Riverine or slow rise floods

Erosion

Based on kindly provided information by the Scottish Natural Heritage

Hold the line

Grey infrastructure

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

Breakwaters

nst — Wed, 22 Mar 2017 08:49:13 +0000

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

Erosion

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

EXAMPLE: Reconnecting lakes to the Yangtze River (CHN)

nst — Thu, 16 Feb 2017 11:16:41 +0000

EXAMPLE: Reconnecting lakes to the Yangtze River (CHN) nst Thu, 02/16/2017 - 12:16

Natural flood, runoff, catchment management

Ecosystem based approach

The 6,300 km long Yangtze River in China was facing a reduction of wetlands areas and flood retention capacity. In 2002, the World Wide Fund for Nature (WWF) initiated a programme to reconnect lakes in Hubei
Province to the Yangtze River through opening the sluice gates and facilitating sustainable lake
management. These wetlands can store floodwaters and therefore reducing vulnerability to flooding in the central Yangtze region.

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)

General description

The Yangtze River is 6,300 km long and home to more than 400 million people. The river basin drains a 1,800,000 km basin and has extensive lakes and floodplains of significant environmental and retention importance. In the summer, the basin experiences floods, especially in the central Yangtze. Extensive development in the last fifty years has converted 1,066 lakes 757 coverings along 2,150 km2 into polders, reducing wetland areas by 80% and flood retention capacity by 75%.

Since 1991 there have been several highly damaging flood events that have killed thousands of people and cost billions of dollars. The Lakes and basin have also become extremely polluted, in particular because of the application of fertilizer to aquaculture pens. The loss of connection to the Yangtze River prevents diluting flows and the migration of fish. Drought in recent years has increased water pollution, and climate change and increased temperatures are expected to worsen eutrophication

In 2002, the World Wide Fund for Nature (WWF) initiated a programme of sustainable lake management to reconnect the lakes in the Hubai Province to the Yangtze River through opening the sluice gates. The programme focused on three lakes: Zhangdu (40 km2), Hong (348 km2 and Tian’e Zhou (20 km2). Given the poverty of the populations in the region, finding alternative and sustainable livelihoods and sources of income was important. The average income of residents in the area was just USD 1.34 per day. WWF formed partnerships with government agencies and others to explore options for more sustainable river basin management.

Ecosystem-based aspects

Since 2004-2005 in Hubei Province, the sluice gates at lakes Zhengdu, Hong and Tien’e Zhou have been seasonally re-opened and illegal and uneconomic aquaculture facilities and other infrastructure removed or modified. Now these 448 km2 wetlands can store up to 285 Mm3 of floodwaters, reducing vulnerability to flooding in the central Yangtze region.

The forced ending or removal of illegal or unsustainable aquaculture have reduced pollution levels. In Lake Hong, pollution fell from national pollution level IV (fit for agricultural use only) to II (drinkable) on China’s five-point scale.

Of immediate benefit for the Yangtze River Basin was the increase in wild fisheries species diversity and populations. Within six months of reconnection of Zhangdu Lake, the catch increased by 17 per cent and nine fish species returned to the lake. Similarly the catch increased by 15 per cent in Baidang Lake. Development of certified eco-fish farming by 412 households increased income of fishers by 20 to 30 per cent on average. Similarly, the income from fisheries at the Yangcai Hu area of Hong Lake increased by 25 per cent after restoration. Bamboo farming has also been implemented as a measure to stabilize steeper lands near the lakes. Twelve migratory fish species have now returned to the lakes. At Zhangdu Lake, 60 km2 of lake and marshland were designated as a nature reserve by the Wuhan Municipal Government. To strengthen the effectiveness of wetland conservation efforts in the Yangtze River basin, a Nature Reserve Network was established to link 17 nature reserves (12 later designated) covering 4,500 km2. As a result of these benefits, in 2006 the Hubei Provincial Government adopted a wetlands conservation master plan and allocated resources to protect 4,500 km2 by 2010.

The success of these adaptations was replicated in other areas of the Yangtze and China.

Key lessons learnt

Combined using a green and grey approach. The implementation of sluice gates allowed for seasonal opening and reconnection of regional lakes to the Yangtze River. Reconnecting the water flows required the removal of some aquaculture businesses, but brought up overall levels of fisheries in the river basin with significantly more migratory species returning to the area, which in turn boosted incomes of local fishers. The environmental effects also significantly improved water quality which was extremely polluted prior to the facilitation of water flow via connecting the lakes to the tributaries.

