Sediment Transport in Circular Sewers with Non-Cohesive Deposits.

摘要

The study focuses on transport of non-cohesive sediment in partly filled and full-flowing circular sewers with non-cohesived deposits. Laboratory experiments have been carried out to verify existing and newly derived predictors for bed-shear stress, incipient motion of sediment, bed formation, flow resistance and sediment transport. The maximum bed-shear stress can be predicted using Einstein's separation technique. A new predictor had to be derived, however, in order to predict the average shear stress. Incipient motion of sediment of a flat bed occurred for shear stresses below Shields' critical values. The bed formation showed ripples, dunes, flat beds and isolated bed forms. The bed type could be predicted with the Froude number, the bed-shear stress and the volume of sediment in the sewer. New formulae have been derived to predict the bed-form dimensions. Due to extra energy losses in sewers, as a result of shape effects, flow-resistance calculations for circular sewers differ from those for rivers. Each bed type requires another predictor for the sediment transport rate.