The Flanders Master plan
Integrated Coastal Master plan on how to control coastal flooding risks in Flanders in 2050

German/Danish Coastal Pilot Sites
Assessment of risk scenarios based on five different representative North Sea Region coastal types

Action 5A:
The consequences of climate change in Denmark

The prime objective of the cluster of Danish pilot sites is to study the consequences of climate change for the coastal zone in Denmark. As project Safecoast focuses on forward-looking coastal flood defence solution in low-lying areas in the North Sea region, the Danish subproject will focus on the consequences of climate change at different coastal flood defence systems and the subsequent impact on the socio-economic system. The assessment of the consequences will be based on four pilot sites along the Danish coast (see figure). In this way the focused action aims:

• to improve the knowledge about the effects of climate change on coastal defence systems,
• to improve the understanding of the interplay between the coastal defence system and the related socio-economic system under changing boundary conditions,
• to improve the process of informing relevant parties (policy makers, public, media, etc.) about the consequences of climate change in the coastal zone in a most appropriate way,
• to contribute with knowledge and recommendations based on the pilot-site experiences to the main Safecoast goal of a sustainable, harmonious and balanced strategy for coastal zone management.

However, to limit the subproject’s extent investigations about the impacts on the socio-economic system will only be performed in an introductive, qualitative way. Climate change effects on other aspects (e.g. groundwater deposit, infrastructure, flora and fauna) in the coastal zone will not be considered. However, it is intended to make a proposal for an approach to study the impacts on the socio-economic system in coastal regions and give recommendations for a follow-up project.

The four selected pilot sites represent different types of coast (e.g. exposed littoral coast, tidal flat coast, marshy coast, etc.), different types of coastal defence structures and different degrees of hinterland occupation. The four sites are shown in the figure below.

The approach within this subproject comprises four steps. In the first step, a literature review will form the basis for the impact assessment at the four pilot sites. The review will contain literature on the consequences of climate change (i) on the hydrodynamic and hydrological system, (ii) on the coastal defence system, and (iii) on the socio-economic system in the coastal zone. Further, literature (iv) on public information strategies about climate change and sea level rise will be studied.

Second step comprises the preparation of an erosion atlas for the Danish coastline to illustrate the extra coastal retreat due to sea level rise. Within step 3, the actual impact assessment at the four pilot sites will be performed. Last but not least, the fourth step contains the evaluation of appropriate methods to inform relevant target groups (policy makers, public, media, local administration, etc.) about the project results and the consequences of climate change.

The responsibility for this action (part A) lies with the Danish Coastal Authority (DCA) or, in Danish, Kystdirektoratet [DK]

Action 5B:
Risk assessments in Niedersachsen, Germany

^{Low lying areas of Lower Saxony, Germany}

^{The evolution of sea dikes in Niedersachsen since 1000 AD (source: NLWKN)}

^{Example of a flood simulation in East Frisia, Germany}

Given the various flooding scenarios (especially in East Frisia) many simulations were carried out (see an example above), including the consideration of a number of possible flood mitigation measures such as high forelands, summer dikes, second dike lines and break lines in the hinterland. Many flood simulations were carried out.

The main findings of the case studies were discussed with local and regional expert groups and are summarised below.

1 Flood simulations:
a. The use of state of the art numerical hydrodynamic models for simulations of flooding due to the failure of coastal defence structures is recommended.
b. Simulations of coastal lowland’s floods should include a 1D-stream network in addition to the 2D overland flow.
c. The extent of a dike breach (width and depth) and the number of simultaneous breaches in a certain area are the most influencing parameter.
d. Additionally, the topography of areas sea and landward of the breach location strongly influences
the inflowing volume and the flood propagation.
e. The sea level rise affects coastal flooding in broad coastal lowlands by significantly increasing the inundated area.

2 Risk analysis:
a. About 90% of the direct tangible values at risk are concentrated in four damage categories. Those are private buildings, private inventory, fixed assets and the gross value added.
b. The predictions of future economical changes in flood protected areas and therefore the development of assets at risk is highly uncertain.
c. In case of a flood event, the expected sea level rise results in significantly increased damages of all damage categories, even for constant damage potentials and breach conditions.

3 General recommendations:
a. Development and management of forelands as well as maintenance and expansion of embankments in the hinterland, including 2nd dike lines, street dams etc., are found to be potential flood risk mitigation measures.
b. Despite the benefits of the above risk mitigation measures, two types of possible negative effects were identified that need to be considered during the planning process. The mitigation measures take effect by hindering flood propagation and therefore strengthening the area’s resistance against flooding. One possible negative effect is the flooding of areas which were safe before the measure was introduced. This results from changed flow paths which may occur even if the flooding hazard
comes from the direction the measure was planned for. Another possible negative effect is that, if flooding occurs from another direction, the area which should be protected by the measure could be in even greater danger than before.