The Ranger mine

The Ranger mine, in the wet-dry tropics of the Northern Territory, Australia, lies between Magela Creek and Gulungul Creek. Rehabilitation needs to ensure that waste rock landforms are in equilibrium with the surrounding catchment, that excessive erosion will not occur and excessive fine suspended sediment (FSS) will not be exported to these creeks during rainfall runoff events. Landscape Evolution Modelling (LEM) simulates how a landscape may evolve over extended periods of time. The CAESER-Lisflood LEM is assessing how the final landform would evolve over 1000 years. The challenge is how to assess whether a landform has reached equilibrium with the surrounding catchment and thus can be considered rehabilitated with respect to landform stability.

The aim of this project is to validate a new approach using an event-based stream flow FSS discharge relationship with a LEM to determine when erosion of a rehabilitated landform is at equilibrium with the surrounding catchment. An event based FSS/stream discharge relationship has been developed that is responsive to catchment disturbance. This project will update the FSS/discharge relationship for Magela and Gulungul Creeks. The CAESER-Lisflood model will be calibrated and validated using catchment data. Actual FSS values will be compared with those obtained from the model to determine when and why the system moves in and out of equilibrium over 1000 years. Variation in event FSS loads beyond trigger limits indicates landform instability. This study will show how a mined landform can move in and out of equilibrium until it reaches a steady state with the surrounding environment.