RATES AND PROCESSES OF SHORELINE CHANGE AT FORT PULASKI NATIONAL MONUMENT, GEORGIA

Fort Pulaski is a Civil War era fort located on Cockspur, GA adjacent to the Savannah River shipping channel. The National Park Service is concerned with natural processes and anthropogenic impacts (i.e. port maintenance activities) possibly threatening natural and cultural resources. The objective of this study is to provide relevant information to Fort Pulaski staff so they may effectively devise a management plan and comment on a proposal to deepen the shipping channel.

In order to assess shoreline change rates encompassing 1852-2005, we developed an archive of visual imagery. Major features examined include the island shoreline and a large, dynamic oyster shell ridge located along the north channel of the Savannah River. These features were digitized in a GIS to determine shoreline change rates for time periods that bracket channel deepenings and average rates for the entire period of historic data. The oyster shell ridge was surveyed with a GPS biweekly to analyze short-term change in length, width, distance from cultural resources, and progradation rate in order to document the ridge's history and predict its future behavior.

Cockspur Island tripled in length from 1852 to 1905 due to jetty emplacement along the north shore in 1896 and dredge spoil deposition until 1942. Shoreline change rates varied from +0.7 to +3.5 m/yr prior to the first major channel deepening event in 1929. Annual rates of change from 1942 to 2004 range from -1.8 to +0.9 m/yr for the entire north shore, and -1.1 to +0.7 m/yr along the unstablized shoreline adjacent to the Fort. Long-term mean shoreline change along the southern shoreline ranges between -0.3 to +0.4 m/yr, indicating a dynamic stability. From 1852 to 2005 the northern and southern portions of the eastern shoreline have experienced substantial accretion (at rates up to +7.5 m/yr), whereas the central segment has accreted more slowly (+1.7 m/yr). The oyster shell ridge along the north shore, sourced from an adjacent manmade island created in the late 1800's, was first observed to be migrating in 1970 imagery. Oyster ridge migration onshore is occurring at rates of +2.5 m/yr and alongshore at a rate of +41.7 m/yr for the period 1982-2004. At present rates of migration, the oyster ridge will extend the length of the unarmored shoreline adjacent to the Fort in approximately seven years.