Characteristics Of Scour Hole Research Articles

Local scour at group of bridge piers founded in gravel bed in staggered arrangement

Local scour around bridge piers is the common cause of undermining of bridge foundation. Many researchers have studied local scour around bridge pier in finer sediment bed. The literature survey reveals a limited information is available on scour around a group of bridge piers with and without collar founded in gravel bed. Keeping this in view, an attempt is made to examine experimentally the efficacy of the collar around a group of three piers placed in a staggered triangular arrangement in the gravel bed of 3 mm effective size. The data on temporal variation of scour depth, scour hole characteristics, and areal extent of scour hole were collected. The collected experimental results infer very prominent information to the bridge engineers. The obtained results on equilibrium scour depth and areal extent of scour help in knowing the extent up to which bridge pier protection can be provided against scour. It is found that at longitudinal pier spacing (Z) equals to 8.45 times the pier diameter (b), the equilibrium scour depth at nose of the piers was maximum than that of at other pier spacing. At pier spacing Z/b > 8.45, the equilibrium scour depth at downstream pier without collar decreases with increasing pier spacing and reaches to minimum at Z/b = 40. At pier spacing 8.45 < Z/b < 10, the equilibrium scour depth at upstream pier without collar decreases because of decreasing effect of reinforcement and this effect disappears at pier spacing Z/b > 10. The present study reveals that bridge piers without collar became free of mutual interference effect on local scour at centre-to-centre (c/c) pier spacing of 60 times the pier diameter. It is worth mentioning that for piers with collar, the effect of mutual interference vanished at c/c longitudinal pier spacing of 20 times the pier diameter. The results show that additional shielding of collar makes the piers free from mutual interference effect at lesser spacing than the pier group without collar. This concludes that the present investigation is very useful when limited space is available between the existing and newly proposed bridges.

Modeling of scour hole characteristics under turbulent wall jets using machine learning

The novelty of the present study is to investigate the parameters that depict the scour hole characteristics caused by turbulent wall jets and develop new mathematical relationships for them. Four significant parameters i.e., depth of scouring, location of scour depth, height of the dune and location of dune crest are identified to represent a complete phenomenon of scour hole formation. From the gamma test, densimetric Froude number, apron length, tailwater level, and median sediment size are found to be the key parameters that affect these four dependent parameters. Utilizing the previous data sets, Multi Regression Analysis (linear and non-linear) has been performed to establish the relationships between the dependent parameters and influencing independent parameters. Further, artificial neural network-particle swarm optimisation (ANN-PSO) and gene expression programming (GEP) based models are developed using the available data. In addition, results obtained from these models are compared with proposed regression equations and the best models are identified employing statistical performance parameters. The performance of the ANN-PSO model (RMSE = 1.512, R2 = 0.605), (RMSE = 6.644, R2 = 0.681), (RMSE = 6.386, R2 = 0.727) and (RMSE = 1.754, R2 = 0.636) for predicting four significant parameters are more satisfactory than that of regression and other soft computing techniques. Overall, by analysing all the statistical parameters, uncertainty analysis and reliability index, ANN-PSO model shows good accuracy and predicts well as compared to other presented models.

Hydrodynamic Modeling and Comprehensive Assessment of Pier Scour Depth and Rate Induced by Wood Debris Accumulation

This study mainly investigates the impact of debris accumulation on scour depth and scour hole characteristics around bridge piers. Through controlled experiments with uniform sand bed material, the influence of various debris shapes (high wedge, low wedge, triangle yield, rectangular, triangle bow, and half-cylinder), upstream debris length, downstream debris extension, and debris thickness on scour depth and scour hole area and volume around the cylindrical pier were analyzed. The findings revealed that the shape and location of debris in the water column upstream of piers are key factors that determine the depth of scour, with high wedge shapes inducing the deepest scour and potentially the largest scour hole, particularly when positioned close to the pier and fully submerged. Scenarios in which triangle bow debris was submerged at full depth upstream of the pier closely resembled situations devoid of debris. Conversely, debris extension downstream of the pier was found to reduce local scour depth while concurrently enlarging the dimensions of the scour hole. The existing scour prediction equations tend to overestimate scour depth in scenarios involving debris, particularly when applying effective and equivalent pier width. This discrepancy arises because these equations were originally developed to predict scour depth around piers in the absence of debris. In response, a refined model for predicting scour induced by debris was proposed, integrating factors such as upstream debris length, downstream extension, obstruction percentage, and debris shape factor. This model demonstrated strong agreement with experimental data within the scope of this study and underwent further validation using additional experimental datasets from other research endeavors. In conclusion, this experimental study advances the comprehension of scour processes around cylindrical bridge piers, providing valuable insights into the role of debris characteristics and positioning.

