Current Perspectives on the Lake Erie Water Balance

An analysis was conducted of the Lake Erie water balance for 1940–79, based upon the individual hydrologic components, including thermal expansion and consumptive use. Particular emphasis was given to the continuity of the system. Annual and monthly statistics are presented for each of the water balance components. While the Detroit River contributed 87 percent of the Lake Erie total water supply, the variability of the net basin supplies was also found to be of importance in explaining annual water level fluctuations. A major step function was found to occur in the annual water balance between 1958 and 1959, which illustrates the large discontinuities that can occur when calculating the net basin supplies from residuals rather than directly from precipitation, runoff, and evaporation. The annual water balance for 1959–79 was found to be well satisfied with an average annual residual of about 0.5 percent of the Detroit River or Niagara River flow. A distinct seasonality was noted in the mass continuity of the monthly water balance. Also on a seasonal basis, the change in storage due to thermal expansion was significant during the late spring and early fall months.