Estuarine Turbidity Maxima and Variations of Aggregate Parameters in the Cam-Nam Trieu Estuary, North Vietnam, in Early Wet Season

Vu Duy Vinh,Dinh Van Uu,Sylvain Ouillon

doi:10.3390/w10010068

Abstract

This study aims at exploring the characteristic parameters of the Estuarine Turbidity Maxima (ETM) and at investigating their tidal variations within the Cam-Nam Trieu estuary (North Vietnam) during the early wet season. Six longitudinal river transects were performed at spring tide. Two types of ETM were observed: an upper well mixed ETM with high Suspended Particulate Matter (SPM) concentrations up to the surface at low salinity (0.11 to <1 psu), and a lower ETM confined in a bottom layer over stratified waters at salinities between ~1 psu and 15 psu. Their length depended on the longitudinal salinity gradient and was highest at low tide than at high tide. D50 of the flocs varied between 35 and 90 μm, their excess of density between 60 and 300 kg m−3 and their settling velocity ranged from 0.07 to 0.55 mm s−1 with values between 0.12 and 0.40 mm s−1 in the core of ETMs. The average fractal dimension of flocs was estimated to vary between 1.93 (at high tide) to 2.04 (at low tide).

Highlights

Estuarine Turbidity Maxima (ETMs) are zones of elevated suspended particulate matter (SPM)concentration at the interface between the river and the sea
The river discharge measured at the Cam hydrologic station
13 May 2015) was typical of intermediate discharge between values measured in the Cam River in dry season (181 m3 s−1 ) and in wet season (806 m3 s−1 ) in 2008 and 2009 [38]

Summary

Introduction

Estuarine Turbidity Maxima (ETMs) are zones of elevated suspended particulate matter (SPM)concentration at the interface between the river and the sea. Because of the strong influences of marine water, tide and river discharge, the occurrence of ETMs is complex and difficult to predict [1,2]. They are trapping a lot of suspended matter and encompass a huge range of SPM concentrations with maximum values from less than 100 mg L−1 like in the Kennebec Estuary, USA [3,4] to >200 g L−1 like in the Severn Estuary, UK [5]. Olsen et al [9] showed that the deposition rate reached up to 30 cm year−1 in certain parts of the ETM in the Hudson estuary on timescales of 5–10 years.

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Conclusion