Laboratory Flume Research Articles

Scale‐Dependent Evanescence of River Dunes During Discharge Extremes

AbstractDuring high river discharge extremes, the growth of dunes can reach a maximum beyond which a transition to upper stage plane bed may occur, enhancing the river's conveyance capacity and reducing flood risk. Our predictive ability of this bedform regime shift in rivers is exclusively built upon high Froude number flows dominated by asymmetric dunes with steep downstream‐facing slipfaces that are rare in natural rivers. By using light‐weight polystyrene particles as a substrate in an experimental flume setting, we present striking dune morphodynamic similarity between shallow laboratory flow conditions and deep rivers, preconditioned that both flow and sediment transport parameters are accurately scaled. Our experimental results reveal the first observation of upper stage plane bed in a shallow laboratory flume that is reached for a Froude number well below unity. This work highlights the need to rethink widely used dune scaling relationships, bedform stability diagrams, predictions of flow resistance, and flood risk.

The impacts of bioturbation by common marsh crabs on sediment erodibility: A laboratory flume investigation

Accelerating sea-level rise (SLR) threatens salt marshes globally, and thus understanding how these ecosystems respond to this stress is vital to increasing their resiliency. In order to maintain their surface elevation as sea level rises, salt marshes must add below ground biomass and accrete sediment. In many cases, biota can significantly affect marsh accretionary and erosional processes by stabilizing or helping to mobilize sediment, which in turn can profoundly affect the morphological evolution of the marsh. However, these effects are poorly understood. Bioturbation by dense populations of the marsh crab Sesarma reticulatum has been found to facilitate expansion of tidal creeks and creek bank erosion in multiple areas. The influence of S. reticulatum bioturbation on sediment erodibility has not yet been quantified, due to difficulties involved in measuring the processes in a field setting. In this study, we used a laboratory flume to examine the effects of burrowing by common marsh crab species S. reticulatum and Uca pugnax on sediment surface roughness and erodibility. Measurements and observations of surface elevation, flow velocities, and sediment movement indicate that burrowing and feeding by S. reticulatum, and to a lesser extent, Uca pugnax, increase surface roughness and decrease the threshold velocities and shear stresses required for sediment erosion. Erosion associated with observed burrowing is of a similar magnitude to mean annual marsh surface accumulation, and, consequently, this mechanism for sediment loss in heavily burrowed areas has the potential to produce large-scale morphological changes. TaxonomyEcological engineering, Coastal setting, Salt marsh, Geomorphological aspects, Soil erosion. Regional index termsUSA, Texas, Galveston.

Experimental and Simulation Study on Validating a Numerical Model for CO2 Density-Driven Dissolution in Water

Carbon dioxide density-driven dissolution in a water-filled laboratory flume of the dimensions 60 cm length, 40 cm height, 1 cm thickness, was visualized using a pH-sensitive color indicator. We focus on atmospheric pressure conditions, like in caves where CO2 concentrations are typically higher. Varying concentrations of carbon dioxide were applied as boundary conditions at the top of the experimental setup, leading to the onset of convective fingering at differing times. The data were used to validate a numerical model implemented in the numerical simulator DuMux. The model solves the Navier–Stokes equations for density-induced water flow with concentration-dependent fluid density and a transport equation, including advective and diffusive processes for the carbon dioxide dissolved in water. The model was run in 2D, 3D, and pseudo-3D on two different grids. Without any calibration or fitting of parameters, the results of the comparison between experiment and simulation show satisfactory agreement with respect to the onset time of convective fingering, and the number and the dynamics of the fingers. Grid refinement matters, in particular, in the uppermost part where fingers develop. The 2D simulations consistently overestimated the fingering dynamics. This successful validation of the model is the prerequisite for employing it in situations with background flow and for a future study of karstification mechanisms related to CO2-induced fingering in caves.

