20240820 17054400 1.0 ISO 19139 Metadata Implementation Specification GML3.2 FALSE 20241002 12550700 TRUE Depth to watertable less than 20m.lyr 005 20240926 16383700 5000000 5000 ISO19139 Depth to watertable less than 20m raster digital data external 3bffef6799cf6f03264126ed047e91a Geoscience Australia client services GPO Box 378 Canberra ACT 2601 clientservices@ga.gov.au AU +61 2 6249 9111 True client services <DIV STYLE="text-align:Left;"><DIV><DIV>The standing water level (SWL) in a bore is a measure of the depth to groundwater from a certain reference point at the surface, usually the top of the bore casing or the ground level. It represents the level that groundwater can rise within the bore if unimpeded by the overlying rocks and sediments. The depth to the standing water level does not necessarily represent the depth a bore needs to be drilled to intersect the watertable, although it provides a useful indicator. The screened interval in a bore is commonly set well below the watertable surface so that sufficient supply can be obtained unimpeded by drawdown in the bore when pumping starts. The depth to watertable trend surface for the KT-LEB is derived from interpolation of water level data available for the shallowest aquifers intersected across the entire KT-LEB region (Evans et al. 2024).While most of the water level data are sourced from bores screened in Cenozoic sediment aquifers, additional water level data from near-surface aquifers in older pre-Cenozoic rocks and sediments (to maximum depths of 100 m below surface) were also included in the analysis. This approach enabled broader regional understanding of groundwater level trends across the entire basin in places where Cenozoic aquifers do not occur. The water level data was obtained from the state and territory groundwater bore databases. Sources of archival groundwater bore data evaluated for the KT–LEB included Queensland Government (2023), NT Government (2023), SA Government (2023) and NSW Government (2023).In some places, the depth to watertable surface may not represent the local watertable in the unconfined aquifer, particularly where the shallowest aquifer is semi-confined, as can be the case in the southernmost portions of the Callabonna Sub-basin. The water level data used to create these maps were not corrected for variations in water density due to the regional scale nature of the assessment, the lack of bores with co-located salinity and water level data, and the highly variable groundwater salinity in many Cenozoic aquifer (Evans et al. 2024). Developing local-scale water level maps, particularly in areas of highly saline groundwater, would require data to be corrected for variations in water density. Such areas include near salt lakes such as lakes Eyre and Frome, or areas where groundwater salinity varies considerably across short distances such as on the Strzelecki Sandplain to the west of Strzelecki Creek.The depth to watertable mapping does not account for perched aquifers that may occur in some places above the level of the regional watertable. Perched aquifers can be locally important water sources for wetlands and GDEs, although they are generally of limited areal extent.Most bores screened in Cenozoic aquifers in the KT–LEB have only a single water level reading. These readings are generally measured soon after the bore was constructed. Hence, the composite water level mapping does not represent a particular point in time. There are some areas on the depth to watertable map indicated as zones of low confidence. These are areas with insufficient water level data available to adequately constrain the gridding process, which can locally introduce errors (artefacts) into the map. Although other gridding processes could be employed to improve definition in these areas, these could mask locations where more water level data are required. In some places, the use of airborne electromagnetics (AEM) data may be able to provide new information on depth to the watertable. Some areas with little available groundwater level data are known to be regional groundwater discharge features for underlying aquifers (such as Kati Thanda –Lake Eyre and surrounds) or areas where the regional watertable is reported as being within a few metres of the surface (e.g. Costelloe 2017).Despite some of the limitations, the watertable regional trend surface, contours and depth to standing water level water mapping is consistent at the basin scale and demonstrates that shape of watertable correlates strongly with the regional topographic features such as