Hydrodynamic and Mass Transport at Freshwater Aquatic Interfaces

Frontmatter

Time-Averaged Hydrodynamic Equations for Mobile-Bed Conditions

Abstract

The objective of this paper is to expand the framework of the conventional Reynolds-Averaged Navier-Stokes equations for the study of mobile-boundary flows. The temporal averaging concept is discussed first, including relevant definitions and theorems. Time-averaged continuity, momentum, mass-transport and stress balance equations are then derived. These new equations contain additional terms that represent the mobile-boundary effects. Potential applications of the proposed equations include flow-biota interactions and sediment dynamics, among others.

Konstantinos Papadopoulos, Vladimir Nikora, Stuart Cameron, Mark Stewart, Hamish Biggs, Christopher Gibbins

Potential Application of Mesh-Free SPH Method in Turbulent River Flows

Abstract

A comprehensive review has been completed on the simulation of turbulent flow over rough beds using mesh-free particle models. Based on the outcomes of this review, an improved Smoothed Particle Hydrodynamics (SPH) method has been developed for open channel flows over a rough bed, in which a mixing length model is used for modeling the 2D turbulence and a drag force equation is proposed for treating the boundary shear. The proposed model was applied to simulate a depth-limited open channel flow over a rough bed surface. The results of the velocity profile and shear stress distribution show a good agreement with the experimental data and existing analytical solutions. This work reveals that in order to correctly model turbulent open channel flow over a rough bed, the treatment of both flow turbulence and bed roughness effect is equally important.

Ehsan Kazemi, Simon Tait, Songdong Shao, Andrew Nichols

Interaction Between Storm Water Conduit Flow and Overland Flow for Numerical Modelling of Urban Area Inundation

Abstract

Nowadays we can observe increasing frequency of inundations in cities. This makes accurate predicting of inundations more important than ever. Numerical modeling of this issue requires complex approach with simultaneous calculations of pipe flow and surface flow. In this paper, after a short review of known methods used for solving pipe and surface flow, we will try to answer the question if presented methods would be sufficiently accurate for inundation modeling. We will also investigate if known formulas used for modeling interaction between pipe and surface flow describe the issue well and if they can be developed in any direction. There will be presented comparison between results of calculations and experiments built on test stand made for this purpose in Gdańsk University of Technology. The results could be treated as a starting point for further recognition of the phenomenon.

Jakub Hakiel, Michał Szydłowski

Modeling of Ice Passage Through Reservoirs System on the Vistula River

Abstract

A numerical model was used to assess ice passage through proposed reservoir on the lower Vistula River. Model results were compared with observation on the Vistula River, but because the dam is not constructed yet, the direct comparison was not possible. The study focused on ice movement and accumulation in the reservoir for variety of low flow condition with and without wind effect. Bridge’s piers in the upper part of the reservoir were found to be one of the most important parameters affecting ice passage at the proposed dam. The other parameter which hampers or may even lead to stopping ice movement is western wind. The study took place within the framework of exclusive analysis for selecting the final location of a new dam which is critical for ensuring permanent safety of the Włocławek dam. Based on the performed study, the Przypust and Siarzewo variants accomplished the required goals to the largest extent at acceptable risk of ice stoppage and accumulation. Icebreaker operation is required during the ice sluicing operation in the new reservoir.

Tomasz Kolerski

Development of a Laboratory System and 2D Routing Analysis to Determine Solute Mixing Within Aquatic Vegetation

Abstract

A laser induced fluorometry (LIF) system was developed to quantify mixing within spatially variable aquatic vegetation. A comparison is made between intrusive fluorometry techniques and the application of LIF, to quantify mixing in real vegetation in the laboratory setting. LIF provides greater spatial resolution when compared to point fluorometry. Furthermore, LIF is non-intrusive. A two-dimensional routing procedure is used to calculate the longitudinal and transverse velocities and mixing coefficients from a single pulse injection of tracer within a vegetation patch.

