Lower Barwon wetlands

The Barwon Basin and the Lower Barwon Wetlands.
This map includes the Moorabool catchment, a major tributary of the Barwon River
(VEWH, 2015)

The Barwon River rises in the Otway Ranges and flows through Geelong, joining the ocean at Barwon Heads. It includes significant inflows from major tributaries, including the Moorabool and Yarrowee-Leigh Rivers, which rise in the Victorian Central Highlands region of the Great Dividing Range.

Prior to entering the sea, the Barwon River drains through a large estuarine zone comprising a lake and wetland complex including Lake Connewarre, Reedy Lake, Hospital and Salt Swamps, Murtnaghurt Lagoon and the Barwon River estuary at the river mouth.

The wetlands are connected by various degrees to the Barwon River and/or Lake Connewarre, which lies centrally in the complex.  These wetlands form part of the internationally significant Port Phillip Bay (Western Shoreline) and Bellarine Peninsula Ramsar Site.

The wetlands consist of a diverse range of aquatic vegetation communities, providing important feeding and breeding habitat for native fish and a number of wetland-dependent bird species, including a number of rare and endangered flora and fauna.  It is a culturally significant area for Wadawurrung Traditional Owners. Culturally sensitive areas persist as it has long been a place of sourcing food and artefacts.  Within the Lower Barwon Wetland Complex, environmental water can be actively delivered to and from Reedy Lake and Hospital Swamps, which lie within the Connewarre State Game Reserve managed by Parks Victoria.

A flow ecology investigation was undertaken by Lloyd, et al. in 2012 to identify the most appropriate watering approach for Reedy Lake and Hospital Swamps based on maintaining the ecological character of the wetlands. The watering regime at each wetland should be considered as a whole. All watering actions, whether they be wetting, drying or connecting flows contribute to a balanced ecosystem.

Reedy Lake

Reedy Lake’s biodiversity includes 16 ecological vegetation communities (EVCs), such as coastal saltmarsh, herbfields, sedgelands, open water (semi emergent/macrophyte communities) and reed beds, which all play an important role in providing habitat diversity for a variety of flora and fauna species.

Maintaining the ecological character of the wetland requires a balance between these vegetation communities. Wetting and partial drying regimes produce a mosaic of different habitat types as the water availability fluctuates providing specialist habitat for a wide variety of different flora and fauna to utilise. Productivity at wetlands adapted to a wetting and drying regime, such as Reedy Lake, is driven by the disturbances caused by fluctuating water levels, occasional periods of high water and occasional periods of very low water.

The findings from the flow ecology investigation (Lloyds et al, 2012) recommended that the lake’s watering regime be modified to include more regular lowering of water levels to restore the site’s threatened ecological values. The recommended watering regime is a four-year water cycle, which includes low water levels over summer for 3 years, and a full water level in the fourth year (Figure 6). All four years include a full water level in winter. These recommendations have been subsequently supported by two further independent expert reviews.

Hospital Swamps

The Hospital Swamps ecosystem has retained its ecological character and biodiversity values predominantly due to the regulated management (by graziers and others) of the natural wetting and drying regime since the 1970s (Lloyd, et al. 2012). 

Lloyd, L.N., Cooling, M.P, Kerr, G.K., Dahlhaus, P. and Gippel, C.J., 2012. Flow/ecology relationships and scenarios for the lower Barwon Wetlands environmental entitlement

Since the entitlement was established in 2011, the CCMA has continued to implement the historical wetting and drying regime.  Variable climatic conditions over the past seven years have also provided a level of seasonal fluctuation in conditions, which provides additional environmental benefits to existing watering activities (i.e. floods, fresh events and extended drying events).

As a consequence, the wetland’s internationally significant waterbird population and diversity has been maintained and the diverse ecological vegetation communities have remained largely unchanged since the 1980s. The water regime of Hospital Swamps is seen as currently beneficial to the ecosystem values of the site (Lloyd, et al. 2012). The environmental values of the wetland are in good condition, supporting large areas of threatened subtropical and temperate coastal saltmarsh and a diversity of fish and waterbird populations. The recommended watering regime for Hospital Swamps is to continue the wetting and drying regime below, nine out ten years. In the tenth year, it is recommended to maintain the wetland dry or shallow flooding all-year round .

Watering Priorities 2020-21

Reedy Lake

For Reedy Lake, with a full wet year recently achieved, the water actions for 2020-21 will involve partially drawing down Reedy Lake in summer guided by the patterns of Barwon River flows where possible, with timing also informed by monitoring of breeding birds. The wetland will be re-filled in mid-April to early May 2021.

