Scour

This paper uses a minimum depth of cover data set from pipeline inspections at watercourse crossings to at-tempt to determine if a correlation between river geomorphology and location where either degradation or scour has occurred.
As part of an on-going integrity management program for watercourse crossings the minimum depth of cover at pipeline watercourse crossings has been collected at approximately 50,000 locations, mostly in Cana-da but also in parts of the USA.  The data set includes approximately 200,000 individual measurements across 50,000 separate watercourse crossing, so multiple measurements at some sites.  The data has been collected in the last 19 years. 
The measurement data available is variable in the following ways: the construction date varies from pre-1950 until 2016, the initial burial depth is most often not known, the expected initial depth of cover is variable based on the code (the codes have typically specified the 0.91 m (4 feet) to 1.2 m (5 feet) range of initial depth) and also the codes set different depths for different river widths, depth of cover could be changing due to lateral movement of the watercourse, and finally variations in the accuracy of the depth of cover meas-urement.  In addition to these factors, the history of flooding (the rarity of the flood) can also influence changes to the depth of cover.

Local scour downstream the box culverts outlet may cause to a complete failure of the culvert structure. New research is employed to reduce the max scour depth downstream the outlet of the box culvert under a different flow conditions based on an experimental investigation. A sharp edge sill is proposed on a rigid bed to dissipate the flow excess energy. Consequently, a great reduction of the scour hole dimensions is obtained by using the sharp edge sill. The experimental study was carried out using a different positions, heights and shapes of the sharp edge sill with different flow rates as well as tail water depths too. The results indicates that the sharp edge sill is a promising tool to reduce the scour dimensions. The reduction of the scour depths by using the sharp edge sill are 60%, while the reduction in the scour depths are 64%,that is because of using of rigid apron of length 7 times the height of culvert, compared to previous results without rigid bed.

Local scour downstream the box culverts outlet may cause to a complete failure of
the culvert structure. New research is employed to reduce the max scour depth
downstream the outlet of the box culvert under a different flow conditions based on an
experimental investigation. A sharp edge sill is proposed on a rigid bed to dissipate
the flow excess energy. Consequently, a great reduction of the scour hole dimensions
is obtained by using the sharp edge sill. The experimental study was carried out using
a different positions, heights and shapes of the sharp edge sill with different flow rates
as well as tail water depths too. The results indicates that the sharp edge sill is a
promising tool to reduce the scour dimensions. The reduction of the scour depths by
using the sharp edge sill are 60%, while the reduction in the scour depths are
64%,that is because of using of rigid apron of length 7 times the height of culvert,
compared to previous results without rigid bed.

A screening level model was developed to estimate bank erosion at pipeline watercourse crossings to provide estimates of the probability of pipeline exposure resulting from various extreme flood events. The model uses estimates of flood duration and maximum water velocity during flooding to predict the amount of bank erosion that would occur and compares the results to the horizontal " setback " distance. When the predicted horizontal erosion is equal to horizontal distance between the pipeline and the bank position, the probability of that flood occurring is equal to the probability of pipeline exposure due to bank erosion. The results of the bank erosion calculation can then be compared to: the probability of the flood causing exposure by scour and/or avulsion; regulatory acceptance criteria for pipelines; and company integrity objectives to assess the need for additional investigation or proactive mitigation.

Triangular weirs are commonly used to measure discharge in open channel flow. They
represent an inexpensive, reliable methodology to monitor water allocation. A compound
sharp-crested weir consisting of two triangular parts with different notch angles was used. The
lower triangular part of the weir handles the normal range of discharges while the upper part measures
the higher peak flows. This paper evaluates experimentally the local scour downstream compound
sharp crested V-notch weir. Forty-eight (48) experimental runs were conducted. Three
models of weirs with different geometries (combination of notch angles), four upstream water levels,
three water levels at the tailgate, and two bed materials were used. Multiple regression equations
based on energy principal and dimensional analysis theory were deduced to estimate the local scour
downstream of the weir models. The developed equations were compared with the experimental
data. The comparison between the local scour downstream classical V-notch weir and a compound
sharp-crested weir consisting of two triangular parts with different notch angles was found to be
unnoticed. The study recommended using the compound V-notch weir to pass high discharges
instead of the classical V-notch weir.

