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 Lower Barwon Review, conducted in 2020 to review the adopted watering regime, supported the wetting and drying regime with the advice to initiate a gentler, more evaporative draw down at Reedy Lake. In addition, it recommended going no lower than 0.3m AHD if possible and using bird monitoring information to inform the timing and rate of draw down.
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’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.
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 .
For Reedy Lake, with full wet years recently experienced, the planned watering actions for 2022-23 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 2023.
|Flow component & timing||Rationale|
|Autumn refill to winter full of approximately 0.8m AHD from April, topping as required and allowing for some natural variation.||The current recommended water regime for Reedy Lake involves a full wetland every winter and spring, and a partial draw down over summer in 75% of years. This watering action is in line with that advice, and is not influenced by watering in previous years. 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. A full wetland through winter and spring will support breeding events and increase spring feeding for waterbirds.
The high-water level will also maintain fish breeding, movement and recruitment.
Draw-down to summer low- gradually reduce water levels to approximately 0.3 m AHD by natural evaporation or flow through adjustment and assisted draw down (if required). Topping or drawing down as required to maintain approximately 0.3m AHD. From December to May (as informed by bird monitoring).
|A partial summer draw down is recommended in 75% of years.|
In 2020-2021 draw down was delayed and full draw down not achieved, due to probable breeding of Australasian bitterns. In the 2021-22 water year Reedy Lake did not achieve draw down again. This would makes 3 full years in a row. Draw down in summer for 2022-2023 will still be the priority in line with drawing down 75% of years.
A draw down no earlier than December will support waterbird and frog breeding and it is aimed to provide muddy margins for migratory shore birds when it is most needed between January and March.
A slow draw down rate will reduce the risk of disruption to any breeding marsh birds or colonial nesting birds. Exact timing of draw down commencement will be informed by bird monitoring.
A faster draw down will be employed if water levels are not dropping sufficiently to provide muddy margins through January-March or later, depending on breeding activity.
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 2023.
|Flow component & timing||Rationale|
|Autumn refill to winter full|
Fill and maintain a full wetland at 0.5m AHD
from April to at least December
|The current watering regime recommended for Hospital Swamps involves drawing down the wetland over summer and refilling in autumn to provide a full wetland through winter and spring, most years. This watering action is in line with that advice and is not influenced by watering in previous years.|
Gradually reduce water levels to approximately 0.1m-0.3 m AHD from December to May. Topping up or drawing down as required to maintain 0.1-0.3m AHD.
|The system is recommended to have a wetting and drying cycle most years, meaning a summer draw down in 2022-23. A draw down no earlier than December will support waterbird and frog breeding (where present) and will also provide muddy margins for migratory shore birds when they are most needed between January and March.|
Specific timing of draw down will be informed by water bird monitoring for breeding (if possible). It will be slow in early summer to mimic natural dry out as flows in the Barwon decrease. However, if draw down at Hospital Swamps is delayed due to bird breeding, a faster draw down may be carried out to make sure some muddy margins are provided to migratory waders through January-March.
Where draw down at Hospital Swamps is delayed, offset habitat may be available at other nearby wetlands such as the CoGG-managed Sparrovale wetlands.
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 has also conducted 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.
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.
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