Morphology and hydrodynamics of wave-cut gullies

Wave-cut gullies are sub-triangular incisions common along deteriorating marsh scarps. Wave gullies may be equispaced to quasi-equispaced and enlarge in time, incising the marsh boundary. A high resolution survey is provided for ten wave gullies formed along the chenier plain of the Rockefeller Wildlife Refuge, Louisiana, USA. The measurements capture the morphologic character, evolution, and erosion rates of wave-cut gullies over a two month period. The data relate changes in morphology to geometric factors and shoreline retreat. Finally, the first analysis of wave data measured by acoustic Doppler velocity profilers is presented to show how propagating waves are transformed inside a wave-cut gully in order to describe the processes leading to their formation. Results show that waves of intermediate period (4–6 s) yield very strong swash currents that hit the gully head, detaching marsh substrate and triggering headward erosion. A conceptual model of wave gully evolution is presented as an explanation for this non-uniform, episodic shoreline erosion.

Research highlights
► A previously unstudied mechanism for salt marsh boundary erosion via wave-cut gullies.
► Convergent gully geometry magnifies wave energy resulting in high run-up velocity.
► Gully incision into the marsh is 3–5 times the overall boundary erosion.
► First investigation of the hydrodynamics within wave-cut gullies.