Abstract
Despite recent advancement in the field of sediment transport, the integration of cohesive sediment properties in large-scale transport models remain a challenging task. In order to model adequately the change in particle size that occurs in different environmental conditions, flocculation models based on the so-called Population Balance Equations (PBE) are often used. These models have to be efficient enough to be implemented in numerical transport models, and as full PBE's are time-expensive to run and depend on a huge amount of a-priori unknown parameters, simplifications have to be made. These simplifications comes unavoidably at the cost of properly accounting for the complex particle-particle and particle-fluid interactions. In order to stay as close as possible to the physical processes, we propose a different approach based on a logistic growth model that mimics the Particle Size Distribution (PSD) measured over time for all size classes. The parameters of the model can easily be found from laboratory measurements. In contrast to most models, the particle classes we propose are not defined by particle size, but in terms of mineral sediment composition. One class is composed of (unflocculated) mineral sediment particles, another of flocculated sediment particles and a third one of organic particles. The mass balance between classes and the way to obtain their corresponding average settling velocity are given. Mass balance and settling velocities are the required input parameters for all sediment transport models. The simplicity of the derived expressions, and their link with measurable variables, makes them good candidates for future implementation in such models.
Highlights
Large-scale numerical models, such as DELFT3D (Lesser et al, 2000), (Lesser et al, 2004), ECOMSED (Blumberg and Mellor, 1987), (Blum berg et al, 1996) and TELEMAC (Hervouet, 1991), (Le Normant, 2000), (Sherwood et al, 2018) enable to study the transport of sediment and from this derive their impact on the environment
In order to model adequately the change in particle size that occurs in different environmental conditions, flocculation models based on the so-called Population Balance Equations (PBE) are often used
In order to stay as close as possible to the physical processes, we propose a different approach based on a logistic growth model that mimics the Particle Size Distribution (PSD) measured over time for all size classes
Summary
Large-scale numerical models, such as DELFT3D (Lesser et al, 2000), (Lesser et al, 2004), ECOMSED (Blumberg and Mellor, 1987), (Blum berg et al, 1996) and TELEMAC (Hervouet, 1991), (Le Normant, 2000), (Sherwood et al, 2018) enable to study the transport of sediment and from this derive their impact on the environment. The particles present in the water column will change size, and the concentrations of the different size classes will vary over time This has important consequences in terms of sediment transport, as by aggregation (flocculation) for example, the concentration of a large size class will increase while the concentration of a small size class will decrease . Realizing that every size class has a different mineral sediment content, this implies that the spreading of mineral sediment within the water column will be very different from the case where no aggregation occur. Another conse quence of flocculation is that a change in particle settling velocity will occur. Mineral sediment particles will be transported less far than organic flocs of same size under the same conditions
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