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Georgian Bay Water Levels - a follow-up
By John Grant

The front-page article in the Fall 2005 Tiny Cottager reported on a study commissioned by the Georgian Bay Association (the “Baird Report”) that found that dredging in the St. Clair River over the years is contributing to an unexpectedly rapid drop in the level of Georgian Bay relative to Lake Erie. The International Joint Commission has indicated that further analysis of the St Clair River channel will be undertaken within their Upper Great Lakes Study. It is imperative that this analysis be adequately and immediately funded. Adequate funding will also be needed if remedial action is required.

In the meantime we have looked further into the matter. Whereas the Baird Report discussed the level of Georgian Bay (or Michigan-Huron) relative to that of Lake Erie over the period from 1860 to 2000, it is also of interest to look at the actual lake levels (relative to sea level).

The chart makes clear that the annual variation of both lakes is driven basically by the same forces. Both lakes are well below trend at this time. However, the trendline for the annual average level of Michigan/Huron has fallen by 0.09 metres since 1960, whereas that for Erie has risen by 0.19 metres. Michigan-Huron’s trend has thus dropped relative to Erie by roughly 0.28 metres, about eleven inches, over this period of time.

Trend is one thing, but annual averages vary considerably around their trends. As the accompanying chart illustrates, both lakes were below their 1960-2005 trendlines last year, Michigan-Huron by about 0.42 metres, Erie by about 0.28 metres.

A comment on the recent behaviour of the Michigan-Huron lake levels, and recent policy actions, can be found at page 17 of the latest update report of the Georgian Bay Association:
http://www.georgianbay.ca/pdf/update/vol16no1.pdf

The data from which our chart was taken can be found at http://www.lre.usace.army.mil/greatlakes/hh/greatlakeswaterlevels/historicdata/greatlakeshydrographs/

The U.S. Army Corps of Engineers has issued a formal comment on the Baird Report; it can be found under “Hot Topics” at http://www.lre.usace.army.mil/

Also, the International Joint Commission’s press release of May 11, 2005, announcing its intention to respond to the Baird Report by adding the St Clair River channel to its proposed Upper Great Lakes Study can be found at
http://www.georgianbay.ca/ijc_press11may05.htm