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Low-slope bedrock meandering rivers widely exist in areas controlled by geological structures (the bed slope is less than 5‰). Flood has a great influence on riverbed sedimentation and erosion in bedrock meandering rivers, however, we have a poor understanding of dynamic structure of flood for bedrock meandering rivers. By geometrically generalizing bedrock meandering reaches, considering the Froude similarity and side wall roughness, a generalized model of a bedrock meandering channel is established in order to analyze the water surface profile distribution, time average flow fields and turbulence structure characteristics for bends under flood. The results show that under the flood flow, the minimum water surface transverse gradient, separation of flow on the convex bank, development of double circulation on the concave bank, velocity-dip-phenomenon and maximum secondary circulation intensity are caused at the upstream of the bend apex, and the maximum water surface transverse gradient and circulation splitting are caused at the downstream of the bend apex; the bed shear stress is distributed in the flow separation area at the convex bank as well as the center of the upstream of the bend apex, and the transverse momentum transport is concentrated at the upstream of the bend apex. The experiment results show an explanation in view of hydrodynamics in respect to bed erosion and sedimentation in bedrock meandering rivers. [ABSTRACT FROM AUTHOR]

We develop a numerical model that encompasses wave induced current as well as advective and diffusion models to examine the effects of Stokes drift on pollutant transport within the surf zone on a plane beach. We also carried out dye diffusion experiments in the surf zone, and modelled wave-induced currents by applying the concept of radiation stress. We based wave propagation on the equation of wave energy conservation, while the advective diffusion model, including Stokes drift, was used to describe pollutant transport in the surf zone. We then used the alternative direction implicit finite difference method to differentiate between models, and evaluated the validity of these numerical approaches using a Gaussian pulse with a known exact solution. The numerical results of this study are in close agreement with analytical solutions. Finally, we applied our model to simulate pollutant transport within the surf zone on a plane beach. Results show that numerical modeling including Stokes drift more closely agrees with experiments than do results that exclude this drift. Thus, in general, we show that a pollutant will be more obviously transported shoreward in addition to the extent of expected drift. We therefore suggest that Stokes drift plays an important role inpollutant drift within thesurf zone, especially in ashoreward direction. [ABSTRACT FROM AUTHOR]

Upper- and lower-flow regimes are formed under different conditions. To identify them is important for predicting mobile bed resistance. Based on the dimensionless resistance equation, a new discriminant function to flow regimes is deduced, which contains two dimensionless parameters, namely, the suspension number and the flow action number. The concepts of the flow regime transition angle and the flow regime transition path are proposed. The problem of the discriminant flow regime is revisited from the perspective of flow resistance. The discriminant function is calibrated by 4 176 sets of flume and field measurement data at home and abroad, and the critical equation between the upper-and lower-flow regimes is determined. The results show that the prediction accuracy of the proposed critical equation is approximately 91% in the lower regime and 85% in the upper regime, and the comprehensive accuracy is approximately 89%. In fine-sand rivers, when the water temperature decreases, the transition from the lower-flow regime to the upper-flow regime is more likely to occur. The discriminant function proposed in this study can not only identify the flow regime with high accuracy but also analyze the effect of water temperature on the flow regime transition. [ABSTRACT FROM AUTHOR]

Consolidated silt is a special depositional landform. The properties,formation and evolution of consolidated silt,which relate to the fields of marine sediment dynamics and marine engineering geology,are of crucial importance for shore protection,navigation safety,and marine construction. This paper introduces the concept,characteristics and distribution of consolidated silt and focuses on mechanisms of formation and evolution. Recent research progress on consolidated silt is reviewed according to the three modes formation and evolution (i.e. primary deposition mode,coarsening and sorting mode,and liquefaction and seepage mode). New research ideas and methods with regards to consolidated silt are considered after analyzing the advantages and disadvantages of emphasizing the three modes. It is proposed that future research directions should:combine basic approaches of marine soil mechanics and sediment dynamics;carry out simultaneous observations of multiple-factors characterizing the water,seabed surface,and internal seabed;build an integrated conceptual model to describe the physical process;establish corresponding mathematical models to evaluate the formation and evolution of consolidated silt. [ABSTRACT FROM AUTHOR]