Patrick West, James Hart, Ian Guymer, Virginia Stovin

Feasibility of the Porous Zone Approach to Modelling Vegetation in CFD

Abstract

Vegetation within stormwater ponds varies seasonly and its presence affects the flow field, which in turn affects the pond’s Residence Time Distribution and its effectiveness at pollutant removal. Vegetated flows are complex and, as a result, few suitable tools exist for evaluating realistic stormwater pond designs. Recent research has suggested using a porous zone to represent vegetation within a CFD model, and this paper investigates the feasibility of this approach using ANSYS Fluent. One of the main benefits of using a porous zone is the ability to derive the relevant parameters from the known physical characteristics of stem diameter and porosity using the Ergun equation. A sensitivity analysis on the viscous resistance factor \(1/\alpha\) and the inertial resistance factor \(C_{2}\) has been undertaken by comparing model results to data collected from an experimental vegetated channel. Best fit values of \(C_{2}\) were obtained for a range of flow conditions including emergent and submerged vegetation. Results show the CFD model to be insensitive to \(1/\alpha\) but very sensitive to values of \(C_{2}\). For submerged vegetation, values of \(C_{2}\) derived from the Ergun equation are under-predictions of best-fit \(C_{2}\) values as only the turbulence due to the shear layer is represented. The porous zone approach does not take into account turbulence generated from stem wakes such that no meaningful predictions for emergent vegetation were obtained. \(C_{2}\) values calculated using a force balance show better agreement with best-fit \(C_{2}\) values than those derived from the Ergun equation. Manually fixing values of \(k\) and \(\varepsilon\) within the porous zone of the model shows initial promise as a means of taking stem wakes into account.

Fred Sonnenwald, Virginia Stovin, Ian Guymer

A Comparison of Three Solute Transport Models Using Mountain Stream Tracer Experiments

Abstract

Stream ecology may be influenced by the temporary trapping of solutes in geomorphologic structures, which is usually quantified by fitting the Transient Storage Model to tracer data. This paper explores the relationships between the parameters of this model and those of two simpler models, namely the Advection-Dispersion Model and the Aggregated Dead Zone model. It is motivated by the possibility of obtaining more reliable transient storage parameter values by correlating them with the parameters of the other models instead of evaluating them directly. Results were obtained by fitting all three models to a set of tracer data from mountain streams, predominantly in Iceland. Some strong correlations were found between some of the parameters of the transient storage model and the advection-dispersion model, but no strong correlations were found between the parameters of the transient storage model and the aggregated dead zone model. For all three models, combinations of the optimized parameters correctly described the bulk movement of the solute cloud, giving confidence in the optimized parameters.

J. Russell Manson, Steve G. Wallis, Benoit O. L. Demars, John D. Mick, Gisli M. Gíslason, Jon S. Ólafsson, Nikolai Friberg

Vegetation and Flow Rate Impact on In-stream Longitudinal Dispersion and Retention Processes

Abstract

This paper is an attempt to explain influence of vegetation and flow rate in natural stream (Epre, Germany) on mixing and transport processes. For this purpose, we conducted two tracer tests in Germany using rhodamine WT (RWT) as a fluorescence dye. Both tests were performed under different vegetation and flow rate conditions. The STIR (Solute Transport In Rivers) code was used for calibration of dispersion coefficients, exchange rates and residence times. We used the STIR model to separate short—and long—time retention. Our tracer test results confirm previous findings and also reveal a correlation between storage zone exchanges rate and reach lengths, strong influence of vegetation and flow rate on transport and mixing parameters, and the significance of the equipment on storage domain characterisation.

