Water from the Bow and Elbow rivers meets the urban and agricultural needs of much of southern Alberta. Reservoirs along both rivers provide Calgarians with fresh water, and irrigation canals carry water to farms east of Calgary. The rivers also provide a natural retreat within Calgary and attract trout fishermen from around the world.
Floods can occur during the summer when exceptionally heavy rainfalls combine with rapid snowmelt in the mountains. In June 1929, flooding on the Elbow River washed out the 25th Avenue SE bridge and created a lake where Victoria Park had been. The last major summer flood to hit Calgary was in 1932, when the Bow River inundated Sunnyside and other communities.
Ice jams form during spring breakup or during Chinook winds in midwinter. They are caused by surface ice breaking into floes, which pile up against obstructions and block the river's flow.
Bow River summer flood of 1932 (Photo: courtesy of Glenbow Archives)
The risk of flood damage has been reduced by the construction of dams on the Bow River upstream from Calgary and of dikes around the floodplain areas of the city. However, the dams are too far upstream and the storage capacity of the reservoirs is too small to prevent the largest spring or summer floods. A 1996 estimate of the damage to Calgary resulting from a '100-year flood' (a flood that has 1 chance in 100 of occurring in any given year) is $131 million.
Flood zones of the 100-year flood. (Airphoto: courtesy Alberta Sustainable Resource Development
Floodzones: City of Calgary)