Post-mining landform evolution modelling: 2. Effects of vegetation and surface ripping

Computer simulations of the topographic evolution of the proposed post-mini ng rehabilitated landform for the ERA Ranger Mine, showed that for the unve getated and unripped case, the landform at 1000 years would be dissected by localized erosion valleys (maximum depth = 7.6 m) with fans (maximum depth = 14.8 m) at the outlet of the valleys. Valley form simulated by SIBERIA h as been recognized in nature. This indicates that SIBERIA models natural pr ocesses efficiently. For the vegetated and ripped case, reduced valley development (maximum 1000 year depth = 2.4m) and deposition (maximum 1000 year depth = 4.8m) occurre d in similar locations as for the unvegetated and unripped case (i.e. on st eep batter slopes and in the central depression areas of the landform). For the vegetated and ripped condition, simulated maximum valley depth in the capping over the tailings containment structure was c. 2.2 m. By modelling valley incision, decisions can be made on the depth of tailings cover requi red to prevent tailings from being exposed to the environment within a cert ain time frame. A reduction in thickness of 1 m of capping material over ta ilings equates to c. 1 000 000 Mm over a 1 km(2) tailings dam area. This re presents a saving of c, $1 500 000 in earthworks alone. Incorporation of SI BERIA simulations in the design process may result in cost reduction while improving confidence in environmental protection mechanisms. Copyright 2000 (C) Environmental Research Institute of the Supervising Scientist, Commonw ealth of Australia.