Scour Depth Research Articles

Prediction of contraction channel scour depth: based on interpretability analysis and PCA-enhanced SVR

ABSTRACT Due to the numerous uncertain factors affecting contraction scour depth, although many traditional empirical formulas have been proposed in past research, their prediction accuracy is generally low. In recent years, with advancements in machine learning (ML) technology, these techniques have been able to accurately capture the nonlinear characteristics of scour-depth data. However, in pursuit of higher prediction accuracy, researchers have explored a wide range of diverse ML models that require various combinations of input parameters. These input parameter combinations often lack reliability, and the models themselves have poor interpretability, increasing the ‘black-box effect.’ Therefore, this study uses a principal component analysis (PCA)-enhanced support vector regression (SVR) model to construct a scour depth prediction model, combined with the interpretability method of SHapley Additive exPlanations (SHAP). The results show that the SVR model's predictions are highly consistent with physical experimental laws, and the model primarily identifies features that are strongly linearly correlated with the dependent variable (scour depth and SHAP values). The application of PCA enhances the correlation, and when using the CC-PCA-4 input parameter combination, the SVR model achieves high accuracy (R2 = 0.971, mean absolute percentage error = 7.54%). Moreover, its comprehensive evaluation in terms of stability, accuracy, and conservativeness surpassed that of other ML models and empirical formulas.

Seismic performance of continuous rigid-frame bridges affected by flood-induced scour

River-crossing bridges in high-intensity seismic regions can be vulnerable to the combined action of earthquake and flood hazards; in particular, flood-induced scour of the substructure can have a notable influence on the seismic behavior of bridge structures. Currently, long-span continuous rigid-frame bridges are widely used to cross large rivers worldwide, yet related studies on their seismic performance under flood-induced scour have been lacking. This paper focuses on the effects of time-varying flood-induced scour on the seismic performance of long-span continuous rigid-frame bridges incorporating complex thin-walled reinforced concrete piers with pile group foundations. A detailed finite element (FE) model for a representative bridge structure is developed and the scour depth risk of the bridge is evaluated under several flood events for different return periods. The influence of flood-induced scour on the pile-soil interaction is examined throughout the bridge service life. Detailed seismic fragility assessment is carried out through nonlinear time-history analyses using a large suite of 100 seismic records. Particular focus is given to evaluate the time-varying scour effects on the pile and soil deformations as well as on the component and system level seismic fragility functions. It is shown that the total flood-induced scour depth exhibits a nonlinear increasing trend with the increase in service time, particularly in the initial 10 years of the bridge service life. The deformations of the scoured piles, within a depth of 20 m, are also shown to increase significantly with the increase in service time. The results indicate that the scour has a pronounced effect on both the component and system level seismic fragility functions. Importantly, although the piles (or pile groups) are typically designed to remain elastic under seismic loading, they are shown to be subjected to significant inelastic demands and governing damage levels as a result of time-varying flood-induced scour effect. Overall, this study provides a methodology to assess the time-varying seismic fragility of the scoured long-span rigid-frame bridges with complex thin-walled reinforced concrete piers, which can enhance the multi-hazard time-varying seismic resilience assessment for bridge structures with similar configurations.

On increasing the scour funnel size upstream of a bottom orifice by using a cuboid pile

Scour funnels formed before bottom orifices are of vital importance regarding intaking water with low-concentration and small-sized sediment to protect the water turbine. Via flume experiments, this work investigates the effect of a bottom-mounted cuboid pile on the formation of a scour funnel upstream of a bottom orifice. A phenomenon we call as “reverse sediment collapse” is observed for the first time, which causes a rapid increase in the scour depth upstream of the orifice. Instantaneous velocity measurements show that the turbulence kinetic energy near the cuboid pile is significantly higher compared with that in a case without a pile or with a cylinder under a same waterhead condition, indicating that large-scale vortex motions are enhanced due to the use of a cuboid pile. The equilibrium scour funnel depth upstream of the orifice is found to be increased by as much as 124.6% when a cuboid pile exists compared with that in a case without a pile under a same waterhead condition. The scour process is highly accelerated when a cuboid pile exists, and it is found that the time required when a cuboid pile exists to reach for the first time the same equilibrium scour depth without a pile is dramatically reduced by 97.2%–99.7%. A formula was established to calculate the equilibrium scour depth. The findings provide guidance for future optimization of the form and placement of structures upstream of an orifice to efficiently achieve a larger-sized scour funnel.

