Nature-based flood protection

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(1)Delft University of Technology. Nature-based flood protection Using vegetated foreshores for reducing coastal risk Vuik, Vincent; Jonkman, Sebastiaan N.; Van Vuren, Saskia DOI 10.1051/e3sconf/20160713014 Publication date 2016 Document Version Final published version Published in 3rd European Conference on Flood Risk Management (FLOODrisk 2016) : Lyon, France, October 17-21, 2016. Citation (APA) Vuik, V., Jonkman, S. N., & Van Vuren, S. (2016). Nature-based flood protection: Using vegetated foreshores for reducing coastal risk. In 3rd European Conference on Flood Risk Management (FLOODrisk 2016) : Lyon, France, October 17-21, 2016 (Vol. 7). (E3S Web of Conferences 7; Vol. 7, No. 13014). https://doi.org/10.1051/e3sconf/20160713014 Important note To cite this publication, please use the final published version (if applicable). Please check the document version above.. Copyright Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policy Please contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim.. This work is downloaded from Delft University of Technology. For technical reasons the number of authors shown on this cover page is limited to a maximum of 10..

(2) E3S Web of Conferences 7, 13014 (2016) FLOODrisk 2016 - 3rd European Conference on Flood Risk Management. DOI: 10.1051/ e3sconf/2016 0713014. Nature-based flood protection: using vegetated foreshores for reducing coastal risk Vincent Vuik. 1,2,a. 1. , Sebastiaan N. Jonkman and Saskia van Vuren. 2,1. 1. Delft University of Technology, Civil Engineering and Geosciences, P.O. Box 5048, 2600 GA, Delft, The Netherlands HKV Consultants, P.O. Box 2120, 8203 AC, Lelystad, The Netherlands. 2. Abstract. Vegetated foreshores such as salt marshes, mangrove forests and reed fields can reduce wave loads on coastal dikes due to depth-induced wave breaking and wave attenuation by vegetation. Here we present field measurements of wave propagation over salt marshes during severe storm conditions, a modelling approach to describe the effect of vegetated foreshores on wave loads on the dike, and a probabilistic model to quantify the effect of vegetated foreshores on failure probabilities of the dike due to wave overtopping.. 1 Introduction Coastal flood risk reduction by creating and restoring eco-systems is increasingly seen as a promising supplement to conventional coastal engineering methods (e.g. [1]). Salt marshes, mangrove forests and reed fields can act as a vegetated foreshore in front of a coastal dike. In such a combined dike-foreshore system, the foreshore plays a role in attenuating storm waves, whereas the dike retains the surge and the remaining wave energy. The current study focuses on this type of (eco)systems.. secondly, ecosystems are characterized by a relatively high degree of uncertainty with respect to spatial and temporal variations. Quantification of these uncertainties is required for determining the efficiency and reliability of a vegetated foreshore as a component of the flood management system.. 2 Methods

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(19) !. Figure 1. Example of a vegetated foreshore along a Wadden Sea dike in the Netherlands. Large-scale implementation of vegetated foreshores in flood risk policy is still lacking worldwide. This has a number of reasons. Firstly, mechanistic descriptions of relevant physical processes are mainly based on moderate conditions, with small water depths and low waves. And a. Figure 2. Schematic view of dike-foreshore system. #

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(27) . Corresponding author: V.Vuik@tudelft.nl. © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/)..

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(48) . DOI: 10.1051/ e3sconf/2016 0713014. 3 Results

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(113) +* % . . . Figure 5. Example of the computation of a failure probability per year as a function of the crest height of the dike, for the situation without foreshore (blue), with a bare foreshore (red), with a vegetated foreshore (green) and with a vegetated foreshore, where also uncertainties in foreshore characteristics and models involved were taken into account (purple).. 2

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(160) . Figure 3. Set-up of probabilistic model, in which the foreshore model is used to compute the change in wave conditions over the vegetated foreshore (Figure 2). '

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(164) : *. *. Figure 4. Salt marshes along the Wadden Sea dike (Source: https://beeldbank.rws.nl, Rijkswaterstaat). 2. )

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(339) . 3. Temmerman, S., Meire, P., Bouma, T.J., Herman, P.M.J., Ysebaert, T., and De Vriend, H.J. (2013). Ecosystem-based coastal defence in the face of global change. Nature, 504, 7983. Vuik, V., Jonkman, S.N., Borsje, B.W. and Suzuki, T. (2016). Nature-based flood protection: the efficiency of vegetated foreshores for reducing wave loads on coastal dikes. Journal of Coastal Engineering doi: 10.1016/j.coastaleng.2016.06.001 Gautier, C., & Groeneweg, J. (2012). Achtergrondrapportage hydraulische belasting voor zee en estuaria. Technical report, Deltares (in Dutch). Van Wesenbeeck, B. K., de Boer, W., Narayan, S., van der Star, W. R., and de Vries, M. B. (2016). Coastal and riverine ecosystems as adaptive flood defenses under a changing climate. Mitigation and Adaptation Strategies for Global Change, 1-8..

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