Morphologic Evolution of a Well-Constrained, Complete Subaerial-Subaqueous Source to Sink System: Wabush Lake

Since 1964, Iron Ore Company of Canada has deposited iron tailings resulting from mining operation into Wabush Lake. Multibeam bathymetric surveys were carried out between 1999 and 2011 as well as sampling surveys, seismic surveys, airborne Lidar survey and a photogrammetric survey. The objective of this study is to present the evolution throughout the years of this anthropic source-to-sink system, from the pipes to the bottom of the Lake. The information acquired throughout the years allows following the evolution of the Lake, which is subjected to accumulation of more than 10 x 106 m3 of sediments each year. Furthermore, in order to refine our understanding of the dynamic of this system, physical modeling was also done. Analysis of the subaerial and the subaqueous dataset allows evaluating the effect of disposal strategies on the delta topset and on tailings accumulation. Disposal strategies influence the evolution of the channels on the topset, thus influencing the accumulation of tailings throughout the Lake as well as the shoreline advancement rate. Subaqueous erosional channels are present in the Lake: they influence the depositional pattern of the tailings as well as their granulometric distribution. These erosional channels are created by the upstream migration of knickpoints. In some places, this migration can be described over multiple surveys. The formation of these knickpoints were studied throughout physical modeling and were found to be, most of the time, initiated when there is disequilibrium between the slope angle of the foreset and the equilibrium slope angle dictated by the turbidity current characteristics. This disequilibrium is typically caused by a change in the flow dynamics on the topset, i.e. the transition between sheet flow and channelized flow. Experimental results show that migration of the knickpoints is controlled by two factors: erosion by the turbidity current and a landsliding process in the knickpoint head scarp. Finally, the sequential analysis of the 1999, 2004, 2006, 2008 and 2011 surveys proved to be useful to evaluate the rate of infilling of the Lake, the migration of sediment depocenters along with the mechanism of emplacement and the evolution of various bedforms, including sediment waves.