Winter streamflow variability in two groundwater-fed sub-Arctic rivers, Yukon Territory, Canada

Frequent discharge measurements were made during the winter of 1994-1995 in two groundwater-fed streams near Whitehorse, Yukon Territory, to evaluate the nature and causes of winter discharge variability in sub-Arctic rivers. Observations were also made of near-stream hydraulic head, snowmelt percolation, and water quality. A linear reservoir model provided a poor fit to the streamflow recessions at both rivers, whereas three relatively complex models provided good fits to the data used for calibration. A pronounced discharge depression occurred at M'Clintock River associated with an increase in stage at freeze-up. The volume of water represented by the depression was about three times the maximum amount that could be accounted for by channel storage. This discrepancy could have been caused by stream-aquifer interactions. Piezometric observations were consistent with a reversal of hydraulic gradient across the stream bed, which would block or reduce groundwater inflow, as well as cause water to go into bank storage. A sustained discharge depression did not occur at Ibex River, probably because the volume of channel storage is small with respect to discharge and could be satisfied over the period of freeze-up without measurable deviation from the recession trend, and because the near-stream hydraulic gradients were strong enough not to be influenced by stage increases. Discharge at Ibex River was uncorrelated with air temperature. At M'Clintock River, residuals from the layered linear reservoir model appeared to be weakly correlated with air temperature.