The Lake Superior shoreline should be good for picking agates these days. On January 2, the lake level was 13 inches below its long-term average for the start of the New Year, one inch lower than this time last year. According to the International Lake Superior Board of Control that oversees the lake’s outflow at the St. Mary’s River, the level is expected to decline further this month.
The level of Lake Superior fell two inches in December, although on average it falls three inches. While precipitation of 1.14 inches in the Lake Superior basin was only 56 percent of what it usually is in December, the lake lost less to evaporation than it does in an average year.
In an average December (calculated from data from 1900 to 2008), the amount of water that evaporates from Lake Superior exceeds the amount that comes in from precipitation and runoff by 22,000 cubic feet per second.
Lake Superior’s water level has been below its average depth of 601.7 feet since the late 1990s. In December, it averaged 600.59 feet. The water level is expected to be 6 to 11inches above record low water levels in the first six months of this year and 12 to 14 inches below the long-term average.
Lake Superior’s lowest level since 1918 was 600.1 in 1925, and the highest level was 603.1 in 1985.
Controlling the outflow
The first lock along the St. Mary’s River that connects Lake Superior with Lake Huron was built in 1797 to allow boats to bypass rapids in the river, which falls 20 feet in three-quarters of a mile. Today, the waters of Lake Superior pass through numerous structures including three hydropower plants, five locks, and a gated dam known as the Compensating Works. The release of water from Lake Superior through these structures has been regulated since the Compensating Works were completed in 1921.
The International Lake Superior Board of Control, established in 1914 by the International Joint Commission which supervises projects affecting U.S./Canadian boundary waters, takes into consideration domestic, municipal, and industrial uses of water in the St. Mary’s River, the amount of water needed to operate the locks, environmental needs such as sustaining fish habitat, the operation of the hydropower plants, and the effect on the land bordering the river.
The plan regulating Lake Superior outflow since 1979 calls for keeping Lake Superior levels between 599.6 and 603.2 feet, but the effect on Lakes Huron and Michigan also must be taken into consideration in doing that. According to the International Lake Superior Board of Control, “The main objective of the present regulation plan is to determine a flow that will bring the levels of Lake Superior and Lakes Michigan and Huron to nearly the same relative position within their respective ranges of actual historic levels.
“The ability to regulate the outflow from Lake Superior does not mean that full control of lake levels is possible. This is because the major factors affecting the water supply to the Great Lakes – over-lake precipitation, evaporation, and runoff – cannot be controlled; neither can they be accurately predicted over the long term.”
The Indiana Department of Natural Resources website states: “The regulation of Lake Superior influences the whole Great Lakes system….Changes in water levels of the Great Lakes from diversions and control works require a significant amount of time to take effect due to the amount of surface area of this lake system. On the upper lakes, it takes approximately three and one half years for one half of the anticipated result to occur. The full effect of change could take between 12 and 15 years.
“From May 1 to December 1 the gates of the control works [on the St. Mary’s River] are set monthly. The outflow is a function of the mean Lake Superior level and other factors from the prior months as well as forecasts of future outflows. This flow can vary from 55,000 to 134,000 cubic feet per second.”
Possible trends
In an online National Geographic News Watch article, conservationist Lisa Borre stated that not only has Lake Superior’s water level been low for more than a decade, ice cover has been declining and temperatures have been rising.
“Lake Superior is one of the most rapidly warming lakes in the world,” Borre said. She cites a study that found that surface temperatures increased about 4.5 degrees between 1979 and 2006.
A large change, called a step-change, occurred in 1997 and ’98, which resulted in a drop of ice duration of nearly 40 days, a 5.4-degree increase in summer water temperature, and a near doubling of July- August evaporation rates, according to researcher Katherine Van Cleave. Borre said Lakes Superior, Michigan, and Huron have been fluctuating below average levels since this extreme event. She referred to a teleconference in which the Army Corps of Engineers indicated that the upper lakes are not likely to recover from this event anytime soon. She quoted Keith Kompoltowicz of the Army Corps: “We would need several months and seasons in a row of very wet weather to get us back to long-term average.”
“This extended period of low water raises questions about whether climate change is contributing to declining lake levels,” Borre said, “but the Corps maintains the position that it’s difficult to know, because the lakes continue to fluctuate within their normal range.”
Borre stated that a study by the International Joint Commission acknowledges that while the complexity of the Great Lakes Basin is not fully understood, precipitation in the Lake Superior Basin over the past 60 years has not kept pace with evaporation, although in the Lake Michigan-Huron basin it has.
Borre said lake and climate scientist John Lenters of the University of Nebraska- Lincoln told her, “Lake Superior’s rapid warming is like a canary in the coal mine. We’re seeing changes in ice cover, water temperature, and evaporation that indicate major shifts are underway on the world’s largest lake.”
Lake Superior facts
According to the Minnesota Sea Grant, Lake Superior has:
. 3 quadrillion gallons of water, making it the third largest freshwater lake in the world by volume,
. enough water to put North and South America under a foot of water,
. 10 percent of the world’s fresh surface water, and
. over half of the water in the Great Lakes.
Lake Superior:
. covers 31,700 square miles, making it the largest freshwater lake by surface area in the world,
. has an average outflow of 75,574 cubic feet per second,
. averages 45 degrees Fahrenheit, . takes 191 years to be completely replaced with new water,
. pours about 2.5 feet of water into Lake Huron each year, and
. loses an average of 1.6 feet to evaporation each year.
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