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Full report

• SSR134 - Effect of vegetation and surface amelioration on simulated landform evolution of the post-mining landscape at ERA Ranger Mine, Northern Territory (PDF - 5,680 KB)

Separate sections

• Preliminary pages and Chapter 1 (PDF - 658 KB)
• Chapters 2 – 4 (PDF - 1,638 KB)
• Chapters 5 – 6 (PDF - 3350KB)
• Appendices and References (PDF - 416 KB)

Executive summary

The effect of vegetation and surface ripping on evolution of the ERA Ranger Mine (ERARM) post-mining landform was assessed using the SIBERIA landform evolution model.

Data were collected from four sites on the waste rock dump at ERARM-(1) the cap site which was unvegetated and unripped with a surface slope of 0.028 m/m; (2) the batter site, surface slope 0.207 m/m, also unvegetated and unripped but with a covering of coarse rock material; (3) the soil site, surface slope 0.012 m/m, which had ≈ 90% vegetation cover of low shrubs and grasses and had been topsoiled and surface ripped; and (4) the fire site, surface slope 0.023 m/m, which was topsoiled and ripped and is presently vegetated with well established trees, grasses and shrubs.

Natural rainfall events were monitored on the four sites to collect rainfall, runoff and soil loss data to parameterise the SIBERIA sediment discharge equation. The SIBERIA sediment discharge equation was calibrated using output from a sediment transport model of the form T=βSⁿ¹∫Q^m1dt, and the DISTFW rainfall-runoff model. Low frequency high intensity events resulted in the greatest soil loss. Therefore, it is important that sediment loss during high intensity events is predicted accurately. Storms with a range of intensities were selected to derive the sediment transport model. DISTFW hydrology model parameters were derived by fitting four monitored events simultaneously.

SIBERIA simulations of post-mining rehabilitated landform evolution showed that for the unvegetated and unripped surface, the landform at 1000 y would be dissected by localised erosion valleys (maximum depth = 7.6 m) with deposited fans (maximum depth = 14.8 m) at the outlet of the valleys. Simulated valley form has been recognised in nature which indicates that SIBERIA models natural processes efficiently. For the vegetated and ripped condition reduced valley development (maximum 1000 y depth = 2.4 m) and deposition (maximum 1000 y depth = 4.8 m) occurred in similar locations as for the unvegetated and unripped case (ie on steep 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 about 2.2 m. By modelling valley incision, decisions can be made on the minimum depth of tailings cover required to prevent tailings from being exposed to the environment within a certain time frame. A reduction in thickness of 1 m of capping material over tailings equates to about 1 000 000 Mm³/km² tailings dam area. This represents a saving of about $1 500 000/km² in earthworks. Incorporation of SIBERIA simulations in the design process may result in cost reduction while improving confidence in environmental protection mechanisms.