Scour Phenomenon Research Articles

Study on non-point source pollution characteristics under different spatial scales: a case study of Hanjiang River Basin, China.

In recent years, the research on non-point source (NPS) pollution has been deepening, but it is focused on the large-scale watershed or region. There are a few studies on the scales of small watershed and runoff plot, and it is even less to analyze the characteristics and mechanism of non-point source pollution in certain watershed by combining three different scales. Based on the combination of natural rainfall monitoring and MIKE model simulation, the Shaanxi section of Hanjiang River Basin in China was taken as an example to study the characteristics of NPS pollution at different spatial scales. The results showed that there was an obvious correlation between rainfall and runoff/sediment yield. The order of runoff yield/sediment yield per unit area was as follows: woodland > forested and grassy land > arable land. There was a significant relationship between the loss of total phosphorus and the sediment yield in the runoff plots. The total nitrogen pollution was serious, with an average concentration of 3.8mg/L. The nutrient loss was in the form of nitrate nitrogen, with an average proportion of 63.06%. For small watershed scale, the characteristics of rainfall runoff pollution generation were like runoff plot scale, both have obvious initial scour phenomenon. However, compared with runoff plot scale, the pollutant loss concentration increases with a strong lag. The MIKE model based on the coupling of hydrology, hydrodynamics, and pollution load had a strong applicability in the basin. The critical source areas of NPS pollution were identified, and five scenarios were laid out in the areas for the control of NPS pollution. Centralized livestock and poultry farming had the best reduction effect.

CFD-CGDEM coupling model for scour process simulation of submarine pipelines

Scour is a key issue affecting the service life of submarine pipelines. Understanding the scour process and scour mechanism around the pipelines is crucial for developing the reasonable and effective scour prevention measures. In this paper, the computational fluid dynamics and coarse-grained discrete element method (CFD-CGDEM) is used to simulate the scour process around the pipeline. The influence of the drag force model which is an important factor for analyzing the scour process of the submarine pipelines is investigated, and the results indicate that the choice of the drag force model has less influence on the simulation results. The characteristic of the CG method is studied considering different CG factors, particle radius and flow velocities. The results show that the CG method which can reduce the large need of computing resources and excessive computation time does not bring large deviation to the results, especially the scour depth beneath the pipelines. The evolution of the scour depth obtained by the CFD-CGDEM model agree well with the experimental results. A reasonable scour phenomenon around the pipeline is shown by the numerical simulation, which implies that the CFD-CGDEM model established in present study can simulate the scour process around the pipelines well.

Estimation of time dependent scour depth around circular bridge piers: Application of ensemble machine learning methods

Scour is a major issue which impacts the life of a hydraulic structure. In this work, we have considered a bridge as an example of a hydraulic structure. Scour depth increases or decreases from time to time because of variations in flow scenarios. Scour phenomena have been extensively studied and many empirical as well as data-driven approaches have been proposed to estimate the scour depth. However, there are relatively few studies which can predict the time-dependent scour depth. In this study, we use a laboratory dataset compiled from several sources to predict time-dependent scour depth using ensemble and standalone machine learning methods. For scour depth estimation, various factors such as river bed properties (d50), sigmag, rhos, Ucr), flow properties around a pier (rhof, U, mu, g, y), bridge pier geometry (Al, Sh, Dp), and time (t, tR) are used. In this study, we apply two ensemble methods: Bagging Regressor (BR), AdaBoost Regressor (ABR), and one standalone machine learning method, Support Vector Regression (SVR), for the prediction of time-dependent scour depth. Out of these machine learning methods, both the ensemble methods provide superior predictions in comparison to the standalone variant and empirical equations, viz., Bagging Regressor (r2 = 0.913), AdaBoost Regressor (r2 = 0.887), followed by Support Vector Regressor (r2 = 0.814). We have also developed an open-source web-based tool to predict the time-dependent scour depth with the proposed machine learning methods. The web-based tool is generic enough to work with any dataset and allows the end user to select various input combinations, visualizations, and error metrics.

