IV. Retreating Shorelines
169
Profiles are needed from both zones because modalities are clearly different in
one and the other. While hydrographic charts are adequate to make a profile for
deeper offshore zones, recent surveys are necessary for waters 20 m (66 ft), and
less, deep.
Profiles are needed because of long-term stability of the swell profile and shortterm transposition from swell to storm beach profile.
The envelope of a profile defines fluctuations of sand level at a site, data that is
needed for beach nourishment as well as groin design.
The nearshore profile is usually measured aboard with an echo-sounder or a leadline. The beach profile is surveyed by leveling and taping techniques ; the latter is
less affected by such errors as sounding, spacing, closure and sea bottom
temporal fluctuations, than the nearshore profile.
When a beach is subjected to constant wave action for a sufficiently long time, an
essentially stable beach profile is established. The form of this profile is a
function of the wave parameters (usually wave height and wave length) and the
size characteristics of the beach material (usually the average grain size and the
relative proportions of difference grain sizes).
Several workers (Swart, 1974 ; Dean, 1984 ; Vellinga, 1984) have sought to
establish a mathematical relationship between these parameters.
In general, a proportionality has been found between the depth of water and the
distance from the limit of uprush. Although an average profile related to normal
conditions is often referred to, the profile of the beach is never fully fixed because
of variations in wave action changes considerably and the limit of uprush (storm
surge level) rises up the beach which is then eroded. The new profile can be
calculated By inserting the appropriate values for the wave parameters into the
mathematical relationships.
The beach profile is the intersection of the ground surface with a vertical plane ;
it may extend from the top of the dune line to the seaward limit of sand
movement. A profile perpendicular to the shoreline reflects the action of littoral
processes ; all features are not necessarily shown, though dune, berm and
foreshore are. Across a beach, the profile adapts to imposed wave conditions.
The typical beach profile left by a severe storm is a simple, concave-upward curve
extending seaward to low-tide level or below.
It should never be lost sight of that beach profiles are a momentary picture, not a
long-term condition. Seasonal profiles, storm and swell, can develop earlier.
169
Profiles are needed from both zones because modalities are clearly different in
one and the other. While hydrographic charts are adequate to make a profile for
deeper offshore zones, recent surveys are necessary for waters 20 m (66 ft), and
less, deep.
Profiles are needed because of long-term stability of the swell profile and shortterm transposition from swell to storm beach profile.
The envelope of a profile defines fluctuations of sand level at a site, data that is
needed for beach nourishment as well as groin design.
The nearshore profile is usually measured aboard with an echo-sounder or a leadline. The beach profile is surveyed by leveling and taping techniques ; the latter is
less affected by such errors as sounding, spacing, closure and sea bottom
temporal fluctuations, than the nearshore profile.
When a beach is subjected to constant wave action for a sufficiently long time, an
essentially stable beach profile is established. The form of this profile is a
function of the wave parameters (usually wave height and wave length) and the
size characteristics of the beach material (usually the average grain size and the
relative proportions of difference grain sizes).
Several workers (Swart, 1974 ; Dean, 1984 ; Vellinga, 1984) have sought to
establish a mathematical relationship between these parameters.
In general, a proportionality has been found between the depth of water and the
distance from the limit of uprush. Although an average profile related to normal
conditions is often referred to, the profile of the beach is never fully fixed because
of variations in wave action changes considerably and the limit of uprush (storm
surge level) rises up the beach which is then eroded. The new profile can be
calculated By inserting the appropriate values for the wave parameters into the
mathematical relationships.
The beach profile is the intersection of the ground surface with a vertical plane ;
it may extend from the top of the dune line to the seaward limit of sand
movement. A profile perpendicular to the shoreline reflects the action of littoral
processes ; all features are not necessarily shown, though dune, berm and
foreshore are. Across a beach, the profile adapts to imposed wave conditions.
The typical beach profile left by a severe storm is a simple, concave-upward curve
extending seaward to low-tide level or below.
It should never be lost sight of that beach profiles are a momentary picture, not a
long-term condition. Seasonal profiles, storm and swell, can develop earlier.