Free Water Surface Research Articles

How does mine tailings slurry solids concentration affect stability of dam embankment slope?

ABSTRACT In view of many past failures of tailings storage facilities, practising engineers have been analysing current design guidelines for different elements of these facilities, including for tailings dams. In this paper, an attempt is made to investigate how varying tailings slurry solids concentration ( c s ) affects the stability of tailings dam embankment slope. To achieve this, elaborate two-dimensional limit equilibrium and finite element simulations were conducted and a steady-state seepage analysis was performed so as to obtain accurate free surface water flux through the slope. Initially, numerical analyses were performed for the downstream embankment slope when no material is retained upstream. Subsequently, with all parameters kept constant, the same slope was then checked when water is retained upstream, and finally for varying slurry solids concentration. Special attention was paid to the boundary between sedimentation and consolidation, defined as the solids concentration limit beyond which effective stresses start to develop. From the stability analyses performed, it is found that the factor of safety of embankment slope varies nonlinearly with total unit weight of the slurry. For coal tailings slurry, factor of safety reduced from 1.24 when water is retained to 1.15 when tailings slurry with c w = 60% is retained, representing a drop by 7.3%.

A fully coupled dynamic water-mooring line system: Numerical implementation and applications

Several numerical challenges exist in the analysis of water-mooring line systems which require robust, yet practical, methods to address this type of fully coupled nonlinear dynamic problems. The present study proposes a novel class of numerical techniques for the formulation and implementation of a fully coupled dynamic system which involves water flows and catenary mooring line system. In particular, the three-dimensional water flow model is replaced by a simplified multilayer shallow water system with mass exchange terms between the layers including frictional forces at the bed topography and wind-driven forces at the water free-surface. Coupling conditions between the multilayer shallow water model and the mooring line system are also investigated in the current work. As numerical solvers we implement a fast finite volume method for the multilayer shallow water equations and a nonlinear dynamic analysis for the mooring line based on elastic catenary cable elements. Efficient calculations of the interaction forces between the shallow water flow and the submerged mooring line system and associated numerical implementations are also discussed. The accuracy and computational advantages of the proposed fully coupled system are verified using a series of well-established benchmark problems and wind-driven flows over both flat and non-flat beds. The computational results obtained show high performance the developed model and demonstrate the ability of the method to simulate fully coupled dynamic water-mooring line systems.

Merging of two droplets at an air-water interface driven by surface tension gradient

This study reports the unique phenomena of merging of two oil droplets floating on the free surface of water. For the first time, the coalescence has been initiated through the creation of a surface tension gradient by depositing the drop of surfactant at the free surface of water. The experiment reveals that droplets over water and surfactant-laden water surfaces do not merge in the absence of an external gradient, and we experimentally delineate the necessary conditions under which the coalescence of droplets will occur on the imposition of a surface tension gradient. Due to the presence of a surface tension gradient, the droplets experience a substitutional reduction in size even before coalescence, and for obvious reasons, the droplet close to the point of administration of the surfactant suffers a higher reduction in size; it also has a higher initial velocity. We studied the time-dependent variation in the neck radius (rn) formed upon the initial contact of two droplets of both identical and non-identical sizes. The final size of rn is proportional to the diameter of the droplet at the inception of the coalescence when the droplets are of identical size. For droplets of non-identical size, the final value of rn never exceeds the initial diameter of the smaller droplet. During the initial period of coalescence, rn grows with time (t) as rn≈t, but at the later stage, the rate of growth reduces as rn≈tn, where n is between 0.3 and 0.4. The relationship of rn with time in these two stages is similar to that reported in literature. However, the limit of rn for the transformation of one phase to another is significantly different in the present case compared to the other reported results.

Efficient dissipation of acetamiprid, metalaxyl, S-metolachlor and terbuthylazine in a full-scale free water surface constructed wetland in Bologna province, Italy: A kinetic modeling study

The study investigated the dissipation ability of a vegetated free water surface (FWS) constructed wetland (CW) in treating pesticides-contaminated agricultural runoff/drainage water in a rural area belonging to Bologna province (Italy). The experiment simulated a 0.1% pesticide agricultural water runoff/drainage event from a 12.5-ha farm by dissolving acetamiprid, metalaxyl, S-metolachlor, and terbuthylazine in 1000 L of water and pumping it into the CW. Water and sediment samples from the CW were collected for 4 months at different time intervals to determine pesticide concentrations by multiresidue extraction and chromatography-mass spectrometry analyses. In parallel, no active compounds were detected in the CW sediments during the experimental period. Pesticides dissipation in the wetland water compartment was modeled according to best data practices by fitting the data to Single First Order (SFO), First Order Multi-Compartment (FOMC) and Double First Order in Parallel (DFOP) kinetic models. SFO (except for metalaxyl), FOMC and DFOP kinetic models adequately predicted the dissipation for the four investigated molecules, with the DFOP kinetic model that better fitted the observed data. The modeled distribution of each pesticide between biomass and water in the CW highly correlated with environmental indexes as Kow and bioconcentration factor. Computed DT50 by DFOP model were 2.169, 8.019, 1.551 and 2.047 days for acetamiprid, metalaxyl, S-metolachlor, and terbuthylazine, respectively. Although the exact degradation mechanisms of each pesticide require further study, the FWS CW was found to be effective in treating pesticides-contaminated agricultural runoff/drainage water within an acceptable time. Therefore, this technology proved to be a valuable tool for mitigating pesticides runoff occurring after intense rain events.

Performance of a multi-stage hybrid wetland system for the treatment of a dairy effluent

This work evaluates the performance of a pilot-scale hybrid wetland (HW) system for the effluent treatment from a dairy industry, located in Santa Fe (Argentina). The system consists of three stages in a serial configuration: vertical flow (S1) – free water surface (S2) – horizontal subsurface flow (S3) wetlands. The HW was operated during nine months. Wastewater, plant and sediment samples were taken from the system. Main pollutant concentrations were determined in wastewater. N and P concentrations were determined in plant tissues and in sediments to evaluate the accumulation in the system. The mean COD, BOD, TN, and TP removals in the whole HW system were 91 %, 94 %, 76 %, and 64 %, respectively. Organic matter concentration decreased due to aerobic and anaerobic degradation processes in all stages, mainly in S2. S1 presented proper conditions for nitrogen compounds interconversions by ammonification and nitrification processes. The highest total nitrogen removal was achieved in S2. Plant uptake contributed significantly to nutrient retention in S2 and S3. In S2, sediment did not participate significantly in nutrient retention. Phosphorus removal showed the lowest system efficiency. The obtained results determine the system performance under site-specific conditions, which contributes to the scaling process of the treatment wetland.

Clarifying the correlations between hydraulic indicators evaluating the hydraulic performance of free water surface constructed wetlands.

Previous studies have shown a strong linear correlation between the common hydraulic indicators of free water surface constructed wetlands (FWS CWs), which results in the waste of computing resources and confusion in evaluating the hydraulic performance of FWS CWs. There is an urgent need to define a relatively independent and authoritative hydraulic indicator. In this study, based on three years' data, the correlations among five representative hydraulic indicators, that is, short-circuit index (φ10), Morrill dispersion index (MDI), effective volume ratio (e), moment index (MI), and hydraulic efficiency (λe), were analyzed by combining a variety of methods. The results of the correlation analysis and principal component analysis clearly showed the positive correlations among φ10, e, MI, and λe (p < 0.01), and the strong negative correlations between MDI and the remaining four indexes, which were further confirmed by redundancy analysis (RDA). Most importantly, the significant correlations between MI vs e and φ10 vs e were proved through rigorous mathematical reasoning for the first time. Besides, the results of RDA indicated that the studied design parameters, namely, water depth, hydraulic loading rate, plant spacing, aspect ratio, layout of inlet and outlet, and plant species, could generally explain the variation in hydraulic indicators. The layout of inlet and outlet displayed positive effects on hydraulic performance, and the water depth exhibited negative effects. Combining the clarity of physical meaning, convenience of calculation, and universality of reflecting both hydraulic and treatment performances, e was recommended as the most authoritative hydraulic indicator to evaluate hydraulic performance. The clustering results based on e were highly consistent with those based on the comprehensive principal component score. Wetlands with a combination of lower water depth and better layout of inlet and outlet usually have better hydraulic performance. This study successfully revealed the significant correlations among hydraulic indicators and their sources, and recommended a unique hydraulic indicator to authoritatively evaluate the hydraulic performance of FWS CWs.