Jevgenijs Savickis, Mattia Zaramella, Andrea Bottacin-Busolin, Gunnar Nützmann, Andrea Marion

Effects of Vegetation Density and Wetland Aspect Ratio Variation on Hydraulic Efficiency of Wetlands

Abstract

Hydraulic efficiency of wetlands, evaluated through retention time and mixing levels, was investigated as a function of wetland shape and vegetation density using a two-dimensional numerical model. The numerical model was applied to four different aspect ratios of a rectangular wetland (i.e. 1:1 to 1:4) with 1-ha area and vegetation density varying from 20 to 1500 stems/m². The results, modeled velocity field and the simulated transport of a continuously injected tracer, were used to develop Residence Time Distribution graphs (RTDs). Analysis of RTDs showed that the efficiency measure related to retention time, e, and the measure of mixing, λ _p , improved for denser vegetation before reaching to a constant value. It was also observed that narrow rectangular-shaped wetlands (higher aspect ratio) have better efficiency than square wetlands. The results from the study provide a quantitative understanding of hydraulic efficiency in connection with wetland vegetation and shape which may help engineers to design more efficient and cost-effective water systems.

Nima Sabokrouhiyeh, Andrea Bottacin-Busolin, Heidi Nepf, Andrea Marion

Experimental Investigations on the Oxygen Transfer Efficiency at Low-Head Hydraulic Structures

Abstract

The aim of this work was to examine the oxygen transfer efficiency at two hydraulic structures located on the Narew and Wilga rivers in order to assess their impact on downstream oxygen conditions. This has been done through the continuous ‘in situ’ measurements of dissolved oxygen concentrations over 24-h periods of time above and below the considered structures. Simultaneous measurements have been taken in the river channel downstream of these structures. Gas transfer efficiencies and deficit ratios have been calculated according to the available formulae reported in the literature. The obtained transfer characteristics were compared with the results of shorter measurements carried out at the same structures, but under different oxygen deficits. Moreover, a brief discussion on the measurement techniques, gas transfer uncertainties and temperature correction factor is given.

Agnieszka Rajwa-Kuligiewicz, Robert J. Bialik, Paweł Rowiński

Effect of Aquatic Plant Patches on Flow and Sediment Characteristics: The Case of Callitriche platycarpa and Elodea nuttallii

Abstract

In lotic ecosystems, submerged aquatic vegetation has important effects on hydrodynamic and sediment processes. These effects depend on plant morphology and patch structure. This study aimed to test the effect of 2 aquatic plant species on flow and sediment characteristics. For this purpose we measured under natural conditions 3D velocity profiles and sediment characteristics along the main axis of one patch of each species. The 2 species presented contrasting effects on velocity, turbulence profiles and sediment characteristics: one species had significant effects on hydrodynamics and accumulation of fine sediment also further downstream of the patch, whereas the second one accumulated very fine sediment mainly in the upstream half of the patch. These results emphasize the role of plant morphology on hydrodynamics and sediment physic-chemical characteristics.

Sofia Licci, Cécile Delolme, Pierre Marmonier, Marc Philippe, Loreta Cornacchia, Vanessa Gardette, Tjeerd Bouma, Sara Puijalon

Flow Velocity and Morphology of a Submerged Patch of the Aquatic Species Veronica anagallis-aquatica L.

Abstract

The interaction between macrophytes and hydrodynamic conditions is an important feature in many aquatic ecosystems. Submerged macrophytes can form monospecific patches that interact with the flow and alter current velocity; within the same vegetation patch, plants are exposed to different levels of hydrodynamic stress. Due to the high morphological variability of aquatic plants, we expect different architectural and morphological traits to emerge for individuals located at different positions within the same patch. In this study, we have measured the flow velocity around a patch of Veronica anagallis-aquatica in submerged conditions and measured the morphological traits of individuals along a gradient of exposure to flow velocity within the patch. Results show that the more exposed individuals present smaller sizes than the sheltered ones, lower relative allocation to stems, higher allocation to roots and reduced water content in roots and stems. The knowledge obtained helps to clarify the role of morphological adaptations to flow stress in the context of plant-flow interactions.

