

After several years of beach erosion, and degradation of the existing sea wall, Quend-Plage beach lost much of its dry sand and recreational activities moved inland toward the dunes, which increased erosion of the dune foot and reduced tourism income. In response, the community of Quend-Plage invested in researching various coastal protection strategies, and the implementation of a beach drainage system was chosen.

Funding was received by European and national funds. The French government authority “Direction départementale des territories et de la mer” later requested a five-year long monitoring survey be undertaken to determine the effectiveness of the largely experimental technique for that region of France.

Exploring a new technique

One of the reasons why a beach drainage system solution to coastal erosion was selected by the Quend-Plage authorities was because it had never been done before in northern France and on the Picardy coastline. This was an opportunity to explore a new technique that, if successful, could be replicated along the coastline where deemed appropriate. The initiation of an extensive 5-year monitoring program, considering topographic, geomorphic, and granulometric factors, by the French “Direction départementale des territories et de la mer” indicates the experimental focus of the project and the commitment for long-term solutions.

Key lessons learnt

The use of a beach drainage system to combat coastal erosion along the Picardy coastline is a feasible and effective solution. In the case Quend-Plage, the beach morphology was significantly altered in the first five years after the system was installed. The upper beach and foot of the dunes recovered and increased in size. However, there was some erosion of the middle and lower beach and a small directional change of the bars and troughs. Overall, the drainage system facilitated a complete re-establishment of the Quend-Plage beach features, which ultimately brought more stability and usability to the community

Relevant case studies and examples

Beach drainage

Measure category

Riverine or slow rise floods

EXAMPLE: Beach recharge at Pevensey Bay (UK)

nst — Fri, 13 Jan 2017 08:17:06 +0000

EXAMPLE: Beach recharge at Pevensey Bay (UK) nst Fri, 01/13/2017 - 09:17

The beach of Pevensey Bay (UK) is a shingle barrier beach under threat from flooding and coastal erosion. Today, the beach is managed in an adaptive manner developed by Pevensey Coastal Defence, where management activities respond to changes in risk and beach recharge and beach recycling is undertaken.

Based on: Sutherland, James, and Ian Thomas. "The Management of Pevensey Shingle Barrier." Ocean & Coastal Management 54 (2011): 919-29.

General description

Pevensey Bay, located between Eastbourne and Cooden in East Sussex on the southern coast of England, surrounds a nine kilometre beach under threat from flooding and coastal erosion. The beach is a shingle barrier beach, a mix of sand, gravel and cobbles protecting important animal habitats, properties, roadways and other infrastructure. Additionally, approximately 50 km² of valued low-lying conservation and agricultural land could be flooded should the beach become breached at high spring tide. The challenge facing local authorities and residents is that each wave of sea water on the barrier beach takes more sediment away than it brings, resulting in a net loss of coastal land as time progresses. This issue is compounded by sea level rise, and both contribute to increased risk of flooding and loss of land through erosion.

In general, the strategy of the Pevensey Bay beach management plan can be classified as “hold the line”, which involves strengthening and upgrading the existing coastal defences. In Pevensey, it was decided to thicken the barrier beach through beach nourishment, recharge, and recycling to bring more protection from breaching.

In response to the flood and erosion risk, the UK Environmental Agency has tasked the Pevensey Coastal Defence consortium to manage the barrier beach of Pevensey Bay. The consortium implements activities in response to assessed risk that are determined through monitoring. This strategy is representative of an adaptive management approach whereby risk and uncertainty are managed through an continuative process of informed decision making that responds to regular monitoring.

Beach management

Pevensey Coastal Defence was able to meet their tactical objectives by following a three-part process of measurement, benchmarking and implementation. The three stages helped maintain the natural and social health of the Pevensey Bay. Firstly, both the Environmental Agency and Pevensey Coastal Defence performed cross-shore profiles and beach surveys several times a year to get a better understanding of the level of erosion. The measured values are compared, or benchmarked, to set threshold values of various coastal state indicators that would indicate existing and predicated erosion and flooding. Finally, the differences between measurements and thresholds let decision makers compare intervention strategies as well as the locations to implement these strategies. Considered and implemented strategies include variations of beach nourishment, recharge, recycling and re-profiling through the use of dump trucks or boats. This last stage has a temporal factor with different strategies being more efficient and environmentally sound at different times of the year.

