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Although much of the water flowing in the South Saskatchewan River originates high in the Rocky Mountains of western Alberta, the South Saskatchewan River is a prairie river. Born where the Bow and Oldman Rivers meet at Grand Forks in southern Alberta, the river flows north and east through a wide valley carved deeply into gently rolling plains covered with grasslands.
Three hundred and twenty kilometres from Grand Forks, on the Saskatchewan side of the provincial border, the South Saskatchewan River joins with the Red Deer River. From there, the river creates a meandering path to join with the North Saskatchewan River forming the Saskatchewan River, which then crosses into Manitoba. After draining into Lake Winnipeg, water that began as meltwater from glacial ice, snow and rain eventually ends its journey in the Hudson Bay.
The landscape across this watershed is a testament to the power of ice, water and wind.
When glaciers retreated from this area at the end of the last ice age they left a scoured landscape with long narrow valleys carved into glacial debris by huge volumes of meltwater; post-glacial floods that also initiated the formation of badlands in local coulees and valleys. The glaciers also left undulating plains pockmarked with depressions that evolved into shallow wetlands as well as glacial sediments that were carried and shaped into fields of sand dunes by prevailing winds.
Superimposed upon this landscape, the SSRSB covers a drainage area of approximately 13,200 square kilometres. Because of its unique topography only about 50% of that land area actually contributes water to downstream flow; a large part of the sub-basin is made up of smaller, internally draining, closed sub-watersheds; areas that receive runoff, but do not feed into the South Saskatchewan River.
Most of the South Saskatchewan River Sub-basin lies within the Dry Mixedgrass Natural Subregion of Alberta, a semi-arid prairie that supports many short-lived and deep-rooted grasses, shrubs and herbs adapted to summer droughts.
In this region winters are short, cold and dry, and often punctuated by warm, westerly Chinook winds. The summers are long and warm and this corner of the province enjoys the longest frost-free period, longest growing season, highest average temperatures, and the most sunlight hours in Alberta.
The average precipitation is less than 300mm, the lowest in the province, and more precipitation falls as rain in the warm season than as snow in cold season. Given its unique climate and landscape characteristics, this region provides habitat for many species of plants and animals that do not occur anywhere else in Alberta.
The South Saskatchewan River follows a natural flow regime with high flows during spring runoff events, rising to a peak in June due to mountain snowmelt, and then dropping to its lowest flows in winter. The mean annual natural flow of the South Saskatchewan River at Medicine Hat is 7.0 billion cubic meters (m3), but this value can vary considerably. Annual runoff from the tributaries in the region is highly variable; the flow in the river is essentially the sum of the flows in the Oldman River and Bow River, and river flows can change dramatically from year to year in response to regional precipitation and water usage across southern Alberta.
Like quantity, the water quality of the South Saskatchewan River largely reflects what is happening in upstream basins. Treated wastewater effluent, stormwater, agricultural runoff and other human and industrial activities upstream can contribute to increased levels of minerals, nutrients, organic matter and sediments in the South Saskatchewan River Sub-basin.
The average population density of this primarily rural region is about five people per square kilometre. The largest regional users of water include the only large urban centre in this corner of the province, the City of Medicine Hat, which has its own power plant and draws water under its licence to support that facility, and irrigation agriculture. The development of irrigation throughout Alberta led to the construction of several reservoirs in the area, many of which are linked to the St. Mary River Irrigation District irrigation network. District and private irrigation are used to supply water for agriculture and a number of other uses including: commercial activities like golfing, parks and recreation; industry; oil and gas production; and habitat enhancement projects.