J.L. Hench et al. / Continental Shelf Research 22 (2002) 26152631
2618
ax; y; t is the streamline angle (the angle between
streamwise acceleration (Figs. 2e and f). However
the positive x-axis and the local flow vector). With
on the sound side of the inlet (the ``jet'' region), the
flow is decelerating (Fig. 2e) under the influence of
this choice of coordinate system there is, by
bottom friction (Fig. 2g). In the normal direction,
definition, no normal component to the flow at
the rotary acceleration (Fig. 2h) is small except in
any point. Therefore the Coriolis term is zero in
the s-equation, as is the bottom friction term in the
the center of the transient eddies (Fig. 2a). The
n-equation. Moreover, the advective acceleration
primary lateral balance within the entire inlet
straits is between the centrifugal acceleration and
terms collapse to a single term in each equation;
streamwise in the s-equation and centrifugal in the
the normal direction pressure gradient (Figs. 2i
n-equation. The horizontal diffusion/dispersion
and j). Coriolis is strongest within the inlet straits
where the flow speeds are largest (Fig. 2k), but is
terms were generally much smaller than the other
overwhelmed by the centrifugal acceleration.
terms, and are omitted from Eqs. (4) and (5), as
well as the discussion below. Results are presented
3.2. Idealized inlet II
in terms of momentum fluxes (obtained by multi-
plying each term by the total water column) to
Inlet II has the same width as inlet I but is
provide a more physically intuitive picture of the
2.5 km longer. The local accelerations are small
force balances.
(Figs. 3d and h). In the streamwise direction, there
are two distinct momentum balance zones, but
they are different than for inlet I. Immediately
3. Momentum balances
offshore from the inlet the primary balance is
between the streamwise pressure gradient and the
Although inlet momentum balances change
streamwise acceleration (Figs. 3e and f). In the
dramatically over a tidal cycle, previous results
inlet straits, however, the balance is between the
(Hench and Luettich, in review) have shown that
pressure gradient and bottom friction (Figs. 3f and
the dominant balances for the majority of the time
g). There are two small flow separation areas in the
are quite similar to what is found during maximum
lee of the inlet headlands where adverse pressure
flood and maximum ebb. Here we focus on a single
gradients (Fig. 3f) are balanced by streamwise
tidal phase, maximum flood, to explore the effects
deceleration (Fig. 3e). The normal direction bal-
of different inlet configurations. Maximum flood
ances exhibit two zones as well. Near the inlet
was defined as the time of maximum velocity at a
mouth centrifugal acceleration and lateral pressure
point located at the geometric center of the
gradients dominate (Figs. 3i and j). But within the
southern end of each inlet. Momentum balances
straits, the balance is between Coriolis and the
are shown for each inlet in Figs. 25.
normal direction pressure gradient (Figs. 3j and k).
3.1. Idealized inlet I
On the sound side of the inlet (not shown in Fig. 3)
the balances in both the streamwise and normal
directions resemble those seen on the sound side of
Circulation and momentum balances for idea-
inlet I. The balances for this inlet are distinct from
lized inlet I are shown in Fig. 2. The flow is
inlet I in that a middle zone appears where
strongest within the inlet straits and symmetric
advective accelerations (i.e. streamwise and cen-
transient eddies are seen on the sound side of the
trifugal) tend toward zero. Here the streamlines
inlet (Fig. 2a). The flow has reached near steady
are straight and the flow radius of curvature
state in both the streamwise and normal directions
approaches infinity.
as evident by small local accelerations, except
within the center of the transient eddies (Figs. 2d
3.3. Idealized inlet III
and h). The primary streamwise momentum
balances occur in two distinct zones. On the ocean
Inlet III has the same length as inlet I, but the
side (the ``sink'' region), the main balance is
headlands were spaced 2 km wider. The flows
between the streamwise pressure gradient and the
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