Natural and anthropogenic-induced changes in a tidal inlet: Morphological evolution of Oregon Inlet

Abstract

Natural processes driving the dynamics of tidal inlets have been studied in length, however, as human influence in the coastal environment persists, there is a need to comprehend how both natural and human-induced processes drive different aspects of tidal inlet morphological evolution. An effort to understand the combined effects of natural and anthropogenic-induced processes in a tidal inlet is pursued by studying Oregon Inlet, considered one of the most dynamic inlets in the Outer Banks of North Carolina, USA. The temporal and spatial scales of the anthropogenic processes driving the morphological evolution of this tidal inlet are studied by means of remotely sensed data and in-situ observations gathered from 2005 until 2015. Effects of natural process that cannot be gathered from observations are studied via a morphological model based on Delft3D. Evolutional trends include the cyclical response of the main channel of the inlet to dredging, a 13° northward rotation of the main channel, and frequent sediment transport reversal in the southern shoulder. Simulations indicate a net sediment transport rate into the inlet of 205,000m3/yr. Tidal currents are responsible for 55% of such transport, while waves account for the remaining 45%. After a 2-year non-dredging modeling scenario, sediments from the subaqueous spit form a detached shoal in the north side of the flood delta and the main channel remains open branching into two dominant channels. Observations and model results indicate that Oregon Inlet has been in a state of stable equilibrium in the past decade. Natural and human-induced processes contribute to such equilibrium. This study exemplifies the decadal behavior of a tidal inlet influenced by natural processes, infrastructure, and dredging.