Non-capacity transport of non-uniform bed load sediment in alluvial rivers

Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.

Study on the Thermal Insulation Performance of a New Seabed Sediment Fidelity Sampler Based on ANSYS

A new seabed sediment fidelity sampler was developed and its thermal insulation performance was studied and analyzed. The temperature distribution simulation indicated that the sample quality could be insured by using this new sampler. Based on ANSYS10, the temperature finite element model of the sample cylinder was established. According to the law of conservation of energy, the unsteady heat transmit equation of the sampler under solid-liquid coupling condition was derived, then the mathematical model calculation was carried out by using a mixed finite-element finite-difference method, and two thermal insulation methods were used. The simulation was carried out by using the thickness of the thermal insulation layer and heat conductivity as the variable parameters and the temperature distribution of the sampler and related influencing factors were obtained. Optimization analysis was conducted using the simulation data and related parameters and the magnitude ranges of the parameters were obtained that could meet the design temperature requirements. The experimental data and simulation results indicated that the results were in good agreement with the realities, and this sampler might be of value for seabed sediment sampler design and manufacture.

Influence of tributaries on downstream bed sediment grain sizes under flysch conditions

Tributaries are one of the most important factors contributing to variability in the downstream evolution of bed sediment grain size.The primary aim of this work is to evaluate the response of the bed sediment texture in the recipient channel induced by ten tributaries of the?ernáOstravice stream and find reach-scale and catchment-scale parameters that would be able to predict this response.The research was based on collecting information on the grain size distributions at sites adjacent to confluence zones.A significant change in sediment texture occurred in the vicinity of five confluences.Considering the other factors contributing to grain size variability(e.g.,local channel geometry,lithology,and lateral sediment sources),it was assumed that only four of them were associated with a sufficient bedload influx to alter the sediment calibre below the junction.Moreover,a significant morphological effect in the form of a large confluence bar was observed in one case.These tributaries had several common features:(i)they had a larger relative catchment area than that of nonsignificant tributaries;(ii)they were characterized by different bed grain sizes,with some exceptions;and(iii)they had a higher unit stream power close to the confluence in relation to that of the mainstream.These characteristics were represented by the proposed relative parameters,including the relative unit stream power and bed material texture,which allowed the best classification of significant and nonsignificant tributaries.In their simplified form,the parameters described the transport capacity and grain size distribution,which were generally considered to be primary factors responsible for a redefinition of the sediment texture in the recipient channel.However,it should be noted that these results are subject to some degree of uncertainty due to the relatively small sample size of only 10 tributaries.

Pollution of bed sediments and its changing process of Nansihu Lake

In order to research the changing process of the pollution from the formation of Nansihu Lake, this study determined the isotope age and depositional rate and analyzed the organic geo-chemical quotas and heavy metal quotas of two sedimentary profiles of Weishan and Dushan lakes. Research results showed that from the formation of Nansihu Lake, the change of the pollution could be divided into four phrases. At the early phrase of the formation, the organic matters of the lake mainly derived from the exotic matters and had a close relation to the effect on the water and sands from the Huanghe (Yellow) River. At the middle and late phrases of the development, the endogenous matters of the lake became the main and stable source of the organic matters. The overflow of the Huanghe River, the excavation of the Grand Canal and the cut of trees caused the changes of the historic pollution. In recent 20 years, the modern industrial pollution from the organic matters and heavy metals has an increasingly heavy tendency.

Development of All-Weather and Real-Time Bottom-Mounted Monitor of Bed Load Quantity

Quantity of bed load is an important physical parameter in sediment transport research. Aiming at the difficulties in the bed load measurement, this paper develops a bottom-mounted monitor to measure the bed load transport rate by adopting the sedimentation pit method and resolving such key problems as weighing and desilting, which can achieve long-time, all-weather and real-time telemeasurement of the bed load transport rate of plain rivers, estuaries and coasts. Both laboratory and field tests show that this monitor is reasonable in design, stable in properties and convenient in measurement, and it can be used to monitor the bed load transport rate in practical projects.