Loreta Cornacchia, Sofia Licci, Johan van de Koppel, Daphne van der Wal, Geraldene Wharton, Sara Puijalon, Tjeerd J. Bouma

The Influence of Rating Curve Uncertainty on Flow Conditions in the River Vistula in Warsaw

Abstract

The flow forecasting system for the middle reach of the River Vistula consists of a distributed flow routing model and rainfall-runoff modules. The MIKE 11 flow routing model, applied in the study, requires specification of a number of input variables, including roughness coefficients, initial conditions, river geometry and boundary conditions. All listed variables introduce errors into the system that have an impact on the uncertainty of flow predictions. This work focuses on the estimation of uncertainty of flow predictions resulting from inaccuracy of boundary conditions and parametric uncertainty. In particular, we are interested in the influence of a stage-discharge relationship (rating curve) uncertainty applied as the downstream boundary condition. The influence of parameter and rating curve (RC) uncertainty on model predictions is studied using the Generalised Likelihood Uncertainty Estimation GLUE framework. We parameterised downstream RC using a power law. The RC parameters were optimised together with the model roughness coefficients. The optimal parameter values were subsequently used as mean values of a priori distribution within the GLUE approach to derive the flow routing model prediction uncertainty. The results were superior to those without RC uncertainty taken into account only in Warsaw Port Praski gauging station. The proposed methodology was applied to the Middle Vistula reach between Zawichost and Warsaw Port Praski gauging stations. Model performance was estimated using both water level and discharge observations at gauging stations situated along the river reach.

Emilia Karamuz, Marzena Osuch, Renata J. Romanowicz

Morphological Changes of a Restored Reach: The Case of the Spree River, Cottbus, Germany

Abstract

The main goals of the European Water Framework Directive (WFD) are the improvement of the ecological status of all water bodies by 2027 and continuous monitoring to prevent future degradations. When applied to rivers, the WFD considers hydromorphological elements only as supporting elements for watercourses at good or lower status, while biological elements are considered as fundamental. Nonetheless, various scientific studies have demonstrated that rivers need to be considered in a more holistic way, involving all their characteristics, principally water, sediment and biota. The aim of the present study is to demonstrate the importance of considering sediments during the WFD implementation cycles. To give a practical example, the case study of a restored reach of the Spree River near the city of Cottbus, Brandenburg, Germany, was chosen. The analysis proposed here utilized aerial images, DGMs and cross-section profiles for the pre- and post-project periods, giving information about the morphological changes due to the restoration works. Preliminary results show that the river morphology is affected by fine sand, transported in particular during high flow conditions. This study illustrates that if only biological parameters had been monitored as recommended by WFD, then potential issues would not have been identified for the effective river management.

Michael Nones, Christoph Gerstgraser

Impact of River Restoration on Hydromorphological Processes: The River Flinta as a Case Study

Abstract

This paper deals with problems related to the improvement of the hydromorphological conditions of the river Flinta in its sections located in the Natura 2000 area. Based on a comprehensive study of the hydromorphological status of the river, four sections have been selected, where restoration measures can efficiently improve the river habitat conditions. For each of these sections we propose a set of technical and biological measures. One of the proposed solutions, investigated as a pilot project, was to construct plant barriers (sediment traps—vegetative baskets). Systematic measurements were carried out during one and a half year. These measurements provided information on the possible consequences of such actions in terms of hydromorphological changes.

Tomasz Kałuża, Krzysztof Szoszkiewicz, Artur Radecki-Pawlik, Natalia Walczak, Karol Plesiński

River-Bed Morphology Changes During the Winter Season in the Regulated Channel of the Wilga River, Poland

Abstract

Field investigations of the river bed morphology in the regulated channel of the Wilga River in Poland are presented. All data were collected with the use of an echo sounding system mounted on the ADCP (acoustic Doppler current profiler), which was also used to obtain the water flow velocities, discharges and river bathymetry during the days of measurements. It is shown that the analysed channel consists mostly of regular sand waves, which change their length and height during the winter season. The dependence of the shape of bedforms and channel bed morphology on the existence of a vegetation patch, which is directly associated with decreasing water temperature, is discussed briefly. The paper confirms changes in bed profiles with the increase in the water discharge. Moreover, a 3-dimensional digital elevation model of the channel obtained with the use of the ArcGIS software is introduced. In addition, the single-sided spectra of bed-elevation are analyzed. The results suggest that in the case of vegetation existing in the channel, the spectra are characterized by a scaling region with the exponent “−2”, which tends to be “−3” when the plants disappear.

