Temporal Scour Research Articles

Experimental investigation of clear-water temporal scour variation around bridge pier in gravel

Variation of temporal scour depth around circular piers under clear-water scour condition was studied experimentally for a variability of configuration studies, including different size of circular piers. A total of 96 experiments were carried out with more than 800 data sets of temporal scour depth in non-uniform gravel bed. The experimental data were used to calculate the temporal scour depth at different planes i.e. 0°, 90°, 180° and 270°, 0° plane indicates the maximum and 180° plane indicates minimum scour zones. Some of the previous methods of estimating temporal scour depth at 0° plane are studied in this study. Three temporal scour depths equations for 0°, 90°, 270° and 180° planes have been proposed in this study. The predictions of the temporal scour depth improved after the revised methods of Kothyari et al. (J Hydraul Eng 133(11):1229–1240, 2007). Results of the present proposed equation for 0° plane were compared with latest available relationships in literature and found in good agreements with observed values.

Temporal scour evolution at non-uniform bridge piers

Scour at uniform cylindrical piers has received considerable attention in the past. However, bridge foundations can be subjected to the flow due to single or combined effects of long-term riverbed degradation, lateral shifting of the stream, contraction scour, local scour or other factors. This paper focuses on bed morphology changes due to local scour at piers founded on piles or caissons when the foundation is located at the initial bed level. Experiments were carried out in a 1 m wide 20 m long rectangular channel under clear-water and steady flow conditions. The majority of runs were of long duration in order to guarantee sufficient interaction between the flow and pier foundation and to approach the equilibrium phase. Two nearly uniform bed sediments were considered to assess grain size effects. The experimental data obtained provided new information on the temporal variation of scour depth, the areal extent of the scour hole and the scour volume, which are useful for validation of advanced numerical models. In this paper, scour depths are compared with the HEC-18 approach and agreements appear suitable only at the equilibrium phase. Moreover, scour progress is compared to that of uniform cylindrical piers and foundation effects are emphasised. A generalised scour equation is proposed, accounting for such effects.

Evaluation of existing equations for temporal scour depth around circular bridge piers

Scour is defined as the processes of removal of sediment particles from water stream bed by the erosive action of activated water, and also carries sediment away from the hydraulic structures. Scour is the main cause of pier failure. Numerous equations are available for estimating temporal and equilibrium scour depth. The present study describes the phenomenon of temporal scour depth variation at bridge piers and deals with the methods for its estimation. The accuracy of six temporal scour depth equations are also checked in this study. After graphical and statistical analysis, it was found that the relationship proposed by Oliveto and Hager (J Hydraul Eng (ASCE) 128(9):811–520, 2002) predicts temporal scour depth better than other equations. Three equations of equilibrium time of scour are also used for computing equilibrium time. Equilibrium time equation proposed by Choi and Choi (Water Environ J 30(1–2):14–21, 2016) gives better agreements with observed values.

Modified Einstein Sediment Transport Method to Simulate the Local Scour Evolution Downstream of a Rigid Bed

AbstractThe present study consists of a new mathematical-numerical modeling formulation to simulate the spatial and temporal scour development downstream of a rigid bed for both a noncohesive sediment bed and a cohesive sediment mixture with relatively small percentage of cohesive material. Laboratory tests were conducted in a rectangular tilting flume having a recessed box filled with the selected bed sediments and placed downstream of a rigid rough bed. The scour pattern was accurately acquired with a three-dimensional laser scanner at various time instants. The numerical code was calibrated through the scour profile data obtained under steady-state flow condition and then validated on the basis of scour patterns acquired under both steady and unsteady flow conditions (symmetric and asymmetric hydrographs). Contrary to most previous studies conducted with an issuing jet, the present study’s experiments were performed under non–strictly uniform flow conditions. The numerical model utilized information co...

Prediction of temporal scour hazard at bridge abutment

The scour around abutments is a major damage of bridge which appears during the flood hazard. Accurate prediction of scour depth at abutment is very essential to estimate foundation level for a cost-effective design. The accuracy of conventional method is low for prediction of temporal scour depth. However, in this study, two robust techniques, adaptive neuro-fuzzy inference system (ANFIS) and artificial neural networks (ANNs), were employed to estimate temporal scour depth at abutment. All experiments were conducted under clear-water conditions. Extensive data sets were collected from present and previous studies. To determine the best method, two models of ANNs, feed forward back propagation (FFBP) and radial basis function (RBF), and two kinds of ANFIS, subtractive clustering and grid partition, were investigated. The results showed that the accuracy of the FFBP with two hidden layers (RMSE = 0.011) is higher than that of RBF (RMSE = 0.055), multiple linear regression method (RMSE = 0.049) and previous empirical equations. A comparable prediction was provided by the ANFIS-grid partition method with RMSE = 0.041. This research highlights that the ANN-FFBP and ANFIS-grid partition can be successfully employed for prediction of scour hazard and reduction in bridge failure.

