A vegetation-resolving CH3D-SWAN surge-wave modeling system is used to examine the role of mangroves and salt marshes along the shore of Biscayne Bay in buffering surge, wave, and inundation in Southeast Florida during Hurricane Andrew (1992). First, the 3D vegetation-resolving model is validated by comparing the simulated and measured high water marks from post-hurricane field survey, debris lines, and time series of water level at the Haulover Pier. The simulated water levels and magnitude and extent of maximum inundation agree well with the observed data, whereas the removal of vegetation from the model leads to massive flooding with increased total inundation volume and total inundation area in the highly populated low-lying area behind the Biscayne Bay. Additional simulations show that the surgewave-inundation buffering capacity of the mangrove forest depends on the vertical structure of the wetted leaf area index, A w and the frontal leaf area index, A f . The study demonstrates the capability of CH3D-SWAN in quantifying the role of mangroves in buffering storm surge, wave, and inundation, and demonstrates its potential application for assessing the effectiveness of coastal wetland restoration projects. Meanwhile, the accurate representation of vegetation's vertical structure can enhance the numerical modeling of flow-vegetation interaction processes.

Coastal communities in New Jersey (NJ), New York (NY), and Connecticut (CT) sustained huge structural loss during Sandy in 2012. We present a comprehensive science-based study to assess the role of coastal wetlands in buffering surge and wave in the tri-state by considering Sandy, a hypothetical Black Swan (BS) storm, and the 1% annual chance flood and wave event. Model simulations were conducted with and without existing coastal wetlands, using a dynamically coupled surge-wave model with two types of coastal wetlands. Simulated surge and wave for Sandy were verified with data at numerous stations. Structural loss estimated using real property data and latest damage functions agreed well with loss payout data. Results show that, on zip-code scale, the relative structural loss varies significantly with the percent wetland cover, the at-risk structural value, and the average wave crest height. Reduction in structural loss by coastal wetlands was low in Sandy, modest in the BS storm, and significant in the 1% annual chance flood and wave event. NJ wetlands helped to avoid 8%, 26%, 52% loss during Sandy, BS storm, and 1% event, respectively. This regression model can be used for wetland restoration planning to further reduce structural loss in coastal communities.

Phragmites marshes, which are found in every continent except in Antarctica, are being removed by resource managers in the US because it is considered an invasive species with little ecosystem service value. Here we present a comprehensive study on the ecosystem service value of an invasive Phragmites marsh vs a native Typha marsh for flood protection during tropical cyclones. Using a vegetation-resolving three-dimensional surge-wave model and observed vegetation and building data, we assessed the value of the Piermont Marsh in buffering Piermont Village, New York, USA from wave, flood, and structural damage during Superstorm Sandy in October 2012. Observed and simulated wind and water level data along the Hudson River were used as boundary conditions. Model results showed that the Marsh, with predominantly invasive Phragmites australis, dissipated more than half of the wave energy, but negligible flood, at the Village during Sandy. River-borne debris could not be transported across the Marsh to the Village. If Phragmites were replaced with the shorter, native cattail, Typha angustifolia, simulations of Sandy suggested that Piermont Marsh’s wave and debris buffering capacity would be preserved. However, had Sandy occurred in non-growth season when Typha is much shorter and sparser, the Marsh would be unable to buffer the wave and debris. Simulated residential structure damage during Sandy (>$10 M) agreed well with reported losses. If the Marsh were absent, the total loss would have increased by 26%. Since damage is dependent on the storm characteristics, we estimated the protective value of the Phragmites marsh for a 1% annual chance flood and wave event to be more than $2 M. This confirms the significant value of Piermont Marsh in protecting Piermont Village from flood and wave damage. To develop a balanced restoration plan, marsh managers should consider biodiversity as well as the significant ecosystem service value of Phragmites-dominated marsh for flood protection.

Wetlands such as tidal marshes and mangroves are known to buffer coastal communities from wave, flood, and structural loss during storms. Coastal communities and resource managers seek to understand the ecosystem service value of coastal wetlands for reducing storm-induced flood loss in a changing climate. A recent modeling study found that a tall and dense Phragmites-dominated Piermont Marsh reduced the flood loss in the Village of Piermont, New York, U.S.A. during Superstorm Sandy and the 1% annual chance flood and wave event by 8% and 11%, respectively. Here we used the same modeling approach to examine the marsh’s buffering capacity in a changing climate (from 2020 to 2100), considering a potential marsh restoration plan (from 2020 to 2025) and potential marsh loss due to sea-level rise. Results showed that from 2020 to 2100, the 1% annual chance flood, wave, and structural loss would increase due to sea-level rise, storms, and marsh loss. However, the marsh will buffer ~ 11–12% of structural loss until 2050. Under the extreme SLR scenario of 2.89 m and a low accretion rate, Piermont Marsh is expected to lose its buffering capacity by 2080–2100 but will retain some buffering capacity with a high accretion rate of 10 mm/year and marsh growth. The marsh’s buffering capacity will remain during extra-tropical storms during winter and spring unless the wind has a significant northerly component. Lessons learned from this study can be used by coastal communities and marsh managers to develop coastal resiliency and marsh restoration plan.