FLOW CHARACTERISTICS OF OPEN CHANNELS WITH FLOATING VEGETATION

Floating vegetation (Water hyacinth) causes many problems in waterways where it retards flow movement and changes flow structure. In this study the impact of water hyacinth on flow behavior in open channels was investigated in a laboratory flume. Water hyacinth was harvested from natural streams. Four different vegetation densities, three different vegetation root depths and three different vegetation zone lengths were used for smooth and rough channel bed. The case without water hyacinth was considered as comparative case. The water surface profiles for all cases were investigated. Results show that in the presence of water hyacinth water surface profile rises before vegetation zone then goes down until reaches to normal water surface. Results also show that water surface profile influenced by vegetation density, vegetation root depth, and vegetation zone length and bed roughness. Also the effect of vegetation parameters (density, root depth, zone length) on heading up, discharge and equivalent Manning's roughness coefficient was investigated and it is found that these parameters have a great effect on it. Multiple regression equations based on the dimensional analysis theory were deduced to calculate heading up, discharge and equivalent Manning's roughness coefficient.

Bedload transport rate prediction: Application of novel hybrid data mining techniques

The accurate prediction of bedload transport in gravel-bed rivers remains a significant challenge in river science. However the potential for data mining algorithms to provide models of bedload transport have yet to be explored. This study provides the first quantification of the predictive power of a range of standalone and hybrid data mining models. Using bedload transport data collected in laboratory flume experiments, the performance of four types of recently developed standalone data mining techniques - the M5P, random tree (RT), random forest (RF) and the reduced error pruning tree (REPT) - are assessed, along with four types of hybrid algorithms trained with a Bagging (BA) data mining algorithm (BA-M5P, BA-RF, BA-RT and BA-REPT). The main findings are four-fold. First, the BA-M5P model had the highest prediction power (R2 = 0.943; RMSE = 0.061 kg m−1 s−1; MAE = 0.040 kg m−1 s−1; NSE = 0.945; PBIAS = −1.60) followed by M5P, BA-RT, RT, BA-RF, RF, BA-REPT, and REPT. All models displayed ‘very good’ performance except the BA-REPT and REPT model, which were ‘satisfactory’. Second, the M5P, BA-RT, and RT models underestimated, and the BA-M5P, BA-RF, RF, BA-REPT and REPT models overestimated, bedload transport rates. Third, flow velocity had the most significant impact on bedload transport rate (PCC = 0.760) followed by shear stress (PCC = 0.709), discharge (PCC = 0.668), bed shear velocity (PCC = 0.663), bed slope (PCC = 0.490), flow depth (PCC = 0.303), median sediment diameter (PCC = 0.247), and relative roughness (PCC = 0.003). Fourth, the maximum depth of tree was the most sensitive operator in decision tree-based algorithms, and batch size, number of execution slots and number of decimal places did not have any impact on model’ prediction power. Overall the results revealed that hybrid data mining techniques provide more accurate predictions of bedload transport rate than standalone data mining models. In particular, M5P models, trained with a Bagging data mining algorithm, have great potential to produce robust predictions of bedload transport in gravel-bed rivers.

Experimental Study of Composite Inclined Weir – Gate Hydraulic Structure

Composite hydraulic structure is widely used in irrigation system which consists of two parts. The first part is responsible for overflow regime and is represented by a weir, whereas the second part is responsible for underflow regime and is represented by a gate. Both elements play significant role to control, measured, and divert the flow. So it dominates the hydraulic regimes of open channel or river with high responsibility and accuracy. The target of this study is to investigate the effect of the composite hydraulic structure installation at various inclination angles (from 45-135 degree) with the flume bed, which is horizontal, and adopt the normal position of composite device ( angle equal to 90 degree) as guide in discussion with various angles. Several experimental works were carried out in hydraulic laboratory flume at the Basrah Engineering Technical College under free flow condition with various geometrical dimensions of combined rectangular weir and rectangular gate in order to investigate the effect of inclination angle on major flow factors such as actual discharge, discharge coefficient, depth of water in downstream zone of flume, cross sectional area of flow that cross or pass the weir and gate respectively. Also, this study mentions the percentage of increase in discharge coefficient and variation in actual discharge, discharge coefficient and Reynolds Number with cross sectional area of flow that cross the gate.

