Radar Inlet Observing System (RIOS) at Oregon Inlet, NC: Sediment transport pathways at a wave-dominated tidal inlet

摘要

Challenges to maintaining safe, navigable tidal inlets across the U.S. while minimizing deleterious effects to adjacent property and the environment, can be daunting, and often encompasses many government agencies and stakeholders with varying interests and missions. When this maintenance requires dredging of the navigation channels, the U.S. Army Corps of Engineers is typically the responsible agency, while the U.S. Coast Guard dictates placement of the various aids to navigation. These missions alone (and there are many others) are difficult to accomplish on a continual, up-to-date basis across many of our shallow, wave-dominated tidal inlets because the position of the channels and associated shoals can be incredibly dynamic, and the volume of infilling sediment can stretch available resources. The Radar Inlet Observing System (RIOS), introduced here, is designed to provide near real-time navigation and engineering support at tidal inlets over extended, hourly time periods, and to do so cost-effectively in remote locations. Specific RIOS products include shoal migration and encroachment into navigation channels, wave conditions in the navigation channel, and sediment transport pathways over event and seasonal time scales. An eight-month RIOS deployment at Oregon Inlet, North Carolina, from August 2016 to April 2017 indicates: 1) Three dominant pathways of sand-sized sediment transport expressed by shallow, migrating bedforms around Oregon Inlet; 2) Asymmetry in alongshore input largely from Bodie Island which is consistent with substantial growth in the Bodie Island recurved spit and persistent narrowing of the inlet channel width since 1962; 3) Importance of ebb flows, particularly during strong sub-tidal events, in exporting sediment seaward to the ebb shoals along the flank of the ebb channel; and 4) Substantial recirculation of sediment around a large, southern ebb shoal and back into the inlet sediment budget with a smaller amount ultimately reaching Pea Island and completing the inlet bypassing.