Velocity sedimentation data processing

CFaT riverine models were presented for both the water column and bed sediment. They were then simplified to focus onto the non-flow resuspension soluble fraction using the quasi-steady state assumption to isolate the key water-side and sediment-side process elements. Field evidence of soluble release based on CFaT model derived data was reviewed for three rivers. Both the traditional particle background resuspension process and more recent soluble fraction process algorithms data interpretation were covered. Numerical field calibrated resuspension velocities and soluble mass-transfer coefficients were presented. Candidate water-side and sediment-side transport processes, selected from the literature were reviewed. Those that provided the best theoretical explanation and contained laboratory and/or field data support were selected. Finally, the flux and the overall transport coefficient which captures the essential features of the framework were presented. Following this the theoretical mass-transfer coefficients were applied to a site on the Fox River below De Pere Dam. Numerical calculations were made for the transport coefficients for both individual and combined processes. 

Particles of >10 nm diameter are subject to significant sedimentation rates as a result of gravitational forces (the velocity may be estimated crudely by use of Stoke s Law). Consequently their atmospheric lifetime is severely limited by the gravitational settling process, and by impaction upon surfaces. Particles of <10 jum diameter are removed only relatively slowly from the atmosphere, those greater than ca. 0.3 /im by impaction processes and the smaller particles by diffusive deposition. The deposition flux may be estimated from the deposition velocity and some data are presented in Section 4.2.2. 

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