January 13, 2004
14:38
WSPC/101-CEJ
00092
D. M. Fitzgerald, G. A. Zarillo & S. Johnston
566
inlet cross section and provides almost instantaneous discharges for small and moderately
sized inlets. In a slightly different mode, ADCP technology has been used for directional
wave measurements. Finally, significant upgrades in the manipulation of information, in-
cluding Geographic Information System (GIS) and image analysis methods, have greatly
facilitated the analyses and interpretation of the field data. These advancements have pro-
vided scientists with more effective means of gathering data, testing numerical models,
and finding solutions to coastal engineering problems.
1. Introduction
Traditional geomorphic investigations of tidal inlets have attempted to produce con-
ceptual models and predictive relationships that can be applied to inlets in similar
physical settings. One successful approach in the investigation of tidal inlets has
been through regression analysis of related morphologic and hydraulic characteris-
tics. The most widely used of these relationships are Jarrett's (1976) refinement of
LeConte's (1905) and O'Brien's (1931, 1969) correlation between tidal prism and
inlet cross-sectional area, and Walton and Adam's (1976) correspondence between
tidal prism and ebb-tidal delta volume. Since these early discoveries, several other
useful predictions based on inlet tidal prism have been identified, including Shige-
mura's (1981) equilibrium throat width, Gibeaut and Davis's (1993) equilibrium
ebb-tidal delta area, and Buonaiuto and Kraus's (2003) limiting depth over the
ebb-tidal delta.
In addition to these quantitative relationships, numerous conceptual models have
been presented that aid our understanding of tidal inlet processes. For example, net
sediment transport through inlets has been inferred using a variety of data including
migration and orientation of bedforms (Boothroyd and Hubbard, 1975; Hine, 1975;
Zarillo, 1982; Zarillo, 1985; Sha, 1989; Fenster et al., 1990; FitzGerald et al., 2000,
etc.), grain size distributions (Hubbard, 1975; Sha, 1990; Fenster and FitzGerald,
1996; FitzGerald et al., 2002), velocity asymmetries (Dalrymple et al., 1978; FitzGer-
ald and Nummedal, 1983; Fry and Aubrey, 1990), and distortions of the tidal wave
(Dronkers, 1964; Boon and Byrne, 1981; Speer and Aubrey, 1985). Models of barrier
breaching and inlet formation have been proposed by Pierce (1967), FitzGerald and
Pendleton (2002) and Kraus et al. (2003). Factors affecting channel geometry and
rates of tidal inlet migration have been discussed by DeAlteris (1973), FitzGerald
and FitzGerald (1977), and Kraus (1998). Processes governing shoreline recession
and progradation have been identified at numerous inlets and are summarized in
FitzGerald (1988, 1996). The pathways and processes of inlet sediment bypassing
first recognized Bruun and Gerritsen (1959) have been further defined by FitzGerald
(1988), Kraus (2000), and FitzGerald et al. (2001). These subsequent studies have
also increased our knowledge of the cyclical pattern of channel switching and bar
development at tidal inlets.
Despite the advancements in our understanding of tidal inlets, there are still diffi-
culties in using traditional numerical and conceptual models because they are usually
based on large populations and their predictive relationships do not provide for tidal
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