Temporal variation of clear-water scour at compound Abutments

Most of actual abutments in rivers are built on foundation, while there is limited number of study available on the effects of the foundation on the local scour. In this study, temporal variation of local scour around compound abutment was investigated experimentally under clear-water conditions. The results showed that a suitable level of foundation is able to decrease the scour depth and increase scour time during the flood events. The trend of temporal scour depth at compound pier and abutment is similar. The scour depth develops to top of foundation quickly, and then the foundation postpones the scour development (lag–time). Duration of lag–time depends on the foundation level, velocity ratio (U/Uc) and foundation dimension. This study highlights that proper design of foundation level increases duration of scouring and provides enough time to treat bridge foundation after the flood events.

Scour control at bridge piers using macro-roughness elements

A new approach involving macro-roughness elements is proposed as a scour countermeasure at circular bridge piers subject to debris accumulation. Experiments were carried out under clear water conditions with the approaching flow velocity set at the threshold of sediment motion. The efficiency of the method was investigated in terms of scour morphology reduction and temporal scour evolution. The results show the effectiveness of the method in reducing maximum scour depth. In some cases, the elements did not reduce the maximum scour depth but were effective in reducing the volume of the scour hole. Based on the experimental data, empirical equations were derived to estimate the temporal local scour depth in the presence of debris accumulation and macro-roughness elements.

Semi-analytical model for temporal clear-water scour at prototype piers

Semi-analytical model for temporal clear-water scour at prototype piers

TIME DEVELOPMENT OF LOCAL SCOUR DEPTH BELOW PIPELINES EXPOSED TO WAVES

In this study, local scour depths beneath the submarine pipelines, under the wave effect, were investigated experimentally in a time-dependent manner. In the experiments, three different diameter of pipe, three different size of bed materials and four different characteristics of wave were used. The experiments were conducted in a wave channel with dimension of 3.6 m wide, 1.2 m height and 33 m long. The channel is equipped with a regular wave maker on the offshore side, a wave absorber system at the end of the channel and high-precision measurement devices, which operate on the ultrasonic principle. Six ultrasonic transducers were installed into test pipe, has a length equal to the channel width, to record the temporal scour depths simultaneously. Extra one transducer is located offshore side of the test pipe to measure the horizontal component of water particle velocity at a level of pipe axis. The wave characteristics were determined using another ultrasonic device and its two sensors at different channel sections. The experimental measurements allowed us to determine all of the dimensionless parameters associated with the phenomenon. The time-dependent scour depth measurements were used both for modeling the development of the scour, and for obtaining the equilibrium scour depth. The experiments performed with the same non-cohesive bed material with different grain sizes, indicate that both Keulegan-Carpenter number and Shields parameters are effective in the variation of the scour depth.

Pier scour monitoring system by bed-level image tracking

A scour monitoring system with a micro camera tracking the bed-level images is proposed in this study. Two image recognition algorithms have been developed to support the bed-level image tracking approach. Through the laboratory experiments of pier scour, this study demonstrates that the proposed system is able to accurately monitor the scour-depth evolution in real time. In addition, five commonly-used temporal scour models are employed to simulate scour-depth evolution and their results are compared with monitoring data. In general, the results indicate that the proposed scour monitoring system has the potential for further applications in the field.

Influence of large woody debris on sediment scour at bridge piers

Large woody debris (LWD) reduces the flow area, deviate the flow and increases the velocity in correspondence of the bridge pier, therefore increases the maximum scour hole depth and accelerates sediment removal. Logs and drifts accumulated on bridge piers are of different dimensions. According to logs characteristics and river morphology, drift accumulations can either extend downstream the bridge pier or they can accumulate totally upstream. This paper aims to analyze the effect of drift accumulation planimetry on bridge pier scour. The experimental investigation has been carried out at the PITLAB hydraulic centre of Civil Engineering Department, University of Pisa, Italy. Drift accumulation was characterized by different relative longitudinal lengths, flow area occlusions, length of longitudinal drift and downstream planimetrical positions relative to the pier center. The experimental investigation has been carried out in clear-water conditions. Several pier sizes, channel widths and sediment materials have been tested. Maximum scour hole in presence of drift accumulation have been compared to the maximum scour hole for an isolated pier. Finally, data were compared with previous literature findings, which highlight the effect of the downstream extension of drift accumulation on bridge pier scour. New relationships have been proposed to predict the effect of drift accumulation on bridge pier scour, both in terms of relative maximum scour and temporal scour evolution.

Bridge Pier Scour under Flood Waves

The effect of a single-peaked flood wave on pier scour is investigated both theoretically and experimentally. The conditions considered involve clear-water scour of a cohesionless material of given median sediment size and sediment nonuniformity, an approach flow characterized by a flow depth and velocity, a circular-shaped cylindrical bridge pier, and a flood hydrograph defined by its time to peak and peak discharge. A previously proposed formula for scour advance under a constant discharge was applied to the unsteady approach flow. The generalized temporal scour development along with the end scour depth are presented in terms of mainly the densimetric particle Froude number based on the maximum approach flow velocity and the median sediment size. The effect of the remaining parameters on the end scour depth is discussed and predictions are demonstrated to be essentially in agreement with model observations.

