Thewave base, inphysical oceanography, is the maximum depth at which awater wave's passage causes significant water motion. At water depths deeper than the wave base, bottom sediments and theseafloor are no longer stirred by the wave motion above.[1]
Inseawater, the water particles are moved in a circularorbital motion when a wave passes. Theradius of the circle of motion for any given water molecule decreasesexponentially with increasing depth. The wave base, which is the depth of influence of a water wave, is about half thewavelength.
At depths greater than half the wavelength, the water motion is less than 4% of its value at the water surface[2] and may be neglected.
For example, in a pool of water 1 metre (3.3 ft) deep, a wave with a 3 metres (9.8 ft) wavelength would be moving the water at the bottom. In the same pool, a wave with a wavelength of 0.5 metres (1.6 ft) would not be able to cause water movement on the bottom.
There are typically two wave bases, the fair weather wave base (FWWB) and the storm wave base (SWB).[1]
The fair weather wave base refers to the depth beneath the waves under normal conditions and the portion of theseafloor that is agitated by this everyday wave action, known as theUpper 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 theLower 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, whereasUpper offshore is the name given to the zone only affected by storm waves andLower offshore a zone not disturbed by any surface wave. (e.g.[3])
