Tuesday, January 5, 2016

Seiches and Surges

The Lake at Grimsby Beach is the subject of our pictures today.  This is the point where Forty Creek empties, and there is a walking path that follows the creek and joins up with the Bruce Trail.  There are usually bird here in the inlet, even though there are some sizeable waves that come in.  Lake Ontario's largest waves have been higher than 20 feet, usually in spring and fall. Twenty-five feet is considered the upper limit.

The Wikipedia entry tells me this information about waves:

Lake Ontario has a natural seiche rhythm of eleven minutes. The seiche effect normally is only about 3⁄4 inches (2 cm) but can be greatly amplified by earth movement, winds, and atmospheric pressure changes.

(A seiche (/ˈseɪʃ/ 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, harbours and seas. The key requirement for formation of a seiche is that the body of water is at least partially bounded, allowing the formation of the standing wave.)

A storm can produce both surges and seiches - I found this explanation here

"Storm surges may cause seiches. The word seiche is French for “to sway back and forth.” After a storm moves past the lake, and the wind and pressure are no longer pushing the water, the piled up water moves toward the opposite end of the lake. The water sloshes from one end of the lake to the other a few times until the water level is returned to normal. This sloshing back and forth is called a seiche. Often a seiche can be spotted because the water level will be high along the shore and within a relatively short period of time, the water level will then drop, sometimes leaving bottomlands exposed. Seiches may “slosh” back and forth like this several times before reaching equilibrium."

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