Key lessons learnt

A study of the Pevensey Bay barrier beach concludes that early decisions made during the adaptive management process should carefully consider several coastal state indicators and thresholds that will determine when to intervene and by how much. Additionally, Pevensey Bay, like other similar shrinking beach areas, is best protected by beach recharge sourced from external sediment reservoirs in tandem with beach recycling, all the while considering the health and impact on natural systems.

Relevant case studies and examples

Beach Nourishment

Measure category

EXAMPLE: Dune rehabilitation in Praia de Faro (PT)

nst — Mon, 12 Dec 2016 11:00:36 +0000

EXAMPLE: Dune rehabilitation in Praia de Faro (PT) nst Mon, 12/12/2016 - 12:00

Reduction

Dune strengthening, rehabilitation and restoration

Ecosystem based approach

A construction of an elevated wooden pathway alongshore and cross-shore of about 1500 m, and the construction of a dune fences were implemented in the coastal town of Praia de Faro (Portugal). The fences helped to trap sand in the dune areas leading to a growth of the dune system. The wooden path played also an important role in the dune recovery.

The Ria Formosa coastal lagoon is a RISC-KIT Case Study site and is located on the southern coast of Portugal. The coastal town of Praia de Faro is located partly on a natural dune area separating a lagoon from the open sea. Due to tourism and housing activities the dunes were in bad conditions, so two main actions were undertaken in 2000/2001: construction of an elevated wooden pathway alongshore and cross-shore of about 1500 m, and the construction of a dune fences. A row of fences was placed along the ocean side for about 1 km and additionally fences were built as a a reticulate for 670m (continuous rectangles or about 7x5.5 m). The fences helped to trap sand in the dune areas leading to a growth of the dune system. Over the past 15 years the dunes grew around 10 meters in width and about 1.3 meters in height, leading to an almost natural ecological state. The wooden path played an important role in the dune recovery, because it led to reduction of wild paths through the dunes. Wild path through the dunes caused a destabilization of the dune system. With the pathway, tourists, fishers, and inhabitants use the path to reach the shore or other areas. The fences were also an additional obstacle which minimized the usage of wild paths through the dunes.

Over the time span of 15 years, the measure showed an improvement of the dune systems where the pathway and the fences were built. Before the measure was implemented there were overwashes in the area, but these did not occur in the last years. With no extreme storm events or human intervention, the dunes should stay rehabilitated for the next decades.

Political & social feasibility:

The constructed wooden path was well received by inhabitants and tourists. For recreational purposes the measure had a positive impact, because it is now easier and faster to get to different spots ate the oceanic shore and the back barrier beach, where the area is used for bathing, surfing, or kite-surfing. To get to these areas, the pathway is used.

Cost of implementation & maintenance

The initial costs of the measures were around 1250000€. 4/5 of the costs were paid with EU funds, 1/5 was paid with national funding. There is no money assigned for maintenance costs. If maintenance is needed, is overtaken by local fisherman or house owner (basically by replacing broken parts of the wooden path or the fence). For a more detailed cost effectiveness analysis see here.

Ecological feasibility

With the measure the ecological status of the dune system is near to natural values with natural (autochthon) species dominating the ecosystem. Allowing the natural evolution of the dune ecosystem, this approach can be classified as ecological feasible. Problems could arise if the new system attract a lot more tourists, that could put additional pressure on the ecosystem (e.g. too many bird watchers, too many visitors at the beach, etc.).