Numerical Study of Local Scour and Hydrodynamic Pressure of Complex Bridge Piers

This study uses Computational Fluid Dynamics to investigate bridge foundations' scouring process and hydrodynamic pressure caused by an extreme flood. A Large Eddy Simulation model, compiled with a Navier-Stokes equations model, is used to compute the fluid motion with the Volume-of-Fluid to track the motion of the water surface. A Discontinuous Bi-viscosity rheological model describes the river's muddy bottom properties. The numerical results are further analyzed to understand the influence of exposed, closely spaced piles bridge on the scouring process. The results show that the extended foundation (with ten piles) has a maximum scour depth of approximately 10 m, which is 2.0 m greater than the non-extended foundation (with six piles). Specifically, the high velocity surrounding the exposed, tightly spaced piles may exacerbate the scouring problem. The design code suggests a hydrodynamic pressure of 10.9 kPa and 10.1 kPa for six and ten piles, respectively. The front-row piles' hydrodynamic loading is underestimated in the bridge design code. The maximum hydrodynamic pressure occurs at the front piles at roughly 1.8PI, where PI represents the hydrodynamic pressure. The velocity and hydrodynamic pressure at each pile are calculated, comparable with that in the bridge design code. This finding is important for the design of bridge foundations with exposed piles.

Numerical and experimental study on local scour in front of OWC-BWS under waves

In this paper, a system of an oscillating water column wave energy converter integrated with a vertical breakwater (OWC- BWS) was established, and the scour mechanism in front of OWC-BWS under wave actions was studied by laboratory scale experiments and gas-liquid-particle flow numerical simulation, respectively. The experiment investigates the comparison of scour test results between a conventional vertical breakwater and OWC-BWS. It shows that compared to a vertical breakwater without an OWC, the local scour phenomenon in front of the OWC-BWS was effectively mitigated (test results showed a 46.7% reduction in the maximum scour depth). For numerical simulation, a scour model under wave actions was established for further research on the local scour mechanism in front of the OWC-BWS. It was found that the local scour topography of an OWC-BWS is different from that of a vertical breakwater. The OWC device effectively weakens the scour in front of the OWC-BWS, which is because the flow field in front of the OWC-BWS shows frequent generation and shedding of vortexes. In addition, as a crucial part of the OWC-BWS, the effect of PTO was also studied, which found that the maximum equilibrium scour depth was significantly influenced under different PTO.

Influence of scour depth and flow velocity field on large-diameter pier group pile foundations

Influence of scour depth and flow velocity field on large-diameter pier group pile foundations

Predicting equilibrium scour depth around non-circular bridge piers with shallow foundations using hybrid explainable machine learning methods

Scouring around bridge piers is a critical concern, as the risk of bridge failures poses significant economic and safety threats to the public. Traditional models often struggle to accurately estimate the equilibrium scour depth (deq) at bridge piers due to the complexity of scour processes and their reliance on simple regression methods. This study combines two metaheuristic optimization techniques—Siberian tiger optimization (STO) and brown-bear optimization algorithms (BOA)—with artificial neural networks (ANNs) to enhance deq prediction accuracy for both round- and sharp-nosed piers using both field and laboratory data. The findings indicate that BOA and STO effectively optimize ANN hyperparameters, resulting in improved prediction accuracy. Furthermore, both BOA–ANN and STO–ANN outperformed empirical equations and other machine learning techniques. An explicit equation was also derived from the BOA–ANN model. The influence of independent variables on deq was further examined using SHAP, revealing that pier width has the greatest impact on deq estimates.

Numerical investigation of local scour around a 2-degree of freedom vibrating subsea pipeline in steady flow under sagging condition

Numerical simulations are conducted to investigate the local scour below a sagging subsea pipeline vibrating in two degrees of freedom (2-DOF), covering a sagging ratio from −0.3 to 0 and a wide range of reduced velocities from 0.5 to 15. A negative sagging ratio means that the static balance position of the bottom surface of the pipeline is below the sand surface. The combined effects of the sagging and 2-DOF vibration of the pipeline on the scour are investigated. The maximum scour depth of the 2-DOF vibrating pipeline in the lock-in range of the vibration increases by 10% compared to the 1-DOF; however, the reduced velocity where the maximum scour depth occurs changes from 5 to 6. The variations of the vibration amplitude with the reduced velocity for all the sagging ratios follow a similar trend. For embedment ratios of −0.4 to −0.3, initial condition of scour simulation affects the equilibrium scour depth and vibration amplitudes. Simulations with a flat sand surface as initial condition prevent full scour development because the pipeline reaches its static balance position due to weak flow through the pipeline-to-bed gap. However, if the simulation starts with a sufficiently large initial scour depth, scour can reach its equilibrium.

New insights into local scour characteristics around vibrating monopiles under combined wave-current conditions

Cyclic lateral vibrations on monopile foundations of offshore wind turbines throughout their service life may affect the local scour around the foundations. While previous studies have explored local scour around vibrating monopile foundations under current-only conditions, the local scour characteristics around these foundations under combined wave-current conditions remains unclear. This experimental study presents new insights into local scour characteristics around vibrating monopile foundations under combined wave-current conditions. A novel dimensionless parameter, the friction velocity-based Froude number (Fr∗), is proposed to quantify the effect of hydrodynamic intensity on the scour process. Based on the Fr∗ values obtained in the experiment, three distinct regimes were identified to characterize the impact of vibrations on the scouring process: In Regime 1 (Fr∗ < 0.055), scour dimensions are more pronounced, while in Regime 3 (Fr∗ > 0.06), they are less significant compared to the equilibrium scour hole around static monopile foundations. In the transitional phase, Regime 2 (0.055 <Fr∗ < 0.06), scour dimensions fluctuate by up to 10.9% relative to static conditions. Additionally, an estimation equation for equilibrium scour depth based on Fr∗ is developed, demonstrating good prediction accuracy and broad applicability. These insights advance the understanding of scour features and provide a valuable reference for predicting scour depth around vibrating monopile foundations in diverse hydrodynamic environments.

Predicting temporal clear water scour depth around bridge piers with XGBoost and SVM–PSO approaches

Predicting temporal clear water scour depth around bridge piers with XGBoost and SVM–PSO approaches

Effects of flow splitters on local scour downstream of type-A trapezoidal piano key weir

This study investigates the effectiveness of flow splitters in reducing scour downstream of trapezoidal Piano Key Weirs through a comprehensive experimental study. Three distinct geometries of flow splitters—square, rectangular, and circular—are examined under various hydraulic conditions to assess their impact on local scouring. The experiments were conducted in a dedicated channel measuring 10 m in length, 0.75 m in width, and 0.80 m in height. The results indicate that flow splitters facilitate flow separation by linking trapped air beneath the flow to the free surface, thereby mitigating nappe oscillation. Additionally, the geometric variations of flow splitters did not significantly influence the upstream water head, with rectangular-shaped flow splitters proving more effective than square and circular splitters. On average, the maximum scour depth for the weir with rectangular, square, and circular splitters is reduced by approximately 13, 11, and 10%, respectively, compared to the weir without splitters. Furthermore, the volume of scour holes in tests with rectangular, square, and circular splitters showed reductions of 18.53, 17.77, and 14.92%, respectively, compared to tests without splitters. As discharge decreases, the effectiveness of these flow splitters in reducing scour depth becomes more pronounced. Due to the existence of splitters, the location of maximum scour depth approaches the weir. New equations were developed for predicting scour hole parameters with and without flow splitters, incorporating various splitter geometries. These equations were formulated using non-linear regression, achieving high accuracy with a correction factor, yielding R2 values between 0.78 and 0.94, and RMSE values ranging from 0.09 to 0.54. Overall, the findings underscore the significance of flow splitter geometry in mitigating scour effects, providing valuable insights for future engineering applications.

Rapid Assessment Method of Buckling Stability of Bridge Pier–Cap–Pile System Under Scour Effect

A novel analytical method for evaluating the buckling stability of the pier–cap–pile system under scour effect is proposed, and furthermore, the concept of rapid assessment of bridge buckling stability based on natural frequency is innovatively introduced in this paper. First, the total potential energy function of the bridge pier–cap–pile system is established, and the closed-form solution of structural system critical buckling load under scouring is solved according to the principle of stationary potential energy. Second, the sensitivity analyses of pier height, pier width, bending stiffness reduction in pier, pile slenderness ratio, pile bending stiffness reduction, m-value of soil and structural gravity to the buckling load are carried out. On this basis, 60 sets of sensitive parameter sample combinations are extracted by the Latin Hypercube Sampling algorithm, and a proxy model relating the critical buckling load to scour depth and the sensitive parameters are then developed using the McQuarter global optimization algorithm. Finally, the regression relationship model between the critical buckling load and the natural frequency is formed by combining the proxy model and the existing relationship between the scour depth and the first-order natural frequency. The feasibility of the proposed assessment method is demonstrated by the finite element method using a bridge case study, which provides an insight and a new means of quantitatively evaluating the safety of bridges under scour effect.

