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A transboundary depoldered area for flood protection and nature: Hedwige and Prosper Polders

A transboundary depoldered area for flood protection and nature: Hedwige and Prosper Polders

The Hedwige-Prosper Polder project is part of the Belgian Sigma Plan: this integrated plan is reinforcing dikes and quay walls and opening flood areas to protect land along the Scheldt Estuary and the upstream basin against floods. In this project, the outer defences of the Hertogin-Hedwige (hereinafter referred to as Hedwige) and the Prosper Polders – low lying areas of reclaimed land – will be removed, reopening these areas to the tides. This process (which can be called ‘depoldering’) involves moving dike protection inland. Doing so will provide room for water during tidal surges, thereby reducing the risk of floods, and re-establishing an estuarine natural area. While nearly all Sigma Plan projects take place on Belgian territory, this is an exception as the Hedwige polder lies on Dutch territory.


Case Study Description


The occurrence of storm surges in the North Sea has increased significantly since the 1950s, and sea-level rise is projected to further raise this threat in coming decades. Storm surges threaten Antwerp (Belgium) in particular as the Scheldt estuary narrows considerably at this point, thereby boosting high water levels. The Hedwige and Prosper Polders are crucially located just before the Scheldt reaches Antwerp. Opening these two polders will provide ‘storage’ for storm surge waters, reducing the water level at Antwerp and upstream and thereby improving safety in this urban and industrial area.


The main objective is to create new estuarine intertidal natural area. The project will also improve flood protection as part of the overall Sigma Plan.


The Hedwige-Prosper Polder project is one of a series of projects being undertaken along the Scheldt and its tributaries as part of the Sigma Plan. It creates a new estuarine nature area and contributes to flood protection. The new nature areas and increased flood protection will be achieved by moving dike protection inland, thereby exposing the currently protected polders to the tidal influence of the Scheldt River. The new dikes constructed inland will provide flood protection for the low-lying hinterland.  This type of project can be called ‘depoldering’ (it is also part of ‘managed realignment’, a term used in the UK). The new dikes will have a height at 10.2 meters above sea level (measured by Normaal Amsterdams Peil, Standard Amsterdam Level, NAP) across most of their length.

In total, a natural area of 465 hectares will be developed in the two former polders, of which 295 hectares will be on Dutch territory and 170 hectares in Belgian territory. These 465 hectares will combine with the adjacent Saeftinghe wetlands area to create a brackish intertidal area of approximately 4100 hectares in total. The Hedwige-Prosper polders will not be directly connected with Saeftinghe, however, as a dike containing pipelines separates the two areas and will remain in place. The creation of new estuarine nature areas is part of the Scheldt Agreements between the Netherlands and Flanders: the work at Hedwige polder will contribute to fulfilling the Dutch commitment to create 600 hectares of such areas. (The resulting intertidal nature areas will be part of the work that the Netherlands and Belgium will undertake to meet obligations under the EU Habitats Directive, also as compensation for natural areas taken over the Port of Antwerp as well as dredging of the Scheldt).

To promote the creation of the desired natural area, a system of creeks will be dug in the polders. Accompanying works include filling in the existing drainage system and removing other drainage related infrastructure, removing hard infrastructure such as roads, and removing existing vegetation and where necessary some existing marshland.  Following these modifications, natural processes will be allowed to shape the area into increasingly natural conditions. These marshlands will contribute to the self-cleaning capacity of the estuary; moreover, the wetlands are an important source of silica for diatom algae which are at the basis of the food web. The creation of the new intertidal nature area is expected to result in new recreational opportunities. The proposed design includes the construction of a nature pavilion and eco-lodges, as well as a number of walking and biking paths, viewpoints, information signs, benches and parking places for visitors.

As of late 2014, the outer dikes had been removed at the Belgian Prosper polder, opening this area to the tide. The new inland dike was completed in 2015. The building permit for the new inland dike on the Dutch part – Hedwige Polder - is granted. Construction is expected to start at the end of 2017 and will take approximately three years.


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

Additional Details

Stakeholder Participation

The project encountered opposition: in particular, the work planned for the Hedwige Polder was a contentious issue in the Netherlands and especially in the province of Zeeland where it is located. The Belgian owner of agricultural land in the Hedwige Polder mounted an extensive legal opposition to the project (His legal opposition to the depoldering of the Prosper Polder in Belgium, where he also owned lands, had ended in 2011). Some farmers and residents in the Netherlands joined the protests (opposition was comparatively mild in Belgium). Their concerns included the loss of agricultural land plus resistance to depoldering in general and a fear that more depoldering projects might be undertaken in Zeeland. This opposition led the project to be postponed by the Dutch national government, which requested studies of alternatives, including different sites and alternative work in the project area. The analysis did not identify an acceptable alternative and the Dutch government in 2012 decided to go ahead with the works at Hedwige polder.

