VEWH - Upper Murray wetlands

This is the first year the upper Murray wetlands have been included in the VEWH’s seasonal watering plan and the first time water for the environment is planned to be delivered to the Ryans Lagoon wetland complex. The Ryans Lagoon wetland complex is a network of wetlands positioned downstream of the Lake Hume water storage and upstream of the Kiewa River confluence with the Murray River.

Flows into the complex are mainly influenced by regulated releases from Lake Hume, which travel via Ryans Creek, an anabranch of the Murray River. The complex begins to fill from Ryans Floodway when flows in the Murray River exceed 23,000 ML per day, but flows above 26,000 ML per day for extended periods are needed to completely fill both lagoons. High unregulated flows that move across the Kiewa River floodplain during wet conditions can also inundate the site. Since 2014, the maximum regulated flow from Lake Hume has reduced from 25,000 ML per day to less than 20,000 ML per day. These changes have greatly reduced the frequency of watering at Ryans Lagoon, which currently only fills if large, unregulated flows are released from Lake Hume or the reservoir spills.

Temporary pumps will be used to deliver water for the environment to restore the ecological health of the complex by providing a wetting and drying regime that is closer to the natural flow regime that existed before the regulation of the Murray River. Water can be pumped into Ryans Lagoon from the Ryans Lagoon floodway, which carries water when the flow in the Murray River exceeds 8,000 ML per day.

North East CMA is investigating options to improve watering regimes at other wetlands along the upper Murray floodplain.

Environmental values

North East CMA’s North East Waterway Strategy recognises the Ryans Lagoon wetland complex as a high-value wetland complex, and it is listed as a nationally significant wetland in the Directory of Important Wetlands in Australia. The complex provides habitat for species listed under the Commonwealth Environmental Protection and Biodiversity Conservation Act 1999 and the Victorian Flora and Fauna Guarantee Act 1988, including seven bird, three fish and one perennial plant species. Ecological surveys conducted at the site since 1975 have recorded 250 species of waterbugs and 29 species of waterbirds, including the Australian white ibis, great egret and rufous night heron. The complex also supports native wetland vegetation types that are expected to improve in condition once a seasonally aligned, more variable watering regime is re-instated.

Environmental objectives in the upper Murray wetlands

Restore carbon and nutrient cycling within the wetlands to increase ecosystem productivity

icon-objectives-fish

Increase the extent of fringing and aquatic vegetation

Provide feeding habitat for a range of waterbird species

Increase the abundance and diversity of waterbugs to support aquatic food webs

Traditional Owner cultural values and uses

Traditional Owners have lived for tens of thousands of years on the upper Murray floodplain. Wetlands in the region have immense cultural value to Traditional Owners, including those represented by the Dalka Warra Mittung Aboriginal Corporation, the Dhudhuroa Waywurru Nations Aboriginal Corporation and the Duduroa Dhargal Aboriginal Corporation.

North East CMA is building relationships with each corporation, and it aims to support Traditional Owners’ input to planned environmental flows at the Ryans Lagoon wetland complex in the coming years. In the long term, North East CMA aims to support the defined objectives of Traditional Owners for the complex and Traditional Owners’ obligations to Country more broadly.

Traditional Owners from Duduroa Dhargal Aboriginal Corporation have expressed an interest in developing a cultural plan for the Ryans Lagoon wetland complex. They have also communicated that they have little internal capacity or time to do so at present.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 5.2.1, North East CMA considered how environmental flows could support values and uses, including:

water-based recreation (such as fishing)
waterway recreation and amenity (such as birdwatching and camping)
community events and tourism (such as visitation by schools, Landcare groups and other community groups)
socio-economic benefits (such as incidental visitation to local towns and businesses).

Recent conditions

The upper Murray wetlands experienced above-average rainfall and temperatures for most of 2021-22. Inflows to Hume Dam were above average, and the storage reached 100 percent capacity in early spring for the first time since 2016. Additional water was released periodically from Hume Dam from September 2021 to create airspace and manage flood risk. These releases generated a peak flow in the Murray River below the dam of 33,000 ML per day in late November, which filled Ryans Lagoon 1 and partially filled Ryans Lagoon 2. This was the first time the site had received flows since 2016.

