Annual and seasonal flow variations through the Straits of Mackinac

Abstract

The present emphasis on Great Lakes water quality studies requires a knowledge of the average and variability of the net flow between Lakes Michigan and Huron. Average annual and average monthly flows through the Straits of Mackinac were computed for the 1950–1966 period by use of a water budget technique applied to Lakes Michigan and Huron. In addition, water budget computations were compared with a 100‐day period of current meter observations taken in 1973. The computations and measurements agreed quite closely, within approximately 2%. A variation of greater than 500% was found between the maximum and minimum annual flows observed during the 17‐year computation period. The gross residence or flushing time for Lake Michigan was determined by two methods. The first determination used the mean annual flow through the straits, resulting in a flushing time of 137 years. The second procedure using the results of the current study, which found a deep return flow into Lake Michigan through the straits during stratification, gave a flushing time of 69 years.