Experimental and numerical investigation of bed load transport in unsteady flows

An elaborate experimental system is designed and built in Hydraulics Laboratory of DEÜ, in order to study bed load transport in unsteady flows. The steady flow experiments are done with fixed and mobile bed. The unsteady flow experiments are conducted with the hydrographs having rising and falling durations of 15 seconds to 120 seconds, from the steady state value of 12.0 l/s and 30.3 l/s to the peak value of 53.5 l/s and 89.9 l/s. The bed load is collected at the channel downstream end. The sediment motion is analyzed by image processing technique.The critical point for inception of sediment motion is investigated for steady flow case. The bed load values measured in both steady and unsteady flow conditions are compared with those calculated from the empirical relations given in the relevant literature. The most compatible empirical relations are identified.In image processing analysis, the average grain velocity is investigated throughout the hydrograph. From the camera records, it is revealed that the bed load motion is sporadic, which results in fluctuating character. When the dimensionless bed load obtained from the video recordings and the dimensionless shear stress are used a hysteresis between these parameters is not observed. If the dimensionless bed load obtained from baskets and the dimensionless shear stress is compared, a hysteresis is observed.The one dimensional partial differential equations for the continuity of water and for sediment and the differential momentum equation are numerically solved. An acceptable accordance between experimental findings and numerical results is observed.