The management of water supply in south-east Queensland over the last decade provides an interesting example of engineers working in new and rapidly changing contexts. They have had to manage their own time, set priorities, and learn to operate the water supply and flood mitigation systems during periods of extreme weather conditions: firstly, during long periods of drought between 2001 and 2009, when the combined water storage in the region’s three largest dams dropped to less than 17 per cent; and then over the 2010–11 summer, when record-breaking rainfall events were experienced.

The largest dam in the system, Wivenhoe Dam, was built by the Queensland government following the devastating Brisbane flood in 1974. The dam was designed to augment Brisbane’s water supply and to protect the city from similar flood events in the future. It holds 1 165 000 megalitres (ML) when its water supply compartment (i.e. its base capacity) is at 100 per cent, and a further 1 420 000 ML when its mitigation compartment (i.e. its top-up capacity) is at 100 per cent.2 Thus, the dam’s total capacity is 2 585 000 ML. The flood mitigation compartment is designed to temporarily store upstream floodwaters and then release that water in a controlled manner to minimise flows in the Brisbane River, and thus minimise downstream flooding in Brisbane and Ipswich. The personnel who manage the dam are, under Queensland legislation, required to follow the operating manual to avoid any liability for losses resulting from water releases from the dam. Because approximately 50 per cent of the Brisbane River catchment lies below Wivenhoe Dam, the dam can only be used to mitigate floods, not prevent them.

During 2010, the controlling weather pattern shifted from El Niño to La Niña, resulting in increased rainfalls and, in some areas, record-breaking rains. There had been celebrations in April 2009 when Wivenhoe Dam reached 40 per cent capacity and water restrictions were relaxed. However, many people did not believe the drought was over until the dam reached 100 per cent of its water supply capacity on 4 October 2010 and the flood gates were opened for the first time since 2001. By the end of December 2010, the dam was at 102 per cent capacity, and the catchment was saturated following record rainfalls during the month. At 12.26 pm on Wednesday 5 January 2011, operations personnel at Brisbane’s Wivenhoe Dam received a timely alert from Wivenhoe Dam engineering officer Graham Keegan. It was entitled ‘Bureau of Meteorology (BOM) severe weather warning — dam flood operations’, and warned that significant rainfall of 100 mm to 200 mm ‘may occur during the next few days’ and that:

Somerset and Wivenhoe Dams are still above (full supply level) and rising slowly due to continuing base-flows from their catchments. As the catchments are still wet it is likely that we will be releasing floodwaters in the near future if BOM’s forecasts are accurate. Please be prepared. We will keep you up to date with our plans as this event develops.

Instead of draining the dam’s flood compartment as the waters rose with the heavy rainfall on 9–10 January 2011, the water levels were permitted to rise, eroding the dam’s capacity for flood storage. This delay resulted in an emergency release of water on 11 January when the levels got so high that they threatened the stability of the dam. Prior to this, the government advised the residents of south-east Queensland that the release of this water into the Brisbane River, together with the peak flows from Lockyer Creek and other tributaries, would lead to severe flooding in Brisbane and Ipswich on Thursday 13 January. The rest is history and, although the flood did not reach the 1974 peak, it caused enormous damage to both cities.

QUESTIONS

1. What information sources (or potential information sources) could have been used to assist with the decisionmaking process for Wivenhoe Dam in this case?

2. With reference to decision-making theory covered in the chapter, describe the type of managerial decisionmaking evident in this case, and the conditions under which decisions were made.

3. Evaluate the decisions made in the case in relation to the classical, behavioural and judgemental heuristics approaches to decision-making that are outlined in the chapter. Which model do you believe best describes the situation and subsequent decision-making process in this case? Justify your answer.