Subaqueous Cohesive Sediment Gravity Flows from Open Water Pipeline Dredge Disposal: Laboratory Experiments and Mathematical Modeling

Abstract

Subaqueous sediment gravity flows generated in open water pipeline dredge disposal operations were investigated through laboratory experiments and mathematical modeling. Three laboratory experiments that simulate typical open water pipeline dredge disposal operations in the coastal environment were conducted by discharging mud slurries with three different initial concentrations in a large pool. The discharged mud slurries descended as vertical buoyant jets through the water column. After impinging the bottom, they formed a short-lived momentum-driven axisymmetric horizontal flow that transformed into an axisymmetric gravity flow soon after. The analysis of the radial spreading of those fluid mud gravity flows showed that their flow dynamics were governed by a balance between the driving buoyancy force and the resisting inertia force. A simple mathematical model (compositional box model) that does not consider the presence of suspended sediment was used to predict the experimental observations. The predictions of the box model solution were observed to be notably in good agreement with experimental observations, despite the box model exhibiting several simplifying assumptions. It is concluded that the radial propagation of fluid mud gravity flows in the inertia-buoyancy propagation phase can be modeled by a compositional box model solution. This study is motivated by the need for deterministic predictive modeling capabilities for coastal dredging operations.