Accurate Determination of Far-Field Source Terms of Barge Overflow Dredge Plumes Based on Near-Field Monitoring and Modeling

Abstract

This study presents a comprehensive monitoring campaign combined with near-field computational fluid dynamics (CFD) plume dispersion simulations for the overflow plumes originating from a barge being filled by a cutter suction dredger (CSD) in a project in Southeast Asia. The combination of measurements and CFD is used to derive the far-field source terms (FFSTs). The FFSTs are linked to the dredge production and compared with literature values. The presented methodology and insights are generally valid for any dredging project. The outcomes can serve as comparison material for similar projects under similar conditions. Our results show that because of the low flow velocities the dredge plume spreads like a density current close to the seabed. Such a plume is difficult to monitor and its sediment flux reduces quickly due to rapid sediment deposition. The plume measurements and CFD simulations for our case study show a FFST of only 8%–24% of the dredging production (or 15%–46% of the overflow flux) at a vertical location very close to the seabed. Guidelines are provided on the coupling distance of a FFST, which determines whether the upper or lower limit of the presented range can be applied. A combination of advanced computer simulations and extensive field monitoring is used to investigate the mixing of an overflow sediment plume in the vicinity of a barge. The sediment plume originates from the overflow of a barge being filled by a cutter suction dredger. It is determined where in the water column the overflow plume ends up and how big its flux is. Typical plume fluxes are found to be just 8%–24% of the dredging production and the plume is located very close to the seabed. Guidelines are provided when to use the upper or lower limit of the presented range as far-field model source term.