Cross-references
Anthropogenic Impacts
Beach Management
Beach Processes
Estuarine Beaches
Shoreline
SHORELINE UNDULATIONS
Miguel Ortega-Sánchez, Alejandro López-Ruiz,
Asunción Baquerizo Azofra and
Miguel A. Losada Rodríguez
Andalusian Institute for Earth System Research,
University of Granada, Granada, Spain
Synonyms
Shoreline sand waves
Definition
Shoreline undulations are medium to large spatial scale
shoreline geomorphic features with longshore dimensions
ranging from hundreds to thousands of meters and amplitudes from tens to hundreds of meters.
Description
Shoreline undulations are generally classified under rhythmic coastline features, although many examples are neither periodic nor regularly spaced (López-Ruiz et al.,
2012). They can be episodically or persistently found
along many shorelines all over the world, including regular rectilinear or slightly curved beaches and river mouths
and estuaries. They are also frequently found associated
with sudden changes in the orientation of the coast such
as at spits (Kaergaard and Fredsoe, 2013) and near human
infrastructures. Many authors refer to these features as
shoreline sand waves, but the latter are generally considered rhythmically spaced and migrating alongshore. It is
generally assumed that, when an undulation is present at
the shoreline, the bathymetry is parallel to this undulation
down to a certain depth.
The mechanism(s) behind the formation of shoreline
undulations is still not well understood. The main working
hypothesis in recent years is that coastlines with a wave
climate dominated by very oblique incidence commonly
feature large-scale undulations, suggesting that this instability mechanism could be mainly responsible for the formation of regularly spaced shoreline undulations. Recent
advances reveal that the variation of alongshore sediment
transport with the angle formed by the wave crests and the
coastline, as well as the surf zone width, plays a major role
in the development of shoreline undulations. This process
is important at estuarine and river mouths, littoral spits,
and curved coastlines and close to human interventions
(e.g., jetties) where the nearshore wave regimen is intensively modified. Whatever the case may be, detailed
description of the nearshore hydrodynamics is required
for modeling shoreline undulations.
Bibliography
Kaergaard, K., and Fredsoe, J., 2013. Numerical modeling of shoreline undulations part 2: varying wave climate and comparison
with observations. Coastal Engineering, 75, 77–90.
López-Ruiz, A., Ortega-Sánchez, M., Baquerizo, A., and Losada,
M. A., 2012. Short- and medium-term evolution of shoreline
undulations on curvilinear coasts. Geomorphology, 159–160,
189–200.
Cross-references
Coastal Barriers
Coastal Landforms
Sand Ridge
Sediment Transport
Shoreline
Spit
SIDE-SCAN SONAR IMAGING OF SEDIMENT
BEDLOAD
Juan A. Morales and Irene Delgado
Department of Geology, Excellence Campus of Marine
Sciences (CEIMAR), University of Huelva,
Huelva, Spain
Synonyms
Side-imaging sonar of bottom sediments; Side-scan sonar
of bed morphology; Side-scan sonar of sedimentary beds
Definition
Side-scan sonar is a type of acoustic sonar system used to
obtain clear images of the surface of underwater floors.
The system works by means of a beam of acoustic pulses
which open vertically as a fan shape to both sides of the
ship. Each acoustic pulse reflects on the floor and returns
to the sensor. The intensity of the received reflected pulse
depends on the nature and morphology of the bottom.
The conjunction of all the received pulses can build an
accurate image of the bed.
Sediment bedload refers to coarse sedimentary particles
like sand and gravel that are transported very close to the
bed because the relationship between the grain size and
flow velocity is near the transport threshold.