Comparative analysis and selection criteria for residence time distribution models in free water surface constructed wetlands

The assessment of wetland performance requires consideration of flow characteristics. Although various systemic models (also known as network of ideal reactors) have been proposed to simulate residence time distribution (RTD) in wetlands, these models have only been tested with very few observations. In addition, the applicability of RTD models is affected by the shape characteristics of RTD curves. However, suitable indexes and quantitative relationships are absent to represent this effect. It remains unclear how to choose a suitable model when using the RTD modeling method to analyze tracer data. This study is designed to (i) test the accuracy of typical systemic models using sufficient observations and (ii) establish model selection criteria based on the shape characteristics of RTD. Firstly, the tanks in series (TIS) model, tanks in series plus delay (TISD) model, tanks in series with exchange (TISE) model, and tanks in series with delay and exchange (TISDE) model are compared using 36 sets of observations from tracer tests in two types of free water surface constructed wetlands (vegetated ditches and vegetated ponds). The results show that the widely used TIS model is unsatisfactory for more than half of the data, the TISD model is effective for rapidly rising RTD curves, the TISE model is preferred for long-tailed RTD curves, and the TISDE model can effectively fit all RTD curves except those with multiple peaks. Then, model selection criteria are established based on ∫trtpf(t)dt (the area for the rising stage of RTD), trtp (the degree of early peak), and tdtp (the degree of long tail), where tr represents the time when tracer concentration begins to rise, tp represents the time of peak concentration, and td represents the time when concentration decreases to 1/10 of peak concentration. The optimal model for an RTD curve can be identified based on the above three indexes and the corresponding critical conditions. Finally, the relationship between wetland design parameters and RTD shape indexes is examined. The results indicate that low hydraulic loading rates, small aspect ratios, and dense vegetation favor the creation of long tails. Large water depths tend to cause multiple peaks. Long-tailed and multi-peaked RTD curves are more likely to appear in ponds than ditches. Models that account for multiple nonideal flow phenomena are required to simulate water movement in ponds.

A Coupled Numerical Solver for Modeling Free Surface Water Waves Over Complicated Shape of Submerged Structures

A Coupled Numerical Solver for Modeling Free Surface Water Waves Over Complicated Shape of Submerged Structures

NUMERICAL SIMULATION OF THE IMPACT OF A GAS JET ON A FREE WATER SURFACE

In this work, we are interested in the numerical simulation of a high-speed hot jet impinging on a free liquid surface at rest by means of diffuse interface models. We first consider the case of a low-temperature subsonic jet; a 4-equation model is used on a 2D axi-symmetric setup. Turbulence is accounted for by solving the Reynolds averaged equations and using a k-&amp;omega; turbulence model. Numerical results are evaluated by comparing the depth of the cavity formed in the liquid surface to the predicted values using theoretical models from the literature. We then consider the case of a high-temperature jet. We start by showing equilibrium assumption between the liquid and gas phases which is no longer valid. A 5-equation model that does not rely on this assumption is presented. Both models are compared numerically on a simplified set-up.

Project solution of intervention measures at the dam of the "Šaški potok" tailing dump

There was an increase in the groundwater level and increased waterlogging of the terrain at the "Šaški potok" flotation tailing dump in Majdanpek, due to a damage of drainage collector. The stability of man-made materials of the landfills is directly dependent on the position of the free water surface in the body of the landfill. The rise of the underground water level leads to a decrease in the strength parameters of the materials from which the dam is built, which reduces the safety factor of the outer slope. For the purpose of interventional lowering the high level of underground water in the main dam body of the landfill, a hydrodynamic terrain model was created and various conceptual solutions were evaluated, using the hydrodynamic analysis. A group of wells was selected as the most optimal technical solution for lowering the groundwater level below the designed elevation.

