About the area
- The Werribee basin is located west of Melbourne. The Werribee and Lerderderg Rivers meet upstream of Melton Reservoir and flow through Werribee before entering Port Phillip Bay.
- Annual rainfall in the basin is over 900 mm in the headwaters of the Lerderderg River, but only averages 400-600 mm annually in the rest of the catchment, resulting in low flows in many of the waterways during the summer months.
- The flow regimes of rivers in the basin are highly regulated and water is diverted for irrigation and urban use.
More information on water management and accounting is detailed in Water .
2021-22 overview
Available water
Catchment inflow was higher than the previous year.
Licensed diversion restrictions
There were more restrictions on licensed diversions than the previous year.
Seasonal determinations
Werribee system reached 100% allocation to high-reliability water shares – the same as the previous year.
Water use
A similar volume of water was diverted for consumptive purposes to the previous year.
When compared to the previous year, in 2021-22:
- around the same amount of rainfall was received
- storage levels peaked at higher levels
- catchment inflows were higher – the highest received since 2016-17
- seasonal allocations for high and low-reliability entitlements reached 100% allocation 3 to 4 months earlier
- there were more restrictions on licensed diversions from unregulated streams
- a similar volume of water was diverted from the basin for consumptive uses.
Climate
Rainfall
In 2021-22, rainfall in the Werribee basin was above average in most areas, like the year before. Rainfall was:
- average in the north-west of the basin around Ballan and Lerderderg State Park
- above average in the rest of the basin from Bacchus Marsh down to the coast.
River basin water balance
In 2021-22, 17,174 ML of water was diverted for consumptive uses: town, domestic and stock, irrigation and commercial supply. This was similar to the 15,646 ML diverted in the previous year.
Water balance table
The table below shows the total volumes of water available and supplied from water resources in the Werribee basin in 2021-22.
Table 1: Water balance, Werribee basin
Storages
Major — greater than 1,000 ML — on-stream storages in the Werribee basin are included in the water balance.
Storage levels
Major on-stream storage levels in the Werribee basin were 63% on 30 June 2022.
Lower than the previous year
Storage levels in the Werribee basin were 76% on 30 June 2021.
Table 2: Storage levels, Werribee basin
Catchment inflow
Catchment inflow represents the volume of water flowing into the waterways of a basin. It is calculated to be the difference between the total outflows, the known inflows and the net change in storage volume.
Above average inflow received
Catchment inflow was 138% of the long-term average of 88,600 ML.
More than the previous year
This is higher than the previous year (98% of the long-term average).
Wastewater treatment plants
Water treated at wastewater treatment plants can be used to supplement water available in the basin. Water discharged to waterways from treatment plants is included as an inflow to the water balance.
Information on treatment plants is now reported in the Water Supply local reports for the water corporation responsible for managing the plant.
In this basin, wastewater treatment plants are managed by Greater Western and Melbourne .
Small catchment dams
Water harvested, used, and lost by small catchment dams (farm dams) is included in the water balance.
Table 3: Small catchment dams, Werribee basin
Entitlements and compliance
Entitlements provide the basis for how water is shared in the basin.
Entitlements to water in the regulated Werribee system provide for the right to carry over unused allocation to the next season. In the Werribee basin, entitlement holders can carry over unused water (except for 15% of the unused volume which is deducted for evaporation), and they can hold up to 100% of their entitlement volume. The VEWH holds an environmental entitlement in the Werribee basin, which also enables it to carry over unused water at the end of each year, subject to storage capacity and losses. The water available under the entitlement is used to provide environmental flows in the Werribee River and is not diverted out of the waterway.
Entitlement volumes
Rights to water in the Werribee basin are shown in table 4 below.
Entitlement volumes represent a maximum volume that can be taken in a one-year period. The volume available in a particular year is dependent on the rules for allocating water set out in the entitlement and the seasonal conditions in that year, which varies. The rules for allocating water under an entitlement can differ between entitlements and systems. This affects the ability and likelihood of water being taken in a particular year.
