Central Plains

The Central Plains region extends from the town of Athabasca in the north, through Edmonton, Camrose, Stettler, Brooks, and further south past Lethbridge to the Canada-U.S. border. The classic prairie landscape of this region is undulating to rolling and mostly covered with agricultural development. The region, along with the neighbouring Western Plains and Benchlands region, is home to a large portion of Alberta’s population. Compared to the other hydrogeological regions, the Central Plains region has a wide range of temperature, moisture, and natural habitat. The northern part of the region is covered by boreal forest, with cool and wet conditions. There is a transition to warmer and drier parkland in the central part of the region, and to dry, hot grassland in the south. Agricultural activity correspondingly changes from mixed crop, hay and grazing in the north, to grain production in the central part, and grassland grazing in the south. Irrigation is prevalent in the southern part of the region.

Two different scales of groundwater flow are discussed here. Deep within the bedrock, groundwater slowly flows eastwards from the neighbouring Western Plains and Benchlands region. In some areas, this deeper groundwater emerges in rivers, wetlands, or salt-crusted depressions often seen on the Prairies. In other areas, deeper groundwater may flow into shallower aquifers.

Closer to the ground surface, the undulating to rolling terrain supports more localized groundwater movement from small hills to nearby depressions (sometimes also salt crusted), creeks, and rivers. The dominant form of groundwater replenishment in this region is “depression-focused recharge”. In the spring, when water use by vegetation is low, melted snow collects in small surface depressions. As the ground thaws, the collected snowmelt and ponded surface runoff percolates quickly into the ground rather than being used by plants. 

Groundwater also has a complex interaction with surface water in this region. Alberta’s major rivers, including the Athabasca, North Saskatchewan, Red Deer, Bow, Oldman, and South Saskatchewan pass through the Central Plains region. Along some stretches, groundwater slowly discharges to these rivers, but along other stretches, river water may recharge the groundwater system. Patterns of recharge and discharge along rivers may also change with the seasons.

The Central Plains region is mostly low-lying, but there are belt-shaped areas of elevated hummocky terrain consisting of rounded hills and semi-circular depressions, referred to as “knob and kettle topography”. This type of landscape can be seen around Elk Island National Park east of Edmonton, the area around Buffalo Lake and Bashaw, and the Rumsey Natural Area in the south-central part of the region. Most hummocky terrain was formed by stagnant glacial ice, which created rugged terrain with individual hummocks (or “knobs”) ranging in height from about 5 m to as much as 20 m.

Hummocky terrain plays an important role in the availability of moisture at the surface, and promotes the development of local groundwater flow systems.

Low-lying depressions (or “kettles”) between hummocks may contain seasonal ponds, or more permanent wetlands or lakes, some of which may receive local groundwater discharge, while others function as areas of groundwater recharge. The region also contains more conspicuous landscape features, such as the isolated higher elevation areas of Two Hills and Hand Hills, which are the result of increased relief of the underlying bedrock surface, and the Neutral Hills, which are a series of ridges formed by deformation and thrusting of the bedrock and sediment by glacial ice.

In general, bedrock formations in the Central Plains region are made of alternating layers of sandstone, siltstone, mudstone, and coal. The variation in properties of these geological materials leads to a wide variation in the availability and quality of groundwater.

In the western part of the region, the Horseshoe Canyon Formation is the uppermost bedrock unit. It contains sandstone beds that were deposited in floodplains and coastal water bodies (estuaries). These sandstone beds also typically contain silt and mud, meaning that they don’t transmit groundwater as easily as other sandstone bodies in Alberta, such as in the Western Plains and Benchlands region. In some locations, the mud within the Horseshoe Canyon Formation is bentonite, which is a type of clay that absorbs water and swells. Bentonite can be found as distinct layers or mixed within siltstone and sandstone. Bentonite greatly reduces groundwater movement. The Horseshoe Canyon Formation also contains coal beds that are brittle and fractured, which tends to enhance groundwater movement. The varying properties of the Horseshoe Canyon Formation mean that aquifers are fairly localized within the formation, rather than forming widespread regional aquifers.

In the central part of the region, the Bearpaw Formation is the uppermost bedrock unit, which is mostly siltstone and mudstone that also contains bentonite. Generally, the Bearpaw Formation does not transmit groundwater very easily and is considered an aquitard rather than an aquifer.

Finally, in the eastern part of the region, the Belly River Group is made up of several formations containing layers of sandstone, siltstone, mudstone, and coal. Similar to the Horseshoe Canyon Formation, some of the layers in the Belly River Group act as aquifers, while others act as aquitards. In the southern part of the Central Plains region, the Foremost Formation, in the bottom part of the Belly River Group, is a productive sandstone aquifer.

