Proceedings of the Great Lakes Paleo-Levels Workshop: The Last 4000 Years

The Great Lakes, Figure 1, are one of North America’s largest water resource systems with a basin area of about 770,000 km2, of which about one third is lake surface. It is one of the most intensively used freshwater systems in the world, serving multiple interests including navigation, hydropower, recreation, water supply, food supply, and riparian. The outflows from Lakes Superior and Ontario are regulated by regulatory works in the St. Marys and St. Lawrence Rivers, respectively. The remainder of the system is naturally regulated through the large surface areas and limited outflow capacity. Great Lakes water levels change slowly due to the large lake surface areas and constricted outlet channels, which integrate short-term climate fluctuations. Because of the relatively small range in lake levels, about 1.8 m, significant uses have become dependant upon small changes in water levels and outflows, resulting in system sensitivity to relatively small changes in climate variability and change. The Great lakes water levels constitute one of the longest high quality hydrometeorological data sets in North America with master gage records beginning about 1860 with other sporadic records back to the early 1800’s. However, from a longer term perspective under the current system hydraulic regime, which has been in place for about 3000 years, we have only observed/measured about 5 percent of the time series. There is a highly likely probability that we could experience runs of high and low lake levels with extremes significantly higher than our present measurements would indicate. For example, few if any envisioned in the 1960’s that we would have a 30 year run of well-above-average high lake levels and set two record highs within 13 years. A longer term lake level perspective can only be obtained by examining paleo information from the geologic record, or in a more limited fashion, from stochastic hydrologic analysis based upon the historic record. The workshop was convened to place the historical lake level measurements in a longer term perspective through a series of papers and discussion by highly qualified experts in the specialized field of Great Lakes paleo lake level reconstruction. This perspective will serve a broad range of uses from evaluation of potential Great Lakes shoreline damages to the development of more robust lake level regulation and water resource policy.