The turbidity maximum in a mesotidal estuary, the Tamar Estuary, UK: II. The floc properties.

Measurements have been carried out in the turbidity maximum of the Tamar Estuary at neap and spring tides of floe size, settling velocity and effective density. These measurements were complemented by suspended sediment concentration and turbulence profiles. The overall dynamics of the turbidity maximum have been presented in the companion paper (Part 1), and form a context for the results presented here. The floe size increased from about 50 to about 350 microns across the turbidity maximum, and settling velocity changed from 0.0-6.0mms(-1). The equivalent change in floe effective density was 50-750kgm(-3), Within the turbidity maximum the proportion of macroflocs (>160microns) increased. The changes in floe properties were correlated with changes in concentration and the turbulence parameter G, the root mean square of the gradient in turbulent velocity fluctuations. An empirical equation representing the settling velocity Ws (mms(-1)) in terms of SPM (mgl(-1)) and G (s(-1)) is: Ws = -0.243 + 0.000567SPM + 0.981G - 0.0934G(2).