No abstract

No abstract

During bedload movement by saltation, streamwise momentum is transferred from the flow to the saltating grains. When the grains collide with other grains on the bed or in the flow, streamwise momentum is reduced, and there is a decrease in streamwise flow velocity and an increase in flow resistance, herein termed bedload transport resistance f bt . Based on experiments in two flumes with fixed and mobile plane beds and previously published data, an equation is developed that may be used to predict f bt for both capacity and non-capacity flows. The variables in this equation are identified by dimensional analysis and the coefficients are determined by non-linear regression. This equation applies to rough turbulent open-channel flows, where the relative submergence is between 1 and 20 and the entire sediment load moves by saltation. An investigation of the relative magnitudes of f bt and grain resistance f c suggests that where dimensionless shear stress θ is less than 1 and saltation is the dominant mode of bedload transport, f bt /f c increases with θ but never exceeds 1.

No abstract

40The concept of sediment-transport capacity has been engrained in geomorphological literature

No abstract

Data from flume studies are used to develop a model for predicting bed-load transport rates in rough turbulent two-dimensional open-channel flows moving well sorted non-cohesive sediments over plane mobile beds. The object is not to predict transport rates in natural channel flows but rather to provide a standard against which measured bed-load transport rates influenced by factors such as bed forms, bed armouring, or limited sediment availability may be compared in order to assess the impact of these factors on bed-load transport rates. It is suggested that this remarkably high transport efficiency is achieved in sheet flow (1) because the ratio of grain-to-grain to grain-to-bed collisions increases with bed shear stress, and (2) because on average much more momentum is lost in a grain-to-bed collision than in a grain-to-grain one.

Suspended sediment at the watershed scale has played a critical role in sediment pollution, water-quality degradation, and the impairment of riparian ecosystems, and thus has been widely studied in many disciplines. This paper synthesizes a variety of methods adopted in suspended sediment monitoring, estimation and modelling for understanding sediment transport processes and determining the suspended sediment load. Methods for sediment monitoring are described in terms of direct and indirect approaches. Estimation of suspended sediment load is commonly achieved by establishing a sediment rating curve. Different approaches toward the establishment of a sediment rating curve are examined thoroughly. Techniques of sediment modelling are summarized via depiction of various hydrological and sediment models at the watershed scale. The paper ends with the discussion of future developments in suspended sediment studies at the watershed scale.