Search Results (847)

Accurate prediction of burial depth and suspended length for oil and gas pipelines crossing rivers is critical for ensuring structural integrity. Systematic flume experiments were employed to examine local scour under varying hydrodynamic conditions, emphasizing relationships between scour hole expansion rate and flow velocity, water depth, and pipe diameter. Bedload transport predominantly governs riverbed evolution and scour hole development. Larger pipe diameters significantly reduce scour hole formation beneath the pipeline. Vertical expansion rate peaks immediately upon initial erosion, then progressively declines due to canalized flow, while cumulative scour depth continues increasing. Vertical dynamics at the pipe bottom conform to a first-order dynamic response equation, yielding a normalized time-dependent scour depth equation. Ultimate scour depth is collectively influenced by hydraulic parameters, pipe diameter, and sediment characteristics. Dimensionless correlations among scour depth, relative sediment size, and Froude number (Fr) were established via Gauss–Seidel iteration. Horizontal expansion exhibits distinct regimes: single-phase dominates at Fr > 0.6, whereas a secondary phase emerges at Fr ≤ 0.6. Integrating experimental data with empirical vertical expansion models, we propose a comprehensive horizontal scour expansion calculation model. These findings provide substantive insights into scour evolution mechanics and directly inform safety assessments for river-crossing pipelines. Full article

Scour has been a topic of significant concern among coastal geotechnical engineers in recent years. The Shields number serves as a crucial parameter for erosion calculations, reflecting the balance between sediment particle conditions and hydrodynamic forces, derived from the mechanics of sediment particle equilibrium. Seepage flow, a common phenomenon driven by pressure in soil, further influences the movement of sediment particles. Building upon the classical three-dimensional two-slope angle erosion model, this study incorporates the vertical seepage force. It comprehensively considers slope angles, sediment response angles, incident current angles, and vertical seepage intensities to adjust the Shields number for sediment particles on slopes. The calculation encompasses both transverse and longitudinal slope configurations. Based on the derived formula and parametric analysis, the study draws the following conclusions: 1. The modified Shields number (${\theta }_{cr}/{\theta }_{cr0}$) decreases non-linearly with the increase of slope angle; 2. ${\theta }_{cr}/{\theta }_{cr0}$ is central and has axial symmetry about 180° incident current angles for transverse and longitudinal slopes, respectively; 3. ${\theta }_{cr}/{\theta }_{cr0}$ increases non-linearly with the increase of soil angle of response; 4. ${\theta }_{cr}/{\theta }_{cr0}$ decreases linearly with the increase of seepage intensity; 5. There exists an approximately zero ${\theta }_{cr}/{\theta }_{cr0}$ area when the response angle approaches the slope angle, and the area increases non-linearly as the seepage intensity becomes greater. Full article

The interaction between circular piers and turbulent open-channel flow generates complex three-dimensional structures, including horseshoe vortices at the pier base and wake vortices downstream. These structures increase vertical velocities, pressure fluctuations, and shear stresses, contributing to erosion and structural instability. Although these phenomena have been widely studied, limited attention has been given to surface geometric modifications as a flow-control strategy. This study employs Large Eddy Simulation (LES) to evaluate the influence of a hexagonal dimple pattern on circular piles in a free-surface channel. The dimples were defined by varying diameter, depth, and spacing to reduce vertical velocity and alter vortex formation. The computational domain represents a 0.40 m wide, 12 m long, and 1.2 m high rectangular channel, with an inlet mass flow of 9.4 kg/s and 0.10 m water depth. Model validation against particle image velocimetry (PIV) data showed 99% correlation, confirming numerical accuracy. Results demonstrate that textured surfaces modify flow dynamics by enhancing kinetic energy dissipation and generating micro-vortices that weaken dominant structures. The optimal configuration (6 mm diameter, 2 mm depth, 1 mm spacing) reduced downward vertical velocity by 42% and wake vortex shedding frequency by 24%, indicating improved hydraulic stability and erosion mitigation potential. Full article

