Flow regime classification for barged sediment disposal

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Jenn Wei Er, Bing Zhao, Adrian W.K. Law

Thursday 2 july 2015

17:30 - 17:45h at Asia (level 0)

Themes: (ST) Impacts of pollutants on the water environment, (T) Hydro-environment

Parallel session: 13G. Environment - Impact

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Activities such as land reclamation and dredging of navigation channels often involve open-water disposal of sediment. The transport of disposed sediment is mainly determined by the source conditions (e.g. type of sediment and method of release) as well as ambient conditions. It is necessary to understand the near-source transport mechanisms to minimize the environmental impacts on surrounding receptors (e.g., industrial water intakes, corals, fish farms, etc.). The present investigation focuses on the releases from bottom split barges, which are commonly used for disposing large amounts of sediment. In past studies, the sources of release were idealized as either three-dimensional (3D) point sources (Rahimipour and Wilkinson, 1992; Ruggaber, 2000; Gu et al., 2008) to simulate the case when the water depth was very much larger compared to the dimension of the release mechanism; or two-dimensional (2D) line sources (Noh and Fernando, 1993; Noh, 2000) at the other extreme. Temporally, releases were categorized either as quasi-instantaneous (thermal) when the time of discharge was short compared to the duration of descent, or continuous (plume) otherwise. However, with a finite amount of sediment and varying water depths, the release from a split barge cannot be described uniquely by any of the above cases. The barge’s geometry may also play a role. We have conducted experiments in a glass tank with dimensions of 2.4 m (length) × 2.2 m (height) × 1.2 m (width). Finite amounts of sediment were released from a model barge, which was designed and scaled based on actual split barges. Observations showed that, upon release, sediment clouds experienced complex transitions from 2D to 3D and from plume to thermal flow regimes. In the paper, the behavior of the sediment clouds is discussed in detail and a newly developed classification scheme is introduced to classify the flow regimes.