Event Timing and Sequence in Coastal Shoreline Erosion: Hurricanes Bertha and Fran and the Neuse Estuary

Abstract

The magnitude of storm events is only one determinant of their geomorphic effects. The timing and sequence of storms and the initial conditions of the shoreline also exert important controls on the geomorphic impacts. Two category three hurricanes struck coastal North Carolina during the summer of 1996, Bertha in July and Fran in September, with similar wind velocities and storm surges in the Neuse River estuary. There was little evidence of wave attack on the faces of shoreline bluffs along the Neuse estuary following Bertha, but the same bluffs experienced retreat of three to 12 meters following Fran. The dominant long-term process of slope retreat is mass wasting. Bertha removed toeslope sedimentary aprons and woody debris, which absorbed the majority of the wave energy. Thus, when the second storm arrived, waves came into direct contact with the unconsolidated bluffs and initiated slope failures by undermining the lower bluffs. The effects of the hurricanes illustrate the importance of event sequencing and initial conditions rather than energy or magnitude in determining shoreline response, and the important interactions between slope (mass wasting) and coastal processes in causing bluff retreat along the Neuse.