Aseiche (/seɪʃ/SAYSH) is astanding wave in an enclosed or partially enclosedbody of water. Seiches and seiche-related phenomena have been observed onlakes,reservoirs,swimming pools,bays,harbors,caves, andseas. 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 in 1890 by the SwisshydrologistFrançois-Alphonse Forel, who was the first to make scientific observations of the effect inLake Geneva.[1] The word had apparently long been used in the region to describe oscillations in alpine lakes. According to Wilson (1972),[2][3] thisSwiss French dialect word comes from the Latin wordsiccus meaning "dry", i.e., as the water recedes, the beach dries. The French wordsec orsèche (dry) descends from the Latin.
Seiches in harbours can be caused bylong-period orinfragravity waves, which are due to subharmonic nonlinear wave interaction with thewind waves, having periods longer than the accompanying wind-generated waves.[4]
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.[citation needed]
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, ortsunamis.[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 inhydrostatic equilibrium.[citation needed]
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 naturalperiod of a seiche is the period associated with the fundamental resonance for the body of water—corresponding to the longest standing wave. For a surface seiche in an enclosed rectangular body of water this can be estimated using Merian's formula:[6][7]
whereT is the longest natural period,L andh are the length and average depth of the body of water, andg theacceleration of gravity.[8]
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.[citation needed]
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.
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.Harbours, bays, andestuaries are often prone to small seiches with amplitudes of a few centimetres and periods of a few minutes.[citation needed]
The original studies inLake Geneva byFrançois-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'sLake Wakatipu, which varies its surface height atQueenstown by 20 centimetres in a 27-minute cycle. Seiches can also form in semi-enclosed seas; theNorth Sea often experiences a lengthwise seiche with a period of about 36 hours.
TheNational Weather Service issues low water advisories for portions of the Great Lakes when seiches of 0.6 metres (2 ft) or greater are likely to occur.[10]Lake Erie is particularly prone to wind-caused seiches because of its shallowness and its elongation on a northeast–southwest axis, which frequently matches the direction of prevailing winds and therefore maximises thefetch 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 astorm 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 ofHurricane Hazel piled up water along the northwesternLake Ontario shoreline nearToronto, 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 onLake Superior caused the water level to fall and then rise again by one metre (three feet) within fifteen minutes, leaving some boats hanging from the docks on their mooring lines when the water retreated.[11] The same storm system that caused the 1995 seiche on Lake Superior produced a similar effect inLake Huron, in which the water level atPort Huron changed by 1.8 metres (6 ft) over two hours.[12] On June 26, 1954, onLake Michigan in Chicago, eight fishermen were swept away from piers at Montrose and North Avenue Beaches and drowned when a 3-metre (10 ft) seiche hit theChicago waterfront.[13]
Lakes in seismically active areas, such asLake Tahoe inCalifornia/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]
Earthquake-generated seiches can be observed thousands of miles away from the epicentre of a quake.Swimming pools are especially prone to seiches caused by earthquakes, as the ground tremors often match the resonant frequencies of small bodies of water. The 1994Northridge earthquake inCalifornia caused swimming pools to overflow across southern California. The massiveGood Friday earthquake that hitAlaska in 1964 caused seiches in swimming pools as far away asPuerto Rico.[15] Theearthquake that hit Lisbon, Portugal in 1755 also caused seiches 2,100 kilometres (1,300 mi) farther north in Loch Lomond, Loch Long, Loch Katrine and Loch Ness inScotland,[16] and incanals inSweden. The2004 Indian Ocean earthquake caused seiches in standing water bodies in many Indian states as well as inBangladesh,Nepal, and northernThailand.[17] Seiches were again observed inUttar Pradesh,Tamil Nadu andWest Bengal inIndia as well as in many locations inBangladesh during the2005 Kashmir earthquake.[18]
The1950 Assam–Tibet earthquake is known to have generated seiches as far away asNorway and southernEngland. Other earthquakes in or near the Indian sub-continent known to have generated seiches include the1803 Kumaon-Barahat,1819 Allah Bund, 1842 Central Bengal,1905 Kangra,1930 Dhubri,1934 Nepal-Bihar,2001 Bhuj,2005 Nias and the 2005 Teresa Island earthquakes. TheFebruary 27, 2010 Chile earthquake produced a seiche onLake Pontchartrain,Louisiana, with a height of around 150 millimetres (0.5 ft). The2010 Baja California earthquake produced large seiches that quickly became an internet phenomenon.[19]
Seiches up to at least 1.8 m (6 feet) were observed inSognefjorden,Norway, during the2011 Tōhoku earthquake in Japan.[20][21]
Seiches have been observed in seas such as theAdriatic Sea and theBaltic Sea. This results in the flooding ofVenice andSaint Petersburg, respectively, as both cities are constructed on former marshland. In St. Petersburg, seiche-induced flooding is common along theNeva River in the autumn. The seiche is driven by a low-pressure region in theNorth Atlantic moving onshore, giving rise tocyclonic lows on theBaltic Sea. The low pressure of the cyclone draws greater-than-normal quantities of water into the virtually landlocked Baltic. As the cyclone continues inland, long, low-frequency seiche waves with wavelengths up to several hundred kilometres are established in the Baltic. When the waves reach the narrow and shallow Neva Bay, they become much higher—ultimately flooding the Neva embankments.[22] Similar phenomena are observed at Venice, resulting in theMOSE Project, a system of 79 mobile barriers designed to protect the three entrances to theVenetian Lagoon.
