J.L. Hench et al. / Continental Shelf Research 22 (2002) 26152631

2625

Rs1 is the length scale at which the centrifugal and

for 20 inlets were taken from the literature and

Coriolis accelerations come into balance (also

combined with those for the four inlets analyzed in

known as the inertial radius). We now want to

this study (see list in Fig. 7). The inlets chosen are

compare Rs1; the length scale set by the dynamics,

not an exhaustive list, but should be representative

with the inlet geometric length scales. We define

of many inlets found in nature. The velocity scales

the dynamic length and dynamic width as

were chosen from published values for maximum

ebb or flood. In some cases, parameter values were

L=2

W =2

L

W

11

;

estimated from published figures when the actual

Rs1

Rs1

numbers were not cited, so the values used here

where the inlet length and width scales, L and W ;

may not be exact.

The inlet classification diagram using L versus

are divided by two because of symmetry. The

physical interpretations of L and W are

W is shown in Fig. 7. For the 24 inlets analyzed

the parameter space for both L and W spans

straightforward. First consider flow curving

over an order of magnitude. Since f varies only by

around headlands at a very wide inlet (or taken

to the limit, around a single headland, i.e.

a factor of 3 among the inlets, most of the variance

in L and W is due to differences in flow speed

W N). Adjacent to either of the headlands

(varies by a factor of 10) and geometry (L varies by

one would expect the momentum balance to be

a factor of 15, W by a factor of 80). The clustering

cyclostrophic. However, with increasing distance

of data around a line L W suggests that in

from a headland the centrifugal acceleration

nature there is a tendency for the aspect ratio of

diminishes, and the water surface relaxes into a

cross-stream balance with Coriolis. Here the inlet

dynamic lengths to widths to be close to one. The

correlation between L and W may be a

width does not constrain the lateral dynamics, and

W is large. Thus if the inlet is much wider than

consequence of flow having feedback with a

movable seabed and tending toward equilibrium

the inertial radius, flow around each headland is

topography. However many of these inlets are

not in strong dynamic communication with the

fictitious (idealized) and others have been modified

opposing headland. Now consider a narrower

by jetties and dredging. We tentatively picked 0.1

inlet. The balance at each of the opposing head-

as the dividing line between ``narrow'' and ``wide'',

lands is still cyclostrophic, but here the inlet width

and between ``short'' and ``long''; based on the

is too narrow for the water surface in the middle of

results of our numerical experiments, this appears

the inlet to relax to geostrophy. Rather, the

to be roughly where the transition takes place.

centrifugal acceleration from each headland is

These lines should provide a rough guide of which

balanced by opposing pressure gradients, forming

dynamical regime one might expect an inlet to fall

a ``dome'' of water across the inlet. Since the

within.

barotropic pressure gradient is uniform with

depth, flow around each headland is effectively

constrained to one side of the inlet, in much the

same way as the solid outside boundary pushes

6. Discussion and conclusions

against the flow around a river bend. In this case

W is small and the flows around each headland

Our analysis of inlet dynamics has shown that

momentum balances can vary significantly over

are in strong dynamic communication. A similar

sub-kilometer scales. Near the inlet headlands, and

dynamical situation exists along the length of the

often over the entire inlet, the first-order balances

channel. When the inertial radius is greater than

the geometric length (small L) then the balance is

are the pressure gradient and a combination of

different nonlinear terms. A common assumption

cyclostrophic along the entire length of the inlet.

Conversely, a large L would indicate that a

in one-dimensional inlet analyses is that the

streamwise pressure gradient is balanced by non-

geostrophic region exists within the inlet straits.

linear bottom friction. Our two-dimensional re-

We use these two parameters to classify and

sults indicate this assumption is only valid within

compare inlets from previous studies. Parameters

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