Comparison of flood index characteristics and channel morphology of two Canadian Shield rivers based on wetland area in southern Quebec (Canada)

Two characteristics (magnitude and duration-frequency) of two indices of high (Qmax, annual flooding) and low intensities (Q90) floods and the morphology (bankfull width and sinuosity) of channels were compared for the Matawin (1,390 km²) and Petite Nation (1,330 km²) rivers on the Canadian Shield, which are differentiated mainly by wetland and forest areas. Wetlands cover 9% and 15% respectively in the Matawin and Petite Nation watersheds. This comparison revealed that the magnitude of high floods (Qmax) in the Matawin River was on average about twice the magnitude of high floods in the Petite Nation River from 1945–2019. No significant difference was observed in the magnitude of low floods (Q90) between the two rivers. As for the duration-frequency of heavy floods (Qmax), it was, on average, about three times higher in the Petite Nation River watershed than in the Matawin River watershed. The opposite is true for low floods (Q90). Morphologically, this difference in the magnitude and duration-frequency of heavy floods is seen in the bankfull width and sinuosity between the channels of the two rivers. The Matawin River channel is narrower and more sinuous than the Petite Nation River channel. This study is the first to demonstrate the impact of wetlands on channel morphology for Canadian Shield rivers in southern Quebec.