Planning documents were then drawn up and made available to the public in September 2013 for a six-week comment period. Approximately 2000 individuals and organizations submitted comments regarding the plan. There was also a meeting at the local town hall on 10 September 2013. Prior to this meeting, a group symbolically burnt the government plans for the Hedwige Polder in front of the town hall. Despite this local opposition, the Dutch government committed to completing the project by 2019. The Dutch Council of State on 12 November 2014 ruled all legal opposition to the project unfounded.

Success and Limiting Factors

For the Sigma plan overall, economic analysis showed that a combination of projects, including the Hedwige-Prosper Polder project, would be more cost-effective in protecting urban areas and economic activities than building a large storm surge barrier. For the project itself, the estuarine natural areas envisioned will need to be maintained over time. Concerns have been expressed that the sedimentation rates in the project areas could be too high, resulting in areas not compatible with the natural or flood protection objectives of the project. Opposition in the Netherlands was a delaying factor.

Costs and Benefits

A cost-benefit analysis for the Dutch government studied several project alternatives and indicated that the selected project option for depoldering the Hedwige polder in the Netherlands would cost between 40.0 to 49.3 million Euros (The costs for depoldering the Prosper polder in Belgium was estimated at 25.8 million Euros).

Benefits from the project taken into account in the cost-benefit analysis include: improvement in water quality, increase in natural area, changes in recreational opportunities, improvement in air quality due to a reduction in fine dust originating from ploughed fields (reduction of 30 tonnes per year PM10), reduction in pesticide use and a reduction in water level during storm surges. The flood protection benefit will be experienced mainly on Belgian territory, though other benefits will be experienced on both Belgian and Dutch sides of the border.

Losses that were identified include the reduction of part of the cultural (farming) landscape and removal of current recreational opportunities, living space and agricultural land.

The project costs for both the Hedwige and Prosper Polders will be covered mainly by the Belgian Sigma Plan, due to the importance of the project for Belgian integrated water management objectives, including maintaining shipping accessibility within the Scheldt and flood protection. Thus, a large portion of the costs for Hedwige Polder in the Netherlands will be paid for by the Flemish government. The Flemish government will cover the preparation and development costs related to the development of the estuarine natural area, including the costs of moving dike protection land inwards.  Flanders will also reimburse the Netherlands for the costs of expropriating the land. The Netherlands is responsible for other costs, such as support for agriculture following the project, the improvement of an internal dam and costs related to the analysis of alternatives to the project.

The depoldering of the Hedwige polder was agreed in 2005 in the treaty between the region of Flanders and the Dutch national government regarding the development of the Scheldt Estuary Development Plan 2010. In this agreement, the Netherlands agreed to develop at least 600 hectares of estuarine natural areas on Dutch territory. Flanders agreed to develop 1100 hectares of wetlands on Belgian territory. The Netherlands also committed to starting the depoldering of the Hedwige Polder at the latest by 2007 and to create at least 440 hectares of intertidal natural areas in this location. Following this agreement, however, opposition in the Netherlands led to delays. The European Commission started a legal procedure against the Netherlands with regard to its nature obligations. Following a review of alternatives, in 2012 the Dutch Government decided that Hedwige Polder would be depoldered as planned.

The project itself will contribute to the international obligations of the Netherlands and Belgium to conserve estuarine habitats (H1130, H1330) under the Habitats Directive. The site will become a Natura 2000 site that borders the already existing Natura 2000 site Westerschelde & Saeftinghe.

Implementation Time

The building permit for the new inland dike on the Dutch part – Hedwige Polder - is granted. Construction is expected to start at the end of 2017 and will take approximately three years; work on the Hedwige Polder should be completed by 2019. As of mid-2014, the Belgian Prosper Polder had been turned into a new flood area through depoldering (removal of its outer dykes) and the new inland dike was completed in 2015.

Life Time

The lifetime of the project has not been indicated; with regular upkeep and maintenance, it is expected to remain in place for many decades. As noted above, sedimentation could affect its nature and flood protection functions.

Reference Information


Dorien Verstraete
Waterwegen en Zeekanaal NV – Department Sea Scheldt
Anna Bijnsgebouw - Lange Kievitstraat 111-113 bus 44 - 2018 Antwerpen
Tel. +32 (0)3 224 93 68

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

Published in Climate ADAPT Jun 07 2016   -   Last Modified in Climate ADAPT Dec 22 2020

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