On the scaling of large-scale structures in smooth-bed turbulent open-channel flows

This paper investigates the existence and scaling of the so-called large-scale and very-large-scale motions (LSMs and VLSMs) in non-uniform turbulent open-channel flows developing over a smooth bed in a laboratory flume. A laser Doppler anemometry system was employed to measure vertical profiles of longitudinal and bed-normal velocity statistics over a wide range of hydraulic conditions. Pre-multiplied spectra of the longitudinal velocity fluctuations revealed the existence of two peaks occurring at wavelengths consistent with those associated with LSMs and VLSMs as detected in the past literature pertaining to wall turbulence. However, contrary to so-called canonical wall flows (i.e. flat-plate boundary layers, pipe and closed-channel flows), the LSM and VLSM peaks observed in the open-channel flows investigated herein are detectable over a much larger extent of the wall-normal coordinate. Furthermore, the VLSM peak appears at von Karman numbers $Re_{\unicode[STIX]{x1D70F}}$ as low as 725, whereas in other wall flows much higher values are normally required. Finally, as conjectured by a recent study on uniform rough-bed open-channel flows, the present paper confirms that LSM wavelengths scale nicely with the flow depth, whereas the channel aspect ratio (i.e. the ratio between channel width and flow depth) is the non-dimensional parameter controlling the scaling of VLSM wavelengths. The intensity and wavelengths of the VLSM peaks were also observed to depend on the spanwise coordinate. This result suggests that VLSMs might be dynamically linked to secondary currents, as these are also known to vary in strength and size across the channel width.

Starved versus alluvial river bedforms: an experimental investigation

AbstractLaboratory experiments were conducted to investigate the formation of river bedforms under sediment supply‐limited conditions, i.e. when a motionless substratum is bared by the dynamics of the mobile sediments. Three series of experiments were organized in a laboratory flume by fixing all the hydrodynamic and morphodynamic parameters but varying the thickness of the initial layer of mobile sediments which covers the rigid bottom of the flume. At the end of all the experiments, which lasted for the same amount of time, the formation of transverse sand dunes was observed. For decreasing , the rigid bottom of the flume was bared progressively earlier during the experiment and the measurements showed a clear tendency of the bedforms to lengthen, i.e. to increase their crest‐to‐crest distance. Moreover, under strong supply limitation, the two‐dimensional transverse dunes turned into three‐dimensional barchanoid forms and into isolated barchan dunes characterized by an abrupt reduction in bedform heights. A two‐dimensional Fourier analysis of the bottom profile was performed, providing the amplitude of the main streamwise and spanwise harmonic components of the bottom morphology as a function of . © 2019 John Wiley & Sons, Ltd.

Local scour around submerged tandem and offset cylinders due to change in alignment angle

A study on scour around submerged tandem and offset cylinders was carried out with the aim of characterising the scour process and the influence of various parameters on the variation of scour depth over time. An experimental campaign was undertaken in a laboratory flume over a shallow range of submergence ratios (1·95–2·60) and alignment angles between the tandem cylinders (0°–40°). The formation of dunes in between tandem cylinders was observed for experiments with reduced flow velocity. The scour depths around both cylinders increase with the increase of Froude number and decrease with an increase in the submergence ratio and sediment size. The scour depth around the downstream cylinder increases with increase of alignment angle. Equations to representi the various combinations of cylinders and arrangements have been proposed. On the basis of the experimental results, adjustment factors and a timescale are proposed. The degree of deviation and adjustment factors to correlate scour depth around tandem and single cylinders have been determined. The time variation is represented using a timescale that decreases with increase of densimetric Froude number.

Dissipation energy of Flow by Stepped Type Gabion Weir

The energy of flow can be defined in general form as a measure of an object’s capability to perform work, and it can be done in many different forms. The present study aims to investigate the dissipated energy of flow in the stepped shape of gabion weir with three steps. A set of 25 laboratory experiments and 175 operation tests were carried out by using a laboratory flume channel with different discharges. The tested gabion weir has five different lengths, and the filling material used is natural quarry gravel with five different median diameter. The experimental data have been analyzed to correlate the energy dissipation with the independent dimensionless terms of the other variables. The results of analysis showed that the energy dissipation has a direct proportion with discharge, and an inverse proportion with both the ratio of length of the third step to total length of the weir, the diameter of the gravel sample, and the porosity in general form, respectively. The concluded equation of energy dissipation gives good agreement for comparison between measured and predicted values of energy dissipation.