Experimental study on dynamic characteristics of a monopile foundation based on local scour in combined waves and current

Scour is one of the key factors causing the collapse of buildings (structures) in water. Pile foundations are often subject to the combined actions of waves and current, resulting in weakened soil overturning resistance and changes in natural vibration frequency, which may lead to vortex-induced vibration under the action of fluid flow and cause fatigue damage. A series of experiments under current-only, wave-only, and combined wave-current conditions were carried out in a wave-current flume to investigate the scour phenomenon around a monopile and the change in natural vibration frequency of the monopile foundation along the flow and vertical directions caused by local scour. The scour depth under combined wave-current conditions is greater than that under current-only conditions, and increases accordingly with the increase of the flow velocity and the decrease of the water depth. Furthermore, the scour phenomenon under different flow patterns was analyzed according to the variation of pulsation pressure. The empirical formula for the natural vibration frequency of the monopile foundation considering the local scour under current-only and combined wave-current conditions was established respectively. Compared with the experimental results, the maximum error is 10%, indicating that the empirical formula has a high degree of confidence. The above empirical formula obtained from the indoor scale model is applied to the field test, and the maximum relative error is 14.37%, which indicates that the empirical formula is also suitable for the prototype scale.

First Principles‐Based Approach for 3D Scour Processes Under Variable Jet Discharge

AbstractScour processes caused by plunging jets are particularly important in hydraulic engineering because of the connected risk of structural failure. Therefore, many investigations have been conducted on this topic, focusing on jet‐induced scour under constant flow discharge (i.e., steady case). Yet, to the best of the authors' knowledge, no studies have analyzed the scour mechanism under variable jet discharge (i.e., unsteady case) and clear‐water conditions. Following recent theoretical advancements on scour phenomena for steady cases based on the phenomenological theory of turbulence, we address in this study the general validity of such an approach for time‐dependent (i.e., unsteady) jet inflow conditions, in non‐cohesive soils. Results show that scour evolution is consistent with that obtained for steady jet flows. In particular, they confirm the existence of two distinct phases—developing and developed—and indicate that the transition time between the two phases does not depend on the jet inflow characteristics. Once again, this study confirms that the phenomenological theory of turbulence is a valid tool for all jet‐driven scour problems.

Physical Mechanism for Seabed Scouring around a Breakwater—A Case Study in Mailiao Port

According to a field survey in 2012, the bathymetry near Mailiao Port, located in central Taiwan’s west coast, has a scouring hole that extends approximately 500 m × 100 m with a maximum scour depth of 26 m (eroded from its design depth −22 m to −48 m). To investigate the scour mechanism near the breakwater head and prevent the breakwater from collapsing, this study conducts comprehensive analysis by analyzing field observed data, performing hydraulic model tests, and conducting numerical modeling for the area near the Mailiao Port. The results show that the current plays an important role in the scour process. The physical model tests and numerical simulations both can reproduce the scour phenomenon of the study site. By analyzing field observed data we validated through physical and numerical models. This study concludes that the current caused by the ebb and flood tide, as well as the steep and shallow seabed topography, together comprise the seabed scour mechanism near the Mailiao Port breakwater head.

Estimation of Scour Propagation Rates around Pipelines While Considering Simultaneous Effects of Waves and Currents Conditions