Key lessons learnt

The rehabilitation of dunes with the help of two strategies worked very well in this case study area. The damages of dunes due to wild paths are limited by the guidance of visitors and inhabitants along the wooden paths. This alleviated impairments of the dunes. Additionally the set-up of fences helped to trap sand and accelerate the process of dune rehabilitation.

Relevant case studies and examples

Further Readings

RISC-KIT Case Study

Cost-Effectiveness analysis of a wooden path over the dune (Praia de Faro)

Measure category

Protecting and restoring reefs (coral and oyster)

nst — Tue, 06 Dec 2016 09:18:12 +0000

Protecting and restoring reefs (coral and oyster) nst Tue, 12/06/2016 - 10:18

Based on kindly provided information by UNEP's "Green Infrastructure Guide for Water Management: Ecosystem-based Management Approaches to Water-related Infrastructure Projects " (UNEP, 2014)

Ecosystem based approach

Coral and oyster reefs are considered to be types of coastal wetlands. As a natural coastal defense they are a buffer for coastlines against waves. Reefs are threatened by rapid environmental change, making it very important to protect and restore reefs.

Coral reefs are shallow-water marine ecosystems characterized by massive calcium carbonate formations secreted by colonies of coral polyps and algae living in their tissues (Sheppard et al. 2005). Reefs build up as each coral species secretes uniquely shaped carbonate skeletons over older skeletal remains. The foundations of older reef structures are riddled with tunnels and channels created by physical and chemical erosion and the effects of reef inhabitants. Coral reefs are home to high fish and invertebrate biodiversity, all uniquely adapted to reef life, yet fundamentally dependent on coral survival. They tolerate little environmental variation and are particularly vulnerable to small changes in water quality, but they can recover once adverse events end, as long as local sources of colonizing organisms and suitable substrates are available (UNEP-WCMC 2006).

In their natural setting, oyster reefs are often found seaward of salt marshes (Scyphers et al. 2011) and are a source of valuable services both to ecosystems and humans. It is estimated that up to 80 per cent of the world’s oyster reefs have been lost, a rate unprecedented for any other marine habitat (TNC 2012). This loss also represents an enormous reduction in the ecosystem services provided by these reefs including food, habitat for bird and marine species and a buffer for coastlines against waves.

The sustainability of both coral and oyster reefs is also threatened by rapid environmental change, which overwhelms reef-species adaptation and resilience following destructive events. The pressures on reefs include human activities (such as sedimentation, water pollution, resources extraction and commercial fishing) (Waddell 2005; Burke et al. 2011), as well as the effects of climate change. Among the latter is the increasing atmospheric concentrations of carbon dioxide and excessive heat, which cause intolerable acidity and water temperatures (Hoegh-Guldberg et al. 2007; De’ath et al. 2009).

Where possible, conservation measures can be put in place and actions taken to deal with the pressures and causes of degradation of coral and oyster reefs. In addition to eliminating or mitigating the source of reef impact, methods of oyster reef restoration and coral transplantation are often used to increase the rate of coral and oyster colonization at damaged sites (Epstein et al. 2001).

For coral reefs, transplantation ideally starts with collecting fragments of living coral rock as soon as possible and storing them in a suitable location until they can be moved to the restoration site (Japp 2000; Epstein et al. 2001). Fragments can then be attached to suitable substrate. In difficult locations, artificial structures can be installed to provide a stable foundation for coral transplants (Japp 2000). Transplantation success depends on the species, transplant shape and type, status of substrate attachment and environmental conditions (Japp 2000). Where that is not possible, coral may be transplanted from nearby reef locations or from coral nurseries prepared in advance for restoration needs.

Similarly, oyster reefs can be constructed artificially to replicate their natural functions. Case studies show that creating large-scale man-made coral reefs is possible, and they are able to replicate many of the functions provided by naturally occurring coral reefs (TNC 2012).

Benefits

For a long time, grey solutions have been dominant in coping with coastal hazards. Approaches include artificially hardening the shoreline or creating artificial barriers by dumping gabions made of cement and rock into the water (World Risk Report 2012). This is not only damaging to marine ecosystems, but can also shift the impacts of storms to communities down shore, increasing the need for additional defence structures.