Table 4: Annual entitlement volumes at 30 June, Werribee basin
Available water and take under entitlements
Total water available under entitlements represents the volume of water that was available to be taken by entitlement holders in 2021-22. The volume includes carryover from the previous year, seasonal allocations and net trade into the basin.
Water taken
There was 17,266 ML taken under entitlements in 2021-22, more than the year before (15,513 ML).
Seasonal allocations and restrictions on licensed diversions from unregulated rivers
- High-reliability entitlement allocations reached 100% in September 2021 (4 months earlier than the previous year). Low-reliability entitlements reached 100% in January 2022 (3 months earlier than the previous year).
- In 2021-22, the Cockatoo and Shepherd Creek was restricted between February and March 2022. This is a higher level of restriction than the previous year when there were no restrictions on licensed diversions from unregulated streams.
Available water and take table
This table shows the volume of available water and the volume taken under entitlements in 2021-22.
More information on available water and take has been detailed in the How do we account for surface section on the How do we account for water page.
In 2021-22, more water was taken under entitlements than the previous year.
Table 5: Available water and take, Werribee basin
Compliance
Compliance against water entitlements is reported for this basin in three areas:
- entitlement issued: the volume of entitlements issued in a basin does not exceed formal caps, and has not increased without appropriate approvals
- water taken: the volume of water taken during the year does not exceed the volume considered to be available for consumptive and/or in-stream use during that year
- bulk entitlement provisions: holders of entitlements do not breach any provisions that are documented in their bulk entitlement orders.
Total entitlement volume
There was no net increase in the total entitlement volume from the previous year
Total volume diverted
The total volume diverted (17,266 ML) was within the volume available for the year (44,564 ML).
Individual bulk entitlements
No individual bulk entitlement holder took more than the annual volume made available to them.
Exceptions to compliance
Individual bulk entitlement holders complied with all provisions in their entitlements.
Water for the environment
Environmental watering sites
Environmental watering sites and environmental values in the Werribee basin that depend on water for the environment include:
- platypus that inhabit the lower reaches of the Werribee River
- the freshwater-saltwater interface of the Werribee River estuary: it is a regionally significant ecosystem, due to the many aquatic plants and animals it supports and its provision of nursery habitat for juvenile freshwater fish species and estuarine species (such as black bream)
- Australian grayling, tupong and red gums.
Environmental water reserve
In 2021-22, water for the environment in the Werribee basin comprised:
- the Werribee River Environmental Entitlement 2011 comprising 10% share of inflows (on average 1,500 ML per year) held by the VEWH in Lake Merrimu
- 734 ML of high-reliability water shares and 361 ML of low-reliability water shares held by the VEWH the environment in Melton Reservoir
- water set aside for the environment through the operation of passing flow conditions:
- on consumptive bulk entitlements held by Central Highlands Water, Greater Western Water and Southern Rural Water
- on licensed diversions (regulated and unregulated waterways)
- all other water in the basin not allocated for consumptive uses: this water also provides social, recreational and cultural benefits.
Environmental water use
In 2021-22, a total of 2,262 ML of environmental water was delivered in-stream in the Werribee basin.
Management responsibilities
Management of water in the Werribee basin is undertaken by various parties.
| Authority | Management responsibilities |
|---|---|
| Southern Rural Water |
|
| Greater Western Water |
|
| Melbourne Water |
|
| Central Highlands Water |
|
| Water supply system | 2021-22 (ML) | 2020-21 (ML) |
|---|---|---|
| Blackwood & Barrys Reef System | 54 | 54 |
| Main integrated system | 1,902 | 2,516 |
| Myrniong | 35 | 49 |
| Water supply system | 2021-22 (ML) | 2020-21 (ML) |
|---|---|---|
| Bacchus Marsh Irrigation District | 2,253 | 2,539 |
| Werribee Irrigation District | 10,322 | 8,575 |
