A COMPARISON OF FLOODING IN MICHIGAN AND ONTARIO: ’SOFT’ DATA TO SUPPORT ’SOFT’ WATER MANAGEMENT APPROACHES

The months of August and September 1986 produced four unique and extreme rainfall events. Average values of precipitation for each event ranged between 50 and 180 mm for 24-hour and 48-hour periods respectively. The heavy precipitation caused extensive flooding and damage in Michigan ($500 million US for the two months), while little flooding or damage occurred in Ontario (under $500, 000). The paper examines the soils, watersheds and flood management practices in Michigan and Ontario to determine if they are comparable. Next, the climatological events are described for the months of August and September. Analysis of each event for individual watersheds is performed using observed hydrograph characteristics such as volumes of runoff, flood yields, flood hydrographs and stream discharges. Flood damages are then tabulated and compared for each site, and a documentation of each respective site’s floodplain management policies is provided. It was concluded that although Michigan sustained extreme damages and suffered loss of life, Ontario had higher flood yields for September. Even though Ontario’s yields were higher, the province recorded only a small fraction of Michigan’s damages. The study also identifies the need for establishing procedures for quantifying benefits that are accrued from implementing sound floodplain management, and in reducing otherwise intangible floodplain mapping benefits.