Non-intrusive measurements of wave nonlinearity over movable bed of sediment with different beach slopes

A series of laboratory experiments were undertaken to qualitatively investigate the evolution of wave nonlinearity over a movable bed of sediment with five different beach slopes under regular waves in a medium-scale wave flume. An innovative non-intrusive data collecting system, which mainly consists of three side-looking high-speed cameras, was developed to collect high-resolution and synchronous data on free-surface water elevation of waves and bed level changes without causing any disturbances to wave motions and the movable bed of sediment. On analyzing the collected experimental data, it is found that regular waves become nonlinear when they propagate to the shoaling zone and start breaking, and linear wave theory is quite accurate for calculating wave parameters such as orbital velocity with the correlation coefficient r2 = 0.8–0.95 before the waves break, but becomes less accurate after the waves break or are in the breaking zone with the smaller correlation coefficient r2 = 0.4–0.6. Four parameters, wave skewness Skη, asymmetry Ayη, Ursell number Ur, and Rocha number NP0, are introduced to describe the wave nonlinearity, of which Skη and Ayη are found to be of largest amplitudes at the wave breaking point and then start to decrease in the breaking zone and are almost unchanged for different beach slopes, while Ur further increases in the breaking zone and exceed the first larger value as waves approach to shoreline, but NP0 is almost linearly proportional to wave orbital velocity amplitude and quite sensitive to beach slope. The location of sandbar is found close to the wave breaking point in the wave flume and may be also considered as the point where wave nonlinearity becomes important for sediment transport in the surf zone, and the linear wave theory becomes less accurate.

Research on the Protective Effect of Twin-groyne Arrangement on Riverbank

A curved channel with intersecting streams can be easily scoured by incoming flow, and the concave bank is badly damaged. This research showed that the twin-groyne could effectively adjust and optimize the flow velocity distribution, change the shape of the free water surface of the bend, prevent erosion, and promote silting on the concave bank, and it could provide a scouring and silting effect on the convex bank. When the spacing of twin-groyne was increased to more than four times the body length of the single-groyne (spur dike), the protective effect on the concave bank was weakened, and the scouring and silting effect of the convex bank was reduced. Excessive spacing of the twin-groyne could cause local erosion damage to the concave bank. When the distance exceeded the theoretical optimum, it was equivalent to the effect of single-groyne. With the increase in the submergence degree, the velocity of the concave bank decreased first and then increased, while the velocity of convex bank decreased continuously. The protective effect of a non-submerged twin-groyne with a dam spacing of four times the body length of the single-groyne was better than that of other conditions, and it is recommended to be used in practice.

Quantification of Ammonium Release from an Aging Free Water Surface Constructed Wetland To Improve Treatment Performance

Quantification of Ammonium Release from an Aging Free Water Surface Constructed Wetland To Improve Treatment Performance

Water-free surface silanization on composite zeolite 13X/MgSO4 in a direct-contact adsorption heat pump for stable steam generation

Direct-contact method has been utilized in an open-loop adsorption heat pump based on composite adsorbent for high-temperature steam generation. Deliquescence problem arisen from the loss of salt in adsorbent under high humidity environment limits the stable performance during adsorption process. The composite zeolite was functionally modified with octyltrimethoxysilane (OTMOS) agent during water-free process based on liquid chemical grafting method. Measurement results from XRF (X-Ray Fluorescence) confirm the stable amount of salt is kept inside the modified zeolite. Characterization results from BET (Brunauer-Emmett-Teller) reveal the facts that pore volume and diameter are reduced simultaneously with the decrease in surface area. During regeneration dry air at 130 °C is used for removing water out of the packed bed filled with S8-7.5 (the composite adsorbent modified with 7.5 % OTMOS). During generation process superheated steam at 200 °C is obtained directly from hot water at 72 °C. GTL (Gross Temperature Lift) reaches 115 °C. COPh (coefficient of performance for heating) and SHP (specific heating power) for steam generation are increased by 16.2 % and 10.4 %, respectively after modification. The corresponding increases in system indicators stem from the promotion of steam mass, as adsorption abilities for composite zeolite are maintained well during direct contact with liquid water after modification.