Fine Sediment Deposition and Filtration Under Losing and Gaining Flow Conditions: A Particle Tracking Model Approach

AbstractFine particle deposition within riverbeds plays a major role in riverine ecology and biogeochemistry by altering hyporheic exchange flux. Moreover, it is ubiquitous within streams and rivers across all flow stages. However, the dynamics of fine particle deposition are still not completely understood in rivers, and continuum models like the advection dispersion equation require modifications to represent the processes accurately. To enhance understanding of fine particle dynamics, we developed a novel numerical particle tracking model that simulates fine particle deposition as a stochastic process under losing, neutral, and gaining streamflow conditions. These flow conditions generate three different velocity profiles by combining the free surface and groundwater flows. In addition, a novel aspect of our model is the storage of filtered particles to estimate concentration fields within the bed. Our simulated results are qualitatively compared with previous laboratory flume experimental results of kaolinite deposition under similar conditions. The model indicates that fine particle deposition patterns and residence time functions depend heavily on the exchange flux between stream and groundwater, as well as bed filtration properties as the deposition of particles occurs at greater depths in the losing stream condition than in the neutral and gaining cases. Therefore, the spatial pattern of particle deposition is a direct result of pore water velocity profiles, while the concentration depends on filtration dynamics within the bed.

Combined effects of predation, flow speed, and sub-lethal exposure to insecticide on the feeding behavior of a spionid polychaete

Behavioral responses of infauna to predation have received limited study, especially in varying hydrodynamic conditions above estuarine sediments. Many estuaries also are impacted by chemical pollution, including runoff of terrestrial insecticides such as chlorpyrifos. We tested how feeding behaviors of a tube-dwelling, interface-feeding worm, Polydora cornuta, change due to predation by an omnivorous estuarine fish, Fundulus parvipinnis, in the contexts of hydrodynamic regime and sub-lethal exposure to chlorpyrifos. We performed two experiments in a laboratory flume at two flow speeds (6 or 15 cm s−1). We analyzed feeding behaviors of P. cornuta when F. parvipinnis were either actively feeding on the worms, caged upstream to prevent predation, or absent from the flume. In our first experiment, the presence of actively feeding F. parvipinnis reduced the time P. cornuta spent feeding by half relative to when fish were absent. Fish caged upstream had no effect on worms' feeding activity, indicating that P. cornuta reduced their feeding in response to tactile stimuli or sensing light shadows, rather than chemical alarm cues. Our second experiment tested the effects of actively feeding F. parvipinnis on the feeding behaviors of P. cornuta that had undergone a 96-h exposure to chlorpyrifos. Worms exposed to chlorpyrifos reduced feeding relative to unexposed worms, but only in the absence of predatory fish. Flow speed also influenced worms' behavior, with worms preferentially suspension feeding at the faster flow. In both experiments, individual worms that were observed to be attacked by F. parvipinnis resumed feeding approximately 10–11 min after the attack. The combined results demonstrate that the close proximity of actively feeding fish has a consistently greater effect on the feeding behavior of an infaunal polychaete than does sub-lethal exposure to a toxicant or variation in water flow.

Velocity Fields at Horizontal Bar Racks as Fish Guidance Structures

Horizontal bar racks used as fish protection measures at hydropower plants have rapidly gained importance in recent years. Despite the large number of installed racks in Europe, systematic investigations of the hydraulic losses and velocity fields were missing. To fill these research gaps, the hydraulic performance of horizontal bar racks was systematically investigated in a laboratory flume for a large number of rack parameters and different hydropower plant layouts. The results of the head loss assessment are published in a paper entitled Head Losses of Horizontal Bar Racks as Fish Guidance Structures, whereas the present paper focuses on the velocity fields. The measurements show that the bar shape, the horizontal approach flow angle, and the clear bar spacing have only a minor effect on the velocity fields. In contrast, bottom and top overlays might enhance the fish guidance efficiency for bottom and surface oriented fish, while the asymmetric downstream velocity field can reduce turbine efficiencies. The hydropower plant layout strongly affects the approach flow field to horizontal bar racks. For block-type hydropower plants, the installation of a dividing pier or partial opening of the spillways improves the flow field for better fish guidance.

