at a submarine canyon or deep water at the foot of a headland, a high 
terminal groin is used on the downdrift end to prevent the loss of sand 
from the littoral zone. Such a system is beneficial in conserving sand 
under these circumstances since an erosion problem immediately downdrift 
would not exist. 
Groin systems are the most universally used structures for beach re- 
tention and enlargement. Frequently it is found desirable, when building 
and maintaining a protective beach, to supply additional protection to 
highly valuable property behind the beach berm and dune line. To accom- 
plish this, a seawall, bulkhead or revetment is installed to protect the 
backshore during storm periods (Figure 8). Although an adequately wide 
beach affords excellent protection, it may be overtopped during major 
storms, resulting in dune deterioration and major interior flooding. 
Occasionally a breach through the beach may occur forming an inlet from 
the ocean. In this case the secondary defense structures prevent severe 
changes in the land forms. 
Harbor jetties, either alone or with an offshore breakwater, accom- 
plish the purpose of protecting an entrance through a barrier beach, but 
will result in a considerable change in the land form unless a sand by- 
passing operation is effected. The offshore breakwater creates a calm 
area shoreward of its center, resulting in the deposition of littoral 
material at that point. As the point builds, it acts as a natural groin 
and a great expanse of beach is built updrift. Further, as this wide 
expanse of sand dries, it is frequently moved by the wind into a sub- 
stantial dune system. This change in land form can create other problems. 
Instances are recorded where sand movement by wind from impounded areas 
has built dunes around and completely over shore installations, including 
buildings, When this occurs, beach or dune stabilization measures such as 
sand fences and vegetal plantings are indicated. The storage of such large 
quantities of littoral material upsets the natural regimen of the area by 
removing the downdrift shores from the system of natural nourishment. 
Erosion is thus accelerated in this downdrift area. In order to reduce 
or eliminate this type of change in land form, the material can be moved 
downdrift by a hydraulic dredge working in the lee of the breakwater to 
re-establish natural conditions. To date sand-bypassing operations at 
jettied entrances which do not include an offshore breakwater have not 
been completely satisfactory. 
Where natural features permit, it is frequently more economical to 
supply sand to the beach than to build groins. The artificially nourished 
beach is the most satisfactory shore protection system (Figure 14). It 
is the one system that maintains the balance of nature, and is relatively 
free of the undesirable features of other systems. 
33 
