Particle saltating motions during bed load transport are dominated by the forces acting upon particles and the random process of the particles impacting on and rebounding from the channel bed. A real-time flow visualization technique is developed in this study to measure particle saltating trajectories, corresponding velocities, and impacting and rebounding angles. Based on the experimental data, regression equations for the dimensionless saltating length, height, and velocity were obtained. A numerical model that is able to simulate the continuous saltating process of a single particle was developed. The model was calibrated and verified with the experimental data, and the results were satisfactory. The model was also used to generate a series of synthetic data. Based on these data and the flume data collected by previous investigators, a bed load equation was derived.

The purpose of this study is to develop a three-dimensional continuous saltation model which is able to simulate the saltating behaviors of a single particle near the channel bed. A real-time flow visualization system, including two charge-coupled device cameras, an image-grabbing card and an OPTIMAS image-processing software, is developed to measure the three-dimensional saltating trajectories and corresponding velocity components. The averaged dimensionless saltation length, height and width were found to follow Pearson type III distributions and the dimensionless saltation velocity follows a normal distribution. The impacting and rebounding angles increase as the flowtransport capacity T_* increases. The rebounding angles, under various impacting conditions, follow a normal distribution. Based on the data colleted, an impacting and rebounding mechanism is derived, and thus a three-dimensional saltation model is established to simulate the dynamic characteristics of the saltating particles. Regression equations for the important saltating characteristics, including saltation length, height, width and three-dimensional velocity components were obtained. Based on these equations, bed load equation was derived. This equation tends to slightly overestimate the bed load transport. Nevertheless, the overall accuracy is satisfactory.

Gravity currents play an important role in many aspects of natural processes and engineering practice. This paper presents a systematic lock-exchange experimental study to investigate the influence of linearly stratified environments and ramp slope on the hydrodynamics of gravity currents. A high-speed camcorder and particle image velocimetry (PIV) are applied to analyze the macro- and microstructures of gravity currents. It is observed that the front velocity of the gravity currents increases first then decreases for both stratified and unstratified environments. However, the density contrast that drives the currents decreases more quickly in stratified environments as the currents descend the ramp, causing more intense deceleration of the front velocity, which indicates the damping of ambient stratification on gravity currents. Based on the thermal theory, a new set of analytical formulas is then developed to determine the front location and velocity at the deceleration stage by considering the ...

The purpose of this study is to investigate the interacting mechanism between the saltating particles near the channel bed. A real-time flow visualization technique was developed to measure the interparticle collision behaviors during the saltating process. A two-dimensional continuous saltation model was also developed. This model was calibrated and verified with the experimental data collected with satisfactory results. The model is able to simulate the continuous saltating trajectories of several particles. The simulated maximum saltation height is about 2–2.5 times the values calculated by a single-particle saltation model. Due to the effects of particle collision, the simulated saltation velocities of the multiple particles model are less than those derived from a single-particle model. Regression equations for the saltating height and velocity were obtained.