Seabed offshore pipelines are widely applied to carry fluid over long distances of the seafloor. The design of offshore pipelines is conducted to bear quite a few environmental loading circumstances in order to provide a well-guarded and reliable fluid transition. Fluid leakage and pipeline vibration due to a failure of the pipeline are the prime causes of accidental catastrophes. Scour phenomena occur around offshore pipelines due to currents and/or wave conditions, consequently causing the susceptibility to pipeline failure. Then, scouring propagation rates require to be studied in three dimensions, namely beneath and normal to the offshore pipeline and the longitudinal direction of itself. In this research, Artificial Intelligent (AI) models are used to derive new regression equations based on the laboratory data for the estimation of 3D scour propagation patterns while seafloor offshore pipelines are exposed to simultaneous impacts of currents and waves. In this way, chiefly based on the experimental investigations conducted by Cheng and colleagues, seven sets of dimensional parameters were given in terms of the Shields’ parameter due to currents and waves, the Keulegan–Carpenter number, the ratio of embedment depth to pipeline diameter, the ratio of orbital velocity to current velocity, and the wave/current angle of attack. Dimensionless parameters were used to provide regression-based equations to evaluate scour propagation rates in three dimensions. The performance of AI models was evaluated by various statistical measures. The model based on our proposed equations performed better than the reported models in the literature. Even more importantly, we indicated that our model inherently has a reliable physical consistency for variations of dimensionless parameters against the scour propagation patterns.

Combined Effects of Soil Stress History and Scour Hole Dimensions on Laterally and Axially Loaded Piles in Sand and Clay under Scour Conditions

Removal of soil around a bridge foundation due to scour results in a reduction of the lateral and vertical foundation capacity due to the loss of soil support. The common approach in modeling the scour phenomenon of removal of soil springs without modifying the parameters of the remaining soil fails to consider the change of stress state of the remaining soil and the formation of scour hole geometry around the pile foundation. In practice, both of these factors impact the mechanical properties of the remaining soil and the resulting expected structural response of the pile under loadings. This paper proposed a methodology to comprehensively evaluate the combined effects of stress history and scour hole dimensions on piles under scour conditions in uniform soil. It enabled the examination of the lateral and axial behaviors of a loaded pile subject to scour and is applicable for both cohesive and cohesionless soils. The methodology was validated with results from field tests for no-scour scenarios and verified with existing numerical models for scour scenarios. Quantification of the soil effects was investigated through lateral pile deflection and load-settlement curves for lateral and axial behaviors, respectively. Load-settlement curves demonstrated that including the effect of stress history results in increases of up to 34.1% and 61.1% in estimated pile settlement for sand and clay, respectively, leading to potential unconservative designs if soil effects are not properly included in the analysis.

New Formula for Calculating Local Scour around Bridge Piers

Several researchers working on the axes of solid particle transport, river flow, as well as the vulnerability of structures built on rivers have focused their work on the phenomenon of local scour, where many scour formulas have been proposed. Most of these formulas have been developed using laboratory data, estimated from simplified scaled-down models. This led to uncertainties and considerable inaccuracies in the scour estimation, sometimes causing serious consequences for the stability of structures subject to scour. These formulas were rarely tested using field data, where, until recently, there was very little data to validate them. This study aims to propose a new local scour formula using multiple nonlinear regression (MNLR). The data used is in situ data from an extensive database. The new proposed formula includes different parameters of the three fields involved in the triggering and development of the local scour, namely; the bridge, the flow, and the suspended characteristic of the eroded particle. The results obtained in the training phase and the validation show relatively better performances of the new formula compared to the existing empirical formulas.

Effect of mutual interference of piers on their local scour phenomenon

Effect of mutual interference of piers on their local scour phenomenon

A Damage Detection and Location Scheme for Offshore Wind Turbine Jacket Structures Based on Global Modal Properties

