Wadden Works at the Afsluitdijk: a safe sea defence through new nature

The Afsluitdijk has to be reinforced on account of climate change.

According to the client, the Directorate-General for Public Works and Water Management, this reinforcement must be finished by 2015. As an alternative to “normal” reinforcement, the consortium of which IMARES is part has proposed the creation of a wide soft dike instead of the traditional approach of dike-raising.


  • If the Afsluitdijk were to be wide and soft, this would have a number of advantages:
  • It can soon be in use
  • It can be created within the available budgets
  • It increases safety, forming a “climate buffer” for the mainland
  • It offers at least the same level of safety as traditional dike-raising
  • It will establish 1,500 hectares of new natural area
  • It will boost recreation

Soft wide Afsluitdijk

A soft wide Afsluitdijk can be created by establishing tidal marshes on the Wadden side of the dike. Tidal marshes are flats covered by vegetation, of which the top parts are only submerged under storm conditions. Thanks to the plant growth and the introduction of sediment, the tidal marshes will grow on their own. “Experience tells us that this method works: tidal marshes have been active on the Groningen and Friesland coasts for hundreds of years and measurement data is available on them,” explained Kees Dijkema (senior researcher at Wageningen UR). “The plan uses proven technology with a modern touch and is therefore a serious alternative to normal reinforcement. In addition, the proposed solution can be achieved within the available budgets.”

Access bridges

The establishment of thirty kilometres of tidal marshes on the Wadden side of the Afsluitdijk will create a new 1,500-hectare natural area. The establishment of the tidal marshes will be optimised through the use of a test marsh, to determine the level to which sand will have to be introduced and at which point nature can take over. A protected cycle path will offer a view over the flats. Motorists, however, will not be able to see much of the tidal marshes since they will be travelling on the IJsselmeer side of the Afsluitdijk. The consortium recommends building access bridges over time. This will offer flexibility in terms of the intersection of the road and water traffic. These access bridges will offer a view over the new nature reserve.

Future exploration

The establishment of tidal marshes on the Wadden side of the Afsluitdijk is the recommendation from the consortium Consultancy and Engineering Agency DHV, IMARES and design firm Alle Hosper that was submitted to the Directorate-General for Public Works and Water Management. In cooperation with the provinces of Friesland, North Holland and the municipal councils of Wieringen and Wûnseradiel, the Directorate-General for Public Works and Water Management is working on the future exploration of the Afsluitdijk, which was commissioned by the Ministry of Transport, Public Works and Water Management.

Wadden Works

In December 2008, plans were presented to the State Secretary of Transport, Public Works and Water Management by four consortia, including the consortium with Wageningen IMARES. In June 2009, an advisory committee led by Ed Nijpels recommended that the Wadden Works plan should be considered as a serious alternative during further decision making.

Advies - en ingenieursbureau DHV