Introduction

The Upper Murray River Basin forms the catchment of Hume Reservoir and covers an area of 15,280 km² in New South Wales and Victoria. The Victorian portion of the catchment, covering an area of 10,150 km², has been subdivided into two components: the Mitta Mitta River catchment and land draining to the Victorian bank of the Murray River.

The Mitta Mitta River SWMA is located in north- east Victoria and covers an area of 6,250 km? (2.7% of the State). The area extends from the Murray river in the north, to the Great Dividing Range in the south and is bordered by the Kiewa River Basin in the west and the Upper Murray River (VIC) SWMA in the east. The topography of the area is mainly mountainous and consists of alpine peaks and plateaux and highly dissected valleys. Victoria's highest peak, Mt Bogong, is located on the south-west boundary of the area. In the south of the area around Omeo, a more moderate topography exists which includes upland plains and hills.

The main stream network is the Mitta Mitta River, with major tributaries including the Big, Bundara and Cobungra Rivers in the headwaters of the basin and the Gibbo, Dart and Tallangatta rivers in the centre of the Basin. The main storage in the SWMA is Lake Dartmouth, which serves consumers supplied from the Murray River. Lake Hume is located at the furthest downstream point of the management area and regulates water from the Mitta Mitta River and the Upper Murray River Basin, which is supplemented by water from the Snowy River.

Lake Dartmouth was completed in 1980 with a capacity of 4,000,000 ML, which is approximately four times the mean annual. inflow to the storage. It acts as a carry- over storage for drought security, supplementing Lake Hume. The dam incorporates a hydroelectric power station through which all releases are passed.

Lake Dartmouth is a popular location for recreational boating and fishing.

The climate is temperate and average annual rainfall in the SWMA ranges from over 1500mm in the alpine areas to about 700mm at Omeo and 700 mm where the Mitta Mitta River enters Lake Hume. The highest annual rainfall in the catchment is 2,400 mm at Mt Bogong.

The mean annual flow of the basin is 1,439,000 ML, which represents 7.1 % of the total runoff generated in the State.

In the north of the management area, broad alluvial valleys exist around the Mitta Mitta and Murray Rivers in the vicinity of Lake Hume. Major land uses in the Management Area include Water Conservation Forestry, dairying, sheep for meat and wool and beef cattle.

Average annual surface water use is 20,835 ML with urban/industrial representing 3% of total use, irrigation 95%, 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).

All consumption is supplied from within basin resources. There is no imported water.

In addition to the volume of water diverted for use within the management area, 577,000 ML of water is released on average each year from Lake Dartmouth for supply to the New South Wales Murray River water users and to supply NSW share of South Australian requirements.

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:

While Victoria has a variety of programs under way aimed at identifying, improving and protecting environmental water requirements, the necessary investigations take considerable time and resources.

Given the short time frame of the Audit, 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.

Within the Murray Darling Basin, sustainable yields were determined in the context of the 1996 agreement to cap diversions within the Basin at 1993/94 levels of development. By ensuring that diversions in the Murray-Darling Basin will not increase, the Cap protects the security of supply of existing users at a regional scale while, in effect, defining the remaining water as an environmental allocation. The sustainable yields for the SWMAs located within the Basin were reported as the average annual diversions from each SWMA with the Cap in place. The average annual diversions were estimated using water resource allocation models (REALM) of the relevant water supply systems. It should be noted that the Cap is a critical first step in countering ecological degradation. To halt degradation fully it may need to be lowered (and therefore sustainable yields may need to be redefined), but it is too early to tell whether this is the case.

This approach assumes that the current environmental water provisions represent the maximum volume of water that can currently be made available to the environment after consideration is given to the rights of existing users, and related social and economic impacts. In some situations these provisions may not fully meet the environments requirements.

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 Mitta Mitta River SWMA has been reported as fully developed (Category 3*) with respect to both allocation and diversion. This is consistent with the Murray-Darling Basin Cap, which sets the average allocation to equal the volume of water that would have been diverted under 1993/94 levels of development. 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 through improvements in distribution and water-use efficiency, or via use of alternative sources of water (e.g. reclaimed water).

How saline are the surface water resources in the Mitta Mitta River 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