With the wet spring we've had this year, water levels have now risen and are now slightly above the levels of last year at this time. There was 5.43 inches or 209% of the much needed precipitaiton in April and even more in May in Lake Michigan-Huron and while that is good news for water levels, it still leaves the Lakes about 15" below their long term averages. Average precipitation is only 2.6 inches in April. Erie and Ontario on the other hand are over 10" above their long term averages. The latest figures from US Army Corp of Engineers still show expected peak levels of 7" above chart datum in July which is 15" below the long term average.
You can see the latest US Army Corp of Engineers graphs here:
USACE - Monthly Bulletin of Lake Levels for the Great Lakes
USACE - Daily Great Lakes Water Levels
Or for the hourly data sets from Environment Canada click here
The latest figures on Great Lakes water levels show a continued below average forecast for the single body of water that makes up Lakes Michigan, Huron and Georgian Bay. The USACE is now forecasting that levels are expected to rise to 7" above chart datum this summer and then fall below chart datum again this fall. All time lows were last recorded in 1964. Chart datum is the reference level used for navigational chart water depths. Chart datum is selected so that the water levels rarely fall below it and is used as a basis for navigational depth soundings on nautical charts.
The recent International Joint Commission study on the St. Clair river found that there has been an unexpected head loss between Lakes Michigan/Huron and Lake Erie of 23 cm (9 inches). The study attributes up to 14 cm ( 2.8 - 5.5 inches; 7 - 14 cm) of this head loss decline to unapproved changes occurring in the St. Clair river while the bulk of the remaining losses are attributed to glacial isostatic rebound (1½ - 2 inches; 4 - 5 cm) and climate change impacts (3.5 - 6.7 inches; 9 - 17 cm) with more expected to come.
Anyone who has looked at the water level graphs over the years notices a familiar pattern on how the levels change within a year – they start off low in the winter, go up steadily in the spring and then start dropping off gradually from July until the end of the year.
