Publications

3 Environmental research and monitoring (continued)

3.4 Assess Ranger rehabilitated landform geomorphic stability using landform evolution modelling and GIS technology

The SIBERIA landform evolution model and ArcView GIS software packages have been integrated through a software interface known as ArcEvolve,⁸ and used to predict the geomorphic stability of a draft rehabilitated landform at the Ranger mine. SIBERIA uses a series of hydrology and erosion parameters to model long-term changes in elevation with time from the average effect of mass transport processes, such as tectonic uplift, fluvial erosion, creep, rain splash and landsliding. The input parameters are applied to a series of ‘regions’ that represent different surface conditions over the landform being modelled. For the purposes of evaluation, surface conditions representing best and worst case scenarios were modelled.

Using the methodology described in Lowry et al (2004),⁹ the draft landform was modelled for a period of 1000 years, with hydrology parameters held constant for the entire landform,and erosion parameters varied for each region of the landform representing different surface treatments. Through the GIS interface, it was possible to identify areas of potential erosion/deposition by subtracting the 1000-year modelled surface from the current surface (Figure 3.8).

Simulated surface denudation rates (Table 3.2) were calculated using ArcEvolve, and found to compare favourably with regional denudation rates of 0.04 mm/y for natural undisturbed surfaces.¹⁰

Through the use of the ArcEvolve interface, it was possible to identify areas of the landform that needed to be redesigned to minimise erosion.

As shown in Figure 3.8, a gully with a maximum depth of up to 14 m was predicted to form on the left side of Pit 3 over a period of 1000 years, with the size and extent of the gully varying for the different scenarios. Whilst recognising limitations with the modelling process, such as the inability to incorporate the different hydrology characteristics associated with different surface conditions on the landform within the model, the current process is able to perform distributed erosion modelling. This has enabled ‘best case’ and ‘worst case’ scenarios to be modelled with confidence within a range of erosion and deposition parameters.

Figure 3.8 Areas of potential erosion / deposition on v3 landform after 1000 years using parameters for (a) ‘worst case’ scenario; (b) ‘best case’ scenario

Footnotes

⁸ Boggs GS 2003. GIS application to the assessment and management of mining impact. Unpublished PhD thesis, Charles Darwin University, Darwin.

⁹Lowry JBC, Moliere DR, Boggs GS & Evans KG 2004. Application of landform evolution modelling to the Nabarlek minesite. Internal Report 480, July, Supervising Scientist, Darwin. Unpublished paper.

¹⁰ Cull RF, Hancock G, Johnston A, Martin P, Martin R, Murray AS, Pfitzner J, Warner RF & Wasson RJ 1992. Past, present and future sedimentation on the Magela Plain and its catchment. In Modern sedimentation and late Quaternary evolution of the Magela plain, ed RJ Wasson, Research Report 6, Supervising Scientist for the Alligator Rivers Region, AGPS, Canberra, 226–268.