SCOUR MECHANISM AROUND PIERS AT CLEAR WATER EQUILIBRIUM CONDITION

Abstract

This paper presents a review work of local scour mechanism around pier scour holes at clear water
equilibrium conditions. Many researchers have carried out various studies to determine the velocity profiles around the
scour holes. The contours and spatial distributions of the time-averaged (mean) velocities, turbulence intensities,
turbulent kinetic energy and Reynolds stresses at different azimuthal planes were determined. Velocity vector plots of the
flow field at azimuthal planes are used to explain further flow features. The vorticity and circulation of the horseshoe
vortex are determined by using finite difference technique of computational hydrodynamics and Stokes theorem,
respectively. Bed-shear stresses are also estimated from the Reynolds stress distributions. The flow and turbulence
characteristics of the horseshoe vortex are discussed from the standpoint of similarity with velocity and turbulence
intensity characteristic scales. These detailed measurements are obtained with a non -intrusive instrument, the acoustic
Doppler velocimeter (ADV), which measures three-dimensional instantaneous velocities. This instrument is very
practical for the measurements related to scour. This instrument can also be used as a tool during the investigation for
enhancement of sediment transport as an alternative to dredging mechanism in future which is to be explored. It is
therefore felt that more studies are still necessary to enhancement of sediment transport effectively for dredging purpose
and also to measure the turbulence using ADV.