catchment boundaries. </DIV></DIV></DIV> This raster provides information on depth to the watertable across the whole of the Kati Thanda - Lake Eyre Basin (KT-LEB) region. So as to provide coverage across the whole region, the regional watertable was constructed using waterlevel measurements from any near surface aquifer, not just aquifers in the Cenozoic. Reference datum is metres below ground surface (m below ground). Depth to watertable less than 20m layer classes show spatial distribution of areas where groundwater is within 10m, 10 to 20m, or 'above surface'. Areas where depth to watertable is shown as ‘above surface’ are zones where little or no groundwater data is available. However, the occurrence of GDEs) in some of these zones suggests shallow groundwater. The depth to the watertable should be verified in areas shown as ‘above surface’ where GDEs are present. Most bores in the KT–LEB have only a single water level reading, which generally was measured soon after the bore was constructed. Hence, the composite water level mapping does not represent a particular point in time. In addition, waterlevel measurements that were used to create the surface were not density corrected due to many bores missing salinity data. Despite some local limitations such as this, the watertable trend and depth to water mapping is generally consistent at the basin scale, and correlates strongly with the regional topography. Evans et al. (2024) details the hydrogeology of the KT-LEB region. © Commonwealth of Australia (Geoscience Australia) 2026. This product is released under the Creative Commons Attribution 4.0 International Licence. http://creativecommons.org/licenses/by/4.0/legalcode Version 6.2 (Build 9200) ; Esri ArcGIS 10.7.1.11595 National Groundwater Systems hydrogeology groundwater Cenozoic sedimentary cover Kati Thanda - Lake Eyre Basin bores regional watertable standing water level depth to watertable 131.352500 East 146.755000 North -18.812940 South -34.327940 131.352500 146.755000 -34.327940 -18.812940 0 4283 GCS_GDA_1994 <DIV STYLE="text-align:Left;font-size:12pt">© Commonwealth of Australia (Geoscience Australia) 2026. This product is released under the Creative Commons Attribution 4.0 International Licence. http://creativecommons.org/licenses/by/4.0/legalcode</DIV> 20241002 ArcGIS Pro Layer file 3.2.2 dataset external 3bffef6799cf6f03264126ed047e91a Geoscience Australia client services GPO Box 378 Canberra ACT 2601 clientservices@ga.gov.au AU +61 2 6249 9111 True client services The water level data was obtained from the state and territory groundwater bore databases. Sources of archival groundwater bore data evaluated for the KT–LEB included Queensland Government (2023), NT Government (2023), SA Government (2023) and NSW Government (2023). Depth to watertable was derived from subracting interpolated watertable rester in meters above Australian Height Datum (AHD) from the SRTM-1second DEM (Wilson et al. 2011). Watertable trend raster was interpolated using ArcGIS software suite Topo to Raster tool and watertable observation points compiled for bores and springs in meters above AHD. Flowing spring location points were sampled with elevation values from SRTM-1sec DEM (Wilson et al. 2011) and were added 1m to represent hydraulic head of the local watertable. Generated regional trend watertable surface was clipped with the Cenosoic cover polygon dataset extracted from surface geology (Raymond et al. 2012). NSW Government (2023) NSW groundwater bore database [data set], NSW Department of Primary Industries and Environment, https://water.dpie.nsw.gov.au/science-data-and-modelling/groundwater-management-and-science, accessed 1 May 2023. NT Government (2023) NT bore locations, water quality and groundwater levels [data set], NT Open Data Portal, https://data.nt.gov.au/dataset/nt-bore-locations-water-quality-and-groundwater-levels, accessed 1 May 2023. Queensland Government (2023) Queensland groundwater bore database [data set], Queensland Open Data Portal, https://www.data.qld.gov.au/dataset/groundwater-database-queensland, accessed 1 May 2023. Raymond, O.L., Liu, S., Gallagher, R., Zhang, W., Highet, L.M. 2012. Surface Geology of Australia 1:1 million scale dataset 2012 edition. Geoscience Australia, Canberra. https://dx.doi.org/10.26186/74619 SA Government (2023) South Australian groundwater bore database [data set], WaterConnect, South Australian Government Environmental Data, https://www.waterconnect.sa.gov.au/Systems/GD/Pages/Default.aspx, accessed 1 May 2023. 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