80 mph and forward speed of 50 mph will have relative
winds of 130 and 30 mph on opposite sides of the storm.
Timing: The time of the storm with relation to the tide
makes a significant impact on the magnitude of storm
surge. For example, consider an area with an 8 ft normal
tide range. If storm surge is 10 ft, at low tide the additional water level would only be 2 ft above the normal
high tide elevation; however, if the surge occurs at high
tide, the water level would be 10 ft above the normal
high tide elevation at that time.
Storm Size: The greater the storm size (radius of maximum
winds speed), the larger the surge and area the surge
will impact.
Angle of Approach: The angle of the storm path relative to
the coast will play a significant role in determining the
overall surge. Comparing two similar storms, the surge
from a storm moving along the coast will be significantly less than one making direct landfall.
Central Pressure: For significant storms (i.e., hurricanes),
the central pressure on the water surface makes a small
but finite contribution to the overall surge.
Bibliography
Coastal and Hydraulics Laboratory (CHL), 2013. U.S. Army Corps
of Engineers. U.S. Department of Defense (available at http://
chl.erdc.usace.army.mil/glossary). Accessed 22 April 2013.
National Hurricane Center (NHC), 2013. National Oceanic &
Atmospheric Administration (NOAA), U.S. Department of
Commerce (available at http://www.nhc.noaa.gov). Accessed
1 May 2013.
Cross-references
Extratropical Storms
Extreme Events (Hurricanes)
STRATIGRAPHY OF ESTUARIES
Vic Semeniuk
V & C Semeniuk Research Group, Warwick,
WA, Australia
Definition
The stratigraphy of estuaries is the vertical and lateral
array of sediments that occur in smaller-scale environments within an estuary, as well as longitudinally and
transversely across the whole of an estuary.
Stratigraphy of estuaries: overview and settings
Estuarine stratigraphy can be viewed at two scales: firstly,
the environmentally distinct small-scale stratigraphy,
reflecting processes and products of internal estuarine
geomorphic units and their sedimentary environments,
and, secondly, at the larger scale, the stratigraphy for the
whole estuary that represents the amalgamation of smallscale stratigraphic suites into estuarine-longitudinal and
estuarine-transverse mosaics. At both scales, there are
a range of environmental factors and processes which contribute to a striking spatial variability of stratigraphy. Prior
to describing the small-scale stratigraphy and the lithologic detail of the large-scale stratigraphy, the setting of
estuaries and the processes and determinative factors leading to sediment generation and accumulation are
described to provide an understanding of the development
of sedimentary and stratigraphic suites.
The landform settings and origin of estuaries are variable, ranging from incised valleys, such as rias and fjords,
to flooded valleys on coastal plains, to barred rias, and to
barred coastal plain lagoons that have a riverine input
and an ocean outlet. Depending on their original geomorphology, the extent of inundation by the Holocene
postglacial transgression, and local wave and wind energy,
the forms of estuaries range from open estuarine bays, to
narrow estuarine bays or gulfs, to inlets that are partly
barred or nearly fully barred basins. Estuaries also occur
in a wide spectrum of climates and reside in different
coastal energy settings dominated either by waves, tides,
or wind or combinations of the three. Sediments derive
from a range of drainage basin types and sizes, and from
different source rock provenances in different climatic settings, resulting in variable volumes of sediment influx,
and different types and sizes of sediment particles. As
such, estuaries exhibit diverse attributes such as size and
shape, sediment sources, sediment influx rates, hydrodynamic/sedimentary dynamics, and, of course, stratigraphic
packages. Reflecting this variability in setting, coastal and
estuarine processes, and estuarine form (Figure 1), there
are a wide range of stratigraphic packages that can occur
in estuaries.
One of the settings in which estuaries also occur is in
the outlet mouths of distributary channels of large marine
deltas, but in this context, the stratigraphy therein is that of
the enclosing delta (see Gould, 1970; Coleman et al.,
1970; Allen, 1970; Reineck and Singh, 1980) and will
not be described here.
The essence of an estuary is that it is a river-to-marine
transitional environment where marine salinity is measurably diluted by (riverine) freshwater in a valley tract, an
inlet, a coastal lagoon, or an embayment, producing
a salinity gradient from the river to the sea. In terms of
hydrochemistry, biota, and processes, there are a riverine
component toward the landward part of an estuary and
a marine component toward the seaward part (Figure 2).
This salinity gradient from river to sea is mirrored in the
gradients in sedimentary processes, sediment types,
facies, and stratigraphy. While this is a hydrochemical perception, geologists have emphasized the sedimentologic/
stratigraphic aspects of an estuary (Dalrymple
et al., 1992), viewing the basin of an estuary as
a sedimentary sink for sediments deriving from both
STRATIGRAPHY OF ESTUARIES
623
winds of 130 and 30 mph on opposite sides of the storm.
