5 Outcome synthesis for the Clarence-Moreton bioregion

Executive summary

​Rainforest waterfall in Border Ranges National Park, NSW, 2008 Credit: Liese Coulter, CSIRO

About the bioregion

This synthesis presents the key findings from the bioregional assessment of the Clarence-Moreton bioregion.

The Clarence-Moreton bioregion covers 24,292 square kilometres (km2), including the towns of Casino, Lismore and Grafton in northern NSW, and Gatton in south-east Queensland (Figure 1). Land is predominantly used for dryland farming and plantations, and as grazing land for livestock. The bioregion contains large river systems, national parks and forest reserves, and nationally significant wetlands.

The bioregion has one operating coal mine, Jeebropilly Mine, in the Bremer river basin near Ipswich in Queensland. Exploration and pilot production testing for coal seam gas (CSG) resources have mainly occurred near Casino in northern NSW.

Potential hydrological changes

This assessment considered potential cumulative impacts of the existing Jeebropilly Mine and the proposed West Casino Gas Project in the Richmond river basin near Casino. The West Casino Gas Project had been proposed at the start of the Bioregional Assessment Programme; however, licences for the West Casino Gas Project were acquired and then cancelled by the NSW Government in December 2015. The potential for commercial production of CSG resources is very limited in the Queensland portion of the bioregion within the foreseeable future, and no other coal mining development was identified in the bioregion.

The assessment investigated potential hydrological changes in groundwater and surface water due to coal resource development for two futures (Box 2). The baseline future includes the Jeebropilly Mine. The coal resource development pathway (CRDP) future includes the baseline coal resource development and one additional coal resource development, the West Casino Gas Project. Analysis of a three-dimensional geological model indicated that the West Casino Gas Project is hydrologically disconnected from the Jeebropilly Mine by a geological basement ridge that forms a natural barrier separating the groundwater and surface water systems in the Richmond river basin from those of the Bremer river basin. There is no hydrological influence from the baseline Jeebropilly Mine on the West Casino Gas Project, and hence no potential for cumulative impacts. Because of this, and because the assessment focused on potential impacts due to additional coal resource development (Box 2), only the West Casino Gas Project was modelled. Hydrological modelling predicted that potential changes to surface water and shallow groundwater due to the proposed West Casino Gas Project are minimal.

The surface exposures of the Lamington and Main Range volcanics are the bioregion’s major areas of groundwater recharge. Recharge from the volcanics to the near-surface aquifers would dwarf any potential drawdown (Box 4) due to additional coal resource development, thus minimising potential impacts.

The assessment found that the zone of potential hydrological change (Box 3) covers an area of 249 square kilometres (km2) and extends no more than 10 km west of the West Casino Gas Project (Figure 5). Outside this zone, hydrological changes (and hence impacts) are very unlikely (less than 5% chance). Within this zone, the maximum chance of exceeding the 0.2 metre (m) drawdown threshold due to additional coal resource development is estimated at 36% (Box 5). It is very likely (95% chance) that the drawdown is less than 1 m anywhere in the near-surface aquifer.

In the Richmond river basin, impacts on annual streamflow due to additional coal resource development are very likely to be minimal for all but the very lowest streamflows.

Multiple regionally extensive aquitards (which share boundaries) directly overlie the Walloon Coal Measures (the main coal-bearing resource in the bioregion) in the area of the West Casino Gas Project. The very low permeability of these aquitards, and their combined thickness of over several hundred metres, impedes almost all of the hydrological effects of coal seam depressurisation from reaching the surface.

Impact and risk analysis was not undertaken in this assessment because the projected hydrological changes from the West Casino Gas Project at the surface are very small.

Last updated:
12 July 2017