The entire Wadden Sea, from Den Helder to Esbjerg, has been designated as a UNESCO World Heritage site. It ranks among the world’s most important wetlands and has unique natural values. The area is also of major importance in terms of flood risk management. The ebb-tide deltas, the Wadden islands, the flats and the salt marshes together protect the northern coast of the Netherlands.
The point of departure in the Preferential Strategy regarding flood protection of the the Wadden Region is that the important values of the Wadden Region are maintained by opting for measures that are as ecological as possible. The focus in the years ahead will be on fleshing out the strategy. The region will explore opportunities for an integrated approach to the measures. The Delta Decisions and the Decision on Sand constitute the framework in this regard.
The long intertidal zone in the shallow Wadden Sea (mudflats, salt marshes, and channels) constitutes a buffer against the high waves of the North Sea. Without this buffer, the flood defences along the mainland and island shores would have to be stronger and higher. The intertidal zone of the Wadden Sea requires additional sand in order to adapt to the rising sea level. If the rise in sea level accelerates, more sand will be needed, and a situation may arise in which the intertidal zone can no longer keep pace with the rising sea level, which will reduce its buffering effect.
In addition, a stretch of flood defences along the mainland and island shores of the Wadden Sea spanning approx. 100 kilometres fails to provide the statutory level of protection. Moreover, some sections of the flood defences need to provide a higher level of protection, in particular with a view to the key role that the province of Groningen plays in gas extraction and (inter)national gas transport. A final important issue is rendering the dykes in Groningen earthquake-proof.
Preferential Strategy with three elaborations
A Preferential Strategy has been drawn up for the Wadden Region, comprising three elaborations.
The Preferential Strategy focuses on the preservation of the buffering function of the islands, ebb-tide deltas, and intertidal areas against violent North Sea waves. This goal is primarily achieved by continuing the sand replenishments on the island coasts, thus ensuring a sufficient sand budget in the sand system (the coastal base). These efforts are supplemented by developing more knowledge on the sand system.
The current sea level scenarios seem to indicate that, in terms of flood protection, no measures will be required until 2100, neither in the Wadden Sea itself nor in the Eems-Dollard and its estuary. The system is capable of adapting to seabed subsidence and the rising sea level. Nor is intervention desirable in terms of ecological value. For the time being, sand replenishment along the North Sea coast of the Wadden Islands (on the coastal base) and possibly on the ebb-tide deltas will suffice. Pilots such as the Sand Replenishment pilot being conducted on the ebb-tide delta of the Ameland tidal inlet (see Coast Delta Programme) and monitoring programmes will show whether the sand will be transferred to the mudflats and salt marshes of the Wadden Sea naturally, and in good time (“learning while working”). The pilots and monitoring programmes are implemented under the Coastal Genesis 2.0 research programme launched by Rijkswaterstaat, which provides insight into the operation and future changes of the sand system.
Regular coastal management involving sand deposits is proceeding as scheduled. In 2017, the channel margin replenishment off the island of Ameland was completed. A similar replenishment off the island of Vlieland was completed in 2019. The effectiveness of the sand deposits is being monitored.
With respect to dyke improvements, the Preferential Strategy sets out an area-based and integrated approach. This is substantiated by having modifications to the flood defences tie in with area developments, thus creating added value for functions such as nature, leisure activities, and the regional economy.
Innovative dyke concepts
Along the mainland shoreline, added value for the nature, leisure activities, and regional economy functions can be created by implementing innovative dyke concepts, such as wide green dykes, multi-functional dykes, and dykes that can withstand overtopping. The three district water boards – Wetterskip Fryslân, Noorderzijlvest, and Hunze en Aa’s – have examined such innovative flood defence concepts in pilots conducted within the Wadden Sea dykes General Exploration. The results are presented on the pov-waddenzeedijken.nl website.
The Noorderzijlvest district water board is already implementing innovative dyke concepts in the Eemshaven-Delfzijl dyke improvement section. The dyke improvements set out in the Flood Protection Programme are on schedule. The Eemshaven-Delfzijl dyke improvement was completed in 2019. Potential solutions for the Vlieland dyke improvement are being developed.
3. Wadden Islands
In principle, the Preferential Strategy encompasses the same building blocks for each of the Wadden Islands: sand replenishment, dynamic coastal management, salt-marsh development, innovative dyke concepts, keeping pace with the sea level through re-distribution of sand, habitation outside the dykes, infrastructure outside the dykes, disaster management, and freshwater supply. These aspects are inter-related. Ergo, an integrated approach to flood risk management would seem obvious, yet each of the islands calls for an individual strategy because the inter-relation between the building blocks may differ from one island to the next.
The Wadden Region Delta Programme only covers the coastal municipalities along the Wadden Sea mainland and the Wadden Island municipalities. Spatial adaptation in the Wadden Region involves a larger territory (the province of Friesland, the province of Groningen, and part of the northern section of the province of Drenthe). For this reason, spatial adaptation in the Wadden Region (all the municipalities) is addressed by the Rhine North / Nedereems Regional Consultation Committee. The spatial adaptation strategy pursued in the Wadden Region is explained elsewhere on this website.
Under the Frisian Administrative Water Chain Agreement 2016-2020, all the Frisian municipalities, the province of Fryslân, and the Wetterskip Fryslân district water board are working on spatial adaptation as the regional substantiation of the Delta Programme and the Delta Plan on Spatial Adaptation. The collective project involving a climate stress test for the province of Fryslân has been completed (www.frieseklimaatatlas.nl, in Dutch). This project has explored the risks entailed in climate change with respect to the topics of waterlogging, heat stress, drought, and urban flooding. The results of the climate stress tests will serve as input for the Environmental Vision process.
The stress tests conducted in the area governed by the Noorderzijlvest district water board have also been completed. In the territory of the Hunze en Aa’s district water board, three stress test pilots were conducted in 2018. The lessons to be learned from these pilots will be taken into account in the stress tests to be completed in 2020.
Potential amendment of the Preferential Strategy
The potential acceleration in the rise in sea level may affect the Preferential Strategy. As yet, amendment is not being considered.
For the time being, the dykes can be improved or raised even further, whilst sand replenishment will safeguard a sufficient sand volume in the coastal base. Thus, in the decades ahead, the Wadden Sea can continue to keep pace with the rising sea level and soil subsidence. Recent research has shown that the key question is when and at what pace the sea level will be rising. This depends on factors such as climate developments. Cf. the Sea Level Rise Knowledge Programme . The erosion and sedimentation processes in the Wadden Sea are likely to change. More clarity regarding the rising sea level will be gained in the years ahead, once the IPCC (Intergovernmental Panel on Climate Change) and KNMI (Royal Netherlands Meteorological Institute) findings become available, and new knowledge and insights have consolidated.
Delta Programme 2020
Read about the progress made in the Wadden Region in Delta Programme 2020.