Date of Award
Master of Science in Geology
John J. Fisher
For shore protection analysis, the collection of data on coastal erosion by extensive field measurements is expensive and is complicated by the problem of extrapolating results obtained from short-term field observations into long-term erosional trends. On the other hand, surveys utilizing quantitative aerial photogrammetric techniques are less expensive than field surveys and accuracy on the order of three meters is possible. Aerial photographs show the location of the beach and features adjacent to the beach. These features can be used as stable locations to reference these shoreline and duneline photogrammetric measurements.
Photogrammetric measurements of the distance from a stable reference location to the dune and high tide lines were made at 300 m. (1000 ft.) intervals along the Rhode Island shoreline on four sets of aerial photographs taken between 1939 and 1972. These measurements were converted to ground distances by scale determination using ground control surveys and, subsequently, compared in order to determine shoreline changes over the study period. Shoreline changes were determined for the 11-year average time intervals among the four sets of aerial photographs and also, for the entire 33-year study period. Mean annual amounts of change were also computed for each time interval and for the entire study period. The long-term trend of shoreline change was generally erosional, averaging 0.2 m./yr. (0.7 ft./yr.), but within shorter term (11-year) time intervals, considerable variation from this trend occurred. Locally, headlands or barrier beaches, on a shorter time basis, eroded or even accreted up to 2.0 m./yr., but in general, headlands and barriers both eroded an average of 20 cm//yr. or about 6-7 m. over the 33 year study period.
Contrary to a model of a submerging shoreline with headland erosion and barrier accretion, the entire Rhode Island shoreline appears to be eroding. Locally, sea level rise has averaged 0.3 cm./yr. over the past 40 years, or accountable for about 15 percent of the vertical component of average annual shoreline retreat for Rhode Island.
Shoreline readjustment on an offshore profile of equilibrium according to the Bruun model, is by deposition equal to the rate of sea level rise. On a submerging shoreline, beach erosion occurs if no other sediment source is available, as in the case of the Rhode Island shore. With the above rate of sea level rise, the potential sediment loss from the Rhode Island beaches to maintain equilibrium is 1500 times greater than the actual loss of material along this shoreline as determined in this study.
Regan, Donald Robert, "An Aerial Photogrammetric Survey of Long-Term Shoreline Changes, Southern Rhode Island Coast" (1976). Open Access Master's Theses. Paper 2066.