Objective (iv) of the National Water Initiative (NWI) is that all overallocated
or overused water resource systems be returned to environmentally sustainable
levels of extraction. The desired outcome is that all systems reach a sustainable
balance between competing uses: including urban, industrial, agricultural,
cultural and environmental.
The NWI has recognised the importance of striving for sustainable management.
Factors that need to be considered include the wide variability in rainfall
runoff and recharge processes, and water quality (especially salinity). The
variability in flows within and between years in a single catchment means that
single annual measures for sustainable yield cannot be relied on as a sole
measure of sustainable management of a catchment. Australia 's collective understanding
of sustainable yield for surface water and groundwater is likely to change
as improved knowledge and data are made available through further research
Measuring and managing the sustainability of water resource systems across Australia is an important part of the NWI. A key component of this is the identification of the sustainable yield for water management areas in each state and territory. There is, however, no agreed, standardised method to calculate and report sustainable yield across Australia, despite this being a key recommendation from the Australian Water Resources Assessment of 2000.
Caps are often placed on the amount water that can be used from an area
in order to protect the environment
Image by Arthur Mostead, sourced from the Murray-Darling
Most states and territories have reported that the sustainable yields of surface water and groundwater management units have been calculated where necessary. Queensland was able to report surrogates for sustainable yield only in four of the six priority water management areas used in the Level 2 assessment.
According to the feedback received from the states and territories, only a few areas (in New South Wales) are reported to have a current resource allocation above the level of sustainable yield. In many areas, the states and territories appear to have based the sustainable yield volumes and resource caps on the current level of entitlements, rather than on any detailed assessment of resource sustainability, until further investigations can be undertaken (such as environmental flow assessments and sustainable yield calculations). In areas where sustainable yields have been assessed, resource caps generally do not exceed the calculated sustainable yields. Many outback areas of Queensland, Western Australia and South Australia have not reported sustainable yields because of the low level of development of resources in these areas.
There are only a few examples of areas where sustainable yields have been assessed and take into account interactions between surface water, groundwater, consumptive users and the environment. These include, from a surface water perspective:
- the Clare and Barossa prescribed water resources areas in South Australia
- the Hunter and Clarence River areas in New South Wales;
and from a groundwater perspective:
- The Atherton Area A in Queensland
- Carnarvon Area in Western Australia.
A number of states and territories have reported that they are abandoning the concept of using a single annual volume to identify sustainable yield and moving into a more sophisticated way of sustainably managing water resources. One argument against using a single volume for sustainable volume is its limitations in allowing for seasonal variability in demand and supply. For example, in some areas of Australia, irrigation often creates high demand for water during summer at a time when river flows are naturally low. In contrast, naturally high flows in winter are not required by irrigators.
Other indicators of sustainability include the use of trigger levels, pressures, and mean annual flows.
Resource sustainability is discussed in more detail in the following sections: