Ota, Y., 1986. Marine terraces as reference surfaces in late Quaternary tectonics studies: examples from the Pacific Rim. Royal
Society of New Zealand, 24, 357–375.
Wellman, H. W., 1967. Tilted marine beach ridges at Cape
Turakirae, N. Z., In Ikebe, N. (ed.), Sea level changes and crustal
movements of the Pacific during the Pliocene and post-Pliocene
time. Journal of Geosciences, Vol. 10, pp. 123–129.
Cross-references
Mean Sea Level
Uplifted Coasts
SHORELINE CHANGES
A. C. Narayana
Centre for Earth & Space Sciences, University of
Hyderabad, Hyderabad, Andhra Pradesh, India
Synonyms
Coastline changes
Definition
Shorelines change boundary conditions in an estuary or
ocean due to sea level fluctuations, circulation patterns,
waves and tides, and the amount of sediment supply. The
shoreline is quite narrow, linear in extent, and always in
contact with the estuarine waterbody or sea. It is
a physical interface of land and an estuary or sea and
defined in both temporal and spatial terms.
Introduction
Morphodynamics of a coast can be defined as the “mutual
adjustment of topography and fluid dynamics involving
sediment transport” (Wright and Thom, 1977) or, alternatively, the “dynamic behaviour of alluvial boundaries” of
fluid motions (De Vriend, 1991). The evolution of coastal
systems is the result of morphodynamics that develop in
response to change in external conditions (Wright and
Thom, 1977) and controlled by various factors such as
morphology, geology, and size of the catchment area;
nature of sediments; climate leading to rainfall and river
discharge at coastal zone; freshwater input; and coastal
hydrodynamics – waves, tides, and currents (Albert and
Jorge, 1998). Many of the regional controls on sea level
involve long-term geological processes (subsidence, isostasy) and have a profound influence on controlling shortterm dynamics. As sea levels fluctuate, the morphology
of a coastal zone will further evolve, changing the boundary conditions of other coastal processes, viz., circulation,
waves, tides, and deposition of sediments on shorelines.
The shoreline is a part of coastal land in contact with the
estuary or sea and is continuous around ocean basins. It
has remarkable linear extent but is usually quite narrow.
The width of shorelines is defined by tidal flux – the zone
between the lowest low tide and the highest high tide.
Because of the dynamic nature of the shoreline boundary,
the definition must consider the shoreline in both
a temporal and spatial sense (Boak and Turner, 2005).
An idealized definition of shoreline is that it coincides
with the physical interface of land and water (Dolan
et al., 1980). In reality, the shoreline position changes continually through time, because of cross-shore and alongshore sediment movement in the littoral zone and
especially because of the dynamic nature of water levels
at the coastal boundary (e.g., waves, tides, storm surge,
setup, run-up, etc.).
The shoreline is the position of the land–water interface
at one instant in time. A shoreline may also be considered
over a slightly longer time scale, such as a tidal cycle,
where the horizontal/vertical position of the shoreline
can vary between centimeters and tens of meters
(or more), depending on the beach slope, tidal range, and
prevailing wave/weather conditions. Over a longer time
scale, such as 100 years or more, the position of the shoreline may vary by hundreds of meters or more (Komar,
1998). The shoreline is a time-dependent phenomenon
that may exhibit substantial short-term variability
(Morton, 1991).
The shoreline is a vital part of the coastal zone. The
study of shorelines is very important to understand the
interactions between parts of the hydrosphere, atmosphere, and solid earth. The atmosphere is involved in
transferring the energy from wind to water, thereby causing waves, which in turn generate nearshore currents.
The gravitational attraction of the moon and sun on ocean
waters is responsible for the rhythmic rise and fall of tides.
As a dynamic system, shorelines continuously adjust to
any change that takes place, such as increased wave
energy or an increase or decrease in sediment supply.
Due to the dynamic nature of the shoreline boundary, it
can be used as a proxy to represent the “true” shoreline
positions. The shoreline positions can be investigated
and classified based on (1) visual observation
(a previous high-tide line or the wet/dry boundary),
(2) tidal datum-based shoreline indicator (mean high water
or mean sea level), and (3) application of image
processing techniques to extract proxy shoreline features
from digital coastal images (Boak and Turner, 2005).
Shoreline position measurements of different time periods
can be used to derive quantitative estimates of the rate of
progradation/retrogradation (Fenster et al., 1993). Human
intervention in coastal regions has modified pristine coastlines around the globe by deforestation, cultivation,
changes in habitat, urbanization, and upstream obstructions to river flows. The rate of change in coastal landforms and shoreline position is important in the
development of setback planning, hazard zoning, erosion/accretion perspectives, sediment budgeting, and conceptual/predictive modeling of coastal morphodynamics
(Sherman and Bauer, 1993; Chandramohan et al., 1994;
Al Bakri, 1996; Zuzek et al., 2003; Kumar and Jayappa,
2009; Kumar et al., 2010). The discussion below focuses
on shoreline processes, erosion and deposition, impact of
590
SHORELINE CHANGES
Society of New Zealand, 24, 357–375.