Introduction
Side-scan sonar imaging is a geophysical method used in
marine engineering, underwater archaeology, and military
applications (mining detection). It is also used for
sedimentological interpretations of bed configurations
(Wright et al., 1987; Anthony and Leth, 2002; Kuijpers
et al., 2002; Gómez et al., 2010). In this case, the application of the acoustic geophysical techniques enables the
602
SHORELINE UNDULATIONS
Anthropogenic Impacts
Beach Management
Beach Processes
Estuarine Beaches
Shoreline
SHORELINE UNDULATIONS
Miguel Ortega-Sánchez, Alejandro López-Ruiz,
Asunción Baquerizo Azofra and
Miguel A. Losada Rodríguez
Andalusian Institute for Earth System Research,
University of Granada, Granada, Spain
Synonyms
Shoreline sand waves
Definition
Shoreline undulations are medium to large spatial scale
shoreline geomorphic features with longshore dimensions
ranging from hundreds to thousands of meters and amplitudes from tens to hundreds of meters.
Description
Shoreline undulations are generally classified under rhythmic coastline features, although many examples are neither periodic nor regularly spaced (López-Ruiz et al.,
2012). They can be episodically or persistently found
along many shorelines all over the world, including regular rectilinear or slightly curved beaches and river mouths
and estuaries. They are also frequently found associated
with sudden changes in the orientation of the coast such
as at spits (Kaergaard and Fredsoe, 2013) and near human
infrastructures. Many authors refer to these features as
shoreline sand waves, but the latter are generally considered rhythmically spaced and migrating alongshore. It is
generally assumed that, when an undulation is present at
the shoreline, the bathymetry is parallel to this undulation
down to a certain depth.
The mechanism(s) behind the formation of shoreline
undulations is still not well understood. The main working
hypothesis in recent years is that coastlines with a wave
climate dominated by very oblique incidence commonly
feature large-scale undulations, suggesting that this instability mechanism could be mainly responsible for the formation of regularly spaced shoreline undulations. Recent
advances reveal that the variation of alongshore sediment
transport with the angle formed by the wave crests and the
coastline, as well as the surf zone width, plays a major role
in the development of shoreline undulations. This process
is important at estuarine and river mouths, littoral spits,
and curved coastlines and close to human interventions
(e.g., jetties) where the nearshore wave regimen is intensively modified. Whatever the case may be, detailed
description of the nearshore hydrodynamics is required
for modeling shoreline undulations.
Bibliography
Kaergaard, K., and Fredsoe, J., 2013. Numerical modeling of shoreline undulations part 2: varying wave climate and comparison
with observations. Coastal Engineering, 75, 77–90.
López-Ruiz, A., Ortega-Sánchez, M., Baquerizo, A., and Losada,
M. A., 2012. Short- and medium-term evolution of shoreline
undulations on curvilinear coasts. Geomorphology, 159–160,
189–200.
Cross-references
Coastal Barriers
Coastal Landforms
Sand Ridge
Sediment Transport
Shoreline
Spit
SIDE-SCAN SONAR IMAGING OF SEDIMENT
BEDLOAD
Juan A. Morales and Irene Delgado
Department of Geology, Excellence Campus of Marine
Sciences (CEIMAR), University of Huelva,
Huelva, Spain
Synonyms
Side-imaging sonar of bottom sediments; Side-scan sonar
of bed morphology; Side-scan sonar of sedimentary beds
Definition
Side-scan sonar is a type of acoustic sonar system used to
obtain clear images of the surface of underwater floors.
The system works by means of a beam of acoustic pulses
which open vertically as a fan shape to both sides of the
ship. Each acoustic pulse reflects on the floor and returns
to the sensor. The intensity of the received reflected pulse
depends on the nature and morphology of the bottom.
The conjunction of all the received pulses can build an
accurate image of the bed.
Sediment bedload refers to coarse sedimentary particles
like sand and gravel that are transported very close to the
bed because the relationship between the grain size and
flow velocity is near the transport threshold.
Introduction
Side-scan sonar imaging is a geophysical method used in
marine engineering, underwater archaeology, and military
applications (mining detection). It is also used for
sedimentological interpretations of bed configurations
(Wright et al., 1987; Anthony and Leth, 2002; Kuijpers
et al., 2002; Gómez et al., 2010). In this case, the application of the acoustic geophysical techniques enables the
602
SHORELINE UNDULATIONS