Coastal structures may cease to function properly due to seabed scouring. Hence, prediction of the maximum scour depth is of great importance for the protection of these structures. Since scour is the result of a complicated interaction between structure, sediment, and incoming waves, empirical equations are not as accurate as machine learning schemes, which are being widely employed for the coastal engineering modeling. In this paper, which can be regarded as an extension of Pourzangbar et al. (2016), two soft computing methods, a support vector regression (SVR), and a model tree algorithm (M5), have been implemented to predict the maximum scour depth due to non-breaking waves. The models predict the relative scour depth (S max /H 0) on the basis of the following variables: relative water depth at the toe of the breakwater (h toe /L 0), Shields parameter (Â), non-breaking wave steepness (H 0 /L 0), and reflection coefficient (Cr). 95 laboratory data points, extracted from dedicated experimental studies, have been used for developing the models, whose performances have been assessed on the basis of statistical parameters. The results suggest that all of the developed models predict the maximum scour depth with high precision , the M5 model performed marginally better than the SVR model and also allowed to define a set of transparent and physically sound relationships. Such relationships, which are in good agreement with the existing empirical findings, show that the relative scour depth is mainly affected by wave reflection.

The presence of some high voltage towers in flood stream is one of the most important problems that may lead to the collapse of these towers. The main reason for collapse is the soil erosion around the tower foundation during flood. The shape of the foundation is a vital factor in scouring process. This research is focused on studying different shapes of a tower foundation and its effect on the maximum scour depth. A sediment scour model has been investigated by using Flow 3D V 11.2 Program. The numerical simulation results of the maximum scour depth surrounding a single square pile model have been assured using prior experimental findings and showed good agreement. After that, different four shapes of footing and five values of the inclination angle for pyramid and cone footing have been investigated. The results of cuboid footing have been used as a reference to compare with different shapes. Seventy-two numerical runs have been carried out considering the wide range of Froude number ranging from 0.26 to 0.50 under clear water condition. It is found that, for pyramid and cone footing, the lager the inclination angle, the smaller the scour depth will be and vice versa. The cone footing is better than the other footing shapes. An empirical equation has been developed by using the nonlinear regression to predict the relative maximum scour depth around the footing.

Accurate prediction of maximum scour depth is important for the optimum design of seawall
structure. Owing to the complex interaction of the incident waves, sediment bed, and seawalls, the
prediction of the scour depth is not an easy task to accomplish. Undermining the recent
experimental and numerical advancement, the available empirical equations have limited accuracy
and applicability. The aim of this study is to investigate the application of robust data-mining methods
including genetic programming (GP) and artificial neural networks (ANNs) for predicting the
maximum scour depth at seawalls under the broken and breaking waves action. The performance of
GP and ANNs models has been compared with the existing empirical formulas employing statistical
measures. The results indicated that both the GP and ANNs models functioned significantly better
than the existing empirical formulas. Furthermore, the capability of GP was used to produce
meaningful mathematical rules, and an analytical formula for predicting the maximum scour depth at
seawalls under breaking and broken waves’ attacks was developed by utilizing GP.

By analysing and comparing the results of post-disaster field studies and literature regarding the mechanisms by which coastal structures failed due to the 2004 Indian Ocean Tsunami and the 2011 Tohoku Tsunami events (the focus being on defence structures where applicable), trends were identified and examined. This paper highlights the most commonly occurring / major failure mechanisms identified in the various locations affected by the two tsunami events. The failure modes found in over twenty locations throughout the Fukushima, Iwate and Miyagi Prefectures of Japan were categorised into seven failure modes: a) leeward toe scour, b) crown armour failure, c) leeward armour failure, d) parapet wall failure, e) overturning, f) seaward toe scour, and g) sliding. Leeward toe scour was found to be the major failure mechanism in seawalls and dikes, and sliding was found to be the major failure mechanism in concrete breakwaters. The failure modes found throughout regions affected by the Indian Ocean Tsunami were categorised into five failure mechanisms: a) scouring of foundations, b) beam /column failure, c) joint failure, d) wall failure, and e) total disintegration. The 'total disintegration' caused by seismic forces, debris collision and hydrodynamic forces was the major failure mode throughout the studied regions. Some of the major tsunami induced forces found to have been among the causal factors of structural failure included hydrostatic and hydrodynamic forces. Flow velocities as high as 13.4 m/s were found in areas of Japan, and flow velocities of up to 10.4 m/s were found in regions affected by the 2004 Indian Ocean Tsunami. Potential strengthening measures were suggested for structures such as seawalls and coastal dikes, which were most vulnerable to scouring at the toe. By producing armoured components to protect the toe of the structures, they would become less susceptible to toe scour failure.

