Towards the development of a baseline for surface movement in the Surat Cumulative Management Area

Abstract

Ground surface movement can result from several natural and anthropogenic processes. Understanding the mechanisms that drive ground surface movement and their contribution to the net movement is crucial in assessing the impact of resource development projects and other human activities. Consequently, there is an interest in understanding ground surface movement in the Surat Cumulative Management Area (CMA), Queensland, and how it is influenced by coal seam gas (CSG) production, if at all. This paper presents the analysis of a large InSAR (interferometric synthetic aperture radar) dataset covering the CMA regions featuring no active CSG wells. These non-production areas were specifically examined in order to develop an understanding of background surface movement and its contributing processes. Of the regional dataset, four focus areas showing measurable changes over time were selected for more detailed investigation. All the focus areas exhibited an overall downward surface movement (subsidence), with three showing cycles of subsidence and uplift that appeared to be very well correlated with rainfall events. The soil types in these three areas were consistent with the hypothesis that the observed surface movement is due to rainfall infiltration-induced consolidation of the shallow soil layers and subsequent moisture-induced shrinkage and swelling. The fourth focus area, however, did not exhibit a strong seasonal fluctuation, and unravelling the mechanisms driving surface movement in this area was more difficult. This investigation resulted in a foundation for further research into the complex problem of surface movement, and in particular, deconvolution of the various contributions that occur at different depths, lengths, and time scales.