Prediction of scour hole characteristics caused by water jets using metaheuristic artificial bee colony-optimized neural network and pre-processing techniques

Abstract Preventing plunge pool scouring in hydraulic structures is crucial in hydraulic engineering. Although many studies have been conducted experimentally to determine relationship between the scour depth and water jets in several fields, available equations have deficiencies in calculating the exact scour due to complexity of scour process. This study investigated local scour depth in plunge pool using Metaheuristic Artificial Bee Colony-Optimized Feed Forward Neural Network (ABCFFNN), variational mode decomposition (VMD) and ensemble empirical mode decomposition (EEMD) techniques. To set modeling, the input parameters are impact angle, densimetric Froude number, impingement length, and nozzle diameter. The models' training and testing were conducted using data available in the literature. The models' performances were compared with experiments. The results demonstrate that scour depth, length, width, and ridge height can be calculated more accurately than available equations. A rank analysis was also applied to obtain the most critical parameter in predicting scour parameters in water jet scouring. ABC-FFNN, VMD-ABCFFNN and EEMD-VMD-FFNN hybrid models were performed to obtain scour parameters. As a result, ABC-FFNN algorithms produced the best solution to predict the scour due to circular water jets, with the values for training (R2: 0.331 to 0.778) and testing (R2: 0.495 to 0.863).

Investigation of the Effects of the Arrangement of Triplex Inclined-Vertical Group Piers in a Sharp Bend on the Characteristics of Scour Holes

Investigation of the Effects of the Arrangement of Triplex Inclined-Vertical Group Piers in a Sharp Bend on the Characteristics of Scour Holes

Flow boundary effects on scour characteristics upstream of pipe intakes

Intakes are used to take water from reservoirs, lakes, and oceans. Depending on flow and geometrical conditions in which the intakes are located, sediment particles may also be entrained by the intake flow, resulting in a scour hole. Characteristics of scour hole are affected by the bed sediment properties, intake discharge, and intake position with respect to flow boundaries (i.e., dead-end wall, channel bottom, channel side walls). In this study, experiments were conducted to investigate the effects of the intake discharge, sediment size, and intake position relative to flow boundaries on scour hole characteristics. Entrainment conditions of sediment particles at the bed of the channel were also examined. Experimental results indicated that the maximum scour depth along the centerline of the channel was mostly affected by the sub-surface vortices extending from the channel bed to the intake. As the distance between the dead-end wall and the intake center decreased, the strength of the sub-surface vortices also decreased due to the effect of the friction imposed by the dead-end wall on the sub-surface vortices. Furthermore, the width and length of the scour hole decreased as the distance between the intake center and the dead-end wall increased.

Accuracy evaluation of scour depth equations under the submerged vertical jet

Abstract Scouring of sediment materials under submerged vertical jets is shown at grade-control structures, downstream of weirs, and submerged vertical water jets have several uses, including seabed sediment removal and dredging in ocean engineering. Numerous studies have been conducted to demonstrate the scour process and the variation of scour profile utilizing various influencing parameters. Many researchers developed equations for predicting the scour hole characteristics. Previous studies identified two types of scour hole depth configurations: static and dynamic scour depth and the variation of scour hole variations differs for long- and short-impinging jet height conditions. In this study, extensive data on non-dimensional static and dynamic scour depth under short- and long-impinging jets acquired from prior literature, and the previously proposed equations of static and dynamic scour depth were analyzed using graphical and statistical analysis. The findings demonstrated that the relationships proposed by Aderibigbe and Rajaratnam (1996) for long-impinging jets and Amin et al. (2021) for short-impinging jets predict the static scour depth better than the other equations. The proposed equations for dynamic scour depth under long- and short-impinging jets are highly biased and inaccurate.

Experimental Study on the Influence of New Permeable Spur Dikes on Local Scour of Navigation Channel

The depths and areas of the scour holes around spur dikes are the most concerning issues regarding spur dike design. In this study, using a moving bed experiment, the influence of traditional rock-fill spur dikes and new permeable spur dikes with different permeabilities on riverbed scour under unsteady flow was studied, and the spatial characteristics of scour holes at dike heads were analyzed. The results show that with increases in the permeability coefficient of the spur dike, the depth and area of the scour hole at the dike head gradually decreases; however, when the permeability coefficient is more than 17.6%, the depth and area of the scour hole downstream of the dike body increases with an increase in the permeability coefficient. According to comprehensive evaluation, when the water permeability is 17.6%, the stability of the spur dike is at its best. The maximum depth of the scour hole at the dike head is affected by factors such as the spur dike permeability coefficient, effective scouring time, and width bottom protection structure. On this basis, a new formula for calculating the maximum depth of the scour hole at a dike head is proposed. These research results will be beneficial to the reliability of spur dikes and the sustainability of navigation channels.

