The history of Lake Superior regulation: Implications for the future

Lake Superior outflows have been regulated for the past 80 years. The last 15 years have encompassed both extremely high water supplies and lake levels and subsequent drastic declines in the levels of Lakes Superior and the lower lakes. The IJC is considering a study whose purpose would be the reexamination of the current Lake Superior regulation plan, which has been in use since 1990. In preparation for that discussion, several different aspects of past and potential future Lake Superior levels were analyzed. The stage-discharge equation representing natural flow conditions for the pre-1900 Lake Superior outlet was used to simulate unregulated Lake Superior outlet conditions, using actual water supplies. Net basin supplies developed for a climate change study were used to evaluate the potential effects of regulation on future levels. A 50,000 year set of stochastic net basin supplies, based upon the present climate, was also used to provide hypothetical upper and lower bounds. By comparing recorded Lake Superior levels to what might have happened in the absence of regulation and what may occur with future supplies, it is hoped that the development and/or evaluation of any future adjustments to the regulation criteria for Lake Superior might be aided.