Search

The maximum sediment transport capacity of river channel is affected by hydrodynamic force, resistance and boundary conditions. Based on the hydraulic radius segmentation method, the isosceles trapezoid with the bank slope angle θ was adopted as the water crossing section, and the relative roughness of the river bank to the bottom（λ）,the median particle size of the transported sediment(d50),the roughness of the bed sediment (nb), the discharge (Q), and the gradient (S) were taken into account. The impact of each influencing factor on the maximum sediment transport capacity and equilibrium form of the channel when the alluvial river reaches the equilibrium state was analyzed with the river equilibrium theory. The results show that: when other factors are fixed, the maximum sediment transport rate increases with the increase of λ and decreases with the increase of θ; That is to say, the relative increase of river roughness or the decrease of river slope will enhance the maximum sediment transport capacity of river channel. The increase of Q and S leads to higher river dynamics, thus enhancing the sediment transport capacity of the channel. The maximum sediment transport capacity of the channel will be reduced when the bottom roughness coefficient nb decreases and the flow remains unchanged; The decrease of the median particle size d50 of bed sediment will increase the maximum sediment transport capacity of the river. The channel which is neither too wide and shallow nor too narrow and deep has the maximum sediment transport capacity. [ABSTRACT FROM AUTHOR]

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]

Ｓｅｄｉｍｅｎｔ ｉｓ ｃａｒｒｉｅｄ ｂｙ ｆｌｏｗ ｔｏ ｔｈｅ ｌａｋｅ ａｒｅａ ｄｕｒｉｎｇ ｔｈｅ ｆｏｒｍａｔｉｏｎ ｐｒｏｃｅｓｓ ｏｆ ｔｈｅ ｉｎｉ⁃ ｔｉａｌ ｓｅｇｍｅｎｔ ｏｆ ａ ｄｅｌｔａ， ｗｈｉｃｈ ｍａｉｎｌｙ ｄｅｐｅｎｄｓ ｏｎ ｔｈｅ ｉｎｉｔｉａｌ ｍｏｍｅｎｔｕｍ ｔｏ ｍａｉｎｔａｉｎ ｉｔｓ ｏｗｎ ｃｏｎ⁃ ｔｉｎｕｏｕｓ ｍｏｖｅｍｅｎｔ． Ａｃｃｏｒｄｉｎｇ ｔｏ ｔｈｅ ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ ｏｆ ｔｈｉｓ ｐｒｏｃｅｓｓ， ｔｈｅ ｔｈｅｏｒｅｔｉｃａｌ ｍｏｄｅｌ ｆｏｒ ｔｈｅ ｐｌａｎｅ ｊｅｔ ｂｏｕｎｄａｒｙ ｌａｙｅｒ ｉｎ ｔｈｅ ｉｎｉｔｉａｌ ｓｅｇｍｅｎｔ ｏｆ ｔｈｅ ｄｅｌｔａ ｗａｓ ｅｓｔａｂｌｉｓｈｅｄ ｂａｓｅｄ ｏｎ ｔｈｅ ｓｈａｌｌｏｗ ｗａｔｅｒ ｅｑｕａｔｉｏｎｓ ｆｏｒ ｍｕｄｄｙ ｗａｔｅｒ， ａｎｄ ｔｈｅ ｆｌｏｗ ｆｉｅｌｄ ｄｉｓｔｒｉｂｕｔｉｏｎ ｏｆ ｔｈｅ ｉｎｉｔｉａｌ ｓｅｇｍｅｎｔ ｏｆ ｄｅｌｔａ ｆｏｒｍａｔｉｏｎ ｗａｓ ｏｂｔａｉｎｅｄ ｗｉｔｈ ｔｈｅ ｓｉｍｉｌａｒｉｔｙ ｓｏｌｕｔｉｏｎ ｍｅｔｈｏｄ． Ｂａｓｅｄ ｏｎ ｔｈｅ ｇｅｎｅｒａｌ ｍａｔｈ⁃ ｅｍａｔｉｃａｌ ｍｏｄｅｌ ｏｆ ｒｉｖｅｒ ｂｅｄ ｅｖｏｌｕｔｉｏｎ， ｔｈｅ ｔｈｅｏｒｅｔｉｃａｌ ｅｘｐｒｅｓｓｉｏｎ ｏｆ ｔｈｅ ｍｏｒｐｈｏｌｏｇｉｃａｌ ｃｈａｒａｃ⁃ ｔｅｒｉｓｔｉｃｓ ｏｆ ｔｈｅ ｉｎｉｔｉａｌ ｓｅｇｍｅｎｔ ｗａｓ ｄｅｒｉｖｅｄ， ａｎｄ ｔｈｅ ｅｒｏｓｉｏｎ ａｎｄ ｄｅｐｏｓｉｔｉｏｎ ｏｆ ｔｈｅ ｉｎｉｔｉａｌ ｓｅｇｍｅｎｔ ｗｅｒｅ ｑｕａｎｔｉｔａｔｉｖｅｌｙ ａｎａｌｙｚｅｄ． Ｔｈｒｏｕｇｈ ｔｈｅ ｅｘｐｅｒｉｍｅｎｔａｌ ｖｅｒｉｆｉｃａｔｉｏｎ， ｔｈｅ ｔｈｅｏｒｅｔｉｃａｌ ｓｏｌｕｔｉｏｎ ｃａｎ ｗｅｌｌ ｄｅｓｃｒｉｂｅ ｔｈｅ ｅｒｏｓｉｏｎ ａｎｄ ｄｅｐｏｓｉｔｉｏｎ ｔｒｅｎｄ ａｎｄ ｍｏｒｐｈｏｌｏｇｉｃａｌ ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ ｉｎ ｔｈｅ ｅａｒｌｙ ｓｔａｇｅ ｏｆ ｄｅｌｔａ ｆｏｒｍａｔｉｏｎ． [ABSTRACT FROM AUTHOR]

