Continuous simulation of hydrologic systems requires the use of long sequences of high resolution climate data. Continuing advances in stochastic rainfall methods indicates that continuous simulation is likely to become a practical tool for hydrologic risk assessment. This study examines the case for adoption of continuous simulation. Two case studies are employed to compare the performance of continuous simulation and the Australian Rainfall and Runoff design storm approach. Both consider peak flow estimation in the context of volume-sensitive systems for detention basins and rainwater tanks. The case studies demonstrate the potential for large errors when using design storms to simulate the flood performance of volume-sensitive systems. It is significant that there does not appear to be an obvious way to “fudge” the design storm approach to make it reliable. Given the wide usage of detention and retention systems in urban stormwater management, one has to seriously question the fundamental assumptions that underpin Australian flood estimation practice. The case for adopting rigorous joint probability approaches such as continuous simulation is considerable

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