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An integrated plan incorporating flood protection: the Sigma Plan (Scheldt Estuary, Belgium)

An integrated plan incorporating flood protection: the Sigma Plan (Scheldt Estuary, Belgium) (2014)

The Sigma Plan is an integrated flood protection plan that was first established in 1977 in reaction to a major storm surge flood in 1976. The Sigma Plan offers protection against storm surges as well as floods caused by excessive rainfall. Its objectives also include nature protection and navigation. The plan protects approximately 20,000 hectares of land in Belgium bordering the Scheldt River and its tributaries such as the Rupel, the Nete and the Durme Rivers. In order to achieve adequate protection, the plan combines ‘grey’ infrastructure measures, mainly strengthened dyke protection, and ‘green’ measures in the form of a network of controlled flood areas. In early 2014, approximately 500 hectares of controlled flood areas were operational and in 2015 the total area should increase to 1200 hectares; ongoing work will continue to expand this area in coming years. 

Case Study Description

Challenges

The original Sigma Plan conceived in 1977 was designed to protect the coastlines of the Scheldt and its tributaries against storm surge floods. However as the execution of the plan progressed, new requirements arose including the need for further adaptation to climate change. When the Sigma Plan was updated in 2005, it was understood that the existing plan was insufficient to provide adequate protection both under current conditions as well as for the likely conditions predicted by climate change models. The 2005 update referred to a projected sea level rise of 9 to 88 cm by 2100, taking into account varying estimates of seawater expansion, melting of the icecaps and glaciers and climate sensitivity; this was based on the IPPC Third Asessment Report, released in 2001.

The updated Sigma Plan used as a baseline for its protection measures a sea level rise of up to 25 cm by 2050 and 60 cm by 2100. The current level of flood protection offered by the works already completed, plus the soon to be completed Kruibeke controlled inundation area should protect up to an event that occurs only once every 350 years without sea level rise. With a sea level rise of 25 cm by 2050, the current level of protection is decreased to an event occurring once in 70 years. By 2100 the level of protection would be reduced even further to once in 25 years.

The current plan is now focused on protection until 2050. Belgium has chosen to apply differentiated flood protection levels along the Scheldt based on the likelihood of deaths and the potential extent of economic damage; the minimum level of protection is a flood event occurring once in 1000 years. A number of possible additional measures are prepared for after 2050 in case they are needed to address higher sea-level rise; these will be undertaken depending on the projections then available.

It should also be noted that the average tidal amplitude of the river has increased significantly during the past century: in Antwerp the average high tide level has increased by 56 cm. These changes are largely due to human interventions affecting the flow of water through the Scheldt. Changes include the diverting of water to feed into canals, the removal of river meanders by straightening the river and increasing the depth of shipping channels. These changes exacerbate impacts from climate change.

Objectives

The main objectives of the actualised Sigma Plan are: to protect the land bordering the Scheldt River and its tributaries such as the Rupel, the Nete and the Durme Rivers from storm surges and river flooding; and to help Belgium meet its EU obligations for nature protection.

Solutions

While the Sigma Plan’s main purpose is flood control, it is based on an integrative perspective on river management which acknowledges various river functions and their importance for society. These include: shipping, nature development, landscape values, cleansing functions, fish nurseries and more. The Sigma Plan was originally conceived in 1977 with flood control as its main purpose; since then perspectives on water management have evolved. An updated Sigma Plan was adopted in 2005. It was based on three main pillars; flood protection, access to Scheldt Ports and a natural functioning of the physical and ecological system.

The original Sigma Plan called for dykes stretching a total length of 512 kilometres to be raised and strengthened, the establishment of 13 controlled flood areas covering a total of 1133 hectares, as well as the construction of a storm surge barrier. Plans for the storm surge barrier were later suspended after analysis showed that the benefits did not outweigh the costs. The realisation that the storm surge barrier was prohibitively expensive, together with an increased demand for a healthier river ecosystem, led to a greater application of a concept called ‘room for the river’. The revision also took into account projected climate change impacts. The revised plan gives a greater role to controlled flood areas (CFAs) and depoldered areas that counter storm surges by temporarily storing excess water.

Controlled flooding areas have low dykes, called overflow dykes, along the river, and higher dykes on the inland side to maintain flood protection: the overflow dykes allow water to flood during storm surges; after high water levels have receded, drainage outlets allow water to exit. The CFAs help attenuate the impacts of flooding events by increasing the river catchment area, thus reducing upstream water levels. The volume of many CFAs is increased as their ground levels are below the average water level due to historic compacting of the soil and loss of natural sedimentation processes. These low ground levels however mean that overflow dykes and artificial water regulation are needed. The predominant use for land within CFAs has been as nature areas that contribute to achieving conservation objectives and improving water quality. Under EU nature legislation – in particular, requirements to compensate for the loss of natural areas taken by the expansion of the Port of Antwerp – the total area set aside as flooding areas was increased for the purpose of nature development: by 2030, a total of 2458 hectares are to be created. Another 656 ha have been indicated as possible future flood zones to be constructed after 2030 if necessary to guarantee flood safety beyond 2050.