There has been growing awareness and evidence of coral and oyster reefs playing a major role in coastal stabilization and coastal defence (World Risk Report 2012). Coral reefs provide natural breakwaters that can mitigate flooding and the erosive effects of storms along low-lying shores (Japp 2000; UNEP-WCMC 2006). They have shown to reduce the wave energy and height that impacts coastlines (Sheppard et al. 2005) attenuating and reducing more than 85 per cent of incoming wave energy (World Risk Report 2012). By forming a natural barrier, the reefs are the first line of coastal defence from the damaging impacts of waves, erosion and flooding.

Like coral reefs, oyster reefs protect from coastal erosion and wave erosion (TNC 2012). Evidence oyster reefs also prevent coastal marsh retreat (Scyphers et al. 2011). Due to their complex structure, these natural barriers reduce water velocities, increase sedimentation rates and provide improved conditions for settlement and retention of propagules, thereby improving the chances of species survival (Scyphers et al. 2011).

Co-benefits

Coral reefs and oyster reefs have enormous significance in the lives of millions people. Tropic coastal populations in particular depend heavily on the resources provided by these ecosystems (World Risk Report 2012), where many reef species support fisheries and other livelihood sources (Burke et al. 2011). The reefs also play an important role in sustaining traditional lifestyles and carry cultural significance to local communities. In addition, they are home to rare species with relevance to e.g. production of medicinal products. Coral reefs are also popular tourist attractions (Burke et al. 2011) creating basis for significant income from the tourism sector, such as recreational scuba diving and snorkelling.

Oyster reefs are shown to provide food and shelter for crabs and fish species, which in turn increases the catch for fisheries. They also have shown to remove nitrogen from coastal waters, preventing algal blooms and dead zones (TNC 2012).

Costs

Restoring coral reefs is usually a very expensive and technologically complex exercise. The critical features making coral reefs such effective protection barriers, are the size, height, hardness and structural complexity of the reefs (i.e. friction) (World Risk Report 2012). Once lost, such features are very difficult and expensive to replicate. The best approach, therefore, is to protect reefs from external stressors before they are degraded, focusing on the sources of human impact. The creation of no-fishing zones at reefs, for example, appears to restore reef resilience and may make them somewhat less susceptible to increases in global temperature and carbon dioxide (Mumby and Harborne 2010; Selig and Bruno 2010).

A study on oyster reef restoration projects in the Gulf of Mexico, for instance, has shown that investments in restoration activities could yield a several-fold return on investment through gains in fisheries and avoided damage for properties and public infrastructure. The case study assessed a USD 150 million investment over ten years in restoring 160 km of oyster reefs in the Northern Gulf of Mexico. The assessment showed that the initial investment would be returned twofold in the period via new jobs and goods and services delivered to the local communities (TNC 2012).

The accelerated rate of global climate change requires particular consideration in relation to the long- term fate of restored reefs. The risks of eventual coral reef loss at the warmest edges of coral reef ranges, for example, can occur regardless of the success of the restoration efforts and need to be considered in connection with investment decisions. A troublesome concern is also elevated ocean acidity from increasing carbon dioxide (Hoegh-Guldberg et al. 2007). However, many studies have shown that in most cases investments in coral and oyster reef protection yield manifold benefits, once the socio- economic co-benefits are considered.

Literature sources

Burke, L., Raytar, K.,Spalding, M. and Perry, A. (2011). Reefs at risk revisited. Washington, D.C.: World Resources Institute.

De’ath, G., Lough, J.M and Fabricius, K.E. (2009). Declining coral calcification on the Great Barrier Reef, Science, vol. 323, pp. 116-119.

Epstein, N., Bak, R.P.M. and Rinkevich, B. (2001). Strategies for gardening denuded coral reef areas: The application of different types of coral material for reef restoration. Restoration Ecology, vol. 9, pp. 432-442.

