Resting water level

Geometry of a trochoidal deep water wave: To define the wavelength, the calm water level, the wave height, the horizontal and the vertical wave asymmetry.

The surface of a body of water is referred to as the water level at rest when - such as when there is no wind - there is no water level deflection . Since fixed structures in a body of water, in the additional absence of currents, are only loaded by the hydrostatic water pressure in the area of ​​their wetting , the still water level forms the reference level for every unsteady, dynamic water wave movement. For wave sequences it is defined by the fact that the cross-sectional area under the wave crest (above the calm water level) is equal to that of the wave trough (below the calm water level), see hatched areas in the figure on the right. Gravity waves differ in shape from the regular cosine shape in such a way that they are asymmetrical both horizontally and vertically. Their maximum deflection from the still water level upwards (positive) is referred to as the crest of the waves and their maximum deflection downwards (negative) as the wave trough . The sum of the amounts of both neighboring maximum deflections is the wave height ${\displaystyle H_{\mathrm {o} }}$ ${\displaystyle H_{\mathrm {u} }}$

${\displaystyle H=H_{\mathrm {o} }+H_{\mathrm {u} }}$

Are defined. The amount of the maximum positive water level deflection exceeds the maximum negative water level deflection the smaller the water depth becomes. With waves in shallow water, the height of the wave crest can be up to 3/4 of the total wave height , while the wave trough is below the calm water level. The horizontal wave asymmetry is given by the quotient ${\displaystyle H_{\mathrm {o} }}$ ${\displaystyle H_{u}}$ ${\displaystyle H}$ ${\displaystyle H/4}$

${\displaystyle H_{\mathrm {o} }/H_{\mathrm {u} }>1}$

characterized and the vertical wave asymmetry relates to the proportions of the lengths of the ridge area and the valley area in the wavelength ${\displaystyle L_{\mathrm {B} }}$ ${\displaystyle L_{\mathrm {T} }}$

${\displaystyle L=L_{\mathrm {T} }+2\cdot L_{\mathrm {B} }/2}$

${\displaystyle L_{B}/L_{T}<1}$

In trochoid waves, the water level at rest is around the measure

${\displaystyle \delta ={\frac {\pi \cdot r^{2}}{L}}=r-H_{\mathrm {u} }}$

below the center of the orbital circle.