SoE 2006 > Water > 5.4 Groundwater extraction

5.4 Groundwater extraction

Over the last 20 years, demand for groundwater resources in NSW has increased as access to surface water supplies has become constrained. Some groundwater resources have been used beyond their sustainable yield in recent years, although use is now stabilising in the major aquifer systems.

Groundwater management areas where over-extraction has occurred since SoE 2003 are the upper and lower Namoi, the lower Murrumbidgee and lower Lachlan alluvial aquifers. Areas at risk of over-extraction because of the level of licensed entitlements include the Murrumbidgee, Macquarie–Bogan, Lachlan, Hunter, lower Murray, upper Namoi, lower Gwydir and Peel River groundwater systems. The Great Artesian Basin is not over-allocated, but the current program of capping and piping bores is required to conserve groundwater resources. It has resulted in significant water savings and improvements in groundwater pressure.

The drought has increased the demand on groundwater resources, which has induced localised stress on some groundwater systems. However, further groundwater development is possible in some areas, such as the Sydney catchment area, where groundwater is still available for allocation and urban uses.

The development of statutory groundwater-sharing plans to reduce entitlements to a long-term sustainable level is a significant step forward in managing future extraction.

NSW indicators

Introduction

NSW has most of the larger fresh groundwater resources within Australia suitable for human uses. Many ecosystems in NSW also depend on groundwater for their ongoing health and maintenance. These include surface water bodies, such as wetlands, rivers and lakes, which may be highly connected to groundwater, and also some terrestrial ecosystems.

Groundwater is a vital resource, particularly where surface water supplies are limited or unreliable through dry years. More than 200 towns in NSW use groundwater as their principal water supply, and many regional economies rely on its availability. Approximately 11% of the water used in NSW for drinking, irrigation, watering stock, and domestic and industrial purposes comes from groundwater sources.

Changes in climatic conditions affect the amount of groundwater used. Extraction may increase substantially in times of drought to offset the lack of surface water, while in periods of high rainfall, groundwater will recharge more and be used less. The intent of groundwater management plans (see 'Response to the issue') is to manage the resource to a long-term sustainable yield. This means that over-extraction in times of drought for one or a few years would be permitted, providing that extraction levels drop back below the sustainable yield after the drought period to allow water levels to recover. This natural flexibility of groundwater systems provides for a reliable and secure water resource.

However, continued over-extraction of groundwater places pressure on the integrity of the aquifer and on any dependent aquatic and terrestrial ecosystems because it can:

• reduce base flows to rivers and decrease the water available to other groundwater-dependent ecosystems
• alter water quality by allowing saline water to intrude into an aquifer
• in extreme cases lead to land subsidence, as well as a reduction in the amount of groundwater available for future extraction.

Current status and trends

As the limits of surface water supply have been reached in NSW, demand for groundwater resources has generally increased. Across NSW, groundwater extraction increased from 1008 GL per year in 1996–97 (NLWRA 2001) to 1300 GL in 2002–03. However, annual extraction is highly variable. Figure 5.5 shows groundwater extraction from the major inland alluvial systems within NSW over the past five years. During this period, with the exception of 2002–03, extraction was between 500 and 800 GL per year. Most extraction occurs from these major inland alluvial aquifer systems which provide high-yielding good quality supplies and are used extensively for irrigation. Since the 1980s, an embargo on further licences has been in place in these systems, and annual limits placed on extractions.

Figure 5.5: Groundwater extraction in major inland alluvial systems in NSW

Source: DNR data 2006

The major inland alluvial systems shown in Figure 5.5 represent approximately 80% of the total groundwater extraction across NSW. The total sustainable yield is that amount of the long-term average annual recharge that can be extracted each year without causing unacceptable impacts on the environment, aquifer integrity, or other groundwater users.

A peak in usage in 2002–03 can be attributed mainly to drought conditions. Subsequent years have also been impacted by the drought. However, many groundwater irrigators accessed their carryover water entitlement in the 2002–03 water year, but not in following years, and would also have been subject to lower annual allocations. Usage in 2003–04 and 2004–05 has therefore returned to lower levels, although it still slightly exceeds total sustainable yield.

To ensure the future sustainability of groundwater sources, the levels of entitlement and extraction need to be managed to the sustainable yield.