The variation in properties of the bedrock has a large influence on groundwater quality. The presence of siltstone and mudstone containing bentonite causes groundwater to travel more slowly than in other sandstone aquifer systems and allows groundwater to acquire more salts and other dissolved solids. Where the climate is dry, groundwater recharge is also limited, and does not replenish groundwater as easily as in areas with a moist climate. The result is generally poorer water quality in the bedrock compared to the neighbouring Western Plains and Benchlands region, but water quality does vary throughout the region. Analysis of water samples from water wells by the Alberta Geological Survey and the Government of Alberta has helped develop maps of salinity for some of the formations. These maps help identify where groundwater may be more suitable for various uses. 

Despite its varying quality, groundwater from the bedrock is often a better quality than groundwater from the sediments above bedrock. There are, however, exceptions and some shallower aquifers within the sediments do exist.

The sediments above bedrock are thin to moderately thick, averaging about 20 m. There is substantial variation in sediment thickness ranging from less than a few metres in areas such as Beaverhill Lake east of Edmonton, to more than 50 m along the axes of buried bedrock valleys. Major buried valleys include the High Prairie and Dapp valleys in the north, the Beverly, Onoway, and Red Deer valleys in the central part, and the Calgary Valley in the south.

Coarse, permeable sediments like sand and gravel are typically found along the bottom of these buried valleys and can serve as important local aquifers. These buried valley aquifers are often covered by clay or diamicton, which is a mixture of clay, silt, sand, and boulders, and is called till when deposited by glacial ice. The clay or till covers and often conceals the buried valley aquifers. In addition to buried valley aquifers, there may be small, isolated deposits of glacial sand and gravel within thick till or on higher bedrock steps (terraces) that can form localized aquifers able to supply groundwater to low-volume users.

The following maps describe the geology, physiography, climate, and groundwater use in the region. The maps are discussed in more detail in the Overview. Click each button to turn the maps on and off.

Andriashek, L. comp. (2018): Thalwegs of bedrock valleys, Alberta (GIS data, line features); Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Digital Data 2018-0001, URL < https://ags.aer.ca/publications/DIG_2018_0001.html >.

Atkinson, L.A., Liggett, J.E., Hartman, G., Nakevska, N., Mei, S., MacCormack, K.E. and Palombi, D. (2017): Regional geological and hydrogeological characterization of the Calgary-Lethbridge Corridor in the South Saskatchewan regional planning area; Alberta Energy Regulator, AER/AGS Report 91, 175 p., URL < https://ags.aer.ca/publications/REP_91.html >.

Bam, E.K.P., Ireson, A.M., van der Kamp, G. and Hendry, M.J. (2020): Ephemeral ponds: Are they the dominant source of depression-focused groundwater recharge?; Water Resources Research, v. 56, e2019WR026640,  doi: 10.1029/2019WR026640 .

Barker, A.A., Riddell, J.T.F., Slattery, S.R., Andriashek, L.D., Moktan, H., Wallace, S., Lyster, S., Jean, G., Huff, G.F., Stewart, S.A. and Lemay, T.G. (2011): Edmonton-Calgary Corridor groundwater atlas; Energy Resources Conservation Board, ERCB/AGS Information Series 140, 98 p., URL < https://ags.aer.ca/publications/INF_140.html >.

Ceroici, W.J. (1979): Hydrogeology of the southwest segment, Edmonton, Alberta; Alberta Research Council, Alberta Geological Survey, ARC/AGS Earth Sciences Report 1978-05, 17 p., URL < https://ags.aer.ca/publications/ESR_1978_05.html >.

Klassen, J., Liggett, J.E., Pavlovskii, I. and Abdrakhimova, P. (2018): First-order groundwater availability assessment for southern Alberta; Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Open File Report 2018-09, 37 p., URL < https://ags.aer.ca/publications/OFR_2018_09.html >.

Nakevska, N. and Singh, A. (2019): Distribution of total dissolved solids in the Wapiti / Belly River hydrostratigraphic unit, Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Map 542, URL < https://ags.aer.ca/publications/MAP_542.html >.

Noorduijn, S., Hayashi, M., Mohammed, G., and Mohammed A. (2018): A coupled soil water balance model for simulating depression-focused groundwater recharge; Vadose Zone Journal. v. 17, 170176,  doi: 10.2136/vzj2017.10.0176 .

Woods, L.G. (2019): A conceptual model for the development and persistence of soap holes (unique prairie groundwater discharge features); M.Sc. thesis, University of Calgary, 131 p., URL < https://prism.ucalgary.ca/handle/1880/110219 >.