Wivenhoe, January 2011: the dam truth

ABSTRACT

The January 2011 flood event that impacted southeast Queensland is amongst the most extensive and severe floods in terms of loss of life and property damage that the region has experienced, despite it being only the eighth highest flood on record at the Brisbane City Gauge. The spring of 2010 was the wettest on record for Queensland, New South Wales, and the Murray-Darling Basin (Bureau of Meteorology 2011a) at that time. The flood mitigation dams in the region, Somerset Dam and Wivenhoe Dam, had to be operated for flood mitigation purposes during October 2010, which was the first occasion since February 2001 that Wivenhoe Dam had been called into action due to the Millennium Drought. The wet October was followed by a very dry November which, in turn, was followed by the wettest December on record for Brisbane. Somerset Dam and Wivenhoe Dam were again pressed into action on three separate occasions during December 2010. The resultant releases ensured that only minor flooding resulted in the Lower Brisbane River during these events. However, on the 5th of January 2011, another rainfall event started to unfold across the catchments of the dams. By the 10th of January 2011, an upper-level low combined with a humid easterly flow to bring very heavy rainfall and flash flooding to southeast Queensland and northeast New South Wales. The heaviest falls were in the areas north and west of Brisbane, with three-day totals exceeding 200 mm over most of the Brisbane River catchment. This rainfall event resulted in a flood of record in the Upper Brisbane River and Upper Lockyer Creek catchments that sadly resulted in a substantial loss of life in Toowoomba and the Lockyer Valley, and which required record releases from Wivenhoe Dam. The resultant downstream flooding saw some 14,000 properties impacted, principally in the Lockyer Valley Regional Council, Somerset Regional Council, Brisbane City Council, and Ipswich City Council local government regions. Flood damage was estimated to be around $2.53 billion. This paper discusses the event as it unfolded and the subsequent judicial inquiries, engineering reviews, and legal proceedings that resulted from the consequences of the operation of Somerset Dam and Wivenhoe Dam.

KEYWORDS:

• Somerset Dam
• Wivenhoe dam
• flood hydrology
• flood mitigation
• flood damage, January 2011 flood

Acknowledgements

The authors wish to thank the National Committee of Water Engineering for the invitation to present this paper. This is the first opportunity for the Flood Engineers to provide their perspective of the events of January 2011 in a public forum, without the spectre of legal processes hindering the ability to speak openly.

The four Flood Engineers note the contribution of the nine Flood Officers who assisted in the Flood Operations Centre during the event. They also wish to acknowledge the actions of the Dam Supervisors and Standby Operators who operated the dams under extremely difficult circumstances. They are the unsung heroes of the event.

Lastly, but certainly not least, the authors wish to thank our partners and families who have supported us throughout this experience.

Disclosure statement

No potential conflict of interest was reported by the authors.