The pile foundations of hydraulic crossing structures are vulnerable to scour, which can significantly reduce bearing capacity and threaten structural safety. In existing studies, simplified assessment approaches have mainly been used, such as pre-defined scour holes or instantaneous scour, which cannot fully capture the progressive development of scour holes. In addition, there are limited systematic comparisons of the lateral responses of piles with different cross-sectional shapes under scour conditions. To address these issues, a series of finite element simulations were carried out in this study and the numerical model was validated against centrifuge test results. The “model change” technique was then used to simulate the progressive development of general scour. Circular and square piles with equal cross-sectional areas were considered under scour conditions, and the effects of instantaneous and progressive scour were compared at the same depth. The load–displacement response, pile–soil deformation and failure mode, bending moment, and pile displacement were analysed, with the results showing that square piles exhibited a higher lateral bearing capacity than circular under both no-scour and two types of general scour conditions. Scour altered the pile–soil failure mode and reduced the extent of the wedge-shaped failure zone around the pile, with that induced by square piles being larger than that induced by circular. At the same scour depth, the difference between the effects of instantaneous and progressive scour on lateral bearing capacity was not significant. The results indicate that the pile cross-sectional shape is a key factor affecting scour resistance and that square piles show a relative advantage. The findings provide useful guidance for the cross-sectional selection and lateral bearing capacity assessment of pile foundations in scour-prone areas. Full article

Hydropower development in high-altitude regions increasingly confronts a challenging “trilemma”: high hydraulic heads, large unit discharges, and spatially constrained narrow valleys. Under such conditions, conventional energy dissipation measures frequently fail to prevent downstream riverbed scour, thereby threatening both ecological integrity and infrastructure safety. This study aims to propose, parametrically optimize, and physically validate a novel composite energy dissipation structure designed to resolve this specific trilemma based on a pressure-dividing transition mechanism. Using the Louli Hydropower Project as a case study (Q_max = 6944 m³/s, unit discharge q = 119 m³/(s·m), available basin length L = 78 m), we conducted systematic 1:100 scale physical model tests. The results demonstrate that conventional optimizations, such as secondary stilling basins and dentated sills, are ineffective under these boundary conditions, leading to incomplete hydraulic jumps and extended high-velocity zones. In contrast, the proposed composite structure, which integrates a deepened stilling basin (depth = 9 m), asymmetric sidewall widening (20 m offset), and a gentle slope transition (1:20 gradient), achieved superior performance. Under the 50-year design flood with controlled discharge operation, the energy dissipation rate increased significantly from 32.11% (baseline) to 63.49% (composite) at the end sill. Furthermore, the structure reduced comprehensive turbulence intensity by 17.8% and floor slab impact stress by 23.4%. These findings validate the composite system as a sustainable solution for high-head dams in constrained settings, offering benefits for riverbed protection and structural durability. Full article

Riverine bridges are critical infrastructure that are increasingly exposed to severe hydrological hazards. This study proposes and validates a synergistic methodology for the assessment of riverine bridge resilience, integrating the conceptual 4R framework (robustness, rapidity, resourcefulness, and redundancy) with field inspections, hydrological and hydraulic modeling, including scour evaluation, within a multicriteria analysis scheme. The methodology comprises: (i) a systematic review of literature and regulations to construct a 30-parameter matrix across five dimensions (technical, economic, social, organizational, and environmental); (ii) data acquisition through field inspections, detailed topography, and technical studies; and (iii) one-dimensional hydraulic modeling in HEC-RAS under extreme scenarios (return periods of 100 to 750 years and a critical 500 m³/s scenario representing a potential overflow of the Aguada Blanca reservoir). The Bridge Resilience Index (BRI) is computed through a weighted additive model and a sensitivity analysis. Application to the San Martín Bridge (Arequipa, Peru), a structure with more than 60 years of service and recurrent preventive closures during flood events, revealed critical conditions: minimum freeboard of 0.26 m, absence of hydraulic protections, and limited institutional capacity. The resulting BRI value (1.898) indicates a low resilience level. The proposed framework provides a useful tool for risk-informed decision-making, the prioritization of interventions, and the strengthening of resilience in critical infrastructure. Full article

