The effects of dams on mean anual flow characteristics according to management mode and basin drainage area in Québec
We compared the impacts of dams on the characteristics (magnitude-frequency, inter-annual variability and distribution curve shape) of the mean annual flows in three regulated flow regimes (inversion, homogenization and natural type) in Québec. We applied the “proportionality method”, which consists of comparing the flow characteristics of natural rivers to regulated rivers according to watershed size. A change in the flow-frequency volume and its inter-annual variability was observed only in the inversion flow regime. This result translates into a decrease in average annual flows during dry hydrological years and a relatively high inter-annual variability relative to natural rivers. These changes are mainly ascribed to the reservoir management mode because less water is released during dry hydrological years. Finally, the changes of the coefficients of asymmetry and skewness are particularly observed in homogenization flow regime. This study shows that, contrary to the commonly accepted opinion, dams can alter all the characteristics of annual average flows.