ComCoast - Combined Functions in Coastal Defence Zones | Umweltbundesamt

The scenarios developed for Nessmersiel comprise specifications with regard to the societal, economic and natural environment. They take into account the possible demographic and economic developments as well as changes in land use over the next 50 years. Climate scenarios mainly include assumptions about climate change, sea-level rise and storm surge intensity.

• Sea-level rise (continuation of secular trend: 25 to 30cms),
• precipitation (annual total increase of 10%),
• wind (wind speed increase of 5%)

The climate change will place increasingly higher demands on the defences along the North Sea coastlines. For example, where the sea-level rise coincides with a simultaneous subsidence of the land, this can result in an increased salinisation of the coastal region concerned. The traditional methods of coastal defence, usually single lines of defence, could reach their limits under these changing conditions.

The sensitivity of the floodplain ecosystems to the rising sea level is assessed. Sensitivity to erosion processes is comparatively high. The adaptive capacity of the floodplain ecosystems to compensate the sea-level rise by means of a land uplift (self-induced growth) is assessed. The adaptive capacity is comparatively high.

In the German pilot area Nessmersiel, there is no need for adaptation measures to the existing main dike, neither in the short term nor in the long term (in the sense of the time horizon for planning the coastal defences), since it meets the required safety standard proscribed by the Lower Saxony Dikes Act (Niedersächsisches Deichgesetz). Apart from this fact, however, it still makes sense to develop new coastal defence strategies.

Since the traditional methods of coastal defence could reach their limits under the changing climate conditions, new and innovative methods need to be tested and investigated. For example, the ComCoast concept envisages a more gradual transition from sea to land, with the aid of so-called "transition zones" The key premise for the use of such methods is that they guarantee the necessary safety of the population in the coastal regions from flooding. The transition zones provide benefits for both the environment and for the population through new land uses. The project illustrates the need for new and sustainable coastal defence strategies, so that future developments and new options can be taken into account in future planning.

The project develops individual adaptation solutions tailored to local conditions, with the aim of

1. Meeting increased wave activity through appropriate overflow structures,
2. Improving the breakwater effect of the defence zone,
3. Creating suitable conditions for saline wetlands behind the primary defence line with the aid of culverts or similar constructions,
4. Dealing with increased intrusions of salt water,
5. Informing political and planning agents, and the population,
6. Achieving widespread public support for the developed multi-functional zones (transition zones) and
7. Ensuring the comparability of different use strategies so that these can be evaluated by decision-makers in the region.

Development of spatial use concepts up to 2050

In the development options for the coastal zones, ecological, social and also economic concerns are taken into account. This will support the development of sustainable alternatives to the traditional coastal defence methods and the identification of possibilities for the multi-functional use of the newly-developed coastal defence zones. The potential for conflict can be reduced by creating so-called "win-win" situations.