Comprising over 25,000 square kilometres, the Bow River basin covers more than 4% of Alberta, and about 23% of the South Saskatchewan River drainage area in Alberta.
The headwaters of the basin are fed by the snow and glacial ice of the Rocky Mountains along the eastern side of the Continental Divide. The Bow River begins in Bow Lake and then flows in a southeasterly direction through a steep valley corridor in Banff National Park.
Exiting Banff National Park, the river continues eastward and passes through the foothills onto the prairie, gradually widening and decreasing in gradient. It meanders through a wide, deep valley across the prairies to its confluence with the Oldman River. The meeting of the Bow and Oldman Rivers creates the South Saskatchewan River, the southwest tributary of the Saskatchewan-Nelson River system that eventually flows to the Hudson Bay, and then on to the Arctic and Atlantic Oceans.
On its journey from the Rocky Mountains through the foothills and prairies, the Bow River encounters many different landscapes and ecosystems. Riparian areas can be found along stream banks and floodplain of the river and its tributaries, as well as along the margins of wetlands and lakes.
The variety of lakes is as diverse as any other region in Canada, ranging from cold alpine lakes to shallow prairie wetlands and irrigation reservoirs. Wetlands are found throughout the prairies, and are primarily located in the eastern regions of the basin. These areas provide habitat for a variety of mammals, birds, aquatic plants, benthic invertebrates, and fish.
The climate in the basin is typical of southern Alberta, with long, cold winters and short, warm summers. Dry westerly Chinook winds can produce dramatic mid-winter changes, as much as a 30°Celsius change in temperature, and a 40% change in humidity within a few hours. Annual precipitation in the upper regions of the Bow River ranges from 500 to 700 millimetres, with about half of that amount falling as snow. At Calgary, annual precipitation is 412 millimetres, with about 78% of this precipitation coming in the form of rain.
LET’S TAKE A CLOSER LOOK...
The Bow River is approximately 645 kilometres in length. It begins at Bow Lake, at an elevation of 1,920 metres above sea level, then drops 1,180 metres before joining with the Oldman River. In the mountains, the Bow River is relatively steep with gradients averaging 7 metres per kilometre. But, when the Bow becomes a prairie river, the gradient gradually reduces to 0.5 metres per kilometre at the confluence with the Oldman River.
With approximately 1.2 million people (34% of Alberta’s population), and a population density of 41 residents per square kilometre, the Bow River basin is the most highly populated river basin in Alberta. In the last ten years, the population of the basin has grown by more than a quarter million people. The current population is 95% urban (22 urban municipalities, including the City of Calgary) with 4% residing in 12 rural or regional municipalities, and less than 1% residing in Aboriginal settlements. The hydrology of the Bow River is significantly affected by 13 dams, 4 weirs, and 8 reservoirs, making it the most managed or regulated river in Alberta.
The Bow River is the largest tributary of the South Saskatchewan River, contributing nearly 43% to its 9.5 billion cubic metres of average annual flow. The Bow River receives most of its water from the progressive melting of spring and summer snow packs. Peak discharges generally occur during June, with minimum flows occurring in January. Flows decline over the late summer, fall and winter. Glacial melt contributes about 2.5% to the total annual flow during late summer and early fall, while flows during winter are heavily influenced by groundwater.
Water quality varies along the Bow River, with more pronounced changes occurring downstream of the City of Calgary. As water moves along the river from west to east, there are increasing amounts of sediment, minerals, nutrients, and organic material found in the river. Some of these changes are natural, while others are due to treated wastewater effluent, stormwater, agricultural runoff, and human and industrial activities.
The river channel is wide and relatively shallow, and is composed of boulders, cobble and gravel. It has well-developed riffle, run and pool sequences that provide fish habitat. The headwaters of the Bow descends from alpine tundra through forests of lodgepole pine, spruce, fir and trembling aspen. The undulating prairie consists of open grassland. The high natural fertility and good moisture-holding capacity of the underlying dark soils, high in organic matter, have given rise to productive agriculture.
The most important point is that ultimately, every person living in the Bow River basin bears some responsibility for its present and future state..
For additional information and profiles of the Bow River Basin, click the links below: