Background

This proposed investigation is part of a cooperative program with the U. S. Geological Survey Coastal and Marine Geology Program (USGS) and regional academic and public agencies to map the Quaternary geologic framework of northeastern North Carolina and the adjacent continental shelf extending approximately 5 nautical miles offshore.  The proposed work falls under an existing Memorandum of Understanding between the USGS and the Virginia Institute of Marine Science (VIMS).

The underlying Quaternary geology is an important controlling factor in this coastal system and plays a role in coastal and estuarine shoreline erosion, sand resources, storm impacts, sea level change, water resources, and habitat availability.  The physical processes and mechanisms by which underlying geology influences shoreline erosion, however, are poorly understood.  Particularly in the nearshore where data are sparse and observations are extremely difficult.  We believe shoreline behavior is closely linked to the underlying geology in the surf zone but before this relationship can be modeled and cast in a format most useful for management and policy decisions we must define these mechanisms more clearly.  Toward this goal, VIMS will continue its examination of the nearshore, defined here as the region between the 10-m isobath and the shoreline, thereby completing the coverage between the inner-shelf and the back-barrier surveys obtained by others in the NC cooperative program.

Proposed Work and Budget Justification

An extensive nearshore coring effort, delayed from 2004, will be undertaken in spring/summer 2005 to 1) groundtruth seismic reflection data collected over the previous two years, 2) test the hypothesis proposed in (McNinch, 2004) regarding a difference in ravinement-surface lithology between regions with outcrop/shore-oblique sandbars and the surrounding shoreface, 3) address potential relationships of sorted bedforms to framework geology in the nearshore, 4) collect pore water to assess groundwater discharge in the surf zone, and 5) obtain datable material to assist linking the continental shelf framework geology with the beach. Through collaborative support from the Army Research Office and the NCGS a nearshore survey, including swath bathymetry and sub-bottom chirp profiles, will be conducted from Oregon Inlet to Cape Hatteras. This reconnaissance survey will entail six shore-parallel track lines run between the bar (2-3 m depths) and the 10-12 m isobath. Smaller areas will be surveyed with greater coverage if the reconnaissance reveals features of interest (e.g. paleo-channels, shore-oblique bars). Lastly, funds are requested to support travel and logistics for field experiments using a mobile sandbar and swash imaging radar (BASIR), developed in 2002-2003 (McNinch, in review). BASIR experiments will focus on mapping bar and swash evolution/maintenance through numerous weather/wave events. Measuring the position, morphology, and migration of sandbars will enable us to address questions of sediment exchange between the beach and nearshore, and ultimately identify possible alongshore differences in sediment exchange mechanisms that may exist between regions with exposed relict substrates and shore-oblique sandbars and those with more ‘textbook’, planar shorefaces.

Funds are also requested to support vessel costs and travel associated with the nearshore coring and geophysical surveys as well as coring supplies (e.g. core barrels, core catchers, X-ray supplies) and equipment. Only partial salary support is requested for the principal investigator and field technicians; a full year of support for a graduate student (stipend and tuition) is needed.