IAHR, founded in 1935, is a worldwide independent member-based organisation of engineers and water specialists working in fields related to the hydro-environmental sciences and their practical application. Activities range from river and maritime hydraulics to water resources development and eco-hydraulics, through to ice engineering, hydroinformatics, and hydraulic machinery.
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You are here : eLibrary : IAHR World Congress Proceedings : 32nd Congress - Venice (2007) : THEME A: Engineering and Management of Fresh-water Systems : Near-bed flow field measurements at threshold of sediment motion
Near-bed flow field measurements at threshold of sediment motion
Author : Andrea Marion, Andrea Bottacin Busolin, Simon J. Tait, Matteo Tregnaghi
Several experimental tests were carried out using a gravel bed tilting flume and an advanced Particle Image Velocimetry (PIV) system. Sediment movement at the threshold was surveyed at the grain scale under uniform flow conditions. A natural river gravel with well sorted sediment was used. Flow field measurements were made over an area of approximately 400 cm2, on a plane located at 5 mm above the original sediment bed. Image processing and cross-correlation techniques were used to obtain flow velocities. Sequences of images of the bed surface were taken simultaneously with the measurements of the flow field. Statistics of the movements of the grains were collected through a semi-automatic procedure. Significant changes in the local flow field were observed in the proximity of the entrained or deposited particles. Such variations of velocity, which can be either in terms of the longitudinal and lateral components or in terms of the relevant fluctuations from the time average, appear as a direct effect of the removal or deposition of individual grains. A strong correlation is shown between the changes in the streamwise velocity and the movement of the particles: local velocity increases were observed to correspond with the entrainment of grains, while local velocity reduction occurred as a grain was deposited. Thetheory of Grass is revisited and further developed. The new formulation provides a way to estimate the probability distribution of individual grain resistance from statistics of the near bed velocity field and of the entrainment risk.
File Size : 315,959 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 32nd Congress - Venice (2007)
Article : THEME A: Engineering and Management of Fresh-water Systems
Date Published : 01/07/2007
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