CALIBRATING ESTUARINE SEA-LEVEL BASE ELEVATIONS FOR COMBINING GEOSPATIAL AND SEA LEVEL MODELS FOR THE TIDEWATER REGION OF THE CHESAPEAKE BAY

The Chesapeake Bay and its regional network of tidal tributaries is experiencing a mean rate of relative sea-level rise twice that of the global rate of 1.7 mm/yr. In order to more accurately predict the geographic impact that this accelerated rate will have on the landscape, it is important to understand the local geologic history. Our objective is to accurately determine the relative elevation of subsurface coring sites, incorporating digital terrain models with geophysical surveys as well as paleo- and future sea-level models. We aim to produce a methodology to accurately model past and future landscape modification through sea-level change.

The study site on the Potomac River in Westmoreland County, Virginia is a tidally influenced, oligo- to mesohaline, partially mixed estuary roughly 90 km upstream of its mouth at the Chesapeake Bay. Single beam sonar (200 KHz) tracks were run in tightly spaced (~12 m) grid patterns surrounding four long core sites in order to accurately model the subsurface terrain. Following calibrating the GPS receiver to National Geodetic Survey benchmarks located near Westmoreland State Park, the bathymetry data were projected from the North American Vertical Datum of 1988 into a local mean sea-level datum. The newly projected subsurface models were then utilized to calibrate smaller scale, regionally encompassing digital terrain models (> 10 m resolution) to more precise water depths for use in sea-level projections.

Future sea-level trends were estimated from various National Oceanic and Atmospheric Administration (NOAA) and US Army Corps of Engineers (USACE) projections and incorporated into terrain model calculations. High resolution (< 1 meter) LiDAR digital elevation models, also projected into a local mean sea-level datum, were mosaicked with the subsurface terrain models to model future sea-level inundation scenarios based on NOAA and USACE projections. These results will eventually be used to vertically calibrate seismic surveys such as CHIRP and sedimentary analyses of long core samples to local mean sea-level.