STUDY OF SEDIMENT TRANSPORT RATE OVER DUNE-COVERED BEDS

River bed configuration, as a roughness element, exerts flow resistance and influences sediment transport process. In this study, a movable bed experiment has been carried out to evaluate the influence of form drag, exerted by microscale bedforms, on sediment transport rate. The experimental results have been compared with the bedload transport rate calculated by using Ashida & Michiue's and Meyer-Peter & Muller's formulae. The bedload transport rate, measured directly in the present experiments, appears to be in good agreement with the bedload transport estimated by both relationships. Furthermore, experimental result has been compared with the result of bedload transport calculated by using a numerical model proposed by Giri & Shimizu. This numerical model incorporates a stochastic pick up-deposition model for non-equilibrium sediment transport with a distribution function of mean step-length proposed by Nakagawa & Tsujimoto. It is revealed that the mean step-length has an effect on sediment transport rate, thereby exerts influence on bedform geometry, particularly on wave-length. Consequently, a basic attempt has been made to calibrate parameter mean step-length based on experimental result and numerical analysis. Comparison between experimental and numerical simulation results shows reasonably good agreement for both the bedload transport rate and geometric characteristics of bedforms.