MIL-HDBK-1025/5
4) To minimize danger
of massive wave overtopping of rubble-
mound breakwaters, the crown shall be
three or four armor units wide and the
units on the back slope down to about
wave-height distance below the surface
should be as large and as well placed
as those on the front slope.
5) If a rubble breakwater is too porous, it will allow
transmission of a high percentage of the longer-period wave energy through it,
and excessive wave disturbance will occur within the interior channels, and
berthing basin and areas.
Design Details. For analysis and design details, refer to Shore
2.5.2.7
Protection Manual, Volume II; DM-26.1; and DM-26.2, Coastal Protection.
Groins
2.5.3
Groins may be used to:
Purpose.
2.5.3.1
Build or widen a beach by trapping littoral drift.
a)
Reduce the rate off longshore transport out of an area by
b)
reorienting a section of the shoreline to an alignment more nearly
perpendicular to the predominant wave direction.
Reduce loss of material out of an area by compartmenting the
c)
beach.
Prevent accretion in a downdrift area by acting as a littoral
d)
barrier.
Stabilize a beach, subject to excessive storms or seasonal
e)
periods of advance and recession, by reducing the rate of loss.
These include:
Types.
2.5.3.2
Timber groins.
a)
Steel groins.
b)
Concrete groins.
c)
Rubble-mound groins (see Figure 24).
d)
Asphalt groins.
e)
Design Criteria. These are the same as for breakwater design.
For
2.5.3.3
details, refer to DM-26.2 and Shore Protection Manual, Volume II.
Jetties
2.5.4
A jetty is a structure extending into the water to:
Purpose.
2.5.4.1
Direct or confine tidal flow into the channel or boat basin.
a)
Prevent or reduce the shoaling of the channel by littoral
b)
material.
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