Ground Penetrating Radar (GPR) is a non-invasive shallow geophysical
technique now being used to investigate barrier island sedimentation
and patterns of geomorphologic evolution. The technique is also
being used to investigate barrier island aquifers. Previous studies,
including in Hatteras Island, North Carolina have demonstrated
heterogeneities in aquifer dynamics based on the distribution of
inter-dune recharge areas, coastal strata geometries, and
permeability differences within sedimentary units.
This research is being carried out on a barrier island along the
coast of eastern Virginia at NASA’s Wallops Island Flight Facility
(WIFF). Here we have collected both shore parallel and shore normal
profiles along established transect sites in order to investigate
both patterns of sedimentation as well as the extent of the
freshwater lens and the position of the salt-water interface.
Although analysis and post-processing of more than 60 transect sites
is ongoing, investigations have revealed significant heterogeneities
in the response of GPR signals detected with Mala’s X3M GPR (250,
and 500 Mhz shielded antennas). Ground truthing in the form of
excavated pits, shallow monitoring wells outfitted with data
recorders, and field surveys at low tide are enabling qualitative
and quantitative assessment of initial returns. Although analysis is
incomplete, similar to studies elsewhere, it appears that
along-shore variations in morphologic features of beach/back-beach
areas strongly control the position of the saltwater interface and
the discharge points of the freshwater surface aquifer. This study
shows that the concept of a freshwater lens needs to be re-evaluated
for barrier islands.
Preliminary investigation of a barrier
island beach aquifer at Wallops Island, Virginia using ground
penetrating radar