GREAT-LAKES FLOOD THRESHOLDS AND IMPACTS

Using the location, data, and water levels from flood events along the Canadian shore of Great Lakes, flood damage thresholds were determine d to identify and compare water levels at which static and storm-induc ed high water impact shoreline interests on several shore reaches of L ake Erie, Huron, Ontario, and St. Clair. Spatial differences identifie d may be related to several factors, including: 1) nearshore bathymetr ies; 2) extent of residential development along low-lying shorelines; 3) degree of riparian adjustment to flooding; and 4) location relative to dominant wind or storm directions. Correlation analyses found that flood damage levels are more closely correlated to fluctuations in st atic levels on Lakes Ontario, Huron, and St. Clair, while flood damage levels are more closely correlated to maximum instantaneous water lev els on Lake Erie. Correlation analyses of individual gauge data identi fied locations possibly more susceptible to storm surges. A conservati ve approach to determining flood damage thresholds is suggested, being based on a standard deviation below the mean of maximum instantaneous flood levels for a given gauge. The standard deviation threshold, whi le lower than current ''critical levels'' used in management, is more representative of the majority of flood damage levels than thresholds based on lowest maximum instantaneous lake levels. However, caution is urged in applying any critical level solely based on water level gaug e information as Great Lakes flooding is a highly site-specific phenom enon influenced by meteorologic factors.