Multi-layer safety in the Wadden Sea: possible measures in spatial planning and disaster management in view of climate change.
In the National Water Plan the concept of multi-layer safety was introduced for sustainable water security. Within the concept of multi-layer safety three layers can be distinguished: flood prevention, sustainable spatial planning and disaster management. We apply this concept to the mainland coast of Friesland and Groningen, or 'Dike Ring 6', and the Frisian Islands. Second layer measures are not cost effective when used in large areas as it is almost always cheaper to further improve the first layer water safety. Where the second layer measures may be cost-effective: (1) It certainly makes sense to look for the second layer measures in areas outside the dikes where no first layer action is possible; (2) Because the Eems delta has hardly any resistance to a flood a second layer can be considered, especially if it is combined with other functions than just water safety; (3) Components of critical infrastructure (such as gas distribution) in an area with major flooding risk could be protected with second layer measures to prevent a cascade of disasters. Third Layer measures are valuable under all circumstances and can certainly be further optimized in the Wadden Sea area. For the islands an extra effort is needed in the third layer safety.