OBSERVED ICE PASSAGE FROM LAKE HURON INTO THE ST-CLAIR RIVER

Ice entering the St. Clair River from southern Lake Huron has caused large ice jams on the river, which have inundated large inhabited areas and delayed navigation. Study and forecasting of these ice jam events require that the ice passage from the lake into the river be described quantitatively. This paper analyzes data obtained from time-lapse photography of ice conditions at the entrance of the river at Lake Huron over six winters. For each day of record when ice was observed in Lake Huron or the river, the presence or absence of an ice arch and the daily average surface concentration of ice entering the river were noted. For the months of January through April, separate means, standard deviations, and distributions of the surface ice concentration were determined for periods when the ice arch was present or absent. The existence of the ice arch can be predicted by a simple indicator based on air temperature. The statistical distributions of ice concentration are strongly influenced by the presence or absence of the ice arch. The overall mean surface ice concentration was 9.5% with an arch present and 27.3% with no arch. Based on this finding, ice passage can be forecasted.