2004 – Decommissioning of Mount Morgan Dams

Richard West, John Sullivan, Russell Paton and Peter Allen

Mount Morgan dams Nos. 4, 5 and 6 were originally built on the Dee River in central Queensland in
the 1880s and 1890s to provide water to the Mount Morgan mine. The largest of the dams, Dam 6 is a mass concrete structure 9.7 metres high storing 63.6 ML.

Today the dams are no longer used for water supply and the stored water is highly acidic and heavily
contaminated by the runoff and tailings from the mine site. They are also in a seriously degraded state with major undermining and significant structural decay. Failure of these dams either individually or in cascade would put lives at risk and severely contaminate downstream areas. The decision was
therefore made to decommission the dams and remove that risk.

As well as the substantial removal of the dams, the decommissioning process involves dredging or
excavation of approximately 500,000 tonnes of tailings from the dam storages and the storing of this
material in the mine pit.

The challenge was to decommission the dams in a safe, economical and environmentally friendly
manner while retaining as much of the heritage value of the three dams as possible. To avoid carrying the risk over another wet season, the work needs to be substantially completed prior to the end of September 2004.

The paper discusses the investigations and the planning that has gone into the project including:

  • the real time flood warning system to provide early warning of conditions likely to cause dam
  • the decontamination of the storages;
  • the contingency provisions to minimise the risk of further contamination;
  • the removal of the dams; and
  • the measures to improve the long term quality of water in the Dee River.
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