The wave base, in
physical oceanography, is the maximum depth at which a
water wave
In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction of t ...
's passage causes significant water motion. At water depths deeper than the wave base, bottom sediments and the
seafloor
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth an ...
are no longer stirred by the wave motion above.
Process
In
seawater
Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appr ...
, the water particles are moved in a circular
orbital motion when a wave passes. The
radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
of the circle of motion for any given water molecule decreases
exponentially
Exponential may refer to any of several mathematical topics related to exponentiation, including:
*Exponential function, also:
**Matrix exponential, the matrix analogue to the above
*Exponential decay, decrease at a rate proportional to value
*Expo ...
with increasing depth. The wave base, which is the depth of influence of a water wave, is about half the
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
.
At depths greater than half the wavelength, the water motion is less than 4% of its value at the water surface and may be neglected.
For example, in a pool of water deep, a wave with a wavelength would be moving the water at the bottom. In the same pool, a wave with a wavelength of would not be able to cause water movement on the bottom.
Distinctions
There are typically two wave bases, the fair weather wave base (FWWB) and the storm wave base (SWB).
The fair weather wave base refers to the depth beneath the waves under normal conditions and the portion of the
seafloor
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth an ...
that is agitated by this everyday wave action, known as the
Upper shoreface
Upper Shoreface refers to the portion of the seafloor that is shallow enough to be agitated by everyday wave action, the wave base.
Below that is the lower shoreface.
Process
The continuous agitation of the sea floor in the upper shoreface en ...
.
The storm wave base refers to the depths beneath storm-driven waves and can be much deeper. The portion of the seafloor that is only agitated by storm-driven wave action is known as the
Lower shoreface
Lower Shoreface refers to the portion of the seafloor, and the sedimentary depositional environment, that lies below the everyday wave base.
It is also used for the sandstone sedimentary structure rock formations that were produced by this proce ...
.
Note that another classification exists, which considers that the zone affected by both fair weather and storm waves is to be defined as shoreface, whereas ''Upper offshore'' is the name given to the zone only affected by storm waves and ''Lower offshore'' a zone not disturbed by any surface wave. (''e.g.''
[Bayetgoll ''et al.'', 2015,
Ichnology and sedimentology of a shallow marine Upper Cretaceous depositional system (Neyzar Formation, Kopet-Dagh, Iran): Palaeoceanographic influence on ichnodiversity, ''Cretaceous Research'', 56, 628-646])
Types Of Wave Bases
fair weather base: it is a sea depth of 5 to 15m below sea level where the sea bed is unaffected by the action of waves in the calm wave conditions.
See also
*
Upper shoreface
Upper Shoreface refers to the portion of the seafloor that is shallow enough to be agitated by everyday wave action, the wave base.
Below that is the lower shoreface.
Process
The continuous agitation of the sea floor in the upper shoreface en ...
— ''above wave base''
*
Lower shoreface
Lower Shoreface refers to the portion of the seafloor, and the sedimentary depositional environment, that lies below the everyday wave base.
It is also used for the sandstone sedimentary structure rock formations that were produced by this proce ...
— ''below wave base''
*
Airy wave theory
In fluid dynamics, Airy wave theory (often referred to as linear wave theory) gives a linearised description of the propagation of gravity waves on the surface of a homogeneous fluid layer. The theory assumes that the fluid layer has a uniform mea ...
*
Dispersion (water waves)
In fluid dynamics, dispersion of water waves generally refers to frequency dispersion, which means that waves of different wavelengths travel at different phase speeds. Water waves, in this context, are waves propagating on the water surface, ...
*
Waves and shallow water
References
{{physical oceanography, state=open
Water waves
Wave mechanics
Physical oceanography