Comparing Vegetation and Substrate Performances on Nutrient Removal and Biomass Establishment Using a Natural Swimming Pool Experiment

Natural swimming pools (NSPs) rely on the interaction of bog vegetation, bacteria, and substrate to maintain water quality. Nitrogen (N) and phosphorus (P) levels in NSPs are critical because of their involvement in eutrophication. We conducted a 15-week greenhouse study to address the significant literature gap regarding nutrient removal capabilities of substrates and vegetation in the low-nutrient environment of NSPs. We used mass balance analyses to compare the performances of four substrates [river gravel (control), recycled glass, expanded clay, expanded shale] and two plant species [blue flag iris (Iris versicolor) and lizard’s tail (Saururus cernuus)] under two flow conditions: free water surface and subsurface flow. At the end of the experiment, except for the recycled glass group, all other substrate groups reduced water nitrate (NO3) levels to less than 30 mg⋅L−1, the standard of the 2011 Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau (FLL) guidelines. However, only the expanded clay group closely approached the P standard (≤0.01 mg⋅L−1). Expanded clay and expanded shale demonstrated potential as substrates for NSP bogs. The final aboveground biomass dry weight was strongly negatively correlated with the final NO3 and P water concentrations. However, direct plant uptake proved insufficient to remove all nutrient inputs, especially for P. Except for the recycled glass group (34%), a significant portion of N (79%–90%) from total N added was removed by aboveground biomass. However, P uptake by biomass was substantially lower (18%–37%). With acceptable vigor and biomass accumulation, blue flag iris may be a suitable species for vegetated NSPs, whereas lizard’s tail is not because of uncertain establishment. Compared with controlling N, managing P for FLL standards in NSPs will be more challenging. Our work begins to fill the essential gap in the NSP literature regarding nutrient removal capabilities of substrates and vegetation. Future work should continue to study alternative substrates and plant species for P removal, particularly in field conditions and over longer periods.

Pelton turbine jet flow investigations using laser Doppler velocimetry

Hydropower is a sustainable and clean renewable energy source. The Pelton turbine is an impulse type of hydraulic turbine and operates under high head and low discharge. It comprises an injector, which converts high-pressure water into kinetic energy as a high-speed free surface water jet that impinges on the runner generating power coupled with an electric generator. The water is highly accelerated in the nozzle, which produces turbulent kinetic energy in the jet flow. Before impinging on the runner, the surrounding air is entrained into the jet, which causes the jet dispersion. The effective conversion of water energy into mechanical energy and the quality of a jet depend significantly on the uniformity of the jet. However, the jet encounters instabilities and non-uniformity caused by secondary flow and turbulence. Jet surface and velocity distribution do not remain symmetric. Investigation of the jet's velocity profile and turbulence intensities is important to understand the flow behavior and improvements in the design of injector. In this study, the experimental investigation of the jet has been performed using the laser Doppler velocimetry (LDV) system. The turbulent intensity and instantaneous velocity of the jet are analyzed at different locations along the jet flow. The velocity wake zone occurs around the center of the jet, which diminishes in the axial direction of the jet, with non-dimensional jet velocities values 0.91, 0.92, and 0.94 at x/Do of 0.5, 1, and 2 for ∼98% nozzle opening. The secondary flow velocity magnitude is larger for 90°–60° injector jet flow than for 90°–50°. The jet velocity profile obtained from the LDV has been compared with computational fluid dynamics analysis.

Nature-based alternative-water landscapes for water security and green space health

Abstract This paper is concerned with highlighting and learning from Alternative-Water Urban Landscapes (AWULs) from around the world. Such systems contribute to issues such as water security and greenspace health. Nature-based methods for treating alternative-water can provide for secure water supplies in local landscapes and a wide range of social and environmental co-benefits. However, such treatment methods have raised concerns about efficacy, safety, public opinion, and cost, which have often led to a reliance on centralised, and high-energy and chemical treatment methods. To move forward, more understanding about AWULs is required. The aim of this research is to reveal principles for the design of nature-based AWULs. A framework for the analysis of AWULs was developed from relevant literature works. The framework comprised two sets of criteria based on conservative and innovative aspirations for the AWUL design. A search of AWUL and landscape literature revealed 26 precedents as suitable. These were then analysed using the two sets of criteria which revealed three key outcomes. These included making use of free-water surface flow landscape-based treatment, large AWUL footprints and, partial decentralisation. These findings helped to fashion a set of design principles to guide and encourage adoption of nature-based AWUL by implementers.

