Sedimentation modeling

Negev, M. A Sediment Model on a Digital Computer. Dept, of Civ. Eng., Stanford Univ., Stanford, CA. Tech. Rep.76. 1967. 109 pages. 

Figure 1.4 gives an example of the adsorption of a compound to suspended sediment, modeled as two resistances in series. At first, the compound is dissolved in water. For successful adsorption, the compound must be transported to the sorption sites on the surface of the sediment. The inverse of this transport rate can also be considered as a resistance to transport, Ri. Then, the compound, upon reaching the surface of the suspended sediment, must find a sorption site. This second rate parameter is more related to surface chemistry than to diffusive transport and is considered a second resistance, R2, that acts in series to the first resistance. The second resistance cannot... 

Two-Box Model for Lake/Sediment System Box 23.3 Solution of Linear Water-Sediment Model PCBs in Lake Superior (Part 3)... 

Typical values for the sediment model are given in Table 23.6. The sizes of zmix and pres should be understood as rough estimates chosen with the aim of analyzing the possible influence of the sediment memory on the PCB concentrations in the open water of Lake Superior. We are interested in the size of ksedex relative to the other removal rates (Box 23.1, Eq. 3), and in the relative contributions of diffusive exchange and particulate resuspension to this exchange coefficient. 

Application of the dynamic water/sediment model to the fate of the PCBs in Lake Michigan is summarized in Table 2 3.7. As it turns out, for both congeners the steady-state concentrations are virtually unchanged relative to the values calculated for the three-phase one-box model of Table 23.5. We also note that in the model the sorbed concentrations are still significantly smaller than the measured values. The same is... 

Application of steady-state solution of linear water-sediment model (Box 23.3) to two PCB congeners in Lake Superior. The steady-state is calculated from Box 21.6. 

Compared to the situation in lakes, the sediment-water interactions in rivers are more complex. Because the flow velocity is constantly changing, particles may either settle at the bottom or be resuspended and deposited again further downstream. In order to adequately describe the effect of these processes on the concentration of a chemical in the river, we would need a coupled water-sediment model with which the profile of the chemical along the river of both the aqueous concentration in the river and the concentration in the sediment bed are described. This is a task to be left to numerical modeling. We choose a simpler approach by approximating the net deposition of the particles and the chemicals sorbed to them as a linear process (see Eqs. 23-16 and 23-17) ... 

Jorgensen, B. B. Fencher, T. (1974). The sulfur cycle of a marine sediment model system. Marine Biology, 24, 189-201. 

Figure 3. Movement and degradation of aminocarb in a water/sediment model.

In conclusion, water/sediment model studies suggest that the dissipation pathways for aminocarb and fenitrothion would be primarily via volatilization and microbial action as schematically represented in Figure 5. 

Figure 5. Dissipation pathways of aminocarb and fenitrothion in water/sediment model systems.

Blackburn, T. H. (1997). Release of nitrogen compounds following resuspension of sediments Model predictions. J. Marine Syst. 11, 343-352. 

A global oceanic sediment model for long term climate smdies. Global Biogeochem. Cycles 13, 221—250. 

Fig. 2.2 Two types of sediment models, (a) The layered, volume-oriented model for bulk parameters only depends on the relative amount of solid and fluid components, (b) The microstructure-oriented model for acoustic and elastic parameters takes the complicated shape and geometry of the particle and pore size distribution into account and considers interactions between the solid and fluid constituents during wave propagation.

Table 2.2 Physical properties of sediment grains, pore fluid and sediment frame used for the computation of attenuation and phase velocity curves according to Biot-Stoll s sediment model (Fig. 2.12).

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