INVESTIGATING THE MORPHOLOGICAL EVOLUTION AND CLOSURE DYNAMICS OF THE RELICT CABBAGE INLET, MASONBORO ISLAND, N.C

Analysis of surface geomorphology and subsurface stratigraphy at former inlet sites can be used to improve understanding of inlet dynamics and to develop qualitative models that may predict the future behavior of active or future inlets. This study examined Cabbage Inlet, a closed inlet, located on an undeveloped, wave-dominated barrier island in southeast North Carolina. The purpose was to establish a chronology of key stages in the inlet’s evolution and determine if the behavior is consistent with the general, inlet life-cycle models (i.e. counter-clockwise rotation, clockwise rotation, or no rotation) as recently described by Seminack (2016). According to historical charts and anecdotal reports, Cabbage Inlet was active from 1737 to 1783 and closed following a large storm. Relict inlet features, including an extensive flood-tidal delta and recurved ridges are visible in aerial photographs and were used to constrain the location of ground-penetrating radar (GPR) surveys and compressed high-intensity radar pulse (CHIRP) tracklines. GPR indicated three separate breaches within the former inlet complex which included one main ebb channel with a width of 84 m. Stratigraphic analysis of channel-fill suggests that the main ebb channel prograded roughly 21 m to the north before infilling conformably. CHIRP surveys, conducted in the adjacent nearshore, detected an ebb channel at 100 m offshore. At this location, the ebb channel was 160 m wide and filled conformably. Based on the preliminary results, given the multiple breaches and northerly migration of the ebb channels, the clockwise rotation model appears to most closely relate to Cabbage Inlet’s behavior prior to closure. Given current sea level rise projections and the potential for increased storm frequency, inlets and breaches are likely to become increasingly common on barrier island shorelines. Because these shorelines are often highly developed, tidal inlet evolution models are needed to predict the behavior of these features. This study demonstrates that examination of surface and subsurface features of a closed inlet can be used to verify existing tidal inlet evolution models thus supporting a generalized model of inlet behavior that may have broad geographic applicability.