Some CFAs also include controlled tidal areas, where a regular, reduced tide is produced through an adjustable weir system in the overflow dyke. During high tide, water from the Scheldt flows into the area through a weir and during low tide it flows out through a low weir. The controlled tidal areas allow for the creation of tidal habitats while maintaining the CFA’s functions.

Other Sigma Plan projects consists of depoldering areas, where dyke protection is moved inland exposing a former polder (land reclaimed from the water) once again to tidal influences. Depoldered areas provide room for river water during high water levels, and thus they, like the CFAs, attenuate storm surge levels. They also provide room for estuarine nature.

The updated Sigma Plan also calls for raising an additional 24 kilometres of dykes and increasing the land set aside solely for flood protection to 1523 hectares (390 ha more than in the original plan). The dykes and weirs on the Scheldt Estuary were raised as follows:

  • to level +11.00 m TAW (Tweede Algemene Waterpassing = Second general water elevation level measurement) from the Dutch border to Oosterweel;
  • to level +8.35 m TAW from Oosterweel to Temse;
  • to level +8.00 m TAW from Temse to Schoonaarde;
  • to level +7.50 m TAW from Schoonaarde to Gentbrugge.
Relevance

Case mainly developed and implemented because of other policy objectives, but with significant consideration of CCA aspects

Additional Details

Stakeholder Participation

The Flanders Region has followed a strategy of open communication in order to implement the Sigma Plan in a way that maximizes public acceptance and support. The communication strategy is coordinated by Waterwegen en Zeekanaal NV (W&Z) (Waterways and Sea Channels), a department of the regional government, with consultation at ministerial level and under the oversight of a steering group (stuurgroep Sigmaplan). The Steering Group includes representatives of the Department of Waterways and Sea Channels, the Agency for Nature and Forests, the Department for Land Use Planning, the Department for Housing Policy and Heritage Buildings, Department of Environment, Nature and Energy, Department for Agriculture and Fisheries, Flemish Land Agency, the Executive Secretariat of the Flemish-Dutch Scheldt Commission and the OS2010 working group.

Communication is carried out using various tools including brochures, newsletters and educative materials for children as well as meetings to disseminate information and discuss key issues with stakeholders. Specific types of stakeholders have been actively involved in the planning, including agricultural organisations, environmental NGOs, hunters, fishers and the tourism and hospitality industry.

The communication strategy focuses on three outcomes from the Sigma Plan. The first and primary pillar is the increase in flood safety; the other two pillars are recreation and nature protection. Each project is extensively communicated to the public and focus groups are organised at both regional and local levels. In Belgium, the Kruibeke project was the only project that saw significant opposition, and support there has now increased as it nears completion. A trans-boundary project involving the depoldering of the Hedwige Polder, located in the Netherlands, has resulted in stakeholder and public opposition.

Success and Limiting Factors

Main success factors include:

  • The coordinated identification of suitable areas for the development of controlled flood zones, providing increased safety with limited damage caused to agriculture, land use and economy. 
  • The integration of climate change and sea level rise predictions.
  • The integration of compensation for areas lost by port expansion and the dredging of the Scheldt in the plan’s overall objectives, strengthening its profile in negotiations with local governments and stakeholders. 
  • The availability of areas for the compensation of natural habitats lost due to infrastructure works in the Scheldt Estuary.
  • The ability to expropriate the land necessary for the controlled flood areas. Landholders are compensated for the existing price of the land plus 20%. Where feasible, expropriation can be delayed to the time when a farmer retires or is near to retirement. 
  • The ongoing engagement of plan managers with stakeholders during the phases of each project and in the overall decision-making process – this has addressed initial opposition (see limiting factors). 
  • Application of cost-benefit analysis (CBA) and environmental impact assessment (EIA) to strengthen plan and project design.

Limiting factors include:

  • Stakeholder opposition has been an issue for the construction of the Kruibeke CFA and also in the Netherlands for the Hedwige Polder project.
  • Budget restrictions are slowing implementation of the plan, which could push its completion beyond the intended date of 2030.
Costs and Benefits

In 2005, the total costs for realising the updated Sigma Plan were estimated at 882 million Euros: 830 million for construction works and 52 million Euros for accompanying measures. In 2010, an update of the estimates resulted in a cost estimate of 994 million Euros for the works and 62 million Euros for the accompanying measures, due to mainly to overall price increases. The cost for remaining work on the Sigma Plan from 2010 to 2030 was estimated at 928 million Euros (reflecting work undertaken since 2005).