Flow structure and phosphorus adsorption in bed sediment at a 90° channel confluence

The distribution of the phosphorus（P） adsorption in a bed sediment at channel confluences is an important issue for understanding the transport of contaminants in channel networks. In this study, the flow structure and its effect on the P distribution in the bed sediment were investigated in a 90° confluence flume. It is shown that the P adsorption amount in the sediment varies significantly in different hydrodynamic zones. The P adsorption amount is high in the flow separation zone where the horizontal velocity of the flow is very small, and it is low in the maximum velocity zone where the flow velocity reaches a maximum. The low P adsorption amount is observed in the downstream portion of the distorted shear layer, while the P enrichment is found in the upstream portion, as is related to the significant downwelling flow in this zone. Thus, the flow structure, especially, the flow velocity, has a significant effect on the distribution of the P adsorption in the bed sediment at the channel confluences.

Motion characteristics of binary solids in a liquid fluidised bed with inclined plates

Rectangular inclined channels prove promising for solid classification based on the principle of parti- cle differential sedimentation. In the present work, we investigated the motion characteristics of binary solids in a modified fluidised bed （mFB） with inclined plates. We developed a theoretical model for the particle motion behaviour that accounts for the average solid volume fraction in the inclined channel and interactions between binary solids. The experimental system was designed to be consistent with the idealised theoretical arrangements to maximise the measurement accuracy. The experimental particles were mixtures of silica sand particles of sizes 425-710 i^m and 710-880/~m, respectively. Specifically, we investigated the flow hydrodynamics of the binary suspension in terms of the settling length of both par- ticle species and the bed expansion behaviour. We also analysed the utilisation factor and the separation efficiency of the mFB. The results showed that the average solid volume fraction in the inclined channel fluctuated slightly for a given total solid inventory. The utilisation factor and separation efficiency of the system decreased when increasing either the fluidisation velocity or the solid inventory. The prediction results were in good agreement with the experimental data with an absolute deviation of less than 15%.

Oscillatory velocity in boundary layer over mobile sediment bed under asymmetric wave and current conditions

The oscillatory flow provides the major dynamic force for the mass and energy transport in estuary and coastal areas.An analytical approximate velocity formula is proposed to evaluate the oscillation in the boundary layer over the mobile sediment bed of the sheet flow induced by the asymmetric wave and current.The velocity formula consists of an oscillatory force part and a constant force part corresponding to the Navier-Stokes equation of the asymmetric oscillatory sheet flow over the mobile sediment bed.The mobile sediment bed is defined by an erosion depth formula with consideration of the phase lag,the acceleration and the flow asymmetry.The wave part includes the phase lead parameters from all components of the free stream velocity.The development of the wave part is affected by the current part through the erosion depth and the boundary layer thickness.The erosion depth,the roughness height and the boundary layer thickness of the mobile sediment bed are introduced into the current part without a transition area for the wave-current eddy viscosity.The current part is induced by the wave eddy viscosity within the boundary layer and influenced by the wave-current apparent roughness outside the boundary layer.The velocity profile and duration are evaluated by an approximate velocity formula through experiments for both asymmetric wave and wave-current cases.The oscillation feature in the boundary layer is illustrated by the approximate velocity formula through the asymmetric wave cases over the mobile sediment bed.

Experiment study of the effects of hydrodynamic disturbance on the interaction between the cyanobacterial growth and the nutrients

The eutrophication of shallow lakes is sensitive to dynamic currents （i.e., disturbances） because of their shallow depths and high contents of nutrients in bed sediments. The relation between the sediment resuspension and the algae bloom is not well understood in the field scale because the interwoven influencing factors cannot be examined individually. By combining the laboratory experiment and the field observation, this paper proposes a sediment-water-algae concept to simulate the effects of hydrodynamic disturbances on the algae growth in the Taihu Lake located in east China. The sediments are sampled from the Taihu Lake while the Microcystis aeruginosa （M. aeruginosa） algae is cultured in the laboratory and then transplanted into the experiment cylinders. The temperature and the light intensity in the experiment are adjusted to be similar with the prevalent in situ conditions. The results indicate that the M. aeruginosa populations under the disturbance condition of the rotational speed ≤300 rad/min in the experiment （corresponding to the bottom velocity flow ≤0.059 m/s, the shear stress ≤ 0.069 N/m2 , or the wind speed ≤ 4 m/s in the field） are higher than those under the disturbance condition of the rotational speed is 400 rad/min （corresponding to the bottom flow velocity 0.079 m/s, the shear stress 0.124 N/m2）. It is suggested that a low to moderate disturbance prompts the release of the nitrogen as welt as the phosphate nutrients from the bed sediments, amplifying the eutrophication of the Taihu Lake.