Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the bursting phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1) the contribution of turbulent bursting events remained identical in both experimental conditions, (2) ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3) wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment.

In order to understand sediment transport process based on knowledge of their soil properties and hydrodynamic behaviour a series of 2D laboratory controlled small-scale experiments were conducted using the Ahlborn sediment mobile bed tank (4.0×0.6×0.2 m). Experiments were conducted in smooth and rough bed conditions with purposely-built Soil Protrusion Apparatus (SPA) to measure the basic parameters on which erosion depends. Sediment deposition patterns in equilibrium stage associated with different bed roughness and particle size distributionswere fundamentally investigated. Extended physical modelling of crescent zones also included analysing their grain size distribution. Dimensional analysis and multiple linear regression methodswere employed to derive a simple empirical relationship for erosion rate (ER) in terms of the shear stress (τ_s), average grain diameter (d50) and soil protrusion (z) for smooth and rough sediment bed conditions. These analyses also suggest ways to refine empirical models, examining transport rates to explore the limits of erosion and deposition influences in shallow flow conditions.

Laboratory experiments were undertaken in a unidirectional current flume in order to examine the role of turbulence on incipient sediment motion. An acoustic Doppler velocimeter was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter (related to suspended sediment concentration). The relationship between wall turbulence (in particular, the "bursting" phenomenon) and resuspension of a non-cohesive sediment bed was examined. The results within a range above and below the measured critical velocity suggested that: 1) the contribution of turbulent bursting events remained identical in both experimental conditions; 2) ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events; and 3) wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured critical velocity highlighted the need to re-evaluate the accuracy of a single time-averaged critical velocity for the initiation of sediment entrainment.