Search Results (126)

Results are reported for a series of small-scale experiments that examine the dispersion of dense gas released upstream of an isolated building. The experiments replicate the geometry of the Thorney Island Phase II field tests and show good qualitative agreement with the flow regimes observed therein. The experiments were run in a water flume, and the flow is characterized by the Richardson number ($Ri$), where high $Ri$ represent relatively high density releases. For low $Ri$ the dense cloud flows over and around the building and any fluid drawn into the building wake is rapidly flushed. However, for high Ri, the dense cloud collapses, flows around the building, and is drawn into the wake. The dense fluid layer becomes trapped in the wake and is flushed by small parcels of fluid being peeled off the top of the layer and driven up and out of the wake. Results are presented for the concentration field along the center plane (parallel to the flow) of the building wake and time series of concentration just above the floor and downstream of the building. The time series for low-$Ri$ and high-$Ri$ flows are starkly different, with differences explained in terms of the observed flow regimes. Full article

The role of weirs in flow regulation in water resources infrastructure and flood control is well known. In the meantime, the study of full-width plate weirs (FWPW), due to their wide application and lacking findings, is of great importance. In this study, experimental models were conducted at Babol Noshirvani University of Technology to investigate flow passing through FWPWs with five different heights (p = 0.07, 0.09, 0.11, and 0.15 m) under eight discharge conditions (Q = 1.4 to 6.3 L/s). The experiments were carried out in a flume measuring 4 m in length, 0.6 m in width, and 0.2 m in height. The discharges were measured with a calibrated flowmeter, and the water depths upstream of the weir (h) and the tailwater depths (h₁) were measured with a point gauge with an accuracy of 0.1 mm. For each test, the discharge coefficient (C_d), relative residual energy (E₁/E₀), and relative energy dissipation ((E₀ − E₁)/E₀) were computed. The proposed equation for calculating discharge achieved good accuracy with RMSE = 0.0002, MAE=0.0002, and R² = 0.997. Results show a reducing trend of C_d by increasing h/P, which is compatible with previous results. It was observed that at a constant discharge, relative residual energy reduces by an average of 47% by increasing weir height, and at a constant P, increasing flow discharge increases it a little. A novel accurate equation for relative energy dissipation in FWPW was proposed based on h/P that provided specific constant coefficients for each p value. Full article

Warm conditions during typically cold winters impact runoff and resulting hydraulic processes in channels where ice-cover would typically dominate. This field study on a short, low-slope reach in Southern Ontario, Canada, examined hydrologic and hydraulic processes with a focus on winter runoff events and subsequent bed shear stress variability. Through winter 2024, six cross-sections over a ~100 m reach were monitored near-weekly to measure hydraulic geometry and velocity profiles. These data characterized channel processes and estimated bed shear stress with law of the wall. In this channel, velocity increased more rapidly than width or depth with rising discharge and influenced bed shear stress distribution. Bed shear stress magnitudes were highest (means ranged ~2–6 N/m²) and most variable over gravel beds compared to the exposed bedrock (means ranged ~0.05–2 N/m²). Through a rain-on-snow (ROS) event in late January, bed shear stress estimates decreased dramatically over the rougher gravel bed, despite minimal changes in water depth and velocity. Pebble counts before, during, and after the event, showed that the proportion of finer-sized particles (i.e., <5 cm) increased while median grain size did not vary. These observations align with findings from both flume and field studies and suggest that milder winters reduce gravel-bed roughness through finer-sized sediment deposition, altering sediment transport dynamics and affecting gravel habitat suitability. Additionally, limited ice-cover leads to lower bed shear stresses and thus finer-sized materials are deposited, further impacting gravel habitat suitability. Results highlight the importance of winter hydrologic variability in shaping channel processes and inform potential stream responses under future climate scenarios. Full article

Barrier lakes formed by debris flows blocking rivers can burst rapidly, posing significant threats to downstream areas. Mitigating the risk of barrier lake breaches caused by debris flow blockages is crucial for ensuring safety in affected regions. This study employed physical experiments to investigate the influence of connection angles between the main flume and the tributary flume, as well as the installation of diversion dikes, on the morphological characteristics of debris flow deposits and the resulting barrier lake breach behavior. The findings reveal that when the debris flow enters the main flume at an intersection angle of 60°, compared to vertical entry (90°), the deposit’s height and volume are significantly reduced, while its length is increased. However, with the installation of a diversion dike, the height, volume, and length of the deposits are minimized, achieving the smallest values observed. Specifically, compared to vertical entry and a 60° connection angle without a diversion dike, the deposit volume decreased by 31.54~56.26%, height by 10.81~34.75%, and length by 2.33~25.05%. Post-breach observations indicate that the installation of a diversion dike results in the widest breach, the smallest peak flow, and the earliest occurrence of the peak flow. These findings demonstrate that diversion dikes effectively mitigate the barrier lake breach disaster caused by debris flow by altering the deposit morphology. The results provide valuable insights for the prevention and management of debris flow-induced river blockages and associated disasters in mountainous regions. Full article

Local scour around bridge piers poses significant challenges to the stability and safety of bridge structures. Local scour results from the combined effects of increased longitudinal flow velocity, the direct impact of the flow in front of the pier, and the suction effect of horseshoe vortices. This study utilizes a three-dimensional mathematical model to simulate the flow field around the pier, employing the SWASH (simulating waves till shore) model. Experimental observations in a bed load flume were conducted to analyze the contribution of different factors to local scour. The results indicate that the scour depth caused predominantly by the flow accounts for approximately 75–80% of the total scour depth. Analysis of the longitudinal flow velocity distribution suggests that the scour depth due to the redistribution of longitudinal flow velocity generally accounts for 15–30% of the total scour depth. These findings provide insights into the local scour mechanism and have implications for the design and maintenance of bridge foundations. Full article

Salt marsh vegetation significantly changes water motion and sediment transport in coastal wetlands, which further influences the geomorphological evolution of coastal wetlands. Accurate determination of the vegetation drag coefficient (Manning’s roughness coefficient) is critical to vegetation flow resistance research. Previous studies on the vegetation roughness coefficient mainly conducted flume experiments under the one-dimensional steady flow condition, which could not reflect the two-dimensional unsteady flow condition in salt marsh vegetated zones. Through theoretical formula analysis and synchronized field observations in a salt marsh vegetated zone, we propose a novel method for calculating the roughness coefficient of salt marsh vegetation especially under the two-dimensional unsteady flow condition. The results indicate that the vegetation roughness coefficient under the two-dimensional unsteady flow condition can be obtained by integrating the flow resistance equation with the discretized momentum conservation equation. Then, in combination with field observation data, the temporal variations in the vegetation roughness coefficient can be derived. The salt marsh vegetated zone in the Jiuduansha Wetland is dominated by flooding currents, and ebbing currents are of secondary importance. The flow resistance of vegetation on flooding and ebbing currents is remarkable. Moreover, the roughness coefficient shows an inverse power-law relationship with the product of flow velocity and water depth (i.e., U_fh_f) at the control volume center. Under the same U_fh_f scenario, due to the increase in the water-facing area of vegetation, the roughness coefficient during the submerged period is generally greater than that during the non-submerged period. The calculated roughness coefficients and their relationships with U_fh_f are consistent with those shown in previous flume experiments, indicating that our proposed method is reasonable. This new method could help determine vegetation flow resistance accurately (particularly under the two-dimensional unsteady flow condition), and it may provide implications for eco-geomorphological simulations of coastal wetlands. Full article

