Victoria summary from water balances

For Victoria, water balances have been prepared for eight water management areas: Melbourne (incorporating the Werribee River, Bunyip River, Maribyrnong River and Yarra River water management areas), Broken River, Ovens River, Goulburn River, Moorabool River, Glenelg River, Wimmera River and Snowy River (an interjurisdictional area).

The Grampians, western Victoria, November 2005Image by Ann Kollmorgen

Key points

• While rainfall conditions across many of these catchments were close to long term average values, streamflows generally remained below long term averages.
• In most catchments, surface water volumes in large storages (i.e. >1000ML capacity) and reservoirs increased over the 2004-05 period, although in most cases volumes remained significantly below capacity. As such, a range of urban and irrigation water restrictions, particularly for surface water, were in place across the State. The water balances for these catchments highlight that in most Victorian water management areas; surface water was utilised for consumptive and irrigation purposes more than groundwater. Groundwater use was generally higher in catchments to Victoria’s west (e.g. Glenelg River).
• The Melbourne water supply area water balance differs slightly from the other catchments in that items relating to stormwater run-off in urban areas and volumes captured by rain tanks have been included in the surface water component of the balance. These components are a significant component of surface water outflows in developed urban areas, but are probably less relevant in rural catchments.
• Much of the information contained within the water cycle reports has been sourced from the Victorian State Water Report 2004-05. Reliable information on surface water storage volumes, inflows and extractions is available for all catchments. In addition, REALM models have been developed for most catchments, enabling estimates of in-stream infiltration to groundwater and flows to floodplain to be calculated with a fair degree of reliability (i.e. ±25%).
• Figures for evaporation from open water (other than large reservoirs and storages) and wetlands generally have a data code ‘D’, meaning they were derived without investigation data. Evaporation data for minor dams was not available.
• Reliable information on groundwater inflows and outflows in most catchments is generally lacking. In particular, there is little information available on groundwater storage volumes, groundwater-surface water interaction (particularly baseflow volumes) and groundwater discharged to evaporation. Also, groundwater usage is generally un-metered, particularly in unincorporated groundwater management units. This has lead to large error terms in the groundwater component of the water balance for many catchments.
• In Victoria, groundwater management areas and water supply protection areas are currently managed using extraction rates and groundwater levels, rather than volumes in aquifers. An assessment of changes to groundwater storage volumes over a period can be made by comparing management trigger groundwater levels with representative hydrographs from the aquifer. With the exception of the Shepparton WSPA in the Goulburn catchment, this information was not available for Victorian priority catchments. Many groundwater management units are located in more than one water management area. This presents further difficulties in estimating groundwater storage volumes and groundwater usage within the catchment.
• In unincorporated groundwater management areas the level of groundwater use is very low, therefore the risk is also low and does not warrant more intense management.
• Programs are currently in place to increase the water metering (of both unregulated surface water and groundwater). All new licences for commercial or irrigation use are required to be metered and funding incentives are available for installation of meters on existing significant un-metered water extractions.
• The lack of baseflow figures, particularly in areas where groundwater-surface water interaction is significant, may lead to ‘double counting’ of some water. In the Ovens catchment, the significant volume of groundwater discharged to streams has been recognised by the managing authorities and this catchment will be the first in Victoria managed with a conjunctive management plan for surface and groundwater in the near future.
• In Victoria, all water that is not otherwise allocated for consumptive use is allocated to the environment. Since 2006, the DSE have included an environmental reserve in their allocation framework, giving rivers a legal share of water for the first time.
• Indications from stakeholders suggest that the water balances for Victoria are of marginal benefit, given the existence of State Water Report 2004-05. However, the incorporation of groundwater into the water balances (which is not done in the State Water Report 2004-05) is seen as being beneficial in highlighting the importance of groundwater/surface interactions. The layout of the water balances is also expected to assist in the identification of data gaps.

Further discussion of the water balances for Tasmania is provided in the Water Availability National Perspective report, and the Regional Water Balances report, which are both available on the Publications page.

For individual results of water balance assessments go to Regional Water Resources Assessments

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