Weather pattern most likely brought about a seiche in South Haven

The docks at the South Side Municipal Marina in South Haven are nearly covered with water Wednesday morning after an apparent seiche occurred on Lake Michigan causing the already high water level on the Big Lake to rise even more.

SOUTH HAVEN — Earlier this month the U.S. Army Corps of Engineers issued a report that Lake Michigan water levels will continue rising over the next six months, contributing to erosion and potential flooding.

That prediction is becoming a reality in South Haven where South Beach is now a fraction of what it was at the start of spring, and marina owners are wondering if their docks will disappear.

The rising water level became very noticeable Monday morning when most of South Beach lay under water. Upriver from the channel, water had risen to the top of docks lining the city’s harbor, prompting some to wonder if the lake had experienced a seiche.

“I believe we did,” said the city’s Harbormaster Kate Hosier.

Hosier has been steadily watching the rising water levels on the Black River where the city operates three marinas.

Wednesday at 8 a.m. she took photos of the docks of the South Side marina where water had reached the tops of the docks.

“Within a half an hour the water had lowered 4-6 inches,” Hosier said.

A similar situation occurred at South Beach where Hosier also snapped photos. Her photos on Wednesday showed a beach under water. However, by Thursday afternoon, some of the beach could be seen again.

Seiches occur in enclosed bodies of water, like the Great Lakes, according to the National Oceanic and Atmospheric Administration.

Seiches are most often caused when strong winds and rapid changes in atmospheric pressure push water from one end of a lake to the other. When the wind stops, the water rebounds to the other side. The water can oscillate back and forth for hours or even days.

It’s not 100 percent certain whether a seiche occurred on Lake Michigan by the city’s harbor, but according to Andrew Dixon, service hydrologist for the National Weather Service in Grand Rapids, there’s a strong possibility one did.

“Since the time period from high water to low water was a few hours, it is hard to pinpoint whether it was the line of thunderstorms that crossed Lake Michigan Wednesday morning that caused this, or whether it was a general wind shift that got the lake sloshing a little bit,” he said. “The lake is always responding to changes in the weather and wind patterns, and small seiches are not uncommon.”

South Haven has experienced seiches in the past. One that occurred in 1909 was said to have caused an eight-foot wave that crashed into the city’s harbor damaging boats and some cottages. Other seiches that have happened over the years on the Great Lakes proved deadly, sweeping people off piers and boats.

Another seiche could happen in South Haven with the weather the area has been experiencing, according to Dixon.

“We’ve been, and are still in a weather pattern where lots of fast-moving storms are crossing right over Lower Michigan, so it’s entirely possible more sloshing waves/seiches like this will be observed over the next week or so,” he said.

And that prediction is causing concern for marina operators and boat owners.

“It is problematic for many boaters. Besides the erosion, high water causes, many boaters are needing steps to get into their boats, many have their docks under water, power lines under water, water lines under water, etc.,” Hosier said.

Hosier warned that the higher-than-normal water levels could lead to instances of electric shock drowning, or ESD.

“Boaters and people near docks need to be aware that there is always a danger for electric shock drowning,” Hosier said. “No one should enter the water near docks where there is electric power.”