Extensive research has been carried out to predict bridge pier scour, with laboratory and field data, using different modelling techniques. This study introduces a new soft computing technique called gene expression programming (GEP) for pier scour depth prediction using field data. A functional relationship has been established using GEP and its performance is compared with other inductive modelling techniques such as artificial neural networks (ANNs) and conventional regression-based techniques. Field data comprising 370 data sets were collected from the published literature and divided into calibration and validation (testing) data sets. The performance of GEP was found to be satisfactory and encouraging when compared with regression and ANN models in predicting bridge pier scour depth.  GEP has the unique capability of providing a compact and explicit mathematical expression for computing bridge scour. This advantage of GEP over ANN is one of the main motivations for this work. The resulting GEP models add to the existing literature on artificial intelligence based inductive models that can be used effectively for bridge scour modelling.

Flow and scour characteristics are investigated experimentally on a modified roughened bed. The water surface profile is recorded at different sections. The paper investigated the effects of using curved steel sheets as roughness elements for strip and staggered arrangement, on different flow and scour characteristics. It was found that the apron of 90% staggered roughness length increases the relative energy loss by 17%, reduces the relative jump length by 19% and it decreases the relative jump depth by15.5% compared to the smooth bed. Generally, the experiments indicate that the case of staggered roughness elements gives the best relative jump characteristics. Moreover, it plays an important role to control the scour downstream the basin. The derived theoretical equations for relative depth and the relative energy loss give an acceptable agreement with the experimental data. Prediction equations were developed using the multiple linear regression (MLR) to model the hydraulic jump characteristics. A good agreement was obtained between the predicted and the measured values. Finally, this study yielded conclusions which can be recommended in the design procedure and practical applications. Les caractéristiques de débit et de l'affouillement sont étudiés expérimentalement sur un lit rugueuse modifié. Le profil de la surface de l'eau est enregistré à des sections différentes. Le document a étudié les effets de l'utilisation de tôles d'acier incurvées comme des éléments de rugosité de bande et la disposition en quinconce , sur le débit différent et caractéristiques de l'affouillement. Il a été constaté que le tablier de 90 % de la longueur de rugosité décalée augmente la perte relative d'énergie de 17%, réduit la longueur de saut relatif de 19% et il diminue la profondeur de saut relatif by15.5 % par rapport au lit lisse. En général, les expériences montrent que le cas des éléments de rugosité décalés donne les meilleures caractéristiques de saut relatif. En outre, il joue un rôle important pour contrôler l' affouillement en aval du bassin. Les équations théoriques dérivées de profondeur relative et la perte d'énergie par rapport donnent un accord acceptable avec les données expérimentales. Les équations de prédiction ont été développés en utilisant la régression linéaire multiple (MLR) pour modéliser les caractéristiques de ressaut. Un bon accord a été obtenu entre le prévu et les valeurs mesurées. Enfin, cette étude a abouti à des conclusions qui peuvent être recommandés dans la procédure de conception et d'applications pratiques. MOTS CLÉS: expérimentaux, théoriques , le débit , les caractéristiques de diarrhée , de la rugosité du lit.

The detailed structure of the 3-D flow (mean velocity, turbulence, and Reynolds stress components) in a scour hole formed by a plane jet is measured using a high resolution Acoustic Doppler Velocity Profiler (ADVP), which can simultaneously measure the profiles of quasi-instantaneous velocity components. The use of pulse-to-pulse coherent technique provides high spatial (O(6mm)), temporal (O(30Hz)) and velocity (O(1mms-1)) resolutions. The measurements reveal the importance of the apron on the behaviour of the jet and the structure of the flow. The proper orthogonal decomposition (POD) method is used to extract dynamically significant information on the large-scale coherent structures. 1.