Flow component & timingRationale
Winter fill
(Continue to) Maintain a full wetland to 0.8m AHD
July to December 2020
Following the 2020-21 summer full lake level, maintaining the full level over winter is in line with higher winter/spring rainfall and flows in the Barwon River. It will support breeding events and increase spring feeding for waterbirds.
The high-water level will also maintain fish breeding, movement and recruitment.
Drawdown
Gradually reduce water levels to approximately 0.3 m AHD by natural evaporation and assisted draw down (if required).
December 2020 to mid April early May 2021
A draw down no earlier than December, will support waterbird and frog breeding and will also provide muddy margins for migratory shorebirds when it is most needed between January and March.
The slow evaporative drawdown rate, assisted by active draw down if required will reduce the risk of disruption to any breeding marsh birds or colonial nesting birds. The exact timing of draw down commencement will be informed by bird monitoring.
Assisted drawdown will be employed if water levels are not dropping sufficiently to provide muddy margins through January – March.
Top Ups
Maintain a lake level of approximately 0.3m AHD via tops ups from the Barwon River, or via tidal inflows through the outlet.
December 2020 to mid April/early May 2021
Top ups may be required to prevent complete drying. Preference is given to tops ups from the river to maintain the level at 0.3m, because opening the outlet, while preventing complete drying, could allow levels to get as low 0.1m on low tides.
Drain overbank flows
Restart drawdown following overbank flows in summer, if any.
December 2020 to mid April/early May 2021
Some assisted drawdown may be required again, if overtopping flows temporarily halt or reverse the draw down or increase levels too high above the 0.3m AHD summer hold point.
Autumn refill to 0.8m AHD
Begin mid April/ early May 2021
Given most migratory shorebirds depart between mid-March and late April, the low water level (0.3m AHD) is important to ensure that there are mudflats available prior to this to allow them to prepare for migration.
Ducks are expected to be utilising the wetland at lake level of 0.3m before water levels are increase, because there will still be expanses of shallow water favoured by most duck species at this level. Subsequent influxes of fresh water (from mid-April/early May) are expected to attract further influxes of ducks before June.

Hospital Swamps

Hospital Swamps will be maintained at a full height of approximately 0.5m AHD over the winter and spring periods with as much connectivity to the Barwon as possible, without straying too far from this level. Some natural variation around 0.5m is good for the system and will be permitted.

As in recent years the wetland will be partially drawn-down in early summer guided by the patterns of Barwon River flows where possible, before refilling in in early winter 2021.

Flow component & timingRationale
Winter fill
Maintain a full wetland at 0.5m AHD
May 2020 – September 2020
This action allows the wetland to fill in winter, in line with increased flows in the Barwon River.
Spring high flow
Allow flow freshes to flush the wetland.
(September to November 2020)
This action occurs naturally. Flow freshes will inundate shallow wetland basins and vegetation beds, flush salt and biomass and provide connecting flows to the river and between wetlands.
Early summer
Drawdown to a level of less than 0.3 m AHD by the end of January
(December 2020 to January 2021)
Allowing water levels to drop gradually, mimics natural dry out as flows in the Barwon River decrease.
Late Summer
Allow wetland to draw-down further in late Summer/Autumn
(February to March/April 2021)
Further drying allows salts to accumulate over a greater area and prevent reed establishment.
Early Winter Fill to 0.5m AHD
(May to September 2021)
Allow wetland to fill with moderate to high flows in the Barwon River, mimicking historical conditions.

Increasing knowledge of the Lower Barwon

Monitoring stations are located at Reedy Lake and Hospital Swamps. Corangamite CMA can monitor the height of the water, electrical conductivity (EC), temperature and dissolved oxygen (DO) at these sites.

The Arthur Rylah Institute also conducts ongoing monitoring at Reedy Lake to track changes in the vegetation communities, as part of the state-wide WetMAP (Wetland Monitoring and Assessment Program). 

In 2018-19 a program of risk monitoring was commenced, focusing on metals, pH and associated water quality parameters to pick up any trends that might indicate an activation of acid sulphate soils in the wetland.

Reports

Seasonal Watering Proposal

Lower Barwon Wetlands Community Advisory Committee

The Lower Barwon Wetlands Community Advisory Committee has been established to provide feedback on planned water management in the Lower Barwon Wetlands from a community perspective. The committee will provide an honest and open environment for concepts, issues and knowledge to be shared in a safe and collaborative environment.