Water level

The St. Lawrence: a long and busy river

River and ocean navigation are two very different things. The St. Lawrence, like all major rivers, has its own specific characteristics:

  • The water flows out of the river and does not return. Lakes and other rivers, which are subject to climatic conditions, supply the St. Lawrence with its water.
  • The riverbed is not flat. Water depth is much greater between the mouth of the Gulf of St. Lawrence and Quebec City than it is between Quebec City and Montreal.
  • One section of the river is subject to tides. Tides exist from the mouth of the Gulf to Lake St. Pierre, near Trois-Rivières. The tide at Quebec City can reach up to six metres, meaning that the water level at high tide can be six metres higher than the water level at low tide.
  • Bridges and high-voltage power lines that cross the St. Lawrence restrict the height of vessels that can sail the river.

To meet the requirements of the commercial shipping industry, work has been carried out on four separate occasions to deepen the navigation channel between Quebec City and Montreal:

  • 1883: dredging work to increase the minimum depth of the channel to 7.5 metres (25 feet).
  • 1910: dredging work to increase the minimum depth of the channel to 10.7 metres (35 feet).
  • 1992: dredging work to increase the minimum depth of the channel to 11 metres (36 feet).
  • 1999: dredging work to increase the minimum depth of the channel to 11.3 metres (37 feet).