Conceptual modelling for the Hunter subregion Product 2.3 for the Hunter subregion from the Northern Sydney Basin Bioregional Assessment 2018 A scientific collaboration between the Department of the Environment and Energy, Bureau of Meteorology, CSIRO and Geoscience Australia The Bioregional Assessment Programme The Bioregional Assessment Programme is a transparent and accessible programme of baseline assessments that increase the available science for decision making associated with coal seam gas and large coal mines. A bioregional assessment is a scientific analysis of the ecology, hydrology, geology and hydrogeology of a bioregion with explicit assessment of the potential impacts of coal seam gas and large coal mining development on water resources. This Programme draws on the best available scientific information and knowledge from many sources, including government, industry and regional communities, to produce bioregional assessments that are independent, scientifically robust, and relevant and meaningful at a regional scale. The Programme is funded by the Australian Government Department of the Environment and Energy. The Department of the Environment and Energy, Bureau of Meteorology, CSIRO and Geoscience Australia are collaborating to undertake bioregional assessments. For more information, visit http://www.bioregionalassessments.gov.au. Department of the Environment and Energy The Office of Water Science, within the Australian Government Department of the Environment and Energy, is strengthening the regulation of coal seam gas and large coal mining development by ensuring that future decisions are informed by substantially improved science and independent expert advice about the potential water related impacts of those developments. For more information, visit https://www.environment.gov.au/water/coal-and-coal-seam-gas/office-of-water-science. Bureau of Meteorology The Bureau of Meteorology is Australia’s national weather, climate and water agency. Under the Water Act 2007, the Bureau is responsible for compiling and disseminating Australia's water information. The Bureau is committed to increasing access to water information to support informed decision making about the management of water resources. For more information, visit http://www.bom.gov.au/water/. CSIRO Australia is founding its future on science and innovation. Its national science agency, CSIRO, is a powerhouse of ideas, technologies and skills for building prosperity, growth, health and sustainability. It serves governments, industries, business and communities across the nation. For more information, visit http://www.csiro.au. Geoscience Australia Geoscience Australia is Australia’s national geoscience agency and exists to apply geoscience to Australia’s most important challenges. Geoscience Australia provides geoscientific advice and information to the Australian Government to support current priorities. These include contributing to responsible resource development; cleaner and low emission energy technologies; community safety; and improving marine planning and protection. The outcome of Geoscience Australia’s work is an enhanced potential for the Australian community to obtain economic, social and environmental benefits through the application of first class research and information. For more information, visit http://www.ga.gov.au. ISBN-PDF 978-1-925315-54-7 Citation Dawes WR, Herron NF, Macfarlane C, Rachakonda PK, Henderson BL, Ford JH, Wilkes PG, Marvanek SP and Ramage A (2018) Conceptual modelling for the Hunter subregion. Product 2.3 for the Hunter subregion from the Northern Sydney Basin Bioregional Assessment. Department of the Environment and Energy, Bureau of Meteorology, CSIRO and Geoscience Australia, Australia. http://data.bioregionalassessments.gov.au/product/NSB/HUN/2.3. Authorship is listed in relative order of contribution. 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If you are having difficulties with accessing this document please contact [email protected]. Cover photograph Oblique view west of Muswellbrook showing Bengalla coal storage (left foreground) with irrigated agriculture and riparian vegetation either side of the Hunter River and Mount Arthur coal mine in the distance (right background), NSW, 2014 © Google earth (2015), Sinclair Knight Merz Imagery date 16 December 2008. Position 32°17’58’’ S, 150°48’51’’ E, elevation 136 m, eye altitude 1.59 km v20180302 Executive summary Conceptual models are abstractions or simplifications of reality. During development of conceptual models, the essence of how the key system components operate and interact is distilled. In the bioregional assessments (BA), conceptual models are developed to describe the causal pathways, the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development and potential impacts on water resources and water-dependent assets. Methods This product details the conceptual model of causal pathways for the Hunter subregion, following the methods described in the companion submethodology M05 (as listed in Table 1) for developing a conceptual model of causal pathways. It identifies the: key system components, processes and interactions, which essentially define pathways over and through which water can move (Section 2.3.2) ecosystems in the Hunter subregion in terms of landscape classes and their dependence on water (Section 2.3.3) baseline and coal resource development pathway (CRDP) (Section 2.3.4) causal pathways from coal resource developments using an Impact Modes and Effects Analysis (IMEA) hazard analysis approach (Section 2.3.5). Summary of key system components, processes and interactions The Hunter subregion is a little over 17,000 km2, and contains portions of the Western, Hunter and Newcastle coalfields. The subregion is not considered to have any groundwater connections with areas to the north-east due to the geological basin divides that define its boundary, although the Hunter river basin extends north-east of the subregion boundary. Surface water catchments define the subregion boundary to the south and west of the subregion, but regional-scale groundwater connections with the Sydney Basin and Northern Inland Catchments bioregions may exist where suitable gradients and conductive aquifers exist. Although cross-boundary flows are not expected to be significant to the water balance of the Hunter subregion, suitable margins and boundary conditions are required in numerical modelling to minimise possible edge effects. Regional groundwater systems extend east of the coastline, which defines the eastern boundary. The surface water catchment of the Hunter subregion contains rivers that flow into the Hunter river basin and Macquarie-Tuggerah lakes basin. Salinity of the Hunter River has been a significant issue; however, since the introduction of the Hunter River Salinity Trading Scheme (HRSTS), this has improved considerably. The Hunter River lies within an extensive alluvial aquifer, which has exchanges with the river as both a source and sink, and with the underlying fractured rocks where permeable pathways exist. Under HRSTS rules, industries may release saline water to the river under high-flow conditions as long as this does not elevate river salinity above target levels. The use of dam releases and the HRSTS have tended to reduce some of the variability in river flow and stage in the regulated reaches of the river. Conceptual modelling for the Hunter subregion | i Ecosystems The landscape classification describes the main ecological and human systems (including agricultural production systems, industrial and urban uses), and provides a high-level conceptualisation of the subregion at the surface. Most assets are related to one or more landscape classes, which are defined for BA purposes as ecosystems with characteristics that are expected to respond similarly to changes in the groundwater and/or surface water due to coal resource development. The Assessment team refined the landscape classification and high-level conceptualisation of the subregion following discussions at the ‘Conceptual modelling of causal pathways’ workshop held in August 2015. The landscape classes were grouped into five broad landscape groups, defined to reflect different connections to surface water and groundwater systems: ‘Riverine’ ‘GDE’ ‘Estuaries and coastal lakes’ ‘Non-GDE vegetation’ ‘Economic land use’. These landscape groups are expressed as a percentage of the preliminary assessment extent (PAE) area, which in the Hunter subregion coincides with the subregion boundary. Of the approximately 17,000 km2 of the Hunter PAE,