Abstract Structural failures of offshore wind substructures might be less likely than failures of other equipments of the offshore wind turbines, but they pose a high risk due to the possibility of catastrophic consequences. Significant costs are linked to offshore operations, like inspections and maintenance activities, thus remote monitoring shows promise for a cost-efficient structural integrity management. This work aims to investigate the feasibility of a two-level detection, in terms of anomaly identification and location, in the jacket support structure of an offshore wind turbine. A monitoring scheme is suggested by basing the detection on a database of simulated modal properties of the structure for different failure scenarios. The detection model identifies the correct anomaly based on three types of modal indicators, namely, natural frequency, the modal assurance criterion between mode shapes, and the modal flexibility variation. The supervised Fisher's linear discriminant analysis is applied to transform the modal indicators to maximize the separability of several scenarios. A fuzzy clustering algorithm is then trained to predict the membership of new data to each of the scenarios in the database. In a case study, extreme scour phenomena and jacket members' integrity loss are simulated, together with variations of the structural dynamics for environmental and operating conditions. Cross-validation is used to select the best hyperparameters, and the effectiveness of the clustering is validated with slight variations of the environmental conditions. The results prove that it is feasible to detect and locate the simulated scenarios via the global monitoring of an offshore wind jacket structure.

Taxation and public spending in Peru 2000-2018


 In general, when the river flow increases, a scour phenomenon will occur, in which the substructure of the bridge, be it abutment and / or piers, will be affected, resulting in a partial or total collapse of the structure. All of the above is the key to achieving our research objectives, which is to carry out an evaluation and protection design against the hydraulic scour process of the Unocolla bridge in the city of Juliaca, Puno. The population will be the Unocolla bridge and the sample will be a substructure of the bridge. The method used is applied and its design is pure experimental, using quantitative methods, in which the research problem is described as realistic results. To determine the scour effects, topographic, hydrological and sedimentological information was collected to later carry out hydraulic modeling in the Hec-Ras program. Scour depths were determined in reference to pillars, determining in pillar 1 scour depth 1.2 m, in pillar 2 scour depth 2.46 m, in pillar 3 scour depth 1.2 m, in pillar 4 scour depth 1.2 m, for which the castling process is proposed as an alternative solution.

Equilibrium morphology and scour evolution at blunt nosed chevrons

AbstractBlunt nosed chevrons are low‐head river restoration structures commonly used in large rivers to enhance the navigation and aquatic habitat. These structures usually create scour regions in their vicinity, which provides habitat for various aquatic organisms. Furthermore, the scour pools represent suitable locations for fish nursery. In some cases, the noses of islands are protected by constructing chevrons which reduce the intensity of erosive action. Only a few studies deal with the analysis of the scour phenomena due to chevrons. Therefore, this paper aims at investigating the scour evolution and characteristics at equilibrium due to chevrons inserted in both straight and curved channels. The most influential parameters governing the scour mechanisms (e.g., densimetric Froude number) were identified via dimensional analysis. Experimental evidence allowed us to distinguish and classify different scour morphology types for chevrons in curved channels: Types Ab, Bb and Cb were identified, corresponding to Types A, B and C in straight channels. Moreover, useful empirical relationships are provided to estimate the maximum scour hole depth and length, and the dune height with sufficient accuracy (R2 ranging from 0.63 to 0.86). Finally, the equations are validated with the data from previous studies, showing a good predicting capacity.

Pressure-Flow Scour Due to Vertical Contraction: A Review

Climate and land-use/land-cover changes are amplifying hydrological uncertainties, which are increasing the probability of flood magnitudes exceeding their design values. Consequently, bridges are more likely to get submerged. The vertical contraction of flow during a submergence event causes the flow beneath the bridge to accelerate and transit from atmospheric flow to pressure flow. The pressure flow increases the velocity gradient and bed-shear stresses, thereby increasing the scouring potential of the flow and the risk of bridge failure. Laboratory and numerical experiments have been performed to relate the magnitude of pressure-flow scour to the flow geometry and flow, bed, and fluid properties. These developed prediction equations have found a place in design manuals. Nevertheless, many aspects of the pressure-flow scouring are confounding and are still unknown after 3 decades of research. In this article, an overview of the pressure-flow scour phenomenon is presented. The focus is on the important but special case of pressure flow with no pier that has received maximum attention in the literature. The experimental studies on pressure-flow scour are summarized, and inconsistencies and gaps in the reported results are highlighted. A compendium of data compiled from all existing data sets is used for evaluating the design equations and investigating their relative strengths and shortcomings. Based on the anomalies identified in the literature, the article questions the applicability of empirical and semitheoretical models for the pressure-flow scour phenomenon and suggests directions for future research.

