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Scour of sediments around bridge foundations by the stream is the most significant contributing factor for bridge failures. The scour failures tend to occur without prior warning and have led to fatalities and economic loss every year. A significant amount of work has been conducted on bridge scour. Such efforts can be broadly classified into two major categories, namely science driven and engineering driven. The science-driven research focuses on understanding the scour mechanism and aims to explain the cause of scour due to different factors. Meanwhile, engineering-driven research focuses on the estimation, monitoring and countermeasures of bridge scour. This paper presents a comprehensive and up-to-date literature review of bridge scour research and practice. Firstly, a brief introduction is given which includes recent cases of failures caused by bridge scour. Then, both scientific and technical research on bridge scour is reviewed, which are categorized into four aspects: macroscopic and microscopic mechanism, scour depth prediction carried out by experimental and field data, direct and remote monitoring methods and active and passive countermeasures. Finally, a summary is provided covering both experimental and computational methods for scour research. Discussion is also provided on emerging ideas to investigate bridge scour from both science and engineering perspectives.

Bridge scour remains one of the leading causes of hydraulic failure in bridge foundations, posing severe economic and safety risks. Conventional countermeasures such as riprap may be costly, while Portland cement raises sustainability concerns. This study investigates the use of Alkaline-Activated Cement (AAC) as an innovative and eco-friendly stabilization method to determine the optimal extent of treated streambeds around cylindrical and rectangular piers, as well as wing-wall and vertical-wall abutments. Laboratory flume experiments were conducted under flow intensities of 0.75 and 0.9, with trial-and-error testing applied to establish effective protection geometries. Results show that with the AAC optimal extent found in each case, maximum scour depths reduced by 70–80% compared to untreated conditions and successfully shifted scour holes downstream without compromising stability. The findings highlight AAC-treated streambeds as a practical and sustainable countermeasure for bridge scour, while also underscoring the need for further research on the influence of flow angle of attack, Froude number, and live-bed conditions to refine design guidelines.

In this paper, experimental results of clear-water scour on a sand bed under short contractions were studied. Sequences of test runs were performed under clear-water conditions for three different contraction ratios. The outcomes of the experiments were employed to define the effects of various parameters on equilibrium scour depth under clear-water scour conditions. In this work, the precision of three maximum scour depth equations was tested from previous studies for contraction scour cases. Two new analytical equations were proposed to calculate time-dependent scour depth and maximum scour at equilibrium conditions, respectively, from the study. The proposed equations were validated using measurements from the present study as well as from previous literature, and the equations show a reasonable agreement between measured and computed values of scour depth under clear-water conditions in short contraction. The presented equations can be used for studying protection of the submerged portion at a bridge abutment or any similar structure.

Local scour of bridge piers is one of the main threats responsible for bridge damage. Adopting scour countermeasures to protect bridge foundations from scour has become an important issue for the design and maintenance of bridges located in erodible sediment beds. This paper focuses on the protective effect of one active countermeasure named an “anti-scour collar” on local scour around the commonly used cylindrical bridge pier. A cylindrical pier model was set up in a current flume. River sand with a median particle size of 0.324 mm was selected and used as the sediment in the basin. A live-bed scour experimental program was carried out to study the protective effect of an anti-scour collar by comparing the local scour at a cylindrical bridge pier model with and without collar. The effects of three design parameters including collar installation height, collar external diameter and collar protection range, on the scour depth and scour development were investigated parametrically. According to the experimental results, it can be concluded that: the application of an anti-scour collar alleviates the local scour at the pier effectively; and the protection effect decreases with an increase in the collar installation height, but increases with an increase in the collar external diameter and the protection range. Design suggestions for improving the scour protective effect of the anti-scour collar are summarized and of great practical guiding significance to the development of anti-scour collars for bridge piers.

Downstream scour at grade-control structures (GCSs) poses a serious threat to structural stability and riverbed integrity. Among various countermeasures, riprap has long been recognized as a cost-effective and readily available solution for scour protection. This research examines the role of riprap in reducing scour downstream of a vertical drop GCS, with emphasis on the influence of riprap thickness (T r /h, where h is structure height) and tailwater depth (y t /h). Experiments were conducted under clear-water conditions to monitor both the temporal and spatial development of scour and to establish new empirical relationships for normalized maximum scour depth (d s /h) and length (l s /h). The results show that riprap substantially reduces scour dimensions and accelerates stabilization. In the absence of protection, maximum scour depth reached up to 1.2 h under high discharges. Increasing riprap thickness to T r /h ≈ 0.5 reduced scour by nearly 70% and further increases to T r /h ≈ 0.66 achieved reductions exceeding 89%, with scour almost eliminated at low flows. Tailwater depth provided an additional stabilizing effect, reducing jet impact velocity and vortex intensity. Doubling the tailwater depth decreased scour by 20–30%, and when combined with thick riprap layers, reductions greater than 90% were achieved in both depth and length. The proposed empirical equations demonstrated strong predictive capability for both d s /h and l s /h, yielding R² values of 0.913 and 0.902, RMSE values of 0.107 and 0.405, and MAE values of 0.082 and 0.310, respectively. The sensitivity analysis further identified riprap thickness and tailwater depth as the most influential parameters governing the protective performance. These findings confirm the riprap effectiveness as a simple, economical, and robust strategy for mitigating downstream scour, offering valuable guidance for the hydraulics and geotechnical design of grade-control systems.

