Marquette Mining Journal photo MCCARTY’S COVE ON Lake Superior near Marquette.

MARQUETTE — Sunday was Lake Superior Day, which annually inspires celebrations of the “greatest Great Lake” in many communities along its shores.

With Lake Superior’s water levels surpassing previous record highs in recent months, residents of shoreline communities such as Marquette may wonder about the causes and impacts of the high water levels, as well as what the future may have in store for Lake Superior’s shoreline.

While many area residents may remember when Lake Superior hit record-high levels in the late 1980s, Lake Superior had its highest water levels in over 100 years during May and June this year.

“The May and June levels were 1 and 3 inches higher than the previous May and June record high levels, respectively,” said Lauren Fry of U.S. Army Corps of Engineers Detroit District Great Lakes Hydraulics & Hydrology Office. “These records are relative to the monthly mean lakewide average water levels dating back to 1918. The previous record high water levels were set in 1986.”

As of Friday, water levels on Lake Superior had reached 603.25 feet, 2 inches higher than the highest monthly average for July since water level records began in 1918.

Friday’s water level was 14 inches higher than the long-term monthly average for July, 8 inches higher than the average for July 19, and 1 inch higher than water levels were a month prior on June 19, according to data from the U.S. Army Corps of Engineers Detroit District.

It’s projected that more of the same is in store for the coming months, Fry said.

“The latest 6-month forecast suggests that all of the Great Lakes except Lake Michigan (and Lake) Huron will set new record high water levels for the month of July and then remain well above their long-term average water levels,” she said.

One of the factors contributing to this is an especially precipitation-heavy year around the lake, with the total yearly precipitation exceeding the average by nearly 8 inches at the National Weather Service office in Negaunee Township.

“It has been a very wet year around the entire Great Lakes basin so far,” Fry said. “All of the Great Lakes states have received well-above-average precipitation for the January-to-June period.”

Precipitation impacts water levels on the lakes in two ways: precipitation over the lake directly adds to the water levels, while precipitation that falls over land can add also to water levels by running off into the lake, Fry said.

“The combined influence of precipitation over the lakes, runoff into the lakes and evaporation from the lakes is referred to as ‘net basin supply’ and is the primary driver of water levels,” she said.

Precipitation, runoff and evaporation all contribute to Lake Superior’s natural seasonal fluctuations in water levels, which are typically higher in the summer than the winter and fall.

“In the winter, water levels are at their lowest. During this time, precipitation falls mainly as snow and accumulates on the ground instead of running off into the lakes via streams,” she said. “In the spring, the snow begins to melt, which in combination with more precipitation falling as rain, results in high runoff and rising lake levels. During the summer, the sun’s energy is transferred into the lakes, warming them. This warming sets the lakes up for enhanced evaporation during the fall and early winter, when cold dry air comes into the basin, so lake levels fall.”

While these seasonal fluctuations in lake levels are normal, this year’s seasonal fluctuation was particularly notable, setting up water levels that prepared the lake to break the 33-year-old records for May and June.

“In March, when the lake was at its lowest levels for the year, Lake Superior water levels were about 13 inches above the long-term average March water level and 2 inches below the record high March level,” Fry said. “Since March, the lake has undergone its seasonal rise starting from very high water levels, bringing water levels to record high May and June water levels.”

It’s important to recognize, Fry said, that while Lake Superior’s water levels will begin to decline this year because of this normal seasonal pattern, they are likely to remain well above average and “the continued very high water levels will mean that the region will continue to see localized coastal flooding and shoreline erosion, especially during storm events.”

While coastal erosion occurs at all water levels, record-setting water levels make the erosion “more impactful, because it is happening close to property and infrastructure,” she said.

One major piece of infrastructure on Lake Superior that many think of is the Soo Locks, but “there aren’t currently any impacts to the locks themselves, or the control gates,” said Charles Sidick of the U.S. Army Corps of Engineers Detroit District Great Lakes Hydraulics & Hydrology Office.

However, Sidick said, “With these levels, we do see some localized flooding to Whitefish Island and also have some minor impacts to power generation in the area.”With these record-high water levels on Lake Superior, Fry wants shoreline communities to know: “The U.S. Army Corps of Engineers has authority to support communities in flood fighting by providing technical expertise, and in certain instances, provide flood fight supplies, such as sandbags and plastic sheeting.”

To learn more about current and forecasted water levels on Lake Superior and other Great Lakes, visit https://www.lre.usace.army.mil/Missions/Great-Lakes-Information/Great-Lakes-Information.aspx#ICG_ETH_22302.

For those viewing and interpreting the data, Fry emphasizes forecasted and reported water levels are monthly mean lakewide average water levels.

“Significant variation can occur within a month and even from location to location on a given day, so on a given day and location, people may experience levels that are very different from the monthly mean values that report,” she said.

Marquette Mining Journal photo

MCCARTY’S COVE ON Lake Superior near Marquette.