Extensive repair and maintenance works to the Morwell River Diversion (MRD) structure at the Yallourn mine following an unprecedented flooding event in 2021 are nearing completion, EnergyAustralia says.
During June 2021, an extreme rain event and subsequent flooding of the Morwell River saw more than 30 times the average flood volume of water run through the MRD, an embankment created to carry the river through the mine.
The flood event – the largest since records began 60 years ago – resulted in cracking in one part of the MRD structure. Failure of the MRD would have resulted in the Morwell River inundating the coal mine, which would have impacted power production at Yallourn power station. The Yallourn power station provides up to 22 per cent of Victoria’s energy supply or eight per cent of the National Electricity Market.
The Victorian Government declared an energy emergency and fast-tracked approvals for EnergyAustralia to undertake urgent maintenance works to the MRD and a multi-agency Yallourn Emergency Response and Recovery Project was assembled to oversee the works.
Construction of a set of water diversions on the Yallourn mine site and upstream at the Hazelwood mine site has enabled temporary diversion of normal water flows into the Latrobe River. This allowed engineers to investigate the extent of damage, implement maintenance works and assess what longer-term monitoring and management might be required. The water diversions were designed to enable the assessment and repair of the MRD.
The inspections revealed some cracking in the southern area of the MRD both in the Low Flow Channel, which carries regular river flows, and the High Flow Channel, which carries irregular flows during flooding.
Maintenance works involved relining a section of the MRD by stripping back the MRD’s clay liner in the damaged area, recompacting the area beneath the clay liner, replacing the clay liner with an engineered layer of clay and grading the surface to improve surface water run-off.
The Low Flow Channel was returned to service in late April 2022. It can carry up to 2GL (or 800 Olympic-size swimming pools) of river water per day. Maintenance works to the High Flow Channel were completed in late May.
Works to create an offsite water diversion at the Hazelwood Mine, which can carry a maximum of 3GL (or 1200 Olympic-size swimming pools) of flood water per day, are also complete.
The water diversions are only used to divert water during higher flow events.
Additional onsite diversions at the Yallourn mine are also underway and expected to be ready in the near future. This will allow extra water diversion capacity onsite at Yallourn of up to 4.5GL (or 1800 Olympic-size swimming pools) of flood water per day and will provide additional protection for the MRD to enable repairs to be verified well before the diversion licences expire on 30 June 2023.
Geotechnical investigations have also identified additional longer-term measures to help guard against the impacts of a future high flood events and maintain the structural integrity of the Yallourn mine and surrounding areas.
Throughout the assessment and execution of the works, EnergyAustralia has met strict environmental conditions set by the state government and enforced by the Environment Protection Authority.
This included closely monitoring water quality in the Morwell and Latrobe Rivers to ensure water quality was maintained. The results published online show impact to date is negligible. EnergyAustralia continues to closely monitor the MRD throughout high-rainfall period during winter and into the future.
EnergyAustralia was responsible for the financial cost of the repairs.
EnergyAustralia has committed to running the Yallourn power station until mid-2028. The ongoing maintenance of the MRD will not influence the long-term rehabilitation outcomes for the Yallourn or Hazelwood sites.
Greg McIntyre, EnergyAustralia’s Head of Yallourn, said:
“We appreciate the strong support of the Victorian Government, local community, unions, regulators and especially our Yallourn workforce during this time.”