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Towards a better prediction of dredging plumes: numerical and physical modelling of the near-field dispersion
Decrop, B. (2018). Towards a better prediction of dredging plumes: numerical and physical modelling of the near-field dispersion, in: PIANC Yearbook 2017. pp. 3-18
In: (2018). PIANC Yearbook 2017. PIANC: Brussels. , meer

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Trefwoorden
    Dredging
    Environmental impact assessments
    Properties > Physical properties > Turbidity
    Suspended sediments
Author keywords
    Trigger levels; Overflow plumes

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Abstract
    Construction and maintenance of ports and waterways involves dredging activities in many cases. Dredging projects require assessment and mitigation of a number of environmental impacts. Some of the potential impacts are related to turbidity plumes resulting from hydraulic and mechanical dredging processes bringing sediment into suspension.

    In the recent past, environmental awareness and by consequence environmental legislation has become stronger. As a result, dredging contractors and dredging consultancy have been faced with the challenge to implement better control mechanisms for environmental management purposes. More specifically, turbidity plumes have been monitored closely in the past to follow up on their fate. Numerical simulations allow for real-time forecasting of the fate of the turbidity plumes in the near future. By means of a well-calibrated tidal flow model, planned dredging activities can be implemented as sediment sources in the numerical flow models. In this way, the plume dispersion due to interaction of the tidal flows and the timing of activities spilling sediments can be predicted up to a week ahead.

    In the past, large-scale numerical flow models have been applied, and covered the wider areas around the project site that can potentially be affected by the works. Overflow losses from Trailer Suction Hopper Dredgers (TSHD) are one of the main sediment spills during the execution of dredging projects. In the past, near-field sediment distributions from overflow spills have been determined using simplified laws and crude estimates of losses.

    In the presented work, efforts have been made to improve the accuracy of plume simulations by performing highly-detailed computational fluid dynamics (CFD) simulations of the flows of the water-sediment-air mixture around the ship hull and its interaction with the propellers. These detailed simulations have several benefits, such as assessment of overflow design and insights in the three-dimensional distribution of sediments near the dredger, but are too time-consuming to be used in operational forecasting of turbidity plumes. In the work presented in this paper, the CFD results have been applied to develop a parameterised model, significantly faster compared to the CFD simulations, but more accurate compared to the previous generation of near-field models.

    The coupling of this new generation of near-field spill models with the far-field (large-scale) flow models allows for a significant increase in accuracy of turbidity forecasting. In this way, using forecasting models, dredge and disposal productions can be optimised while complying with turbidity levels imposed in the environmental criteria.


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