3.1 Overview


The Bioregional Assessment Programme provides transparent scientific information to better understand the potential impacts of coal seam gas (CSG) and coal mining developments on water resources and water-dependent assets such as wetlands and groundwater bores. A bioregional assessment (BA) is a regional-scale analysis of the ecology, hydrology, geology and hydrogeology of a bioregion to quantify the likelihood and scale of potential impacts and risks on water resources and water dependent assets, improving the available information for future regulatory approvals and government decision making at both national and state levels.

The Namoi subregion, situated in the Murray-Darling Basin, covers approximately 29,300 km2 and is home to approximately 27,000 people with the main centres Gunnedah and Narrabri located along the Namoi River. Agriculture is a major land use, covering 70% of the subregion, and irrigation is a significant part of the agricultural production in the subregion. The Namoi alluvium, located in the Liverpool Plains, supports a highly valuable agricultural development, which includes cropping of cotton and grains, with the less arable soils being under livestock grazing.

The Liverpool Plains also contain endangered native grasslands. Its riparian vegetation is dominated by river she-oaks and willows, and river red gum communities are found along the major streams. The Pilliga contains the largest remaining area of dry sclerophyll forest west of the Great Dividing Range in NSW and the Pilliga Nature Reserve in the upper catchment of Bohena Creek is the largest reserve in the region. A wide range of aquatic habitats, including large areas of anabranch and billabong wetlands downstream of Narrabri, add to the ecological significance of the Namoi subregion.

There are five currently operating coal mines and 10 additional coal mine developments are planned. The potential water-mediated impacts and risks to the environment associated with these future coal resource development are of concern for this Assessment, which considers two potential futures: the baseline and the coal resource development pathway (CRDP). Baseline drawdown is the maximum difference in drawdown (dmax) under the baseline relative to no coal resource development. Additional drawdown is the maximum difference in drawdown (dmax) between the CRDP and baseline, due to additional coal resource development. The interaction of groundwater drawdown and surface water changes identifies the areas with hydrological changes for assessments of impact and risk to assets. This is the zone of potential hydrological change.

BAs focus solely on water-mediated impacts related to water quantity, groundwater level or water resource availability. The design of a BA is specifically aimed to analyse the cumulative impacts of coal resource developments. The modelled baseline and CRDP may each consider a suite of developments, the potential impacts of which may overlap to varying degrees in both time and space.

The BA defines a set of landscape classes as ecosystems to deal with the complex landscapes that encompass a wide range of ecological systems and their interaction with human activities. Because of this complexity, a direct analysis of each and every point, or water-dependent asset, in the landscape across the subregion is not currently possible. Abstraction and a systems-level classification can manage the challenges of the dimensionality of the task. The assessment of impacts on and risks to water-dependent ecological assets relies heavily on the landscape classification.

The risk analysis approach used in BAs differs from the traditional deterministic hydrological modelling. The quantitative representation of the predictive uncertainty through probability distributions allows the consideration of the likelihood of impacts or effects of a specified magnitude and underpins the impact and risk analysis.

A BA identifies areas of the subregion that additional coal resource development is unlikely to impact. Potential impacts are ruled out where possible, both spatially and in terms of specific groundwater or surface water effects, so as to identify where potential impacts have a higher probability of occurring.

Last updated:
6 December 2018
Thumbnail of the Namoi subregion

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