The Impacts of Sea-Level Rise on Tidal Flooding in Boston, Massachusetts

In Boston, Massachusetts, chronic tidal flooding due to sea-level rise will occur in many developed parts of the city over the next several decades and beyond. This study examines the frequency and severity of tidal flooding due to increases in sea level of between 0.3 to 1.8 m (1.0 and 6.0 ft), as well as where flooding will generally occur. Local tide gauge data are compared to the National Weather Service's flood stage categories to determine how frequently they will be reached at high tide as sea level rises. GIS data are used to demonstrate where flooding is likely to occur, and U.S. Census data are used to identify assets that will be impacted. The study also depicts the relationships among the multiple datums currently used to measure water levels in Boston. Results of the analysis indicate that in the absence of any new flood barriers, the incidence of minor tidal flooding will increase to about 75 times per year within Boston Harbor with 0.3 m (1 ft) of sea-level rise. Nine-tenths of a meter (3 ft) of sea-level rise will result in about 30 occurrences of moderate flooding per year, and 1.2 m (4 ft) will bring that same frequency of major flooding incidents. Tidal flooding due to 1.8 m (6 ft) of sea-level rise will affect approximately 20% of the population and land, as well as housing, public facilities, transportation infrastructure, and hazardous waste sites. The study suggests that future conditions will require the development of nonemergency responses to flooding as well as a new approach to urban floodplain management.