Cradle Mountain Water dam portfolio risk assessment
Client: Cradle Mountain Water
Location: Tasmania, Australia
Date: February 2013 – July 2013
Assessing relevant dam risks to prioritise risk mitigation strategies for safe and sustainable dams.
Cradle Mountain Water (CMW) was formed by combining the water authorities and water assets of a number of local councils in the west and north-west of Tasmania, to provide water and sewage services to these regions. As a result, CMW acquired a large portfolio of water supply dams, most of which have limited design and construction information and minimal maintenance history.
To effectively manage such a large portfolio of dam assets with limited knowledge of the existing safety status of the dams, an initial cost-effective approach was required for CMW to better understand the risks associated with these dams, and hence to prioritise dam safety management strategies to ensure ongoing safe operation.
Entura undertook a dam portfolio risk assessment (PRA) of ten of CMW’s dams previously assessed as ‘high consequence’. These dams are of various sizes and types, including homogeneous earthfill dams, zoned earthfill dams, timber dams and concrete-faced-rockfill dams.
The objective of the PRA was to identify the highest risk dams in the portfolio and provide a prioritised investigation or upgrade program to mitigate and reduce the risk to comply with the tolerability limit and regulatory requirements.
Entura scoped, facilitated and managed a series of special inspections and risk assessment workshops with CMW’s relevant dam safety managers and operators to assess and quantify key failure modes of each dam. The PRA included a desktop engineering assessment of the selected dams, reviews and updates of the consequences of dam failure, flood hydrology, and a detailed risk analysis in accordance with industry best-practice guidelines. Entura also used the latest Piping Toolbox, which is a unified method for estimating probabilities of failure of embankment dams by internal erosion and piping.
Entura successfully demonstrated the use of a cost-effective PRA approach to develop first-pass dam safety risk positions for a dam portfolio, which assisted the dam owner to prioritise risk mitigation strategies and dam safety works, and improve the existing surveillance and monitoring program to target key risk items. Entura also provided recommendations for further investigations and studies necessary to confirm the dam details and risk assessment, adding value for the client.