A 1-D Hydraulic-Sediment Model to Simulate the Movement of Mine Tailings in Sand Bed Rivers

Abstract:

River pollution caused by mine tailings dumping has increased particularly in Latin America and Asia over the past 20 years. One of the best-known cases is the Ok-Tedi-Fly river system (Papua New Guinea), that have continuously received tailings and rock material from the Ok Tedi copper mine from 1984 to 2013. More recently, two major dam breach took place in the state of Minas Gerais in Brazil, leading to countless social and environmental impacts. These accidents have reached main streams spreading this harmful material downstream not only affecting different water uses but also changing the natural sediment regime in the associated drainage network. Despite some modeling efforts that have been performed to predict the movement of mine tailings in natural streams, further research is required to better understand the interactions of this external material with the natural river sediment. Generally, mine tailings are finer and heavier than sand river material and depending on the content of fines (clay and silt) they might behave as a cohesive material. Therefore, conventional sediment transport formulae must be modified or reformulated to account for such characteristics and to predict the movement of sand-tailings mixture in a river environment. Here we proposed a generic 1-D hydraulic-sediment model to simulate the movement of mine tailings in a hypothetical scenario in which a pile of high-density mine tailings is dumped in the upstream-end of a river. A modification of the active layer concept is proposed along with the simulation of mixtures differing in size distribution and density that vary over time and space, in order to capture the following processes: downstream fining, downstream lightening (lighter particles moves further downstream) and vertical upward heavying (preference of denser particles to deposit close to the water-bed interface).