Combined approach (grey + green)

Coastal floods or storm surges

Estuarine floods

Hold the line

Based on the information available on the ClimateAdapt Platform

Grey infrastructure

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

Reconnecting rivers to floodplains

nst — Mon, 20 Feb 2017 09:27:15 +0000

Reconnecting rivers to floodplains nst Mon, 02/20/2017 - 10:27

Natural flood, runoff, catchment management

Water flow regulation

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)

River restoration contributes to flood risk management by supporting the natural capacity of rivers to retain water. As flood risk consists of damage times occurrence, flood risk management needs to reduce either the damage, or the likelihood of floods to occur, or both. River restoration reduces the likelihood of high water levels, and improves the natural functions of the river at same time.

In a natural river system a river spreads water beyond its banks and over extended areas of a floodplain during periods of high water. In order to protect property and contain waters, the classic flood risk management approach is to constrain watercourses with rivers being straightened and building dykes to increase discharge capacity, dredging to deepen channels, and building reservoirs and artificial retention areas to store excess waters.

While this generally reduces the likelihood of flooding, in the event of extremely high waters it increases the amount of damage if the engineered system is overwhelmed or fails. Without natural features such as wetlands and meanders, excess waters cannot be absorbed. Any breach will release an enormous amount of water, with potentially catastrophic consequences. Continuously reinforcing and building higher dykes cannot overcome this weakness, and is a very expensive option. Historically, engineering solutions upstream have created peak flows downstream, leading to more engineering. Moreover, climate change scenarios predict more extreme weather events and higher sea levels. A new approach is needed.

Advantages

By re-connecting brooks, streams and rivers to floodplains, former meanders and other natural storage areas, and enhancing the quality and capacity of wetlands, river restoration increases natural storage capacity and reduces flood risk. Excess water is stored in a timely and natural manner in areas where values such as attractive landscape and biodiversity are improved and opportunities for recreation can be enhanced. In these ways, river restoration directly contributes to climate change strategies aimed at mitigating the effects of increased and erratic peak flows and droughts.

River restoration is increasingly being delivered by flood risk managers to create space for flood water. Reconnecting floodplains to the river and managed realignment in estuaries is an important mechanism of water management.

Future climate change will potentially affect all aspects of the rainfall regime. The precise nature of these changes is uncertain, particularly for those extreme events, whether of short or long-duration, which tend to lead to flooding. Increases in rainfall at all scales will increase the risk of flooding to a greater or lesser extent, depending on how these increases manifest themselves in space and time and of the rainfall-runoff characteristics of the catchment in question.

Benefits

River restoration improves flood protection, but it also brings about co-benefits that are multifold. Firstly, river restoration can improve flood storage capacity of a river and reduce the volume and speed of water. Some of the co-benefitst can include cost reductions by removing the need to maintain hard infrastructure and also improving the quality of water, and thus in turn drinking water costs. Improved biodiversity and the creation of natural wetlands is another adjunct result of river restoration using green infrastructure. Finally it improves resilience to climate change by creating new floodplanes for increased water storage, green networks and more natural space for people and wildlife during higher temperatures.

Costs

There are different kinds and degrees of river restoration. A larger scale project can include an entire floodplane, removing past structures and restoring natural processes and channels of a water course. A smaller project may simply be removing structures in one place, and replacing them with more natural features.

Barriers to Implementation

Lack of funding is often cited as a key reason for failing to restore watercourses and rivers, as well as, consensus in agreement of users of a river. Given that restoration can take place on either a large or small scale, the associated barriers often also relate to how extensive the project is.

Measure category

Coastal floods or storm surges

Land claim

nst — Tue, 07 Feb 2017 13:09:59 +0000

Land claim nst Tue, 02/07/2017 - 14:09

Move seaward

EXAMPLE: Artificial Island - Amager Beach, Copenhagen (DK)

Grey infrastructure

The main objective of land claim is neither erosion nor storm reduction. The aim of land claim is to create new land from areas that were previously below high tide. These measures can be taken to reduce the exposure of these areas to coastal flooding. For example, in Singapore and Hong Kong, there are enforced minimum reclamation levels to account for future sea level rise

Based on information from ClimateTechWiki.

General Description

Land claim is likely to be accomplished by enclosing or filling shore or nearshore areas (Bird, 2005). Several alternative terms may be used when referring to land claim; these may include land reclamation, reclamation fill and advance the line. Typically this measure is undertaken to gain land (French, 1997), today especially around coastal cities (like Singapore and Hong Kong), where very high land values are justifying the costs.

