Hydrogeology of the Cache Percotte Basin, Alberta, Canada

Hydrogeological reconnaissance in Cache Percotte forest, including Cache Percotte and Whiskeyjack basins, produced descriptions of hydrogeologic environments, of the nature of groundwater discharge features and of the quality of waters. Recharge and groundwater discharge areas were recognized and outlined on aerial photographs and a groundwater map of the area constructed. The lateral and upper boundaries of groundwater flow systems of the field model were generally defined from a synthesis of the groundwater map, the topographic map and water quality data.

The drilling program produced examples of changes in hydraulic head with depth in recharge and discharge areas, and a regional value of hydraulic conductivity (0.20 igpd/ft², or 1.32 x 10^-2 darcys).

Two-dimensional analogs of the groundwater flow systems were constructed and quantified to evaluate groundwater movement. The average specific volume recharge is 0.031 igpd/ft2 in Cache Percotte basin, and 0.037 igpd/ft² in Whiskeyjack basin. Contribution to regional groundwater flow, or leakage out of the basins, is approximated as 75 percent under the floodplains of the main creeks, and 15 percent under remaining areas. These values were applied to the field model of Cache Percotte and Whiskeyjack basins and the following respective hydraulic properties calculated: natural basin yields are 4.13 x 10⁵ igpd (0.77 cfs) and 2.72 x 10⁵ igpd (0.51 cfs); basin leakage values are 1.6 x 10⁵ igpd (0.30 cfs) and 0.82 x 10⁵ igpd (0.15 cfs); specific volume discharges are 0.019 igpd/ft² and 0.029 igpd/ft², and coefficient of recharge in both basins is approximately 55 percent of precipitation, assuming seven months of active groundwater recharge. The total volume of groundwater discharge, from groundwater balance analyses, per square foot of discharge area, or equivalent specific volume discharge, cannot be calculated unless all the components of the groundwater balance equation are evaluated independently or measured directly. Applying the values of specific volume discharge to the groundwater balance equation during dry periods produces the following interpretation of the distribution of groundwater discharge in Cache Percotte and Whiskeyjack basins, respectively: 25 and 23 percent forms streamflow, 2 percent forms underflow, and the remaining 73 and 75 percent forms evapotranspiration.

Annual precipitation, (averaged over 4 years), over Cache Percotte and Whiskeyjack basins is 23.1 inches and 24.3 inches, respectively. Precipitation received by Cache Percotte basin is distributed in the following manner:

1.76.0 percent forms evapotranspiration;

2.16.1 percent forms streamflow (11.9 percent surface water, 4.2 percent groundwater);

3.7.4 percent forms basin leakage;

4.0. 5 percent forms underflow.

Precipitation received by Whiskeyjack basin is distributed in the following manner:

1.66 percent forms evapotranspiration;

2.24.8 percent forms streamflow (19.4 percent surface water, 5.4 percent groundwater);

3.8.5 percent forms basin leakage;

4.0. 7 percent forms underflow.

Discharging groundwater is diluted with surface waters at the ground surface, in the shallow subsurface, and in streams. Total dissolved solids contained in groundwaters discharging at the ground surface vary directly with the lengths of underground flow.

Most of the groundwaters and surface waters in the basins were of the calcium bicarbonate type. Waters from the west subbasin of Whiskeyjack basin were of the sodium-calcium bicarbonate type.