Flood behaviour of the Burdekin River, tropical north Queensland, Australia

Abstract

Abstract Strongly seasonal rainfall in north Queensland, Australia, causes extremely variable fluvial discharge, and tropical cyclones commonly produce high-magnitude, short-duration floods. In the Burdekin River catchment (129 500 km 2 of eastern Queensland), rapid runoff and channel floodplain configuration lead to very fast flood-wave speeds (up to 4.34 m s −1 calculated). The large catchment and varying tropical cyclone paths result in extreme variations in flood history at different sites. Changes in channel conditions (bed elevation, vegetation, bedforms, sediment surface character) in successive events, combined with complex rainfall patterns and highly unsteady flow, make flood estimates extremely difficult. Because of the short duration of flow events and very rapid rate of change in discharge during individual events, sediment transport rate, bedforms, and bed elevation change continuously. For most of the year the channel is occupied by an underfit stream, but this small perennial stream does not significantly rework the deposits or change channel form before the next major discharge event. Consequently, there is little channel form recovery between major discharge events. Successive events have very variable size and consequently the bedforms and channel morphology are normally out of equilibrium with the flow, and record the result of the most recent major events. High-magnitude floods transport coarse sediment onto the floodplain and the short duration of flooding and rapid runoff results in relatively low preservation of mud in the channel or overbank environment. The Holocene flood deposits include thick, coarse sand and medium sand units and generally thin, fine-grained units.