Water resource development

Australia is on balance a very dry continent and water resources are scarce in many areas. Striking an appropriate balance between the consumptive use of the resource and the health of rivers and wetlands is a key element of the National Water Initiative (NWI). An important first step in this process is to identify the environmentally sustainable level of extraction (often referred to as sustainable yield) for water management areas in each state and territory.

Key messages from Level 1 assessment:

• Most states and territories have reported that the sustainable yield of each of the surface water and groundwater management areas has been calculated and reported. However, in outback areas of Australia where there is a low level of water resource development, the sustainable yields are generally not calculated.
• Across Australia, there is no nationally agreed, standardised method for the calculating and reporting sustainable yield, despite this being a key recommendation from the Australian Water Resources Assessment 2000.  The National Water Commission has recently initiated new work to develop best practice methods for the calculating and reporting sustainable yield.
• In many areas, the states and territories appear to base the sustainable yield volumes on the current level of entitlements, rather than on a detailed assessment of resource sustainability. This highlights the need for better understanding of the relationships between river health and river flow regimes under current levels of use.

Key messages from Level 2 assessment:

AWR 2005 collated data from a range of sources, including the Level 1 AWR 2005 assessment, the water balances for 51 priority geographic areas, the ABS Water Account and supporting projects and the BRS’ Water 2010 project. This data was used to answer questions about water resource development in Australia in 2004-05.

Entitlements, allocations and sustainable yields

• AWR 2005 concludes that there are concerns with the use of the term overallocation as defined in the NWI. It suggests that consideration be given to a new term, ‘over-entitlement’, that would be synonymous with the National Land and Water Audit’s term ‘over-development’.
• Data for environmentally sustainable levels of extraction and sustainable yields used in this study were provided by the states and territories. Given that they are implicit to the calculation of overallocation and overuse, there is concern that they are determined differently from jurisdiction to jurisdiction and that they may not reflect the effect of climate variability, climate change and land use trends during the past decade.
• Fifty-one representative water management areas across Australia have been assessed, with detailed water balances compiled for the period July 2004 to June 2005. These water balances show all aspects of the hydrological cycle, including water flows in and out of the area, water extraction, and changes in storage. They provide a baseline against which future changes can be assessed and an understanding of where data and information is lacking or uncertain.
• Groundwater – surface water interactions are significant across most of the areas considered for the detailed water balances. The potential for double counting appears high, given the levels of interaction.
• Seventeen out of the 51 water management areas that were investigated showed interconnectivity between surface water and groundwater that was higher than 10 per cent of total runoff and recharge. This highlights the need for integrated management to prevent double counting and overallocation of the connected surface and groundwater resources.

Hydrogeologists supervise the drilling of groundwater bores
Image by Ryan Morris, sourced from SKM

Level of water resource development

• The Level 1 assessment reported that of 340 surface water management areas, three (1 per cent) were overallocated, with a further 44 (13 per cent) highly developed. For groundwater management units the figures were 19 (5 per cent) for overallocation and 85 (23 per cent) highly developed, respectively. This was based on self-assessment by each jurisdiction. It was noted that these estimates are significantly lower than that assessed for the previous Australian Water Resources Assessment 2000 (NLWRA 2001). While in some cases this was due to management changes, in other cases it was a result of changes to definitions of sustainable yield and level of development.
• In the current assessment of 51 representative water management areas, a nationally consistent set of water resource development ratios has been developed to help identify those areas that are likely to be under the most significant water use pressure and environmental stress due to a significant volume of the total available flow being allocated or used in 2004-05. This assessment is still dependent on the states and territories own assessments of sustainable yield. The results of the current analysis of the 51 representative water management areas are more consistent with the previous findings in 2000 (NLWRA 2001).
• AWR 2005 has determined the level of water resource development pressure from allocation and use regimes in 2004–05 for the 51 priority geographic areas considered, and based on available data.  The results from the 51 water management areas considered (based on available data for 2004–05) indicate that there were:
  • 4 water management areas with consumptive use greater than sustainable yield (overused)
  • 17 water management areas with a high level of consumptive use as a proportion of inflows
  • 11 water management areas with a high level of consumptive use as a proportion of the total water resource.
• Two water management areas (Great Artesian Basin and Mereenie Sandstone in Northern Territory) appear to have had consumptive use greater than the total annual inflow in 2004–05. In the Mereenie Sandstone there is an acknowledged mining of the resource, with the sustainable yield determined to limit extraction to 80 per cent of total aquifer volume over 320 years.
• It must be emphasised that, as these assessments are based on only one year’s data, they can be considered only as a starting point against which future change and trends can be assessed. These results, therefore, are potentially indicative of the most highly utilised systems. Longer periods of measurement and assessment are required to determine the degree of environmental stress and its impact on identified environmental assets.
• For determination of water availability, improved and consistent methods that take into account longer time sequences and future climate predictions are required. The Murray-Darling Basin Sustainable Yields Project being conducted by CSIRO is doing this for catchments within the Murray-Darling Basin, but there is a major need for all overused or highly used water management areas elsewhere to be investigated in a similar manner.
• Of the capital city areas, the Adelaide urban water supply area has shown the highest proportion of extractions and diversions (77 per cent) in relation to 2004–05 inflows.
• In addition to the assessment of level of water resource development for the priority geographic areas, an assessment has also been undertaken at the state and territory level. The table below allows comparison of data on total water use with the total sustainable yield for each state and territory.

Sustainable yield and total 2004–05 consumptive use for the states and territories

1.  Where determined from AWR 2005
2.  From ABS
3.  Sustainable Yield refers to long term averages.

• Even amongst those jurisdictions that used a sustainable yield figure as a management tool, there was not a consistent method employed when calculating it or when using it to manage the resource.
• Groundwater – surface water interactions are significant across most of the priority areas. The potential for double counting to occur appears high, given the levels of interaction.
• Farm dams appear to be a significant interceptor of runoff. Investigations have shown that for every megalitre stored in farm dams, streamflow is reduced by 0.84 megalitres. Furthermore, estimates from Victoria suggest that up to 70 per cent of the stored water is lost to evaporation. In the Murray-Darling Basin alone, 2200 gigalitres can be stored in hillslope farm dams. This reduces average annual streamflow by 1900 gigalitres. The increase in storage over the last ten years in the Murray-Darling Basin is estimated to have reduced streamflow by 450 gigalitres.

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