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Hydrology: changes in dynamics and aquifer interconnectivity

Coal seam gas extraction may increase the risk of interconnectivity between groundwater aquifers with potential consequences for fresh water aquifers both in terms of quantity and quality. Changing interconnectivity between aquifers can also have implications for surface water resources. Large coal mines, on the other hand, may disrupt surface flow through river diversions and flood protection works, and dewatering of the mine can also disrupt groundwater flow patterns.

Consideration will also be given to how these issues contribute to the overall cumulative impacts of coal seam gas extraction and coal mining, according to different scales (local-regional) and timeframes (tens to thousands of years).

Projects commissioned to date include:

Project title Project description
Background review -
bore integrity
The review captures the state of knowledge on bore integrity issues as they relate to coal seam gas extraction in Australia. The review examines issues associated with bore construction, integrity, monitoring and reporting, decommissioning, and legacy issues. The focus of the review is the Australian coal seam gas context, but a summary and synthesis of case histories from overseas and within other industry sectors is provided.
Background review -
subsidence from coal mining activities
The review captures what is currently known about predicting, monitoring, assessing and remediating subsidence and other movement-related impacts associated with coal mining activities, including:
Background review -
subsidence from coal seam gas extraction in Australia
The review captures the state of knowledge on the water-related impacts of subsidence and other ground-related movements as a result of coal seam gas extraction, including:
Background review -
aquifer connectivity within the Great Artesian Basin, and the Surat, Bowen and Galilee Basins
The review captures the state of knowledge on aquifer connectivity, particularly within the Great Artesian Basin (GAB), and the Surat, Bowen and Galilee (geological) Basins, including:
  • types of connectivity, its implications and measurement
  • groundwater flow models, which may both rely on an understanding of aquifer connectivity, and predict the extent of connectivity between aquifers and actions that can alter connectivity
  • connectivity within the GAB, a large and high-priority groundwater resource, and within the Surat, Bowen and Galilee geological Basins, which are linked to the GAB and are highly prospective areas for coal seam gas development and/or coal mining.
  • Background review: Aquifer connectivity within the Great Artesian Basin, and the Surat, Bowen and Galilee Basins
Monitoring and management of subsidence induced by longwall coal mining This project aims to improve understanding of the critical issue of subsidence induced by longwall coal mining, and its consequent effects on water systems and on land use.
Monitoring and management of subsidence induced by coal seam gas extraction This report examines the monitoring and mitigation of subsidence induced by coal seam gas (CSG) extraction. It provides a synthesis of experiences relating to CSG subsidence in Australia and overseas, the assessment approaches being used to predict the scale and extent of subsidence, and monitoring and management options for subsidence induced by CSG extraction. A review of publicly available literature identified no reference to adverse impacts of subsidence due to CSG production. The review process also found that:
  • predictive subsidence modelling provides estimates of both compaction of hydrogeological units due to changes in groundwater pressure and compaction of the coal seam due to degassing
  • model predictions can be used to inform subsidence monitoring schemes and the management or mitigation of potential impacts on assets
  • the collation of subsidence monitoring data across Australian coal seam gas developments would be useful to review critical conditions and improve subsidence prediction models.
It is recommended that subsidence monitoring be undertaken in areas of CSG development, noting that:
Coal seam gas extraction: modelling groundwater impacts Groundwater models are important at a range of scales to predict the hydrological impacts of coal seam gas (CSG) and coal development. This report describes typical Australian CSG environments and the process involved in CSG extraction. While also identifying issues to consider when undertaking groundwater modelling and outlining a range of modelling tools and approaches used to simulate associated groundwater impacts, this report also discusses:
  • the effectiveness of groundwater models to represent hydrogeological conditions at specific scales
  • different approaches to modelling ranging from simple analytical models to more complex numeric regional groundwater models
  • the functionality and optimal spatial resolution of numeric groundwater models.
Areas for future research have also been identified to address priority knowledge gaps and improve model performance.
Regional hydrogeological characterisation studies in four coal basins in Queensland, South Australia and Victoria Multidisciplinary characterisation of the detailed geology and hydrostratigraphy of the Laura, Maryborough, Otway and St Vincent Basins.