Mitigation

Coastal floods or storm surges

Estuarine 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

Coastal floods or storm surges

Estuarine floods

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

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)

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.

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: Constructed wetlands to compensate for urbanization in souther Finland (FIN)

nst — Thu, 16 Feb 2017 09:00:50 +0000

EXAMPLE: Constructed wetlands to compensate for urbanization in souther Finland (FIN) nst Thu, 02/16/2017 - 10:00

Flash floods

Urban floods

Surface Water Management

In Finland urban wetlands are being implemented to help improve water quality, absorb storm water volume and flow control, and improve the land-water habitats for urban communities. The wetlands are designed to respond to the needs and negative impacts of urbanization and therefore, public acceptance and multifunctional benefits are central to the design and implementation of the wetlands. The acceptance and understanding of the importance of urban dwellers is important and thus the project sought to demonstrate several benefits of functional wetlands.

Based on Wahlroos et al. (2015): Urban wetland parks in Finland: improving water quality and creating endangered habitats. In: Urban wetland parks in Finland: improving water quality and creating endangered habitats. In: International Journal of Biodiversity Science, Ecosystem Services & Management Volume 11, Issue 1: Pages 46-60

General description

Urbanization is affecting water quality and there is increasing severity of flooding and drought periods in Southern Finland. This is expected to become worse because of climate change. During flooding events, run off from rain and melting snow are quickly carried over urban surfaces and overwhelm receiving streams. Habitat degradation is occurring as harmful water from urban areas is transferred into connected habitats. These urban streams in turn cause flooding and channel erosion. The creation of wetlands is an alternative ecosystem approach to conventional responses that have been to seal natural waterways into culverts or clearing, and stabilization for augmented conveyance and erosion control.

Two urban wetlands, the Nummela Gateway and the Nummela Niittu were designed and implemented. The wetlands are 6ha and 7ha respectively and are within 550 ha of the urbanized Kilsoi stream watershed in the catchment of Lake Enäjärvi, in the Nummela community, Municipality of Vihti, Southern Finland. The lake has poor water quality from algal blooms and fish kills that result from runoff from its catchments and phosphorus load from human activities. The Stream Kilsoi is an inland clay-soil stream that drains into the Baltic Sea. The habitat type and clay-stream is red listed in the Red list Assessment of Finnish habitat types as critically endangered.

Ecosystem-based aspects

The creation of wetlands is an ecosystem approach and replaced hard infrastructure and conventional responses that have previously been implemented in the area to control storm water volume. In the past, the convention has been to seal natural waterways into culverts or clearing, and stabilization for augmented conveyance and erosion control.

The two wetlands, Nummela Gateway and the Nummela Niittu, were established over five years and closely monitored. The ecosystem service that was deemed most important for the wetlands to provide was water quality management. Water treatment by wetlands depends on the plants and their associated microbes. Storm water and flooding events are the main carriers of potential pollutants from urban areas, and thus a high density and diversity of plans and microbes is necessary. In this case, the native origin of the plants was also found to be important to protect urban streams from the erosive effects of storms and snowmelts. Plant self-establishment occurred quickly and construction only required the monitoring of water levels, especially during winter. The existing shoreline and old drainage ditches acted as a seedbank and no maintenance of native plants was necessary.

In addition to improving biodiversity, water quality improvements were also achieved. There was an increase in phosphorus reduction after the third year. Despite that the Gateway wetland is just 0.1% of its 550 ha watershed area, it does achieve an annual 10% for total phosphorus reduction.

Key lessons learnt

The establishment of two wetlands near to an urbanized area was able to mitigate against various challenges stemming from urbanization. The Gateway and Niittu wetlands were successful in creating high biodiversity at the clay-stream habitats and relied on little human maintenance due to the naturally occurring habitat which was conducive to wetland creation and existence.

Some compromises were made in order to ensure the acceptance of the wetlands and their appreciation and support by the community. Both wetlands were designed to accommodate open water areas for recreational purposes and thus do not fulfill the most efficient capacity for pollution removal.

Despite the establishment of the wetlands, they do not address source control directly which remains an issue. If action is taken to reduce pollution at the source, then the wetlands will be more productive in response.

Continued monitoring during and after the establishment of the wetlands allowed for there to be definitive conclusions on the impact of the created wetlands on water pollution mitigation, self establishment of vegetation, and biodiversity development. Water quality improvements were demonstrated with continuous monitoring which would not have been deciphered via discrete water sampling.

