CETN-III-22
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PREDOMINANT
WAVE DIRECTION
LONGSHORE
(-)NET LONGSHORE
AND MAGNITUDE
WAVE DIRECTION
WAVE DIRECTION
AND MAG,NITUDE
BREAKWATER
HEIGHT
WAVE DIFFRACTION
AND POROSITY
Offshore
Breakwater
Design
Considerations
Figure 2.
The magnitude and direction of the predominant incoming waves also play
important
roles.
For instance, large, long-period waves tend to diffract
more into the.lee of a breakwater than do smaller waves, resulting in a more
pointed
shoreline.
Smaller,
short-period waves diffract less, resulting in
a mo're rounded shoreline.
Highly
oblique, p redominant
waves
induce
strong
longshore currents which restrict the amount of accretion in the lee of a
breakwater;
in this case, breakwaters can be orientated normal to the domi-
nant incident wave direction.
Sites with a broad spectrum of wave approach
will require more general protection to the shore.
which are generally less important con-
Breakwater
height
and
porosity,
siderations,
should be designed to reduce the transmitted wave energy enough
to prevent the protective beach from being stripped away and back beach fea-
The degree of transmitted wave energy which the structures
tures
endangered.
Where
tidal
energy
allow will influence the future shoreline configuration.
significant, the potential effect of the breakwater system on nearshore
is
currents should also be considered.
The protective beach itself is an important part of the offshore break-
If the structures are to be placed in a high littoral
water
system
design.
transport rate zone and damage to downdrift beaches due to longshore trap-
ping is a concern, beach fill should be incorporated into the project plan.
The functional design of protective beaches is discussed in CETN-III-11
(March 1981).
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