Assessing the hydrological impacts of coal resource development: a case study from Australia

The objective of this study is to predict regional-scale cumulative impacts on water resources caused by coal resource developments in the Gloucester subregion of New South Wales (NSW), Australia. A key outcome of the assessment is identifying areas where water resources are very unlikely to be impacted (with a less than 5% chance) from those where water resources are potentially impacted (at least a 5% chance). Governments, industry and the community can then focus on areas that are potentially impacted when making regulatory, water management and planning decisions. Potential impacts were ruled out using a zone of potential hydrological change. This zone was defined based on at least a 5% chance of exceeding defined thresholds in multiple hydrological response variables including groundwater drawdown and eight streamflow metrics (only reductions in annual streamflow are reported here). The zone of potential hydrological change in the Gloucester subregion covers 250 km(2) and includes 242 km-of-stream network. This represents 52% of the area and 70% of the stream length assessed. Groundwater drawdown exceeding 0.2 m in the near surface aquifer due to additiohal coal resource development is very likely (>95% chance) for an area of 20 km(2) but is very unlikely (<5% chance) to exceed an area of 100 km(2). Although 242 km of streams are identified as being potentially impacted, changes in streamflow are small, with a little over 5% reduction in annual flow in some streams close to the coal mines, and reductions in annual flow in the major rivers not exceeding 1 - 5%.