CETN-III-10
3/81
THEIR APPLICATIONS AND LIMITATIONS
To describe the functional applications, limitations, and general
PURPOSE:
design concepts of groins.
This note is intended to provide a brief,
general discussion of groins for Corps personnel who do not have a back-
ground in the functional design of coastal structures, and to provide use-
ful information for answering inquiries from the general public concerning
the use and construction of groins.
FUNCTIONAL APPLICATIONS: Groins are long, narrow structures placed ap-
proximately perpendicular to the shoreline to:
Build or widen a beach by trapping littoral drift (wind-blown sand
1.
may also be trapped).
Stabilize a beach by reducing longshore transport out of the groin
2.
compartmented area.
Reduce the rate of longshore transport out of an area by reorienting
3.
a section of the shoreline to an alignment more nearly perpendicular
to the predominant wave direction.
4.
Prevent loss from an area by acting as a littoral barrier (terminal
groins).
The sand accumulated by the groins acts as a wave-energy-spending beach to
provide additional shore protection.
The use of beach fill as a shore pro-
tection structure is discussed in CETN-III-11 (Protective Beaches).
Figure 1 shows groins in a beach environment.
Note that the accumulation
of material (accretion) on the updrift side is accompanied by a corre-
sponding amount of erosion on the downdrift side of the groin.
As a re-
sult, two site considerations that are vital to the applicability of groins
are: (1) in order for sand to be trapped, there must be an adequate supply
U.S. Army Corps of Engineers, Coastal Engineering Research Center, Kingman Building, Fort Belvoir, VA 22060
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