Timing: The time of the storm with relation to the tide
makes a significant impact on the magnitude of storm
surge. For example, consider an area with an 8 ft normal
tide range. If storm surge is 10 ft, at low tide the additional water level would only be 2 ft above the normal
high tide elevation; however, if the surge occurs at high
tide, the water level would be 10 ft above the normal
high tide elevation at that time.
Storm Size: The greater the storm size (radius of maximum
winds speed), the larger the surge and area the surge
will impact.
Angle of Approach: The angle of the storm path relative to
the coast will play a significant role in determining the
overall surge. Comparing two similar storms, the surge
from a storm moving along the coast will be significantly less than one making direct landfall.
Central Pressure: For significant storms (i.e., hurricanes),
the central pressure on the water surface makes a small
but finite contribution to the overall surge.
Bibliography
Coastal and Hydraulics Laboratory (CHL), 2013. U.S. Army Corps
of Engineers. U.S. Department of Defense (available at http://
chl.erdc.usace.army.mil/glossary). Accessed 22 April 2013.
National Hurricane Center (NHC), 2013. National Oceanic &
Atmospheric Administration (NOAA), U.S. Department of
Commerce (available at http://www.nhc.noaa.gov). Accessed
1 May 2013.
Cross-references
Extratropical Storms
Extreme Events (Hurricanes)
STRATIGRAPHY OF ESTUARIES
Vic Semeniuk
V & C Semeniuk Research Group, Warwick,
WA, Australia
Definition
The stratigraphy of estuaries is the vertical and lateral
array of sediments that occur in smaller-scale environments within an estuary, as well as longitudinally and
transversely across the whole of an estuary.
Stratigraphy of estuaries: overview and settings
Estuarine stratigraphy can be viewed at two scales: firstly,
the environmentally distinct small-scale stratigraphy,
reflecting processes and products of internal estuarine
geomorphic units and their sedimentary environments,
and, secondly, at the larger scale, the stratigraphy for the
whole estuary that represents the amalgamation of smallscale stratigraphic suites into estuarine-longitudinal and
estuarine-transverse mosaics. At both scales, there are
a range of environmental factors and processes which contribute to a striking spatial variability of stratigraphy. Prior
to describing the small-scale stratigraphy and the lithologic detail of the large-scale stratigraphy, the setting of
estuaries and the processes and determinative factors leading to sediment generation and accumulation are
described to provide an understanding of the development
of sedimentary and stratigraphic suites.
The landform settings and origin of estuaries are variable, ranging from incised valleys, such as rias and fjords,
to flooded valleys on coastal plains, to barred rias, and to
barred coastal plain lagoons that have a riverine input
and an ocean outlet. Depending on their original geomorphology, the extent of inundation by the Holocene
postglacial transgression, and local wave and wind energy,
the forms of estuaries range from open estuarine bays, to
narrow estuarine bays or gulfs, to inlets that are partly
barred or nearly fully barred basins. Estuaries also occur
in a wide spectrum of climates and reside in different
coastal energy settings dominated either by waves, tides,
or wind or combinations of the three. Sediments derive
from a range of drainage basin types and sizes, and from
different source rock provenances in different climatic settings, resulting in variable volumes of sediment influx,
and different types and sizes of sediment particles. As
such, estuaries exhibit diverse attributes such as size and
shape, sediment sources, sediment influx rates, hydrodynamic/sedimentary dynamics, and, of course, stratigraphic
packages. Reflecting this variability in setting, coastal and
estuarine processes, and estuarine form (Figure 1), there
are a wide range of stratigraphic packages that can occur
in estuaries.
One of the settings in which estuaries also occur is in
the outlet mouths of distributary channels of large marine
deltas, but in this context, the stratigraphy therein is that of
the enclosing delta (see Gould, 1970; Coleman et al.,
1970; Allen, 1970; Reineck and Singh, 1980) and will
not be described here.
The essence of an estuary is that it is a river-to-marine
transitional environment where marine salinity is measurably diluted by (riverine) freshwater in a valley tract, an
inlet, a coastal lagoon, or an embayment, producing
a salinity gradient from the river to the sea. In terms of
hydrochemistry, biota, and processes, there are a riverine
component toward the landward part of an estuary and
a marine component toward the seaward part (Figure 2).
This salinity gradient from river to sea is mirrored in the
gradients in sedimentary processes, sediment types,
facies, and stratigraphy. While this is a hydrochemical perception, geologists have emphasized the sedimentologic/
stratigraphic aspects of an estuary (Dalrymple
et al., 1992), viewing the basin of an estuary as
a sedimentary sink for sediments deriving from both
STRATIGRAPHY OF ESTUARIES
623