Joanna Sziło, Robert J. Bialik

Optimizing Multi-purpose Reservoir Operation Using Particle Swarm Intelligence

Abstract

Developing an efficient multi-objective reservoir operation policy is one of the most challenging water resources tasks due to a big number of involved parameters, in addition to the question of proper system representation. Therefore, the aim of the paper is to apply Particle Swarm Optimization (PSO) technique to optimal operation of the Atbara River basin reservoir system. An objective function is defined to minimize the squared difference between targeted and generated hydropower as well as irrigation demands to be solved using a set of tuned (PSO), and then applied in Girba multi-purpose reservoir. The results showed a tangible improvement in power production, up to 15 % increase, satisfying at the same time the irrigation demands. Three performance measures of reliability, resilience, and vulnerability have been applied based on model outputs and required release values that satisfy the system’s demands. All measures indicated an improvement of the system’s performance, exhibiting the reliability increase to 97 %, instead of current 86 %.

Mohammed Abdallah, Jürgen Stamm

Flume Experiments on Gravel Bed Load Transport in Unsteady Flow—Preliminary Results

Abstract

This chapter presents settings and results of laboratory experiments on bed load transport. Experiments were performed for unsteady hydrographs and for steady flow conditions. Continuous measurements of transported mass and flow rate reveal a clockwise hysteresis of bed load rate versus flow rate. A comparison between bed load rate in unsteady and steady flow shows that it depends to a large extent on sediment supply. The results are discussed in the light of variable sediment supply, and suggestions for procedure of further experiments are presented.

Magdalena M. Mrokowska, Paweł Rowiński, Leszek Książek, Andrzej Strużyński, Maciej Wyrębek, Artur Radecki-Pawlik

Experimental Investigation of Hydraulically Different Surface Roughnesses

Abstract

Surface roughnesses present hydraulic differences that can be characterised investigating time averaged velocity profiles, turbulence, Reynolds and form induced stresses. The latter, unlike the other flow characteristics, have not been considered in detail in previous studies. An experimental study of the turbulent flow over five different surface roughnesses is presented. They have been constructed with natural and artificial materials, and with different geometries. The experiments were carried out in a laboratory flume and the 3D flow field has been measured with a Nortek Vectrino Profiler. The double averaged Navier-Stokes equations methodology has been applied to study the spatial heterogeneity of the time averaged flow. The results confirm the studies made in previous works with different surface roughnesses and the form induced stresses reveal the hydraulic differences and similarities for the different investigated roughnesses.

Paride Nardone, Katinka Koll

Sensitivity of the Flow to the Inclination of a Single Submerged Groyne in a Curved Flume

Abstract

In order to investigate the effect on the flow field due to small changes in the inclination of a single submerged groyne, laboratory tests have been conducted. A double curved S-flume with a length of 26 m, width of 2.4 m and depth of 0.4 m was used. The investigations were done at a reference inclination of 60° for a single submerged groyne. The inclination was then varied by ±5° and ±10°. The groyne width and height as well as the hydraulic conditions (discharge of 130.6 l/s and water depth of 10 cm) were kept constant to ensure that the effect is only due to the change in the inclination. The groyne was installed in the first cross-section of the first curve. The 3D flow field was measured using a Nortek Vectrino Plus in nine cross-sections with seven vertical profiles each. The total flow measurement points were 325 in each run. The results of the experiments have shown no significant changes in the flow field due to the change of inclination up to ±10° given that the projected length and the hydraulic boundary conditions were kept constant. However, localized effects at cross-section no 1 are evident and the inclination of 60° showed the lowest stream-wise velocity. Comparison of the flow field with and without groyne revealed decreasing velocities at the outer bank and increasing velocities at the inner bank supporting the purpose of the structure which is bank protection.

