Czech Academy of Sciences, Institute of Hydrology

An analytic model of free-surface flow over an erodible bed is developed and used to investigate the stability of the fluid-bed interface and the characteristics of the bed features. The model is based on the potential flow over a two-dimensional, moving, wavy bed with a sinusoidal profile of varying amplitude, and a sediment transport relation in which the transport rate is proportional to a power of the fluid velocity at the level of the bed. By assuming that the dominant wavelength is that for which the rate of amplitude growth is the greatest, expressions are obtained for the wavelength and velocity of the bed features. In addition, conditions for the occurrence of the different configurations, dunes, flat bed, and antidunes, are found from the model. The predicted wavelengths of antidunes and ranges of wavelengths of dunes, and the predicted conditions for change of bed configuration are found to be in good agreement with experimental data. Finally, brief consideration is given to the factors involved in determining the maximum heights of the bed features and surface waves.

The oscillatory flow near the sea bed under a wave motion is always rough turbulent in a coastal zone. This type of an oscillatory boundary layer (or “wave boundary layer”) was therefore chosen as a subject for detailed velocity measurements, from which characteristics such as shear stresses, eddy viscosities, energy loss, and boundary layer thickness were determined.

Abstract Laboratory flow visualization experiments, using glass beads as the porous medium, were conducted to study air sparging, an innovative technology for subsurface contaminant remediation. The purpose of these experiments was to observe how air flows through saturated porous media and to obtain a basic understanding of air plume formation and medium heterogeneity effects. The experiments indicate that air flow occurring in discrete, stable channels is the most probable flow behavior in medium to fine grained water saturated porous media and that medium heterogeneity plays an important role in the development of air channels. Several simulated scales of heterogeneities, from pore to field, have been studied. The results suggest that air channel formation is sensitive to the various scales of heterogeneities. Site‐specific hydrogeologic settings have to be carefully reviewed before air sparging is applied to remediate sites contaminated by volatile organic compounds.

Abstract A new online streaming video and multi‐media application called eTEACH, http:eTEACH.engr.wisc.edu was used to reform a large, lecture‐based computer science course for engineering majors. In‐class lectures were replaced with videotaped lectures and other materials that students viewed on the Internet on their own schedule, making it possible to use the live class periods for small, team problem‐solving sessions facilitated by the professors and a teaching assistant. By using the eTEACH application to transform course lectures into “homework” and free up the face‐to‐face class time for working on problems that were similar to homework assignments, the professors effectively reversed the lecture and homework paradigm of a typical large lecture course. A thorough course evaluation over two semesters showed that students who took the online lecture version of the course gave significantly higher ratings to all aspects of the course, including lecture usefulness, professor responsiveness, the course overall, and the instructor. Although a few students missed having the opportunity to ask questions during lectures, about two‐thirds of the 531 students surveyed felt it was easier to take notes and understand the lectures presented via eTEACH than it would have been while attending the same lecture live, and 78% of students appreciated the ability to view and review course lectures on their own schedule.

The proliferation of algal and cyanobacterial blooms globally has led to renewed interest in understanding the impact of cell populations on water treatment plant (WTP) performance and the resultant water quality, particularly the role of algogenic organic matter (AOM). This review discusses current knowledge on the composition of AOM, how it interferes with water treatment process technologies applied for the treatment of algal blooms, and how it affects water quality. Specifically, it was shown that AOM can lead to increased coagulant demand, increased propensity of membrane fouling, and contribute to disinfection by-products (DBPs). Identified knowledge gaps included a need for further research on the impact of cellular organic matter (COM) after an algal bloom collapses and the impact of interactions between AOM and natural organic matter (NOM).

Abstract. Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land–atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The “sapfluxnetr” R package – designed to access, visualize, and process SAPFLUXNET data – is available from CRAN.