This paper measured the evolution and wave data of the nourished beach, estimated the contributions of erosion amount and effective wave height to beach erosion by taking the West Beach of Beidaihe as an example. The results show that the beach has an overall erosion trend after the nourishment, with the maximum erosion height of 1.7 m. The cumulative influence of the wave height on the beach erosion is an exponential distribution. Although large waves with lower recurrence frequencies (significant wave height>0.6 m) can cause greater beach erosion, their cumulative contribution to the total beach erosion is only about 25%, while the contribution of regular waves with heights of 0.3 m to 0.6 m can reach 75%. This study can provide reference for maintaining the quality of artificial beach, and beach evolution prediction after artificial nourishment. [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]

This paper proposed an improved method for automatic extraction of multi-band spectral relationship of narrow and deep rivers in mountains and valleys with high sediment concentration from Landsat 8 OLI images, which overcame the mixed pixel effect of mountain shad ow and exposed bedrock in the downstream section of the reservoir. Taking Jingeun to Dongzhuang Reservoir section in the middle reaches of Jinghe River on the Loess Plateau as an example, it separated the water body and mountain shadow, bare mountain and bedrock beach by considering the characteristics of the multi-band spectral, and then constructed a water body extraction model suitable for narrow and deep rivers with high sediment concentration in valleys. Compared with other water extraction models, the method proposed in this paper can over come the influence of shadow close to river channel and bedrock downstream of reservoir on water extraction, and improve the extraction accuracy of narrow and deep rivers with high sediment concentration in mountain canyon. [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]

