EM 1110-2-1100 (Part II)
30 Apr 02
V cos θ
F'
(II-6-30)
1
2
g dT
and
1
dT
2π
2
Ω'
(II-6-31)
g
T
where
T = wave period
dT = channel depth
θ = angle wave orthogonal makes with current
V = velocity in channel
(2) Current-channel interaction. As flow converges on an inlet entrance, the angle at which flow
approaches a dredged channel can be important with regard to change in current direction and can ultimately
relate to channel shoaling. The direction of current approach will depend on bottom configuration and
structure(s) location. Boer (1985) developed a mathematical model to study currents in a dredged channel.
He found that a current approaching obliquely to a channel is refracted within the channel and the streamlines
contract within the channel causing a velocity increase (Figure II-6-35). This effect becomes relatively small
for angles larger than 60E (angle between channel axis and current direction). This effect is largest near the
bed and smallest near the surface. Due to continuity, depending on the relative depth of the channel to the
surrounding depths, there is a decrease factor because of increased depth in the channel.
m . Other methods of inlet analysis. As mentioned in Part II-6-2, paragraph a, follow-up studies using
techniques presented in previous sections and numerical and/or physical models, can be conducted after an
initial examination of the inlet. Some available tools are discussed below.
(1) Automated Coastal Engineering System (ACES). ACES (Leenknecht et al. 1992) contains an inlet
model that operates in the PC environment and estimates inlet velocities, discharges, and bay levels as a
function of time. This model is designed for cases where the bay water level fluctuates uniformly. Seaward
boundary conditions are specified as water level fluctuations associated with astronomical tides, storm surges,
seiches, and tsunamis. Figure II-6-36 shows a flow net and Figure II-6-37 is a typical cross section indicating
that the model can handle up to two inlet entrances to a single bay and that the entrance channel(s) can be
divided into sub-channels to accommodate change in depth across the inlet. The model will permit up to
seven sub-channels and up to sixteen cross sections of the flownet. Figures II-6-38 and II-6-39 show sample
output from the program.
Hydrodynamics of Tidal Inlets
II-6-43
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