freshwater inflow is minimal, and

the ocean tide is approximately sinusoidal, then a good approximation for

the current velocity is

2 π as Ab

(5-2)

Vm =

Ac T

=

average cross-section velocity at

where Vm

maximum tidal flow [ft/sec]

T

=

period of tide [sec]

Ab

=

surface area of basin [ft2]

=

cross section of opening at mean tide

Ac

level [ft2]

as

=

range of the ocean tide [ft]

The circumstance that the entrance is not constrictive, together with the condition in

Equation 5-1, imply that the water surface in the bay fluctuates uniformly and equals the

ocean tide.

5-6.1.3.2

If the entrance is constrictive, as shown in Figure 5-12, it reduces the tide

range in the bay, so the above expression will overestimate the tidal currents. If

conditions outlined in (1) are satisfied, the maximum current in the entrance can be

determined from this equation:

2π as Ab e

(5-3)

Vm =

Ac T

Vm = average cross-section velocity at maximum tidal flow

where

[ft/sec]

2

Ac

=

cross section of opening at mean tide level [ft ]

T

=

period of tide [sec]

=

range of the ocean tide [ft]

as

e

=

dimensionless factor which depends on

coefficients K1 and K2;

see Figure 5-13.

The coefficients K1 and K2 are defined as follows:

(5-4)

as Ab Fc

K1 =

2 lb Ac

2 π lc Ab

(5-5)

K2 =

T g Ac

5-25

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