Hydrodynamics of tidal bore overflow on the spur dike and its influence on the local scour

In estuaries with strong tidal bore, the scour behind the spur dike induced by tidal bore overflow has significant influence on the dike safety. In this study, an experiment study of the local scour induced by tidal bore overflow behind the spur dike was carried out in a physical flume. In addition, the process of the tidal bore overflow on the dike was numerically simulated with the boundary generation method. The stable overflow water depth on the spur dike (hts), unit overflow discharge (qts) and the scour hole characteristics were analyzed based on the experimental and numerical results. It is found that the relative stable overflow water depth (hts/h1) increases with the increase of the Froude number after bore (Fr1) and decreases with the increase of relative dike height (hd/h1). While the relative stable unit overflow discharge (qts/q1) is mainly affected by the relative dike height. Additionally, the results of scour pit behind the spur dike show that the scour depth (s/h1) is directly proportional to the relative current intensity (u1/uc) and the dike height (hd/h1), but inversely proportional to the water depth before bore (h0/h1). An empirical equation for predicting relative maximum scour depth is obtained by fitting the experimental results and the field measured data, and the prediction accuracy is within 30%. The conclusions of this paper can provide technical support for the engineering design and operation evaluation of spur dikes in estuaries with the strong tidal bore.

Comparative study of soft computing models for prediction of scour below two symmetric crossing jets

The scour estimation downstream of the dam’s hydraulic structures is a serious issue and has long been considered an important topic by hydraulic engineers. The literature shows that the computational methods are good alternatives for predicting the scour in hydraulic structures in which the conventional methods demonstrate shortcomings. In the present paper, various machine learning techniques have been used for the first time to predict the scour below the two symmetric crossing jets. Four types of artificial neural networks (ANNs), including feedforward back-propagation (FFBP), cascade-forward back-propagation (CFBP), radial basis function (RBF), generalized regression neural network (GRNN) along with the adaptive neuro-fuzzy inference system (ANFIS), and support vector regression (SVR) were employed and evaluated. Two important scour hole characteristics, namely the maximum scour hole depth and its location relative to the scour hole origin, were predicted at three crossing angles. The soft computing models were also compared with the traditional empirical methods. The results indicated that the applied computing techniques perform satisfactorily and improve the results remarkably. They can estimate the scour more precisely than the regression models and can be considered robust alternative tools. A detailed sensitivity analysis was also performed on the FFBP that shows the crossing angle has a powerful effect on the predictions. The SVR improved the results to 47% and 31.71% for the scour hole depth and its location, respectively, in terms of the correlation coefficient.

Investigation of Blockage Upstream Box Coverage on the Scour Pattern in the Open Channel

Under sub-critical flow conditions, the presence of blockage (solid wastes and weeds) upstream of box coverage and the scours pattern downstream of the coverage was explored in this study. The upstream blocking was simulated using 48 runs in an artificial trapezoidal cross-section with three square box coverages of side dimensions 8.80, 10.40, and 12.90 cm, four water flows of 2, 5, 8, and 11 L/s, and four blockage ratios of 0, 10, 20, and 30% relative to the coverage cross-section area. To estimate the scour hole characteristics, a 2.00 m long, 0.60 m bed width, and 0.30 m deep sand basin filled with D50 = 0.50 mm bed material was constructed directly downstream of the coverage outlet. In each run, the water level, velocity, and scoured hole parameters downstream of the coverage were measured. According to the analysis, the Non-blocked coverage has less scour depth and length than the partially blocked coverage, where the maximum scour depths and length of the Non- blocked coverage for cases 1, 2, and 3 at the discharge of 11 l/s were 73, 72, and 17 % respectively, and 77.56, 77.34, and 83.66 % respectively relative to the maximum scour depth and length of partially blocked coverage at the discharge of 11 l/s and blockage ratio 30 %. The depth and length of the scour hole downstream coverage are increased with the increment of the coverage's blockage ratio and discharge and are reversely proportional to the inlet area of coverage. Increased relative scour depth and length by 3.60 percent and 11.80 percent respectively, by increasing the downstream Froude number of flow (Frd) by 0.01 while the coverage’ relative wetted area (Ar) is constant. The study suggested applying coverage with a suitable area and water discharge, and protection techniques downstream of the coverage to reduce the influence of coverage and blockage on the open channel's hydraulic efficiency and the scour pattern downstream of the coverage. Also, install a trash rack upstream of the covering and remove aquatic weeds and solid wastes periodically upstream and inside the coverage.

