Effects of non-cohesive particles on suspended particle characteristics in a partially flocculated estuary during spring tides

Abstract

Schindler, R.J., Bass, S.J. and Manning, A.J. Effects of non-cohesive particles on suspended particle characteristics in a partially flocculated estuary during spring tides. In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.)We present unique, in-situ data describing suspended particle populations in a meso-tidal estuary over the tidal cycle where the proportion of cohesive and non-cohesive sediment varies temporally. Simultaneous measurements of sediment concentration and hydrodynamics reveal that suspended particle characteristics are highly variable over the tidal cycle primarily due to the variable presence of non-cohesive sands, rather than changes in suspended particulate matter concentration (SPMC) and turbulent shear stress (τ). The particle distributions reveal that sand fractions appear in suspension throughout the tidal cycle as part of flocs and as individual grains. Non-cohesive or dense, consolidated mud fractions are sourced primarily from bedload under high τ, particularly during flood acceleration. However, the flood-deceleration phase experiences an influx of advected marine sands that increase suspended sand content despite declining velocity and turbulent shear stress. This generates bimodality in particle distributions and mean particle characteristics are misleading. Comparison with data collected at the turbidity maximum zone, beyond the extent of non-cohesive particles, shows that population size, settling velocity and density vary significantly between locations despite being <10 km apart. The implications of this spatial variation for our understanding of estuarine sediment transport are discussed.