Transport of Suspended Particulate Matter

The model system allows also a basin wide description of the transport of suspended particulate matter (SPM), which can be transported near the seabed within the so-called fluffy layer and is strongly affected by surface waves in coastal waters. Understanding the settling and resuspension of SPM in response to waves and currents is of great importance to assess the transports of material discharged by rivers from the coastal regions to the final deposit in the sediments of central basins. 

To simulate the transport of sedimentary material in the water column over realistic topography, it is necessary to run a three-dimensional circulation model, which is extended by submodels describing the surface waves, (Schwab et al., 1984), the shear forces within the bottom boundary layer, and the resulting deposition and erosion processes at the seabed. 

In recent years several numerical sediment transport models have been presented, which use either the quasi-Lagrangian or the Eulerian treatment. In the quasi-Lagrangian approach, 

In the Eulerian approach (Jankowski et al., 1996 Lou and Ridd, 1997 Holt and James, 1999 Ribbe and Holloway, 2001 Christiansen et al., 2002), a transport equation is solved for the sediment concentration. Recent studies (Kuhrts et al., 2004, 2006 Seifert et al., 2007) describe moving sedimentary material as a tracer variable in a three-dimensional circulation model. This approach combines a wave boundary layer (Grant and Madsen, 1979) and a friction layer (Smith and McLean, 1977) to compute the wave-induced and the current-induced contribution to the skin friction acting on the seabed. 

If the skin friction exceeds the critical threshold for resuspension, sedimentary material is I ifted off from the bottom and is transported into the water body. Grainy particles may also be moved by the so-called bed-load transport that occurs already at a lower threshold. Deposition results from the settling of the sediment particles, if the shear stress falls below a certain limit. The critical thresholds, the settling velocities, and the erosion and deposition rates are material constants derived from experiments (Soulsby, 1997). 

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Drake, C.L., and Gorsline, D.S. 1973. Distribution and transport of suspended particulate matter in Hueneue, Redondo, Newport and La Jolla submarine canyons. Geological Society of America BuUetin, 84 3949-3%8. 

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