Microplastic pollution in soils and surface waters is a growing environmental concern, yet the mechanisms governing transport by overland flow remain unclear. This study investigated the influence of soil texture and slope gradient on the movement of microplastics with different shapes and polymer compositions under simulated rainfall and typical agricultural conditions in a semi-arid climate. Small soil flumes were subjected to controlled rainfall simulations replicating typical rain patterns, and microplastic transport was quantified using collection flasks. The results indicated that neither soil texture nor slope gradient significantly affected total microplastic transport. However, fibres exhibited greater retention in the soil compared to other shapes. Polymer composition did not play a major role in microplastic mobility, except for polystyrene pellets, which were transported more readily than polyethylene pellets. Field observations of agricultural soils with a history of sludge application confirmed a predominance of fibres in the topsoil, reinforcing the tendency of this shape to resist mobilisation. These findings suggest that microplastic transport by surface runoff is primarily governed by particle shape and buoyancy rather than soil properties or slope inclination. Future research should explore the roles of particle size, rainfall intensity, and organic matter content in microplastic mobility under natural field conditions. Full article

This study investigates the incipient motion and scouring of sediments around simulated submarine cables in a controlled flume experiment, focusing on five distinct grain sizes in an experimental pool. The measured incipient velocity values were compared with predictions from three established formulas, leading to a modification of the Sun Zhilin formula for improved accuracy. By incrementally increasing flow velocity, the scour depth and scour duration were measured required to expose cables buried at varying depths for different sediment sizes, and the relationships between scour rate, relative flow rate, and Froude number were analyzed. The results indicate that as the Froude number increases, both the relative flow velocity and scour rate increase, thereby enhancing the erosion of sediment. The modified formula demonstrated a higher consistency with observed scour depths, providing a reliable tool for assessing submarine cable exposure risks. These findings offer valuable insights for developing effective protection strategies to enhance cable stability in complex marine environments. This research highlights the importance of understanding sediment dynamics and their impact on submarine cable stability, contributing to the development of more effective protection strategies for submarine cables in dynamic seabed conditions. Full article

Engineered loess-filled gullies, which are widely distributed across China’s Loess Plateau, face significant stability challenges under extreme rainfall conditions. To elucidate the regulatory mechanisms of antecedent rainfall on the erosion and failure processes of such gullies, this study conducted large-scale flume experiments to reveal their phased erosion mechanisms and hydromechanical responses under different antecedent rainfall durations (10, 20, and 30 min). The results indicate that the erosion process features three prominent phases: initial splash erosion, structural reorganization during the intermission period, and runoff-induced gully erosion. Our critical advancement is the identification of antecedent rainfall duration as the primary “pre-regulation” factor: short-duration (10–20 min) rainfall predominantly induces surface crack networks during the intermission, whereas long-duration (30 min) rainfall directly triggers substantial holistic collapse. These differentiated structural weakening pathways are governed by the duration of antecedent rainfall and fundamentally control the initiation thresholds, progression rates, and channel morphology of subsequent runoff erosion. The long-duration group demonstrated accelerated erosion rates and greater erosion amounts. Concurrent monitoring demonstrated that transient pulse-like increases in pore-water pressure were strongly coupled with localized instability and gully wall failures, verifying the hydromechanical coupling mechanism during the failure process. These results quantitatively demonstrate the critical modulatory role of antecedent rainfall duration in determining erosion patterns in engineered disturbed loess, transcending the prior understanding that emphasized only the contributions of rainfall intensity or runoff. They offer a direct mechanistic basis for explaining the spatiotemporal heterogeneity of erosion and failure observed in field investigations of the engineered fills. The results directly contribute to risk assessments for land reclamation projects on the Loess Plateau, underscoring the importance of incorporating antecedent rainfall history into stability analyses and drainage designs. This study provides essential scientific evidence for advancing the precision of disaster prediction models and enhancing the efficacy of mitigation strategies. Full article

