Thursday, December 10, 2009

Word of the day: Seiche

Waves batter the Lake Erie shoreline. Ohio's north coast is an inland sea - Erie is the 4th largest of the Great Lakes in surface area. And it is the shallowest, with an average depth of just 62 feet.

Because of its shallowness, Lake Erie is prone to vicious wave action generated by storms pushed along by high winds. Conditions on the lake can go from placid to savage in the blink of an eye, making it one of the world's most dangerous water bodies. Many a ship has been unwillingly moored in Davey Jones' locker, on the floor of the lake. Indeed, one of the highest densities of shipwrecks anywhere on the globe rest on Erie's bottom.

Stretching 241 miles from stem to stern, Lake Erie is bookended by the port cities of Toledo, Ohio, and Buffalo, New York.

As anyone residing in these parts knows, we've had some roof-shaking, limb-cracking, umbrella-obliterating high winds the past few days. This front roared out of the west, and barreled down the center of Erie.

And this created an exceptional example of a fascinating hydrological phenomenon known as a seiche. Inhabitants of the lake are fully aware of seiches, whether or not they know them by name, but many non-lake people are surprised to learn about seiches.

Basically, a seiche is a wind-driven massive shift of water - high prolonged winds push Erie's water from one end to the other, causing water to pile up at a higher depth on the downwind side. It's as if you took a bowl of water, and blasted your hair dryer into the bowl from the side. As long as you kept the air flowing, water would stay higher on the far side of the bowl.

Yesterday's gales produced one humdinger of a seiche on Lake Erie. The chart above, from yesterday, shows the sudden drop in water level at Toledo.

Well, all of the water - Lake Erie holds some 116 cubic miles of the stuff! - has to go somewhere. And that would be Buffalo, at the eastern end. Soon after Toledo lost ELEVEN feet of water, Buffalo's water level spiked by 11 feet. That's a Seiche Royale!


Buford Nature said...

Did wind seiche also raise the water level in the Niagara River and Niagara Falls (by 11 ft)? That'd be a hot time to barrel over the falls! And if so, was Lake Erie's water level lower following the extreme seiche event?

Anonymous said...

Very interesting and informative!
Gary Wayne

Wren said...

This is fascinating - I haven't heard of seiches previously. Eleven feet is a huge shift. Is it something that you'd notice walking by, or is it only obvious when measured?

Jim McCormac said...

Hi all,

I probably should have included a pronunciation of seiche - I usually hear it as "sesh" (rhymes with mesh), but some fancier linguists roll if off as "saysh".

Seiches don't alter the volume of water in the lake; they just shift it around. Winds die down, and equilibrium is once again achieved. A fierce seiche may cause a higher flow rate into the Niagara River - Lake Erie's discharge - but a dam can control artificially the flow rate over the falls at Niagara.

The effects of seiches in the shallow Lake Erie western basin can be extremely noticable. Ditches full of water in the morning soon become waterless, and boats beached at their docks. Seiches play an important role in the ecology of marshes as well, but that's another subject.