Abstract

The sedimentological evolution of the Rivière aux Outardes estuary was modified considerably during and after the construction of the hydroelectric dams on the river. Prior to 1965, the dominant river discharge was 1350 m3/s and the flood peak reached 2700 m3/s. Between 1965 and 1975, during the building activities, it fell to 430 m3/s and since 1955 it remained steady at 555 m3/s. Now, the variations range from 1300 m3/s during discharge periods to 0 m3/s during some filling periods. The most significant variations in the river discharge related to the creation of the reservoirs have modified the sedimentary equilibria and it is the aim of the present study to improve our understanding of the flow of the non-cohesive materials in the estuary.Before regulation, the sedimentary processes were dominated by seasonal variations of the river regime: the floods flushed out the fine material from the estuary. Between 1965 and 1975, the river discharge decreased, and the tidal wedge moved upstream. The erosion rate of the cliff edges decreased during working periods of regulation and the entry of marine material was increased particularly at the mouth of the river. The influence of the swell and the tide is more important than the effect of the river discharge.In the present estuarine system, the sedimentary budget is positive and the source of non-cohesive materials has been changed since the regulation of the river. The principal hydrodynamic processes in the estuarine environment of the Rivière aux Outardes are compared with those of non-regulated rivers in a subboreal climate, such as the Rivière St-Jean and the Rivière La Grande rivers. [Journal Translation]

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