IN SITU CRITICAL EROSION SHEAR STRESS MEASUREMENT AND APPLICATION IN COHESIVE SEDIMENT TRANSPORT

摘要

Critical shear stress is a key parameter in sediment transport calculation in morphology study. Once a critical shear stress exerted by the moving fluids over the bed, is exceeded erosion will occur. An in situ measurement method is used to calculate in situ critical erosion shear stress in marine environment via measurement current speed along the water depth based on Acoustic Doppler Current Profiler (ADCP), sediment concentration based on Optical Backscatter Sensor (OBS) and suspended sediment diameter using a LISST 100 laser diffraction instrument. The sea bed friction velocity is coupled based on a parameter obtained from the measurement current speed distribution along the water depth. Thus the relevant critical erosion shear stress is calculated accordingly. The investigation critical shear stress covering non-cohesive sediment with diameter of the sediment larger than 63μm shows a good consistent with existing empirical formula. For the fine sediment (D ≤ 63μm), an empirical formula for critical stress from the measuremen tresults in this paper is presented for the potential application in cohesive sediment transport calculation including erosion and sedimentation in coastal engineering.