Great Lakes Water Levels Continue Decline

Water levels in the Great Lakes are already low, and they just might keep getting lower. 

Despite above-average precipitation during 1999 on the upper lakes, Lakes Michigan and Huron water levels declined from 3 inches below average at the beginning of 1999 to 19 inches below average at the end of the year. This was a net decline of 16 inches, accounting for the average seasonal fluctuation in water levels. Since the beginning of 2000, the level of these lakes has been falling faster than projected in the U.S. Army Corps of Engineers' December forecast. At the end of January, the two lakes were 20 inches below average and four inches below chart datum, which is 577.5 feet above International Great Lakes Datum, 1985 (IGLD 85). Lake Superior started 1999 at a level 10 inches below average, rose to a late summer seasonal peak that was just 4 inches below average, and ended at a level 9 inches below average.

Although these levels seem low to us today, historical lows have been even lower. Even if Lake Superior continues to decline to the lowest forecasted water level this spring, its level will be at least one foot higher than the twentieth century record low mean monthly level set in 1926. This record low water level is about one foot higher than the estimated lowest lake level that occurred during the early 1800s, and about three feet higher than lowest lake levels that occurred between 350 and 650 years ago, according to Curtis Larsen of the U.S. Geological Survey.

If Lakes Michigan and Huron continue to decline to the lowest forecasted water level this spring, their levels will still be at least nine inches higher than the twentieth century record low mean monthly level set in 1964. The 1964 record low level was at the upper limit of a range of lower lake levels that occurred at several times during the last 1,000 years, according to Larsen. Some of these levels may have been three feet lower than the 1964 record low level.

These historic levels and some of the results from hypothetical models of climate change scenarios at the NOAA Great Lakes Environmental Research Laboratory indicate a possibility of future Great Lakes levels that are much lower than the levels experienced during the twentieth century.

Click here for more information on Great Lakes water levels.

-- Philip Keillor
UW Sea Grant Coastal Engineer

 

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Last updated 28 March 2000 by Karl
All contents copyright 2000 University of Wisconsin Sea Grant Institute

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