Nonuniform Bedload Transport In Turbid Waters

Sediment transport in natural rivers occurs almost in sediment-laden flow. The difference may exist between mechanism of sediment transport in turbid waters and that in clear waters. Especially, it should not neglect the exchange between bedload and suspended load in fine bedload transportation. The effect of suspended load on bedload transport in turbid waters, so far, has hardly been considered becourse of its complexity. Therefore, the study on this problem is of paticular significance.It was a maiden attempt in study on nonuniform bedload transportation in sediment-laden flow. On the basis of three states exchange mode of sediment on the bed surface, the analytical method of combining stochastic theory with mechanics was used. Especially, while exchanging between bedload and bed material, the net transport of bed load towards waters was considered. As a matter of fact, the proportion of bed material, bedload and suspended load may redistribute and adjust to equilibrium exchanging according to flow intensity.Probability of suspension (β_k), which represent characteristic of suspended load, was included in the process of building sediment transportation model in turbid waters. The formulas of fractional, total nonuniform bedload transport rates and bedload size of distribution were established theoretically. Fractional bedload transport rates formula can reflect the degree of bedload reduction due to existence of suspended load, and it was also appicable to sediment transportation in clear waters.Through the flume experiment of bedload transportation in turbid waters, the rationality and reliability of the proposed formulas were verified by the experimental and field measured data. The relationship between sediment transportation intensity and flow intensity has been established. It is found that bedload graduation may coarser than that of original bed material in turbid waters in sediment graduation research, and this phenomenon is of none probability in sediment transportation under clear waters condition. The results show that to the effective estimation of the sandy bedload transport rate, it should not be neglected the content of the suspended load which comes from bedload, and the amount of bedload was relatively decreased.