Is South-east Queensland's largest dam 'full'? Unraveling the Mystery
The Wivenhoe Dam, a crucial water source for millions, is a topic of concern as the wet season begins. But is it truly 'full'? Let's dive in.
The Wivenhoe Dam, located in the heart of southeast Queensland, is a behemoth when it comes to water storage. With a capacity to hold nearly 1.2 million megalitres, it's a vital asset for the region's water supply and flood control. But what does it mean when it's said to be 'full'? And how does it manage to hold so much water?
The Dam's Primary Purpose
Built in 1984, the Wivenhoe Dam was designed with a primary goal: to provide drinking water for the millions of residents in southeast Queensland. But that's not all. It also serves as a flood mitigation system, controlling the flow of the Brisbane and Stanley Rivers, which pass through some of the country's heaviest rainfall areas. So, it's not just about quenching thirst; it's about keeping the region safe from flooding.
What Does 'Full' Mean?
When we say the Wivenhoe Dam is 'full', we're referring to its operational supply level. This is a percentage of its total drinking water supply level, not its actual capacity. So, while it might seem like it's at maximum capacity, there's more to the story. During a flood event, the dam can hold far more than its operational supply level, thanks to an additional compartment located above the drinking water.
The Additional Compartment
Seqwater's principal dam safety and operations manager, Kevin Bartlett, explains that this additional compartment is double the size of the drinking water compartment. So, there's another two million megalitres of flood storage available. This means that during a flood event, the dam can hold far more than its operational supply level.
When Are the Floodgates Opened?
The decision to open the floodgates is made by engineers based at Seqwater's flood operations center in Brisbane. They rely on an array of hundreds of sensors dotted across the catchment, providing real-time data on rainfall, run-off, flow rates, and dam levels. Forecasts from the Bureau of Meteorology are also used to model how a flood event will play out. The floodgates are used to control the flow of water during rain events, and the engineers direct that the gates start to open in accordance with the Wivenhoe flood manual.
The Lessons of 2011
After the 2011 floods, the operators of Wivenhoe were accused of breaching their duty by failing to follow the flood manual. In 2019, the Supreme Court of New South Wales found Seqwater and others had been negligent by not releasing water soon enough. However, Seqwater later won an appeal against that decision, successfully arguing that the senior flood manager at the time followed a legitimate strategy. This prompted several reviews of the flood manual, and today's engineers are devoted to its stipulations.
The Wivenhoe Myth
Even if operated in full accordance with the manual, operators say Wivenhoe will not be able to stop a major flood from affecting those downstream. That's because only the upper Brisbane and Stanley Rivers are controlled by the Wivenhoe and Somerset dams. Other waterways, including the volatile Lockyer Creek, Bremer River, and lower Brisbane River, are all unregulated. So, while the dam is a crucial asset, it's not a panacea for flooding.
Stay Alert, Be Prepared
Dam releases regularly cause Brisbane River crossings to be impassable, and dangerously charge downstream waterways. Seqwater notifies local governments and disaster management teams as early as possible regarding releases. But advanced notice is not always possible. As Emma Thomas, Seqwater's chief executive, explains, they all need to be able to react and respond to the ever-changing weather conditions. So, while the dam is a vital tool, it's important to stay alert and be prepared for any eventuality.
