2006 – Pykes Creek Dam: A Staged Risk Based Approach To Remedial Works

Joseph Matthews, Dr Mark Foster, Michael Phillips

Pykes Creek Dam is a 39m high earthfill dam with a central clay puddle core, first completed in 1911 and raised in 1930. A detailed risk assessment of the dam indicated that the risk did not satisfy ANCOLD societal risk criteria and that remedial works were necessary to address piping deficiencies and inadequate flood capacity. The risk assessment identified that piping at the embankment/spillway interface accounted for over 80% of the total risk. Therefore, interim risk reduction works were implemented in 2005 to address this risk issue while investigations and design studies were progressed for the second stage of works. Following the Stage 1 works, Pykes Creek Dam remains the highest risk in Southern Rural Water’s portfolio of dams and Stage 2 works are planned to commence in 2007 to reduce piping risks and increase flood capacity. The aim of the Stage 2 works is to reduce the risk below the Limit of Tolerability for Existing Dams (ANCOLD 2003) and to increase the flood capacity to a level more appropriate for an Extreme consequence category dam based on ALARP principles. The upgrade will stop short of meeting the PMF as there are other dams in Southern Rural Water’s portfolio requiring attention before an upgrade to this standard would be considered. The design of the works was complicated by the fact that the dam is bisected by a major freeway and has a complex spillway layout. This paper discusses the decision-making process and the methods used to analyse the dam from the initial risk assessment studies through to the design of the remedial works.