Brisbane City Council (BCC) has used hydraulic/hydrologic models to inform flood risk management policy for almost four decades. These models are used to derive Development Control Levels that dictate where and what types of development are within acceptable flood risk levels on the Brisbane River floodplain. Until 2014, Development Control Levels were explicitly dictated by so-called ‘Q100’ flood risk levels. The derivation of flood models and associated Q100 levels for Brisbane requires important preemptive assumptions about the operation of the Wivenhoe Dam. This dam is a dual purpose public asset requiring State government and its agencies to prioritise between flood risk and water resources in a zero-sum game of climate risk management. The assumptions made by BCC therefore require an understanding of State government’s priorities concerning the relative importance of these competing climate risks. Evidence from Queensland’s Commission of Inquiry into the flooding events of 2011 has shown that the assumptions made by BCC regarding the management of Wivenhoe Dam were incorrect at the time of the 2011 floods. Indeed, the Commission’s report suggests that, not only have BCC and State government been working at cross-purposes in relation to the city’s climate risk management, BCC has continually avoided making precautionary assumptions concerning the operation of the Dam in order to maximise urban development in Brisbane's floodplain. This case-study demonstrates the conflicting priorities that can arise across levels of government when managing climate risks, as well as the propensity for policymakers to disguise important political decisions within supposedly impartial technical evidence.