Remarks on the Boundary Conditions for a Serre-Type Model Extended to Intermediate-Waters

Numerical models are useful tools for studying complex wave–wave and wave–current interactions in coastal areas. They are also very useful for assessing the potential risks of flooding, hydrodynamic actions on coastal protection structures, bathymetric changes along the coast, and scour phenomena on structures’ foundations. In the coastal zone, there are shallow-water conditions where several nonlinear processes occur. These processes change the flow patterns and interact with the moving bottom. Only fully nonlinear models with the addition of dispersive terms have the potential to reproduce all phenomena with sufficient accuracy. The Boussinesq and Serre models have such characteristics. However, both standard versions of these models are weakly dispersive, being restricted to shallow-water conditions. The need to extend them to deeper waters has given rise to several works that, essentially, add more or fewer terms of dispersive origin. This approach is followed here, giving rise to a set of extended Serre equations up to kh ≈ π. Based on the wavemaker theory, it is also shown that for kh > π/10, the input boundary condition obtained for shallow-waters within the Airy wave theory for 2D waves is not valid. A better estimate for the input wave that satisfies a desired value of kh can be obtained considering a geometrical modification of the conventional shape of the classic piston wavemaker by a limited depth θh, with θ≤ 1.0.

Prediction of Maximum Scour Depth near Spur Dikes in Uniform Bed Sediment Using Stacked Generalization Ensemble Tree-Based Frameworks

The scouring process near spur dikes could jeopardize the stability of riverbanks. Thus, accurate estimation of the maximum scour depth near spur dikes is crucial in river engineering. However, due to the complexity of the scour phenomenon around these structures, it has been a challenge to accurately estimate the maximum scour depth. Few efforts have been made to develop a machine learning (ML) approach for such a purpose. In this study, two novel multilayer stacked generalization frameworks are developed to model the scour depth near a spur dike in a uniform sediment condition. Stacked tree-based frameworks consist of three standalone ML approaches, including multivariate adaptive regression spline, multigene genetic programming, and kernel extreme learning machine as the first layer and the boosting regression tree (BRT) and bagging regression tree (BGT) as meta learners. A total of 186 data points were collected from previous experimental studies, and 32 flume experiments were further conducted under clear water conditions at the Indian Institute of Technology (IIT) Roorkee Laboratory in this study. The performances of the models were assessed using various statistical metrics [e.g., correlation coefficient (R), root-mean-square error (RMSE), and mean absolute percentage error (MAPE)], graphical criteria, and some existing empirical equations. The modeling results demonstrated that the stacked BRT and BGT frameworks were superior to all the standalone ML approaches (R=0.9786, RMSE=0.1654, and MAPE=11.68 for BRT; and R=0.9742, RMSE=0.1831, and MAPE =11.29 for BGT). This finding was also confirmed by a comparison between the empirical correlations and the artificial intelligence models. In addition, the sensitivity analysis proved that the mean sediment size ratio (L/d50) was the most influential variable in estimating the scour depth near spur dikes.

Role of tree crown height for effective mitigation capability of inland coastal forest considering the flow structures and scour phenomena

This research investigated the relationship of tree crown height with the trunk part under the mobile bed condition for the proper management of inland coastal forests. A series of flume experiments under the quasi-steady flow conditions were performed while varying different parameters like change in crown heights from the ground (highest Hct = 0.7, medium Hct = 0.5, and lowest Hct = 0.3; where Hct = hc/ht: Hct is the non-dimensional parameter, hc is the crown height from ground and ht is the tree height), forest thicknesses in the streamwise direction i.e. L and L/2 (where L is the forest length), and initial Froude number conditions (Fr) ranging from 0.668 to 0.732. The outcomes demonstrated that the flow structures are strongly influenced by the lowest crown height i.e. Hct = 0.3 causing the maximum flow energy reduction i.e. 40-43%. On the contrary, the scour produced around the forest due to the high impact force of overflowing water became excessive that can significantly damage the coastal forest defense system. The optimum results in the form of significant energy reduction of the approaching current and minimum vulnerability (permissible scouring) of the defense system have been observed to be associated with the medium crown height i.e. Hct = 0.5 and largest possible forest thickness.