Local scour downstream the box culverts outlet may cause to a complete failure of the culvert structure. New research is employed to reduce the max scour depth downstream the outlet of the box culvert under a dif erent flow conditions based on an experimental investigation. A sharp edge sill is proposed on a rigid bed to dissipate the flow excess energy. Consequently, a great reduction of the scour hole dimensions is obtained by using the sharp edge sill. The experimental study was carried out using a dif erent positions, heights and shapes of the sharp edge sill with dif erent flow rates as well as tail water depths too. The results indicates that the sharp edge sill is a promising tool to reduce the scour dimensions. The reduction of the scour depths by using the sharp edge sill are 60%, while the reduction in the scour depths are 64%,that is because of using of rigid apron of length 7 times the height of culvert, compared to previous results without rigid bed.

The determination of scour characteristics in the downstream of sluice gate is highly important for designing and protection of hydraulic structure. The applicability of modern data-intelligence technique known as extreme learning machine (ELM) to simulate scour characteristics has been examined in this study. Three major characteristics of scour hole in the downstream of a sluice gate, namely the length of scour hole (Ls), the maximum scour depth (Ds), and the position of maximum scour depth (Lsm), are modeled using different properties of the flow and bed material. The obtained results using ELM were compared with multivariate adaptive regression spline (MARS). The dimensional analysis technique was used to reduce the number of input variable to a smaller number of dimensionless groups and both the dimensional and non-dimensional variables were used to model the scour characteristics. The prediction performances of the developed models were examined using several statistical metrics. The results revealed that ELM can predict scour properties with much higher accuracy compared to MARS. The errors in prediction can be reduced in the range of 79%-81% using ELM models compared to MARS models. Better performance of the models was observed when dimensional variables were used as input. The result indicates that the use of ELM with non-dimensional data can provide high accuracy in modeling complex hydrological problems.

Failures barrages or parts of them may be expected when excessive scour patterns are observed downstream of such structures. Severe and excessive scour may be largely due to unsymmetric operation of gates especially when a multi-vents barrage or regulator is being considered. Previous investigations proved that the scour patterns downstream hydraulic structures are functions of the bottom velocities among other relevant factors such as Froude number, operation of gates, …. etc. In this paper, the results of an experimental investigation on the effects of operations of gates of mutlivents regulators on scour pattern are presented. The observed results on scour patterns are well explained in terms of bottom velocity patterns over the rigid bed upstream of the movable bed. The experimental program was carried under submerged flow conditions. Symmetric and unsymmetric operation of main gates and emergency gates are considered. An electromagnetic flow meter is used to measure the velocity components (in x and y directions) near bed at a predefined mesh over both the rigid bed and the movable bed. Both the pattern of the velocity vectors and the scour pattern for each run are plotted to qualitatively trace the interactive effects between the velocity pattern (relative magnitude and direction of the bottom velocity over the rigid bed) and the scour pattern (distribution of scour holes and the relative location of the maximum scour depth). It is observed that the scour pattern and hence the maximum depth of scour is a function of the bottom velocity pattern, operation of gates, type of gates (main or emergency), Froude number at the vena contracta, and submergence ratio. The qualitative and quantitative effects of all these parameters on the relative maximum scour depths are presented.

The determination of scour characteristics in the downstream of sluice gate is highly important for designing and protection of hydraulic structure. The applicability of modern data-intelligence technique known as extreme learning machine (ELM) to simulate scour characteristics has been examined in this study. Three major characteristics of scour hole in the downstream of a sluice gate, namely the length of scour hole (Ls), the maximum scour depth (Ds), and the position of maximum scour depth (Lsm), are modeled using different properties of the flow and bed material. The obtained results using ELM were compared with multivariate adaptive regression spline (MARS). The dimensional analysis technique was used to reduce the number of input variable to a smaller number of dimensionless groups and both the dimensional and non-dimensional variables were used to model the scour characteristics. The prediction performances of the developed models were examined using several statistical metri...

ABSTRACT One of the main challenges in the design and operation of offshore wind turbines arises from the uncertainty about maximum scour depth around their foundations. Scour action can lead to excessive excavation of the surrounding seabed and is being considered as a major risk for offshore wind farm developments. An ability to gather information concerning the evolution of scouring will enable the validation of models derived from laboratory-based studies, the assessment of different engineering designs and the development of improved scour countermeasure techniques. However, real-time scour data are not being collected due to a lack of available instrumentation techniques. This paper proposes a new scour monitoring technology for offshore wind turbine installations. The monitoring system consists of arrays of small capacitive scour probes installed around the foundation structure and linked to a wireless network to enable remote data acquisition. Based on this research, it is concluded that the sensor is capable of exhibiting high sensitivity to scour and sediment deposition processes for common sea floor mediums under different temperature conditions in saline water. The proposed monitoring system has considerable potential for field applications that will contribute to improving the resilience and sustainability of offshore structures.

