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Highlights in this update

  • Bureau of Meteorology confirms La Niña conditions through spring/summer
  • Water availability has improved in the southern Basin, however northern Basin is still dry
  • Spotlight story: Southern flows to aid nesting Murray cod
Rainfall percentages for April to September 2020, showing above average rainfall in southern catchments, and below average in the north.

Drought

Despite welcome rain in many areas of the Basin since late 2019, the impact of an extended dry period is still being felt, particularly in the northern Basin.

The graphic to the left represents rainfall percentages for the Basin over the past six months. It demonstrates that while most of the Basin received 80–150% of average rainfall, the upper reaches of some northern Basin catchments received as little as 20% of average rainfall during the same period.

This aligns with long-term rainfall deciles highlighting that increased rainfall since late 2019 has improved streamflow conditions in the southern Basin, however the northern Basin remains very dry, and overall the Basin is still experiencing the impacts of ongoing drought.

Rainfall totals for September showing 1-100 millimetres fell across the Basin.

Rainfall

September was the second consecutive month of average to above average rainfall across most of the Murray–Darling Basin. Rainfall was recorded across the entire Basin, ranging from 1–25 mm in the north to 10–100 mm in the south.

Most of this rain fell in the second half of the month, with highest falls over the Great Dividing Range in the east. Localised storms brought flash flooding to the west at Broken Hill, where more than a month’s rain fell in 15 minutes.

The upper Condamine, Moonie and Queensland border river catchments recorded the lowest rainfall.

Rainfall deciles for September contrasted across the Basin, with highest on record rainfall in isolated areas of the south-west, while catchments in the north east recorded very much below average rainfall.

Summary of water in storage as at 30 September 2020 - total storage at 55% of capactiy

Water storages and streamflow

Public water storages across the Basin remained stable throughout September, holding 12,174 GL (55% of capacity) as at 30 September 2020. This was a 3% increase over August.

For the northern Basin, storages at 30 September 2020 were 1,274 GL, or 27% of active capacity – a small increase of 3% over the previous month. This was primarily driven by a 28 GL increase in storage at Burrendong Dam, along with minor increases in smaller storages including Keepit and Chaffey. Several storages in the northern Basin remain below 20% of capacity, including Split Rock Dam upstream of Tamworth, which is currently at 6% of its 397 gigalitre capacity.

Public storages in the southern Basin were holding 10,152 GL, or 62% of capacity, at 30 September 2020. This was up by 2% on the previous month. Inflows to Burrinjuck Dam tapered off through the month following heavy rainfall in the Murrumbidgee catchment in August.

In the Murray, the extended period of unregulated flows into South Australia which commenced 27 June 2020, concluded this week on 25 September. Water from Lake Victoria is now being used to help meet South Australia’s water requirements.

Releases from Hume Dam peaked in late September at 5,500 ML/day, easing slightly in response to inflows from downstream tributaries. Diversions into major Victorian and New South Wales irrigation channels also eased due to rainfall and cooler weather.

Climate outlook - Spring/Summer 2020

In their latest outlook the Bureau of Meteorology has confirmed that La Niña has established in the tropical Pacific and will persist until at least January 2021.

La Niñas vary in strength, and climate models predict that the current event will be moderate to strong, although unlikely to be as strong as the most recent La Niña in 2010–12 that brought sustained heavy rainfall and widespread flooding to many parts of the Basin.

Rainfall in the south-east of the Basin is expected to be above average over the coming months, boosting soil moisture levels and contributing to increased river inflows. Recent rainfall has already primed many eastern catchments, and there is an increased risk of flooding in some areas. The MDBA will continue to monitor this situation, but please note that flood warning services are provided by the Bureau of Meteorology.

Forecast rainfall in the northern Basin is not looking as promising as the south, extending the ongoing dry conditions for many catchments. Significant rainfall is required to improve current low soil moisture and streamflow conditions.

Summary of threats to water quality in the Basin

Water quality and salinity

Forecasts suggest a wetter than average spring-summer period for a large area of the Basin. Despite this, the threat of water quality issues remains as temperatures increase towards summer, and potential rainfall washes organic matter and nutrients into waterways, triggering events such as algal blooms and hypoxic blackwater.

The MDBA and state authorities continue to monitor water quality across the Basin.

For more information on water quality, and a map of threats, see the water quality page of our website.

Blue-green algae red/high alerts

New South Wales sites on RED alert for blue-green algae:

  • Pindari Dam
  • Copeton Dam

Victorian sites on HIGH alert for blue-green algae:

  • Lake Eildon
  • Tullaroop Reservoir (near Maryborough)

Bushfire water quality risks

Risk of contamination continues to decrease as catchments recover from severe bushfires.

Blackwater

Warmer temperatures and other factors can combine to create a risk of hypoxic blackwater. Current watchpoints being monitored for potential blackwater events in NSW include:

  • Lachlan River downstream of Forbes
  • Murray River communities from Tocumwal to the South Australian border,
  • Murrumbidgee River downstream of Narrandera, including the Lowbidgee floodplain from Maude to Balranald
  • Edward Wakool system in the region of Deniliquin and Moulamein

Salinity

Salinity levels across all measurement sites were relatively stable, and most sites were well below target levels throughout September. Flows in the River Murray continued to keep salinity levels in the Lower Lakes below averages recorded in the past 12 months, aided by releases through the barrages allowing water to flow into the Coorong.

Spotlight: Southern flows to aid nesting Murray cod

October is the mid-point of the annual Murray cod breeding season, where these iconic fish build underwater nests and pair up to begin their breeding cycle.

This process is being aided by small releases of water for the environment from Hume Dam, which will keep cod nests submerged and give eggs and larvae the best chance to survive. Importantly this water also supports the health of key wetlands and floodplains in the Murray, including the Ramsar listed sites such as Barmah–Millewa and Gunbower–Koondrook–Pericoota forests, Hattah Lakes, Chowilla Floodplain, the Lower Lakes and Coorong.

Early season rainfall has led to good natural flows in the Murray over autumn and winter. Supplementing these natural flows with water for the environment helps boost water levels in the river at times when plants and animals need it most to feed, breed and thrive.

Coinciding with releases in the Murray, there is also activity in the lower Darling/Baaka, with water for the environment being released from Menindee Lakes to improve river health and help Murray cod breed – their first chance in the region since the devastating fish deaths of summer 2018/19.

Like other water users, the Commonwealth Environment Water Office (CEWO) has a limited amount of water available and makes careful choices about how best to use water for the environment. Although forecasts suggest wetter than average conditions in the southern Basin, a range of scenarios from wet to dry are considered by the CEWO, and future water releases will scale as the season unfolds.

The CEWO will track the flows as they work their way down the river and work with communities and scientists to closely monitor the environmental benefits. The CEWO also works closely with its partners, including the Victorian Environmental Water Holder, NSW Department of Planning, Industry and Environment, SA Department for Environment and Water, MurrayDarling Basin Authority, Goulburn-Broken CMA, WaterNSW and Goulburn Murray Water.


Images: (Top) Juvenile Murray cod, tagged for tracking. (Bottom) Adult Murray cod.