Uncertainty study of data-based models of pollutant transport in rivers

River engineeringTransport and fate of pollutants in river

A numerical study of turbulence influence on saltating grains

River hydrodynamicsTurbulent open channel flow and transport phenomen

Influence of rigid emerged vegetation in a channel bend on bed topography and flow velocity field : laboratory experiments

Trees have been used extensively by river managers for improving the river environment and ecology. The link between flow hydraulics, bed topography, habitat availability, and organic matters is influenced by vegetation. In this study, the effect of trees on the mean flow, bed topography, and bed shear stress were tested under different flow conditions. It was found that each configuration of trees produced particular flow characteristics and bed topography patterns. The SR (single row of trees) model appeared to deflect the maximum velocity downstream of the bend apex toward the inner bank, while leading the velocity to be more uniformly distributed throughout the bend. The entrainment of sediment particles occurred toward the area with higher values of turbulent kinetic energy (TKE). The results showed that both SR and DR (double rows of trees) models are effective in relieving bed erosion in sharp ingoing bends. The volume of the scoured bed was reduced up to 70.4% for tests with trees. This study shows the effectiveness of the SR model in reducing the maximum erosion depth

Response to the slug injection of a tracer-a large-scale experiment in a natural river

A unique, large-scale tracer test performed along a 90-km reach of a natural river is presented. This method was crucial for evaluating the impact of a retention reservoir on protected areas of the river downstream, and to assess the threats due to potentially catastrophic releases of toxic substances into that river. The response to the slug injection of a soluble tracer is assumed to imitate the characteristics of a soluble pollutant, so an understanding of how tracers mix and disperse in a stream is essential to understanding the processes of pollution transport. The procedure applied during this experiment consisted of the instantaneous injection of a known quantity of Rhodamine WT into the stream and the determination of the temporal variation in concentration of the tracer at sites as it moved downstream. The results were analysed from the perspective of a transient storage model. Relevant model parameters were evaluated by fitting the computed breakthrough curves to the observed ones on a reach-by-reach basis

Threshold surface concentration of microplastics triggering higher mobility on gravel bed

To study the effects of different surface concentrations of microplastics (MPs) on their mobility, a series of experiments was run in a flume with gravel bed. Different amounts of two types of compact MPs (with densities of 1.1 and 1.4 g/cm3) were released. The surface concentration of MPs spanned between 0.3 and 30 g/kg of surface clasts (corresponding to a surface cover ranging from 0.04% to 4%) and the MPs were allowed to deposit under low flow velocity conditions. As the flow rate was increased, stepwise, exceeding the MPs-specific reference threshold conditions (observed in previous studies of MPs moving on a microplastic bed) two different behaviours were observed: i) low-density MPs mobilised at conditions similar to the reference ones up to approximately a concentration of 3g/kg surface clasts (0.04% surface cover) while, ii) high-density MPs were not mobilised at their reference threshold conditions up to a concentration of 15g/kg surface clasts, corresponding to 2% surface concentration. As the mentioned values were surpassed, both MPs types showed a higher mobility (compared to the reference), meaning lower mean flow velocities triggered motion of a larger number of particles. Preliminary analysis of mean flow conditions and videos of moving particles suggest that a "critical concentration" exists, above which the chosen microplastic particles assume higher mobility, requiring lower flow velocities to get into motion. This higher mobility may be ascribed to the changed morphology of the bed which corresponds to critical concentrations of added plastic particles over the gravel bed. This n̈ew morphologym̈odifies the near-bed flow characteristics, thus imposing new conditions to the MPs' mobility. Further investigations are needed to confirm such hypothesis, with specific focus on the near-bed flow field. Also see: https://micro2022.sciencesconf.org/426572/documentIn MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nan

Acoustic Doppler Velocimetry (ADV) data on flow-vegetation interaction with natural-like and rigid model plants in hydraulic flumes

Value of the Data • These data were obtained with reference to two vegetation representations in partly vegetated channels: a novel experimental arrangement in which vegetation was simulated by using artificial flexible foliated plant stands and a second configuration with rigid cylinders. The value of these data relies in the hydraulic similarity achieved between the two sets of experiments and in the use of natural-like vegetation of complex morphology. • River engineers, environmental scientists and researchers interested in flow-vegetation interaction and hydrodynamic processes in partly vegetated channels can benefit from these data. • The described data are optimal for investigating the flow-vegetation interaction in partly vegetated channels, with reference to the mean and turbulent flow structure. These data can be used for developing and validating models for velocity prediction for vegetated flows.Vegetation, generally present along river margins and floodplains, governs key hydrodynamic processes in riverine systems. Despite the flow-influencing mechanisms exhibited by natural vegetation and driven by its complex morphology and flexibility, vegetation has been conventionally simulated by using rigid cylinders. This article presents a dataset obtained from hydraulic experiments performed for investigating the flow-vegetation interaction in partly vegetated channels. Vegetation was simulated by using both natural-like and rigid model plants. Specifically, two sets of experiments are described: in the first, vegetation was simulated with natural-like flexible foliated plants standing on a grassy bed; in the second, rigid cylinders were used. Experiments with rigid cylinders were designed to be compared against tests with natural-like plants, as to explore the effects of vegetation representation. The following experimental data were produced: 3D instantaneous velocity measured by acoustic Doppler velocimetry, vegetation motion video recordings, and auxiliary data including detailed vegetation characterization. These experiments are unique both for the use of natural-like flexible woody vegetation in hydraulic experiments and for the similarity achieved between the resulting observed vegetated shear layers. These data are expected to be useful in vegetated flows model development and validation, and represent a unique benchmark for the interpretation of the flow-vegetation interaction in partly vegetated channels