Large floods in South East Queensland, Australia: Is it valid to assume they occur randomly? (original) (raw)

Australasian Journal of Water Resources

Flood frequency analysis and existing engineering practice assumes that flood events are randomly distributed. However, as understanding of large-scale ocean-atmospheric processes and associated hydroclimatic variability (and change) increases, the assumption that flood events are random seems unlikely to be valid. This paper examines historical flood data from 10 major catchments in South East Queensland (SEQ), Australia with the aim of testing for nonrandom patterns in the timing of the largest flood events. The results show that most (~80%) large floods in the study catchments have occurred within sets of 5-year periods separated by 35 years of lower flood risk. This finding is consistent with previous studies that have reported 20-to 40-year cycles in rainfall, flooding and drought across most of eastern Australia. Based on these insights, an explanation for the nominal 40-year cycle in SEQ flooding is proposed, and implications for describing and managing flood risk are discussed.

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