Planform evolution and terrestrial habitat health of two representative mid-channel bars (Baishazhou bar and Tianxingzhou bar) in the urban reach of the Middle Yangtze River in Wuhan City have not been understood under the combined influences of natural forcing and human activities. Using dry-season Landsat imagery (1989–2020), hydrological records from the Hankou gauging station (1990–2019), and field surveys, we quantified bar-morphology changes and examined the mechanisms underlying their differentiated scouring. We also developed an indicator system to evaluate terrestrial habitat health on mid-channel bars. Indicator weights were determined using a combined weighting approach integrating the Analytic Hierarchy Process and the entropy weight method. Since the Three Gorges Dam began operation, the runoff in the Wuhan reach has decreased only slightly (6.72%), whereas sediment load decreased sharply (69.88%), causing net scouring of both bars. Baishazhou bar, in a straight anabranching reach, lost 43.83% of its area (1989–2020), with erosion concentrated at the head and main channel margin and caving. Tianxingzhou bar, in a mildly curved reach, had moderate shrinkage (26.33%, 1992–2022) as revetments curbed head/right margin retreat. Both bars were “very healthy” in natural attributes, with the Baishazhou bar showing longer water–land ecotone exposure (217 d) and higher vegetation cover (92%). Socially, Baishazhou bar was “sub-healthy” due to unprotected shrinkage, and Tianxingzhou bar was “unhealthy” due to area loss and low permeability of hard works. Overall, both bars were “healthy”. These findings provide a basis for ecological conservation and habitat restoration of bar wetlands. Full article

To evaluate the runoff pollution characteristics of roofs in an arid region, this study focused on Yinchuan City, China. It analyzed the runoff properties of various roof materials, including tile, asphalt, and color steel plate. Five rainfall events were monitored during 2024, with samples collected manually at roof pipe outlets and analyzed for suspended solids (SS), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and ammonia nitrogen (NH₃-N). The results indicated that the concentration of pollutants in runoff from these roofs decreased as rainfall duration increased. The event mean concentration (EMC) of TN and COD in runoff from all three roof materials exceeded the Class V surface water quality standards in China. The first flush of pollutants in roof runoff followed a descending order: SS > COD > TP > TN > NH₃-N. Cluster analysis of three rainfall parameters—dry period, precipitation, and rainfall intensity—revealed that dry period exerted the strongest influence on runoff quality, indicating that the overall quality of roof runoff was primarily influenced by the cumulative effects of atmospheric deposition, with rainwater scouring being the secondary factor. These findings provide critical insights for designing stormwater management strategies and rainwater harvesting systems in arid and semi-arid cities, emphasizing the need to prioritize first-flush control and consider local climatic conditions. Full article

To clarify the differences in and mechanisms of soil detachment before and after soil collapse, five typical granite soil layers (red soil, red soil–sandy soil, sandy soil, sandy soil–debris, and debris layers) of Benggang in Anxi County, Fujian Province, were studied via laboratory runoff scouring tests, and the detachment capabilities and influencing factors of undisturbed (original) and disturbed (colluvial deposit) soils were compared. The results showed that disturbance due to soil collapse significantly increases the soil detachment capacity by an average of 1046 times, with the greatest increase occurring in the red soil–sand soil layer (3494 times) and the smallest increase occurring in the debris layer (63 times). The undisturbed soil detachment capacity increases with increasing soil depth, whereas the disturbed soil capacity first increases but then decreases, with the sand layer having the highest capacity. Hydrodynamic fitting results revealed that undisturbed red soil has a linear relationship, red soil–sandy soil and sandy soil layers have power function relationships, and sandy soil–debris and debris layers have logarithmic relationships with flow shear stress. Disturbed red soil and red soil–sandy soil layers are linearly related, whereas the other layers are logarithmically related. Correlation analysis revealed that undisturbed soil detachment is significantly negatively correlated with clay, silt, gravel, free iron oxide, and free alumina contents and positively correlated with sand content. Disturbed soil shows similar correlations, but it has a negative correlation with organic matter instead of gravel. Structural equation modelling (SEM) path analysis revealed that undisturbed soil detachment is affected mainly by negative free alumina oxide content (path coefficient of −0.87) and flow shear stress (path coefficient of 0.14), whereas disturbed soil is controlled mainly by negative shear strength (path coefficient of −0.76) and positive flow shear stress (path coefficient of 0.49). This study elucidates the mechanism by which colluvial deposit disturbance accelerates soil detachment, providing a theoretical basis for the prevention and control of Benggang erosion in the hilly regions of southern China with red soil. Moreover, the comparative research strategy adopted in this study offers a reference for related investigations in similar erosion-prone areas. Full article

