Frequently Asked Questions
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- What information can I get from the GDE Atlas?
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The GDE Atlas shows the general location of groundwater-dependent ecosystems (GDEs). Each polygon represents an area within which groundwater interaction potentially occurs. This does not mean that the whole polygon is interacting with groundwater.
A set of attributes describing the characteristics of each GDE is included and can be viewed by selecting an ecosystem or a group of ecosystems. Literature references that relate to individual GDEs can be viewed. Groundwater-dependent ecosystems with specific literature associated with them will have more attributes than GDEs derived solely from GIS analyses.
- How should the GDE Atlas be used?
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The GDE Atlas provides information to support the recognition and identification of GDEs in natural resource management, including water planning and environmental impact assessment. It indicates where ecosystems potentially interact with groundwater, and some of the characteristics of those ecosystems that may be useful in determining water requirements.
The GDE Atlas shows general areas where groundwater interaction may occur. It does not imply that an entire mapped ecosystem is using groundwater, but rather groundwater interaction may be occurring somewhere within the mapped ecosystem. It is recommended that the GDE Atlas be used to flag the location and characteristics of potential GDEs.
The GDE Atlas makes no assessment of ecosystem value, condition, sensitivity, threat or risk. There are many external factors that need to be considered in these assessments in more detail. In high risk locations, it is recommended that more detailed work is undertaken to assess GDE water requirements. Where this is the case, the GDE Toolbox provides a framework and suite of practical and technically robust tools for conducting detailed assessments. The GDE Toolbox is a detailed methodology report which is divided into two parts, as follows:
- Part One provides an assessment framework, and a monitoring and evaluation program for documenting ecological water requirements.
- Part Two provides a suite of practical and technical approaches to help water managers identify GDEs and determine the impact of changes in groundwater on an ecosystem state or function.
- Which ecosystems are shown in the GDE Atlas?
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The Atlas contains information about three types of ecosystems:
- Aquatic ecosystems that rely on the surface expression of groundwater—this includes surface water ecosystems which may have a groundwater component, such as rivers, wetlands and springs. Marine and estuarine ecosystems can also be groundwater dependent, but these are not mapped in the Atlas.
- Terrestrial ecosystems that rely on the subsurface presence of groundwater – this includes all vegetation ecosystems.
- Subterranean ecosystems – this includes cave and aquifer ecosystems.
- What does the inflow dependent ecosystems likelihood grid show?
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The nation-wide inflow dependent ecosystems (IDE) likelihood grid expresses the likelihood that landscapes are accessing water in addition to rainfall. The likelihood is expressed as a range of values between 1 and 10 (low to high), where 10 indicates landscapes that are most likely to access additional water sources. The additional water source may be soil water, surface water, or groundwater. Pixels with a likelihood of 6 or more indicate that the landscape is more likely to be inflow-dependent and accessing an additional source of water than it is to be relying solely on rainfall. IDEs include a large variety of natural ecosystems (e.g. rivers, wetlands, and forests), as well as altered landscapes such as irrigated farming and channels.
The IDE likelihood grid was constructed from multiple satellite sensors, namely MODIS and Landsat. While MODIS estimates evapotranspiration from land surface (van Dijk et al., 2011 ) and Landsat measures vegetation dynamics sustained during a prolonged dry period (Barron et al., 2012), the two sources were combined by converting these metrics into a standard unit based on likelihood of additional water use ranging from 1 (low) to 10 (high). Within different landscapes, rules were applied to determine the combination of MODIS and Landsat data to develop a continental likelihood of IDE expressed at 25 m resolution.
The limitations of the IDE likelihood grid are that the scale and resolution of the mapped information are only as detailed as the input mapping; and features which do not influence a 30m Landsat pixel are not identified on the map. In addition, the data is dependent on the time period of the data used (2000–2010) and ecosystems’ water use can only be identified if active in the time period; it does not provide information on the future or the past.
References:
Van Dijk, A., Warren, G., Van Niel, T., Byrne, G., Pollock. D., Doody, T. (2011) Derivation of data layers from medium resolution remote sensing to support mapping of groundwater dependent ecosystems. CSIRO Land and Water, Internal Document for GDE Atlas.
- What does the terrestrial GDE layer show?
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The terrestrial GDE layer expresses the potential for groundwater and mapped vegetation communities across Australia to interact. It shows the vegetation communities that interact with groundwater from the watertable or in the capillary zone. The potential for other living organisms (e.g. faunal and microbiotic ecosystems) to interact with groundwater was not assessed, with the exception of burrowing crayfish in Tasmania. Information on the interaction of associated fauna or abiotic features would require additional assessment.
- What does the aquatic GDE layer show?
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The aquatic GDE dataset expresses the potential for groundwater interaction for rivers, springs, and wetland ecosystems across Australia. It shows the ecosystems that rely on groundwater that has been discharged to the surface, for example, as baseflow or spring flow.
- What does the subterranean GDE layer show?
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The subterranean GDE layer shows areas where cave and aquifer ecosystems potentially rely on groundwater beneath the surface – beneath the watertable, in the capillary zone, or in the vadose zone. It generally outlines areas of karstic carbonate rocks which are known to, or potentially, host cave systems or aquifers containing subterranean GDEs.
