COMPARISON OF THE HYDROMORPHOLOGICAL EVOLUTION OF THE L'ASSOMPTION AND OUAREAU RIVER CHANNELS (QUEBEC, CANADA)

The monitoring station method, which is based on comparing data before and after dam construction, is commonly used to quantify the hydromorphological impacts induced by dams. However, in the absence of pre-dam construction data, other analytical methods may be used to detect changes downstream from dams that remain more or less constant over time. The study used one such method, the control station method, to constrain changes which may be linked to construction of the Rawdon Dam, in 1913, on the Ouareau River. Thus, a comparison of the hydrological (seasonal daily maximum flows) and morphological (mean bankfull width and sinuosity) evolution of the Ouareau and L'Assomption Rivers during the period 1930 to 2008 was carried out. The surface area as well as the climatic, lithological, land use and physiographic features of the two watersheds are nearly identical in the study area. The comparison revealed three changes that may be linked to the Rawdon Dam: an increase in the magnitude of daily maximum flows downstream from the dam for all four seasons, which is inferred to have resulted in extensive widening and low sinuosity of the Ouareau river channel downstream from the Rawdon Dam relative to the L'Assomption river channel. These types of morphological changes are consistent with changes observed downstream from some dams. The Rawdon Dam had no effect on the interannual variability of daily maximum flows, which are characterized by a significant increase in mean in winter in both watersheds. This increase, which is abrupt, occurred in 1973 for both rivers. Copyright (c) 2012 John Wiley & Sons, Ltd.