Wellman, H. W., 1967. Tilted marine beach ridges at Cape
Turakirae, N. Z., In Ikebe, N. (ed.), Sea level changes and crustal
movements of the Pacific during the Pliocene and post-Pliocene
time. Journal of Geosciences, Vol. 10, pp. 123–129.
Cross-references
Mean Sea Level
Uplifted Coasts
SHORELINE CHANGES
A. C. Narayana
Centre for Earth & Space Sciences, University of
Hyderabad, Hyderabad, Andhra Pradesh, India
Synonyms
Coastline changes
Definition
Shorelines change boundary conditions in an estuary or
ocean due to sea level fluctuations, circulation patterns,
waves and tides, and the amount of sediment supply. The
shoreline is quite narrow, linear in extent, and always in
contact with the estuarine waterbody or sea. It is
a physical interface of land and an estuary or sea and
defined in both temporal and spatial terms.
Introduction
Morphodynamics of a coast can be defined as the “mutual
adjustment of topography and fluid dynamics involving
sediment transport” (Wright and Thom, 1977) or, alternatively, the “dynamic behaviour of alluvial boundaries” of
fluid motions (De Vriend, 1991). The evolution of coastal
systems is the result of morphodynamics that develop in
response to change in external conditions (Wright and
Thom, 1977) and controlled by various factors such as
morphology, geology, and size of the catchment area;
nature of sediments; climate leading to rainfall and river
discharge at coastal zone; freshwater input; and coastal
hydrodynamics – waves, tides, and currents (Albert and
Jorge, 1998). Many of the regional controls on sea level
involve long-term geological processes (subsidence, isostasy) and have a profound influence on controlling shortterm dynamics. As sea levels fluctuate, the morphology
of a coastal zone will further evolve, changing the boundary conditions of other coastal processes, viz., circulation,
waves, tides, and deposition of sediments on shorelines.
The shoreline is a part of coastal land in contact with the
estuary or sea and is continuous around ocean basins. It
has remarkable linear extent but is usually quite narrow.
The width of shorelines is defined by tidal flux – the zone
between the lowest low tide and the highest high tide.
Because of the dynamic nature of the shoreline boundary,
the definition must consider the shoreline in both
a temporal and spatial sense (Boak and Turner, 2005).
An idealized definition of shoreline is that it coincides
with the physical interface of land and water (Dolan
et al., 1980). In reality, the shoreline position changes continually through time, because of cross-shore and alongshore sediment movement in the littoral zone and
especially because of the dynamic nature of water levels
at the coastal boundary (e.g., waves, tides, storm surge,
setup, run-up, etc.).
The shoreline is the position of the land–water interface
at one instant in time. A shoreline may also be considered
over a slightly longer time scale, such as a tidal cycle,
where the horizontal/vertical position of the shoreline
can vary between centimeters and tens of meters
(or more), depending on the beach slope, tidal range, and
prevailing wave/weather conditions. Over a longer time
scale, such as 100 years or more, the position of the shoreline may vary by hundreds of meters or more (Komar,
1998). The shoreline is a time-dependent phenomenon
that may exhibit substantial short-term variability
(Morton, 1991).
The shoreline is a vital part of the coastal zone. The
study of shorelines is very important to understand the
interactions between parts of the hydrosphere, atmosphere, and solid earth. The atmosphere is involved in
transferring the energy from wind to water, thereby causing waves, which in turn generate nearshore currents.
The gravitational attraction of the moon and sun on ocean
waters is responsible for the rhythmic rise and fall of tides.
As a dynamic system, shorelines continuously adjust to
any change that takes place, such as increased wave
energy or an increase or decrease in sediment supply.
Due to the dynamic nature of the shoreline boundary, it
can be used as a proxy to represent the “true” shoreline
positions. The shoreline positions can be investigated
and classified based on (1) visual observation
(a previous high-tide line or the wet/dry boundary),
(2) tidal datum-based shoreline indicator (mean high water
or mean sea level), and (3) application of image
processing techniques to extract proxy shoreline features
from digital coastal images (Boak and Turner, 2005).
Shoreline position measurements of different time periods
can be used to derive quantitative estimates of the rate of
progradation/retrogradation (Fenster et al., 1993). Human
intervention in coastal regions has modified pristine coastlines around the globe by deforestation, cultivation,
changes in habitat, urbanization, and upstream obstructions to river flows. The rate of change in coastal landforms and shoreline position is important in the
development of setback planning, hazard zoning, erosion/accretion perspectives, sediment budgeting, and conceptual/predictive modeling of coastal morphodynamics
(Sherman and Bauer, 1993; Chandramohan et al., 1994;
Al Bakri, 1996; Zuzek et al., 2003; Kumar and Jayappa,
2009; Kumar et al., 2010). The discussion below focuses
on shoreline processes, erosion and deposition, impact of
590
SHORELINE CHANGES