IMPACTS OF INLET MIGRATION ON BARRIER ISLAND PLANFORM AND OCEANFRONT CHANGES: NEW TOPSAIL INLET, NC

New Topsail Inlet, located 40 km northeast of Wilmington, NC, separates Topsail Island, a developed barrier from Hutaff Island, an undeveloped barrier. Since the inlet opened in early 18th century the inlet has migrated ~10 km to the southwest. A GIS based analysis of 15 sets of historic aerial photographs (1938-2003) provided data on migration rates, the inlet's morphologic changes and the periodicity of ebb delta breaching episodes that impact migration. The inlet's minimum width (IMW) has varied considerably, from a minimum of 324m in 1956 to a maximum of 645m in 1999; the mean IMW was 487m. Since 1938, migration rates have averaged 26 m/yr and varied from a high of 95m/yr (1945-49), to a low of 11m/yr (1956-62). During the past decade the migration rates have averaged 28m/yr.

The migration of the inlet has promoted the development of an expanding erosion hot spot along southern portion of Topsail Beach. During the 1950-1970 development phase, structures were constructed along the primary dune ridge paralleling the recurved portion of the southwesterly extending spit. During the 1960's, the southern 2.0 km of the barrier assumed a pronounced bulbous shape that was a by-product of spit accretion and updrift bar welding associated with the cyclical reorientation of the ebb channel. Chronic erosion that has characterized the southern 3.0 km of oceanfront stemmed in part from the realignment of the trailing shoreline's planform as the inlet migrated. Oceanfront erosion rates between 1974 and 1986 ranged from 1.6 - 5.2 m/yr reflecting increased migration rates. The chronic erosion has been a major management problem and due to the prohibition of shoreline hardening structures the only viable option available for erosion mitigation is beach nourishment. However, the success of the recently proposed major re-nourishment project is likely to be short considering the inlet's history and the poor performance of previous projects.