Bahaeldeen A. Zaid, Katinka Koll

PIV-PTV Measurements of a Tailings Dam-Break Flow

Abstract

To experimentally study transient flows such as dam-break flows, imaging techniques are often used due to the constraints imposed by the highly transient nature of such phenomena. In this paper an experimental laboratory study of tailings dams made with a combined PIV + PTV algorithm is presented. In this algorithm the PIV technique is first applied to determine an estimator for the sediment layer velocity field. The obtained estimator is then used to compute a displacement estimator for the PTV approach. In this method the first step (PIV) provides a global estimation of the sediments velocity field and in the second step (PTV) a particle-by-particle analysis is obtained leading to an increased spatial resolution of the measurements. The obtained algorithm is applied to a laboratory tailings dam-break flow to obtain relevant information about the behavior of the tailings. This paper is a summary of the research presented in other papers by the authors.

Rui Aleixo, Yavuz Ozeren, Mustafa Altinakar

On Evaluating Flow Resistance of Rigid Vegetation Using Classic Hydraulic Roughness at High Submergence Levels: An Experimental Work

Abstract

Vegetation resistance is generally evaluated using drag coefficient C_D related to friction factor f; however, some authors examined a possibility of employing classic hydraulic roughness coefficients (i.e., Nikuradse’s or Strickler’s) to calculate vegetation resistance in case of high submergence (h/k > 5, in which h is flow height and k represents vegetation height). In order to compare conventional roughness at high submergence levels, an experimental methodology was developed, focused, in particular, on fully submerged and rigid vegetation, for different hydraulic conditions and varying non-dimensional vegetation density.

Vittorio Pasquino, Paola Gualtieri, Guelfo Pulci Doria

Effective Method for Continuous Measurement of Bedload Transport Rates by Means of River Bedload Trap (RBT) in a Small Glacial High Arctic Gravel-Bed River

Abstract

The determination of the threshold values and parameters of bedload transport in river beds is necessary for undertaking effective hydrotechnical works, including anti-flood, retention, energy engineering measures, etc. This paper presents a new device for the continuous measurement of movable bed-surface particles, namely the “River Bedload Trap—RBT” [European patent No. EP 2333161]. The article discusses the methodological difficulties in the effective estimation of bedload transport rate. It presents an innovative measurement strategy and device with the potential to satisfy the stringent requirements set by fluvial geomorphology and hydrotechnical analyses. The applied technical solution based on direct continuous measurement and anchored RBT sets is analysed in detail and compared to the existing measurement systems. The study confirmed the high effectiveness of the implemented measurement strategy and technical solution for quantitative bedload transport rates and flux. The application of RBT for continuous monitoring of bedload flux in the conditions of High Arctic gravel-bed rivers was evidenced to permit obtaining high efficiency and credible results.

Waldemar Kociuba

Step Length Influence in Modelling Advection and Diffusion of Bed-Load Particles

Abstract

A bed-load transport model has been derived in order to attain a better prediction of particle motion along river beds. Scientific studies have now moved towards a particle based approach in order to physically address the actual motion characteristics of the bed grains, such as the distance between entrainment and deposition, i.e. the step length. Step length clearly accounts for the heterogeneity faced by a grain along its path, such as bed roughness, flow intensity, river morphology. In this study, particles’ step lengths are regarded as a stochastic variable denoted by a lognormal distribution, whose statistics account for the effect of both bed arrangement and the near bed shearing flow. The 1D Exner equation is then reformulated to account for tracing particles by considering the deposition term as a function of the upstream entrainment events and the displacements computed by a particle before stopping. The implemented numerical method enables the computation of the concentration of bed-load tracers in time and space. As revealed by the model results, the step length distribution acts as a source of diffusion for particle motion along the river bed. The extent of advection and diffusion is not only controlled by the statistics of the step length, but it is also strongly influenced by the level of bed roughness. The thickness of the exchange layer also plays a role in the transport behaviour, as it delays particles temporarily stored in the active layer.

