HR: 14:00h
AN: H13C-03    [Abstracts]
TI: Resistivity Surveys of Seasonal Groundwater Salinity Variations Along Forest-Marsh Transects at North Inlet, South Carolina.
AU: * Carter, E S
EM: ecarter@geol.sc.edu
AF: Department Of Geological Sciences, University of South Carolina 701 Sumter St., EWSC 617, Columbia, SC 29208 United States
AU: White, S
EM: swhite@geol.sc.edu
AF: Department Of Geological Sciences, University of South Carolina 701 Sumter St., EWSC 617, Columbia, SC 29208 United States
AB: Salinity boundary changes each season in a saltwater marsh will help determine if rising and falling tides over a one-year period are threatening groundwater. Monthly resistivity measurements of Crabhaul Creek, a finger marsh basin in North Inlet, South Carolina, were made using Super MiniRes with 530 Vpp at 10 mA. Previous studies show a salinity gradient that disappears and returns to the same area in a one-year period. The goal of this project was to measure the seasonal changes of the salinity in this basin. Three transects across Crabhaul creek are used to form a 2-D interpretation of the salinity variations along the creek and their changes over two seasons, winter and spring. All transects cross the same zones of saline tolerant vegetation. One transect crosses the basin and Crabhaul creek, a second transect upstream extends through the basin where there exists a gradient but there is no definition of the tidal creek, and a third transect 100 meters between the two. A gradient array with a target depth of 3 meters and M-N spacing of 1 meter was used to profile each transect at the end of the month. A dipole-dipole array with A-B spacing of one meter and a target depth of three meters was done every 2-3 months to image the subsurface for any inconsistencies occurring seasonally aside from the salinity gradient. A finite difference inversion of each dipole-dipole survey was made with DCIP2D Version 3.2 developed by UBC - Geophysical Inversion Facility. The first meter of salinity variations is dominated by evapotranspiration and surface water however below this boundary there is a distinct decrease of resistivity from 10 ohm-meters to 2 ohm-meters on the eastern side of each transect corresponding to an increase in salinity. The resistivity remains constant from the upland forest to the tidal creek consistent with fresh water upwelling from the forest. The resistivity drops at the creek and remains low eastward through the basin and into the forested barrier island. Seasonal movement of this gradient will help determine seasonal groundwater flux for this forest-marsh boundary.
DE: 0600 ELECTROMAGNETICS
DE: 0694 Instrumentation and techniques
DE: 0925 Magnetic and electrical methods
DE: 1829 Groundwater hydrology
DE: 4227 Diurnal, seasonal, and annual cycles
SC: Hydrology [H]
MN: 2005 Joint Assembly