Coastal and riverine ecosystems as adaptive flood defenses under a changing climate
Adaptation planning for flood risk forms a significant part of global climate change response. Engineering responses to higher water levels can be prohibitively costly. Several recent studies emphasize the potential role of ecosystems in flood protection as adaptive risk reduction measures while also contributing to carbon fixation. Here, we use a conceptual model study to illustrate the built-in adaptive capability of ecosystems to reduce a wide range of wave heights, occurring at different water levels, to a narrower range. Our model shows that wave height of waves running through a forested section is independent of initial height or of water level. Although the underlying phenomenon of non-linear wave attenuation within coastal vegetation is well studied, implications of reducing variability in wave heights for design of ecosystem and levee combinations have not yet been properly outlined. Narrowing the range of wave heights by a vegetation field generates an adaptive levee that is robust to a whole range of external conditions rather than only to a maximum wave height. This feature can substantially reduce costs for retrofitting of levees under changing future wave climates. Thereby, in wave prone areas, inclusion of ecosystems into flood defense schemes constitutes an adaptive and safe alternative to only hard engineered flood risk measures.
KeywordsNature-based coastal defense SWAN-VEG Climate change adaptation Mangroves Riparian forest Adaptive management Levees Flood risk management
The authors like to thank Jaap Kwadijk and Marc Bierkens and the anonymous reviewers for their comments on previous versions of this manuscript.
- CIRIA, Ecology, M. o. and USACE (2013) The International Levee Handbook (C731), CIRIAGoogle Scholar
- Denny MW (1988) Biology and the mechanics of the wave-swept environment. Princeton University Press, Princeton, pp 329Google Scholar
- Hughes SA (2008) Estimation of combined wave and storm surge overtopping at earthen levees. Coastal and Hydraulics Engineering Technical Note ERDC/CHL CHETN-III-78. Vicksburg, MS: U.S. Army Engineer Research and Development CenterGoogle Scholar
- McIvor A, Möller I, Spencer T, Spalding M (2012) Reduction of wind and swell waves by mangroves. Natural coastal protection series: Report 1. Cambridge coastal research unit working paper 40. The nature conservancy, Arlington, USA/Wetlands International, Wageningen, Netherlands, pp 27Google Scholar
- McIvor A, Spencer T, Möller I, and Spalding M (2012) Storm surge reduction by mangroves. Natural coastal protection series: Report 2. Cambridge coastal research unit working paper 41. The Nature Conservancy and Wetlands International, pp 35. http://www.naturalcoastalprotection.org/documents/storm-surge-reduction-by-mangroves
- McIvor A, Spencer T, Möller I, and M. Spalding (2013) The response of mangrove soil surface elevation to sea level rise. Natural Coastal Protection Series: Report 3, Cambridge Coastal Research Unit Working Paper 42. Published by The Nature Conservancy and Wetlands International, pp 59Google Scholar
- Möller I, Spencer T (2002) Wave dissipation over macro-tidal saltmarshes: effects of marsh edge typology and vegetation change. J Coast Res 36:506–521Google Scholar
- Reid H, Swiderska K (2008) “Biodiversity, climate change and poverty: exploring the links. International Institute for Environment and Development.”Google Scholar