echodale2bIn 1900, the first of many projects that would alter timing and quantity of the flows in the South Saskatchewan River basin was in operation. This was the Great Irrigation Canal, used to divert water from the St. Mary River southeast of Cardston to the Lethbridge area. In 1910, a weir was constructed on the Bow River in Calgary to divert water for irrigation. A hydroelectric project at Horseshoe Falls on the Bow River in 1911 provided electricity to Calgary. These were just the first of many projects, particularly in the Oldman and Bow river basins, that store or divert water for irrigation and power generation.

The dams and diversions of the basin make a major contribution to the economic vitality of the basin. Water supplies permit irrigation development, enable value-added agricultural processing, sustain urban centres, and promote industrial growth. They also help mitigate, to some degree, the environmental consequences of human developments.

Considering the basin as a whole, water supplies are sufficient to meet reasonable needs, if managed wisely. The South Saskatchewan, Bow and Oldman sub-basins are considered fully allocated. Alberta has placed a cap on new water licences in those sub-basins. The current water-supply situation still needs to prompt questions about water supplies under future climate change scenarios, and raises concerns about the environmental effects of existing and proposed development and diversions.

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Water supplies originating with the mountain-fed principal streams of the basin are much more reliable than those of the plains-fed tributaries. For these streams, reliable flow tends to be small so potential investments in water infrastructure tend not to meet economic tests. As much of the land producing plains-runoff is agricultural, land-use change alters runoff.

Across southern Alberta, relative levels of water allocation range from 20 per cent of natural flow in the Red Deer River sub-basin, to almost 70 per cent of natural flow in the Oldman River and Bow River sub-basins, and from 70% to 80% of natural flow across the South Saskatchewan River Sub-Basin (SSRSB).
 
Read more… about water allocation and use in the region.