Major Floods and Droughts

Most major floods and droughts described herein have large areal extent and substantial recurrence intervals--greater than 25 years for floods and greater than 10 years for droughts. Numerous other floods and droughts have occurred in Michigan that were of lesser magnitude and that generally were less widespread than those described but, nonetheless, had a significant impact. Major floods and droughts, and those of a more local or less severe nature, are listed chronologically in table 1; rivers and cities are shown in figure 2.
A record of stream response to precipitation extremes in a watershed is invaluable for water-resources planning. History indicates that streamflow maximums and minimums are continually surpassed; thus long-term, continuous streamflow monitoring is of great value. Streamflow data before 1931 are scarce, especially for unregulated streams. Before that time, most of the State's gaging stations were operated on regulated streams in conjunction with hydropower operations. The most useful streamflow data for this study began in 1931 when gaging stations on unregulated streams became more numerous. Data from 95 gaging stations were used to determine the areal extent and severity of historical floods in Michigan, and data from 40 stations were used for the drought analysis.
To depict floods (fig. 3) and droughts(fig. 4) graphically in Michigan, six streamflow-gaging stations were selected from the statewide gaging-station network. The six gaging stations have long periods of record, are located on unregulated streams, are representative of hydrologic conditions in major areas of the State, and were operational during water year 1988. Streamflow data are collected, stored, and reported by water year (a water year is the 12-month period from October 1 through September 30 and is identified by the calendar year in which it ends).
Because of the State's peninsular configuration, rivers flow relatively short distances from their source areas to the Great Lakes (fig. 2). Most of the basins (93 percent) are entirely within State boundaries (Miller and Twenter, 1986, p. 277). The Great Lakes drain into the St. Lawrence River and ultimately into the Atlantic Ocean. In this report, the upper Grand, Maple, lower Grand, and Thornapple River basins are collectively referred to as the Grand River basin. The Pine and Tittabawassee River basins are denoted as the Tittabawassee River basin.
A discussion of floods and droughts in Michigan would not be complete without mention of water levels in the Great Lakes. The large storage capacity of the Great Lakes generally accommodates most of the variations in water supply. However, water levels are subject to seasonal and annual fluctuations. In the early 1950's and the early 1970's, the average annual levels were record highs following record-low levels in the mid-1930's and the mid-1960's. Record-high water levels occurred again in the mid-1980's as a result of more than a decade of greater than normal precipitation and less than normal air temperature, which translate into less evaporation and transpiration. The greater than normal streamflow that contributed to the rise of the lakes is graphically shown by positive departures from normal in figure 4. Great Lakes diversions and damage caused by high water levels are described by Hitt and Miller (1986).