Relevant case studies and examples

Flood storage systems

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

Prevention

EXAMPLE: Restoring Riparian Forests (BG)

nst — Fri, 27 Jan 2017 10:08:18 +0000

EXAMPLE: Restoring Riparian Forests (BG) nst Fri, 01/27/2017 - 11:08

Natural flood, runoff, catchment management

Ecosystem based approach

Floodplain or riparian forests can be extremely important for the prevention of floods and landslides. Floodplain forests used to be widespread in Bulgaria, but today they are only partially preserved. WWF, in partnership with local Bulgarian partners began a project for restoration and conservation of natural riparian forests of native species along the rivers Danube and Maritsa.

Based on the project description of the WWF and LIFE+

General description

Riparian forests are rich in biodiversity, naturally purifying water, and can prevent floods and landslides. During heavy rain falls, riparian forests collect the water and then slowly return some in the riverbeds, therefore slowing down the water flow. Riparian forests create unique conditions that control and influence the transfer of energy, nutrients and sediments between the aquatic and terrestrial ecosystems.

These riparian forests have experienced frequent disturbance by human impact, resulting in a continuous decrease of the habitat area. In recent decades, they have suffered from a wide range of detrimental actions including: clear fellings; transformation into arable lands or hybrid plantations for intensive production of timber; cleaning/correction of riverbeds; and infrastructure projects or activities (such as the construction of small hydropower plants and the extraction of inert materials). Such long-term adverse human impacts lead to degradation of the priority habitat and negative changes in its structure, composition, stability and functionality.

The WWF together with local Bulgarian partners (National Forestry and regional forestry directorates "Ruse" and "Plovdiv") have applied for a LIFE+ project to restore 48.1 hectares of natural riparian forests. They will plant local tree species and remove exotic species. A guide will be developed for the recovery and management of riparian forests as well as an analysis of the relationship between the targeted areas and the other Natura 2000 sites. Additionally, volunteers will actively be engage in the project and in particular highschool students, who will help with the planting of trees.

The project is co-funded by the LIFE + instrument of the European Commission and will be implemented from September 2014 to 2019 with a total budget of around 500.000€.

Key lessons learnt

Restoring riparian forests can not only mitigate flooding problems to a certain extent, it also provides additional ecosystem services. While this concept could be difficult to implement in coastal urban areas due to the lack of space, it can be a valuable approach in rural areas. But also in rural the aspect of sufficient space is probably the most crucial factor in implementing the measure. If this initial obstacle is solved, the reforestation is a promising ecosystem-based approach.

Relevant case studies and examples

Reafforestation in upland areas and buffer zones

Further Readings

WWF project description

LIFE+ project description

Measure category

EXAMPLE: Early warning system in Sogn og Fjordane (NOR)

nst — Wed, 25 Jan 2017 15:39:06 +0000

EXAMPLE: Early warning system in Sogn og Fjordane (NOR) nst Wed, 01/25/2017 - 16:39

Flash floods

Flood Forecasting and Warning

Urban floods

Non-structural measure

The county of Sogn og Fjordane frequently experiences avalanches and landslides, storm surges and flooding. A demonstration project explored the potential for an effective, reliable and cost-efficient early warning system that has a multi-hazard approach and makes use of location and population-based communication technologies, such as mobile phones, as well as social media such as Facebook and Twitter. The system was tested with a sample warning followed by a survey and data analysis to judge its efficacy.

Based on information from the Climate-ADAPT website.

General description

Sogn og Fjordane is a coastal, mountainous region of Norway that boasts hundreds of thousands of tourist visits annually. Several communities in Sogn og Fjordane are facing numerous hazards such as flooding, avalanches, rock slides and other extreme weather events, that might be exacerbated by climate change. To respond to the challenge an early warning system was developed and tested within a EU research project. The multi-hazard warning system aimed at optimising rescue and other emergency services provided by the county. Due to tourism, it aims to be a cost-effective method reaching all people in the geographic area and not only residents.

A public warning exercise was carried out in 2010 with 2,500 mobile phones receiving the alert as text message and 322 fixed line phones in Aurland received the alert as voice message. The warning exercise was visible on Facebook for 2 hours and received 201,849 viewings. A post-exercise survey was carried out online and a door-to-door survey was conducted in parts of the area to assess the public’s thoughts on the exercise. The population warning exercise was evaluated to measure the efficiency of the warning system by combining an electronic evaluation form and a door-to-door survey.

Key lessons learnt

The project demonstrated how an existing county-encompassing organization could be used to issue the population warning. While the technical aspects of people-centred warning systems are at large readily available, issues concerning confidentiality legislation and system regulations must be solved before successfully implementing efficient location-based warning systems. In order to use social media during crisis situations, the projected concluded that research is needed.

Relevant case studies and examples

Early warning systems

Measure category

Preparedness

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

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

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

Erosion

Hold the line