Flow velocity is a critical factor in determining the suitability of fish habitats. Understanding the preference patterns of the four major Chinese carps (FMCCs) for different flow velocities is crucial for their habitat conservation and restoration. In this study, the preference of individual fish species, approximately 15 cm in length, for flow velocity was investigated at flow velocity gradients of 0.0, 0.4, 0.8, 1.2, 1.6, and 2.0 times their body length. Additionally, a deep learning algorithm based on convolutional neural networks (CNNs) was employed for fish target detection. The results showed that, at this length, black carp (Mylopharyngodon piceus) preferred fast currents when the inlet flow velocity was between 0.4 and 1.6 times their body length, while grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix), and bighead carp (Hypophthalmichthys nobilis) preferred fast currents when the inlet flow velocity of the test flume was between 0.4 and 2.0 times their body length. However, this preference for fast currents decreased as the overall flow velocity increased to a specific threshold, eventually leading to their avoidance. The highest preference for fast currents among the four species was observed at inlet flow velocities of 1.2, 0.4, 0.8, and 0.8 times their body length, respectively. The findings of this study provide important insights into habitat conservation and restoration for the FMCCs in projects focused on the construction of navigation channels and water conservancy. Full article

This study investigates the dynamic response of seabed pore pressure under wave loading, focusing on silty and layered seabed conditions, with the aim of providing insights into seabed stability and coastal engineering design. A series of wave flume experiments were conducted to explore the spatial and temporal evolution of pore pressure under varying wave parameters, soil permeability conditions, and degrees of sediment stratification. The pore pressure signals were analyzed using Daubechies wavelets to distinguish between oscillatory and cumulative components in homogeneous silty seabeds. For layered seabeds, two distinct response patterns were observed. In shallow layers, pore pressure accumulation occurs gradually, enhancing stability by mitigating dynamic stresses. However, in deeper layers, pore pressure accumulation increased significantly, posing potential risks to structural stability. The experiments revealed that the permeability of the surface soil layer plays a critical role in modulating the amplitude and rate of pore pressure oscillations, as well as the accumulation patterns across depths. Based on the experimental findings, a mathematical model was developed to characterize the spatial–temporal evolution of excess pore pressure, incorporating key parameters related to wave properties, water depth, and soil characteristics. These parameters were fitted using nonlinear optimization techniques. Validation against established experimental and analytical data confirmed the model’s accuracy and capability in describing the complex interactions between wave loading and seabed dynamics. The outcomes of this study provide a theoretical foundation for understanding wave-induced pore pressure responses and offer practical guidance for the design and stability assessment of nearshore structures under dynamic wave conditions. Full article

Emergent vegetation in river corridors influences both the flow structure and subsequent fluvial processes. This investigation aimed to analyze the impact of the bending and vegetation components in a sharply curved open channel on the flow field. Experiments were undertaken in a meandering flume (0.9 m wide, wavelength of 3.2 m, and a sinuosity of 1.05) with a 90-degree bend at the end of it, with and without vegetation, to achieve this goal. The individual vegetation elements arranged across the 90-degree bend of the flow channel were physically modelled using rigid plastic stems (of 5 mm and 10 mm diameters). Analysis of the findings from the flow velocimetry, taken at five cross-sections oriented at angles of 0°, 30°, 45°, 60°, and 90°, along the 90-degree bend indicates that as the plant density increases, the effect of centrifugal force from the channel’s bend on the cross-sectional flow patterns decreases. At the same time, the restricting influence of vegetation on lateral momentum transfer becomes more pronounced. Specifically, for increasing vegetation density: (a) higher transverse and vertical velocities are observed (increased by 4.35% and 9.68% for 5 mm and 10 mm reed vegetation, respectively, compared to the non-vegetated case); (b) greater turbulence intensity is seen in the transverse flow direction, along with increased turbulent kinetic energy (TKE); and (c) reduced near-bed Reynolds stresses are found. The average transverse flow velocity for the non-vegetated case is 18.19% of the longitudinal flow velocity and the average vertical velocity for the non-vegetated case and 5 mm and 10 mm reed vegetation is 3.24%, 3.6%, and 5.44% of the longitudinal flow velocity, respectively. Full article

