Analyses of the groundwater accounts were restricted to the area for which a groundwater model will be constructed. The model domain extent and its boundaries were defined based on the following criteria:
- The model’s outermost boundaries were determined based on previous modelling studies in the Clarence-Moreton Basin and Surat Basin and common modelling practice. They were placed to encompass the potential impact zone from previous studies and to be far enough from the coal seam gas development area, such that they do not interfere with the modelling results, that is, it eliminates boundary effects. The distance between the likely development centre and the model boundaries varies from approximately 30 to 70 km.
- Model boundaries should follow existing geological and/or hydrological boundaries.
- Important receptors within and/or close to the development area should be within the areal extents of the groundwater model.
The groundwater model covers a large part of the Richmond river basin, but extends beyond its western border (Figure 5). Hereinafter, the areal extent of the groundwater model is referred to as the model domain.
There are 3934 bores from the National Groundwater Information System (NGIS) (Bureau of Meteorology, ) located within the model domain, 3096 of which have construction information that is required to assign bores to aquifers. Among the bores with screen and/or depth information, 145 bores are recorded as being inactive bores, that is, they are labelled as NON (non-functional), RMV (removed), DCM (decommissioned), PRP (proposed ), RPL (replaced), or ABN (abandoned) for status (Bureau of Meteorology, ). Note that bores in this analysis with unknown status are considered as being active to guarantee that the groundwater model does not under-estimate the likely impacts. There are 2698 of the 2951 active bores that have enough information to be assigned to an aquifer. Furthermore, 187 monitoring bores and 6 exploration bores were excluded from this analysis due to their limited groundwater usage. For the purposes of this report, the total number of bores that were analysed was 2505.
Actual measured groundwater usage data are not available for bores within the model domain; hence, they were estimated using the allocation data in the NSW state groundwater database (Bioregional Assessment Programme, ). It is assumed that 100% of the allocation will be used. Not all bores require a licence to extract water, for example, stock bores under the basic water right. When an allocation entry is missing for a bore, the median value of the bores with allocations within the same purpose group was adopted. For example, 827 domestic bores are not tied with allocations in the model domain, while 429 domestic bores have allocations. The median allocation of the 429 bores was assigned to the other 827 domestic bores as assumed current water usage. Using this interpolation method, the resulting estimates for water usage are shown in Figure 5, which demonstrate that 88.1% of the bores have allocations of less than or equal to 5 ML/year.
Table 7 and Figure 6 show the estimated water usage categorised by purposes. The NGIS and NSW state groundwater database both have a purpose record for most bores of interest; however, the records in the two databases are not always consistent. The NGIS was used as the primary reference for definition purposes. When an assignment was deemed to be unreasonable on a judgment basis, the definition in the NSW state groundwater database was adopted. The definitions of the purpose codes of the NGIS are described in Table 8. Almost half of the water (49.5%) is consumed by irrigation and 42% of the estimated water usage is attributed to domestic and stock bores. The total volume of groundwater consumed by other users is significantly less that that extracted for irrigation and stock/domestic use.
Table 7 Estimated groundwater usage categorised by purpose in the model domain of the groundwater model for the Clarence‑Moreton bioregion
aRefer to Table 8 for the code definition
Table 8 Bore purpose code definition in the National Groundwater Information System (NGIS) for the Clarence‑Moreton bioregion
The estimated water usage by aquifers is described in Table 9 and Figure 7. The Richmond River alluvium and Lamington Volcanics represent the two main groundwater supply aquifers in the model domain with 3474 ML/year and 6501.5 ML/year allocated to 672 and 1325 bores screened in those two aquifers, respectively. Bores screened in the Grafton Formation and the Walloon Coal Measures are allowed to pump 964 ML/year and 514 ML/year, respectively. The sum of the estimated water usage for the other five hydrogeological units represents only 165 ML/year. Although 1833 of the 2505 bores are screened in the bedrock aquifers, most of them were drilled in the unconfined part of the bedrock aquifers (i.e. non alluvial).
Table 9 Estimated groundwater usage categorised by hydrogeological units in the model domain of the groundwater model for the Clarence‑Moreton bioregion
Figure 5 Estimate of groundwater usage per bore within the model domain of the groundwater model for the Clarence-Moreton bioregion. The estimation was based on available allocation data with an assumption that 100% of the allocation will be used
In NSW, water sharing plans (WSPs) are developed to preserve surface water and groundwater by balancing the competing demands by different types of water users. They are defined based on surface river basins and groundwater systems. The model domain is covered mainly by the WSP for the Richmond River Area Unregulated, Regulated and Alluvial Water Sources, although it is also associated with three other WSPs (Figure 8). The public exhibition of the Draft Water Sharing Plan for the Clarence Unregulated and Alluvial Water Sources was being finalised as this report was being drafted . The WSP for the Alstonville Plateau Groundwater Sources overlaps with the WSP for the Richmond River Area Unregulated, Regulated and Alluvial Water Sources, however, it was developed specifically for the Cenozoic basalt aquifer between Lismore and Alstonville. The water sharing plan was originally due in July 2014, but its due date has been extended to July 2015. There has been a proposal to merge this WSP into the North Coast Fractured and Porous Rock Groundwater Sharing Plan to form a uniform WSP for the fractured and porous rock groundwater sources on the North Coast of NSW . More details about these WSPs can be found in .
