STORM INFLUENCE ON SHORELINE CHANGE: CHARLESTOWN, RHODE ISLAND

Charlestown-Green Hill Beach, Rhode Island is a microtidal barrier on a south-facing shoreline. We used a long-term beach profile record (24 years of weekly measurements at profile CHA-EZ) to test the usefulness of the Dolan and Davis (1992) extratropical storm classification system. The D&D system is a function of the square of significant wave height and storm duration. A storm record for the southeastern New England region was compiled that identified 296 extratropical storms that occurred between 1956-2001; 166 occurred during the long-term profile for CHA-EZ (1977-present).

Class I storms changed only the seaward section of the berm and recovery occurred within a few tidal cycles. Class II storms changes also 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 also altered the foredune, ramp and berm and recovery ranged from months to years. The Blizzard of December 1992 was the only Class V storm recorded; the berm was removed and significant washover sand was deposited on the backbarrier flat.

Too few storms of higher intensities occurred during the time of the long-term profile record to make an absolute determination of response and recovery. While storms such as the Blizzard of February 1978 (Class IV) and the Blizzard of December 1992 (Class V) caused significant sediment loss and foredune retreat, a large sediment volume gain was observed on the foredune and ramp during the Perfect Storm of October 1991 (Class IV). An absolute gain in sediment volume also was measured for an additional three Class IV storms. Storms of smaller intensity generally caused minor changes, but sediment volume loss equal to the Blizzard of February 1978 was measured after two Class I storms and one Class II storm.

Storm intensities determined using the D&D system alone could not be used to determine the magnitude of sediment volume loss or redistribution. Tidal phase, storm track and time between storms remain important controlling factors.