Bedload Transport

The mode of sediment transport where the sediment particles slide, roll, and/or travel in succession of low jumps close to the bed is known as the bedload transport. In this chapter, theories of bedload and formulations to predict the bedload transport rate are presented. The pioneering attempt to predict the bedload transport rate was due to MP du Boys in 1879, who expressed bedload transport rate as a function of excess bed shear stress, that is the bed shear stress exceeding the threshold bed shear stress. Thereafter, number of researchers suggested du Boys-type equations making use of the excess bed shear stress in different forms and coefficients. Other concepts to predict the bedload transport rate are the discharge concept (Schoklitsch type), the velocity concept, the bedform concept, the probabilistic concept (Einstein type), the deterministic concept (Bagnold type), and the equal mobility concept. Besides, the application of the turbulence phenomenological theory provides the origin of the scaling law of the bedload transport. The additional features of this chapter are the discussion on particle saltation, sediment sorting, streambed armoring, and sediment entrainment probability to bedload. The effects of bedload on velocity distribution, length scales of turbulence, and von Kármán constant are also discussed in detail. The methods of computation of bedload transport are illustrated through worked-out examples.