Machine learning-based prediction of scour depth evolution around spur dikes

ABSTRACT Spur dikes are pivotal elements in river training, serving to mitigate the dynamic alterations induced by river degradation and aggradation. Traditionally, scour prediction models have relied on regression techniques, but the advent of soft computing and machine learning has offered opportunities for enhanced accuracy. This study focuses on the development of hybrid machine-learning models, including eXtreme Gradient Boosting (XGBoost), random forest (RF), convolutional neural network–long short-term memory, and artificial neural network, optimized using genetic algorithms to predict both temporal scour depth variation and maximum scour depth around the initial spur dike in a series. The analysis reveals strong associations between scour depth and various parameters such as non-dimensional time, spacing, channel width, time-averaged velocity, and densimetric Froude number. The models are established through an iterative process involving four predictor combinations. Results demonstrate XGBoost as the top-performing model, consistently exhibiting superior performance with R2 of 0.99, root mean square error (RMSE) of 0.012, and mean absolute error of 0.008 during training, and R2 of 0.96, RMSE of 0.044, and Kling–Gupta efficiency of 0.98 during testing for predicting temporal scour depth. For non-dimensional maximum scour depth, it reached R2 of 0.99 and RMSE of 0.005 in training, with R2 &amp;gt; 0.91 across all combinations during testing. Although RF showcases commendable accuracy, it slightly lags in precision compared to XGBoost.

Modeling local scour around complex bridge supports using CFD and a shear-stresses-based simplified approach

This study presents a simplified numerical modeling approach that estimates the local scour depths around bridge supports based on the bed shear stresses. It is developed using 3D computational fluid dynamics and coding through ANSYS workbench scripting along with C++ language. The proposed model is called SCFDS (Simplified Computational Fluid Dynamics Scour). The model’s main idea is to lower the bed bathymetry at the locations affected by flow obstruction until the shear stresses reach stable target values. The developed model is assessed by applying it to a complex pier of a real bridge over the Nile-River, and its scour data is calculated using the Hec-18 empirical equations. The outcomes of the model’s assessment show that it can depict the local scour around complex bridge supports. The developed approach is a novel and efficient tool that can help the designers in simulating local scour in the vicinity of flow obstructions. However, more verification studies are necessary to reach a generalized conclusion.

Delineating Flood-Induced Sediment Scour in Bridge-Contracted Channels: Processes, Patterns, and Scour Depth under Various Scour Regimes

Delineating Flood-Induced Sediment Scour in Bridge-Contracted Channels: Processes, Patterns, and Scour Depth under Various Scour Regimes

Numerical modelling of downstream scour in circular culverts: Impact of inlet blockages and variable flow conditions.

An accurate estimate of scour depth downstream of culvert outlets is essential for culvert design integrity. Inadequate designs can result in structural failures, leading to increased costs for maintenance and rehabilitation. The present research evaluates the efficacy of numerical models in predicting scour depth and its location downstream of circular culverts under variable flow conditions. Two hydrographs were created for unsteady flow, featuring nine different flow discharges, while steady flow conditions were analysed at flow rates of 14 l/s and 22 l/s. The study investigated circular culverts with inlet blockages of 0%, 15%, and 30%, comparing outcomes with predictions from the Flow-3D software using the renormalisation group (RNG) turbulence model. Extensive experimental data on circular culverts were utilised, with simulations performed using commercial software. This involved analysing the scour's downstream profile, its maximum depth, and its location, and comparing these metrics with actual observed data. The results revealed that the numerical model predictions closely corresponded to the experimental data, even though the simulated scour was generally less than that observed for steady and unsteady flows. The results showed that in unsteady flow conditions and for the discharge of 22 l/s, 30% blockage increased scour by 6.8% and 14.2%, respectively, compared to 15% blockage and non-blocked flow. This increase was 22% and 9.5% for the discharge of 14 l/s, respectively. In the steady case, when the flow rate was adjusted from 14 l/s to 22 l/s, there was a noticeable increase in scour depth downstream of the culvert. While blockage rates impacted the scour patterns significantly in unsteady flow scenarios, escalating blockage percentages did not lead to uniformly proportional increases in scour depth within steady flow environments.

Influence of tidal asymmetry on local scour near the offshore platform

An in-situ mooring measurement was conducted using a profiling sound of navigation and ranging (SONAR) system to reveal the influence of tidal asymmetry on the local scour near an artificial offshore platform, Southwest Offshore Windfarm Complex, Korea. During the mooring period, the flood tide was significantly dominated by positive tidal duration asymmetry and skewness. The lengths of scour hole were 9.8 m and 5.1 m along the flood and ebb directions, respectively. Flood-dominated currents intensified the horseshoe vortex, resulting in an approximately 10% deeper scour hole on the flood face than the ebb face. The periodic occurrence of bidirectional currents generated vortices that facilitated the mixing and redistribution of seabed sediments, forming a gentle slope within the scour hole. The average slope angles ranged from 14° to 16° on the flood face and 6° to 8° on the ebb face. Despite the strong influence of local scour, variations in scour depth (Ds) consistently remained around −2.15 m, suggesting the exposure of the underlying consolidated sediment layer. During the intermediate period from spring to neap tide, the Ds on the lower slope of scour hole increased by 0.12 m, while it decreased by 0.11 m from neap to spring tide, suggesting that the net Ds gradually approached zero over the tidal cycle. These findings underscore the importance of understanding tidal impacts on the local scour morphology to enhance the stability and design of offshore wind turbine foundations.

