setup or storm surges are created by strong winds. The height of storm
surge dépends on wind velocity and direction, fetch, water depth, and
nearshore slope. In violent storms, storm surge may raise sea level at
the shore as much as 20 feet. In the United States, larger surges occur
on the Gulf coast because of the shallower and broader shelf off that
coast compared to the shelves off the Atlantic and Pacific coasts. Storm
surges may also be increased by a funneling effect in converging estuaries,
When waves approach the beach at an angle, they create a current in
shallow water parallel to the shore, known as the longshore current. This
current, under certain conditions, may tum and run out to sea in what is
known as a rip current.
1.34 TIDAL CURRENTS
If water level rises and falls at an area, then water must flow into
and out of the area. Significant currents generated by tides occur at inlets to lagoons and bays or at entrances to harbors. At such constricted
places, tidal currents generally flow in when the tide is rising (flood
tide) and flow out as the tide falls (ebb tide). Exceptions can occur
at times of high river discharge or strong winds, or when density currents are an important part of the current System.
In addition to creating currents, tides constantly change the level
at which waves attack the beach.
1.4 THE BEHAVIOR OF BEACHES
1.41 BEACH COMPOSITION
The size and character of sédiments on a beach are related to forces
to which the beach is exposed and the type of material available at the
shore. Most beaches are composed of fine or coarse sand and,in some
areas, of small stones called shingte qt gravel. This material is supplied to the beach zone by streams, by érosion of the shores caused by
waves and currents and, in some cases, by onshore movement of material
from deeper water. Clay and silt do not usually remain on océan beaches
because the waves create such turbulence in the water along the shore
that these fine materials are kept in suspension. It is only after moving away from the beaches into quieter or deeper water that these fine
particles settle out and deposit on the bottom.
1.42 BEACH CHARACTERISTICS
Characteristics of a beach are usually described in terms of average
size of the sand particles that make up the beach, range and distribution
of sizes of those particles, sand composition, élévation and width of berm
slope or steepness of the foreshore, the existence (or lack) of a bar, and
the general slope of the inshore zone fronting the beach. Generally, the
larger the sand particles the steeper the beach slope. Beaches with
gently sloping foreshores and inshore zones usually hâve a prépondérance
1-9
surge dépends on wind velocity and direction, fetch, water depth, and
nearshore slope. In violent storms, storm surge may raise sea level at
the shore as much as 20 feet. In the United States, larger surges occur
on the Gulf coast because of the shallower and broader shelf off that
coast compared to the shelves off the Atlantic and Pacific coasts. Storm
surges may also be increased by a funneling effect in converging estuaries,
When waves approach the beach at an angle, they create a current in
shallow water parallel to the shore, known as the longshore current. This
current, under certain conditions, may tum and run out to sea in what is
known as a rip current.
1.34 TIDAL CURRENTS
If water level rises and falls at an area, then water must flow into
and out of the area. Significant currents generated by tides occur at inlets to lagoons and bays or at entrances to harbors. At such constricted
places, tidal currents generally flow in when the tide is rising (flood
tide) and flow out as the tide falls (ebb tide). Exceptions can occur
at times of high river discharge or strong winds, or when density currents are an important part of the current System.
In addition to creating currents, tides constantly change the level
at which waves attack the beach.
1.4 THE BEHAVIOR OF BEACHES
1.41 BEACH COMPOSITION
The size and character of sédiments on a beach are related to forces
to which the beach is exposed and the type of material available at the
shore. Most beaches are composed of fine or coarse sand and,in some
areas, of small stones called shingte qt gravel. This material is supplied to the beach zone by streams, by érosion of the shores caused by
waves and currents and, in some cases, by onshore movement of material
from deeper water. Clay and silt do not usually remain on océan beaches
because the waves create such turbulence in the water along the shore
that these fine materials are kept in suspension. It is only after moving away from the beaches into quieter or deeper water that these fine
particles settle out and deposit on the bottom.
1.42 BEACH CHARACTERISTICS
Characteristics of a beach are usually described in terms of average
size of the sand particles that make up the beach, range and distribution
of sizes of those particles, sand composition, élévation and width of berm
slope or steepness of the foreshore, the existence (or lack) of a bar, and
the general slope of the inshore zone fronting the beach. Generally, the
larger the sand particles the steeper the beach slope. Beaches with
gently sloping foreshores and inshore zones usually hâve a prépondérance
1-9