The author of the original paper presents an interesting study to predict river pipeline scour using multivariate adaptive regression splines (MARS) technique. The subject matter is practical in river works (Azamathulla and Ghani 2010; Najafzadeh and Barani 2013). The author compared the results of MARS with multilayer perceptron (MLP) neural network and empirical formulas. He used the gamma test for the study of the most-important parameters on scour depth. While the results of the empirical formulas were far away from measured data, promising results were obtained using two approaches of the original paper. However, the discusser would like to add a few points.

A geoforensic analysis of Agba bridge, in Abakaliki, Ebonyi State was carried out using a combination of geotechnical, geophysical and hydrological techniques. The results indicate a highly geotechnically variable, partially weathered meta-sediments as foundation. The weathered profile as confirmed by VES indicated a much thicker weathered soft soil to the south-west. An initial shallow foundation for the South-West Abutment was thus inadequate, leading subsequently to sliding movement, which displaced the reinforced concrete piers. Hydrological analysis of the Agba river revealed critical flow velocities capable of generating local scour of up to 3.5m deep, that equally threaten stability of shallow pier foundation. Accordingly, bored piles extended to 15m have been recommended for the second half of the bridge to the south-west as a remedial measure to guaranty the stability of the structure.

Bridges are critical structures that require a substantial investment to construct and serve an important role in economic development. There is need to protect these assets by continuous monitoring, maintenance, proposing any required repair works. Al-Kufa bridge is an important and old structure in Al-Najaf city in Iraq, so computing and monitoring the scour around its piers is a significant thing to know if the bridge in safe from failure. HEC-RAS program was used, and from the collected data field measurements and laboratory results analysis, the maximum local scour depth around Al-Kufa bridge piers was evaluated. Where found that the computed scour depth from HEC-RAS program compares well with the observed value. It was found that the HEC-RAS model is a good tool for predicting local scour depth for bridge piers. And the study showed that the piers of Al-Kufa bridge are safe against the scouring in the present time.

Background and objectives: Many built structures in rivers have been destroyed or damaged due to lack of proper understanding of scouring. Therefore, predicting the maximum scour around structures in the river has a great importance. Groins widely are designed and constructed in order to river training in the country. This method, which is one of the most effective ways to stabilize the river banks are expanding day by day. In this research, bed deformation around permeable and close groins with different percentage of permeability was numerically simulated by using some of turbulence closure models. Then numerical simulation results were compared with experimental advantages.and at leastAnd, by using the best model of turbulence and calculating the transverse flow criteriaes created by the presence of a groin, the effect of the permeability of groine on the transverse flow power and the longitudinal distance in the downstream of which the continuity of the transverse flow continues is determined.
Materials and methods: In other to compare the obtained results from numerical simulation with laboratory advantages, laboratory results around close and permeable groins with 30, 50 and 70 percent of permeability in a flume were used.
The length of mentioned flume was 14m, the flume width and height’s was respectively 2 and 0.5m. The slope of its floor was near Zero. Discharge is 50 liters per second, and the average diameter of the bed materials is 0.26 mm and clear water conditions. For numerical modeling, Flow-3D software was used.
Results: The comparison of results of numerical simulation and experimental advantages shows that numerical simulation can predict the bed topography around permeable groins with different percentage of permeability and close groins in channel by live bed as well. In the following, the effect of permeability on power of vortices created around the permeable groins was studied. For this purpose, some criteria that demonstrate the power of secondary flows were computed. Then the changes and continuity of these criteria before and after the permeable groins with different permeability was studied. In the following the same criteria were predicted by ANN method and the advantages of ANN method was compared with results of numerical simulation method.
Conclusion: numerical simulation and especially Flow-3D software can predict the location and maximum scouring around impermeable and permeable groins with different percentage as well. And also the changes of power of secondary flow at the upstream and downstream of groin have a relation with percent of permeability of groin. The ANN results for predicting the criteria of power of secondary flow in different cross section and for different percent of permeable groin shows that this method also has good performance. The results for the calculated cross-flow criteria also indicate that the deviation of the flow by a groin can be roughly ignored with a permeability percentage of more than fifty percent, and for impermeable groin, cross flow continue to extend over 1.4 times the length of the groin.

