Sustainable yield definitions

The term environmentally sustainable level of extraction' , is called sustainable yield' in this assessment (refer to the Glossary & definitions). It is defined in the National Water Initiative (NWI) as:

The level of water extraction from a particular system that, if exceeded, would compromise key environmental assets, or ecosystem functions and the productive base of the resource.

There is no standardised method across Australia for the determination of the sustainable yield. This lack of consistency was identified during the Australian Water Resources Assessment 2000, which contains a description of the methods used in each jurisdiction to estimate sustainable yields for surface and groundwater resources.

Most states have used their own methods to assess the level of development and to identify whether surface water management areas or groundwater management units are allocating entitlements within sustainable limits.

The tables below list the definitions used by each state and territory in the Australian Water Resources Assessment 2000 for groundwater and surface water sustainable yields. These definitions have changed in some states and territories, but updated definitions have not been provided for this assessment. The definition used in the request for information for the Australian Water Resources 2000 (for both surface water and groundwater) is the one that was adopted by the NWI (refer to the Glossary & definitions).

Defining sustainable yield for surface water

Sustainable yields for states and territories have been determined in a variety of ways (refer to table below providing surface water sustainable yield definitions). These have ranged from rule-of-thumb' techniques to methods that include an assessment of the environmental water requirements of a catchment. Queensland has not provided figures for sustainable yield.

Surface water sustainable yield definitions (NLWRA 2000)

Measuring the water table is useful for determining sustainable groundwater yield

Image by Arthur Mostead, sourced from the MDBC

Note: Methods for measuring sustainable yield continue to vary across the states and territories.

Defining sustainable yield for groundwater

A national groundwater sustainable yield definition has been agreed to by the National Groundwater Committee, but it has not been adopted by all states and territories. The definition is as follows:

The groundwater extraction regime, measured over a specified planning timeframe, that allows acceptable levels of stress and protects dependent economic, social and environmental values.

In considering the groundwater sustainability, this assessment considers: whether the sustainable yield of the resource has been determined for each groundwater management unit and compares the sustainable yield to:

• the cap that has been set within that management area
• the level of water entitlements

Non-renewable groundwater aquifers are treated differently (refer to the Glossary & definitions). Non-renewable aquifers have no current recharge mechanism and policy on use of these waters differs across the country as to how or if at all these resources should be utilised. Some refer to use of these waters as mining', others define use of the entire resource over a 50 to 100 year time frame as appropriate.

The Australian Water Resources Assessment 2000 included an assessment of how each jurisdiction defined the groundwater sustainable yield, and how it was calculated (refer to table below). For nearly all jurisdictions, there were differences not only in the level of detail that was used for the calculation, but also in the actual definition of sustainable yield (AWRA 2000).

Groundwater sustainable yield definitions (NLWRA 2000)

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