Hoegh-Guldberg, O., Mumby, P. J., Hooten, A. J. et al. (2007). Coral reefs under rapid climate change and ocean acidification. Science, vol. 318, pp. 1737-1742.

Japp, W.C. (2000). Coral reef restoration, Ecological Engineering, vol. 15, pp. 345-364.

Mumby, P. J. and Harborne, A.R. (2010). Marine reserves enhance the recovery of corals on Caribbean reefs. PLoSONE, vol. 5, pp. e8657.

Scyphers, S.B., Powers, S.P., Heck Jr., K.L. and Byron, D. (2011). Oyster Reefs as Natural Breakwaters Mitigate Shoreline Loss and Facilitate Fisheries. PLoS ONE, vol. 6, p. 8.

Selig, E.R, and Bruno, J.F. (2010). A global analysis of the effectiveness of marine protected areas in preventing coral loss. PLoS ONE, vol. 5, p. e9278

Sheppard, C., Dixon, D.J., Gourlay, M., Sheppard, A. and Payet, A. (2005). Coral mortality increases wave energy reaching shores protected by reef flats: Examples from the Seychelles. Estuarine, Coastal and Shelf Science, vol. 64, p. 223–234.

TNC (2012). The Nature Conservancy, The Economics of Oyster Reef Restoration in the Gulf of Mexico: A Case Study in Mobile Bay, Alabama.

UNEP-WCMC (United Nations Environmental Programme/World Conservation Monitoring Center. (2006). In the front line: shoreline protection and other ecosystem services from mangroves and coral reefs. Cambridge UK: WCMC/UNEP

Waddell, J.E. (2005). The State of the Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2005. NOAA Technical Memorandum NOS NCCOS 11. Silver Springs, Maryland: NOAA/NCCOS Center for Coastal Monitoring and Assessment’s Biogeography Team.

World Risk Report (2012). Available from http://www.worldriskreport.com/.

Measure category

Mitigation

EXAMPLE: Foreshore sand replenishment (DK)

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EXAMPLE: Foreshore sand replenishment (DK) nst Thu, 11/03/2016 - 11:48

Coastal Protection on the West Coast of Jutland

Ecosystem based approach

The case study shows how sand replenishment at the west coast of Denmark has become the main measure to face coastal erosion. Experiences in the last years showed, that replenishments at the foreshore seem to be the most effective and ecosystem friendly version of beach nourishments.

Based on the WWF study "Klimaanpassung an weichen Küsten - Fallbeispiele aus Europa und den USA für das schleswig-holsteinische Wattenmeer"

A sea level rise due to climate change will enhance the erosion processes. The partly low-lying areas in the hinterland are protected by an up to 10 km wide belt of dunes. Without coastal defense measure coastline recession of up to eight m a year in some places could occur. In 1981 a particularly severe storm has lead to land losses of up to 30 m in some coastal areas. Especially in places with relatively narrow dunes, with some less then 100m wide for example at the Ringkøbing Fjord, this is seen as a problem. For more than 30 years this problem is faced by the replenishment of sand on the beach and in near shore areas.

In 1983 the Danish Coastal Authority (Kystdirektoratet) started in cooperation with the local municipalities’ coastal protection in this area by implementation of slope protection, breakwaters and nourishments. Since then, more than 59 million m³ of sand have been replenished. Usually the sand is removed 5-10km offshore by boat an than either being dumped on the sandbar or placed directly on the beach. Average annual costs for this approach are approximately € 10 million per year.

Up until the 1990s, 145 breakwaters were built to reduce the sand transport from the beach. While these elements could only slow down the erosion rate, employment of nourishment has meant that the recession has been brought to a halt. This is the reason why today, the work almost only consists of nourishment.