In order to enclose areas for land claim, hard coastal defences must be constructed seaward of the existing shoreline. Dike and seawalls are typically constructed to protect the claimed land from flooding by the sea (Burgess et al., 2007). Two main methods of land claim are: (1) enclosing and defending shore or nearshore areas; and (2) filling shore or nearshore areas, often using the same techniques used in beach nourishment. When considering adaptation to climate change, land claim using fill methods is perhaps more appropriate as it does not carry such a great flood risk.

Advantages and disadvantages of the technology

The key advantage of land claim is the gain of additional coastal land for uses such as agriculture or development. Apart from the valuable land, this additional coastal land can function as a buffer and reducing the risks of flooding.

Land claim can also generate a number of negative impacts. The process of land claim requires either the enclosure of intertidal habitats by hard defences, or the raising of their elevation above that of sea level to prevent inundation. This causes the direct loss of intertidal habitats such as saltmarshes, intertidal flats and sand dunes (French, 1997). Another disadvantage is dewatering. By draining reclaimed land which has a high water content, land is caused to dry out, compact and shrink (French, 1997), thus reducing its elevation in relation to sea level. This causes a difference between land elevations inside the flood defences, where compaction and shrinkage has occurred and outside, where natural intertidal environments continue to naturally accrete sediments. This difference in elevation is also exacerbated by SLR and results in an ever increasing requirement for flood defences (Burgess et al., 2007). It also requires an ongoing commitment to defend these areas (French, 1997).

Any type of land claim will cause the displacement of water during a natural tidal cycle. Because of this displacement, incoming tides have a smaller area to inundate. This will cause water depths to increase and will mean intertidal areas are submerged for longer – this has the potential to cause negative biological consequences and can also increase the tidal range upstream (French, 1997).

Financial requirements and costs

The financial costs of land reclamation are dependent on a number of factors:

Chosen method of reclaim (enclosing previously intertidal areas using hard defences or raising the elevation of previously submerged land)
Availability and proximity of fill material from onshore or offshore sites
Number, type, size and availability of dredgers
Requirement for hard protection measures to defend reclaimed land from coastal flooding and erosion
Project size and resulting economies of scale
Estimated material losses

If land claim is conducted by enclosing previously intertidal areas, the additional costs of providing hard protective measures, such as seawalls or dikes, to prevent flooding and erosion of these areas is important. Ongoing maintenance costs for these structures must also be considered.

If land claim is achieved by raising the elevation of previously submerged land, the cost of fill material is likely to be the main determinant of project cost. In turn, this cost will be influenced by the availability of appropriate materials, their proximity to the construction site and the characteristics of the reclaim site – this influences the type of dredging equipment which can be used. Changes in the cost of fill material are likely to occur in future due to increased demand and greater restrictions on dredging.

Institutional and organisational aspects

The institutional and organisational requirements of land claim projects are likely to depend on the scale and ambition of the project. Small-scale land claim for agricultural uses is more likely to be achievable at the community level than large-scale island enlargement and creation as seen in Singapore or Dubai. These large-scale projects will require the involvement of large organisations and large amounts of funding.

Key lessons learnt

One barrier to the use of land claim is potential long-term costs. Land claim creates land which will require protection from coastal flooding and/or erosion. This requires construction of defences such as seawalls or dikes with associated construction and ongoing maintenance costs. Land claim through elevation raising may also be a cost-effective method of disposing of dredged material from ports, harbours and navigation channels. This could reduce the overall cost and eliminate the need to identify offshore disposal sites for dredge material. As with beach nourishment, pollutant levels in the dredge material should be carefully monitored.

Environmental concerns may provide another barrier to implementation. By reclaiming land in these areas, environmentally important intertidal habitats are lost, and knock-on impacts such as alterations to ebb/flood dominance may also occur. As a result, environmental opposition to land claim may mount. In the EU, compensation for lost habitats is required

Relevant case studies and examples

Further Readings

Wang et al (2014): Development and management of land reclamation in China

Literature sources

Bird, E. (2005) Appendix 5: Glossary of Coastal Geomorphology in Schwartz, M.L. (ed.). Encyclopedia of Coastal Science. The Netherlands: Springer, 1155-1192.

