200 properties were acquired. The catchment area has an average annual rainfall of . The dam holds twice as much water as Sydney Harbour and can hold about seven times more water than the Hinze Dam on the Gold Coast. Wivenhoe Dam contributes to the Gold Coast's water supply. Purpose The dam was designed as a response to the floods that damaged Brisbane in 1974. Built in the late 1970s – early 1980s as a multifunction facility by a consortium of construction companies including Thiess Brothers, Wivenhoe Dam provides a safe water supply to the people of Brisbane and adjacent regions. Additionally, Wivenhoe Dam serves as the lower storage in a pumped-storage, hydro-electric generating facility, the Wivenhoe Power Station. The upper reservoir is formed by Splityard Creek Dam, of earth and rock construction, with a capacity of . Under normal conditions the dam supplies water via pipeline to both Tarong Power Station and Tarong North Power Station, but during drought conditions only supplies water to Tarong North. Flood mitigation During a flood the dam is designed to hold back of additional water for flood mitigation or 225% capacity. Under the water release plan which is defined by law, excess water must be released from the dam within seven days or a week of it reaching 100% capacity. In February 1999, the level reached 135% of full capacity. Between April 2004 and September 2008, a wide auxiliary spillway with a three-bay fuse plug was installed on the western portion of the dam to further mitigate flooding. In 2007, a feasibility study concluded that Wivenhoe Dam failed to satisfy the Australian National Committee on Large Dams (ANCOLD) guidelines on acceptable flood capacity. 2000-2007 Drought Brisbane water levels reduced to under 20% of capacity, having had no substantial inflow for five years. 2011 Queensland floods The largest ever recorded inflows for the dam occurred in January 2011. On 11 January 2011, Wivenhoe Dam reached its highest level ever, 191% of normal water supply storage capacity, as it held back floodwater. Because it is an embankment dam, it was not designed to spill over its crest or overtop and there is a risk that if waters spilled over the crest, this could erode the dam wall and potentially cause the dam to fail. In this scenario the water level would need to rise to 225% capacity. To prevent this, the dam was designed and