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Environmental watering in the lower Murrumbidgee River 2011-13

Status

30 June 2012: These actions have been completed.

Lower Murrumbidgee River blackwater dilution flow, 15-21 May 2012

A total of 28.5 GL of environmental water, including 26.7 GL of Commonwealth environmental water, was delivered to the lower Murrumbidgee River in May 2012 to improve water quality and provide in-stream conditions suitable to support aquatic animals following a blackwater event in the lower Murrumbidgee River.

The blackwater event in the lower Murrumbidgee River occurred in response to large natural floods in the Murrumbidgee Catchment during March/April 2012 and had the potential to severely impact fish and other aquatic animals due to very low dissolved oxygen levels - known as “hypoxic blackwater”. For more information please refer to the Water Quality Bulletin (PDF - 240 KB) and River operations weekly report produced by the Murray Darling Basin Authority.

This watering action was managed by New South Wales Office of Environment and Heritage in cooperation with New South Wales State Water and New South Wales Office of Water.

The Commonwealth environmental water delivered in this action complemented and extended recent efforts by the Murray-Darling Basin Authority and other Commonwealth environmental watering actions in the wider Murray River catchment. This watering action is part of an integrated approach to reduce environmental damage and help to maintain some areas where native fish have reasonable conditions to survive. Water is also being delivered in the:

For example, in April 2012, blackwater from the lower Murrumbidgee River began to enter the Murray River resulting in very low dissolved oxygen levels in the mid-Murray River. Delivery of Commonwealth environmental water to the mid-Murray river in early May 2012 was effective at diluting the blackwater entering from the Murrumbidgee River, provided improved dissolved oxygen levels and suitable habitat for fish and other aquatic species. For more information on the blackwater dilution flow delivered to the Murray River please refer to:

Lower Murrumbidgee River in-stream fresh and top-up of North Redbank Wetlands, 11-29 February 2012

In February 2012, up to 65.2 GL of Commonwealth environmental water was made available for use in the lower Murrumbidgee River and floodplain. The watering action aimed to recreate a more natural pulse flow in the lower Murrumbidgee River and had two components which operated simultaneously:

  • Provide a late summer/autumn pulse flow in the Murrumbidgee River to extend the duration of an unregulated event.
  • Top up North Redbank wetlands while also releasing water from the lower end of the wetlands into the Murrumbidgee River. For more information on this component of the action, please refer to: Environmental watering in North Redbank.

The watering action was suspended on 29 February 2012 and deliveries from dams were halted on 28 February 2012 due to forecast heavy rainfall in the Murrumbidgee catchment. Prior to the suspension of the action, a total of 33.7 GL of Commonwealth environmental was delivered to the lower Murrumbidgee River as an in-stream flow pulse, and 4.7 GL was delivered to the North Redbank wetlands. The remaining unused portion of 26.7 GL was delivered to the lower Murrumbidgee River in May 2012 to mitigate blackwater conditions following the March/April floods (see details above).

The objectives for the watering action in February 2012 were to:

  • Increase the connection of watercourses between the North Redbank wetlands and the Murrumbidgee River to contribute to the transfer of sediment, nutrients and aquatic plants and animals that provide the food and conditions needed to create healthy riparian habitat.
  • Restore hydrologic diversity along the Murrumbidgee River to better replicate a more natural medium summer/autumn flow which would:
    • Inundate native fish habitat, including coarse woody debris and riparian vegetation, and enhance recruitment for small bodied native fish.
    • Improve the transport of sediment, nutrients and carbon and biota.
  • Improve water quality through the use of in-channel flows to dilute low dissolved oxygen return flows from North Redbank, while simultaneously providing fresh flows to Redbank Wetlands, improving wetland water quality.

This watering action was managed in cooperation with the NSW Office of Environment and Heritage and NSW State Water.