Suspended sediment transport in large rivers is constituted mainly by cohesive sediments, which form aggregates or flocs with primary particles less than 65 μm. The removal of cohesive sediments in aquaculture tanks is a difficult problem. Due to its size, density, and shape, the hydrodynamic behavior of flocs is very different from that of non-cohesive sediments as they depend on the interaction with the water column. This chapter describes the experimental results obtained in sedimentation tanks, reduced models of aquaculture recirculation tanks, and a rotating circular flume with Plexiglas walls, in which optical methods were used to determine flocs’ characteristics. These methods include particle tracking velocimetry (PTV) and digital holography for particle image velocimetry (DHPIV). Fractal models for floc density were successfully developed and validated with PTV experimental results in an aquaculture recirculation tank. Also, a model for the settling velocity of the flocs was validated using a permeable drag coefficient definition. Suspended sediments from Mexico’s two largest rivers, Usumacinta and Grijalva, with a mean flow rate near mouth of 1700 and 650 m3/s, respectively, were analyzed in a rotating circular flume. The shear velocity obtained in the field was reproduced in the circular flume and size and shape of flocs were obtained. This allowed to reproduce suspended sediment concentration profiles of rivers. DHPIV techniques were developed in order to obtain the actual size of the flocs based on Fresnel approximation for the reconstruction of holographic images.
Part of the book: Applications in Water Systems Management and Modeling