Evaluation of Land Subsidence and Underground Water Storage Variation Caused by Coal Seam Gas Industry Activities in Western Downs, Queensland, Australia

Evaluation of Land Subsidence and Underground Water Storage Variation Caused by Coal Seam Gas Industry Activities in Western Downs, Queensland, Australia

We use three permanent GPS stations and ~300 groundwater bores to study the impacts of coal seam gas industry activities on both landscape and aquifer storage variation over an area of ~5000 km2 located in the east of Western Downs, Queensland, Australia. GPS observations of vertical land displacement from 2014 to 2020 suggest a constant subsidence of ~1-2 cm/yr across the area, and all of the bores draining into the lower levels for the same period of time. Comparison of the corresponding groundwater storage variation before and after the subsidence (2008–2014 vs 2014–2020) shows ~0.6 GL decrease in the volume of underground water (0.4 vs -0.2 GL) over the region. Although the cumulative precipitation showed a difference of 15% before and after the subsidence, suggesting a slightly wetter time before the subsidence, this factor accounts for only ~20ML of storage variation, based on the maximum recharge rate reported for the area. Following La Nina in 2020, two distinct behaviours can be seen: both GPS and groundwater bores continued to show a decreasing trend in the western region, where most mining wells are located in agricultural areas. However, the eastern side of the region (relatively distant from the mining wells) exhibited a relative recovery after 2020. This suggests that in addition to land subsidence over the region, existing agricultural areas are being affected by the coal seam gas industry in terms of both groundwater resources and water quality. This study provides critical information relating to the interactions between mining, agriculture and the landscape which can contribute to the bank of information and evidence needed to evaluate impacts and inform decision-making to ensure a sustainable future for the Western Downs region.

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