Date of Award
Master of Science in Geology
John J. Fisher
The amount and size of sediment eroded and accreted on the erosional shorelines of the Boston Harbor Islands has been determined from a photogrammetric analysis of the high tide line and cliff line over the period of 1938 to 1977 (the dates of the earliest and latest aerial photographic coverage). Photogrammetric areal measurements of the Boston Harbor Islands were made using a Zoom Transfer Scope and Digital Plainmeter for five series of aerial photographs (1938, 1952, 1963, 1971 and 1977). By using the Coastal Engineering Research Center’s (1973) estimate of the volume of beach lost (0.76m3) per .09m2 change in the areal extent of the shoreline; one can derive a value of 8.44m3 in volumetric change per 1m2 change in areal extent of the shore line. The volume of cliff erosion was determined by using cliff heights actually determined in the field and topographic maps.
The total volume of material eroded from the Harbor Islands high tide line and cliff line between 1938 and 1977 was 2,034,327 m3. The total accretion of the high tide line during the same time span was 363,599m3. This amount of accretion accounts for 18 per cent of volume of material eroded.
The percentages of sediment sizes present in an average sample of drumlin till was compared to the percentage of sediment sizes in a shoreline of accretion. The drumlin till is composed of approximately 25% gravel, 20% sand, 40 to 45% silt and less than 12% clay. From analysis of sediment from the area of accretion, it was seen that 21% of the gravel sized sediment eroded was redeposited in areas of accretion. 21% of the sand sized sediment aroded was redeposited. Only 1% of the silt to clay-sized sediment was redeposited.
The major area of accretion all lie at or near the southern or southwestern extremities of the islands. “Northeasters” may cause the littorial drift to lie in a southern or southwesterly direction.
Riegler, Paul William, "An Aerial Photogrammetric Study of Erosion and Accretion Boston Harbor Islands, Massachusetts" (1981). Open Access Master's Theses. Paper 2063.