The update of the Sigma Plan included a detailed cost benefit (CBA) analysis to assist in determining the optimal plan. In total, 180 potential areas were considered for use as controlled flood areas, with a total surface area of 15000 ha. The CBA took into account the average annual flood risk during the 100 year project life, allowing for a sea level rise of 60 cm and taking into account climate change. The economic risk with only the works of the original (1997) Sigma Plan without the storm surge barrier completed was estimated to be 942 million Euros. From the cost benefit analysis, it was found that the optimal scenario included the raising of dykes and the use of CFAs. The safety benefits of the optimal scenario were estimated to be 736 million Euros.

A cost benefit analysis of the ecosystem benefits was also undertaken. This analysis used various available market prices for goods such as for timber production, reed production, carbon dioxide capture, fish production (shrimp), and the prevention of riverbed erosion leading to a reduction in dredging activities and studies to price goods and services with no available market values. Goods and services with no available price information were studied using contingent valuation methods and hedonistic pricing, for example by seeing how housing prices near the project areas could change. The hedonistic price change was estimated using data from other studies while for the contingent valuation study a total of 1704 questionnaires were collected. The conclusion of the extensive CBA to determine ecosystem benefits found that the benefits range between 143 and 984 million Euros, with the highest level of benefits realised by the maximisation of the use of controlled tidal areas. The non-use value that people attributed by people was the largest benefit measured but also the most contentious. From the cost benefit analysis it was concluded that the benefits outweigh the costs.

From an environmental perspective, several benefits and losses can be identified. Benefits include:

  • Restoration of estuarine processes with accompanying water quality gains;
  • The development of more robust nature areas of high quality that are protected at European level;
  • Desirable changes to the sedimentation regime, with increased sedimentation in the inundation zones leading to a lower turbidity in the river;
  • A reduction in tidal energy.

Losses include:

  • The loss of former cultural landscapes (mainly agricultural landscapes);
  • Impacts on agriculture and other land use functions in flood zones (monetary compensation and in some cases compensation in the form of alternative agricultural land was provided to farmers)
  • Impacts on valuable groundwater upwelling nature zones and valley ecotypes;
  • Sedimentation impacts on the soil quality in the flood zones.
Legal Aspects

Key EU legislation relevant to the plan has included: the Birds and Habitats Directives, the EIA and SEA Directives, and the Water Framework Directive and Floods Directive.

The nature protection aspect was added to the Sigma Plan in large part due to obligations under the EU Birds and Habitats Directives. The expansion of Port of Antwerp, in particular the construction of the Deurganck Dock, led to the need for compensation of lost natural areas. In 2001, construction of the dock area was halted by court order due to its impacts on special protection areas (SPAs) under the Birds Directive; a related issue was the poor quality of the environmental impact study. To continue the project, the Flemish Government approved an emergency decree that unblocked construction of the Deurganck Dock and called for nature compensation within the Kruibeke controlled flood area. This event, together with the ongoing need to comply with EU environmental obligations, contributed to the Flemish government’s decision to make nature protection the second pillar of the updated Sigma Plan that was adopted in 2005.

Individual Sigma Plan projects follow a stepwise plan that follows the legal procedures to obtain the relevant permits. The first step is to design a development plan outlining the zone uses, the exact contours of the controlled flood area, the nature types to be developed and how agricultural land will remain accessible. Next an environmental impact study needs to be undertaken detailing the impacts on surrounding people, effects on the soil and waterways and other impacts. Following the EIA process, and any changes it requires, then the regional land use plan (gewestelijk ruimtelijk uitvoeringsplan) needs to be adapted. Finally, planning permits (stedenbouwkundige vergunningen) are needed. Once all permits have been received the construction can be initiated.

Implementation Time

The Sigma Plan was initiated in 1977 and was updated in 2005. The works under the updated plan will be completed in 2030. Additional works are planned for the period after 2030 depending on the extent of sea-level rise and/or climate change.

Life Time

The project should provide protection at least until 2100.

Reference Information

Contact

Wim Dauwe
Head of unit
Waterwegen en Zeekanaal NV – Department Sea Scheldt
Anna Bijnsgebouw - Lange Kievitstraat 111-113 bus 44 - 2018 Antwerpen
Tel.: +32 (0) 3 2246711
E-mail: wim.dauwe@wenz.be

Stefaan Nollet
Project Engineer
Waterwegen en Zeekanaal NV – Department Sea Scheldt
Anna Bijnsgebouw - Lange Kievitstraat 111-113 bus 44 - 2018 Antwerpen
Tel: +32 (0) 3 2246732
E-mail: Stefaan.nollet@wenz.bel

Source
EC DG ENV Study "Sharing of Best Practices on Integrated Coastal Management (ICM) in a Context of Adaptation to Climate Change in Coastal Areas"

Keywords

Controlled flood area, Habitats Directive, Scheldt estuary, Sigma Plan, depoldering, dyke, embankment, nature restoration, wetlands

Sectors

Biodiversity, Coastal areas, Disaster Risk Reduction, Water management

Climate impacts

Flooding, Sea Level Rise, Storms

Governance level

Sub National Regions

Geographic characterization

Europe

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