exposed during high-energy conditions. Summer wave
conditions return sand back to the beach so that the summer beach is covered with a layer of sand that is moved
south by alongshore currents and onshore by low-energy
wave climate. Other researchers have noted associations
between waves, breakers, and beach gradients – the relationship occurring because breaker type is a function of
wave characteristics (Pethick, 1984). High values of the
surf-scaling factor (e.g., Guza and Inman, 1975) are associated, for example, with wide flat beaches with spilling
breakers, while low values are associated with steep narrow beaches and surging breakers (e.g., Wright et al.,
1979; Wright et al., 1982). Although the relationship
between wave steepness and beach gradient is pronounced, other variables such as the angle of the wave
approach (e.g., Sonu and van Beek, 1971) and tides and
longshore currents (e.g., Davis, 1985) may also be
important.
Morphodynamic beach types
Beach morphotypes range through a sequence of processform-materials systems between end points marked by
low-energy systems with small beach-building waves to
high-energy systems with large waves breaking across
several hundred meters of surf zone (Wright and Short,
1984). Tides are an additional consideration in beach formation as they range from micro (<2 m), meso (2–4 m),
macro (4–8 m), to mega tides (>8 m). Beaches are divided
into the three basic morphodynamic types in order to
accommodate tidal ranges, wave heights, and variations
in grain size (sand to boulders), viz., wave dominated, tide
modified, and tide dominated, based on the relative tide
range (RTR) (Short, 2006). This process-based grouping
of beach morphotypes, as initially conceived by Wright
et al. (1982) and expanded to beaches around the Australian continent by Short (1999, 2006, 2012), provides
a basis for cataloguing a range of beach processes associated with beaches in low latitude and mid-latitude.
Ice-coast beach processes are not yet comprehensively
included in the system. Some essential facets of the
morphodynamic classification of beaches are briefly summarized here from Short (2012) and Short and
Woodroffe (2009).
Wave-dominated beaches are characterized by a RTR
tide range that is less than three times the average wave
height (RTR < 3). These beaches occur in three
morphodynamic states that are referred to as (1) reflective,
(2) intermediate, and (3) dissipative.
Reflective beaches are the result of process-material interactions that are associated with lower waves (H <
0.5 m), longer wave periods, and coarser sediment. As
a result of these process-form relationships, all coarse
sand and cobble-boulder beaches exhibit a reflective
beach state. Reflective beaches contain a relatively
steep beachface (5–20
) that reflects backwash. Reflective beach processes do not produce a bar or surf zone.
Intermediate beaches are common along open coasts and
are produced by moderate waves (H ¼ 0.5–2.5 m)
interacting with fine- to medium-grained sand. These
types of beaches are characterized by a surf zone with
one or two bars up to 100 m wide. The bar is typically
traversed by regularly spaced shore-perpendicular rip
channels and currents.
Dissipative beaches are produced by high waves (H >
2.5 m) interacting with fine-grained sand. These
morphotypes are characterized by gently seawardsloping beachfaces with low-gradient swash (~1
) and
300–500 m wide surf zone that contains at least two
bars. Waves sequentially break on the outer bar first
and then on inner bars and in the process dissipate their
energy as they move through the surf zone.
Tide-modified beaches are characterized by a RTR that
lies between 3 and 10, which implies that the tidal range is
increasing and/or wave height is decreasing. This
morphodynamic beach type usually has a steeply sloping,
cusped, and reflective beachface that is developed in
coarser-grained sediments to produce a so-called high-tide
beach. Tide-modified morphotypes are fronted by a wide,
finer-grained, low-gradient, often featureless, intertidal
zone (up to 200 m wide), seaward of which lies a low-tide
surf zone that may contain bars and rip channels.
Tide-dominated beaches are produced when the RTR
lies between 10 and approximately 50, implying high tides
and/or very low waves (H << 0.3 m). These morphotypes
are characterized by a low elevation, coarse-grained sediments, irregular, high-tide beach that is fronted by
low-gradient (<<1
) intertidal sand or mud flats that
may be hundreds of meters wide. Beyond an RTR of
50, tidal flats typically prevail.
An additional morphodynamic beach type is associated
with a high-tide reflective beachface that is fronted by
intertidal rock flats in middle latitudes. In tropical zones,
the high-tide beach may be fronted by a fringing coral reef
flat. High latitude morphotypes are seasonally exposed to
freezing air and water temperatures that lead to the development of sea ice, shoreface ice, and a frozen snowcovered beach (Short and Woodroffe, 2009).
Summary
Although seemingly simple in appearance, beaches are
complex systems where many aspects of their formation
are incompletely understood. The morphological results
of interactions between processes and materials are categorized in a range of processes-based beach types that
are easily recognizable on beaches of the world. Beach
processes are observed to operate over myriametric
(macro-, meso-, micro-) scales and a range of time frames
with grains on the beachface changing by the second to
some sand bars that may persist for hundreds of years.
