FIELD STUDY ON NEAR-BOTTOM TURBULENCE AND RESUSPENSION OF COHESIVE SEDIMENT IN THE TONE RIVER ESTUARY

Abstract

Near-bottom turbulence and flux of suspended sediment were measured in the Tone River Estuary to study a relationship of resuspension and settling of cohesive sediment with turbulence. An acoustic Doppler velocimeter was deployed because of its advantage of measuring suspended sediment concentration besides turbulence by utilizing acoustic intensity data. Vertical profile of velocity and spatial distribution of suspended sediment were measured with an ADCP and water quality meters.
Three phases for sediment suspension were observed: First phase was characterized by quasi-equilibrium under low Reynolds stress, second phase by resuspension of comparatively fine sediment accompanied by a growing turbidity front moving upstream, and the third phase by strong resuspension of comparatively rough sediment under strong Reynolds stress. Budget analysis of suspended sediment suggested that the settling velocity at the third phase was 10^-3[m/s] while the value at the first phase was 10^-5[m/s].