Experimental investigation of scour of sand beds by submerged circular vertical turbulent jets

The present work investigated the development of sand bed scour by submerged circular impinging vertical turbulent jets over a wide regime of jet diameters, exit velocities and impinging distances. The scour hole profiles were recorded with the optical method in order to present dynamic scour hole characteristics and their variation with any time. The results revealed that the scour profiles in the equilibrium state are similar and the geometries of the sour hole in the jet central region are only determined primarily by jet momentum flux. A semi-empirical equation has been developed for the maximum dimensionless scour depth in equilibrium state based on the obtained experimental data and theoretical analysis. The evolution of scour hole is found to be logarithmic, and three phases of temporal evolution were further distinguished. Finally, models for the prediction of variation of scour depth with time have been developed and validated, which could be used to assess the scour effects generated by impinging turbulent jets. The overall temporal evolution of the scour depth can be predicted by the erosion parameter Ec and the dimensionless time to reach equilibrium τ∞, which is superior to existing models in predicting the scouring process.

Effect of double gate mechanism on scour hole characteristics

Effect of double gate mechanism on scour hole characteristics

Development of scour hole depth around setback abutment in a compound channel

AbstractThis study focuses on scour depth development around 45° wing‐wall setback abutments in a compound channel. The results show that the scour development curves almost have similar shape and they can be described using exponential function. It is generally observed that the scour hole achieved 80% of the equilibrium scour depth at a scour time equals to 25% of the equilibrium scour time. Additionally, an increase in the relative abutment length and the contraction ratio causes an increase in the equilibrium time. However, this time decrease with increasing flow depth ratio. Finally, new empirical equations are proposed to predict the development of scour depth and the time to reach the equilibrium state. These equations will be useful to predict these characteristics of scour hole especially for setback abutments in compound channel and predict the temporal development scour depth for previous studies that have available data related to maximum scour depth.

Lithological control on scour hole formation in the Rhine-Meuse Estuary

River deltas commonly have a heterogeneous substratum of alternating peat, clay and sand deposits. This has important consequences for the river bed development and in particular for scour hole formation. When the substratum consists of an erosion resistant top layer, erosion is retarded. Upon breaking through a resistant top layer and reaching an underlying layer with higher erodibilty, deep scour holes may form within a short amount of time. The unpredictability and fast development of these scour holes makes them difficult to manage, particularly where the stability of dikes and infrastructure is at stake.In this paper we determine how subsurface lithology controls the bed elevation in net incising river branches, particularly focusing on scour hole initiation, growth rate, and direction. For this, the Rhine-Meuse Estuary forms an ideal study site, as over 100 scour holes have been identified in this area, and over 40 years of bed level data and thousands of core descriptions are available. It is shown that the subsurface lithology plays a crucial role in the emergence, shape, and evolution of scour holes. Although most scour holes follow the characteristic exponential development of fast initial growth and slower final growth, strong temporal variations are observed, with sudden growth rates of several meters per year in depth and tens of meters in extent. In addition, we relate the characteristic build-up of the subsurface lithology to specific geometric characteristics of scour holes, like large elongated expanding scour holes or confined scour holes with steep slopes. As river deltas commonly have a heterogeneous substratum and often face channel bed erosion, the observations likely apply to many delta rivers. These findings call for thorough knowledge of the subsurface lithology, as without it, scour hole development is hard to predict and can lead to sudden failures of nearby infrastructure and flood defence works.

Experimental method to predict scour characteristics downstream of stepped spillway equipped with V-Notch end sill

To protect the dam body and downstream area, spillways should be built. Because the difference in water level upstream and downstream spillways is usually very big, energy dissipation facilities should be introduced. Stepped spillways were discovered to immensely enhance energy dissipation. V-notch end sills installed on stepped spillways were not investigated enough. The challenge in using this type of end sills is to know the ideal angle of the notch. The second challenge is to link the energy dissipation percent and the scour hole characteristics with the hydraulic parameters of the spillway and the soil properties. This paper aims to investigate the V-notch end sills in stepped spillways and to assess their effect on energy dissipation and scour. For this purpose, physical models of four steps were built on stepped spillways in the laboratory. V-notch end sills were installed at the end of each step of the spillway. The dimensional analysis was used to link the various parameters influencing the studied phenomena. All V-notch end sill angles used enhanced energy dissipation, reduced the relative scour depth, length, and volume. Minimizing the angle of V-notch end sills enhanced energy dissipation. Three scour equations were developed to predict scour characteristics from easy-to-record measurements.

