A HIGH RESOLUTION EXAMINATION OF COASTAL TRENDS THROUGH THE USE OF ORTHORECTIFIED AERIAL PHOTOGRAPHS SPANNING A PERIOD OF 67 YEARS, RAINSFORD ISLAND, BOSTON HARBOR, MASSACHUSETTS

Rainsford Island, located within Boston Harbor, has a rich and dynamic history stretching back hundreds of years and has numerous historically sensitive sites providing a rich chronology of cultural and environmental developments during the past 400 years. These sites include a revolutionary era cemetery and the remnants of a 19th century quarantine hospital once referred to as the “Greek Temple” due to its elaborate architectural design. Many of these sites are located within the coastal zone and lay vulnerable to erosional events.

The 21.6 acre island consists of two drumlins connected by sandy spit. The north drumlin reaches a height of 16.7 m above sea-level and has steep eroding bluffs buffered from erosional processes by a deteriorating seawall built in 1836. The southern portion of the island consists of a heavily eroded drumlin that has been reduced to a flat plain and a bedrock remnant reaching 7 m above sea-level. Bedrock outcrops on the east and west sides of this drumlin anchor a sandy cove.

The methods used to examine the Island's geomorphology over the past 67 years include the acquisition and georectification of a series of five vertical aerial photographs and three preexisting orthorectified images spanning a time period of 67 years. The aerial photographs were processed and analyzed using spatial analysis and remote sensing software. Combined, these images provide a high-resolution investigation on a medium temporal scale, which would be difficult to achieve through traditional field studies.

As of December, 2008 our analysis of the aerial photographs showed a number of geomorphologic trends on the island. Steady filling and accretion has taken place within the small cove on the southeastern side of the spit which sits between the two drumlins. The spit connecting the two drumlins shows evidence of periodically experiencing overwash and occasional complete submergence. The northern margin of the southern drumlin is experiencing shoreline erosion.

Our present efforts are centered on determining gross and net land loss/gain at vulnerable positions of the Island over the 67-year period. We will also relate the region of high erosion hazard to the presence of historic sites on the Island. Future plans include incorporating ground penetrating radar imagery in areas of land loss or gain.