The rate dependence of unsaturated hydraulic characteristics was analyzed using both steady state and transient flow analysis. One‐step and multistep outflow experiments, as well as quasi‐static experiments were performed on identical, disturbed samples of a sandy and a loamy soil to evaluate the influence of flow rate on the calculated retention and unsaturated hydraulic conductivity curves. For the sandy soil, a significant influence of the flow rate on both the retention and unsaturated hydraulic conductivity characteristic was observed. At a given matric potential, more water was retained with greater applied pneumatic pressures. Matric potential differences of 10 to 15 cm (for given saturation) and water content differences of up to 7% (for given potential) could be observed between the slowest and the fastest outflow experiments, predominantly at the beginning of drainage. The hydraulic conductivity also increased with increasing flow rate for higher saturations, while a lower hydraulic conductivity was observed near residual saturation for the higher flow rates. We observed a continuously increasing total water potential gradient in the sandy soil as it drained, especially for high‐pressure transient one‐step experiments. This indicates a significant deviation from static equilibrium, as obtained under static or steady‐state conditions. For the finer textured soil, these flow‐rate dependent regimes were not apparent. A number of physical processes can explain the observed phenomena. Water entrapment and pore blockage play a significant role for the high flow rates, as well as lack of air continuity in the sample during the wettest stages of the experiment.

Abstract The upward movement of water due to transpiration stops when soil water potential (Ψ s ) drops below leaf water potential (Ψ L ). Under these circumstances, water can move in any direction in the plant‐soil continuum through the passive conduits of roots and stems towards the lowest Ψ s . This is generally termed as hydraulic redistribution (HR), but the positioning and orientation of the driving water potential gradient may vary. Any experimental method that can measure bi‐directional and low flows in the sapwood of roots and stems will be suitable to detect HR. Using one approach for measuring sap flow (the heat field deformation technique, HFD) in several forest species and sites across Europe, we were able to provide evidence on different types of HR: vertical hydraulic redistribution (VHR), horizontal hydraulic redistribution (HHR), foliar uptake (FU) and tissue dehydration (TD). VHR is the vertical water movement through roots in response to water potential differences between deep and topsoil, either hydraulic lift or hydraulic descent. HHR is the lateral water movement through roots in response to horizontal water potential gradients, namely under localised irrigation. FU is the water movement from crown to soil through stems when the crown is wetted by foggy weather. TD is the downward movement of water in stems or roots from above‐ground tree tissues to soil under prolonged drought or frost. Results from direct sap flow measurements indicated the vectoral and widespread nature of HR, a phenomenon of paramount importance for overall physiology and ecohydrology. Copyright © 2010 John Wiley & Sons, Ltd.

Abstract This paper describes water-tunnel investigations into the mechanics of “fixed”-type cavitation and into the probable mechanism through which this type causes material damage. High-speed motion pictures were used to study the cavity mechanics, and indications of the damage pattern were obtained by measuring the pitting rate on soft aluminum test specimens. Information was obtained on the frequency and intensity of the damaging blows, the distribution of damage in relation to the area covered by the cavitation, and the variation of the intensity of cavitation with velocity.

The paper concerns the hydrodynamic turbulent motion in the lubricant layer. Proceeding from the Reynolds equations and introducing the approximations currently used in lubrication problems, owing to the lubricant film thickness, the general motion equations for turbulent lubrication are written. Using the Prandtl mixing length hypothesis, exact and approximate solutions are obtained for the velocity distribution into the lubricant layer. The results are discussed by pointing out the pressure gradient and the Reynolds number influence on the velocity distributions, as well as the differences with respect to the laminar flow. In order to obtain simple formulae, the exact dependence of the rate of flow on the pressure gradient into a dimensionless form is replaced by a linear relation, the slope of which depends on the Reynolds number. This approximation allows the obtainment of the pressure differential equation under a simple form. The pressure equation is integrated in case of journal bearings, by assuming a constant or a variable viscosity of the lubricant. The results are compared to the experimental data obtained by M. I. Smith and D. D. Fuller and the good qualitative agreement is pointed out.

Abstract This paper is a summary of the results of investigations of the drop in potential and boundary resistance in unsteady motion for cases of surface resistance caused by boundary shear stresses and cases of form-type resistance associated with the high shear and generation and diffusion of turbulence accompanying jet formation. These cases were obtained using uniform diameter conduits and orifices in conduits. From tests in the MIT unsteady flow water tunnel, the effects of accelerated and decelerated flows were studied. In the case of flow through a uniform tube, it was found that the boundary resistance at any instant during accelerated motion was slightly greater than the equivalent steady-state case while, for decelerated motion, it was slightly less. In the case of flow through orifices, it was found that the combined resistance of the orifice and the conduit was less during accelerated motion and more during decelerated motion than for the equivalent steady-state cases.