Study on Local Sediment Scour and Stress State of Submarine Cables in Offshore Wind Farms

The laying of submarine cables will destroy the local seabed topography, leading to changes in the submarine hydrodynamic boundary, which will cause the local unbalanced sediment transport phenomenon when the submarine cable is buried. When the submarine cable begins to be exposed or the topography changes greatly, the scour phenomenon will be more severe. This article starts from the safety and stability of the submarine cable during the operation and maintenance of the 200MW offshore wind farm in Xuwen Wailuo, Guangdong Province, China and refers to the partial scour of the submarine cable in the “Southern Main Grid and Hainan Power Grid Second Interconnection Project” near the site near the Qiongzhou Strait. In this case, the measured ocean hydrological data at the site is used as the input condition, and Fluent is used to establish a refined hydrodynamic model of the submarine cable scour, to simulate the development process of the submarine cable scour of the wind farm under real sea conditions, and to perform the force analysis after the submarine cable is exposed. These will provide a certain scientific basis for ensuring the safe and stable operation of submarine cables during wind farm operation and maintenance.

Experimental study on reduction of scouring and tsunami energy through a defense system consisting a seaward embankment followed by vertically double layered vegetation

To countermeasure the scouring and tsunami energy reduction, this study conducted a series of laboratory experiments where vertically double layered vegetation (VDLV) was introduced behind the seaward embankment on a gravel bed. The experimental results demonstrated that the overtopping flow from the embankment experienced a submerged hydraulic jump over the embankment, against all the considered cases. The dense VDLV i.e. dense (G/d = 0.041, where G is the clear gap between the cylinders in the cross-stream direction, and d is the cylinder diameter) short submerged vegetation (L1) incorporated within a sparse (G/d = 2.125) tall emergent vegetation (L2) influenced the scour phenomena. It reduced the relative scoured depth by approximately 29−41% at the embankment toe, the maximum scoured depth by approximately 29−37%, and the scoured length by approximately 28−34%, as compared to that of single embankment system. Furthermore, dense VDLV provided the maximum i.e. 49−53%, loss to the total flow energy. The increase in the density of L1 in VDLV offered a larger drag to the flow by shifting the position of the submerged hydraulic jump more towards the embankment top; hence, consequently resulted in significant reduction of scoured depth, scoured length and energy of the tsunami flow.

Improving the 2D Numerical Simulations on Local Scour Hole around Spur Dikes

Local scour is a common threat to structures such as bridge piers, abutments, and dikes that are constructed on natural rivers. To reduce the risk of foundation failure, the understanding of local scour phenomenon around hydraulic structures is important. The well-predicted scour depth can be used as a reference for structural foundation design and river management. Numerical simulation is relatively efficient at studying these issues. Currently, two-dimensional (2D) mobile-bed models are widely used for river engineering. However, a common 2D model is inadequate for solving the three-dimensional (3D) flow field and local scour phenomenon because of the depth-averaged hypothesis. This causes the predicted scour depth to often be underestimated. In this study, a repose angle formula and bed geometry adjustment mechanism are integrated into a 2D mobile-bed model to improve the numerical simulation of local scour holes around structures. Comparison of the calculated and measured bed variation data reveals that a numerical model involving the improvement technique can predict the geometry of a local scour hole around spur dikes with reasonable accuracy and reliability.