| Autor: |
Ditschke, Dirk, Markofsky, Mark |
| Zdroj: |
Sediment & Ecohydraulics; 2007, p241-253, 13p, 1 Black and White Photograph, 1 Diagram, 3 Charts, 5 Graphs |
| Abstrakt: |
Generally only one sediment class is used in the modeling of suspended-sediment transport in river and estuarine flows. This sediment concentration has a settling velocity, which varies depending on turbulence and the sediment concentration. In order to refine and improve sedimentation predictions, it is important to consider different sediment classes and/or the time dependency of the flocculation process. Therefore, the numerical model TELEMAC-3D was extended to include different sediment classes. The flocculation process is simulated as an exchange from one sediment class into another. In estuarine waters, turbulence-induced flocculation is dominant (Winterwerp, 1999). The dissipation parameter G is used here to quantify the turbulence and a flocculation parameter FLOC introduced to determine whether flocculation or breakup is dominant: 1 + aG/1 + bG² ≡ FLOC → FLOC = {>1 → Flocculation/<1 → Breakup In this study, flocculation implies the transfer from a sediment class with a lower settling velocity to a class with a higher settling velocity. The time dependency is considered by an effectiveness factor. In each time step only a small concentration of a sediment fraction is transferred to a larger fraction. This factor depends on the turbulence, the concentration and the stickiness of the flocs. The model was compared with coagulation theory (Smoluchofski, 1917) and with laboratory tests conducted within the German joint project "SEDYMO" (Fine Sediments Dynamics and Pollutant Mobility in Rivers). It was shown that the model includes the basic processes associated with flocculation and breakup and that it can be calibrated to simulate the measured data. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
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