1.54 BULKHEADS, SEAWALLS AND REVETMENTS
Protection on the upper part of the beach which fronts backshore
development is required as a partial substitute for the natural pro~tection that is lost when the dunes are destroyed. Shorefront owners
hâve resorted to shore armoring by wave-resistant walls of varions
types. A vertical wall in this location is known as a bulkhead, and
serves as a secondary line of defense in major storms. Bulkheads are
constructed of Steel, timber, or concrète piling. For ocean-exposed
locations, bulkheads do not provide a long-term solution, because a
more substantial wall is required as the beach continues to recede and
larger waves reach the structure. Unless combined with other types of
protection, the bulkhead must be enlarged into a massive seawall capable
of withstanding the direct onslaught of the waves. Seawalls may hâve
vertical, curved or stepped faces. While seawalls may protect the upland, they can create a local problem. Downward forces of water created
by waves striking the wall, can rapidly remove sand from in front of the
wall. A stone apron is often necessary to prevent excessive scouring
and undermining.
A revetment armors the slope face of a dune or bluff. It is usually
composed of one or more layers of stone or is of concrète construction.
This sloping protection dissipâtes wave energy with less damaging effect
on the beach than waves striking vertical walls.
1.55 BREAKWATERS
Beaches and bluffs or dunes can be protected by an offshore breakwater that reduces the wave energy reaching the shore. However, offshore
breakwaters are usually more costly than onshore structures, and are seldom built solely for shore protection. Offshore breakwaters are construc
ted mainly for navigation purposes. A breakwater protecting a harbor
area provides shelter for boats. Breakwaters hâve both bénéficiai and
detrimental effects on the shore. Ail breakwaters reduce or eliminate
wave action and thus protect the shore immediately behind them. Whether
offshore or shore-connected, the élimination of wave action reduces longshore transport, obstructing the movement of sand along the shore and
starving the downdrift beaches.
At a harbor breakwater, the sand stream generally can be restored by
pumping sand through a pipeline from the side where sand accumulâtes to
the eroded downdrift side. This type of operation has been in use for
many years at Santa Barbara, California.
Even without a shore arm, an offshore breakwater reduces wave action
and créâtes quiet water between it and the shore. In the absence of wave
action to move sand, it is deposited and builds the shore seaward toward
the breakwater. The buildup serves as a barrier which also blocks the
movement of littoral materials. If the offshore breakwater is placed
immediately updrift from a navigation opening, the structure impounds
sand, prevents it from entering the navigation channel, and affords
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Protection on the upper part of the beach which fronts backshore
development is required as a partial substitute for the natural pro~tection that is lost when the dunes are destroyed. Shorefront owners
hâve resorted to shore armoring by wave-resistant walls of varions
types. A vertical wall in this location is known as a bulkhead, and
serves as a secondary line of defense in major storms. Bulkheads are
constructed of Steel, timber, or concrète piling. For ocean-exposed
locations, bulkheads do not provide a long-term solution, because a
more substantial wall is required as the beach continues to recede and
larger waves reach the structure. Unless combined with other types of
protection, the bulkhead must be enlarged into a massive seawall capable
of withstanding the direct onslaught of the waves. Seawalls may hâve
vertical, curved or stepped faces. While seawalls may protect the upland, they can create a local problem. Downward forces of water created
by waves striking the wall, can rapidly remove sand from in front of the
wall. A stone apron is often necessary to prevent excessive scouring
and undermining.
A revetment armors the slope face of a dune or bluff. It is usually
composed of one or more layers of stone or is of concrète construction.
This sloping protection dissipâtes wave energy with less damaging effect
on the beach than waves striking vertical walls.
1.55 BREAKWATERS
Beaches and bluffs or dunes can be protected by an offshore breakwater that reduces the wave energy reaching the shore. However, offshore
breakwaters are usually more costly than onshore structures, and are seldom built solely for shore protection. Offshore breakwaters are construc
ted mainly for navigation purposes. A breakwater protecting a harbor
area provides shelter for boats. Breakwaters hâve both bénéficiai and
detrimental effects on the shore. Ail breakwaters reduce or eliminate
wave action and thus protect the shore immediately behind them. Whether
offshore or shore-connected, the élimination of wave action reduces longshore transport, obstructing the movement of sand along the shore and
starving the downdrift beaches.
At a harbor breakwater, the sand stream generally can be restored by
pumping sand through a pipeline from the side where sand accumulâtes to
the eroded downdrift side. This type of operation has been in use for
many years at Santa Barbara, California.
Even without a shore arm, an offshore breakwater reduces wave action
and créâtes quiet water between it and the shore. In the absence of wave
action to move sand, it is deposited and builds the shore seaward toward
the breakwater. The buildup serves as a barrier which also blocks the
movement of littoral materials. If the offshore breakwater is placed
immediately updrift from a navigation opening, the structure impounds
sand, prevents it from entering the navigation channel, and affords
1-16