Laboratory investigations of the role of biofilms on stream‐bed surfaces in debris‐flow runout

AbstractDebris‐flow runout is a fascinating process to understand due to its implications for downstream alluvial fans. Based on the propagation‐deposition behaviors of the Dongyuege (DYG) debris flow, in Yunnan, the effect of biofilms on channel surfaces on debris‐flow runout is investigated in laboratory flumes with two different internal surfaces: surfaces are lined with granite slabs (Model I) and gravel (Model II), respectively.Our results show that biofilms can significantly reduce frictional resistance to flows. They increase flow velocities, slow down the deceleration of the snouts, prolong runout distances, and subsequently extend the areas covered with resulting deposits, thus greatly assisting the propagation of experimental debris flows. Slippery biofilms consisting mainly of diatoms and their extracellular mucus (ECM) reduce the contact friction between the flume‐beds and the overlying fluids, and greatly promote the propagation of tested flows.Well‐developed biofilms are found on the underwater channel surfaces of the DYG Creek. Acting as lubricating layers, they likely played a key role in the DYG debris‐flow runout. Most of the debris transported during the DYG event was deposited on overbanks, and the sediment that caused the disaster was transported to the populated fan region through the stream‐bed clad in the thick biofilms. Owing to their impacts on the development and width of the temporary debris dam breach, the stream‐bed covered with biofilms became a direct contributor to the debris‐flow hazard.Because of the ubiquitous presence of biofilms on mountain stream‐bed surfaces, the development of perennial streamflows can be viewed as an indicator of gully susceptibility to debris flows threatening creek fans. The underwater areas of pre‐event channel cross‐sections should be regarded as slip or low‐friction boundaries, and the parts above stream‐levels can be viewed as no‐slip boundaries. © 2019 John Wiley & Sons, Ltd.

Fish guidance structures: hydraulic performance and fish guidance efficiencies

The hydraulic performance and fish guidance efficiency (FGE) for behaviourally-based mechanical fish guidance structures, i.e. louvers and modified angled bar racks (MBRs), were evaluated experimentally and the results are presented herein. Detailed velocity profiling was conducted to assess the hydraulic performance of the 1:1 Froude-scaled racks in an etho-hydraulic laboratory flume. Guidance efficiencies of the studied rack configurations were evaluated through live-fish tests in the same flume. Tests were conducted with five European fish species, namely, barbel (Barbus barbus), spirlin (Alburnoides bipunctatus), European grayling (Thymallus thymallus), European eel (Anguilla anguilla) and brown trout (Salmo trutta). The results demonstrate that MBRs are advantageous over louvers because of reduced head losses, improved hydraulics and higher FGEs. Furthermore, use of a bottom overlay on the MBRs substantially increased the FGE. The results are discussed and compared with literature data. Recommendations for an optimized and economic MBR design are given. The present findings underpin the follow-up studies for further optimization of MBR design.

Laboratory Flume Experiments on Cohesive Sediment Erosion by Oscillating Wall Jet