Martina Cecchetto, Simon Tait, Andrea Marion

An Evolution Volume Balance Approach to Determine Relevant Discharge Threshold for Bed Load Transport

Abstract

The aim of this study is to investigate discharge rates at which a flow hydrograph becomes relevant for bed load transport on the example of the Alpine river Saalach. Two characteristic flow hydrographs of the river Saalach are selected and reduced to discharges above pre-specified values. With each set of reduced hydrographs, a 2D morphological simulation is conducted. Two important morphological parameters, namely total river bed evolution (i) and sorting effects of the active layer (ii) are analyzed and evaluated. Moreover, an additional simulation is conducted with a linearly increasing flow hydrograph as boundary condition to analyze the initiation of bed load transport as a function of discharge (iii). The results are analyzed and evaluated with respect to the total sediment output at the downstream boundary of the model and at some inner control sections to validate the findings for (i) and (ii). The model results show: (i) For regions with fine bed materials, discharge thresholds between 100 and 130 m³/s and for regions with mainly coarse bed materials discharge thresholds in the range between 150 and 180 m³/s can be identified as relevant discharges for bed load transport and may be used for reducing hydrographs without affecting the accuracy of the model results; (ii) The active layer shows no obvious changes in the mean diameter of sediments for all tested hydrographs. (iii) The investigations with a linearly increasing flow hydrograph show that the sediment output from the investigated river reaches increase significantly for discharges exceeding 150 m³/s.

Najibullah Sadid, Felix Beckers, Markus Noack, Stefan Haun, Silke Wieprecht

Significance of the Sediment Properties and Aquatic Environmental Conditions on the Erodibility of Deposited Beds

Abstract

The reliability of the prediction of sediment transport loads in aquatic environments is significantly dependent on the sediment bed behaviour regarding erosion. Besides the ambient environmental conditions, the residence or consolidation period may generate changes in the nature and structure of the sediment deposits. This review highlights the importance of the sediment properties in the assessment of their re-suspension and mobilization. Unconsolidated cohesive beds of sediments often display lower critical shear stress values at the solid-water interface than those observed for the same sediment type but in consolidated beds. When dealing with cohesive sediments, the time dependent physical and biochemical processes are among the main aspects that influence the observed higher resistance to erosion. A prior characterization of the local material accumulated in the studied environment is crucial in enhancing transport prediction performance.

Irene Seco, Manuel Gómez-Valentín, Simon Tait, Andrea Marion

An Analysis of Entrainment and Deposition Rate Fluctuations in Weak Bed Load Transport

Abstract

The kinematics of particles moving over a fixed rough bed was experimentally investigated. Motion of sediment particles was recorded from the top of a pressurized duct using a CCD camera, and the then image processing was applied in order to track each particle. Particle tracking provides quantitative information about the time evolution of particle position and velocity. However, in this paper, the attention is focused onto the entrainment and deposition of particles. The entrainment rate may be used to quantify the solid discharge (through, for example, some pick-up function); the deposition rate is the counterpart of the former, that has however received comparatively less attention in previous studies of sediment transport. Temporal signals of the entrainment and deposition rates were investigated for different spatial and temporal scales, demonstrating how the intermittency of the transport process affects the fluctuation patterns. Consequently, the (spatial or temporal) scale dependency of the statistical moments of these rates was explored. An expected result was found, with scale-independent average values of the entrainment and deposition rates and a strong dependence on the support scale for the standard deviation values.

Seyed Abbas Hosseini-Sadabadi, Alessio Radice, Francesco Ballio

Erratum to: Hydrodynamic and Mass Transport at Freshwater Aquatic Interfaces

Paweł Rowiński, Andrea Marion