EXAMPLE 13.23 Great Lakes water Levels

The water levels of the Great Lakes have received much attention in the media. As the world’s largest single source of freshwater, more than 40 million people in the United States and Canada depend on the lakes for drinking water. Economies that greatly depend on the lakes include agriculture, shipping, hydroelectric power, fishing, recreation, and water-intensive industries such as steel making and paper and pulp production.

In the early 1990s, there was a concern that the water levels were too high with the risk to damage shoreline properties. The fear that the lake would engulf shoreline properties was so high that cities like Chicago considered building protection systems that would have cost billions of dollars. Then in the first decade of the twenty-first century, there were great concerns about the water levels being lower than historical averages! The lower levels caused wetlands along the shores to dry up, which could have serious impacts on the reproductive cycle of numerous fish species and ultimately on the fishing industry. The shipping and steel industries were also feeling the effects in that freighters have to carry lighter loads to avoid running aground in shallower harbors.

Figure 13.41 displays the average annual water levels (in meters) of Lakes Michigan and Huron from 1918 through 2013.²² We see that the lake levels meander about the mean level. Each time the series drifts away from the overall mean level (above or below), it reverts back toward the mean. There does not seem to be any strong evidence for a long-term trend.