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Tasmania has an extensive groundwater resource (as depicted in the map below), trapped by igneous, sedimentary and metamorphic rocks. Although it occurs widely, Tasmania's total estimated groundwater resource (approximately 16 million ML) is not evenly distributed and its yield and quality can also vary depending on the geology of the aquifer: The availability and quality of groundwater is particularly influenced by the aquifer material, the lateral and vertical variations in permeability and porosity properties of the aquifer, the hydrogeological conditions, the proximity to recharge areas and the amount and quality of recharge. Groundwater that has a longer residence time will tend to interact chemically with the aquifer material to a greater degree, affecting the water quality. Water becomes increasingly saline in most rocks depending upon it's residence time in the ground, therefore if recharge is diminished, then baseflows are likely to become more saline with time (Leaman 2003). Risks to groundwater resources in Tasmania include unsustainable use, and point source and diffuse source pollution. Potential pollution sources include: Land use pressures such as clearance also have implications for groundwater levels and quality. Tasmania's Triassic rocks naturally contain very saline water and any widespread clearance of vegetation from areas containing these rock types will result in a rise in the water table and potential salt crystalisation at the soil surface or entry of salts into surface waters (Leaman 2003). These effects can be exacerbated through the application of fertilisers to pastures. Many of the chemicals in fertilisers are water-soluble or can be transferred in water as pollutants. They can enter the groundwater storage, add to the total salt content, and potentially assist rock breakdown resulting in a further release of salts. Long-term fertiliser application to pasture can result in a build up of nutrients washed down from the fertiliser in the groundwater below. Organisms such as algae thrive in nutrient rich environments and therefore it is possible for enriched groundwater seepage at the ground surface to have a proliferation of algal growth (Leaman 2003). Surface and groundwater quality in karst systems may be affected by upstream land uses, particularly if the catchment includes agricultural land or land used for timber production. Water quality affects natural processes of erosion and sedimentation in karst systems, and can influence their aquatic ecosystems (DPIWE 2001). Borehole design, construction and maintenance can also result in aquifer pollution. Boreholes can act as a preferred pathway for polluted near-surface groundwater or surface water to enter aquifers (e.g. stock supply boreholes and monitoring boreholes that surround landfills or industrial operations). The Background Report on Groundwater in Tasmania compiled by DIER (2001) for the Water Development Plan for Tasmania provides an overview of the groundwater status in Tasmania. The National Land and Water Resources Audit (NLWRA 2001) also provides important information on Tasmania's groundwater resources that can be accessed though their website. There is potential for the extraction of groundwater for uses such as irrigation, stock water, domestic or other rural uses to become increasingly unsustainable in many areas of Tasmania. This has implications for future development of groundwater resources (e.g. limited resources), and for the environment (e.g. reduced quantity and quality for maintaining ecosystem health). There are significant links between groundwater and surface water (e.g. many surface waterways are recharged from groundwater, or vice versa), so that alterations to quantity and quality of one can have direct effects upon the other. For example, maintaining water quality parameters of both surface and groundwater within natural ranges is fundamental in managing karst systems for nature conservation (DPIWE 2001). Groundwater pollution from various land use practices have significant effects on water quality (groundwater and potentially surface water) and has serious implications where water is used for human consumption and other purposes. There is also growing concern that various land use changes such as land clearing, may impact upon the local climate of a catchment and long-term catchment yield and water quality for groundwater and surface water. Converting wooded land to annual cropping or plantation forestry is reported to have significant effects on long-term catchment yield (Leaman 2003). However, there have been few Tasmanian specific studies on land use effects on groundwater. A summary of some of the possible causes and effects of falling or rising groundwater levels or pressures are described below. Possible causes for falling groundwater levels or pressures include: Possible effects of falling groundwater levels or pressures include: Possible causes for rising levels or pressures in groundwater include: Possible effects of rising groundwater levels or pressures include: The NLWRA (NLWRA 2001) divided the State up into 14 Groundwater Management Units (GMUs) and three Unincorporated Areas (UAs) (see map below). The definition of GMUs was on the basis of boundaries of significant aquifers, areas of current extensive groundwater use and areas with the potential for future extensive groundwater use. Three broadly defined groundwater provinces (see map below) were also used as an aggregation unit for mapping, as groundwater management units often overlie each other. Broadly, the provinces were defined on the basis of differing geological units and rainfall zones. Further information for each of these provinces and GMUs may be accessed on the NLWRA website.
