What Mechanisms Trigger Coastal Flow Slides?

Authors: Patrick Barrineau*, Coastal Science & Engineering, Inc.
Topics: Coastal and Marine, Hazards, Risks, and Disasters, Geomorphology
Keywords: geomorphology, beaches, inlets
Session Type: Virtual Paper
Day: 4/9/2021
Start / End Time: 4:40 PM / 5:55 PM
Room: Virtual 41
Presentation File: No File Uploaded


Some beaches regularly experience a rapid decrease in volume due to massive movements of sand from the dry beach into deeper water. These events visually resemble landslides, but are mostly submerged and generally located along steep river or tidal channels. On several occasions in recent years, a slide has formed at Seabrook Island (SC); there have been five events since July 2016. Surveys of a January 2017 event show the slide displaced ~35,000 cy into deep water (35–55 ft depths) along North Edisto River Inlet. This volume is comparable to hillside-scale landslides observed in mountainous regions like the Blue Ridge.

The Seabrook slide is consistently located along a marginal flood channel of North Edisto River Inlet, just below a revetment. In this particular location, erosion of the dry beach could cause undermining. Historical charts show a small inlet along this portion of the beach as recently as ~1920. Reviews of available data suggest exceptional rainfall events and spring tide levels may coincide with observed slide events.

This study analyzes available data to identify mechanisms affecting slides at Seabrook Island (SC). A combination of excessive rainfall, spring tides, and sediment variations all appear to affect these events. Because of the unpredictability of these events, and the dynamic nature of the inlet channel adjacent to this portion of the island, it is difficult to observe events in situ and identify specific mechanisms triggering slides. Providing an excess of beach sand may help maintain a shallower shoreface slope and mitigate future slides.

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