Coastal wetlands mitigate storm flooding and associated costs in estuaries

Abstract

As storm-driven coastal flooding increases under climate change, wetlands such as saltmarshes are held as a nature-based solution. Yet evidence supporting wetlands’ storm protection role in estuaries—where both waves and upstream surge drive coastal flooding—remains scarce. Here we address this gap using numerical hydrodynamic models within eight contextually diverse estuaries, simulating storms of varying intensity and coupling flood predictions to damage valuation. Saltmarshes reduced flooding across all studied estuaries and particularly for the largest—100 year—storms, for which they mitigated average flood extents by 35% and damages by 37% ($8.4 M). Across all storm scenarios, wetlands delivered mean annual damage savings of $2.7 M per estuary, exceeding annualised values of better studied wetland services such as carbon storage. Spatial decomposition of processes revealed flood mitigation arose from both localised wave attenuation and estuary-scale surge attenuation, with the latter process dominating: mean flood reductions were 17% in the sheltered top third of estuaries, compared to 8% near wave-exposed estuary mouths. Saltmarshes therefore play a generalised role in mitigating storm flooding and associated costs in estuaries via multi-scale processes. Ecosystem service modelling must integrate processes operating across scales or risk grossly underestimating the value of nature-based solutions to the growing threat of storm-driven coastal flooding.

A Qualitative Analysis of UK Wetland Visitor Centres as a Health Resource

“…The ability of wetlands to provide restoration is especially important where blue spaces are to be operationalised for health interventions [20]. Wetlands too are especially beneficial to health with regard to environmental mitigations (e.g., threats from climate change, flooding and other natural disasters [80][81][82]), so they may be a key environment in delivering 'win-wins' and multiple benefits to society [83].…”

Saltmarsh Resilience to Periodic Shifts in Tidal Channels

“…If a marsh undergoes erosion at one location whilst a marsh elsewhere in the estuary expands, the habitat provision service would remain resilient, since structurally diverse vegetation and geomorphic profiles are maintained at the estuarine scale. Estuarine marshes also effectively attenuate storm surges and the upstream attenuation effect is determined by marsh extent, not specific location in the estuary (Fairchild et al, 2021). The storm surge capacity of marshes is therefore unlikely to be affected by compensatory erosion-expansion cycles.…”

“…Other ecosystem services will likely be undermined by geomorphic compensation. Marsh loss would negatively impact on localized wave attenuation, as wave dissipation is strongly correlated with marsh width (Fairchild et al, 2021). Organic carbon stored in marsh deposits would be released during erosion, and it remains unclear whether the carbon could be reburied during marsh expansion or whether a portion of the carbon would be reintroduced into the carbon cycle (Mueller et al, 2019).…”

The impacts of tidal wetland loss and coastal development on storm surge damages to people and property: a Hurricane Ike case-study

“…Inter-tidal wetlands are an important natural barrier that can mitigate exposure and vulnerability to storm surges by reducing flood extents and heights hazards and thus avoiding hurricane damages and deaths 16 – 18 . A number of studies have evaluated the physics of surge attenuation across wetlands and the subsequent benefits of wetlands to reduce storm surge 19 and property damages 20 – 23 .…”