Assessing and measuring the current situation Groundwater quantity The National Land and Water Resources Audit (NLWRA) has provided an estimate of the sustainable yield for the GMUs, UAs and the State as a whole for 2000. The estimates are based on limited data largely provided by Mineral Resources Tasmania (MRT) and expert opinion (NLWRA 2001). Groundwater extraction data is not routinely collected in Tasmania, but the NLWRA has provided some estimates based on the limited data available and expert opinion. Based on the sustainable yield and groundwater extraction data, the NLWRA provided an indication of the development status of the groundwater resources in Tasmania for 2000, which is the most recent assessment available. Projected values for the rates of groundwater demand and development status for the years 2020 and 2050 were also estimated by the NLWRA. The significant lack of groundwater data available in Tasmania means there is uncertainty in the status of the groundwater resources. Consequently, the NLWRA highlighted the need for more accurate investigation of sustainable yield in Tasmania. Presently in Tasmania, MRT monitors a limited number of boreholes across the State (about 34 observation bores) to identify: The bores, however, do no represent a systematic sampling of Tasmania's hydrogeology, and provide only a limited amount of data for the whole of the State. More monitoring stations would be desirable. Private boreholes being used for extraction that have been drilled close to some of MRT's monitoring boreholes are influencing the monitoring results. The formal allocation of groundwater does not occur in Tasmania, but is proposed under the Water Management Act 1999 through the formal licensing of all bores other than those used for stock and domestic purposes. To date there has been no assessment of the quantity requirements for environmental water use and groundwater dependent ecosystems. A lack of Statewide data prevents measurement against the following indicators: Groundwater quality There has been limited monitoring of groundwater quality in Tasmania. The NLWRA provided an estimate of salinity for the 14 GMUs and three UAs in Tasmania, but acknowledged that there was limited data available and that further investigations should be conducted. The limited groundwater monitoring systems suitable for assessing groundwater levels and trends Statewide also restrict the ability to report on areas of rising watertables and potential groundwater salinity. Data from select production bores across the State provide some information on groundwater level (MRT's 34 monitoring bores), but do not represent a complete picture of Tasmania's hydrogeology. Very limited data is only available for trends in watertable depth from salt affected areas of Longford-Cressy and the Coal River Valley. Direct hydraulic connection between surface and groundwater, and between individual aquifers has the potential to introduce contaminants into groundwater systems. For example, in the Mella area of north-west Tasmania, surface water contaminated by acid sulphate soils has been drawn into the underlying carbonate aquifer through sinkholes and by borehole extraction (DIER 2001). Other measures of groundwater quality, such as Nitrogen (as nitrate-N) and bacteria (E.coli) are common indicators of groundwater quality for drinking or agricultural purposes. Nitrate is a commonly accepted indicator of pollution of unconfined groundwater from agriculture, sewage, and waste management. Although E.coli is rarer in groundwater than some pathogenic bacteria and viruses of human origin, it has not yet been replaced as an indicator of faecal pollution in groundwater. There is no apparent data available in Tasmania, which would enable any assessment of condition or trend. In areas where other identified potential concerns relate to land use or affect the health of the population, other regionally specific indicators would be valuable - e.g. floods, agricultural chemicals, industrial chemicals, hydrocarbons, and other pathogens. The NLWRA provided some anecdotal evidence of sources of point and diffuse pollution within GMUs as a result of discussions with regional water management officers, such as pollution from landfills. However, the NLWRA did not provide any further conclusive data. Further research into the Effects of Waste Disposal on Tasmanian Groundwater Quality has been undertaken by Ezzy (2002) and is reported upon in the Solid Waste Issue Report. This study of the effects of waste disposal on groundwater quality identified groundwater contamination at six of the ten sites that were investigated. If this percentage is extrapolated to the 176 sites identified around the State, potentially up to 100 waste disposal sites may have contaminated groundwater (Ezzy 2002). The actual number of past and present landfill sites across Tasmania is not known. A lack of data prevents measurement of Tasmania's groundwater resources against the exceedences of groundwater quality guidelines (ANZECC key indicators, see also Schedule B1 National Environment Protection (Assessment of Site Contamination) Measure 1999). |
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Groundwater Extraction Versus Sustainable Yield - at a glance
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Groundwater Salinity - at a glance
