The environmental entitlement for the lower Barwon wetlands does not provide access to water held in storage. Instead, it allows water to be diverted from the Barwon River into Reedy Lake and Hospital Swamps when river levels are above 0.7 m AHD. High water levels in the Barwon River can also result in natural inundation of the wetlands.
Environmental watering objectives in the Lower Barwon wetlands
Reedy Lake and Hospital Swamps form part of the internationally recognised Port Phillip Bay (Western Shoreline) and Bellarine Peninsula Ramsar site, which is used by many thousands of migratory birds from around the world. The wetlands support about 47 threatened plant and animal species and communities. These include some of Victoria’s rarest species (such as the brolga, orangebellied parrot, Australasian bittern, growling grass frog, Australian grayling and dwarf galaxias) and subtropical and temperate coastal saltmarsh communities.
Reedy Lake supports a range of vegetation communities including coastal saltmarsh, herbfields and reed beds. Reedy Lake was a partly-ephemeral system, but river regulation meant the lake was permanently inundated from the 1970s until 2016. Permanent inundation favoured the reed bed community in the lake and over time it has increased its extent and replaced much of the coastal saltmarsh and herbfield communities and open-water habitat. While reed beds form an important part of the lake’s ecosystem, their continued expansion has reduced habitat diversity and the number and diversity of internationally-important migratory waterbirds that are able to use the wetland.
The Corangamite CMA and the VEWH have implemented the first three years of a four-year watering regime at Reedy Lake which includes three years of partial summer/ autumn drying and one year of full summer inundation.
The new water regime has already helped to control carp numbers and improve conditions for communities of coastal saltmarsh and herbfields. Achieving a more natural wetting and drying regime will continue to improve the ecology of the lower Barwon wetlands.
Hospital Swamps is made up of five unique wetland basins that support important ecological processes and significant ecological values including large areas of threatened coastal saltmarsh and diverse waterbird populations. Vegetation communities in Hospital Swamps have remained largely unchanged over time due to the maintenance of natural wetting and drying cycles.
Hospital Swamps and Reedy Lake underwent a wetting and drying regime in 2018–19. Water levels in the wetlands peaked in July 2018 in response to localised rainfall. High water levels in winter promoted major fish breeding and recruitment opportunities and supported the growth of vegetation, which provides summer feeding habitat for waterbirds.
Structures that control inflow from Barwon River to the wetlands were closed in November 2018 to allow water levels to draw down slowly over summer. The outlet structure at Reedy Lake was opened shortly after, to allow water levels to fluctuate with tidal influences.
The inlet structures remained closed for longer than normal, because at the end of the planned wetland drying cycle water levels in the Barwon River were below the permissible level of diversion (0.7 m AHD) at the lower barrage gauging station. The inlet structures were opened in late March 2019 and temporarily closed in April 2019, again due to low river levels.
Scope of environmental watering in 2019-20
Table 1 shows potential environmental watering actions and associated environmental objectives.
Potential environmental watering action
Functional watering objective
Autumn/winter/spring fill and
The inlet to Reedy Lake will be opened in autumn in response to a sustained
Autumn/winter/spring fill and top-ups (during March and April to December)1
Hospital Swamps will be connected to the Barwon River for at least six weeks by keeping the inlet and outlet open
Summer/autumn drawdown (during December to March and April)
1 Water can only be diverted into the lower Barwon wetlands when water levels in the Barwon River are above 0.7 m AHD at the Lower barrage gauging station, in line with provisions for accessing water conditions of the environmental entitlement.
Table 2 shows the partners, stakeholder organisations and individuals with which Corangamite CMA engaged when preparing the lower Barwon wetlands seasonal watering proposal.
Seasonal watering proposals are informed by longer-term regional catchment strategies, regional waterway strategies, environmental flow studies, water management plans and other studies. These incorporate a range of environmental, cultural, social and economic perspectives and longerterm integrated catchment and waterway management objectives. For further details, refer to the Corangamite Regional Catchment Strategy and the Corangamite Waterway Strategy.
Over the last six years, the Corangamite CMA has consulted extensively about the planned watering regimes for Reedy Lake and Hospital Swamps with diverse stakeholders and interest groups representing over 1,500 people. These people have been involved in developing the original environmental flows study and in subsequent scientific work about ecological risks, vegetation monitoring, alternative management approaches and infrastructure operations. The results of this work show that lowering water levels at Reedy Lake is the only feasible management practice that will mitigate threats to the ecological health of the wetland and ensure all user groups can continue to use the system in future.
Table 3.7.6 Partners and stakeholders engaged in developing the lower Barwon wetlands seasonal watering proposal
|Partner and stakeholder engagement|