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Lonie I

Queensland Alumina Limited operates an alumina refi nery located at Parsons Point, Gladstone, Central Queensland. Tailings from the refi nery, commonly referred to as red mud, are deposited in two dams, RMD#1 and RMD#2, which have an area of approximately 400Ha and 600Ha respectively.

Continued placement of red mud in RMD#2 had progressively reduced the volume available within the dam. Action needed to be taken to increase storage capacity (based upon water storage and mud storage capacity). Traditionally the volume would be created by raising the embankments, an expensive and time consuming process. An innovative solution was proposed to upgrade the spillway only and avoid the need to raise the embankment.

A workshop was carried out with the stakeholders to assess diff erent spillway options with consideration of spillway performance, downstream impacts, freeboard impact and embankment impacts. A 1.0m high cast in-situ concrete labyrinth spillway, founded on the existing spillway and within the existing spillway walls, was adopted as the fi nal solution. A risk assessment was carried out to verify the acceptability of the spillway raise in accordance with the Australian National Committee on Large Dams risk acceptance criteria.

The solution gave an equivalent storage capacity to an embankment raise of approximately 0.9m.

The project, including design and construction, was completed within 3 months and provided a cost eff ective solution for the capacity increase which was implemented before the 2010/2011 wet season.

This paper presents the process used for evaluating the labyrinth spillway option including wind and wave overtopping evaluation, risk assessment, labyrinth weir design and the advantages and disadvantages of the solution.