Figure 1-6.Various types of seawalls.
boxes called caissons, each of which is floated over its
place of location, and then sunk into position. A
monolithic (single-piece) concrete cap is then cast along
the tops of the caissons. Sometimes, breakwaters and
jetties are built entirely of caissons, as shown in figure
A groin is a structure similar to a breakwater or jetty,
but it has a third purpose. A groin is used in a situation
where a shoreline is subject to alongshore erosion,
caused by wave or current action parallel or oblique to
the shoreline. The groin is run out from the shoreline
(usually there is a succession of groins at intervals) to
check the alongshore wave action or deflect it away
from the shore.
A mole is a breakwater that is paved on the top for
use as a wharfage structure. To serve this purpose, it
must have a vertical face on the inner side, or harborside.
A jetty may be similarly constructed and used, but it is
still called a jetty.
These structures are constructed parallel with the
shoreline to protect it from erosion or other wave
A seawall is a vertical or sloping wall that offers
protection to a section of the shoreline against erosion
and slippage caused by tide and wave action. A seawall
is usually a self-sufficient type of structure, such as a
gravity-type retaining wall. Seawalls are classified
according to the types of construction. A seawall may
be made of riprap or solid concrete. Several types of
seawall structures are shown in figure 1-16.
A bulkhead has the same general purpose as a
seawall; namely, to establish and maintain a stable
shoreline. However, while a seawall is self-contained,
relatively thick, and is supported by its own weight, the
bulkhead is a relatively thin wall. Bulkheads are
classified according to types of construction, such as the