Application of laser anemometry for measuring critical bed shear stress of sediment core samples

• Published in: Continental shelf research Vol. 28; no. 20; pp. 2718 - 2724
• Main Authors: Araújo, M.A.V.C., Teixeira, J.C.F., Teixeira, S.F.C.F.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.12.2008
• Subjects: Brackish; Critical bed shear stress; Cávado; LDA; Mini flume; Natural sediments; Westerschelde; ANE, Portugal; ANE, Netherlands; ANE, Netherlands, Zeeland, Westerschelde; LDA; Westerschelde; Critical bed shear stress; Cávado; Natural sediments; Mini flume
• ISSN: 0278-4343; 1873-6955
• DOI: 10.1016/j.csr.2008.09.011

This work details the application of the Laser Doppler Anemometry (LDA) technique for the direct measurement of the critical bed shear stress of natural sediment beds. This property was determined from variations in the velocity profiles obtained at the interface, for various Reynolds numbers. The onset of erosion was identified as a sudden transition in the local stress. Samples of sediment were collected from Cávado (Portugal) and Westerschelde (the Netherlands) estuaries. Experiments were carried out in laboratory using a circular mini flume, 126.8 mm in diameter, enabling the reproduction of the flow characteristics close to the sediment. It was found that the deformation at the sediment surface is a very important factor affecting the bed shear stress. That deformation is affected by the mud characteristics and composition, namely the particle size. It was also verified that the erosion process is not continuous, the sediment being eroded in layers. From the various experiments, it was concluded that the LDA technique is appropriate for measuring the critical bed shear stress of sediments.