Technical feasibility

Since the 1990s coastal protection at the Danish west coast was mainly undertaken by sand replenishments and partly hard protection measures the foot of a dune or dyke. The construction of breakwaters and revetments was phased out to the end of the 1990s. Today sand replenishment is used almost exclusively. Lately, replenishments at the foreshore are favored because they seem to be more effective than the traditional nourishments at the beach. Although nourishments at the beach are effective in the short term, Danish research results demonstrate that nourishment in the foreshore lead to stabilization of the beach and are more cost effective over a certain period of time. But beach nourishments are still undertaken to protect the foot of dunes. Continuous monitoring showed that the formerly high erosion rate has been reduced to an average of 0.1 m since 1998. Further research is needed to clarify which grain sizes are most effective to resist erosion. In general the composition of the nourished material should correspond to the natural conditions.

Political & social feasibility

In retrospect, the implementation of sand replenishing measures (rather than ‘hard’ coastal defense measures) required are a lot of political will. Today, there is a fundamental shift from "hard" to "soft" coastal protection measures in Denmark acknowledgeable. However, there are still many hard structures existing interfering with the natural processes. Although being partly ineffective, a substantial deconstruction of these structures has not been initiated yet.

Cost of implementation & maintenance

The Danish example shows that replenishments at the foreshore seem to be the best environmentally sound and most effective of beach nourishments. Compared to ‘traditional’ beach nourishment schemes, this approach is less costly and saves energy in the long term, and additionally the beach remains free from tubes.

Ecological feasibility

Ecological studies have shown that biocoenosis at the seabed where the sand extraction took place mostly recovered after a period of one year. But this should not be generalized because, because the recovery rate depends highly on the structure of the seabed and the type of sand extraction.

Concerning the place of the nourishment, Danish studies show that the local fauna needed two to three years for recovery. Moreover, it was noted that the animals found were smaller than before the nourishment.

Key lessons learnt

This example from the west coast of Denmark shows that by using beach nourishment coastal erosion can be slowed down on a large scale and can also be sufficient for the protection of settlements. The introduced sediment can additionally serve as a buffer for an accelerated sea level rise. For sandy beaches this example shows that ‘soft’ coastal measures should be preferred over ‘hard’ coastal measures where possible. In addition, old ‘hard’ structures should be removed, if they have been proven to be counterproductive against erosion. If the protection can be achieved with replenishment of sand, this method should be favored, because it’s more nature-friendly can create co-benefits for tourism and recreation.

Relevant case studies and examples

Beach Nourishment

Further Readings

Literature sources

Ecoshore (o.J.): Projects. Webseite. http://www.ecoshore.com/Projects.htm (20.05.2014).

Hanson, H.; Brampton, A.; Capobianco, M.; Dette, H. H.; Hamm, L.; Laustrup, C.; Lechuga, A.; Spanhoff, R. (2002): Beach nourishment projects, practices, and objectives—a European overview. In: Coastal Engineering, No. 47, S. 81–111.

Jacobsen, P.; Brøgger, C. (2007): Coastal protection based on Pressure Equalization Modules (PEM). In: Proceedings of the International Coastal Symposium, Griffith University, Australia.

Kystdirektoratet (Dänische Küstenschutzbehörde) (2013a): Coastal Protection on the West Coast of Jutland. Webseite. http://eng.kyst.dk/coastal-protection-on-the-west-coast-of-jutland (20.05.2014).

Kystdirektoratet (Dänische Küstenschutzbehörde) (2013b): The National Coastal Protection Strategy. http://eng.kyst.dk/the-national-coastal-protection-strategy.html (20.05.2014).

Margheritini, L.; Frigaard, P.; Wahl, Niels Arne (2008): A holistic evaluation of a typical coast nourishment on the Danish West Coast. In: Journal of Coastal Conservation, No. 12, S. 83–91.

Pickaver, A.-H. (o. J.): Ourcoast Project Case Study – Changing Traditional Coastal Defense Policy to Stop Erosion, DK. http://ec.europa.eu/ourcoast/index.cfm?menuID=8&articleID=82 (20.05.2014).

Measure category