Burgess, K., Jay, H. and Nicholls, R.J. (2007) Drivers of coastal erosion in Thorne, C.R., Evans, E.P. and Penning-Rowsell, E.C. (eds.). Future Flooding and Coastal Erosion Risks. London: Thomas Telford, 267-279.

French, P.W. (1997) Coastal and Estuarine Management. London: Routledge.

Measure category

EXAMPLE: Lowering the floodplain in Emilia–Romagna area (IT)

nst — Fri, 27 Jan 2017 12:48:53 +0000

EXAMPLE: Lowering the floodplain in Emilia–Romagna area (IT) nst Fri, 01/27/2017 - 13:48

River bank relocation – floodplain lowering

Near to the RISC-KIT Case Study in Emilia – Romagna, a LIFE+ “LIFE RINASCE” project has been implemented in 2014 to improve some of Emilia - Romagna drainage channels in the Po floodplain. Project leader is the Emilia Centrale Land Reclamation Consortium, in collaboration with the Emilia -Romagna Region. The project was started in 2014 and will run the end of 2018 with a total budget of almost 2.1 million €.

Based on the project information from LIFE+

General description

The project aim is to reduce the risk of flooding and achieve good ecological status of the waters in the Po floodplain through ecological restoration of the channel network and vegetation management. It aims at demonstrating the feasibility and environmental and socio-economic benefits of such measures on a large floodplain area.

The project plans to develop an integrated restoration programme for floodplain channels using river restoration methods and protocols for sustainable management of aquatic and riparian vegetation. Planned interventions will aim to restore hydraulic functions of the floodplain, reduce the risk of flooding and improve the ecology.

One measure among others will include the lowering of the floodplain and thereby creating an arboreal strip of plants and shrubs. Other measures include the creation of a wetland, the enlargement of a natural channel. These measures are aimed to mitigate flood risks through water retention. Other benefits will be the improvement of drainage, purification of water, and improved ecological status.

It is foreseen that seven kilometer of canals will be restored by the end of the project by the creation and/or the lowering of three hectares of floodplain areas and vegetation. Additionally two hectare wetland should be created by then.

The Participatory process

The project used a participatory process to involve local actors, stakeholders and citizens in the strategic choices regarding the transformation of the territory and to collect ideas and proposals for the design of the rehabilitation interventions. Information, communication, consultation and listening to participants played an important role for the first steps in the project. The process was split into two main plenary sessions, six discussion meetings and a follow-up meeting for the technical and regulatory aspects hosted. These meetings involved a total of 189 participants coming from associations, organizations, companies and citizens. In parallel, the participatory process was supported by a dedicated web space.

Relevant case studies and examples

Further Readings

Website of the project (in Italian)

Measure category

EXAMPLE: The Ekostaden Augustenborg initiative, Malmö (SWE)

nst — Thu, 26 Jan 2017 15:19:26 +0000

EXAMPLE: The Ekostaden Augustenborg initiative, Malmö (SWE) nst Thu, 01/26/2017 - 16:19

Urban floods

Surface Water Management

Sustainable Urban Drainage Systems (SUDS)

Augustenborg is a highly populated neighbourhood in Malmö, Sweden. In order to minimise flood risk, between 1998 and 2002, the ‘Ekostaden Augustenborg’ initiative installed a ‘Sustainable Urban Drainage System’ (SuDS). As part of the project, green roofs, ditches, retention ponds, green spaces and wetlands were created. Due to the installation of the SuDS, rainwater run-off has decreased by half.

Based on RECREATE project results: COASTAL PROTECTION AND SUDS – NATURE-BASED SOLUTIONS.

General description

The neighbourhood Augustenborg in south-western part of Malmö (Sweden) suffered from floods caused by overflowing drainage systems. Resulting flooding was leading to damage to underground garages and basements, and restricted access to local roads and footpaths. In order to minimise flood risk, between 1998 and 2002, the ‘Ekostaden Augustenborg’ initiative installed a “Sustainable Urban Drainage System” (SuDS). The project was carried out collaboratively by the city council and the MKB social housing company, with extensive participation of the residents in Augustenborg. As part of the project, green roofs, ditches, retention ponds, green spaces and wetlands were created. Due to the installation of the SuDS, rainwater run-off has decreased by half. Additional benefits include improved water quality, reduced carbon emissions, aquifer recharge (relieving stress in water scarce areas), and increased biodiversity through the creation of new wetland habitats.