Table 10 provides a breakdown of the number of bores and estimated usage in ML/year as per WSPs. It is shown that 1967 bores (79% of the total) within the model domain are managed under the WSP for the Richmond River Area Unregulated, Regulated and Alluvial Water Sources; 49 Walloon Coal Measures bores, 19 alluvial bores, and 1 basalt bore are located in the Draft Water Sharing Plan for the Clarence Unregulated and Alluvial Water Sources; 434 bores (17% of the total) are screened in the Alstonville basalt that is managed by the WSP of the Alstonville Plateau Groundwater Sources.
Table 10 Estimated groundwater usage categorised by water sharing plan in the model domain of the groundwater model for the Clarence‑Moreton bioregion
The water account analysis presented in this report was based on allocation data rather than metered actual water usage. This type of analysis generally overestimates the actual groundwater usage. Uncertainties also exist in the allocation data with many bores lacking allocation entries in the NSW state groundwater database. There are inconsistencies between the NGIS and the NSW state groundwater database regarding the purpose information of the bores. Although great efforts were allotted to assign bores to different aquifers, the accuracy of the assignment cannot be guaranteed either due to the lack of stratigraphy boundary information or due to its inferior quality.
Bureau of Meteorology (2013) NGIS Core Data Dictionary Version 2.3. Viewed 20 March 2015, http://www.bom.gov.au/water/groundwater/ngis/documentation.shtml.
DPI (2015a) Draft Water Sharing Plan for the Clarence Unregulated and Alluvial Water Sources. NSW Department of Primary Industries, Office of Water. Viewed 20 March 2015, http://www.water.nsw.gov.au/Water-management/Water-sharing-plans/Plans-on-exhibition/Exhibitions-open/Clarence-Unregulated-and-Alluvial-Water-Sources.
DPI (2015b) Alstonville Plateau Groundwater Sources. NSW Department of Primary Industries, Office of Water. Viewed 20 March 2015, http://www.water.nsw.gov.au/Water-management/Water-sharing-plans/Plans-commenced/Water-source/Alstonville-Plateau-Groundwater-Sources/default.aspx.
Moore C, Cui T, Doherty J, Turnadge C, Pagendam D and Peeters L (2014) Uncertainty analysis, data-worth analysis and hypothesis testing: Assessments to support environmental impact assessments related to cumulative impacts of Coal Seam Gas extraction in the Surat Basin, Queensland. CSIRO, Australia.
NSW Office of Water (2015) Water Sharing Plans. NSW Department of Primary Industries, Office of Water. Viewed 20 March 2015, http://www.water.nsw.gov.au/Water-management/Water-sharing/default.aspx.
Parsons Brinkerhoff (2013) Preliminary numerical groundwater modelling report. Prepared for Metgasco Limited, Document No: 2193251B-WAT-PRE-001 RevA, dated 16 December 2013.
QWC (2012) Underground water impact report for the Surat Cumulative Management Area. Queensland Water Commission, Brisbane, Australia. Viewed 20 August 2015, https://www.dnrm.qld.gov.au/__data/assets/pdf_file/0016/31327/underground-water-impact-report.pdf.
Dataset 1 Bureau of Meteorology (2014) NSW Office of Water – National Groundwater Information System. Bioregional Assessment Source Dataset. Viewed 23 March 2014, https://data.bioregionalassessments.gov.au/dataset/7ab9820e-1e43-4600-8875-a0834345fb6d.
Dataset 2 Bioregional Assessment Programme (2014) NSW Office of Water_GW licence extract linked to spatial locations_CLM_v3_13032014. Bioregional Assessment Derived Dataset. Viewed 23 March 2014, https://data.bioregionalassessments.gov.au/datastore/dataset/4b0e74ed-2fad-4608-a743-92163e13c30d.
Dataset 3 NSW Office of Water (2013) NSW Office of Water combined geodatabase of regulated rivers and water sharing plan regions. Bioregional Assessment Source Dataset. Viewed 31 July 2013, https://data.bioregionalassessments.gov.au/datastore/dataset/24157c41-c42f-4e1f-a791-a1ad18c8215d.