Drainage basins

"Drainage basins," "watersheds," "river basins" and "river valleys" are terms used to describe a surface drainage catchment area. The boundaries that delineate a drainage basin usually follow heights of land. For example, the ridge of a mountain range can form a drainage basin boundary separating two drainage catchment areas.

Canada is part of the North American continent's hierarchical hydrological system. There are five great basins in Canada. These are:

Canada's five major basins are divided into 218 sub-drainage basins. These sub-drainage basins can be further divided into 917 sub-sub-drainage basins.

Drainage basin boundaries are fixed over time, making them useful for the development and analysis of socio-economic trends. Drainage basins are also valuable environmental stress impact units. For example, human settlements and industries can have many impacts on water systems, affecting the use, discharge and quality of water. The drainage basin classification used in this publication is adapted from the Water Survey of Canada.