Earth Sciences Report 1974-10

Author(s) Date 1973-12-31

This report supplements the hydrogeological reconnaissance map of the northwest segment of the Edmonton map area (NTS 83H), providing some elaboration and discussion of map features.

The topography of the area is predominantly level to gently rolling. The area is drained by the North Saskatchewan and Sturgeon Rivers. These rivers are incised up to 200 feet below the plain level along parts of their course.

The area has a cold, humid continental climate, receiving 17.5 inches of precipitation on average each year, 70 percent as rain. The ground is frozen for 150 days in the average year.

Most of the area is covered by glacial materials, mainly till and clay and silt. Buried valleys are coincident with the two main rivers and contain sand and gravel deposits which are in hydraulic connection with the rivers. The bedrock is the Wapiti Formation of Late Cretaceous age. It is highly heterogeneous consisting of shales, bentonitic sandstones and coal seams.

Yields are fairly high in the sand and gravel aquifers of the drift, particularly those in connection with the river. In the bedrock, yields are typically less than 5 igpm.

Groundwater flow systems in the upper 300 feet are largely controlled by the connection between the river and buried valley sand and gravel deposits, and by the incised nature of the valleys In general, this connection has the effect of restricting region scale discharge areas to narrow bands paralleling the buried valleys.

The chemistry of the groundwaters shows a marked correlation with soil type and drift lithology. Groundwaters in areas covered by till, and clay and silt are typified by the presence of sulfate and higher total dissolved solids. The exchange of calcium for sodium as flow passes from the drift to the bedrock is pronounced and some sulfate reduction occurs in the bedrock.

Infiltration to groundwater systems is thought to be greatly influenced by drift lithology, soil type and topographic position, in addition to meteorologic factors. Areas of sand and gravel in topographically high positions are thought to contribute greatly to infiltration, in contrast to areas of till, and silt and clay in similar topographic positions. It is also thought that most infiltration occurs in the spring after snowmelt and after the ground has thawed.

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Bibby, R. (1974): Hydrogeology of the Edmonton area (northwest segment), Alberta; Alberta Research Council, ARC/AGS Earth Sciences Report 1974-10, 13 p.