Failures barrages or parts of them may be expected when excessive scour patterns are observed downstream of such structures. Severe and excessive scour may be largely due to unsymmetric operation of gates especially when a multi-vents barrage or regulator is being considered. Previous investigations proved that the scour patterns downstream hydraulic structures are functions of the bottom velocities among other relevant factors such as Froude number, operation of gates, …. etc. In this paper, the results of an experimental investigation on the effects of operations of gates of mutlivents regulators on scour pattern are presented. The observed results on scour patterns are well explained in terms of bottom velocity patterns over the rigid bed upstream of the movable bed. The experimental program was carried under submerged flow conditions. Symmetric and unsymmetric operation of main gates and emergency gates are considered. An electromagnetic flow meter is used to measure the velocity components (in x and y directions) near bed at a predefined mesh over both the rigid bed and the movable bed. Both the pattern of the velocity vectors and the scour pattern for each run are plotted to qualitatively trace the interactive effects between the velocity pattern (relative magnitude and direction of the bottom velocity over the rigid bed) and the scour pattern (distribution of scour holes and the relative location of the maximum scour depth). It is observed that the scour pattern and hence the maximum depth of scour is a function of the bottom velocity pattern, operation of gates, type of gates (main or emergency), Froude number at the vena contracta, and submergence ratio. The qualitative and quantitative effects of all these parameters on the relative maximum scour depths are presented.

... Negm, AM, Abdel-Aal, GM, Elfiky, MI and Mohamed, YA (2003a). “Modeling of Hydraulic Characteristics of Submerged Jump in Non-Prismatic Stilling Basins Using Artificial Neural Networks”. Proceedings of 6 th Int. Conf. ... B The width of gate openning. DS The max. scour depth. ...

The present work aims at presenting an approach on implementing appropriate mitigation measures for the upgrade of rubble mound breakwaters protecting harbors and/or marinas against increasing future marine hazards and related escalating exposure to downtime risks. This approach is based on the reliability analysis of the studied structure coupled with economic optimization techniques. It includes the construction of probability distribution functions for all the stochastic variables of the marine climate (waves, storm surges, and sea level rise) for present and future conditions, the suggestion of different mitigation options for upgrading, the construction of a fault tree providing a logical succession of all events that lead to port downtime for each alternative mitigation option, and conclusively, the testing of a large number of possible alternative geometries for each option. A single solution is selected from the total sample of acceptable geometries for each upgrading concep...

One of the most prevalent causes of bridge failure around the world is “scour” – the gradual erosion of soil around a bridge foundation due to fast-flowing water. A reliable technique for monitoring scour would help bridge engineers take timely countermeasures to safeguard against failure. Although vibration-based techniques for monitoring structural damage have had limited success, primarily due to insufficient sensitivity, these have tended to focus on the detection of local damage. High natural frequency sensitivity has recently been reported for scour damage. Previous experiments to investigate this have been limited as a result of the cost of full-scale testing and the fact that scaled-down soil-structure models tested outside a centrifuge do not adequately simulate full-scale behaviour. This paper describes the development of what is believed to be the first-ever centrifuge-testing programme to establish the sensitivity of bridge natural frequency to scour. A 1/60 scale model of a two-span integral bridge with 15 m spans was tested at varying levels of scour. For the fundamental mode of vibration, these tests found up to a 40% variation in natural frequency for 30% loss of embedment. Models of three other types of foundation, which represent a shallow pad foundation, a deep pile bent and a deep monopile, were also tested in the centrifuge at different scour levels. The shallow foundation model showed lower frequency sensitivity to scour than the deep foundation models. Another important finding is that the frequency sensitivity to “global scour” is slightly higher than the sensitivity to “local scour”, for all foundation types. The level of frequency sensitivity (3.1–44% per scour depth equivalent to 30% of embedment of scour) detected in this experiment demonstrates the potential for using natural frequency as an indicator of both local and global scour of bridges, particularly those with deep foundations.