2013 – Managing the risk of under-designed spillway training walls: an owner’s guide

Chris Topham, Eoin Nicholson and David Tanner

A number of Australian dams have spillways with reinforced concrete training walls designed in the 1950/60s to the standards of the day, but which could be considered under-designed according to modern criteria. Such walls commonly retain significant depths of earth and rockfill embankment materials, where structural failure of the wall could seriously compromise the safety of the dam. This paper presents the journey to mitigate the risk of such training walls, drawing primarily on experience in managing structurally deficient spillway training walls for a High Consequence Category dam in northern Tasmania. Reflections from each step of the risk management process are presented, including how the portfolio risk assessment contributed to a focus on the dam as a whole, and how that led to more detailed analysis and evaluation of the training wall risk. The use of instrumentation and enhanced surveillance for risk monitoring is discussed, including how real-time deformation data ultimately led to installation of temporary wall bracing works and enhanced contingency planning. The long-term risk treatment for the walls is presented, comprising a $6m structural upgrade to the training walls completed in 2013. The paper concludes with the learnings from the risk management journey and highlights the range of interventions available to owners with similar spillway training walls.