Closure planning challenges associated with mining adjacent to large creek lines

Abstract

This paper presents a case study of closure surface water management for mined pits located adjacent to two large creeks in the Pilbara region of Western Australia. The mining footprint presented some significant closure challenges, with pits, waste dumps and land bridges located adjacent to creeks. Hydrological flood modelling of rare and extreme floods affecting both pre-mining and proposed end-of-mining topography was used to guide landform design. A risk-based design approach was adopted based on the likelihood and consequence of closure landform failure. For relatively minor failure consequences (e.g. scour of the toe of a rehabilitated waste dump) more frequent events were used as the design event. Rarer events were used to design controls aimed at avoiding major consequences, such as creek capture, where a natural watercourse scours a path into a mine void effectively terminating downstream flow. These designs informed a closure strategy involving partial pit backfill and scour management controls on landforms, which has been developed to leave a suitable post-mining landform.