Changes in the levels and flows of the St. Lawrence River
Background
Using a single indicator to characterize water conditions in the St. Lawrence River is not a simple matter, as specific local features and short-term fluctuations must be disregarded. The flow at Sorel has several advantages as an indicator: it incorporates inputs from the two main hydrologic sources, the Great Lakes and the Ottawa River; and Sorel is located at approximately the midpoint of the fluvial section of the Great Lakes– St. Lawrence system, upstream of Lake St. Pierre (Figure 1). In addition, because the flow is calculated from the hydrologic inputs, interference effects from wind, tides, growth of aquatic plants and ice cover are not incorporated in the indicator.