Abstract
Water is the key driver of tailings storage facility (TSF) failures, both in operations and closure. In closure, water management changes fundamentally: active decant systems are decommissioned, routine inspections reduce, and operational or emergency interventions can no longer be relied upon to the same degree.
This does not imply an absence of controls in closure. Rather, reliance shifts from active to passive controls. Closed TSFs become permanent landforms that must safely and passively manage water, in the face of deep climatic and geomorphic uncertainty.
This paper explores closure water management strategies for TSFs and asks: to spill or not to spill?
Closure configurations are framed in terms of three idealised types:
- Non‑discharge systems that retain all inflows within the basin;
- Direct‑shed systems that minimise storage and routinely discharge runoff via spillways; and
- Store‑then‑spill hybrids that provide substantial storage but incorporate a controlled overflow pathway.
The paper discusses the strengths, limitations and key design considerations of each type, emphasising the importance of critical storm duration, long‑term evolution of storage capacity, and the sensitivity of non‑discharge concepts to long‑duration, multi‑day events.
Anchored in the ‘hierarchy of closure needs’, physical stability is treated as a non‑negotiable constraint that must be satisfied before prioritising chemical, ecological or socio‑economic outcomes. The paper outlines guiding principles for risk‑based option assessment, advocating for robust and redundant designs for a range of futures.
Two hypothetical case studies illustrate how these principles can be applied: a paddock TSF where a predominantly non‑discharge concept is strengthened by adding an emergency overflow; and a lined TSF with reactive tailings where long‑term ponding is unacceptable, necessitating a direct‑shed landform and engineered cover.
Drawing on these examples, the paper argues that, for most closed TSFs, an emergency spillway or controlled overflow pathway should be regarded as a minimum closure feature to strengthen long‑term safety and resilience.