Seabed response and local scouring around pile groups under combined wave–current loading pose critical threats to the stability and long-term performance of offshore structures, particularly those supporting offshore renewable energy infrastructures. In this study, we present a systematic experimental investigation on the pore-water pressure and local scour around pile groups subjected to regular waves, combined regular wave–current conditions, and irregular waves generated using the JONSWAP spectrum under wave-only conditions. Pore-water pressures and seabed morphology were analyzed for different hydrodynamic conditions, pile spacings, and pile arrangements. The experimental results demonstrate that the presence and magnitude of current are the dominant factors controlling scour development. Increasing the current velocity from 0 to 0.25 m/s leads to a three (3) to five (5) times increase in maximum scour depth, whereas comparable variations in wave height and wave period produce relatively small effects. The direction of a current affects the location of maximum scour, with the wave–forward current condition promoting the development of an interconnected scour area within the pile array and wave–opposing current condition, shifting local scour toward downstream piles. Small-spaced piles ($G/D$ = 1) intensify hydrodynamic interactions and increase scour depth by approximately 30–40% compared with wider spacing. Irregular waves generate more spatially distributed but shallower scour than regular waves of comparable wave characteristics. These findings provide insights into the mechanisms governing seabed instability around pile group foundations and contribute to more sustainable design and operation of offshore infrastructure, such as offshore wind turbine foundations. Full article

The First Member of the Cretaceous Qingshankou Formation (K₂qn¹) in the Gulong Sag, Songliao Basin, contains vast shale oil resources conventionally interpreted as deposits of suspension settling in a quiescent, anoxic deep-lacustrine environment. However, this static “deep-lake” model fails to account for the strong lithofacies heterogeneity and high-energy sedimentary records observed in recently acquired core data. This study reconstructs the sedimentary dynamics of the K₂qn¹ shale through high-resolution core description, thin-section petrography, and flow-loop hydrodynamic simulations. We identify abundant sedimentary structures diagnostic of high-energy combined flows, including Hummocky Cross-Stratification (HCS), Swaley Cross-Stratification (SCS), erosional scour surfaces, and large-scale tabular intraclasts (up to 40 mm). Hydrodynamic simulations, utilizing an “equivalent substitution” method, demonstrate that the Minimum Vertical Suspension Velocity (V_mf) required to transport these large intraclasts exceeds 1.0 m/s. This threshold is 1 to 5 orders of magnitude higher than theoretical values derived from classical settling equations, confirming that the paleolake bottom was frequently perturbed by high-velocity storm-driven currents. Consequently, we propose an “Intermittent High-Energy Deposition Model,” wherein background suspension settling was punctuated by episodic storm events. We argue that these high-energy events facilitated organic matter enrichment through a “Transport-Burial Pump” mechanism, which operated in concert with the chemical stratification associated with the Oceanic Anoxic Event 2 (OAE2) to enable rapid physical burial and sealing of organic matter. These findings challenge the traditional fine-grained sedimentological paradigm and suggest that storm-reworked intervals—characterized by enhanced brittleness and hydrodynamic winnowing—constitute the primary “sweet spots” for lacustrine shale oil exploration. Full article

Tsunami-induced scour around coastal embankments and nearshore structures is a primary cause of structural instability and failure. However, the hydrodynamic mechanisms by which coastal vegetation mitigates this scour remain insufficiently understood. This study employs three-dimensional numerical simulations to investigate the influence of rigid and flexible vegetation on overflow-induced scour downstream of embankments and local scour around structures under tsunami-like inundation. The simulations were conducted using Ansys Fluent 2021R2, utilizing the Volume of Fluid (VOF) method to capture the free surface and the RNG k − ε turbulence model within the Reynolds-averaged Navier–Stokes (RANS) framework. Computational geometries were reconstructed from laboratory experiments, and the model’s reliability was validated against measured water surface profiles. The results demonstrated that vegetation significantly alters flow dynamics, velocity distributions, vortex structures, and both the magnitude and patterns of bed shear stress within scour holes. Specifically, in overflow-induced scour, vegetation suppresses scour intensity by inducing backwater effects, enhancing momentum diffusion, attenuating flow impingement on the bed, and reducing peak bed shear stress. Conversely, for local scour around structures, vegetation increases upstream water depth while intensifying downstream wake vortices, leading to scour hole elongation—particularly under dense and tall vegetation. These findings offer novel insights into the hydrodynamics of vegetation-induced scour mitigation and provide guidelines for optimizing vegetation configurations to enhance the tsunami resilience of coastal infrastructure. Full article