Map 5.5 shows the relationship between water extraction and sustainable yield. Areas where over-extraction has occurred regularly include the lower Namoi alluvium, some zones in the upper Namoi alluvium, and in recent years the lower Murrumbidgee and lower Lachlan alluvium. The Great Artesian Basin, underlying a large proportion of north-western NSW, is not over-allocated; however, this system has lost pressure in some areas due to free-flowing bores. The aquifers in the rest of the State are not over-extracted.

Map 5.5: Groundwater extraction as a percentage of sustainable yield for NSW aquifers

Source: DNR data 2005

Notes: Because only high-yield bores are required to be fitted with a meter, some usage data has been estimated.

Response to the issue

The Water Management Act 2000 requires all aquifers to be managed within their sustainable yield and this will occur through the implementation of statutory groundwater-sharing plans. Five groundwater-sharing plans for coastal groundwater sources commenced in 2004. Plans for five over-allocated major inland alluvial systems commenced in late 2006, with one remaining plan to be commenced in early 2007.

A draft plan for the Great Artesian Basin is also being finalised. Macro water-sharing plans are being developed to cover the remainder of the State with the exception of the Peel Valley alluvium and the Border River alluvium, which will be completed later. All plans aim to achieve sustainable extraction before or by the end of the 10-year life of the plan.

Groundwater usage in the major alluvial systems has stabilised over the last two years. The implementation of water-sharing plans should see usage reduce further and return to more sustainable levels. The plans allow individual licence holders to reduce their usage to sustainable levels over a 10-year plan timeframe.

Eventually all groundwater systems will be subject to water-sharing plans, which will ensure that entitlements are brought into line with the sustainable yield of the aquifer. In the major alluvial aquifers where the sustainable yield is regularly exceeded, extractions are being managed by reducing the announced allocations. For example, annual allocation announcements for the major over-extracted systems ranged from 52% to 100% of entitlement. This type of management aims to hold usage at current levels until water-sharing plans commence in these areas.

Since the 1990s, various programs have been in place to cap and pipe bores across the Great Artesian Basin underlying parts of Queensland, SA and NSW to reduce water wastage and improve groundwater pressure. This basin is one of the largest underground water sources in the world. In 2004–05, the Commonwealth and State governments finalised the Great Artesian Basin Sustainability Agreement to jointly fund the $32-million Cap and Pipe the Bores Program until June 2009. The program provides financial incentives to landholders to offset the cost of rehabilitating bores and installing efficient piped systems. By 2006, almost 40,000 megalitres (ML) of water had been saved. In 2003–06, 20,000 ML alone was saved through the rehabilitation of 83 bores and installation of over 4500 kilometres of pipelines to replace open drains on 344 properties. It has been predicted that groundwater pressure would have increased by the equivalent of 16 metres as a result.

In 2006, it was announced that two separate underground aquifers near Sydney have the potential to supply up to 30 GL per year for three years, as part of the NSW Government's strategy to secure Sydney's long-term water supply in drought. Further investigations are continuing.

Other programs to manage groundwater include work by the Government to improve understanding of the relationship between surface water and groundwater and the impact of groundwater extraction on river systems. Current programs are identifying where groundwater systems are highly connected to surface water systems; future management of such systems will be more closely linked to surface water management.

The statewide natural resource management target for groundwater is: 'By 2015 there is an improvement in the ability of groundwater systems to support groundwater-dependent ecosystems and designated beneficial uses'. The available data may be used as a baseline measure of this target in some parts of NSW, but there is a need for further data on a statewide basis to provide a full picture of progress towards the target.

Future directions

Current knowledge of groundwater recharge and availability is based on estimates using the available data and conceptual models of groundwater systems and recharge. Continued monitoring of extraction will improve the basis of these models and enable greater accuracy when setting extraction limits.

More comprehensive metering needs to be available for extraction in groundwater management areas in NSW. Currently, irrigation and high-yield bores must be metered, but in many groundwater management areas meter readings are not reported. Although the quality of data about groundwater use has improved, more information is needed to fully assess the status of groundwater extraction and manage any subsequent impacts on resource security.

The connections between groundwater and surface water systems need to be better understood. The potential for managing very closely linked systems as a single resource needs to be further developed. There is a risk that more stringent limits on the use of surface water will put more pressure on groundwater as a substitute source.

A better understanding of groundwater-dependent ecosystems is required (see also Biodiversity 6.6). Little is known about the fauna and flora that live within aquifers, or about the volume or water levels they require. This makes it difficult to manage groundwater systems appropriately for conserving dependent biota. In many cases, aquatic ecosystems depend on a certain water level being maintained in the upper, shallow aquifers.