2017 – Tailoring Consequence Assessments for Retarding Basins

Andrew Northfield, Simon Lang, Peter Hill

Melbourne Water currently manages more than230retarding basins (RBs). A large portion of these are less than 4 metres high, and traditionally structures of this size have not been subject to intermediate or detailed ANCOLD Consequence Assessments. However, the need to understand the failure consequences for smaller structures has increased over time, as risk based approaches to managing safety have expanded from large dams to other water retaining assets.

Undertaking detailed consequence assessments for all Melbourne Water’s RBs would not be practical, given the costs and time involved. Therefore, this paper describes a method for assessing the level of ANCOLD Consequence Assessment that is justified, based on the structure’s attributes. It also presents an equation that was used to estimate peak outflows from RB failure. The peak outflow estimates can be used to model approximate failure inundation extents downstream of small dams and RBs.

The paper draws on work that HARC have recently undertaken for Melbourne Water to assess the failure consequences for 88 RBs. The outcomes are relevant to other organisations that own or manage significant numbers of small water dams or RBs.

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