The bed topography is the result of the dynamic response of a complex meandering river system, and is an important factor influencing the further river development. Based on meandering rivers characterized by large depth-to-width ratios, the relation between the hydraulic structure and the bed topography was explored. The flow characteristics and bed topography responses were discussed through coupling of the N-S equations, the sediment transport equations as well as the bed deformation equations, and with the perturbation method. Research results show that shallows and deep grooves present regular responses under the effects of 2D flow disturbances. For a zero curvature, the bed topography shows an anti-symmetric distribution about the channel centerline; while for a non-zero curvature, the channel centerline deviates toward the concave bank. Finally, the criteria for the judgement on the stability of the bed topography influenced by the Reynolds number, the disturbance wave number and the decay ratio of the bed topography, are given. [ABSTRACT FROM AUTHOR]

Ｔｈｅ ｄｉｒｅｃｔｉｏｎｓ ｏｆ ｆｌｏｗ ｉｎ ｎａｔｕｒａｌ ｃｏｍｐｏｕｎｄ ｒｉｖｅｒ ｃｈａｎｎｅｌｓ ａｒｅ ｆｒｅｑｕｅｎｔｌｙ ｉｎｆｌｕｅｎｃｅｄ ｂｙ ｔｈｅ ｄｉｓｃｈａｒｇｅ ａｎｄ ｆｌｏｏｄｐｌａｉｎ⁃ｍａｉｎ ｃｈａｎｎｅｌ ｃｏｎｆｉｇｕｒａｔｉｏｎ， ｗｈｉｃｈ ｍａｙ ｌｅａｄ ｔｏ ａ ｓｍａｌｌ ｉｎｔｅｒｓｅｃ⁃ ｔｉｏｎ ａｎｇｌｅ ｂｅｔｗｅｅｎ ｔｈｅ ｆｌｏｗ ａｎｄ ｔｈｅ ｃｈａｎｎｅｌ． Ｈｅｎｃｅ， ｌｏｔｓ ｏｆ ｅｘｉｓｔｅｎｔ ｔｈｅｏｒｉｅｓ ｆｏｒ ｆｌｏｏｄｐｌａｉｎ ｆｌｏｗｓ ｕｎｄｅｒ ｔｈｅ ａｓｓｕｍｐｔｉｏｎ ｏｆ ｕｎｉｆｏｒｍ ｓｔｒａｉｇｈｔ ｃｈａｎｎｅｌｓ ｍａｙ ｂｅ ｉｎａｐｐｌｉｃａｂｌｅ． Ｔｏ ｉｎｖｅｓｔｉｇａｔｅ ｔｈｅ ｉｎｆｌｕｅｎｃｅ ｏｆ ｏｂｌｉｑｕｅ ｉｎｆｌｏｗ， ｓｈａｌｌｏｗ ｗａｔｅｒ ｅｑｕａｔｉｏｎｓ ｗｅｒｅ ｕｓｅｄ ｔｏ ｄｅｓｃｒｉｂｅ ｆｌｏｗ ｍｏｔｉｏｎ ｉｎ ｃｏｍ⁃ ｐｏｕｎｄ ｏｐｅｎ ｃｈａｎｎｅｌｓ． Ｔｈｅ ｐｅｒｔｕｒｂａｔｉｏｎ ｍｅｔｈｏｄ ｗａｓ ｕｓｅｄ ｗｉｔｈ ａ ｓｍａｌｌ ｐａｒａｍｅｔｅｒ ｏｆ ｔｈｅ ｏｂｌｉｑｕｅ ａｎｇｌｅ ｔｏ ｄｅｒｉｖｅ ｔｈｅ ａｎａｌｙｔｉｃａｌ ｓｏｌｕｔｉｏｎ ｆｏｒ ｆｌｏｗ ｉｎ ｃｏｍｐｏｕｎｄ ｏｐｅｎ ｃｈａｎｎｅｌｓ ｕｎｄｅｒ ｉｎｆｌｏｗ ｗｉｔｈ ｓｍａｌｌ ｏｂｌｉｑｕｅ ａｎｇｌｅｓ． Ｔｈｅ ｓｏｌｕｔｉｏｎｓ ｗｅｒｅ ｖｅｒｉｆｉｅｄ ｗｉｔｈ ｎｕｍｅｒｉｃａｌ ｓｉｍｕｌａｔｉｏｎ ｒｅｓｕｌｔｓ ａｎｄ ｔｈｅ ｆｌｏｗ ｖｅｌｏｃｉｔｙ ｄｉｓｔｒｉｂｕｔｉｏｎｓ ａｇｒｅｅｄ ｗｅｌｌ． Ｔｈｅｏｒｅｔｉｃａｌ ｒｅｓｕｌｔｓ ｓｈｏｗ ｔｈａｔ ｔｈｅ ｏｂｌｉｑｕｉｔｙ ｏｆ ｉｎｌｅｔ ｆｌｏｗ ｌｅａｄ ｔｏ ａｓｙｍｍｅｔｒｉｃａｌ ｖｅｌｏｃｉｔｙ ｄｉｓｔｒｉｂｕｔｉｏｎ ａｃｒｏｓｓ ｔｈｅ ｃｒｏｓｓ ｓｅｃｔｉｏｎ ｏｆ ａ ｃｏｍｐｏｕｎｄ ｃｈａｎｎｅｌ， ｗｈｉｃｈ ｉｓ ｆｅａｔｕｒｅｄ ｂｙ ａｎ ｉｎｃｒｅａｓｅ ｏｆ ｖｅｌｏｃｉｔｙ ｉｎ ｔｈｅ ｕｐｓｔｒｅａｍ ｓｉｄｅ ａｎｄ ａ ｄｅｃｒｅａｓｅ ｉｎ ｔｈｅ ｄｏｗｎｓｔｒｅａｍ ｓｉｄｅ ｏｆ ｔｈｅ ｍａｉｎ ｃｈａｎｎｅｌ． Ｕｎｄｅｒ ａｎ ｏｂｌｉｑｕｅ ａｎｇｌｅ ｏｆ １３° ａｎｄ ａ ｆｌｏｏｄｐｌａｉｎ⁃ｍａｉｎ ｃｈａｎｎｅｌ ｗａｔｅｒ ｄｅｐｔｈ ｒａｔｉｏ ｏｆ ３∶８， ｔｈｅ ｆｌｏｗ ｖｅｌｏｃｉｔｙ ｄｅｖｉａｔｉｏｎ ｍａｙ ｒｅａｃｈ ２１．８％ ｏｆ ｔｈｅ ｖａｌｕｅ ｉｎ ｔｈｅ ｓｔｒａｉｇｈｔ ｆｌｏｗ ｃａｓｅ． Ｓｕｃｈ ａ ｄｅｖｉａｔｉｏｎ ｉｎｃｒｅａｓｅｓ ｗｉｔｈ ｔｈｅ ｄｅｃｒｅａｓｉｎｇ ｏｆ ｔｈｅ ｆｌｏｏｄｐｌａｉｎ⁃ｍａｉｎ ｃｈａｎｎｅｌ ｗａｔｅｒ ｄｅｐｔｈ ｒａｔｉｏ． Ｔｈｅ ｐｒｏｐｏｓｅｄ ｍｏｄｉｆｉｃａｔｉｏｎ ｔｏ ｆｌｏｗ ｖｅｌｏｃｉｔｙ ｄｉｓｔｒｉｂｕｔｉｏｎ ｍａｙ ｉｍｐｒｏｖｅ ｔｈｅ ａｃｃｕｒａｃｙ ｏｆ ｈｙｄｒｏｄｙ⁃ ｎａｍｉｃ ｃｏｎｄｉｔｉｏｎｓ ｆｏｒ ｆｕｒｔｈｅｒ ｒｅｓｅａｒｃｈ ｏｎ ｓｅｄｉｍｅｎｔ ｔｒａｎｓｐｏｒｔ ａｎｄ ｅｖｏｌｕｔｉｏｎｓ ｏｆ ｃｏｍｐｏｕｎｄ ｃｈａｎ⁃ ｎｅｌ ｒｉｖｅｒｓ. [ABSTRACT FROM AUTHOR]