As the project involved significant physical changes in infrastructure, a main challenge was to ensure the acceptance of the local residents. An extensive and iterative process of stakeholder engagement was also initiated during the design and execution of this project, involving a ‘rolling programme’ of consultation with local residents, representatives from the local school, practitioners, city staff and local businesses. The physical improvements in Augustenborg and related projects totaled approximately 21 million Euro. About half of the funds were invested by the MKB housing company. Without the partnership between resident companies and public authorities, the funding for this project would not have been sufficient.

Relevant case studies and examples

Further Readings

Case Study description from Forest Reseach (UK)

Literature sources

Kenna Davis, Ina Krüger & Mandy Hinzmann (2015): COASTAL PROTECTION AND SUDS – NATURE-BASED SOLUTIONS. Recreat Policy Brief No. 4, November 2015, 14 p

Measure category

EXAMPLE: Relocation of Clavell Tower, Dorset (UK)

nst — Thu, 26 Jan 2017 15:00:34 +0000

EXAMPLE: Relocation of Clavell Tower, Dorset (UK) nst Thu, 01/26/2017 - 16:00

Removal or relocation

Managed retreat

Exposed element relocation and removal

By 2002, historic Clavell Tower was deemed to be at serious risk of collapsing under the crumbling Dorset coastline at its base. The most technically, socially, and financially feasible solution was to simply dismantle the empty tower and reconstruct it further away from the cliff’s edge on more stable footing. This resulted in a reinvigorated heritage site saved from the dangers of coastal erosion.

Based on information from The Landmark Trust

General description

Located high on a cliff on the Dorset coast of southern England overlooking Kimmeridge Bay, Clavell Tower is a four story circular tower originally built in 1830. The soft and easily erodible shales of the cliff had been steadily crumbling and retreating towards the tower since its construction.

The responsible organisation for managing Clavell Tower, the Landmark Trust, decided that the most feasible solution for this kind of coastal erosion threat was to dismantle the ageing tower and re-erect it on a more stable base further away from the cliffs edge.

The eroding coastline for which Clavell Tower calls home happens to be a UNESCO World Heritage Site known as the Jurassic Coast. It is a popular tourist destination for its natural beauty and geological significance. As such, it is unlikely that more intrusive coastal erosion measures that could be used to stabilize the cliff would be approved. Relocating the tower itself was a more socially acceptable solution.

Innovative & Cost-effectiveness aspects of the measure

Dismantling and re-erecting Clavell Tower was simply the most technically and financially feasible solution for the Landmark Trust to undertake. Four years of fundraising efforts and external funding from the Heritage Lottery Fund allowed the project to commence by 2006. To offset some of the costs and ensure future revenue for maintenance and heritage preservation, the Landmark Trust also currently manages Clavell Tower as a hotel.

This kind of heritage conservation strategy is clearly the most intrusive possible and would not have been undertaken if it was not the most suitable option. Conservation staff carefully recorded and surveyed all the physical aspects of the tower so that the replication was as true to the original as possible. Sightlines from the tower across the bay and landscapes were also replicated as best as possible when orienting the tower in the new location. Lastly, the new tower was built in such a way as to allow additional future relocation should the eroding cliff’s edge make it necessary again.

Key lessons learnt

Even in heritage conservation, where intrusion and alterations are avoided whenever possible, sometimes drastic measures must be taken to combat the threat of coastal erosion. Relocating heritage sites to safer ground is a suitable solution, especially when the eroding coastline is deemed globally significant and has challenging terrain. Dismantling and re-erecting Clavell Tower was not a decision taken lightly, but it has proven to be a successful measure in preserving the tower’s positing as a valued historic landmark on a World Heritage Site.

Relevant case studies and examples

Measure category

EXAMPLE: Reopening Waterways in Oslo (NOR)

nst — Mon, 23 Jan 2017 15:19:39 +0000

EXAMPLE: Reopening Waterways in Oslo (NOR) nst Mon, 01/23/2017 - 16:19

Flash floods

Urban floods

Based on information provided by the city Oslo.

As in many other cities, the former dominating strategy for Oslo’s rivers and streams was to enclose them for practical reasons. This approach has changed and the City is actively reopening waterways to make them accessible for people, facilitate increased habitat for biodiversity and handle storm water more efficiently.

