Thanos Papanicolaou
IIHR - Hydroscience & Engineering, The University of Iowa

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Application Note: Sediment Transport
 
Noncohesive Sediment: Understanding the mechanisms involved in the transport and fate of noncohesive soils in natural channel systems remains an open case in water-related engineering disciplines.  The main challenge in studying noncohesive sediments is the complex character of the bed geometry which governs the velocity, as well as the turbulence structure of the flow which in turn, control the sediment-carrying capacity of the flow.  Bed geometry is controlled by stochastic processes and subject to drastic changes due to changes in the flow condition.  Bedforms, clusters, step and pools are few examples of such complicated bed geometry.  In addition, sediment may consist of a wide range of grain sizes.
   
Virtual velocity: The advances made in scientific visualization techniques have enhanced our capabilities of tracking sediment particles.  A new experimental approach was incorporated to determine the displacement speed and the virtual velocity of particles rolling atop a well packed bed.  The displacement speed is the speed of a particle moving from one point of rest to another, while the virtual velocity is the velocity of a particle including its resting period.  Experiments were performed in a laboratory flume so that flow and sediment conditions could be precisely controlled. Sediment motion was monitored using a digital camera mounted above the flume to obtain plan view images of the test section and the particles pathways.  Image analysis software developed by Data Translation was employed to calculate the displacement speed of sediment motion.  Average resting periods were determined and used to calculate the virtual velocity.   The objective of this experimental approach was to develop a formula that describes the average speed of particles as a function of the particles’ geometry and weight, settling velocity, and the frictional characteristics of flow.  The virtual velocity formula can be used to estimate bedload transport rate in gravel bed streams.