A continent surrounded by the Indian and Pacific oceans, it might come as a surprise that Australia is the Land of Dams, its large number the result of much of the country suffering from major orography problems and water resource storage issues. Interestingly, over the years Australia has focused heavily on hydroelectric energy, installing power plants to meet ca. 35% of the country’s entire needs. Australia has more than five hundred large dams nationwide. Wivenhoe Dam, along the Brisbane River, is the largest dam in South East Queensland. The 344-kilometre-long Brisbane River is the longest watercourse in the region, rising on the slopes of Mount Stanley, passing through the city of Brisbane and flowing out into Moreton Bay in the Coral Sea. Among other things, the river is infamous for flooding: since 1841, it has burst its banks twelve times in “major floods”, defined as when it rises more than 3.5 metres above its usual level. In 1841, it reached 8.43 metres; the biggest flood in the twentieth century topped out at 5.45 metres in 1974, causing sixteen fatalities, injuring two hundred people, destroying eight thousand homes and causing $980 million worth of structural damage. The Brisbane River’s frequent, dangerous flooding was one of the main reasons for building the Wivenhoe Dam.
Reasons for Building the Wivenhoe Dam
As we have seen, the Wivenhoe Dam was primarily built in response to the Brisbane River frequently flooding. However, the dam serves other purposes too: it guarantees the city and its environs a secure and regular water supply. The Wivenhoe Dam also plays a role in power generation: the reservoir behind the dam serves as the lower storage basin for a pumped storage hydroelectric power plant. Another dam, Splityard Creek, created the hydroelectric plant’s upper reservoir. The Wivenhoe is not the only hydroelectric plant served by the Wivenhoe Dam: via special pipelines, water from the basin is pumped to the Tarong and Tarong North plants for them to use, although these links are shut down during periods of drought.
Construction of the Wivenhoe Dam
The idea of building a dam on the Brisbane River, where the Wivenhoe Dam stands today, was initially floated as far back as the flood of 1893. Topping out at a massive eight metres over the river’s normal level, it caused enormous damage to the city and killed seven people. The scheme was debated again in the 1930s and 1960s, but not until November 1971 did dam construction get the green light. Land purchases began soon after: some 200 properties covering a total of 337 square kilometres were affected. The scheme accelerated after more flooding in 1974; in 1976, a design was approved for a pumping system to serve the new hydroelectric plant, raising the estimated overall cost to $450 million Australian dollars.
The Queensland Water Resources Commission designed the dam, which was built by Thiess Brothers. Even though work wasn’t completed until 1985, the partially erected dam mitigated the impact of a potentially dangerous flood in 1983.
Wivenhoe Dam Capacity, Features, Facts & Figures
Built in an area with 940 millimetres average annual rainfall, the Wivenhoe lake lies behind the dam of the same name. Technically, the dam is a rock and earth-fill embankment dam with a concrete spillway. Located eighty kilometres from downtown Brisbane, it can hold seven times the water contained by the nearby Hinze Dam, which was completed in 1976 (and enlarged in 1989 and 2011) to supply drinking water to the Gold Coast region. The dam is 59 metres high and 2,300 metres long. At full capacity, its 4,140 cubic metres volume holds 1,165,000 megalitres of water, covering a surface area of 1,094 hectares. With five steel weirs twelve metres wide and 16.6 metres high, the spillway can discharge up to 12,000 cubic feet of water per second. To make the structure safer, a second auxiliary drainage channel was added to prevent overtopping and keep the basin’s level within safe limits.
The Wivenhoe Dam’s Ability to Mitigate Floods
Given the dramatic consequences of the river’s many floods over the decades, as noted the Wivenhoe Dam’s primary role is to prevent the Brisbane River from flooding. The data shows that in the event of a flood, the dam can hold 1.45 million megalitres of water, in an emergency raising capacity by up to 225%. However, a 2007 feasibility study revealed that the dam does not fully comply with the guidelines issued by ANCOLD (the Australian National Committee on Large Dams). This caused concern in 2011, when heavy rainfall required the basin to cope with 191% of standard capacity, and the water level rose to just sixty centimetres from the auxiliary discharge channel. Even then, the flood destroyed nearly 30,000 homes across the region. Concern for the Wivenhoe Dam returned in late February 2022, when the dam rose to 183% of normal capacity.