Most pier scour monitoring methods cannot be carried out during floods, and data cannot be recorded in real-time. Since scour holes are often refilled by sediment after floods, the maximum scour depth may not be accurately recorded, making it difficult to derive the equilibrium scour depth. This study proposes a novel approach using 16 proximity sensors (VCNL4200), which are low-cost (less than USD 3 each) and low-power (380 µA in standby current mode), to monitor and record the pier scour depth at eight different positions in a flume as it varies with water flow rate. Based on the regression relationship between PS data and distance, the scour trend related to the equilibrium scour depth can be derived. Through the results of 13 local live-bed sediment scour experiments, this PS module was able to record not only the scour depth, but also the development and geometry of the scour under different water flows. Additionally, based on PS data readings, changes in the topography of the scour hole throughout the entire scouring process can be observed and recorded. Since the maximum scour depth can be accurately recorded and the scour trend can be used to estimate the equilibrium scour depth, observations from the experimental results suggest that the critical velocity derived by Melville and Coleman (2000) may have been underestimated. The experimental results have verified that, beyond achieving centimeter-level accuracy, this method also leverages the Internet of Things (IoT) for the long-term real-time observation, measurement, and recording of the formation, changes, and size of scour pits. In addition to further exploring scouring behavior in laboratory studies, this method is feasible and highly promising for future applications in on-site scour monitoring due to its simplicity and low cost. In future on-site applications, it is believed that the safety of bridge piers can be assessed more economically, precisely, and effectively. Full article

A quantitative understanding of the migration of munitions and canonical objects in the nearshore is needed for the effective management of contaminated sites. Migrations of munitions with a density range of 2000 kg/m³ to 5720 kg/m³ were quantified in a large-scale wave flume. The forcing consisted of six cases of varying wave heights, periods, still water depths, and durations. The cross-shore profile, typical of natural sandy beaches, was sub-divided into swash, surf, and offshore zones. Overall, 2228 migration measurements were recorded with 16% and 84% of the migration observations classified as “motion” (net distance > 0.5 m) and “no motion” (net distance ≤ 0.5 m), respectively. The probability of munitions migration increased with proximity to the shoreline. There was a nearly equal probability of onshore or offshore migration in the swash zone. Migration in the surf zone tended to be offshore-directed (65%), while migration was onshore-dominant (65%) in the offshore zone. Migration in the offshore zone was preferentially onshore due to skewed waves over flat bathymetry. Less dense munitions in the offshore zone may have migrated offshore likely still related to the skewed nature of the wave profile causing transport in both directions through the majority of the wave phase. The largest migration distances occurred in the surf zone likely due to downslope gravity. Migration in the surf and swash zones is a balance between skewed/asymmetric forcing and downslope gravity, with downslope gravity tending to be pronounced provided the forcing is sufficient to initiate motion. An exception was sometimes observed in the swash zone where onshore forcing was sufficient to transport munitions to the seaward side of the berm where they became trapped in a bathymetric depression between the dune and berm. Relating overall migration (Lagrangian) to fixed hydrodynamic measurements (Eulerian) was ineffective. Parameters such as the Shields number, wave skewness, and wave asymmetry estimated from the closest measurement location were insufficient to predict migration. Large scatter in the migration data resulting from competing hydrodynamic, morphodynamic, and munitions response processes makes robust deterministic predictions with flow statistics and dimensionless numbers difficult. Full article

The geotextile mattress with floating plate (GMFP) is an innovative scour protection device. This study examines the potential for seepage failure under the GMFP, which has been previously documented. The effects of flow velocity and GMFP configuration on the potential for seepage failure were analyzed. The variation pattern of the sloping angle was first revealed in flume tests, and the bed pressure near the GMFP with various configurations in steady currents was thereafter simulated. The average hydraulic gradient across the GMFP was observed to increase with an increase in the Froude number before reaching a plateau, which can be explained by the coupled effects of the rising Froude number and the decreasing sloping angle. The average hydraulic gradient was approximately inversely proportional to the mattress length upstream of the floating plate. With the decreasing mattress length downstream of the floating plate, the average hydraulic gradient initially rose and then declined when the downstream mattress was relatively short. This trend can be associated with the amplification of the vortices in the top vortex zone downstream of the GMFP with the shortened downstream mattress, which pushed the bottom vortex to the leeside. The shortened downstream mattress could increase the risk of overturning and slipping of the GMFP, although the average hydraulic gradient decreased. Full article