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The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. At water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion above.


Process

In
seawater Seawater, or sea 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 approximat ...
, the water particles are moved in a circular
orbital motion In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an obj ...
when a wave passes. The
radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...
of the circle of motion for any given water molecule decreases exponentially with increasing depth. The wave base, which is the depth of influence of a water wave, is about half the
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
. 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 that is agitated by this everyday wave action, known as the Upper shoreface. 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. 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)


See also

* Upper shoreface — ''above wave base'' * Lower shoreface — ''below wave base'' * Airy wave theory * Dispersion (water waves) * Waves and shallow water


References

{{physical oceanography, state=open Water waves Wave mechanics Physical oceanography