- What does the remote sensing layer show?
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The nation-wide remote sensing layer expresses the likelihood that landscapes are accessing water in addition to rainfall. The likelihood is expressed as a range of values between 1 and 10 (low to high), where 10 indicates landscapes that are most likely to access additional water sources. The additional water source may be soil water, surface water, or groundwater. A likelihood of 1 indicates landscapes that are most likely to rely solely on rainfall.
The remote sensing layer was constructed from multiple satellite sensors, namely MODIS and Landsat. While MODIS estimates evapotranspiration from land surface (van Dijk et al., 2011 ) and Landsat measures vegetation dynamics sustained during a prolonged dry period (Barron et al., 2011 à Barron et al., 2012), the two sources were combined by converting these metrics into a standard unit based on likelihood of additional water use ranging from 1 to 10 (low to high). Within different landscapes, rules were applied to determine the combination of MODIS and Landsat data to develop a continental likelihood of IDE expressed at 25m resolution.
The limitations of the remote sensing are that the scale and resolution of the mapped information are only as detailed as the input mapping used; and features which do not influence a 30m Landsat pixel are not identified on the map. In addition, the data is dependent on the time period of the data used (2000-2010) and ecosystems water use can only be identified if active in the time period; it does not provide information on the future or the past.
References:
Van Dijk, A., Warren, G., Van Niel, T., Byrne, G., Pollock. D., Doody, T. (2011) Derivation of data layers from medium resolution remote sensing to support mapping of groundwater dependent ecosystems. CSIRO Land and Water, Internal Document for GDE Atlas.
- Are all groundwater-dependent ecosystems captured in the GDE Atlas?
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Mapping in the GDE Atlas relies on broadscale analysis, existing datasets and remote sensing methods. This means certain GDEs are not detected. Situations where GDEs may not be detected include:
- Very small vegetation ecosystems (less than 25 x 25 m) may not influence an entire remote sensing pixel, and therefore may not identify as interacting with groundwater.
- In generally wet environments (e.g. southwestern Tasmania), remote sensing techniques that rely on relationships between evapotranspiration and rainfall cannot accurately differentiate groundwater and surface water dependence. In many cases unsupervised classification of Landsat data has been used to differentiate groundwater and surface water dependence within peatland and wetland environments. However, some areas of vegetation may remain less accurately differentiated.
- Vegetation or surface water ecosystems that were not represented on the ecosystem maps used to create the GDE Atlas maps. These ecosystems therefore do not have a mapped polygon available to represent them in the GDE Atlas.
- Vegetation ecosystems that interact with groundwater seasonally, but do not exhibit constant growth may not have been detected by the remote sensing techniques used. For example, ecosystems on discharge sands in the Northern Territory which rely on groundwater late in the wet season, but die off during the dry season.
- Vegetation ecosystems that did not interact with groundwater during the 10-year period of the remote sensing data (2000–2010) may not have been identified as GDEs.
- Is a whole polygon a GDE?
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- Each GDE polygon shows an area within which groundwater interaction may occur. For example, a large vegetation polygon may be assessed as having high potential for groundwater interaction, but the interaction may only occur in part of the polygon.
- The larger the polygon, the less likely it is to accurately represent the spatial extent of the actual GDE. Large polygons indicate a broader grouping of landscape features. Not all landscapes indicate groundwater use, even if the polygon overall is considered to be a GDE.
- Do groundwater-dependent ecosystems always use groundwater?
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- GDEs shown in the Atlas can use groundwater at sparse intervals and still be classified as a GDE. The temporal nature of groundwater use by GDEs mapped in the Atlas was not assessed; however, where details on temporal groundwater use were available in existing data, this has been included in the attribution of groundwater-dependent ecosystem polygons.
- Is the influence of river supplementation taken into account?
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- The influence of supplementation on rivers (e.g. by inter-basin transfers of water or flow regulation) has not been accounted for. Supplemented rivers may be represented as GDEs in the maps because the methods used cannot distinguish additional flow from supplementation, from that of groundwater contributions.
- How accurate are the geographic locations?
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- The accuracy of the GDE mapping depends on the accuracy of input data. For the national assessment, several hundred input datasets were used so the accuracy varies across Australia. The accuracy also varies for GDEs mapped in regional studies. Details of the input data used are provided in the final GDE Atlas Methodology report.
- How do I download information from the GDE Atlas?
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The three GDE layers can be downloaded for a river region:
- Aquatic GDEs (rivers, wetlands and springs)
- Terrestrial GDEs (vegetation)
- Subterranean GDEs (caves and aquifers).
You can download the datasets using the 'Download' tool from the side panel, specifying the region and format of the dataset.
Other datasets are available by email request to groundwater@bom.gov.au including the inflow-dependent ecosystems likelihood grid, and national aquatic, terrestrial and subterranean GDE layers (current version). Version 1 of the national GDE layers (national assessment) are also available by request.
- Which parts of Australia have updated GDE data?
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The national GDE datasets from 2012 are regularly updated with regional-scale GDE mapping from State and regional agencies as they become available for incorporation in the Atlas. The GDE Atlas has ‘Areas of update’ map layers that show the areas and types of GDEs that have been updated. Refer to the methodology page for more information.