2022 – Risk and ALARP Assessment for Upper Yarra Embankment Upgrade Selection

Gavan Hunter – Hunter Geotechnical Pty Ltd, Director, Mark Foste – Dam Consulting Services Pty Ltd, Directorr2, Mark Arnold – Melbourne Water Corporation, Principal Engineer, Dams and Structures

Upper Yarra Dam is a critical storage within the Melbourne Water harvesting and distribution system supplying potable water to the city of Melbourne. It is a 90 m high earth and rockfill embankment constructed in the mid 1950’s without a formal filter zone.

The risk profile of the dam is dominated by internal erosion and piping through the embankment. The dam is rated as an Extreme Consequence with very high potential societal and economic consequences. The risk and ALARP assessment process for the embankment upgrade at Upper Yarra included assessment of what could practicably be done to reduce risk in consideration of the key potential failure modes including the level of risk reduction that could be achieved, the impact and cost to Melbourne Water, cost effectiveness, comparison to good practice, societal concern and managing construction risk. The ALARP assessment framework developed by AECOM in conjunction Melbourne Water and their reviewers in 2017 was applied at Upper Yarra Dam.

This paper presents the process for evaluation and selection of a preferred concept to take forward to detailed design using the ALARP approach. Key inputs and decision making in the selection process are summarised in the paper along with the risk assessment process from the portfolio risk assessment through to detailed design. Keywords: Dam Safety, Risk Assessment, ALARP, Embankment Dam, Internal Erosion and Piping.

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