Introduction

Bridge pier scour is recognized as one of the most significant hydraulic challenges in the design, operation, and maintenance of bridge structures. It arises from the complex interplay between flow dynamics, alluvial bed characteristics, and pier geometry. Scour occurs when alterations in flow patterns and increased bed shear stress lead to sediment erosion, ultimately compromising structural stability. In recent decades, the growing body of research on localized pier scour underscores its critical importance in mitigating both structural and environmental risks. Despite considerable advancements in numerical, experimental, and analytical modeling, significant uncertainties persist in predicting scour depth and extent. This study aims to provide a comprehensive review of the physical mechanisms governing scour, identify key influencing factors, and evaluate both structural and non-structural mitigation strategies. By examining flow behavior around piers, sediment characteristics, and the application of numerical and artificial intelligence models, this research establishes a scientific framework for scour prediction, management, and mitigation, thereby enhancing the safety and longevity of bridge infrastructure under variable hydrological conditions.

Materials and Methods

• This article employs a systematic review and analytical approach to examine bridge pier scour from the perspectives of physical mechanisms, influencing parameters, and mitigation strategies. Initially, the theoretical foundations and classifications of scour types—including general, local, and combined scour—were synthesized from peer-reviewed literature. Subsequently, flow patterns around piers were analyzed using experimental data and numerical simulations (CFD and two-phase models) to elucidate the formation of vortices, wake currents, and flow separation zones. The influence of hydraulic parameters (e.g., flow velocity, water depth, Froude number) and sediment properties (e.g., density, grain size, cohesion) was evaluated through a comprehensive review and categorization of empirical data from prior studies. In the second phase, scour mitigation techniques were compared across two primary categories: “bed armoring” (e.g., riprap, gabions, and articulated concrete block mats) and “flow alteration measures” (e.g., collars, sacrificial piles, and submerged vanes). These approaches were assessed based on hydraulic efficiency, implementation cost, and long-term durability. Scour prediction methodologies—including empirical equations, single-phase and two-phase CFD models, Smoothed Particle Hydrodynamics (SPH), and machine learning algorithms—were comparatively evaluated to determine their accuracy, advantages, and limitations. Additionally, global case studies were reviewed to assess climatic and geomorphological impacts on scour behavior. The review follows a structured methodological framework comprising the following stages:

• Literature Collection and Screening: Relevant studies were retrieved from reputable scientific databases (e.g., Scopus, Web of Science) using targeted keywords and filtered according to predefined inclusion criteria.

• Thematic Classification: Extracted literature was categorized into core themes: flow dynamics, influencing factors, mitigation strategies, predictive modeling, and future research directions.

• Synthesis and Critical Analysis: Findings from diverse studies were analyzed to identify consensus, discrepancies, and overarching trends, which were then integrated into the article’s conceptual framework.

• Comparative Evaluation: Mitigation and modeling techniques were benchmarked against key parameters, including efficiency, cost-effectiveness, structural stability, and environmental impact.

• Identification of Research Gaps: The final section outlines critical knowledge gaps and future research needs, providing a forward-looking perspective on the field.



Results and Discussions

A comprehensive analysis of bridge pier scour mitigation techniques reveals that no single measure can entirely eliminate scour. However, a strategically selected combination of methods, tailored to site-specific hydraulic conditions, sediment characteristics, and economic constraints, can substantially reduce maximum scour depth. Integrating flow alteration techniques with bed armoring proves to be the most effective strategy. Among bed armoring solutions, riprap—particularly when installed in sloped configurations—can achieve scour reductions exceeding 80%. Articulated concrete blocks and gabions also serve as viable alternatives, albeit with certain design and maintenance limitations. In the category of flow alteration measures, submerged vanes have demonstrated scour depth reductions approaching 88%, while slots achieve reductions of 30–40%, depending on their geometric configuration. Sacrificial piles, despite requiring periodic replacement, can reduce scour depth by up to 50%. The efficacy of collars is highly geometry-dependent: conventional collars exhibit limited performance, whereas modified designs incorporating fins, hooks, or polygonal shapes yield reductions of 50–73%. Advanced configurations, such as lenticular or airfoil collars, show highly variable effectiveness contingent upon specific design parameters. Pervious collars, which guide flow through controlled permeability, achieve approximately 78% scour reduction. Furthermore, bed regulation structures like sills and curved plates dissipate incoming flow energy, resulting in 30–55% reductions and enhancing cross-sectional stability. Ultimately, the synergistic integration of flow alteration and bed armoring techniques represents the optimal mitigation approach. Optimal design must account for local hydraulic conditions, sediment properties, flow intensity, and maintenance requirements to ensure both scour control and long-term structural and economic viability.

In terms of predictive modeling, comparative analysis indicates that two-phase CFD models, particularly those utilizing an Eulerian–Lagrangian framework, offer superior accuracy in simulating scour initiation and evolution, despite higher computational demands. The SPH method has also demonstrated enhanced capability in capturing complex vortex dynamics compared to conventional grid-based approaches. Meanwhile, machine learning models—such as artificial neural networks and random forest algorithms—trained on extensive experimental datasets, exhibit strong potential for rapid, real-time scour depth estimation in practical engineering applications.

Conclusion

Bridge pier scour is a complex, multi-factorial phenomenon driven by the dynamic interaction between flow hydrodynamics, pier geometry, and bed sediment properties. The integration of advanced numerical modeling, data-driven predictive tools, and site-specific mitigation strategies enables effective scour management in bridge engineering. Developing a systematic framework for selecting countermeasures—based on hydraulic performance, long-term stability, and cost-effectiveness—represents a critical step toward enhancing the safety, durability, and environmental resilience of bridge infrastructure. Future research should prioritize investigating bridge vulnerability under climate change scenarios and extreme flood events to improve adaptive design practices.