ABSTRACT

Hein, C.J.; Fitzsimons, G.G., FitzGerald, D.M., and Fallon, A.R., 2016. Records of Migration and Ebb-Delta Breaching at Historic and Ancient Tidal Inlets along a River-Fed Paraglacial Barrier Island. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 228-232. Coconut Creek (Florida), ISSN 0749-0208.

Tidal inlets link backbarrier environments to the coastal ocean and play a dominant role in both longshore and cross-shore sediment transport. Additionally, inlet-fill sequences comprise up to 50% of barrier lithosomes in wave-dominated settings. This study uses historic records to investigate centennial-scale cycles of inlet dynamics and barrier shoreline adjustment at Merrimack River Inlet (Plum Island, Gulf of Maine). Geophysical and sedimentological data reveal geometric and stratigraphic signatures of these recent changes, and allow for comparison to similar records preserved within a nearby 3600-year-old inlet-fill sequence. Driven by processes of longshore transport, spit elongation and ebb-delta breaching, the Merrimack River Inlet once actively migrated across a 2.5-km long section of Plum Island. An ebb-delta breaching event in the mid-1800s caused abandonment of the former inlet channel and the onshore welding of a large sand bar, which developed into the northern 1.5 km of the island. The inlet stabilized by jetties in the late 1800s. Ground-penetrating radar profiles and sediment cores across this former inlet channel capture the details of changes prior to breaching, including the seaward deflection of the otherwise southerly and landward-migrating channel, in response to onshore bar migration and welding. Similar details of inlet migration, bar welding, and ebb-delta breaching are observed stratigraphic records of an ancient inlet in central PI, located 7 km to the south. Comparison between the ancient and historical sequences provides clues to decipher the complex inlet dynamics preserved in the stratigraphic and sedimentologic record.

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