On the effect of aeration on laser ranging measurements of free water surface

Aerated flows pose both challenges and opportunities in the measurement of free water surface. In this study, an amplitude-modulated continuous wave scanning LIDAR device was used to measure a distance from the device sensor to the water column surface subjected to different degrees of aeration, while reference measurements were performed by high-speed imaging. Different aeration conditions were generated by variation of the air flow rate supplied to the liquid and by using perforated plates with different hole arrangements. The LIDAR device was shown to produce level readings consistently below visible water levels. The measurement error of the LIDAR method is largely determined by the volume fraction of air in water and was lowest at about 0.1 air volume fraction. The error increases linearly until a very high air volume fraction (i.e., above 0.55), while the LIDAR method also performs poorly in unaerated water. Although the measurement uncertainty of LIDAR in the range of aerated water is by at least an order of magnitude higher than in the case of measuring dry solid surfaces, the method is viable for free surface measurement under low to moderate aeration conditions that don't produce excessive foaming.

Development and testing of a mechanistic model for wetland treatment of neutral and polar organic contaminants in oil sands process-affected water

A mechanistic model of the fate of neutral and polar organic contaminants in a free water surface flow wetland was developed to assess the removal efficiency of polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (O2-NAs), which are chemicals primarily responsible for oil sands process-affected water (OSPW) toxicity. The model simulates wetland mechanisms of chemical removal based on physicochemical properties, environmental conditions, and wetland design and operation. Good agreement between model estimated and observed concentrations of PAHs and O2-NAs in OSPW in the Kearl Treatment Wetland (Alberta, Canada) was observed over time. Model simulations indicate that the removal of PAHs and O2-NAs from OSPW is highly sensitive to biotransformation rates and that sustained wetland treatment is feasible with robust PAH and NA degrading microbial communities in the wetland. Wetland treatment efficiency is greatest for substances with a log KOW or log D between 3.0 and 5.5 whereas substances with a log KOW or log D >6.0 are not suitable for wetland treatment, even if they can be biodegraded. The log KOW of PAHs and log D for O2-NAs range from 0.7 to 6.7 suggesting most organic contaminants in OSPW are suitable for wetland treatment. Chemical removal via evapotranspiration is not significant pathway of chemical removal from wetlands for PAHs and O2-NAs due to their very low log KAW (less than −1.6). The treatment wetland model presented is the first model to evaluate the fate of both neutral and polar organic contaminants in a flow-through treatment wetland operation, making it a helpful tool to assess the feasibility of these treatment systems for the oil sands industry. The model is particularly useful in evaluating chemical removal efficiency of OSPW contaminants, whether specific water quality objectives can be achieved after treatment, and to assess trade-offs in wetland design and operation to balance treatment performance with design and operational features.

On the settling of aligned spherical particles in various quiescent media

We investigated experimentally the settling behaviour of vertically aligned spherical particles within various quiescent media at different release frequencies. The particles had a diameter of $d = 4$ mm and density of $\rho _s = 2200$ kg m $^{-3}$ , and were released near the free surface of water, ethanol, a G60 water–glycerine mixture (60 % glycerine by weight) and oil media at frequencies of $f_P = 4$ , 6 and 8 Hz, thereby allowing study of Galileo numbers, $Ga \in [16, 976]$ . Particle tracking velocimetry quantified the motion of nearly 800 particles in a 600 mm high tank, and particle image velocimetry examined flow patterns around the particles. Results revealed that the centre of mass of the particle trajectories exhibited preferential in-plane motions, with significant lateral dispersion and large $Ga$ in water and ethanol, and nearly vertical paths with low $Ga$ in the G60 mixture and oil media. Varying degrees of particle separation resulted in higher terminal velocities than for a single particle. Hence, particle drag decreased in all cases, with the oil medium showing the highest drag reduction under the closest particle separation, reaching up to nearly 70 % of that for the single particle. The vertical and lateral pair dispersions, $R^2_z$ and $R^2_L$ , exhibited ballistic scaling, with dependences on the initial separation, $r_0$ , and the type of medium. With large $Ga$ , $R^2_z$ displayed a ballistic regime followed by a slower rate, whereas with small $Ga$ , $R^2_z$ maintained a consistent ballistic regime throughout settling. Finally, normalized $R^2_z$ demonstrated distinct scaling (exponent 2/3 and 1) dependent on the normalized initial separation and $Ga$ .