Landforms of British Columbia 1976 - Department of Geography

British Columbia includes the drainage basins of four major river systems
(see Fig. 11): those of the Yukon River flowing northward and northwestward
through Yukon and Alaska into the Bering Sea, the Mackenzie River flowing
northeastward and northward through northern Canada into the Arctic Ocean,
and the Fraser and Columbia Rivers flowing southward and southwestward into
the Pacific Ocean. In addition, there are a number of coastal rivers that flow
westward into the Pacific Ocean. Drainage areas and volumes of flow are tabulated
in Table I.
The main rivers-the Liard, Peace, Fraser, and Columbia-acquire their
characteristics from the regions which they drain. Peculiarities of flow depend on
climate and the distribution of precipitation, while stream patterns are influenced by
the structural features of the underlying bedrock. The influence of bedrock
manifests itself in the quite obviously structurally controlled pattern of the Columbia
River, in contrast to the very largely dendritic pattern of the Fraser River system.
It may be fortuitous, but it is notable that the headwaters of all four major rivers
flow at some place and in one direction or another in the Rocky Mountain Trench.
Figure 11. Diagram showing the drainage basins within British Columbia.
All the river systems in British Columbia have had a long and eventful develop-
ment. The major systems were initiated early in the Tertiary and were rejuvenated
by late Tertiary uplift. At that time the Liard River maintained its course around
the northern end of the rising Rocky Mountains, and the Peace River continued
to flow directly across them in the region of their minimum uplift. The courses of
the Kootenay, Columbia, Fraser, and Peace Rivers have been profoundly influenced
by stream piracy on a regional scale, as a direct result of differing rates of headward
erosion in the several river systems.
107