Hydrogeology of the Tri-Creek Basin, Alberta

Groundwater flow in the Tri-creek basin, a 23-square mile (60 square km) area of the Rocky Mountain Foothills in western Alberta, is controlled by the surficial and bedrock geology. Flow is the bedrock follows bedding planes and joints; flow in surficial deposits is governed by relative permeability. Flow systems are short, shallow and rapid; the depth of active groundwater flow is probably less than 300 feet (91 m) and metamorphosis of groundwater is limited by the short residence time below the surface. Response to changes in recipitation is generally rapid, although slower responses were noted at some points in the region.

Groundwater discharge features observed include springs of several kinds, seepages, hummocky ground, swamps and amphitheater-shaped depressions.

Quantitative drainage pattern data include a bifurcation ratio of 5.6 (indicative of strong geologic control) in one of the three subbasins, and values of less than 5 (little geologic control) in the other two. Average drainage density is 4.1. Relief ratios of 0.04 to 0.06 indicate glacial derangement of drainage.

Depth to water table, estimated from studies of the various phreatophytic plant assemblages, ranges from 1 to 8 feet (0.3 to 2.4 m). A plant association of lodgepole pine, bearberry and brome grass indicates water table depths of from 4 to 8 feet (1.2 to 2.4 m); an ssociation of black spruce, fir, haircap and sphagnum moss indicates a range of from 11/2 to 21/2 feet (0.5 to 0.8 m). Lodgepole pine- rome grass-bearberry, and white spruce-pine-bilberry-green moss associations indicate natural groundwater recharge conditions; natural groundwater discharge areas are marked by an association of black spruce, haircap and sphagnum moss.

Allowable rates of well pumping vary from 0.5 to approximately 100 imperial gallons per minute (igpm) or 2 to 450 litres per minute L/min); but values greater than 25 igpm (115 L/min) are associated with scattered deposits of ice-contact drift and are not typical of the area. Wells yield 5-10 igpm (25 to 45 L/min) on the average.

Erosion hazard in the area ranges from low to high. Glaciolacustrine deposits, which cover a third of the basin, are easily eroded when vegetation cover is artificially disturbed. Logging and strip mining are not recommended in these areas.

The hydrogeological information given in this report may be applicable to those areas of the Rocky Mountain Foothills where similar geologic and climatic conditions exist.

Explanations of hydrogeological concepts and methods used are found hroughout the text and in the appendixes.