A PARTICLE TRACKING TECHNIQUE FOR BEDLOAD MOTION IN RIVERS

Nowadays, the advances made in scientific visualization techniques have enhanced our capabilities of tracking sediment and measuring sediment rates. The focus of this study is to provide a new experimental approach to determine the displacement speed of particles rolling atop a well packed layer of spheres and provide a formula that describes the average displacement speed of particles as a function of the particles geometry and weight, settling velocity, and the frictional characteristics of flow. Such formulas are lacking because the emphasis, so far, has been placed in developing expressions that provide the displacement speed of particles during saltation only. The nature of the present study is experimental. As such, tests were performed in a laboratory flume so that flow and sediment conditions could be precisely controlled. The motion of three spherical particles with diameters 5/8 of an inch, 7/8 of an inch, and one inch was monitored in a laboratory flume that is 45 ft long, 1.5 ft wide, and 3 ft laboratory under different flow conditions and bed roughness. The flow was varied between the incipient flow conditions and conditions representing general sediment motion in natural gravel bed rivers. Overall, 30 experimental runs were conducted. Once sediment motion was established it was monitored using a digital camera mounted above the flume to obtain plan view images of the test section and the particles pathways. Individual frames depicting a particle’s motion were produced using Asymetrix DVP and Adobe Photoshop 4.0. An image analysis software developed by Data translation was employed to calculate the displacement speed of sediment motion. The results are compared with values predicted against the results of Sekine and Kikkawa and Lee et al.. Although no direct comparison can be made with the above studies since they are primarily focused on sediment saltation, the displacement speed of the particles that is predicted here is found to be in between the predictions of Sekine and Kikkawa and Lee et al. The Sekine and Kikkawa was developed for saltation over smaller size particles that the ones tested here over irregularly packed bed and the Lee et al. study for lighter particles. The ultimate goal of this study is to incorporate the particle displacement speed expression into a sediment transport model, applicable to gravel bed streams.