where lc

=

channel length [ft]

f lc

ken + kex +

=

Fc

4R

entrance-loss coefficient (≈ 0.1)

=

ken

exit-loss coefficient (≈ 1.0)

kex

=

Darcy-Weisbach friction factor (≈ 0.03)

f

=

R

=

hydraulic radius of inlet channel [ft]

(water-level) gradient.

Since the entrance is constrictive, the amplitude of the bay tide will differ from the

amplitude of the tide range in the ocean. The bay-tide amplitude can be determined

from the following relationship:

ab

=ε

(5-6)

as

=

dimensionless factor which depends on the

where

ε

coefficients K1 and K2

(see Figure 5-14)

ab

=

range of bay tide [ft]

Note that for small values of K1, which denotes large inertia forces, the value of ε is

greater than one.

For irregular entrance channels, an effective channel length, lc', can be used in place of

lc.

2

R Ac

n

lc' = ∑ ∆ Xn

(5-7)

i Rn An

where:

=

average hydraulic radius of channel [ft]

R

2

=

average cross section of channel at mean tide level [ft ]

Ac

hydraulic radius at each of n sections of equal length, ∆Xn , [ft]

=

Rn

2

cross section of channel at each of n sections of length, ∆Xn , [ft ]

=

An

This analysis provides an estimate of the channel-inlet hydraulics applicable to design

situations. However, if the assumptions in paragraph 5.5.1.3a are not satisfied, or if the

current velocities are critical to the channel design, a more detailed analysis to include

mathematical or physical-model simulation is necessary.

5-26

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