Observation of mixed grain size sediment transport rate and streamwise nearbed flow velocity in a gravel-worked bed

¹ Researcher, Center for Disaster Risk Management, University of Mataram, Indonesia
² Lecturer, Postgraduate Programme in Civil Engineering, University of Mataram, Indonesia
³ Lecturer, Department of Civil Engineering, University of Mataram, Indonesia

^* Corresponding author: y.saadi@unram.ac.id

Abstract

This experiment observed the prediction of sediment movement for channel bed composed of mixed grain size and its relationship with nearbed turbulence. Changes in transport rate at different time elapsed was obtained by observing bedload transport rate and associated them with streamwise nearbed flow velocity. Regardless of the shape and duration, observations indicate that the total amounts of transported bedload during the antecedent flow hydrographs are the best indicators of bed stability as observed in the stability hydrographs. Experiments also suggest that high turbulence flow caused by dispersion in the average streamwise nearbed velocity roughly disrupted the bed, allowing dislodgement of coarser grain and preventing finer materials from being fully sheltered. As the result the production of transported material was very significantly increased. Systematic change is presumably absent in the variation of average instantaneous shear stress following an increasing and decreasing discharge as evidenced by average streamwise nearbed flow velocity during different pattern of antecedent flow hydrographs. The variations that produced slightly different fashion in transport rate led to the inference that the major difference in the transport rate response during stability tests were created by unsteady flow hydrographs with rapid increase and rapid decrease.