Buzzards Bay NEP / MCZM Study of Flood Zone Expansion with Sea Level Rise


The Buzzards Bay National Estuary Program (BBNEP) and the Massachusetts Office of Coastal Zone Management are evaluating the potential expansion of the existing Federal Emergency Management Agency's (FEMA) 100-year floodplain using Flood Insurance Rate Map (FIRM) base flood elevations for Buzzards Bay municipalities. The floodplain will be expanded with 1-foot, 2-foot, and 4-foot increases in sea level. The existing floodplain will be extrapolated upward based on the FIRM base flood elevations. Using a recent assessor's data set, the number of buildings, their assessed values, and municipal structures are being enumerated within these various sea level rise expansion scenarios.

For this study, we considered only the landward most extent of the FIRM base flood (1% storm floodplain), and the published base flood elevation, to define the baseline flood zone used for this analysis. We then expanded this baseline flood zone by adding 1-, 2-, and 4-foot to the base flood elevation (whether A or V zone). The extrapolations were based on a digital data set of estimated bare earth elevations established by a 2007 aerial survey using LiDAR technology that was obtained from FEMA and which was used in part to prepare the 2009 updated Bristol and Plymouth County FIRMs (CDM, 2008).

The selected 1-, 2-, and 4-foot elevation increases in this study were chosen as convenient management elevation markers. The relative sea level rise in southern New England has been somewhat less than 1 foot during the past century. The International Panel on Climate Change (IPCC, 2007) consensus range for sea level rise, applied to this region, is 1 to 4.5 feet by year 2100. However, some other studies with alternative scenarios with more expanded Greenland Antarctic glacier melting, or changes in the North Atlantic gyre may result in higher local sea level rise rates. We thus leave open ended how quickly the 1-, 2-, and 4-foot elevation increases may occur.

On this page we also provide maps and information on the 1% risk area defined by FEMA in their flood insurance rate maps.

Fig 3. Placement of structures within the expanded flood zones.