Experimental and numerical impact of pier arrangement using collars on scour depth

ABSTRACT This paper studied the scour around bridge piers by conducting laboratory experiments and numerical simulation using Sediment Simulation In Intakes with Multiblock option (SSIIM) program. Six pier models were investigated under different flow conditions in sandy soil for two cases: piers with and without a protective plate (collar). The models were arranged as follows: one pier, two piers side by side, two piers tandem, three piers triangular (1 × 2), three piers triangular (2 × 1), and four piers square (2 × 2). It was found that the relative scour depth (d s /y t ) where d s is the local scour depth and y t is water depth, increases as Froude number (F n ) increases for all models. Two Piers tandem model with a collar significantly reduced scour depth around the piers by over 80% compared to unprotected models. The collars effectively reduced the formation of vortices and minimized the detrimental impact on the sediment around the pier. The simulated results using the SIIM program are consistent with the experimental results, with an error of 10%. Scouring depth relationships were also deduced that are useful in bridge piers protection design in similar cases under the same conditions.

Prediction of Scour Depth for Diverse Pier Shapes Utilizing Two-Dimensional Hydraulic Engineering Center’s River Analysis System Sediment Model

Examining scouring around bridge piers is crucial for ensuring water-related infrastructure’s long-term safety and stability. Accurate forecasting models are essential for addressing scour, especially in complex water systems where traditional methods fall short. This study investigates the application of the HEC-RAS 2D sedimentation model, which has recently become available for detailed sediment analysis, to evaluate its effectiveness in predicting scoring around various pier shapes and under different water conditions. This study offers a comprehensive assessment of the model’s predictive capabilities by focusing on variables such as water velocity, shear stress, and riverbed changes. Particular attention was paid to the influence of factors like floating debris and different pier geometries on scour predictions. The results demonstrate that while the HEC-RAS 2D model generally provides accurate predictions for simpler pier shapes—achieving up to 85% precision—it shows varied performance for more complex designs and debris-influenced scenarios. Specifically, the model overpredicted scouring depths by approximately 20% for diamond-shaped piers and underpredicted by 15% for square piers in debris conditions. Elliptical piers, in contrast, experienced significantly less erosion, with scour depths up to 30% shallower compared to other shapes. This study highlights the novel application of the HEC-RAS 2D model in this context and underscores its strengths and limitations. Identified issues include difficulties in modeling water flow and debris-induced bottlenecks. This research points to the improved calibration of sediment movement parameters and the development of advanced computational techniques to enhance scour prediction accuracy in complex environments. This work contributes valuable insights for future research and practical applications in civil engineering, especially where traditional scour mitigation methods, such as apron coverings, are not feasible.

Influence of outlet keys slope on downstream bed topography in trapezoidal piano key weirs: An experimental investigation

Assessing scour depth downstream of piano key weirs (PKWs) is crucial for maintaining their structural integrity. The slope of the outlet keys significantly influences flow velocity and the associated risk of downstream scouring. This study experimentally investigates the impact of various factors on scour downstream of trapezoidal PKWs, specifically focusing on weir outlet keys slope (So), particle Froude number, sediment size, bed levels, and relative drop height. The research identifies three distinct stages of scouring. Notably, changes in So significantly affect the hydraulic flow over both the inlet and outlet keys. Reducing So by 57 % led to increases of approximately 32 %, 34 %, 49 %, and 54 % in relative maximum scour depth, distance from the weir, length, and volume of the scour hole, respectively, while relative weir toe scour decreased by about 31 %. Additionally, a decrease in So shifted the locations of the maximum scour depth and sediment ridge downstream, enhancing the symmetry of the scour hole. Increasing the particle Froude number and relative drop height, along with decreasing tailwater depth and sediment size, further intensified the scour hole and sediment ridge characteristics. This study provides critical insights for mitigating downstream scouring in PKWs through a comprehensive analysis of varying So. The proposed optimal value for So, along with newly developed design equations, offers practical guidance for engineers and water resource managers in enhancing the stability of hydraulic structures.