Budget and sources of suspended sediment transported in the St. Lawrence River, Canada

A mass balance budget of the suspended sediment in the St. Lawrence River was established for the sector stretching from Cornwall, Ontario, to Quebec City, Quebec, for the period 1989-1993. The approach consisted of analysing the amount of sediment contributed by the different tributaries, on a watershed-by-watershed basis, through 'sediment concentration-discharge' models incorporating more than 4000 data points collected since 1983. Lake Ontario contributes less than 3% of the particulate load at Quebec City, while St. Lawrence tributaries on the south and north shores contribute 19% and 13%, respectively, of the sediment load. Our findings indicate that nearly 65% of the suspended sediments come from erosion of the bed and banks of the St. Lawrence River. This finding is broadly supported by numerous geomorphological and sedimentological observations and is consistent with the geological history of the river and the structures built on its banks in recent decades. Upstream-downstream mass balance studies conducted on individual river sectors indicate that the sources of erosion are located mainly in the Beauharnois Canal region, between Montreal and Les Greves, and further downstream, between the outlet of Lake Saint-Pierre and Portneuf. Copyright (C) 2000 John Wiley & Sons, Ltd.