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Overview of physical processes in large lakes: Surface Waves: Surface Seiches

Seiches are standing waves in an enclosed or partially enclosed body of water. 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 by superposition of incident and reflected wave. Seiches and seiche-related phenomena have been observed in Lake Ontario. The most common cause of seiches is the wind induced tilting of the surface water. The accumulated water mass is gradually pulled down by gravity creating a to-and-fro sloshing motion about one or more nodal points until equilibrium is reached again [9]. Surface seiches occur under barotropic conditions [9]. Once in motion, oscillation of the surface seiche is dampened by gravity as the water mass returns to equilibrium and will cease if supplementary forcing is not exerted on the water surface. The magnitude of the oscillation and the dampening depends on the geometry of the basin. Deep lakes with uncomplicated shapes have low dampening effects and the seiche oscillations can persist well after the storm has passed. In Lake Ontario the main harmonic has a period T = 5.06 hours.

Fig.2 Conceptual seiche