J.L. Hench et al. / Continental Shelf Research 22 (2002) 26152631
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the straits of dynamically long inlets or within the
of buoyant plumes, and therefore neglected the
center region of dynamically wide inlets. For
barotropic tidal dynamics described here.
dynamically short inlets, and near the ends of
The classification diagram (Fig. 7) should be
dynamically long inlets, the streamwise and
useful in comparing the relative dynamics of
centrifugal accelerations are part of the first-order
different inlet systems. However, as with all
dynamics and need to be retained.
classification schemes, there are a number of
Our analysis of lateral momentum balances and
limitations. The morphology at some natural inlets
comparison of natural inlet parameter values has
may be so convoluted that assigning representative
shown a range of different dynamics that can
lengths and widths may be difficult. Other inlets
occur. We have proposed a two parameter
may have geometries so laterally asymmetric that
classification scheme for tidal inlets and identified
they behave more like a river-bend than the
four distinct inlet types:
opposing headland conceptual model described
Type 1. Dynamically short-narrow inlet (small
here. Inlets with river mouth morphologies do not
L and small W ), where a cyclostrophic lateral
fit well on the diagram since their dynamic lengths
balance dominates the entire inlet straits.
are so long, but would be classified as either type 2
Type 2. Dynamically long-narrow inlet (large L
or 4. Inlet morphology may change over time due
and small W ), where at both ends of the inlet a
to natural erosion and deposition, or anthropo-
cyclostrophic lateral balance dominates across the
genic activities such as dredging. It is conceivable
entire width, but relaxes to a geostrophic balance
that such morphological changes could signifi-
within the inlet straits.
cantly modify circulation patterns and dynamical
Type 3. Dynamically short-wide inlet (small L
balances to the extent that the inlet classification
and large W ), where a cyclostrophic lateral
could shift or even change altogether.
For simplicity we have only examined tidal
balance dominates close to the headlands and
forcing and simple inlet geometries but real inlet
extends along the entire length of the inlet.
circulation may have significant additional effects
However, there is a center region along the entire
from: radiation stress and Stokes drift from wind
inlet length where the lateral balance is geos-
waves, direct and remote wind forcing, phase
trophic.
Type 4. Dynamically long-wide inlet (large L
differences in offshore tidal forcing, baroclinicity,
and large W ), where a cyclostrophic lateral
steep bottom topography and irregular shoreline
geometry. Circulation changes over a spring-neap
balance dominates only immediately adjacent to
cycle may also affect inlet classification as Jay and
the four inlet headland corners, and a geostrophic
Smith (1988) showed in their estuarine classifica-
balance exists everywhere else.
tion scheme. We have conducted additional model
The idealized inlets analyzed here (IIV) are
runs (not shown) with increased forcing ampli-
archetypal examples for the classification. Estuar-
tudes and found that the two geometrically wide
ine systems are highly spatially variable, and thus
inlets in this study (III and IV) can change from
multiple classification schemes may be needed for
dynamically wide to dynamically narrow inlets
different regions (Jay et al., 2000). Our proposed
with sufficient forcing and accompanying increase
classification scheme is applicable to the inlet
in Us:
straits and the region in the immediate vicinity of
inlet headlands. The scheme fits spatially between
Despite the simplifications the present analysis
previous estuarine classifications (more appropri-
provides a rational framework with which to
ate upstream of an inlet) and buoyant plume
compare different inlet systems, and to put new
classifications (more appropriate offshore of an
studies in the context of previous work. For a
inlet). W in our scheme is similar in spirit to the
classification scheme to be useful, it should be
constructed in terms of readily observable para-
mouth Kelvin number (ratio of baroclinic radius
meters, yet it must still retain the essential physics.
of deformation to river mouth width) of Garvine
The proposed scheme succeeds in this regard, and
(1987), but the underlying dynamics are different.
to our knowledge is the first classification scheme
Garvine's work centered on sub-tidal propagation
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