Temporal scour evolution at bridge piers: effect of wood debris roughness and porosity

Large wood debris transported by floods affects the scour morphology at bridge piers, thus increasing the bridge failure potential. The characteristic size and shape of the riparian vegetation includes various roughness and permeability conditions of the debris surface. The interaction between two-dimensional flow and rough debris accumulations increases the shear stress, the turbulence and consequently affects the scour evolution process at bridge piers. An experimental study on the bridge pier clear-water scour evolution in the presence of wood debris was conducted at the PITLAB research centre, University of Pisa, Italy. A debris accumulation is characterized by roughness, shape and porosity. Flow intensities range from 65 to 100% of the threshold velocity and included up to 18% of the total flow area. Flow depths were varied from 2.67 to 5.67 times the pier diameter. The effects of wood debris roughness and porosity were analysed in terms of scour temporal evolution and scour morphology.

Generalized Approach for Clear-Water Scour at Bridge Foundation Elements

Extensive studies on the temporal evolution of scour were recently conducted at Versuchsanstalt fur Wasserbau, Hydrologie und Glaziologie VAW, ETH Zurich, Switzerland, along with a computational model for the scour depth estimation. The VAW scour data are revisited in the present study to present a further refinement. Additional experiments conducted on the scour entrainment at piers, at rectangular and sloping abutments, as well as at singular and multiple spur dikes are reported. A general criterion is proposed to determine the densimetric particle Froude number for scour entrainment. A new relationship for the temporal scour evolution at bridge foundation elements is then developed based on the similitude of Froude by relating the scour depth to the difference between the actual and the entrainment densimetric particle Froude numbers. The new relationship is validated by the complete VAW scour data set, and verified by the available literature data. The combination of sediment characteristics, approach...

Scour in hydraulic engineering

As a result of damage and failures due to undermining of foundations and the blockage of water flow caused by sediment aggradation downstream of scour holes, scour in hydraulic engineering has become an important issue in recent decades. This paper presents recent research on: (a) plunge pool scour in which a variety of effects were investigated; (b) bridge piers for which spatial and temporal scour development was described using particle image velocimetry for a test case; (c) the failure of riprap-protected spur dykes in a straight river reach. In all three fields, the main features of scour are described based on similitude according to Froude—that is, using the densimetric Froude number of the approach flow as the dominant parameter. The large number of parameters involved were controlled with suitable experimental setups allowing for the determination of the governing effects of a scour problem. Results are presented that readily apply to river engineering problems.

Temporal scour development at bridge abutments with a collar

This study investigated the reduction of scour around a vertical-wall bridge abutment using rectangular collars for clear-water flow conditions over uniform sediment particles in a laboratory flume. Collars of different sizes and at different elevations were tested to determine the temporal variation of scour depth around the bridge abutment. The development of scour around the abutments with and without a collar for a time period of 6 h was studied, and observed scour depths were compared. Experimental results showed that, in addition to protecting the abutments against erosion, the addition of a collar is effective in reducing the rate of temporal scour development. A comparison of the present results with those from previous studies revealed that the effectiveness of a collar increases with a decrease in the elevation of the collar and an increase in the width of the collar.Key words: bridge abutment, collar, experimentation, hydraulics, scour, temporal variation.

A METHOD FOR LOCAL SCOUR PREDICTION AT RIVER STRUCTURES CONSIDERING TIME FACTOR

A generalized method to determine maximum and temporal evolution of scour-depth at river structures, based on large range of data set from independent physical model studies, has been developed. A relative grain-size-like parameter referred to as alpha parameter was proposed. Likewise, a method was proposed to determine time factor in terms of a parameter, so called, sediment Strouhal number that can be employed as a similarity number in any time dependent phenomenon. It is evident that temporal development of local scour can widely be generalized using this parameter. Proposed method can be applied for structures protruding from the river bank (spurs, abutment etc) as well as pier-like structures. This method can be applied for live-bed scouring case as well. The method was verified using large range of laboratory data from independent investigations on maximum and temporal scour. Likewise, method was tested against field investigation on temporal scour development at pier during flood event.

Temporal Evolution of Clear-Water Pier and Abutment Scour

Scour related to bridge hydraulics received much attention in the past decade, including its relation to flood hydrology and hydraulic processes in addition to steady flow. This paper presents new research on bridge pier and abutment scour based on a large data set collected at ETH Zurich, Switzerland. In total six different sediments were tested, of which three were uniform. Also a large variety of scour elements were considered, from 1 to 60% of the channel width, and flow depths ranging from 1 to about 40% of the channel width. Using similarity arguments and the analogy to flow resistance, an equation for temporal scour evolution is proposed and verified with the available literature data. The agreement of the present scour equation with both the VAW data and the literature data were considered sufficient in terms of river engineering accuracy, provided limitations relating to hydraulic, granulometric, and geometrical parameters are satisfied. These limitations are discussed and refer particularly to e...