Date of Award

2002

Degree Type

Thesis

Degree Name

Master of Science in Geosciences

Department

Geosciences

First Advisor

Jon Boothroyd

Abstract

This study examines how the South Shore of Rhode Island responds to storms. A storm record for the region was created and storm intensities were determined using the Dolan and Davis Classification system (1992). The study is divided into two sections. The first part determines changes that occur in volume and beach shape with respect to extratropical storms using a 24-year record of weekly beach profiles. The second part looks at the impact of tropical and extratropical storm frequency and intensity on shoreline change using aerial photographs obtained over a 60-year time span.

Part one examines profile response to particular storms in the data set. This study identifies 296 extratropical storms that occurred between 1956-2001. Of these storms 166 occurred during the long-term beach profile record at CHA-EZ on Charlestown Beach (1977-present). The CHA-EZ long-term beach profile record does not contain the temporal resolution needed to identify the magnitude of change caused by variations in storm intensity. The angle of the beach face was measured for each profile that was taken before or after an extratropical storm. It was found that there is too much variation in post-storm survey dates (1-14 days) to identify a shape effect on post-storm sediment volume for a particular storm intensity.

Both profile locations, CHA-EZ and SK-TB, showed a relationship between storm Class and the region of beach affected. For Class I storms, changes were limited to the seaward section of the berm; and recovery was immediate. For Class II storms, changes were limited to the berm; recovery ranged from one to two weeks. Class III storms altered the foredune, ramp, and berm; recovery ranged from weeks to months. Class IV storms altered the foredune, ramp, and berm; recovery ranged from months to years. The Blizzard of December 1992 was the only Class V storm to occur during the long-term beach profile record and change was observed along the entire profile length.

There was limited comparison between shape and volume between the two locations. When the beach face had the same slope, volume loss was identical between locations. When the slope of the beach face was greater, that location tended to have a larger volume loss.

Part two focuses on the interpretation of historical shoreline positions. The historical shoreline record was updated from 1939 to 1985 to 1999. Shoreline change rates based on vertical aerial photographs obtained at six-year to twelve-year intervals show significant variation from a -0.40 m·yr-1 average. The highest shoreline losses occurred between 1951-1963.

The Rhode Island shoreline experiences reversals from erosion to accretion as the storm climate changes. These patterns need to be accounted for in construction setbacks. The late 1950s and early 1960s was a time of more frequent, higher-intensity storms than any other time in the 45-year storm record. During this time period, shoreline changes as high as -60.9 to -70.8 meters were measured on the Misquamicut Barrier and the Charlestown/Green Hill Barrier. Changes of this magnitude are greater than current construction setbacks set by the RI Coastal Resources Management Plan in some areas. Current construction setbacks should, therefore, be considered to be a minimum requirement. If the construction setbacks were reduced they would not be adequate during a period of storminess like that of the early 1960s.

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