Flood Insurance and Coastal Flooding

October 29, 2014

The Federal Emergency Management Agency (FEMA) has issued and continues to update new Flood Insurance Rate Maps (FIRMs) for many communities in Massachusetts. As a result of updated information, the extent of the mapped floodplain in the Commonwealth has expanded in many communities. In the city of Boston alone, approximately 18,000 residential and 4,000 commercial properties are now mapped below the updated 100-year flood elevation. There is a 1-percent chance of a storm causing such flooding in each calendar year.

In addition to the controversy these updated maps have generated, due to the methodology used and the increased number of affected properties, these new maps also impact the design of new construction in these flood zones. FEMA utilized revised topographic elevation and rainfall data but has not considered projected sea level rise or recent severe storms in generating the increased extent of flood zone. In response to FEMA’s changes to the FIRMs, many communities in Massachusetts are generally evaluating the implications of sea level rise on new development projects and encouraging or even requiring these projects to anticipate the future sea level rise in the design.

Construction accommodations that anticipate sea level rise and flooding can consist of a variety of measures. For instance, a simple solution is to raise a proposed structure above the anticipated impact of high water, as was done for the pedestrian and vehicular bridge at the World’s End Reservation in Hingham. The timber bridge’s lowest stringers, the horizontal beams supporting the bridge deck, were constructed six inches above the 100-year flood elevation determined by the effective FIRM. In order to attain this elevation, grading and backfill were placed at the banks of the channel. Since the bridge has been constructed, it has weathered high-intensity storm events including Hurricane Sandy and Winter Storm Nemo.

Another successful strategy for flood-conscious improvements in existing buildings is to relocate sensitive equipment, such as generators, electrical transformers and fuel storage, to new locations above the ground floor. The sooner that flood-conscious design features are considered, the more likely these flood zone properties will be prepared for the future.

B+T provides coastal design and permitting services for a variety of waterfront projects throughout Massachusetts.