Lake Superior slide brushes new record territory
By Jack Storey
Soo Evening News
Published December 13, 2006
DETROIT - November water levels on the three Upper Great Lakes continued to run from well below average to near-record territory, according to the Corps of Engineers.
In its Monthly Bulletin of Lake Levels for the Great Lakes, the Corps said Lake Superior, Lake Michigan and Lake Huron were significantly below the seasonal average at the end of November.
The largest of the Great Lakes, Lake Superior, fell a full 17 inches below its long-term average for the start of December - rivaling Lakes Huron and Michigan, which were 19 inches below their norm. While Lake Superior's water level has run below its average for several years, the Big Lake has been running six inches or less under the norm while Lakes Michigan and Huron flirted with two feet.
That changed this summer and fall, when a continuing drought on the Lake Superior watershed drove water levels into the same range as the two Great Lakes below.
In November, for example, precipitation across the Lake Superior watershed was less than half its 100-year average. Corps hydrologists estimate that more water evaporated from Lake Superior than ran into it from tributary streams around its watershed.
Over the last 12 months, the report said Lake Superior region rainfall has been just 83 percent of its 100-year average and was running a full 5.14 inches below average when December began.
Water levels on Lakes Huron and Michigan were still lower, compared to their historic averages, than Lake Superior in November. Rainfall levels around those lakes were less than half an inch below average.
Over a 12-month period, rainfall in the watershed feeding Lakes Michigan and Huron was slightly higher than the long-term average, resulting in lake levels that are still low but falling at essentially the same rate as seasonal variations would predict.
The two lakes continue to run about one foot or slightly less above their long-term low levels, set in 1964.
Lake Superior, meanwhile fell to within a fraction of an inch of a new record low in October and repeated that reading in November. Record low water levels on Lake Superior for October, November and December were set in 1925.
Falling more rapidly than the seasonal average predicts, Lake Superior began its steep slide in August and that decline has continued in each month since.
Most water level experts tie Great Lakes levels almost directly to rainfall over the respective watersheds. Evaporation and winter ice cover modify the rainfall relationship in different ways, changing the impact on lake levels that would be predicted by precipitation alone.
Lower water levels across most of the Great Lakes region complicate year-to-year adjustments by shoreline property owners and create lower draft limits on navigable waterways for commercial shipping.
Not all Great Lakes water bodies monitored by the Corps were nearly as low as the three Upper Great Lakes last month. Lake St. Clair ran just a few inches below its long-term average last month and both Lake Erie and Lake Ontario were appreciably above their long term averages, according to the Corps data.