Remapping the Great Lakes from a Hydrological Perspective

As noted in the two previous GeoCurrents posts, Lake Huron and Lake Michigan are a single body of water, forming the world’s largest freshwater lake (by surface area) by a considerable margin. The Wikipedia article on this greatest of the Great Lakes explains the situation:

Lake Michigan–Huron (also Huron–Michigan) is the body of water combining Lake Michigan and Lake Huron, which are joined through the 5-mile-wide (8.0 km), 295-foot-deep (90 m), open-water Straits of Mackinac. Huron and Michigan are hydrologically a single lake because the flow of water through the straits keeps their water levels in overall equilibrium. Although the flow is generally eastward, the water moves in either direction depending on local conditions. Combined, Lake Michigan–Huron is the largest freshwater lake by area in the world.

 

For casual purposes, there are no problems with regarding this single body of water as divided into two discrete lakes. For both scientific and comparative purposes, however, it is more useful – and accurate – to treat Michigan-Huron as a single lake. Not surprisingly, a National Oceanic and Atmospheric Administration (NOAA) hydrological diagram of the Great Lakes follows this model. But it also divides this massive lake into three basins: Michigan, Huron, and Georgian Bay. Georgian Bay is conventionally regarded as part of Lake Huron, but it hydrologically functions as a separate basin.

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Given these complications, it seems worthwhile to experiment with remapping the Great Lakes. The first map posted below shows the standard five-lake model. The second map depicts Michigan-Huron as a single lake, while adding the much smaller but still substantial (430 sq mi) Lake Saint Clair, which is an essential component of the Great Lakes system. The third map divides Lake Michigan-Huron into its three separate basins. The final map shows how the Great Lakes would be depicted if we were to regard all deep embayments as separate lakes.

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