Lake Michigan-Huron Water Level Decline due to Hydraulic Scour of the St. Clair River

Upper Great Lakes water levels are currently experiencing a precipitous decline. The December monthly mean water levels for Lakes Superior, Michigan-Huron, and St. Clair were 17, 15, and 2 inches, respectively, below average when compared to long-term (1918–2005) averages. At the same time, Lake Erie and Lake Ontario were 7 and 12 inches above average. Concern about declining Lake Michigan-Huron water level from public and private organizations has lead to increased study of the fluvial geomorphology of the St. Clair River and its contribution to the steep decline of the Lake Michigan-Huron water level. The position of this paper, based upon historical construction and dredging records, is that the increased hydraulic scour rate of the St. Clair River is an anthropogenic effect of riverbed armor layer removal influenced by navigational and commercial dredging projects. Hydraulic scour increases the outflow capacity of the St. Clair River which results in a water level decline on Lake Michigan-Huron. The goal of this technical paper is to summarize the causal relationship between St. Clair River erosion and decreasing Lake Michigan-Huron water level. An additional concluding section has been added to suggest an economical mitigation measure.