Introduction

The Thomson-Macalister Rivers SWMA is in south-eastern Victoria and covers approximately 4,597 km². The Thomson River flows from the Dividing Range and the Baw Baw and joins the Latrobe River to the south of Sale. The Macalister River flows from the Alpine National Park in the Snowy Ranges and joins the Thomson River between Maffra and Sale. The southern section of the basin is relatively flat and the Gippsland Plains are topographically uniform. The northern two thirds of the basin contains the mountain forests of the eastern highlands.

The Thomson, Macalister and Aberfeldy rivers constitute the major stream network in the basin. There are two major storages within the SWMA: Lake Glenmaggie, situated on the Macalister River 6 km north of Heyfield, and the Thomson Reservoir in the north- west of the SWMA on the upper reaches of the Thomson River.

Lake Glenmaggie, which was completed to its original capacity of 129,000 ML in 1929 and enlarged to 190,000 ML in 1958, is the main source of supply for the Macalister Irrigation District. The Thomson Dam, completed in 1982 with a storage capacity of 1,123,000 ML, more than doubled the total storage capacity of Melbournes water supply system. The storage is also used to supply the Macalister Irrigation District.

There is a marked rainfall gradient from the mountains in the north to the plains in the south- east. The mean annual rainfall varies from 1,200 mm at Walhalla in the north to around 600 mm in the south of the basin.

The mean annual runoff from the basin is 841,600 ML, which represents 4.2% of the total runoff generated in the State

Major land-uses include agriculture, which is concentrated around the Lake GlenmaggieHeyfield area and the Macalister River flats. Dairying is the main farming activity, mixed farming of beef cattle and sheep for wool and meat is also common, as is vegetable growing. Average annual water use within the basin is 178,920 ML; with urban and industrial use representing 1% of the total use, irrigation 97% and rural 2%. (Note: The reported volume of water used represents the total water consumed within the basin. This estimate of water use does not account for the volume of reclaimed or returned water and does not include water that is allocated for use in other management areas). An additional 230,060 ML is withdrawn from the basins surface water resources and transferred to the Latrobe River Basin, the Melbourne Water Supply System and the Avon River SWMA.

Vital Statistics:

A four-class classification system was developed to provide a simple method to communicate the status of the use and allocation of Australia's water resources in relation to sustainable water management.

It is important to recognise that adequately quantifying a sustainable flow regime or sustainable yield and consequent operating rules is a complex matter. State, Territory and scientific agencies continue to develop and apply methods and measures for determining sustainable flow regimes and sustainable yields.

This categorisation provides a general guide only. Please refer to the State and Territory Overview and Technical reports for detail on the analysis methods used.

* Water use as a percentage of sustainable flow regime (surface water) and sustainable yield (groundwater)

PLEASE NOTE:

Sustainable Yield:

Given the short time frame of the assessment, it was necessary to make some broad assumptions, and use a variety of approaches, to derive estimates of the sustainable yield for surface water management areas (SWMAs) in Victoria. Consideration was given to environmental water requirements (known and likely), existing user rights, and related social and economic impacts. The reported allocations to the environment represent the water that can currently be maintained or made available in an attempt to meet environmental water requirements.

For surface water management areas in the southern part of Victoria where environmental values could potentially be threatened by further allocations, the sustainable yield was limited to the current allocation volume, pending the outcomes of further detailed investigations of environmental water requirements.

The sustainable yield for the ThomsonMacalister River basin has been limited to the current allocation volume pending the outcomes of the Gippsland Lakes environmental study. The allocation volume was determined as the average diversion that would occur when all the entitlements within the basin are taken up. This was estimated using the REALM model of the Thomson- Macalister system.

In the longer term, there may be further scope for freeing up additional water to improve environmental regimes by improving distribution and water use efficiencies (other options for improving environmental regimes will be considered as part of the Victorian River Health Strategy). In SWMAs where a significant portion of the available resource is committed to a downstream SWMA, there is also potential for trading of entitlements between the two SWMAs. This will result in a change to both the sustainable yield and the environmental allocation in both SWMAs. Trade out of a SWMA would decrease the sustainable yield of the SWMA and a trade of water rights into a SWMA would increase the sustainable yield. However, the sum of the sustainable yields for the two SWMAs would remain unchanged.

PLEASE NOTE:

Categorisation:

The categorisation of SWMAs in terms of the current level of water resource development has been determined with consideration given to the level of allocation and actual diversion of the resource relative to the assessed sustainable yield.

Five development categories have been defined:

 Category 1: Low level of development: 0-30% Category 2: Medium level of development: 31-70% Category 3: High level of development: 71-99% Category 3*: Fully developed: 100% Category 4: Over allocated/used resource:>100% 

The development category for the ThomsonMacalister Rivers SWMA has been reported as fully developed (Category 3*) with respect to allocation and as highly developed (Category 3) with respect to diversion. This means that any further surface water-based development in the SWMA can only be achieved via trading of water rights, via water savings achieved distribution and wateruse of alternative sources of water

How saline are the surface water resources in the Thomson-Macalister Rivers surface water management area?

Table: Surface water resource by salinity class.

Major water storages

Table: Major water storage areas:

Further Information

• View the Victoria Water Resources Assessment 2000 Report
• View the Victoria Water Resources Assessment 2000 Technical Report
• Link to data available for download on the:
• Surface Water Management Areas
• Data from the 1985 Review of Australia's Water Resources and Water Use
• Link to the Map Maker to make a map using this information.
• For more information about water and other natural resource issues link to www.dse.vic.gov.au