Experimental Investigation of Scour Hole Characteristics for Different Shapes of Piers Caused by Flood Hydrograph Succeeding Steady Flow

In this study, the scour depth and dimensions of the scour hole around different shaped piers for the cases of hydrographs succeeding steady flow were studied experimentally. The experiments were carried out by using circular, square, rectangular, lenticular and rectangular with trapezoidal nose to compare the various scour hole geometries at the same flow conditions. Numerous experiments were conducted in a rectangular flume (18.6 m long, 0.80 m wide and 0.75 m deep) with different triangular shaped hydrographs. The flume bed of 26 cm thickness consists of uniform graded material with D50 =1.68 mm. The experiments were carried out in clear water conditions. The temporal variations of the equilibrium scour depths in front of the pier and the scour hole dimensions were recorded by two different cameras. The equilibrium scour depths at lateral sides and downstream of the piers were also measured. Regression analysis was performed in order to derive empirical relations to predict temporal variations of the scour depth in the case of unsteady flow. The shape factor values were also investigated based on the experimental findings and the obtained values were compared to those available in literature. The performance of the obtained empirical relation for circular pier was tested by using limited experimental data available in the literature. The smallest scour hole was observed for the rectangular with trapezoidal noses pier. The increase in the scour hole dimensions for other cross-sections was in the following order: rectangular with circular noses, circular, square and rectangular piers.

Bed level variations around submerged tandem bridge piers in sand beds

ABSTRACT The characteristics of scour hole around the submerged tandem pier in alluvial bed plays an important role in analyzing the problem of parallel bridge failures. The present study investigates the scour hole properties around single and tandem pier arrangements with spacing 2d (d, diameter of pier) under varying flow conditions. Experiments were carried out on a mobile bed channel having mean sediment size 0.75 mm and geometric standard deviation (σg ) of 1.27. The cylindrical piers of diameter 4.5 cm are vertically embedded in the mobile channel bed having flow depth of 15 cm with a flow range of 0.02–0.035 m3/s in clear water conditions (U0/Uc = 0.45–0.79). The scour depth around the rear pier is 30% less than the front pier in tandem case for all the flow conditions. Further, with increments of 0.005 m3/s discharge, 20–30% more scour depths are observed around the piers (single and front pier of tandem). In all, 40% more sediment erosion is observed around the piers in tandem case vis-à-vis single pier case. The study reveals that parallel bridge piers are more prone to local scour/erosion than single pier in alluvial beds for similar flow conditions.

Effect of abutment aspect ratio on clear‐water scour in floodplains

AbstractScour around abutments is recognized as one of the main reasons of bridge foundations failure. This paper presents the experimental results of the effects of abutment width and length on the scour development up to its equilibrium condition around 45° wing‐wall setback abutments in a compound channel. The developing scour hole characteristics are tested for three different lengths and widths at different time intervals until its equilibrium scour conditions. The findings showed that the abutment width has a profound effect on the characteristics of the scour hole, contradicting the results of previous studies. Generally, an increase in the relative abutment width leads to a reduction in the scour depth and width. However, the scour length, area, and volume initially increase with an increase in the relative abutment width, Lc/yf, from 1.33 to 10.67, where Lc is the abutment width and yf is the floodplain flow depth, and then these characteristics decrease significantly with a much wider abutment, Lc/yf, from 10.67 to 21.33. Overall, the effects of the abutment width on abutment scour should be accounted. To this end, empirical equations are proposed to predict the scour hole characteristics. Scour data from previous studies are also used to compare with the proposed equations.

Turbulent Flow Structures and Scour Hole Characteristics around Circular Bridge Piers over Non-Uniform Sand Bed Channels with Downward Seepage

In alluvial rivers bridge piers often cause local scour, a complex phenomenon as a result of the interaction between turbulent flow and bed material. In this paper, the results of an experimental study on the scour hole characteristics around single vertical pier sets on a non-uniform sand bed, under no seepage, and with downward seepage conditions, are described. In case of downward seepage, turbulent statistics, such as Reynolds stress, higher order moments, TKE-flux, and consequently sediment transport, decrease upstream of the pier, while increasing on both sides of it, where the enhanced erosive capacity of the flow results in an increase in the scour hole width. Moreover, the scour hole length shifts downstream. Empirical equations for the evaluation of scour hole characteristics, such as the length, width, area, and volume, including the downward seepage parameter, are proposed and experimentally tested. Model predictions give reasonably good agreement with the experimental data.