Subsidence monitoring in the Sydney Basin, New South Wales: Results of the Camden Environmental Monitoring Project

This Geoscience Australia Record documents the scientific analysis undertaken, and results obtained from geodetic monitoring during the Camden Environmental Monitoring Project (CEMP); a collaborative project undertaken with the New South Wales Department of Planning, Industry and Environment. The aim of the CEMP was to determine the environmental impacts, if any, of active coal seam gas extraction projects in New South Wales. Geodetic monitoring, using satellite radar interferometry (InSAR) and Global Positioning System (GPS) measurements, was used to specifically assess if subsidence (downward vertical land movement) is occurring at the Camden Gas Project; at the time the State’s only actively producing coal seam gas project. To address this question, Geoscience Australia undertook a comprehensive InSAR analysis using data sets from three orbiting radar satellites (ALOS, Envisat and Radarsat-2) covering two periods of time (2006 to 2010, and 2015 to 2019). The outputs of this InSAR analysis are vertical and horizontal ground surface displacement and velocity map products, together with a quantification of the uncertainty of these measurements. Furthermore, a new network of 20 ground geodetic monitoring sites was established in May and June 2016 for the purpose of validating measurements made using InSAR. GPS data was collected at these monitoring sites between July 2016 and June 2019 and processed to obtain 3-dimensional ground surface displacement and velocity measurements. From the analysis of independent InSAR and GPS data sets undertaken during the CEMP, we conclude that no measurable subsidence (i.e. a land movement velocity not greater than 10 mm/yr) has occurred as a result of coal seam gas production in the Camden Gas Project during the time periods of monitoring. However, decimetre-scale horizontal and vertical surface movements have occurred in the Southern Coalfields at the locations of subsurface longwall coal mines. Comparison of the measurements made by InSAR and GPS across the 20-site geodetic monitoring network shows that the two independent geodetic techniques agree within 10 millimetres, even when decimetre-scale movement is occurring. This demonstrates the potential for utilising InSAR for accurate remote monitoring of ground surface movements (including subsidence) at large scales and in the absence of sufficient ground geodetic monitoring infrastructure. The conclusions drawn and the measurements made in this work are specific to the area covered by the CEMP geodetic monitoring project, and are therefore not applicable to other resource extraction activities in other areas because of operational and geological differences from site to site. However, the methods described herein would be applicable to monitoring other resource extraction activities.