In Japan, seiches have been observed inNagasaki Bay, most often in the spring. During a seiche event on 31 March 1979, a water-level displacement of 2.78 metres (9.1 ft) was recorded at Nagasaki tide station; the maximum displacement in the whole bay is thought to have reached as much as 4.70 metres (15.4 ft). Seiches in WesternKyushu—including Nagasaki Bay—are often induced by a low in the atmospheric pressure passing South of Kyushu island.[23] Seiches in Nagasaki Bay have aperiod 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,tsunamis can produce seiches as a result of local geographic peculiarities. For instance, the tsunami that hitHawaii in 1946 had a fifteen-minute interval between wave fronts. The natural resonant period ofHilo 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 (solitons) can excite coastal seiches at the following locations:Magueyes Island in Puerto Rico,[24][25][26]Puerto Princesa in Palawan Island,[27]Trincomalee Bay in Sri Lanka,[28][29]and in theBay 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]
In September 2023, an enormous landslide resulting from a melting glacier nearDickson Fjord in Greenland triggered amegatsunami about 200 metres (660 ft) high.[32][33][34] This was followed by a seiche with waves up to 7 metres (23 ft) high oscillating within the fjord.[35] This seiche lasted nine days, reflecting the avalanche's large size and the fjord's long, narrow shape. During that period, it generated unusual seismic reverberations detected around the world, puzzling seismologists for some time before they could identify their source.[32][35][36]
Seiches are also observed beneath the surface of constrained bodies of water, acting along thethermocline.[37]
In analogy with theMerian formula, the expected period of the internal wave can be expressed as:[38]
whereT is the naturalperiod,L is the length of the water body, the average thicknesses of the two layers separated bystratification (e.g.epilimnion andhypolimnion), thedensities of these two same layers andg theacceleration of gravity.
As thethermocline moves up and down a sloping lake bed, it creates a 'swash zone', where temperatures can vary rapidly,[39] potentially affecting fish habitat. As the thermocline rises up a sloping lake bed, it can also causebenthic turbulence by convective overturning, whereas the falling thermocline experiences greater stratification and low turbulence at the lake bed.[40][41] Internal waves can also degenerate into non-linear internal waves on sloping lake-beds.[42] When such non-linear waves break on the lake bed, they can be an important source of turbulence and have the potential for sediment resuspension[43]
On September 19, 2022, a seiche reaching 4 feet (1.2 metres) occurred atDevils Hole atDeath Valley National Park in the U.S. after a7.6-magnitude earthquake hit westernMexico, about 1,500 miles (2,400 kilometres) away. Seiches were also observed in the cave after powerful earthquakes in 2012, 2018 and 2019.[44]
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Engineers consider seiche phenomena in the design of flood protection works (e.g.,Saint Petersburg Dam),reservoirs and dams (e.g.,Grand Coulee Dam), potable water storage basins, harbours, and even spent nuclear fuel storage basins. Structures and beach-dune systems are particularly vulnerable to damage from high water levels.Wetlands may be severely affected even by small fluctuations in water levels, and therefore historical and predicted water level fluctuations are crucial data for any coastal design. Information on seiches, along withstorm surges, and tidal fluctuations is essential.[45]
Theperiod of a seiche depends on the size and depth of thebasin in which it occurs. If an incomingwave train has a period similar to the natural frequency of the harbour, each wave will amplify the seiche's intensity, resulting in rougher waters within the harbour compared to the surrounding sea, which can create problems for shipping. Thelevels of high water in Venice for example, are the result of a combination of storm surge, barometric surge and seiches.[45][46]
General
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