Recent studies have revealed that the frequency and magnitude of floods tend to increase due to climate change. Hence, excessive scouring due to flood events puts river bridges at greater risk of failure. This paper presents the initial findings of an experimental study to improve the understanding of the main characteristics of bridge pier scour under pressurized flow encountered during flooding. The experiments were carried out in four main groups according to two deck alignments with circular and oblong pier shapes. For each group of experiments, thirty-six tests were conducted under partially and fully pressurized flow conditions using four approach flow depths and three discharge values. The validity of the structured design approach for pier scour estimation implemented in the guidelines was investigated. The results showed that the bridge pier scour depths were up to 29.4% and 49.4% greater than the sum of the vertical contraction and local scour depths for 100 L/s for partially and fully pressurized flow conditions, respectively. However, as the discharge increased to 120 L/s, the bridge pier scour depth became 38.3% and 17.8% smaller than the sum of the vertical contraction and local scour depths for partially and fully pressurized flow, respectively. So, the structured design approach was determined to be safe for high discharge values. Furthermore, it was found that tests with a circular pier resulted in higher bridge pier scour depths than the sum of the vertical contraction and local scour depths up to 19.3% even for 120 L/s. Conversely, smaller bridge pier scour depths than the sum of the vertical contraction and local scour depths were observed up to 17.8% for tests with oblong piers. Thus, it can be concluded that the pier shape has a profound effect on scour holes and oblong piers cause smaller scour depths than circular piers in pressurized flow conditions. This study showed that the flow–pier–deck interaction significantly affects the depth and width of the scour hole, especially for small discharges and fully pressurized flow conditions.

Stepped spillways are considered one of the most significant energy-dissipating structures; however, the most complicated problem that threatens the overall stability of the spillway is local scour downstream of the stepped weirs due to hydraulic jumps in the skimming flow. In this study, a series of experiments were conducted under five discharges, three tail-water depths and two sediment sizes to investigate the scour downstream of a stepped spillway to reduce scour and increase the stability of hydraulic structure. Moreover, the optimal design of parameters, including type, crest and slope of chute, step height and type of stepped spillway flow, was determined considering the economic reasons and criteria that lead to more energy dissipation. Generally, the scour dimensions decreased as the sediment size and tail-water depth increased or the particle Froude number (Frd) and critical depth reduced. With the reduction in Frd, the relative scour depth, the relative distance of maximum scour depth and the relative scour length decreased by 68.6%, 75.6% and 73.4%, respectively. Empirical equations of regression analysis were developed to estimate scour depth compared to other studies. The final equations in this study can provide good estimates of the scouring parameters downstream of the stepped weir.

Many experiments were done over a relatively wide range of effective parameters to determine the stable size of riprap stones around wing-wall abutments. The experiments involved five sizes of riprap stones, three abutment lengths, and various flow depths and velocities. The results of this study indicate that in the range of tested parameters, the most important factors influencing riprap instability are the upstream Froude number, the ratio of abutment length to flow depth, and the ratio of abutment width (thickness) to flow depth. Based on the experimental results, a relation for designing the stable size of riprap around wing-wall abutments is presented and compared with previous equations developed for different shapes of bridge abutments.

Precise prediction of scour near the circular uniform pier may lead to the economic design of piers and avoid disastrous instances. Present study mainly deals with cohesionless sediment with gravel particles. Authors checked the three latest bridge pier scour models in this study. Three new relationships are proposed by authors for computing maximum scour depth, maximum scoured length and maximum effected scoured width in cohesionless sediment at equilibrium scour condition. Maximum scour depth equation is validated by the available literature data, and this relationship is applicable for both gravel as well as the sand bed. Graphically and statistically the new maximum scour depth relationship gives better agreements between observed and computed values of maximum scour depth. Relationships for maximum scoured length and maximum effected scoured width are only applicable for gravel and coarse sand bed and also gives better agreement with computed values.

Scouring around the bridge pier is a natural and complex phenomenon that results in bridge failure. Failure of bridges have potential devastation and public safety and economic loss, which lead to political consequences and environmental impacts. Therefore, it is essential to countermeasure the scour around the bridge pier. This paper studies the effects of four different airfoil-shaped collars (i.e., bc1 = 1.5b, bc2 = 2.0b, bc3 = 2.5b and bc4 = 3.0b, where bc and b are the diameter of the airfoil-shaped collar and pier, respectively) as a scour countermeasure. All the experiments are conducted under clear water conditions with uniform sediment and a constant water depth (y) of 10 cm. Airfoil-shaped collar is placed at four elevations, i.e., bed level, y/4, y/2 and 3y/4 above the sediment bed level. It is observed that the maximum percentages of scour reduction of 86, 100 and 100% occurred due to protection provided by the collar bc2, bc3 and bc4, respectively, at sediment bed level. So, collars bc2, bc3 and bc4 are efficient at the sediment bed level. The profiles of scour hole show that the length of the transverse scour hole is greater than that of the longitudinal one. Numerical investigation of the morphological changes in sediment bed and scour depth contours is developed using the FLOW-3D for the pier with and without the airfoil-shaped collar.