Relevant case studies and examples

Wetland restoration

Literature sources

Main source: Outi Wahlroos, Pasi Valkama, Emmi Mäkinen, Anne Ojala, Harri Vasander, Veli-Matti Väänänen, Anna Halonen, Leena Lindén, Petri Nummi, Hannele Ahponen, Kirsti Lahti, Teuvo Vessman, Kari Rantakokko & Eero Nikinmaa (2015): Urban wetland parks in Finland: improving water quality and creating endangered habitats. In: International Journal of Biodiversity Science, Ecosystem Services & Management Volume 11, Issue 1: Pages 46-60

Measure category

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

Reafforestation in upland areas and buffer zones

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

Further Readings

WWF project description

LIFE+ project description

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: 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: Wallasea Island Wild Coast project (UK)

nst — Mon, 16 Jan 2017 12:39:10 +0000

EXAMPLE: Wallasea Island Wild Coast project (UK) nst Mon, 01/16/2017 - 13:39

Erosion

Water flow regulation

Limited intervention

Based on information from the Royal Society for the Protection of Birds (RSPB)

The aim of the Wallasea Island Wild Coast project is to recreate a natural intertidal coastal marshland to combat the threat of climate-induced coastal flooding. The recreated mudflats, salt and brackish marshes, saline lagoons, and pastures will provide a range of habitats for coastal birds and other wildlife on the Essex coast.

General description

The project uses a technique known as “managed realignment” to recreate an intertidal habitat through the breaching of existing seawalls at strategic locations. These breaches, or holes, allow sea water in, and various kinds of ecosystems can be created depending on the height of the land being flooded. The land of the Wallasea Island will be heightened and extended using the clay, chalk, and gravel excavated from new underground rail line connections in central London. In total, nearly 1500 acres of tidal wildlife habitat will be transformed or created new, including approximately 133ha of mudflat, 276ha of salt marsh, 53ha of saline lagoons, 11ha of brackish marsh, 160ha of grassland, and 15ha of rotational arable fields.

Historically, Wallasea ‘Island’ comprised as many as five individual salt marsh islands. When seawall defences were added to the area to prevent coastal erosion, the landscape eventually evolved into the shape that can be seen today.

Since 2008, the Wallasea Island Wild Coast project has been in partnership with an underground rail line development project called Crossrail. The clay, chalk, and gravel excavated from their tunnelling in central London will be reused to heighten and transform the coastlines of the Wallasea area. The addition of these materials to raise land and extend coastlines is expected to allow approximately 2.1Mm³ of tidal water to enter the area once the sea walls are breached. This would require around 7.5Mm³ of imported fill material. The construction schedule to achieve the objectives of the managed realignment plan is determined by the delivery schedule of the materials from the Crossrail project, and is planned between 2016 and 2019.

The site is located near one of the world’s most important estuaries and one of Europe’s largest economic regeneration zones: the Thames Gateway. The Crouch and Roach Estuaries bordering Wallasea Island have been recognized, under the European Union Directive on the Conservation of Wild Birds, as a Special Protection Area, a Special Area of Conservation, and a Wetland of International Importance through the Ramsar Convention.

In July 2009, the final design of the project received planning approval. Local authorities, yacht clubs, and various organizations were publically consulted and included in developing and designing the project plan.

Innovative Aspects

The Wallasea Island Wild Coast project is a bold initiative to address the alarming amount of coastal change that has happened in this region of Europe. Over the past 400 years, the Essex coast has lost over 91% of its intertidal salt marshes due to accelerating coastal erosion and competition with agriculture for land. The project has set a high standard for 21^st century conservation and engineering efforts, and is at a scale never before attempted in the UK. It jointly considers ecological and economic factors, for the benefit of future visitors, wildlife, and local community members for decades to come.

Perhaps the most innovative aspect of the project is the landmark partnership and collaboration between the project operators, the Royal Society for the Protection of Birds (RSPB), and the underground rail development project Crossrail. By deciding to reuse the excavated materials from London’s new underground connections to achieve the managed realignment objectives of Wallasea Island, the two projects set a global standard for how waste material from large-scale infrastructure projects does not have to be disposed of in a landfill. Instead, excavated soils, clays, and rocks can provide flood protection to coastal communities and refortify coastal ecosystems. Equally, the project cooperation showed that it is possible to transport large amounts of excavation spoil from London to the Essex coast in a safe and reliable way.

Key lessons learnt

The Wallasea Island Wild Coast project showed that despite the challenges, major land realignment can be undertaken in a sustainable way. The use of excavated materials from the London Crossrail project also illustrated a mutually beneficial solution for both stakeholder groups and is an example of cooperation that leads to smart solutions for the benefit of the environment.

Relevant case studies and examples

Marsh vegetation in intertidal and coastal zone

Further Readings

PDF: Documentation about the project

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