COASTAL GEOLOGIC HAZARDS AND SEA-LEVEL RISE: CLIMATE CHANGE EFFECTS IN RHODE ISLAND CONTINUE

As stated previously, when assessing the effects of climate change on the shore, it is necessary to separate the impact of geologic hazards, tropical and extratropical cyclones, from the impact of sea-level rise. Superstorm Sandy, a hybrid tropical/extratropical cyclone, provided a benchmark for our long-term profiling data which began in 1977 in a runup to the Blizzard of 1978. Frontal erosion from Sandy resulted in a reset of the barrier core crest 2 meters landward of the 1978 crest and the removal of the entire backshore reservoir (high berm/foredune). Much of this sand was transported landward as overwash, resulting in spectacular washover fans up to 2.5 meters thick and reaching into the lagoons. Measured transects indicate that berm and foredune removal was more extreme than FEMA modeling estimates and may require a rethink of frontal erosion and overwash effects.

Sea-level rise at Newport, RI measured 26.9 cm^.100yr^-1 from 1931-2011, the rate increased to 36.2 cm^.100yr^-1 for 1990-2009, comparable to published global eustatic rates. Rhode Island coastal managers follow guidelines that suggest an accelerated 1 to 1.5 meter rise by 2100 and a 40 cm rise by 2050. Using these guidelines, we can model present and future inundation, both storm surge and “bathtub ring”, using LiDAR altimetry obtained in 2011 and new FEMA flood insurance rate maps. This modeling points out at risk infrastructure including major hurricane evacuation routes, wastewater pump stations and first responder stations. Again, Sandy provided a preview of the future for Rhode Island.