title: The Effectiveness, Costs and Coastal Protection Benefits of Natural and Nature-Based Defences.
abstract: There is great interest in the restoration and conservation of coastal habitats for protection from flooding and erosion. This is evidenced by the growing number of analyses and reviews of the effectiveness of habitats as natural defences and increasing funding world-wide for nature-based defences-i.e. restoration projects aimed at coastal protection; yet, there is no synthetic information on what kinds of projects are effective and cost effective for this purpose. This paper addresses two issues critical for designing restoration projects for coastal protection: (i) a synthesis of the costs and benefits of projects designed for coastal protection (nature-based defences) and (ii) analyses of the effectiveness of coastal habitats (natural defences) in reducing wave heights and the biophysical parameters that influence this effectiveness. We (i) analyse data from sixty-nine field measurements in coastal habitats globally and examine measures of effectiveness of mangroves, salt-marshes, coral reefs and seagrass/kelp beds for wave height reduction; (ii) synthesise the costs and coastal protection benefits of fifty-two nature-based defence projects and; (iii) estimate the benefits of each restoration project by combining information on restoration costs with data from nearby field measurements. The analyses of field measurements show that coastal habitats have significant potential for reducing wave heights that varies by habitat and site. In general, coral reefs and salt-marshes have the highest overall potential. Habitat effectiveness is influenced by: a) the ratios of wave height-to-water depth and habitat width-to-wavelength in coral reefs; and b) the ratio of vegetation height-to-water depth in salt-marshes. The comparison of costs of nature-based defence projects and engineering structures show that salt-marshes and mangroves can be two to five times cheaper than a submerged breakwater for wave heights up to half a metre and, within their limits, become more cost effective at greater depths. Nature-based defence projects also report benefits ranging from reductions in storm damage to reductions in coastal structure costs.
authors.affiliation: National Center for Ecological Analysis and Synthesis (NCEAS), University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Siddharth
authors.initials: S
authors.lastname: Narayan
authors.affiliation: The Nature Conservancy / University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Beck
authors.affiliation: Department of Ocean Sciences, UC Santa Cruz / The Nature Conservancy, Santa Cruz, California, United States of America.
authors.forename: Borja G
authors.initials: BG
authors.lastname: Reguero
authors.affiliation: Instituto de Hidraulica Ambiental, ETSI de Caminos, Canales y Puertos, Universidad de Cantabria, Santander, Spain.
authors.forename: Iñigo J
authors.initials: IJ
authors.lastname: Losada
authors.affiliation: Unit for Marine and Coastal Systems, Deltares / Delft University of Technology, Delft, The Netherlands.
authors.forename: Bregje
authors.initials: B
authors.lastname: van Wesenbeeck
authors.affiliation: Coastal Planning and Engineering, CH2M HILL / University of Southampton, Swindon, United Kingdom.
authors.forename: Nigel
authors.initials: N
authors.lastname: Pontee
authors.affiliation: Department of Environmental Science and Policy, University of California Davis, Davis, California, United States of America.
authors.forename: James N
authors.initials: JN
authors.lastname: Sanchirico
authors.affiliation: Wildlife Conservation Society / Columbia University, New York, New York, United States of America.
authors.forename: Jane Carter
authors.initials: JC
authors.lastname: Ingram
authors.affiliation: Environment and Natural Resources Global Practice, The World Bank, Washington, DC, United States of America.
authors.forename: Glenn-Marie
authors.initials: GM
authors.lastname: Lange
authors.affiliation: Environmental Laboratory, US Army Engineer Research and Development Center, Vicksburg, Mississippi, United States of America.
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Burks-Copes
mesh_terms: D003247:Conservation of Natural Resources / Q000191:economics* / Q000379:methods*; D057894:Coral Reefs; D017753:Ecosystem; D055868:Floods; D053833:Wetlands