Dong, C.; Zhao, P.; Yu, G., and Zhang, M., 2021. Laboratory flume experiments on cohesive sediment erosion by oscillating wall jet. Journal of Coastal Research, 37(1), 179–190. Coconut Creek (Florida), ISSN 0749-0208.Jet scour, a common method of dredging clay, must be accurately estimated. Cohesive sediment is aggregated by adhesion and is sensitive to erosion when the flow shear is appended with oscillation, as indicated by sediment rheology. On the basis of sediment rheology, this study experimentally investigates the timescale of the erosion of cohesive sediment under an oscillating wall jet in a laboratory flume. The oscillating wall jet is induced by a swinging oblique impingement jet. The erosion of the cohesive sediment was performed under an oscillating wall jet with a fixed flow rate but different oscillating intensities. The morphological properties, scouring depths, and rheological characteristics of the sediment were observed. The results show that when the oscillating frequency is zero or low, the sediment particles scatter similarly to aggregates, forming ridges at the intersection of the scouring slope and bed surface. However, these aggregates and ridges disappear when the oscillating frequency increases. Further, evaluations of the cohesive sediment under different oscillating frequencies indicate that the yield stress decreases with an increase in the scouring frequency. Submerged cohesive sediments tend to fluidize under oscillating shear, which indicates shear thinning behavior. Under the conditions of the oscillating wall jet, the scouring depth of the cohesive sediment increases exponentially with the oscillating intensity.

High-intensity light blocks Bighead Carp in a laboratory flume

High-intensity light blocks Bighead Carp in a laboratory flume

Energy dissipation in gabion weirs

The present study investigates the effect of hydraulic jumps as criteria for representation of the energy dissipation of flow in gabion weirs. A set of 25 laboratory experiments and 188 operation tests were carried out using a laboratory flume with dimensions 10 m long by 0.3 m wide, and 0.5 m high. The tested gabion weir had different five possible lengths, 0.4 m, 0.6 m, 0.8 m, 1.0 m, and 1.2 m, and the filling material used was natural quarry mono-graded gravel in five different sample sizes of average equivalent diameter 11.75 mm, 16.50 mm, 22.00 mm, 31.25 mm, and 43.75 mm. Operation discharge values ranged between 0.7 to 15.0 l/s. The data set was subject to dimensional analysis to generate dimensionless groups, and correlated using the Buckingham Pi-Theorem. The results of this analysis showed that the distance of hydraulic jump has a direct relationship with discharge and an inverse relationship with the diameter of the gravel in the sample. For specified discharges, the distance of hydraulic jump had an inverse relationship with the length of the gabion weir and a direct relationship with the proposed energy dissipation parameter.

Flume experiments on log accumulation at the bridge with pier and without pier

Heavy rain causes landslide and debris flow, which produce sediment and woody debris in the mountain river basin. During the process, woody debris and sediment are trapped by the obstacles. As a result, woody debris accumulations at bridges are formed. Trapped woody debris at the bridge caused inundation because the obstacle blocked the water flow in the river course. To get more information regarding the woody debris accumulation at a bridge, laboratory flume was used for experiments to investigate the characteristics of woody debris accumulation at a model bridge without a pier. As a result, the experiments show that the number of trapped wood pieces increases with the number of released pieces. Moreover, the trapped wood pieces caused wood accumulations at the model bridge and backwater rise in its upstream side region. Besides that, the backwater rise increase with a number of trapped wood pieces at the bridges.

A Wavelet Based Deep Learning Method for Underwater Image Super Resolution Reconstruction

In order to solve the scattering degradation by turbulence and suspended particles in underwater imaging, traditional processing methods including image enhancement, restoration and reconstruction have been continuously researched. But most of them rely on degradation models, and there exist problems of ill-posed. Image super resolution reconstruction based on deep learning has become a hot topic in recent years. In order to further improve the effectiveness and efficiency of deep learning based methods, an improved image super-resolution reconstruction algorithm based on deep convolutional neural network is proposed in this paper. The wavelet basis which can effectively simulate the waveform and characteristics of underwater turbulence is selected to replace the neuron fitting function in order to improve the accuracy and efficiency of the algorithm. An improved dense block structure (IDB) is introduced into the network which can effectively solve the gradient disappearance problem of deep convolutional neural network and improve the training speed at the same time. The method proposed in this paper has been verified in laboratory flume, public data set and real water body. The experimental results show that under the same conditions, the proposed algorithm shows improvements on various evaluation parameters compared with DRFN, VDSR and DRCN method. So it can be concluded that the proposed method can effectively improve the quality of deep learning based reconstruction for imaging in natural water.