TasWater – Dam portfolio risk assessment
Location: Tasmania, Australia
Date: September 2011 – March 2012
Assessing dam risks to prioritise risk mitigation programs for safe and sustainable dams
TasWater was formed by combining the Water Authorities within Tasmania and the regional water assets of a number of local councils. As a result TasWater acquired water supply dams from both Southern Water, the other water authorities, and the councils; and lacked comprehensive information on many of the dams.
To better understand the risks associated with these water assets, TasWater decided to undertake a portfolio risk assessment on eighteen of its highest priority dams. TasWater’s portfolio consisted of various types of dams, including embankment dams, concrete faced rockfill dams, concrete gravity dams and slab and buttress dams.
Entura was engaged by TasWater to undertake a dam portfolio risk assessment (PRA) of ten of its dams in its new portfolio, and a review and update of the existing risk assessment of eight ex-Southern Water dams.
To assess the risks, Entura scoped, facilitated and managed a series of risk assessment workshops using external expert reviewers to assess failure modes and commence the quantification of the key failure modes. Entura used this information to then quantify all the risks for the dams and assess the consequences of failure to obtain the risk position for each dam. The work also involved undertaking updates to hydrology and engineering calculations in order to ensure a consistent approach to the risk assessment of each dam.
During this process, Entura used the latest risk assessment methodology, which included a unified method for estimating probabilities of failure of embankment dams by internal erosion and piping. In conjunction with the expert reviewers, Entura used its own methodology for assessing concrete-faced rockfill dams and a new methodology developed specifically for this project for assessing the risk of slab and buttress dams.
Entura provided specialist advice on how to apply the latest risk assessment methodology in an efficient and effective way to the client’s portfolio of dams, and conducted the risk assessment processes necessary to assess the risk position of each dam to determine the risk mitigation required. The portfolio risk assessment conducted by Entura is currently being used by TasWater to prioritise its program for risk mitigation on its existing dam portfolio.