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Monitoring the Variation of Sediment Plume Properties in Western Harbour, Hong Kong

Author(s): O. W. H. Wai; H. S. Lee; A. W. T. Lee; H. Y. Yeung

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Keywords: Sediment plume; Western Harbour; Hong Kong; Drogue tracking; Sediment property; Settling velocity; Sediment flocculation

Abstract: A number of large-scale marine construction projects are taking place in Western Harbour, Hong Kong. These projects may generate sediment plumes that have adverse impacts on the water quality. Information of the temporal and spatial dynamics as well as the composition and properties of suspended-sediment plumes (SSP) is useful to improve the understanding of the fate and transport of SSP and associated environmental issues. This project aimed at monitoring and determining the dispersion and the variation of sediment properties of SSP in the harbor. Drogues, initially placed in the vicinity of the center of selected sediment plumes, were used to track the dispersion of plume and a laser sensor (LISST-100) were profiled in the water column (profiling speed of 1 m/sec) to obtain the suspended sediment particle size distribution and mean suspended solids concentration profiles. Grab samples at designated water depths were collected simultaneously with the laser profiling measurement to determine the respective sediment properties. Based on the field measurements obtained from various parts of the harbor and existing settling velocity equations for suspended aggregates, the solids settling velocity within the observed sediment plumes have been approximated. The overall averaged settling velocity is around 11 m/day and the median is about 8 m/day. The standard deviation is large, around 13.8 m/day. This implies that the dispersion characteristics of each SSP can be quite different in the harbor and this agrees with the plume tracking observation.


Year: 2003

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