Assessing threatened coastal sites: Applications of ground-penetrating radar and geographic information systems

Rainsford Island is an 11-acre island located in central Boston Harbor, Massachusetts. The proximity to the City of Boston resulted in the Island being used as a quarantine facility, poorhouse, veteran's hospital and school for wayward boys from 1737 to 1920. The Island consists of two linked topographic highs of glacial origin connected by a spit formed from reworked glacial material. The majority of the southern “high” is only slightly elevated above present-day sea level and was the site of a cemetery that serviced the quarantine facility, poorhouse and veteran's hospital. Historical research indicates that more than 1100 persons were buried on Rainsford during this time. The records for the cemetery have been lost through fire and only four sandstone posts presently mark the cemetery. Our team sought to (1) assess shoreline change on the southern portion of the Island; (2) map the boundaries of the unmarked cemetery using ground-penetrating radar and (3) determine the vulnerability of the cemetery to coastal erosion caused by long-term sea-level rise and episodic flooding. Shoreline change analysis indicates that the southern portion of the island has eroded on the north-facing beach at a rate of 0.2 m/yr while the south-facing beach has been stable. Topographic analysis of the landscape indicates that the central area of the southern portion is less than 1 m above sea level with a slightly elevated rim approximately 2 m above sea level. The ground-penetrating radar surveys indicated that the low-lying central portion exhibited evidence for burials. The results indicate that the cemetery is vulnerable to erosion and coastal flooding. A storm with a coastal storm surge of approximately 1 m will result in flooding of the cemetery. The northern edge of the cemetery is extremely vulnerable to erosion and the first mapped burial on the northern side will be impacted in approximately 10 years. The southern edge of the cemetery is protected by horizontal and vertical accretion. As a result, conservation resources should be concentrated on the northern edge of the cemetery.