The Behaviour of Suspended Sediments and Muds in an Estuary

Abstract

The fundamental behaviour of suspended sediments and muds was investigated using an annular flume with the condition of cyclically changed shear stress. The results from two series of experiments showed that particle sizes which participate in the variation of suspended sediments were restricted to smaller sizes of the material. It was also found that the cyclically steady state was finally attained with respect to the suspended sediments as the tidal cycle repeated. In that state the suspended sediments were subject to three phenomena: erosion; deposition with dispersed state; and deposition with flocculation. A simple model on the suspended sediments in an estuary was developed and its behaviour in a model estuary was simulated by using the fluxes of erosion and deposition in the experiment. That model well described the variation of the suspended sediments and muds.

Evaluation of two conflicting paradigms for cohesive sediment deposition

“…Their results generally support the "exclusive paradigm," but more extensive experiments are necessary to elucidate depositional behaviors under unsteady flows such as tidal currents. Although some early studies (e.g., Hayter, 1983;Umita et al, 1984;van Leussen and Winterwerp, 1990) also simulated cyclic tidal flows in flumes, their objectives were somewhat different, and thus they did not address the question raised here. Nevertheless, their data were reinterpreted to check the validity of the two conflicting paradigms.…”

“…Previous laboratory studies (e.g., Hayter, 1983;Umita et al, 1984;van Leussen and Winterwerp, 1990) that used the simulated tides (T ≈ 12 h) were compared with the results of this study to reveal the effect of secondary circulation (Table 3 and Fig. 7).…”

“…In order to demonstrate these two kinds of SSC-response patterns under simulated tidal cycles, the conceptual diagram given by Umita et al (1984) was modified based on the strength of secondary circulation in the annular flume (Fig. 8).…”

“…Nonetheless, the variation in time-averaged SSC will be focused on in this section because other early studies (i.e., Hayter, 1983;Umita et al, 1984;van Leussen and Winterwerp, 1990) did not provide any data interpretation on temporal variability. Hayter (1983) showed that the measured SSC is nearly in phase with flow velocity (Fig.…”

“…These processes are primarily controlled by the variation in hydrodynamic and sedimentary conditions (Umita et al, 1984;McAnally, 1999). It is generally accepted that the bottom sediment is eroded when the bed shear stress (τ b ) is above a critical value, i.e., the critical bed shear stress for erosion (τ ce ) (Krone, 1962(Krone, , 1993Sanford and Halka, 1993;Winterwerp and van Kesteren, 2004).…”