BASIC TYPES OF STRUCTURES 
Numerous types of structures are seen in the coastal areas but all 
are variations of a few basic types of which the seawall is possibly the 
oldest type used today. It is defined as a structure separating land and 
water areas, primarily designed to prevent erosion of the backshore and 
other damage due to wave action. Seawalls are generally massive and ex- 
pensive, and are used only where economics dictate their use. Most sea- 
walls are built of masonry or reinforced concrete (Figure 1). They are 
normally designed as gravity structures to resist a frontal attack by the 
waves. Their dimensions, height and length, are generally dictated by the 
natural features of the area to be protected. In some instances the top 
is set at a superelevation to prevent overtopping and flooding of inland 
areas due to storm wave run-up on a superelevated tide. Except in special 
cases the seawall is rarely recommended for use since more economical means 
of protection have been devised. 
A bulkhead is defined as a structure which separates land and water 
areas, primarily designed to resist earth pressures (Figure 2). By defini- 
tion it is not designed for dissipating or absorbing high wave energy. It 
is generally built high on the beach as a delimiting boundary between the 
shore area and the developed upland. Like a seawall the dimensions of 
the bulkhead are determined by the natural features of the area to be 
protected. In some instances, the bulkhead, as a secondary line of defense 
to the beach, is superelevated to prevent overtopping and flooding during 
storm conditions. However, if the beach erodes, the waterline approaches 
the bulkhead with the result that the bulkhead must act as a seawall. 
Revetments are structures related to seawalls or bulkheads, They are 
defined as a facing of stone or concrete shapes built to protect a scarp, 
embankment, or shore structure against erosion or damage by wave action or 
currents (Figure 3). Revetments have evolved from the simple rubble facing 
to the more esthetic structure built of interlocking blocks. The structure 
in a sense replaces the buikhead and its height is designed in a manner 
similar to that of the bulkhead, but due to its ability to absorb wave 
energy, a lesser run-up is experienced, thus resulting in a lower design 
height. The cover or armor stone of the rubble type revetment is designed 
to be stable under prevailing wave action. 
Unlike the preceding structures, which serve essentially as barriers 
between land and sea, other structures have been developed and are used to 
furnish protection by modifying the natural regimen of the area. A jetty 
is classed as a structure extending from the shore into a body of water 
and designed to prevent shoaling of a channel by littoral materials, and 
to direct and confine the stream or tidal flow (Figure 4). It is usually 
built with a trapezoidal section of heavy rubble designed to be stable when 
subjected to wave forces extant in the area. The structure may vary in 
length from a few hundred to several thousand feet, depending of the dis- 
tance from the shore to a water depth equivalent to the depth of channel 
