Fractal geometry of in situ flocs in the estuarine and coastal environments

Abstract

One- and two-dimensional fractal dimensions of in situ flocs were determined from the dependence of the are and perimeter of projection of the flocs on their greatest length, using an underwater camera and image-analysis system. Values for the fractal dimensions of flocs in the Elbe estuary and the North Sea varied among the samples: D₁ in the range of 1.03 to 1.14 and D₂ in the range of 1.41 to 1.81. D₂ as obtained here represents the three-dimensional fractal dimension of flocs, which has been obtained in previous studies from the dependence of settling velocity or porosity of flocs on their characteristic length. Comparisons of environmental factors showed no relationships between the fractal dimension and fluid shear. Salinity effects on the fractal dimension were probably also insignificant in our samples. The relationship of D₁ with the concentration of suspended matter was fairly convincing and suggests that the flocs had a rougher edge of projection at high than at low concentrations.