Lake Levels -  A Puzzle

Chuck Southam

Boundary Water Issue Unit

Environment Canada

Click the Chart to Enlarge the above


The Above NOAA Chart shows Lake levels so far this year vs. 2007.


On Tuesday August 6, 2008 Chuck Southam of Environment Canada gave an interesting lecture at the Chantry Island Institute about water levels past and present on the Great Lakes.  The lecture was attended by about 80 people.  Many questions after the lecture 'peppered' the speaker showing the interest of the audience.  He answered them and was not afraid to say "I don't know".  One got the impression that he was a real expert. 

Lake levels are up about 23 cm over last year at this time due to high snow mass and good rain in the spring and summer along with cooler overall temperatures.

Mr Southam had a single over arching point to make: 

The Great Lakes water levels result from a very complex set of influences that are not well understood, but are under intense study

He told us that if anyone tells you they can predict the future of lake levels, don't believe them.  When and if we can do true long range weather forecasting, then and then only will we be able to predict Lake levels.

He showed us a smaller version of the above lake level chart.  If you enlarge it, you can see that the levels are cyclic and have reached highs and lows before. The most recent high was 1986 and our lows lately have not reached 1934 and 1964 lows

Some of the interesting points that were brought out concerned the rebound of the Lakes.  We are rebounding at about 3 cm per century while Tobermory is rebounding at about 17 cm/century.  This results from the pressure of the glaciers being relieved over after the recession of the glaciers 10,000 years ago.

Other areas are sinking like the Chicago on Lake Michigan so there is a neutral zone lower down from us that runs across Michigan.  Maximum  rise occurs up near Perry Sound in Georgian Bay.

The recent chatter about water being taken out via the Chicago River is not true as the water going out of Huron in the Saint Clair River is over 62 times as much by volume.

He told interesting stories about the panic to reduce lake levels in 1986 as shorelines were eroding.  Charles said:  "People have short memories".

He was asked about further diversions of Great Lake Water.  He pointed to the mutual treaties that govern the Lakes and the fact that although the US has over 60% of the water, Canada and the US share it 50-50 and all the provinces and states that border the waterway have mutual signed agreements about water use.

He also pointed out that London Ontario gets water from both Lake Erie and Huron.

The Bruce County Museum is really doing a great job on bringing interesting lectures to the area.  See the event planner for future lectures


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Background Information

Click to Enlarge

The Great Lakes system is a chain of lakes and connecting channels descending like a series of steps toward the Atlantic Ocean. Lake Superior, located at the top of the chain, is about 183 metres (601.7 feet) above sea level, while Lake Ontario stands at about 74.7 metres (245.1 feet). (Click here to enlarge the above profile)

Water from Lake Superior flows into Lake Huron through the St. Marys River. Since Lake Michigan and Lake Huron are connected by the broad and deep Straits of Mackinac and stand at virtually the same elevation, they are often referred to as one lake hydrologically; that is, Lakes Michigan-Huron. From Lakes Michigan-Huron, water flows through the St. Clair River, Lake St. Clair and the Detroit River into Lake Erie. Lake Erie discharges through the Niagara River and the Welland Canal into Lake Ontario. The portion of flow diverted to Lake Ontario through the Welland Canal is relatively small (about 4 to 5 percent of the total Lake Erie outflow). Water from Lake Ontario flows to the Atlantic Ocean through the St. Lawrence River. The average St. Lawrence River flow, recorded at Cornwall, Ontario, during the period 1900-95, is 6,910 cubic metres (244,000 cubic feet) per second. This average outflow is relatively small (less than 1 percent per year) in comparison to the total volume of water contained in the system.

Only the outflows from lakes Superior and Ontario are regulated via control structures, and may be varied within limits in accordance with their respective regulation plans. The outflows from lakes Michigan-Huron and Erie are controlled exclusively by the hydraulic characteristics of their outlet rivers.

The immense storage capacities of the Great Lakes, in combination with their restricted outflow capacities, allows the lakes to absorb large variations in water supplies, while maintaining remarkably steady outflows compared with other large rivers. For example, the highest St. Lawrence River flow is only 2.3 times greater than its lowest rate. In contrast, the Mississippi River at St. Louis, Missouri, has a maximum flow about 30 times its minimum.

Because of the size of the Great Lakes and the limited discharge capacities of their outlet rivers, extremely high or low levels can persist for a considerable time, even when water supplies change significantly.