The main tidal channel in the central portion of the harbor was relatively stable for 54 years (1938-1992); after which a combination of a migrating flood-tidal delta and expanding intertidal areas restricted flow causing the channel to shift position. Migration of the flood-tidal delta was caused by increased sediment supply and tidal current velocities after the 1987 inlet formation. Expansion of the intertidal zone has two major components. First, is a 34% decrease (65,100 m2) in the surface area of Tern Island, in the central harbor from 1989 to 2007. Second, is the fate of a minimum of 139,270 m3 of dredged material placed on and around the island from 1987 to 1998. This volume of material was sufficient to transform a predominantly sub-tidal area into an intertidal area and redirect ebb-tidal flow.
The tidal channel migration increased the volume of water directly adjacent to the backbarrier shoreline. The expanding intertidal zone in the area caused a restriction which increased the hydraulic head during ebb-tidal flow. These are two of the conditions that increase the potential for new inlet formation through low-lying barrier islands and spits and contributed to the inlet formation of 2007.