Klimaatdijk een verkenning

English. IntroductionClimate change, land subsidence and the increasing economic value of property and activities in flood-prone areas justify the question of how we can maintain flood protection in the Netherlands at its current level, or even improve it. The changing social, scientific and technical developments and insights of our day mean that the time is ripe to consider alternatives for flood protection, other than the customary call to raise the dikes yet higher, time and again.The Climate DikeThe Climate Dike is a logical addition to the current practice of raising and reinforcing dikes. A Climate Dike is defined here as ¿a collective term for design components that result in flood defences so robust that they are virtually impossible to breach, and thus offer lasting protection, even in the face of ongoing climate change The Climate Dike concerns a type of dike that allows some wave overflow and even a limited amount of flooding, but which prevents the uncontrolled catastrophic dike breaks associated with devastating flooding of the hinterland. The number of potential victims and the resulting damage are therefore in no way comparable to those incurred when a traditional dike breaks. The risk, calculated as a product of the probability of occurrence and the resulting damage, is therefore drastically reduced.Another feature of the Climate Dike is its integrated multi-functional character. On it, a wider range of socio-economic interests can be built than on traditional dikes. This means that greater opportunities for financing also become available.Before the Climate Dike can be approached as a serious alternative, clarity is needed on the relevant information, experience, policy and knowledge that exists (and does not yet exist). The current inventory was conducted with that requirement in mind.The authors looked at, among others, projects that presented problems and challenges similar to those expected in development of a Climate Dike. These relate, among others, to technical,economic, social and spatial issues.A long time horizonBecause of its more multidisciplinary character, development of a Climate Dike requires a longer time horizon than a traditional dike. The current system of 5-yearly testing, in which dikes that fail to meet current safety standards are immediately subjected to an urgent upgrade trajectory, provides an inadequate framework for developing the Climate Dike.In the current system, evolving scientific insights, environmental conditions and safety requirements could mean that even immediately after a dike has been strengthened, the next reinforcement is just around the corner. Such a situation is clearly undesired for a multifunctional Climate Dike with, for example, buildings on it. Also, after its construction, a Climate Dike has to be able to guarantee safety for many more decades than a traditional dike, and to do so in a way that other interests can build on, literally and figuratively. A longer planning horizon and new means of anticipating on future developments are therefore essential.ChallengingThe Climate Dike has no set dimensions or form, though it does tend to be wider and less steep than traditional dikes and include a protection zone parallel to existing flood defences. It goes without saying that not every aspect of the Climate Dike concept, which is often broad in both functional and physical terms, will be applicable at every location.One of the many challenges arising in applying the Climate Dike concept is the question of how to effectively look ahead over an extremely long stretch of time (for example, a century), since we cannot predict with any certainty how society will look after such a long period. How can ideas and procedures be tailored to as yet unknown future developments? How can we best ensure the ability to adapt to new situations and insights?One of the complexities involved in developing a Climate Dike is the use of space. How can the required space be secured without having to demolish large numbers of buildings and infrastructure and without excluding large zones of land from any possible socio-economic activity, perhaps for many decades?Costs and benefitsA Climate Dike is costly, if one limits the field of vision to the safety aspect and the traditional time horizon of 50 years. Broaden the view to bring in multiple interests that over a longer time period can, literally and figuratively, build on the presence of the Climate Dike, then this form of flood protection becomes much more financially attractive. Certainly when considering other options for flood protection, such as compartmentalisation dikes or the raising of immense tracts of land.Law and legislationTo give designers and managers of flood defences more opportunity to develop the Climate Dike, modifications are required in current design guidelines and technical prerequisites. Also, it must be made clear whether and how a Climate Dike is to be subjected to the 5-yearly testing cycle. Is such testing needed if the dike is considered to be virtually impossible to breach? How do we deal with the probability of flooding versus the risk of a dike break? Current law and legislation are geared fairly specifically to the traditional dike. Alternative concepts such as the Climate Dike call for modified policies, laws and legislation, as well as newly formulated design requirements and prerequisites. Or it will have to be made clearer how these should be interpreted for such innovative concepts.

Dutch; Flemish. Door het veranderende klimaat is de tijd rijp om na te denken over andere concepten van waterveiligheid dan het steeds maar ophogen van dijken. Een Klimaatdijk is een inrichtingsvorm waarbij de waterkering zo robuust is dat hij niet doorbreekt en dus blijvende veiligheid biedt. Het concept van de Klimaatdijk richt zich op een dijk waarover enige golfoverslag en zelfs beperkte overstroming mogelijk is, maar waarbij oncontroleerbare dijkdoorbraken met allesverwoestende overstromingen van het achterland wordt uitgesloten. Een aantal mogelijkheden wordt verkend; er is aandacht voor het financiele aspect en de wet- en regelgeving. Vanwege het meer multidisciplinaire karakter vergt de realisatie van een Klimaatdijk een ruime tijdshorizon. De huidige systematiek van de 5-jaarlijkse toetsing en bij afkeuring een urgente versterkingsnoodzaak, schept onvoldoende randvoorwaarde voor een Klimaatdijk