Complete understanding of how beaches evolve
(accrete) and devolve (erode) over time in different kinds
of sedimentary environments provides scope for future
BEACH PROCESSES
53
conditions return sand back to the beach so that the summer beach is covered with a layer of sand that is moved
south by alongshore currents and onshore by low-energy
wave climate. Other researchers have noted associations
between waves, breakers, and beach gradients – the relationship occurring because breaker type is a function of
wave characteristics (Pethick, 1984). High values of the
surf-scaling factor (e.g., Guza and Inman, 1975) are associated, for example, with wide flat beaches with spilling
breakers, while low values are associated with steep narrow beaches and surging breakers (e.g., Wright et al.,
1979; Wright et al., 1982). Although the relationship
between wave steepness and beach gradient is pronounced, other variables such as the angle of the wave
approach (e.g., Sonu and van Beek, 1971) and tides and
longshore currents (e.g., Davis, 1985) may also be
important.
Morphodynamic beach types
Beach morphotypes range through a sequence of processform-materials systems between end points marked by
low-energy systems with small beach-building waves to
high-energy systems with large waves breaking across
several hundred meters of surf zone (Wright and Short,
1984). Tides are an additional consideration in beach formation as they range from micro (<2 m), meso (2–4 m),
macro (4–8 m), to mega tides (>8 m). Beaches are divided
into the three basic morphodynamic types in order to
accommodate tidal ranges, wave heights, and variations
in grain size (sand to boulders), viz., wave dominated, tide
modified, and tide dominated, based on the relative tide
range (RTR) (Short, 2006). This process-based grouping
of beach morphotypes, as initially conceived by Wright
et al. (1982) and expanded to beaches around the Australian continent by Short (1999, 2006, 2012), provides
a basis for cataloguing a range of beach processes associated with beaches in low latitude and mid-latitude.
Ice-coast beach processes are not yet comprehensively
included in the system. Some essential facets of the
morphodynamic classification of beaches are briefly summarized here from Short (2012) and Short and
Woodroffe (2009).
Wave-dominated beaches are characterized by a RTR
tide range that is less than three times the average wave
height (RTR < 3). These beaches occur in three
morphodynamic states that are referred to as (1) reflective,
(2) intermediate, and (3) dissipative.
Reflective beaches are the result of process-material interactions that are associated with lower waves (H <
0.5 m), longer wave periods, and coarser sediment. As
a result of these process-form relationships, all coarse
sand and cobble-boulder beaches exhibit a reflective
beach state. Reflective beaches contain a relatively
steep beachface (5–20
) that reflects backwash. Reflective beach processes do not produce a bar or surf zone.
Intermediate beaches are common along open coasts and
are produced by moderate waves (H ¼ 0.5–2.5 m)
interacting with fine- to medium-grained sand. These
types of beaches are characterized by a surf zone with
one or two bars up to 100 m wide. The bar is typically
traversed by regularly spaced shore-perpendicular rip
channels and currents.
Dissipative beaches are produced by high waves (H >
2.5 m) interacting with fine-grained sand. These
morphotypes are characterized by gently seawardsloping beachfaces with low-gradient swash (~1
) and
300–500 m wide surf zone that contains at least two
bars. Waves sequentially break on the outer bar first
and then on inner bars and in the process dissipate their
energy as they move through the surf zone.
Tide-modified beaches are characterized by a RTR that
lies between 3 and 10, which implies that the tidal range is
increasing and/or wave height is decreasing. This
morphodynamic beach type usually has a steeply sloping,
cusped, and reflective beachface that is developed in
coarser-grained sediments to produce a so-called high-tide
beach. Tide-modified morphotypes are fronted by a wide,
finer-grained, low-gradient, often featureless, intertidal
zone (up to 200 m wide), seaward of which lies a low-tide
surf zone that may contain bars and rip channels.
Tide-dominated beaches are produced when the RTR
lies between 10 and approximately 50, implying high tides
and/or very low waves (H << 0.3 m). These morphotypes
are characterized by a low elevation, coarse-grained sediments, irregular, high-tide beach that is fronted by
low-gradient (<<1
) intertidal sand or mud flats that
may be hundreds of meters wide. Beyond an RTR of
50, tidal flats typically prevail.
An additional morphodynamic beach type is associated
with a high-tide reflective beachface that is fronted by
intertidal rock flats in middle latitudes. In tropical zones,
the high-tide beach may be fronted by a fringing coral reef
flat. High latitude morphotypes are seasonally exposed to
freezing air and water temperatures that lead to the development of sea ice, shoreface ice, and a frozen snowcovered beach (Short and Woodroffe, 2009).
Summary
Although seemingly simple in appearance, beaches are
complex systems where many aspects of their formation
are incompletely understood. The morphological results
of interactions between processes and materials are categorized in a range of processes-based beach types that
are easily recognizable on beaches of the world. Beach
processes are observed to operate over myriametric
(macro-, meso-, micro-) scales and a range of time frames
with grains on the beachface changing by the second to
some sand bars that may persist for hundreds of years.
Complete understanding of how beaches evolve
(accrete) and devolve (erode) over time in different kinds
of sedimentary environments provides scope for future
BEACH PROCESSES
53