January 13, 2004
14:38
WSPC/101-CEJ
00092
Recent Developments in the Geomorphic Investigation
567
inlets that undergo cyclic changes. Conversely, some models have been established
using very limit data sets and thus are too narrow in scope or insufficiently accu-
rate to supply the quantitative information needed to solve problems for individual
inlets. However, in recent years new technology has furnished the means to gather
highly detailed and accurate topographic, bathymetric, hydraulic, and geophysical
data during short time frames and over large geographical areas. These new instru-
ments and means of compilation and analysis are producing far greater temporal
and spatial predictability than has previously been possible. Armed with this new
technology, scientists are poised to address long-standing coastal engineering prob-
lems, such as rates of bedload transport in tidal channels, modes of inlet sediment
bypassing, processes of channel shoaling and migration, among many others. It is
the purpose of this paper to describe how recent technology is advancing our knowl-
edge of tidal inlet systems, including Ground-Penetrating Radar (GPR), bathymet-
ric LIDAR, topographic LIDAR, shallow seismic surveys, multibeam bathymetric
surveys, side-scan surveys, ADCP, and GIS manipulations.
2. Technological Advances
2.1. Ground penetrating radar
Ground-Penetrating Radar is a high-resolution geophysical technique, which is be-
ing successfully used in stratigraphic research of sedimentary environments including
those associated with barrier island and tidal inlet settings boundaries (FitzGerald
et al., 1994; Jol et al., 1996; van Heteren et al., 1998). The instrument produces an
"x-ray" view of the subsurface and provides a means of identifying and delineating
sedimentary layers, bedrock horizons, the groundwater table, and buried structures.
The system transmits electromagnetic (EM) waves into the ground having a fre-
quency range of 10 MHz to 2000 MHz. The behavior of the EM waves and their
depth of penetration are controlled by the electric conductivity, magnetic perme-
ability, and dielectric permittivity of the sediments, which in turn is a function of
moisture content, mineralogy, particle size, and salt water. As the instrument is
dragged along the ground, EM waves penetrate the ground and energy is reflected
back to the transreceiver differentially due to changes in the conductivity of the
sediment. Sedimentary layers and other features in the subsurface are represented
in the GPR records by reflectors that are interpreted based on their intensity, con-
figuration, frequency, and continuity.
Ground-Penetrating Radar has been used to locate former tidal inlets as well as
analyze the migrational patterns of existing inlets (FitzGerald et al., 2001; FitzGer-
ald et al., 2002; Buynevich et al. 2003). Along the New England barrier coast the
identification of paleo-tidal inlets has helped to assess the susceptibility of barrier
systems to future breaching. For example, GPR profiles taken along the 8-km long
Duxbury barrier on the Massachusetts south shore revealed the position of 18 former
tidal inlets. The existence of these inlets not only demonstrates the vulnerability of
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