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Area of Rising Watertables - at a glance
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The limited information on hydrogeological properties and groundwater use restricts the accuracy of all aspects of the groundwater data compiled for assessment in Tasmania (NLWRA 2001). There is no strategic planned approach for the investigation and ongoing monitoring of groundwater resources in Tasmania. The requisite studies to reach Statewide sustainable management of this important resource have not been undertaken (DIER 2001). Past management has been limited by a lack of borehole licensing and formal requirements for the investigation of aquifer properties to relevant national or international standards before the commencement of major irrigation or other extraction proposals. Tasmania is the only State in Australia where drillers are not required to be licensed (DIER 2001). In addition, the intricate links between groundwater and surface water systems have caused problems for both resources as a result of different management approaches. There are no formal licensing arrangements linking groundwater and surface water, with each being registered separately. However on-farm conjunctive use of groundwater and surface water is quite common for irrigation purposes (NLWRA 2001). It is anticipated that the new provisions for licensing of existing and new bores under the Water Management Act 1999 will in future provide the required information on groundwater use and application. In particular this process presents an opportunity to increase the number of designated monitoring boreholes throughout the State, particularly in high use areas such as Sorell and Wesley Vale. Proposed additions to Mineral Resources Tasmania's groundwater database (BORIS) will ensure that the system will be an effective tool for ongoing and emerging groundwater management in Tasmania for the future. The State faces a number of groundwater development constraints, particularly in the Sorell and Wesley Vale GMUs as these areas are likely to face restrictions should a formal policy be developed enforcing the sustainable yields estimated as part of the NLWRA. The Statewide sustainable yields are generally considered to be low, because the majority of the groundwater resource is located in fractured rock aquifers, which provides only low yields from individual bores. Other development constraints relate to the fact that many areas within Tasmania are declared wilderness areas, National and State Parks or protected catchments, which restrict groundwater access and development. The key groundwater management issues are as follows. Increased resources are required to conduct investigations of groundwater resources. The current monitoring network that is regularly examined by MRT (34 boreholes across the State) requires expansion as it is regarded as generally insufficient in many areas by the NLWRA (NLWRA 2001). The establishment of a comprehensive network of monitoring boreholes should be focused upon improving information on the condition and trends in groundwater use, watertable depth and quality. In addition, the incorporation of additional groundwater monitoring data from other sources will also assist in providing a more effective Statewide groundwater database. It is recommended that ongoing research and development be focused initially on the Wesley Vale and Sorell GMUs, and then on other GMUs as required. It will also be important to ground-truth via survey the actual numbers of groundwater bores across the State. Greater accessibility to groundwater information is also required and will result in more informed management decisions. In relation to groundwater management, the future direction needs to move from a reactive to a proactive management approach. This will be achieved by the implementation of Water Management Plans in strategic areas of the State (NLWRA 2001). Further research on the interaction of groundwater and surface water resources and other environmental water requirements will also be important as part of this process. With further development of groundwater resources, formal allocations may be required in order to protect significant environmental values (NLWRA 2001). The implementation of the management requirements of the Water Management Act 1999, will contribute to improved groundwater management into the future. In addition, the Groundwater Management Unit concept developed as part of the NLWRA will likely become a framework for management of groundwater. It is anticipated that the concept will be strengthened and expanded as part of the management of State's groundwater resources. Tasmania Together and the RMPS Relevant Tasmania Together goals and standards for 'Inland Waters and Wetlands' are listed in the linked file. The Tasmania Together Progress Board reported on progress toward targets for benchmarks set (Tasmania Together Progress Board 2003). Indicators, targets and baseline data are available in the latest Progress Report June 2003. Further information, including progress report updates, is available from Tasmania Together. Involvement of the community, and the fair and orderly use of resources are also fundamental principles of the RMPS. The RMPS objectives have been developed to advance the principles of sustainable development.
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