The Value of Coastal Wetlands for Flood Damage Reduction in the Northeastern USA, Narayan et al. 2017

The authors address the lack of high-resolution, large-scale assessments of the value of coastal wetlands for reducing property damages from flooding. In the first part of this paper, they assess Hurricane Sandy-induced damages to wetlands. The second part examines the risk reduction benefits of salt marshes in Ocean County, NJ, in terms of average annual economic flood losses. This study involved over 2000 synthetic storm events in Ocean County. The storm events were matched in frequency with actual storms that occurred between 1900 and 2011.  

Wetland extent was positively correlated with damage reduction in all but one of 12 states impacted by Hurricane Sandy. The authors used a hydrodynamic model that calculated the propagation of storm surges from the coastal shelf on to land.  The average amount of damage reduction was slightly over 1%; however, four states with extensive wetlands experienced flood damage reduction of 20-30%.

Losses were less for areas with salt marshes than for those without. On average, salt marshes reduced flood-related damages by 18%. Higher elevations were also correlated with damage reductions.

The authors noted that damage reduction was also apparent at locations several kilometers upstream of affected wetlands. A few areas, however, showed increased storm damage because of their proximity to wetlands. These areas often were dammed, or had their stream channel redirected. Based on their findings, the authors advocate for the increased use of flood risk models  by the insurance industry and small businesses.