Seiche

 

(This 898th Buffalo Sunday News column was first published on June 8, 2008.)

 

File written by Adobe Photoshop® 4.0

A Lake Erie seiche has emptied this harbor near Toledo

and raised the water pounding against Buffalo breakwalls

 

I once overheard an argument that was almost to cost me my life.

 

In order to maintain what he called the "steaming efficiency" of our World War II Navy ship, my captain was ordering our engineering officer and first lieutenant to fill our ballast water tanks only partially full. Although his two officers argued strongly against him, the captain insisted on his prerogative and the water levels were so adjusted.

 

The reason for the officers' concern is easy to illustrate in a dish washing basin. Start the water sloshing back and forth and it will soon exert strong pressure on the basin's sides. In the case of our ship, the effect of a dozen of those half-filled tanks seriously exaggerated our natural rolling caused by sea waves.

 

When we encountered a storm off the Newfoundland coast, our rolls got so bad that I could lean over the bulwark on our main deck, a metal wall normally thirty feet above the waterline and, when we tipped that way, gather suds off wave crests. We came only inches from taking water into our well deck and swamping. Fortunately, before this happened the storm subsided but we continued to roll badly for the rest of our voyage and I was one of the few aboard who wasn't seasick.

 

The kind of bathtub-like water oscillation that occurred in those tanks is called a seiche, pronounced "saysh". Ocean tides are a form of seiche, but the term more often refers to enclosed water bodies like our Great Lakes.

 

Seiches are initiated by some outside force like an earthquake or more often a strong wind. In fact, earthquake-generated seiches can set the water in swimming pools in motion causing them to overflow thousands of miles from where the quake occurred. This is because the ground tremors often match the resonant frequencies of small bodies of water. The most notorious of these effects was due to the 1964 Good Friday Alaska Earthquake, the third most powerful ever recorded. It caused seiches in swimming pools as far away as Puerto Rico.

 

The length of time between successive rises or falls of a seiche is proportional to the length of the body of water. Thus the period in a bathtub is about one second but in Lake Erie it is about fourteen hours.

 

Because much of Lake Erie is quite shallow and it is lined up southwest to northeast with the prevailing wind direction, it is especially prone to wind driven seiches, but they don't always fit the general idea of them as oscillatory. In fact, the U. S. Corps of Engineers definition includes a special section which says: "In the Great Lakes area, [seiches include] any sudden rise in the water of a harbor or a lake whether or not it is oscillatory," but adding the note, "Although inaccurate in a strict sense, this usage is well established in the Great Lakes region."

 

Steve McLauglin of the Buffalo's National Weather Forecast Office agrees with this definition and adds that we get two or three seiches every year that cause water to rise five feet or more at our end of the lake. "This occurs," he says, "whenever we get a sharp front that shifts our winds from south or southeast to west and southwest. If they reach gale force long enough we get the water moving from the west end of the lake to the east end, piling up so to speak. This results in low water problems at Toledo and high water ones here. It almost always occurs from about November to January when we get our most frequent southwest gales, but never in late spring or summer as we never get these gales then."

 

When I asked McLaughlin about recent seiches, he responded, "Normally they cause water rises of between two to three feet, but we had one of our worst ever on January 30 this year when southwest gales of up to 68 miles per hour brought a surge of over nine feet to Buffalo harbor. The lake level there reached eleven feet, its highest level in 22 years and second highest ever. The highest was twelve feet on December 2, 1985.-- Gerry Rising"