Jetties aid navigation by reducing movement of sand into the channel,
by stabilizing the location of the channel, and by shieldmg vessels from
waves. Sand is impounded at the updrift jetty, and the supply of sand to
the shore downdrift from the inlet is reduced, thus causmg érosion of
that shore. Before the installation of a jetty, nature supplied sand by
transporting it across the inlet intermittently along the outer bar to the
downdrift shore.
To eliminate undesirable downdrift érosion, some projects provide for
dredging the sand impounded by the updrift jetty and pumping it through a
pipeline (bypassing the inlet) to the eroding beach. This provides an
intermittent flow of sand to nourish the downdrift beach, and also prevents
shoaling of the entrance channel.
A more recent development for sand bypassing provides a low section
or weir in the updrift jetty over which sand moves into a sheltered predredged, déposition basin. By dredging the basin periodically, déposition
in the channel is reduced or eliminated. The dredged material is normally
pumped across the inlet to provide nourishment for the downdrift shore.
A weir jetty of this type at Masonboro Inlet, North Carolina, is shown in
Figure 1-9.
1.58 BEACH RESTORATION AND NOURISHMENT
As previously stated, beaches are very effective in dissipâting wave
energy. When maintained to adéquate dimensions, they afford protection
for the adjoining backshore. Therefore, a protective beach is classed as
a shore-protection structure. When studying an érosion problem, it is general ly advisable to investigate the feasibility of mechanically or hydraulically placing borrow material on the shore to form and maintain an adéquate protective beach. The method of placing beach fill to ensure sand
supply at the required replenishment rate is important. Where stabilization of an eroding beach is the problem, suitable beach material may be
stockpiled at the updrift sector of the problem area. The establishment
and periodic replenishment of such a stockpile is termed artificial
beach nourishment. To restore an eroded beach and stabilize it at the
restored position, fill is placed directly along the eroded sector, and
then the beach is artificially nourished by the stockpiling method.
When conditions are suitable for artificial nourishment, long reaches
of shore may be protected by this method at a relatively low cost per
1 inear foot of protected shore. An equally important advantage is that
artificial nourishment directly remedies the basic cause of most érosion
problems - a deficiency in natural sand supply - and benefits rather than
damages the adjacent shore. An added considération is that the widened
beach has value as a récréation feature. A project for beach restoration
-
ial d'y16
protection against hurricane wave action, cornai 10° in
^rightsville Beach, North Carolina, is shown in Figure
1-18
by stabilizing the location of the channel, and by shieldmg vessels from
waves. Sand is impounded at the updrift jetty, and the supply of sand to
the shore downdrift from the inlet is reduced, thus causmg érosion of
that shore. Before the installation of a jetty, nature supplied sand by
transporting it across the inlet intermittently along the outer bar to the
downdrift shore.
To eliminate undesirable downdrift érosion, some projects provide for
dredging the sand impounded by the updrift jetty and pumping it through a
pipeline (bypassing the inlet) to the eroding beach. This provides an
intermittent flow of sand to nourish the downdrift beach, and also prevents
shoaling of the entrance channel.
A more recent development for sand bypassing provides a low section
or weir in the updrift jetty over which sand moves into a sheltered predredged, déposition basin. By dredging the basin periodically, déposition
in the channel is reduced or eliminated. The dredged material is normally
pumped across the inlet to provide nourishment for the downdrift shore.
A weir jetty of this type at Masonboro Inlet, North Carolina, is shown in
Figure 1-9.
1.58 BEACH RESTORATION AND NOURISHMENT
As previously stated, beaches are very effective in dissipâting wave
energy. When maintained to adéquate dimensions, they afford protection
for the adjoining backshore. Therefore, a protective beach is classed as
a shore-protection structure. When studying an érosion problem, it is general ly advisable to investigate the feasibility of mechanically or hydraulically placing borrow material on the shore to form and maintain an adéquate protective beach. The method of placing beach fill to ensure sand
supply at the required replenishment rate is important. Where stabilization of an eroding beach is the problem, suitable beach material may be
stockpiled at the updrift sector of the problem area. The establishment
and periodic replenishment of such a stockpile is termed artificial
beach nourishment. To restore an eroded beach and stabilize it at the
restored position, fill is placed directly along the eroded sector, and
then the beach is artificially nourished by the stockpiling method.
When conditions are suitable for artificial nourishment, long reaches
of shore may be protected by this method at a relatively low cost per
1 inear foot of protected shore. An equally important advantage is that
artificial nourishment directly remedies the basic cause of most érosion
problems - a deficiency in natural sand supply - and benefits rather than
damages the adjacent shore. An added considération is that the widened
beach has value as a récréation feature. A project for beach restoration
-
ial d'y16
protection against hurricane wave action, cornai 10° in
^rightsville Beach, North Carolina, is shown in Figure
1-18