Modelling climate change impacts in the Peace and Athabasca catchment and delta: II - variations in flow and water levels with varying winter severity

As freshwater ice is known to significantly affect flows and water levels within the Peace-Athabasca Delta (PAD), a winter severity sensitivity analysis using a one-dimensional open channel hydraulic model was performed for four climate scenarios (from mild to severe), and was examined under three differing flow conditions (low, average, and high hydraulic regimes), in an effort to better understand the multiple interactions between ice cover and the hydrodynamic regime of this complex system characterized by overbank flooding and flow reversal episodes. In general, a reduction of winter severity lowered lake levels and river flows. While the winter severity effect is of relatively short duration in the rivers, the subsequent reduction in lake levels extends over the summer months. High river flows predispose flow reversal conditions, and water enters the lakes at the outlet as the water levels in the rivers feeding the PAD increase significantly over a short period of time. This flow reversal effect is suppressed during milder winters. Numerical modelling results indicate that extending the ice-cover season (severe winter) by 14 days resulted in an increase of up to 5 cm in water level of large takes in the PAD, while reducing it by 28 days lowered the levels by almost 10 cm. Short-term variations in river levels reached up to 1.5 m as a result of varying the extent of the ice-cover season. As the simulation runs did not consider ice-jam events and neglected the effect of ice thickness on water levels, the reported quantitative results must be interpreted with prudence. Copyright (c) 2006 Crown in the right of Canada, and John Wiley & Sons, Ltd.