1.23 BARRIER BEACHES, LAGOONS AND INLETS
In some areas, an additional natural protection for the mainland is
provided in the form of barrier beaches. (See Figure 1-4.) Nearly ail
of the U.S. east coast from Long Island to Mexico is comprised of barrier beaches. These are long narrow islands or spits lying parailel to
the shoreline. Barrier beaches generally enclose shallow lagoons that
separate the mainland from the océan. During severe storms these barrier
beaches absorb the brunt of the wave attack. When barrier-beach dunes
are breached, the resuit may be the cutting of an inlet. The inlet permits sand to enter the lagoon and settle to the bottom, removing sand
from the beach.
1.24 STORM ATTACK
During storms, strong winds generate high waves. Storm surge and
waves may raise the water level near the shore. If storm surge does
occur, large waves can then pass over the offshore bar formation without
breaking. If the storm occurs at high tide, storm surge super-elevates
the water, and some waves may break on the beach or even at the base of
the dunes. After a storm or storm season, natural defenses may again be
re-formed by normal wave and wind action.
1.25 ORIGIN AND MOVEMENT OF BEACH SANDS
Most of the sands of the beaches and nearshore slopes are normally
small, résistant rock particles that hâve traveled many miles from inland mountains. When the sand reaches the shore, it is moved alongshore
by waves and littoral currents. This alongshore transport is a constant
process, and great volumes may be transported. In most Coastal segments
the direction of movement changes as direction of wave attack changes.
1.3 THE SEA IN MOTION
1.3 ! TIDES AND WINDS
The motions of the sea originate in the gravitational effects of the
sun, the moon, and earth; and from air movements or winds caused by differential heating of the earth.
The moon, and to a lesser extent the sun, créâtes océan tides by
gravitational forces. These forces of attraction, and the fact that the
sun, moon, and earth are always in motion with relation to each other,
cause waters of océan basins to be set in motion. These tidal motions of
water masses are a form of very long period wave motion, resulting in a
rise and fall of the water surface at a point. There are normally two
tides per day, but some localities hâve only one per day.
1.32 WAVES
The familiar waves of the océan-are wind waves generated by winds
blowing over water. They may vary in size from ripples on a pond to
1-5
In some areas, an additional natural protection for the mainland is
provided in the form of barrier beaches. (See Figure 1-4.) Nearly ail
of the U.S. east coast from Long Island to Mexico is comprised of barrier beaches. These are long narrow islands or spits lying parailel to
the shoreline. Barrier beaches generally enclose shallow lagoons that
separate the mainland from the océan. During severe storms these barrier
beaches absorb the brunt of the wave attack. When barrier-beach dunes
are breached, the resuit may be the cutting of an inlet. The inlet permits sand to enter the lagoon and settle to the bottom, removing sand
from the beach.
1.24 STORM ATTACK
During storms, strong winds generate high waves. Storm surge and
waves may raise the water level near the shore. If storm surge does
occur, large waves can then pass over the offshore bar formation without
breaking. If the storm occurs at high tide, storm surge super-elevates
the water, and some waves may break on the beach or even at the base of
the dunes. After a storm or storm season, natural defenses may again be
re-formed by normal wave and wind action.
1.25 ORIGIN AND MOVEMENT OF BEACH SANDS
Most of the sands of the beaches and nearshore slopes are normally
small, résistant rock particles that hâve traveled many miles from inland mountains. When the sand reaches the shore, it is moved alongshore
by waves and littoral currents. This alongshore transport is a constant
process, and great volumes may be transported. In most Coastal segments
the direction of movement changes as direction of wave attack changes.
1.3 THE SEA IN MOTION
1.3 ! TIDES AND WINDS
The motions of the sea originate in the gravitational effects of the
sun, the moon, and earth; and from air movements or winds caused by differential heating of the earth.
The moon, and to a lesser extent the sun, créâtes océan tides by
gravitational forces. These forces of attraction, and the fact that the
sun, moon, and earth are always in motion with relation to each other,
cause waters of océan basins to be set in motion. These tidal motions of
water masses are a form of very long period wave motion, resulting in a
rise and fall of the water surface at a point. There are normally two
tides per day, but some localities hâve only one per day.
1.32 WAVES
The familiar waves of the océan-are wind waves generated by winds
blowing over water. They may vary in size from ripples on a pond to
1-5