Alberta’s 2013 flood: Response of a mountain peatland

English Abstract:

In mid-June 2013 heavy rainfall in the Canadian Rocky Mountain foothills led to severe flooding in western Alberta. Consequently, there is interest from flood risk managers and scientists in exploring the role of foothill wetlands and beaver ponds in storage of floodwaters. Sibbald is a 0.63 km² foothills peatland in the foothills of the Rocky Mountains where a series of three beaver ponds, one groundwater well and the stream were instrumented with automated level recording devices one day before the onset of rainfall. A meteorological station recorded standard hydrometeorological variables throughout the event. The total rainfall over 20-22 June was 190 mm, with a 6-hr break in the rain occurring the afternoon of 21 June. Soil coring in the three days preceding the rain event revealed that the peat was frozen in many locations at a depth of 20-60 cm but was not frozen beneath the beaver ponds. Available peat storage above the frost table was filled in the first few hours of the rain event, causing the water table to rise well above the ground surface where it remained until after 22 June. The three beaver ponds offered 10-50 cm of water storage in the initial stages of the rain event. The pond hydrograph recessions during the break in rain indicate that they were losing water to the groundwater system. Although the middle beaver pond in the series outburst through a 10-m long breach during the first wave of rain, it stored 15 cm of water during the second wave. The results suggest that temporary storage of floodwaters offered by beaver ponds can enhance recharge to the groundwater system and attenuate downstream peak flows during flood events.