Natural floodplain vegetation exhibits heterogeneous patterns in height and density that substantially affect flow and bed stability. Most previous studies have examined flows through uniformly distributed vegetation, resulting in a limited understanding of mixed-height canopies. Consequently, existing methods for estimating bed shear stress remain inadequately validated under such heterogeneous conditions. To bridge this gap, we conducted flume experiments to investigate how the density and height configuration of rigid vegetation affect the spatial distribution of bed shear stress, comparing three commonly used approaches: the Law of the Wall, Reynolds stress, and turbulent kinetic energy (TKE). Results showed strong agreement between TKE and Reynolds stress methods; the Law of the Wall produced larger errors (15–25%) due to log-layer disruption in vegetated zones, limiting its use. Vegetation density dominated bed shear stress: high-density areas reduced mean stress by 17–36%, promoting deposition, whereas tall–short vegetation interfaces increased local stress by 15–26%, elevating scour risk. Flow velocity raised overall stress by 15–25%, while water depth had minimal effect. Sparse vegetation led to patchy stress distributions and higher scour potential, while dense vegetation favored uniform stress and sediment accumulation. These findings clarify bed shear stress mechanisms in heterogeneous vegetation and provide a basis for floodplain restoration and stability management. Full article

The scouring of cohesive and non-cohesive materials downstream of sluice gates is primarily based on high-velocity flow. The present study considered an experimental hydraulic model of submerged water flow issuing from a sluice gate installed on an apron that leads to the scour hole and dune in a downstream mixture of sand and clay bed. The purpose was to achieve a suitable efficiency of the weight ratio of clay in the sand–clay mixture (c) for the sediment bed. Scour parameters, including maximum scour depth (d_se) and its longitudinal location (x_se), and maximum dune height (h_d) and its location (x_d), were measured and compared for three variations, c = 0.1, 0.2, and 0.3, under five hydraulic conditions. Results revealed that all scour parameters were reduced by adding clay to the sand soil, and the maximum reduction was for d_se with the maximum value of 27.66%. The observed data were analyzed by multiple nonlinear regression analyses for each scour parameter to present new prediction equations for practical uses. The computed statistical parameters of correlation coefficient (R²), root mean square error (RMSE), mean absolute percentage error (MAPE), Nash–Sutcliffe efficiency (NSE), and scatter index (SI) present good accuracy for the predicted equations in the ranges of experimental data. Full article

Levee overtopping poses a significant risk to flood defense infrastructure by inducing severe erosion and scour, particularly along the landward slope and toe regions. This study investigates the effectiveness of an integrated protection system combining seamless cement coating with strategically placed H-type piles to mitigate scour and modify flow dynamics under prolonged overflowing. A series of physical model tests were conducted to evaluate full and partial concrete slope protection with and without pile integration. Results showed that the seamless concrete revetment significantly delayed slope failure, resisted joint-related seepage, acted as a rigid cantilever, and maintained the structural integrity despite surrounding erosion. The inclusion of emergent H-type piles at the downstream toe disrupted the overflow jet, enhanced early energy dissipation, and reduced scour dimensions. The FC + P_ES (fully coated with emergent piles) configuration exhibited the strongest performance, reducing downstream scour length by 40%, upstream extent by 66.7%, and maximum scour depth by 7.7% compared to the FC_NP (fully coated, no-piles) condition. Partial slope coverage combined with emergent piles delayed scour initiation by approximately threefold, highlighting the synergistic effect of combined surface and flow-deflected structures measures. Conversely, bed-level piles redirected jet energy beneath the surface layer, intensifying vertical scour and upstream erosion, indicating the critical importance of pile placement and elevation. The findings emphasize the importance of integrating seamless surface protection with vertical flow disrupters to effectively manage flow-induced erosion and enhance levee resilience against overtopping floods. This hybrid approach offers a practical solution for flood-prone riverine levee systems. Full article