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. Due to the continually high water levels (until 2016), tall reed communities have expanded in their preferred conditions, whilst a number of other vegetation communities that rely on low water levels or periodic inundation, including the nationally vulnerable coastal saltmarsh, have been out-competed by the tall reeds. At some point, these threatened vegetation communities may be lost from the system forever and will not be able to recover, regardless of watering activities.

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.

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 2019-20

Reedy Lake

2019-20 is the fourth year of the four-year watering cycle, and it is therefore planned to keep the wetland full over summer after the proceeding three years of partial drying. Levels will be maintained at approximately 0.8m with some natural variation, through the 19/20 summer period and through to the end of Spring 2020.

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 to 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 drawn down in early summer to promote a drying event, before refilling in Autumn 2020.

Flow component & timingFlow Objectives
Winter fill
(March/April to September)
• Initiate Stuckenia and Chara growth
• Initiate decomposition of organic matter on wetland bed
• Dilute accumulated soil and surface water salts
• Create habitat for invertebrate populations
• Stimulate fish and waterbird breeding
• Allow fish to colonise wetland from the river
Spring high flow
(September to November)
• Continuous flushing of salt from deep wetland basins
• Inundation of reedbeds and Bolboschoenus beds fringing the main basin
• Sustain growth of Stuckenia and Chara
• Promote growth of Myriophyllum in southern part of main basin
• Waterlog Gahnia filum sedgelands
• Stimulate fish and waterbird breeding
• Stimulate increase in invertebrate populations and biomass
• Create nesting habitat for colonial and other waterbirds.
• Continuous flushing of salt from deep wetland basins
• Inundate shallow wetland basins and promote growth of Ruppia
• Inundate Gahnia filum sedgelands
• Create additional fish and waterbird habitat and invertebrate populations
• Trigger fish spawning
• Provide connecting flows to the river and between wetlands
Early summer lowering of water levels
(December to January)
• Increase wetland salinity as groundwater discharge increases in proportion to surface water
• Shallow wetland basins exposed (creates open water habitat upon refilling)
• Restart wetland processes
• Allow egg banks to be produced and laid
• Provide waterbird food supply from access to tubers, seeds and invertebrates in shallow water
Allow wetland bed to dry
Late summer – Autumn (February to March/April)
• Soil salinity increases in shallow wetland basins and deep wetland basin
• Chara and Stuckenia die back
• Limited colonisation of wetland bed by annual herbland plants
• Reeds and other emergent macrophytes become dormant
• High soil salinity excludes reeds
• Expose mudflats for waterbird feeding
• Allow nutrient re-cycling
• Control carp populations and threat

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