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A statistical analysis of flood hydrology and bankfull discharge for the Mitchell River catchment, Queensland, Australia.

TitleA statistical analysis of flood hydrology and bankfull discharge for the Mitchell River catchment, Queensland, Australia.
Publication TypeReport
Year of Publication2010
AuthorsRustomji, P
Date Published01/2010
Keywords4: Material Budgets
Abstract

This report presents a flood frequency analysis for twenty gauging stations within the Mitchell River catchment. A flood frequency analysis allows the estimation of the magnitude of selected flood quantiles, such as a 1 in 20 year flood, at particular gauging stations. A series of statistical relationships were developed to allow flood quantile estimation at ungauged locations. Gauging station cross sections were examined to identify bankfull discharge and its corresponding recurrence interval. However, this could not be achieved because the majority of gauging stations appear to be incised into either older alluvium (terraces) or bedrock valleys and consequently did not have 'self-formed channels'. An analysis of the downstream trends in fitted flood quantiles along the main stem of the Mitchell River indicates that floods with a recurrence interval of 1 in 2 years are generally contained within the channel (or at least the losses to floodplains and distributaries are proportionally constant downstream). However, for events with recurrence intervals of 5 years or more, losses of flood flows to the floodplain and distributary channels within the Mitchell River mega-fan region are notable. Peak flood flows at the downstream-most gauge (Mitchell River at Koolatah, 919009A) have an effective upper bound of approx. 6600 m3 s-1 for events with a recurrence interval greater than 1 in 20 years; any discharges generated by the upstream catchment in excess of this appear to be diverted onto the floodplain and distributary channel system within the mega-fan region.