Seiche

A seiche (/seɪʃ/ SAYSH) is a standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, harbors, caves, and seas. The key requirement for formation of a seiche is that the body of water be at least partially bounded, allowing the formation of the standing wave.

The term was promoted by the Swiss hydrologist François-Alphonse Forel in 1890, who was the first to make scientific observations of the effect in Lake Geneva.^[1] The word had apparently long been used in the region to describe oscillations in alpine lakes. According to Wilson (1972),^[2][3] this Swiss French dialect word comes from the Latin word siccus meaning "dry", i.e., as the water recedes, the beach dries. The French word sec or sèche (dry) descends from the Latin.

Seiches in harbours can be caused by long-period or

Causes and nature

Seiches are often imperceptible to the naked eye, and observers in boats on the surface may not notice that a seiche is occurring due to the extremely long periods.

The effect is caused by resonances in a body of water that has been disturbed by one or more factors, most often meteorological effects (wind and atmospheric pressure variations), seismic activity, or tsunamis.^[5] Gravity always seeks to restore the horizontal surface of a body of liquid water, as this represents the configuration in which the water is in hydrostatic equilibrium.

Vertical harmonic motion results, producing an impulse that travels the length of the basin at a velocity that depends on the depth of the water. The impulse is reflected back from the end of the basin, generating interference. Repeated reflections produce standing waves with one or more nodes, or points, that experience no vertical motion. The frequency of the oscillation is determined by the size of the basin, its depth and contours, and the water temperature.

The longest natural

${\displaystyle T={\frac {\ \ 2L\ \ }{\!\!\!{\sqrt {gh}}}}}$

where T is the longest natural period, L and h are the length and average depth of the body of water, and g the

Higher-order harmonics are also observed. The period of the second harmonic will be half the natural period, the period of the third harmonic will be a third of the natural period, and so forth.

Occurrence

Seiches have been observed on both lakes and seas. The key requirement is that the body of water be partially constrained to allow formation of standing waves. Regularity of geometry is not required; even harbours with exceedingly irregular shapes are routinely observed to oscillate with very stable frequencies.

Lake seiches

Low rhythmic seiches are almost always present on larger lakes. They are usually unnoticeable among the common wave patterns, except during periods of unusual calm.

estuaries

are often prone to small seiches with amplitudes of a few centimetres and periods of a few minutes.

The original studies in Lake Geneva by François-Alphonse Forel found the longitudinal period to have a 73-minute cycle, and the transversal seiche to have a period of around 10 minutes.^[9] Another lake well known for its regular seiches is New Zealand's Lake Wakatipu, which varies its surface height at Queenstown by 20 centimetres in a 27-minute cycle. Seiches can also form in semi-enclosed seas; the North Sea often experiences a lengthwise seiche with a period of about 36 hours.

The

of those winds. These can lead to extreme seiches of up to 5 metres (16 ft) between the ends of the lake.

The effect is similar to a storm surge like that caused by hurricanes along ocean coasts, but the seiche effect can cause oscillation back and forth across the lake for some time. In 1954, the remnants of Hurricane Hazel piled up water along the northwestern Lake Ontario shoreline near Toronto, causing extensive flooding, and established a seiche that subsequently caused flooding along the south shore.

Lake seiches can occur very quickly: on July 13, 1995, a large seiche on

Lakes in seismically active areas, such as Lake Tahoe in California/Nevada, are significantly at risk from seiches. Geological evidence indicates that the shores of Lake Tahoe may have been hit by seiches and tsunamis as much as 10 metres (33 ft) high in prehistoric times, and local researchers have called for the risk to be factored into emergency plans for the region.^[14]

The

Seiches up to at least 1.8 m (6 feet) were observed in

Sea and bay seiches

Seiches have been observed in seas such as the

.

In Japan, seiches have been observed in

period

of about 30 to 40 minutes. Locally, seiches have caused floods, destroyed port facilities and damaged the fishery: hence the local word for seiche, あびき (abiki), from 網引き (amibiki), meaning 'the dragging-away of a fishing net'.

On occasion,

Hilo Bay

is about thirty minutes. That meant that every second wave was in phase with the bay, creating a seiche. As a result, Hilo suffered worse damage than any other place in Hawaii, with the combined tsunami and seiche reaching a height of 26 feet (7.9 m) along the Bayfront, killing 96 people in the city alone. Seiche waves may continue for several days after a tsunami.

Tide-generated internal solitary waves (

Puerto Princesa in Palawan Island,^[27] Trincomalee Bay in Sri Lanka,^[28][29] and in the Bay of Fundy in eastern Canada, where seiches cause some of the highest recorded tidal fluctuations in the world.^[30] A dynamical mechanism exists for the generation of coastal seiches by deep-sea internal waves. These waves can generate a sufficient current at the shelf break to excite coastal seiches.^[31]

Underwater (internal) waves

Seiches are also observed beneath the surface of constrained bodies of water, acting along the thermocline.^[32]

In analogy with the Merian formula, the expected period of the internal wave can be expressed as:^[33]

${\displaystyle T={\frac {2L}{c}}}$ with ${\displaystyle c^{2}=g{\frac {\rho _{2}-\rho _{1}}{\rho _{2}}}{\frac {h_{1}h_{2}}{h_{1}+h_{2}}}}$

where T is the natural

, L is the length of the water body, ${\displaystyle h_{1},h_{2}}$ the average thicknesses of the two layers separated by stratification (e.g. epilimnion and hypolimnion), ${\displaystyle \rho _{1},\rho _{2}}$ the .

As the

Cave seiches

On September 19, 2022, a seiche reaching 4 feet (1.2 metres) occurred at

Engineering for seiche protection

This section needs expansion. You can help by adding to it. (June 2008)

Engineers consider seiche phenomena in the design of flood protection works (e.g.,

), potable water storage basins, harbours, and even spent nuclear fuel storage basins.

See also

• Clapotis – Non-breaking standing wave pattern
• Earthquake engineering – Study of earthquake-resistant structures
• Severe weather terminology (United States) – Terminology used by the National Weather Service to describe severe weather in the US
• Severe weather terminology (Canada) – Severe weather-related terminology used by the Meteorological Service of Canada
• Tsunamis in lakes
• Villa Epecuén – Tourist village in Argentina
• Vajont Dam, Disused gravity arch dam in Italy, destroyed by a seiche in 1963

Notes

Further reading

• Jackson, J. R. (1833). "On the Seiches of Lakes". Journal of the Royal Geographical Society of London. 3: 271–275.
  JSTOR 1797612
  .

External links

Look up seiche in Wiktionary, the free dictionary.

• "Seiche" . Encyclopædia Britannica. Vol. 24 (11th ed.). 1911.

General

• What is a seiche?
• Seiche. Encyclopædia Britannica. Retrieved January 24, 2004, from Encyclopædia Britannica Premium Service.
• Seiche calculator
• Bonanza for Lake Superior: Seiches Do More Than Move Water Archived 2011-09-28 at the Wayback Machine
• Great Lakes Storms Photo Gallery Seiches, Storm Surges, and Edge Waves Archived 2009-08-25 at the
  NOAA
• Shelf Response for an identical pair of incident KdV solitons

Relationship to aquatic "monsters"

• The Unmuseum
• "The Legend of the Lake Champlain Monster" in
  The Skeptical Inquirer
• Geological page