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Finite dispersal of a divergent nepheloid plume by internal hydraulic jump in a tropical mountainous river estuary

【摘要】:正Field investigations were presented into a tropical mountainous river estuary of Herbert, Australia, following a moderate flood event induced by Cyclone Fritz. In-situ mooring and shipboard measurements were conducted using an acoustic Doppler current profiler, a conductivity-temperature-depth unit, and an optical backscatter nephelometer. Owing to the flood discharge onto the shelf, a river plume forms and is deflected under the along-shelf current induced by the trade wind. Intense stratification at the base of plume suppresses vertical mixing, significantly decreases bottom stresses, and separates the water column into two mixed layers. The normal depth of the plume relative to its critical depth is controlled only by the bed slope and the drag coefficient of the interface, independent of river discharge and buoyancy anomaly. A divergent nepheloid dispersal system usually occurs under combined flow segregation and intense stratification. Two nepheloid layers are both confined to the inner shelf under different dispersal mechanisms. The upper nepheloid layer, primarily controlled by advection and settling, is exponentially decayed away from the river mouth. The lower nepheloid layer dominated by settling is detached seaward near the lift-off point. The plume lift-off and subsequent internal jump are crucial processes for the trapping of the plume sediment because a substantial loss of energy occurs, and farther control the pattern of mud deposit on the shelf. Fronts have important influences on the sediment release from the river plume, with different trapping effect in the presence and absence of stratification.

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