Many studies have overlooked the role of pH in optimizing coagulation. Herein, the authors emphasize the importance of pH value in coagulation during the production of drinking water. We investigate the influence of pH value on the surface charges and forms of coagulants and impurities intended for removal. A methodology is suggested for optimizing key parameters for efficient coagulation – coagulant dosage and pH value. The study points out that various optimal pH ranges are required for coagulation of specific impurities and their mixtures. For natural organic matter of both humic and algogenic origin, acidic pH values are favourable for their removal through charge neutralization mechanism. Algal cells are effectively coagulated at slightly acidic to neutral pH values due to interactions with coagulant hydroxide precipitates. Inorganic particles are eliminated preferably at around neutral pH values. When mixtures of impurities are coagulated, mutual interaction between the impurities may impact dose of coagulant and also optimal pH ranges.

The ensemble-averaged characteristics of the turbulent near-wake flow around two side-by-side identical square cylinders at a Reynolds number ≈23100 have been studied using a two-component laser-Doppler velocimeter system. The work focuses on a single case with a gap/diameter ratio of 2, for which the resulting individual vortex streets are coupled so as to yield a flow predominantly symmetric about the line midway between the two cylinders. Data sorting or conditioning according to phase was performed with the aid of pressure signals taken from taps on a sidewall of each cylinder. The two-cylinder results are compared in detail to results from a previous study of the one-cylinder case. Vortex structures shed on the side towards the flow centreline, termed inner structures, are distinguished from those shed on the free-stream side, termed outer structures, and the differences between the features associated with the two different structures are examined. The circulation associated with outer structures evolves downstream in a manner similar to that observed in the one-cylinder case, but the circulation of the inner structures is found to decrease dramatically downstream. This not only gives support to previous theoretical predictions but also reconciles these with previously apparently conflicting experimental observations. Information regarding vortex structure motion and the relevant length and time scales is obtained. Differences between momentum and vorticity transport, particularly across the flow centreline are pointed out, and effective turbulent vorticity fluxes are defined. Similarities in local flow topologies in one- and two-cylinder cases are discussed, and the role of local velocity-gradient invariants and their relationship to critical points and turbulence statistics are examined.

The stabilizing and cell-shape changing influence of a basic rotation upon thermally produced cellular circulations are developed in a first order, perturbation theory. The theoretical possibility of a special “overstable” oscillating mode in certain fluids under the influence of rotation is recognized. In this preliminary report, the theory obtained for ordinary convection is compared to results obtained in laboratory experiments with rotating cylinders of water, and the existence of the overstable oscillating mode is demonstrated experimentally. Several possible applications of the theoretical results to atmospheric convection are developed by means of numerical examples, including models that are consistent with the observed association of deep convection with cyclonic relative vorticity and the distribution of clouds in regularly spaced clear and cloudy areas.

Abstract The effect of pressure and temperature on the shear and elongational deformation rate–dependent viscosities has been experimentally investigated for several polymers (HDPE, LDPE, LLDPE, PP, PC, PMMA, and PS) on a capillary rheometer with a back‐pressure device. Pressure, β, and temperature, α, coefficients have been determined through simultaneous fitting of the shear and extensional viscosity data by the modified White‐Metzner model. The dependence of β and α on temperature and pressure, respectively, was investigated and it has been found that simple relationships exist between pressure and temperature sensitivity coefficients for individual polymers. Polym. Eng. Sci. 44:1328–1337, 2004. © 2004 Society of Plastics Engineers.

The sedimentation caused by the high density of suspended particles used in magnetorheological fluids is a significant obstacle for their wider application. In the present paper, core–shell structured carbonyl iron–polyaniline particles in silicone oil were used as a magnetorheological suspension with enhanced dispersion stability. Bare carbonyl iron particles were suspended in silicone oil to create model magnetorheological suspensions of different loading. For a magnetorheological suspension of polyaniline-coated particles the results show a decrease in the base viscosity. Moreover, the polyaniline coating has a negligible influence on the MR properties under an external magnetic field B. The change in the viscoelastic properties of magnetorheological suspensions in the small-strain oscillatory shear flow as a function of the strain amplitude, the frequency and the magnetic flux density was also investigated.

