Recommendations for numerical modelling of suspended matter distribution during dredging works

Abstract

The problem of estimating the distribution of suspended matter during dredging works is relevant due to the large volume of annual major and operational dredging activities in the ports of Ukraine constituting more than 4.5 million m3 of soil. The execution of dredging works is associated with the inflow of suspended matter into the marine environment having a negative impact on the marine ecosystem. The magnitude of the inflicted damage depends on the characteristics of a zone of increased turbidity and a reliable assessment of such characteristics makes it possible to determine the actual damage to be indemnified according to the current environmental legislation.
 The numerical modelling of the suspended matter distribution is the easiest way that may be used for evaluation of the characteristics of the zone of increased turbidity. The possibility of obtaining solutions on more general grounds in comparison with analytical methods, much less time and cash to be spent than for field experiments and modern computer software allowed widespread implementation of research methods of such modelling.
 The article is devoted to the study of the numerical model of suspended matter distribution during dredging works. It considers explicit, implicit and mixed finite-difference schemes for solving a stationary differential equation of turbulent suspended matter diffusion in the flat problem formulation. Several series of calculations have been performed for various model parameters based on which the obtained solutions have been analyzed, the assessment of the difference between the calculation results under different schemes has been done and the optimum parameters of the calculation grid have been proposed. The research presents some recommendations for numerical modelling of the suspended matter distribution in the water flow including: use of an explicit scheme; the number of jets in the excavated area should not exceed 3; the number of steps to the control opening – not less than 75; when using an implicit or mixed scheme it is necessary to introduce an adjustment in an unstable zone based on the total amount of matter accumulated into the opening until the final result is achieved.