kA cGD0

k2 c2VG

hence Tf a I — I c m with - < n < -, 1 < m < 2 f 1 W 4 << 2 < <

The flocculation model contains a flocculation parameter kA and a floc break-up parameter kB, which have to be determined empirically. This has been done at present for one set of data only, that is, on the basis of flocculation experiments carried out in the settling column of Delft Hydraulics (see Van Leussen5). This column is a 4.25 m high perspex cylinder with an inner diameter of 0.29 m. Within the column, a grid can be oscillated at various frequencies and amplitudes to generate a homogeneous turbulence field. For details on the calibration, the reader is referred to Winterwerp.8,9,20 From this analysis, we found kA = 14.6 m2/kg and kB = 14.103 sec1/2/m2 (NB: nf = 2). It is stressed that these parameters have been obtained for cohesive sediment from the Ems estuary in The Netherlands, and that no other data are available at present. One would expect, though, that these parameters are not universally applicable. However, as no other data are available, these values will be used anyway in this chapter.

0 0

Post a comment