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44947-AC8
How Deep is Wave Ravinement? Moving Beyond the Break-In-Slope Proxy

Antonio Rodriguez, University of North Carolina (Chapel Hill)

The depth of wave ravinement, which is the depth where erosional wave processes can no longer rework coastal lithosomes, is assumed to equal the depth of the shoreline break-in-slope; however, this has never been rigorously examined. We are testing this by directly measuring ravinement depth in a variety of estuarine focus areas along the Newport River Estuary and Bogue Sound, North Carolina, and comparing these direct measurements to shoreline break-in-slope depths. Core transects were collected along fringing marshes and high-resolution surface elevation data are currently being obtained to constrain marsh accretion and erosion within the area. Fringing marsh environments are separated into 4 types based on paleodepositional, geographic, and hydrologic setting. Paleodepositional environments examined included flood-tidal delta, barrier island, wash-over fan, and bay-head delta. Subsurface geology was variable between sites. The fringing marsh deposits at the flood-tidal delta locale, for example, overlay dark gray interbedded sands and clays, interpreted as tidal couplets, whereas the fringing marsh deposits at the back-barrier site overlay a yellowish brown, parallel to cross-laminated fine-grained sand indicative of foreshore sedimentation. No marsh deposits predating the modern were present in any of the cores. Preliminary results show that variability in underlying lithology (clay versus sand) has little effect on ravinement depth, but may have a large effect on the rate of ravinement.

This project supported one undergraduate summer researcher (Emmit Keeler) and one PhD student (C. Robbin Mattheus) during year 1. The grant also helped the PI reestablish his coastal research program at the UNC. Preliminary results were presented at the 2006 National Geological Society of America meeting in Philadelphia, PA.

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