ABSTRACT The composition and metabolic activity of cysts of the marine dinoflagellate Scrippsiella trochoidea (Stein) Loeblich were examined during dormancy, quiescence, and germination. On a per cell basis, newly formed cysts contained an order of magnitude more carbohydrate but significantly less protein and chlorophyll a than did exponentially growing vegetative cells. Loss of lipid and carbohydrate from cysts during the initial dormancy period reflected a respiration rate estimated to be 10% of the respiratory activity in vegetative cells. Among older, quiescent cysts the calculated respiration rate decreased further to approximately 1.5% of the vegetative rate and appeared to proceed largely at the expense of carbohydrate reserves. These estimated rates of respiration were in good agreement with direct measurements of cyst oxygen consumption. The transfer of quiescent cysts to conditions permissive for germination resulted in a rapid increase in respiration rate, as evidenced by carbohydrate loss and O 2 consumption. The increased respiratory activity was followed by an increase in protein content and, later, by an increase in chlorophyll a content and photosynthetic capacity. Just prior to germination the P/R ratio became greater than 1, and the estimated chlorophyll‐specific photosynthetic activity reached 75% of the rate in vegetative cells. Complete restoration of photosynthetic and respiratory capacity apparently was not achieved until after excystment. These data confirm the common assumption that dinoflagellate cysts represent true “resting” cells, containing extensive energy reserves and displaying greatly reduced metabolic activity.

Abstract Computer simulators are widely used to describe and explore physical processes. In some cases, several simulators are available, each with a different degree of fidelity, for this task. In this work, we combine field observations and model runs from deterministic multifidelity computer simulators to build a predictive model for the real process. The resulting model can be used to perform sensitivity analysis for the system, solve inverse problems, and make predictions. Our approach is Bayesian and is illustrated through a simple example, as well as a real application in predictive science at the Center for Radiative Shock Hydrodynamics at the University of Michigan. The Matlab code that is used for the analyses is available from the online supplementary materials. KEY WORDS: Computer experimentGaussian processMarkov chain Monte Carlo ACKNOWLEDGMENTS This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52-08NA28616 and the Natural Sciences and Engineering Research Council of Canada. The authors are grateful for the encouraging and helpful comments made by the referees, Associate Editor, and Editor. The implementation of the proposed methodology is built upon the Gaussian Process Modeling for Simulation Analysis software (Gattiker, Higdon, and Williams Citation2008) developed at Los Alamos National Laboratory. The authors would like to thank the Los Alamos National Laboratory Statistical Sciences Group for sharing their libraries.

Water level fluctuations induced by tidal strains can be analyzed to estimate the elastic properties, porosity, and transmissivity of the surrounding aquifer material. We review underutilized methods for estimating aquifer properties from the confined response to earth tides. The earth tide analyses are applied to an open well penetrating a confined carbonate aquifer. The resulting range of elastic and hydraulic aquifer properties are in general agreement with that determined by other investigators for the area of the well. The analyses indicate that passive monitoring data from wells completed in sufficiently stiff, low porosity formations can provide useful information on the properties of the surrounding formation.

Flood management is more than ever an issue for dam designers and engineering consulting firms in charge of rehabilitation works. Piano Key Weirs are a new cost-effective type of spillway designed to improve dams discharge capacity. These structures are particularly attractive: they can easily be built on existing structures and enable very high discharge capacities. Therefore, Piano Key Weirs are nowadays studied worldwide. Piano Key Weir description involves a lot of geometrical parameters (more than 30), which designations are not already universally defined. A naming convention is required to enhance exchanges and cooperation between the numerous developers. A naming convention has been developed at EDF – Hydro Engineering Center in cooperation with the Laboratory of Hydraulic Constructions (LCH), Ecole Polytechnique Fédérale de Lausanne and the Laboratory of Hydrology, Applied Hydrodynamics and Hydraulic Constructions (HACH), University of Liege. This paper describes the proposed naming convention and gives definitions and notations of the various geometrical parameters. This work represents a first attempt which should be updated with the contribution of stakeholders involved in this topic.