Sediment-induced buoyancy destruction and drag reduction in estuaries

Abstract

This paper presents an analysis of drag reduction by buoyancy destruction in sediment-laden open channel flow. We start from the log-linear profile proposed by Barenblatt (Prikladnaja Matematika i Mekhanika, 17:261-274, 1953), extended with a second length scale to account for free surface effects. Upon analytical integration over the water depth, an expression for sediment-induced drag reduction is found in terms of an effective Chézy number, water depth, bulk Richardson number, and Rouse number. This relation contains one empirical/experimental coefficient, which was obtained from a large series of numerical experiments with a 1DV POINT MODEL. Upon calibration of this model against field and laboratory observations, we tuned the turbulent Prandtl-Schmidt number and found an optimal value of σ T =2, consistent to observations by Cellino and Graf (ASCE, J Hydraulic Engineering, 125:456-462, 1999). All numerical results could be correlated with the

Interaction between suspended sediment and tidal amplification in the Guadalquivir Estuary

“…Even in the downstream part (GQ150), values of 6-8 g/l are measured. This is more than sufficient for reducing the effective hydraulic drag (Winterwerp et al 2009;Winterwerp and Wang 2013;Winterwerp et al 2013). It is noted that in November 2007, a short high river discharge event occurred.…”

“…Therefore, it is concluded that the anomalous behaviour of the estuary with high tidal amplification is most likely caused by reduction of effective hydraulic drag in those periods. Winterwerp et al (2009) give the following relation for the effective Chézy coefficient as function of the distribution of suspended sediment concentration: Fig. 11 Comparison between numerical model results and field data concerning the relation between the amplification factor and the tidal amplitude …”

“…Although less well known, the suspended sediment transport can also have influence on the tidal flow in an estuary. High sediment concentration can cause reduction in the effective hydraulic drag due to buoyancy destruction (Winterwerp et al 2009), which in turn causes a stronger tidal amplification in an estuary Wang 2013, Winterwerp et al 2013). This phenomenon has been reported to occur on the Amazon shelf (Beardsley et al 1995;Gabioux et al 2005) and in the Ems Estuary (Chernetsky and Schuttelaars 2010).…”

Fine sediment transport into the hyper-turbid lower Ems River: the role of channel deepening and sediment-induced drag reduction

“…This may require a vertical resolution as low as several mm, and therefore a large number of grid cells-the resulting computational time of the model may become very long. A second option is to relate the bed roughness to suspended sediment concentration using expressions such as derived by Winterwerp et al (2009). A third option is to strengthen the effect of sediment on hydrodynamics through a modified Prandtl-Schmidt number σ t .…”

Two-dimensional horizontal modeling of fine-sediment transport at the South Channel–North Passage of the partially mixed Changjiang River estuary, China

“…1DV has been attempted to study the fine (cohesive) sediment transport within the Changjiang River estuary (Shi 2001). Other relevant numerical modeling studies have been attempted since 1988 (Zhao et al 1988;Port and Delta Consortium Ltd 1995;Zhou and Wu 1996;Dou et al 1999;Zhu et al 1999;Zhou et al 2000;van Rijn 2007;Hu et al 2009;and Winterwerp et al 2009). Despite the studies listed above, a couple of fundamental issues relating to the complex processes, i.e., resuspension/erosion, flocculation/settling, and deposition, which occur within the Changjiang River estuary, still remain unanswered.…”