Acoustic imaging of cohesive sediment resuspension and re-entrainment in the Changjiang Estuary, East China Sea

Abstract

Vertical profiles of instantaneous cohesive suspension concentration, obtained from an acoustic suspended sediment monitor in the Changjiang Estuary, indicate that near-bed high-concentration suspensions consist of upper and lower high-concentration suspensions, separated by a natural breakpoint at ca. 2 g l\. Acoustic images revealed near-bed high-frequency resuspension events of a few seconds, which contribute mainly to the formation of the lower near-bed high-concentration suspension. Upper and lower lutoclines are also indicative of re-entrainment of lower and upper high concentration suspension, respectively. Near-bed high-frequency resuspension is caused by turbulence, while re-entrainment is probably attributable to internal wave activity.

Controls on effective settling velocities of mud flocs in the Changjiang Estuary, China

“…Acoustically measured suspended sediment concentrations were obtained at 10-cm water depth intervals. Possible errors in the procedure for converting acoustic signal to concentration estimates have been discussed elsewhere (Shi et al, , 1997(Shi et al, , 1999Hamilton et al, 1998). Comparison between point-sampled (C m ) and acoustically measured (C c ) is shown in Figure 3.…”

“…L. R. Shi et al, 1986;Li et al, 1995;Shi et al, , 1997Shi et al, , 1999Chen et al, 1999;Shi and Kirby, 2003) and numerical modelling (e.g. Wang, 1992;Zhou and Wu, 1994;Shi, 2002).…”

“…Vertical profiles of tidal current velocities should be close to a logarithmic form. Concentration profiles shown in Figures 6 and 7 were interpretated from acoustic images (Shi et al, , 1997(Shi et al, , 1999. The time period for each image is 12 min, which have been evenly subdivided into seven, corresponding (a), (b), (c), (d), (e), (f) and (g) in Figures 6 and 7, respectively.…”

Suspended sediment transport along an idealised tidal embayment: settling lag, residual transport and the interpretation of tidal signals

“…In the context of estuaries, measurements (e.g. Shi et al 1997;Shi 2004) and detailed numerical models (e.g. Cancino and Neves 1999) both suggest that this variation is a highly complex process.…”

Sediment dynamics of turbidity maximum in Changjiang River mouth in dry season

“…Movement of particulate matter in the highly suspended estuary setting is multivariate, and therefore the workload of water sampling collection needs to be deliberate. The application of optical instruments is constrained by high SSC, but observation through acoustic measurement with high resolution has become reasonable (Shi et al, 1996(Shi et al, , 1997Shi and Ling, 1999). Various Acoustic Doppler Current Profiler (ADCP) modules designed for such a turbid estuary can obtain not only three dimensional current velocity data, but also acoustic turbidity information.…”