Life-of-Mine Spillway Strategy: Managing Surface Water Risks at a Tailings Storage Facility
December 14, 2020
Water management at a tailings storage facility (TSF) presents one of the major risks to the safe performance of the facility. International and domestic dam safety guidelines assess a dam’s hazard category based on the consequences of a dam failure and the subsequent downstream damage to the environment and communities. The highest risk event related to water management at a TSF is overtopping of the embankment. This will almost inevitably lead to catastrophic failure of the structure with major downstream consequences from the release of water and tailings. Managing the risk of overtopping is a balance between providing enough outlet discharge and freeboard capacity against the probability of extreme storm events.
There are critical differences between the design and operation of a water dam and a tailings dam that must be considered when developing a spillway strategy for the management of surface water risks over the life-of-mine (LOM). The mine production rates and geometry of the dam determine the rate of rise of a tailings dam and the site topography controls where suitable spillway locations are. As opposed to a water dam where the spillway can be constructed in its ultimate location, emergency and operational spillways for tailings dams must be raised or relocated constantly as the height of tailings increases.The assessment and preliminary design of required spillways through the life of the facility should be undertaken inthe prefeasibility design stage of the mine to ensure that there are suitable locations available for spillways at all stages.
On closure, the spillway is the critical infrastructure for water management. The closure concept plan must allow for the construction of a closure spillway at any stage of the TSF life, including abrupt early closure. Early closure presents a challenge to mine owners who have a responsibility to ensure that the TSF does not present an unacceptable risk to the environment and communities post-closure.
During the design stage of the project, a LOM spillway strategy needs to be developed. This should take into account the level of risk (consequence category) of the tailings dam as the dam height progresses, available spillway locations, environmental impact from construction, cost implications, the tailings deposition plan and hydraulic and hydrological performance. This paper discusses the issues surrounding water management at a tailings dam and presents a framework for developing a LOM spillway strategy to manage the risks associated with water management.
Ind, M.J., M. Rynhoud and K. Brand. 2018. “Life-of-Mine Spillway Strategy: Managing Surface Water Risks at a Tailings Storage Facility,” in From Start to Finish: A Life of Mine Perspective — Victoria, Australia: Australasian Institute of Mining and Metallurgy (AusIMM).