Case study 1 managing groundwater in the Murray Darling Basin

The profile of issues associated with surface water-groundwater interactions is perhaps best represented by the interjurisdictional activities that are in progress in context of the MDB (the catchment for the Murray and Darling rivers; Fig. 15.2). The MDB covers 1,061,469 km2, and includes almost three-quarters of Australia's total irrigated land. About 70% of water used for agriculture in Australia is for irrigation in the MDB. The MDB extends over three-quarters of NSW, more than half of Victoria, significant portions of Queensland and SA and includes the whole of the Australian Capital Territory.

States retain responsibilities for natural resource management. The MurrayDarling Basin Commission (MDBC) is an interjursidictional institution established 'to promote and coordinate effective planning and management for the equitable, efficient and sustainable use of the water, land and other environmental resources of the Murray-Darling Basin' (MDBMC, 1992). The Commission reports to a ministerial council comprising ministers from each of the jurisdictional governments (including the Commonwealth) and a representative of the MDB community. Resolutions of the council require a unanimous vote.

The story of surface water allocation, the Cap on surface water in the MDB, has been presented earlier in this chapter; these policies were based specifically on river management and as such took no account of groundwater (MDBMC, 1996). Concerns relating to irrigation-induced salinity had been registered as early as 1911 within the MDB (Wilkinson and Barr, 1993). Accordingly, initial MDBC interest in groundwater was associated with water quality management and the impact of salinity to in-stream water quality - this interest subsequently expanded to encompass concerns regarding the mobilization of salts from dryland farming areas.

Fig. 15.2. The Murray-Darling Basin.

In 1996, a technical report (MDBC Groundwater Working Group, 1996) was released with the aim of 'progressing the setting of policy and programs to achieve a higher utilization of groundwater within the Basin's water resource allocation'. This report was followed in 1998 by another, which specifically outlined the impact that limited access to surface water would have on demand for groundwater, and the need to manage potential hydraulic impacts between surface and groundwaters (MDBC Groundwater Working Group, 1998). This report fed into general concerns that groundwater development could threaten river base flows - an impact with potential to thrust groundwater management into the central quantitative concerns of Cap agreements. The three means by which groundwater management may threaten the integrity of the Cap are (Fullagar, 2001):

1. reduced quantity of base flows through interception;

2. reduced quality of base flows through poor salinity management;

3. reduced capacity for governments to remain committed to the Cap in the event where viable alternative water supplies are lost.

A number of strategic studies were initiated to assess associated risks. These studies looked at: (i) the projection of groundwater extraction rates and implications for surface water; (ii) estimation of base flow in unregulated catchments of the MDB; and (iii) a review of groundwater property rights in Australia.

To provide a more comprehensive picture of water consumption within the MDB, the annual MDB Water Audit Monitoring Report (1999) began including groundwater consumption statistics in 1999/2000. Subsequent records (see Table 15.7) show a general increasing trend in groundwater consumption within the MDB, which peaked in response to the critical drought conditions of 2002/03.

The Review of the Operation of Cap (MDBCMC, 2000) found that the Cap had been a critical 'first step' in sustainable management of river resources in the MDB. The report included a recommendation to develop a groundwater management strategy for the MDB based on:

• jurisdictional management of sustainable yields;

• investigations clarifying how groundwater management practices may impact upon the integrity of the Cap in the future.

MDBC (2003) publicly released a report estimating an average reduction in surface water flow of 600 million litres for every 1000 million litres of groundwater use (Sinclair Knight Merz, 2003). Under groundwater development of the time, this amounted to a 2% undermining of the Cap, which was projected to increase to 7% in 50 years.

While the geological history of alluvial aquifer development implies some hydraulic relationship between groundwater and surface water, quantifying the potential for 'double allocation' is complicated by management and planning time frames, and time lags between groundwater flows and streams. Perhaps the most significant aspect of this work is the proactive manner in which the multiple jurisdictions have acknowledged and agreed to progress with a highly technical and political issue. This cooperation highlights the political i mportance

Table 15.7. Reported water use (GL) in the MDB 1999-2004.

Year

1999/ 2000

2000/01

Annual growth

2001 /02

Annual growth

2002/03

Annual growth 2003/04

Annual Growth growth 1 999-2004

Ground water Surface water Total

Ground water % total

1,103 8,973 10,076

1,240 11,369 12,609

10.9

10.8

(capped)

1,632 7,445 9,077

14.39

(capped)

(capped)

CO CO

given to ensure the long-term viability of existing surface water agreements underpinning management of the MDB. More broadly, groundwater interest within the MDBC structure is indicative of a wider interest in recognizing and realizing any potential environmental and/or productive opportunities associated with conjunctive water management.

Investigations associated with the development of an MDB groundwater management strategy continue. Consistent with broader water reforms, the primary focus of this research is to:

• establish consistent approaches to calculating sustainable yields for aquifers within the basin;

• build a framework for managing the combined use of surface and groundwaters;

• develop tools to help manage external groundwater impacts from irrigated areas;

• develop an approach to manage groundwater systems that have been overallocated;

• establish an evaluation process to help monitor and report progress against benchmarks and targets for managing groundwater resources.

In the following section, we focus on the development of groundwater policy at state level, with the case of NSW, and then take a more detailed look at an interesting example of efforts to bring an overexploited aquifer system back to sustainable levels in the Namoi Valley, which lies in NSW to the north of the MDB.

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