The desired watering regime for the wetland complex is to fill in spring each year and allow a partial drawdown over summer and autumn. The deeper parts of each lagoon are expected to retain permanent water that will support native fish populations, and the variable wetting and drying of the lagoons’ shorelines will improve the condition and diversity of wetland plant communities and promote carbon and nutrient cycling. The desired watering regime for the Ryans Lagoon wetland complex has only been achieved once in the past 10 years: in 2016-17. Flows that entered the complex between 2012-14 and again

in 2021-22 were insufficient to completely fill both lagoons. An ecological assessment in 2019 found the wetland complex to be in moderate-to-good condition but rated the flow regime as poor. Natural flows that partially filled the wetlands in 2021-22 are expected to have improved the overall condition of the complex. However, annual, temporary pumping to the site in future years will aim to reinstate a more natural water regime, to significantly improve ecological outcomes.

Scope of environmental watering

Table 5.2.1 describes the potential environmental watering actions in 2022-23, their expected watering effects (that is, the intended physical or biological effects of the watering action) and the longer-term environmental objectives they support. Each environmental objective relies on one or more potential environmental watering actions and their associated physical or biological effects.

Table 5.2.1 Potential environmental watering actions, expected watering effects and associated environmental objectives for the upper Murray wetlands

Potential environmental watering action	Expected Watering Effects	Environmental objective
Ryans Lagoon 1 and Ryans Lagoon 2 (fill in spring)	Mobilise carbon and nutrients within the wetlands to support wetland processes Maintain permanent, deep, open-water habitat that supports food resources for waterbirds and native fish Inundate wetland margins to provide refuge and feeding habitat for small- and large-bodied native fish Increase soil moisture to promote the growth of fringing vegetation and the surrounding river red gum community Inundate beds of aquatic and semi-aquatic vegetation to stimulate growth and increase their extent Prevent the encroachment of river red gum saplings into deep areas of the wetland Inundate wetland margins to provide habitat for waterbugs and foraging opportunities for waterbirds

Scenario planning

Table 5.2.2 outlines potential environmental watering and expected water use under a range of planning scenarios.

Ryans Lagoon 1 and Ryans Lagoon 2 would have naturally filled every year before the river was regulated, so watering in spring is a high priority under all climate scenarios. Water for the environment (delivered via temporary pumps) will likely be needed to fill both lagoons under drought, dry and average climate scenarios. High unregulated flows and natural floods are likely to inundate the wetlands under a wet climate scenario, and water for the environment will only be used under a wet scenario to top up water levels in each lagoon if they do not fill naturally.

Planning scenario table

Table 5.2.2 Potential environmental watering for the upper Murray wetlands under a range of planning scenarios

Planning scenario	Drought	Dry	Average	Wet
Expected river conditions	No unregulated flow below Hume Dam Regulated flow from Hume Dam is likely to connect the Ryans Lagoon floodway to allow pumping into Ryans Lagoon 1 and Ryans Lagoon 2	Unregulated flow is unlikely below Hume Dam Regulated flow from Hume Dam will connect the Ryans Lagoon floodway to allow pumping into Ryans Lagoon 1 and Ryans Lagoon 2	Periods of unregulated flow below Hume Dam Regulated and unregulated flow from Hume Dam and/or flow from the Kiewa River will connect the Ryans Lagoon floodway to allow pumping into Ryans Lagoon 1 and Ryans Lagoon 2	Regular periods of unregulated flows below Hume Dam and from the Kiewa River may provide partial inundation to Ryans Lagoon 1 and Ryans Lagoon 2
Expected availability of water for the environment	170 ML
Potential environmental watering – tier 1 (high priorities)	Ryans Lagoon 1 and 2 (fill in spring)
Possible volume of water for the environment required to achieve objectives	170 ML (tier 1a)			0-170 ML (tier 1a)

Page last updated: 01/07/22