General description

The City of Oslo is characterized by urban waterways and their tributaries. Up until the 1980s, the waterways were considered problematic for the sewage system and an obstacle for efficient exploitation of land. Hence large sections of waterways were put in culverts. These culverts have predefined capacities that can cause problems if urban flooding cannot cope with these predefined capacities.

The City of Oslo has decided to reopen closed rivers and streams wherever it is possible and expedient. In order to formalise and streamline the municipal cooperation regarding reopening projects, the relevant municipal agencies have, in collaboration, developed a management document that outlines the principles for reopening projects including a list of prioritised projects. The list is updated annually.

The “Teglverksdammen” Project

In August 2015 a large reopening project in Teglverksdammen was completed. Ca. 650 meters of the Hovinbekken stream was reopened for EUR 10 million. Teglverksdammen is planned and designed as a natural cleaning system, with several sedimentation basins, stream with water rapids, a small lake and shallow waters with dense vegetation. As a result, Teglverksdammen cleans water, provides habitat for biodiversity and has become a popular recreation area for people.

Relevant case studies and examples

Reopening culverts

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

Hold the line

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: Floating roads, Hedel (NL)

nst — Mon, 16 Jan 2017 10:17:31 +0000

EXAMPLE: Floating roads, Hedel (NL) nst Mon, 01/16/2017 - 11:17

Coastal floods or storm surges

Estuarine floods

Removal or relocation

Based on information from the International Intervision Institute

In 1996 the Dutch Department of Transport, Public Works and Water developed a program called ‘Roads to the Future,’ and a component of this project was the testing of a pilot floating road. The testing of the pilot took place in 2003 and aimed to create a 70 meter stretch of road in the town of Hedel, the Netherlands to mitigate against rising ground water levels. The floating road was designed to maintain access and flexibility in traffic and movement and prevent the isolation of a village otherwise cut off by flooding.

General description

The ‘Floating Roads’ pilot project was implemented in Hedel in the Netherlands. The town of Hedel is prone to flooding due to increasing ground water levels which can lead to the isolation or cutting off of the village and impeded traffic flow. The floating road was designed to be some 70 meters in length and withstand vehicles travelling at speeds of up to 80mph. The town of Hedel in the Netherlands has some 5,000 inhabitant. The small size of the town and the infrastructure of the floating road meant that local authorities and government were central to its planning and implementation.

The design and construction of the road consisted of standard linked units made of aluminium and filled with polystyrene foam to facilitate ‘floating’. These flexible links were secured into the river bed using steel piles and the top layer of the road itself was constructed using typical concrete and non-flexible materials. Aluminium was chosen as a lightweight material that requires little maintenance and is recyclable. Moreover, the standardized units allow for easy transportation and replacement, if necessary. The links between the units provide enough stiffness but also flexibility to withstand changing water levels. The innovative element of the design was the attachment ramps on either end of the floating road. The attachment ramps were stiff structures designed to withstand movement but implemented with a further safety option of a remote controlled moveable bridge should water levels change abrubtly.

The floating road was tested using a normal vehicle under both regular conditions and with incoming waves. The structure performed as expected and the driving experience of the vehicle pilot was not affected by the moving water below. In a simulation test of an emergency situation, a breakdown vehicle went through the same tests and the floating road performed successfully.

Cost-effectiveness and ecosystem-based aspects

Floating and elevated roads are alternatives to bridges and tend to be less expensive. Once constructed, they do not require more maintenance than other types of roads. They are, however, a significant piece of infrastructure and therefore the cost and investment may only be returned once flooding has occurred and been mitigated against.

Floating roads take up less space in terms of construction and infrastructure than traditional roads. They also sit on top of groundwater and therefore do not disturb natural flows and therefore also are likely to minimise pollution.

Key lessons learnt

The main question posed in the pilot construction of the floating road was to understand whether there was added value in having floating roads over conventional roads in order to solve traffic problems that ensue amidst extreme flooding and changing groundwater levels. Floating roads were found to be functional in Hedel and also reduce the amount of disturbed space compared to other options such as a traditional road. For example, generally a road floating on groundwater is 20 meters wide whereas a traditional road at one meter above ground level is 45 meters wide. Cost-efficiency was also considered advantageous to that of building a bridge.

Relevant case studies and examples

Exposed elements elevation

Further Readings

PDF: Floating Road Documentation

Measure category

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

Hold the line

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