Erosion of intertidal sediments may be influenced by several factors. In this study, the influence on sediment erosion of some physical mechanisms such as the sediment bed roughness, suspended particles and surface waves was investigated. Because of the complexity of the phenomena involved, careful experiments have been planed in order to make each mechanism dominant and to assess its contribution. Experiments were carried out in laboratory in a circular mini flume, 131 mm in diameter using the laser Doppler anemometry (LDA) technique. Simultaneous measurements of the tangential and axial velocity components and the Reynolds stresses were obtained by the use of two colours (blue and green) of a 6 W Argon ion laser operating on a backscatter mode. The fluid is driven on a tangential flow at controllable speeds by a circular flat lid on the top of the flume, which is linked to the shaft of a rheometer. A comprehensive physical and chemical analysis of the sediment enabled the accurate definition of the laboratory test conditions. Tests were made in natural sediments collected in two estuaries and in artificial (simulated) beds at various Reynolds numbers. For artificial beds, both rigid and deformable (either fluid or grain) surfaces were investigated. For the fixed bed option, three different alternatives were considered: a smooth surface was set as a basis for subsequent comparisons with more complex structures; an exact reproduction of the sediment morphology on a gypsum mould; a sand roughness bed, using a range of glass beads. The deformable bed consisted of a two-fluid layer or by the use of a set of glass and polymer beads, to investigate the influence of entrained particles upon the turbulence. From this analysis, the surface topology proved to be a key factor in the flow field. Therefore, the use of solid replica of marine sediments appears to be an appropriate method to generate a simulated bed. The influence of surface waves upon the flow patterns in the vicinity of the sediment surface, and its contribution to the turbulence, was investigated using special rings with a wavy shape, in which the wave amplitude and wavelength were controlled. The use of LDA in natural sediments enables the direct measurement of the shear stress at the sediment interface. By comparing the changes on the fluid velocity profiles, the sediment critical shear stress was determined. The occurrence of bed deformation in erosion was identified by discontinuities of the shear stress. It was concluded that the suspended particles concentration is the most important factor affecting the fluid turbulence close to the interface. Results also showed that the bed deformation plays an important role in controlling the wall shear stress. The flow inside the mini flume was characterised experimental and numerically, using the CFX code. It was observed the existence of secondary flows near the outer wall, which affect erosion in such mini flumes. It was also found that the numerical models employed cannot predict exactly the flow in channels with strong curvature, as the mini flume, in which the turbulent flow is non isotropic.