Recent trends in local scour countermeasure for bridge piers

Bridge pier scour is a leading cause of hydraulic failure, threatening bridge stability worldwide, driven primarily by downflow and horseshoe vortex systems. This paper presents a systematic review of traditional, combined, and emerging countermeasure techniques developed to mitigate local pier scour. Peer-reviewed studies published between 1990 and 2025 were collected from major scientific databases and classified based on countermeasure type, hydraulic conditions, pier configuration, and validation level. Bed armoring measures such as riprap and gabions provide robust protection but are material-intensive, while flow-altering devices including submerged vanes, splitter plates, slots, collars, and sleeves modify near-bed hydraulics and typically achieve 40–80% scour reduction under controlled conditions. Combined systems, such as slot–collar and vane–collar configurations, demonstrate superior performance, with laboratory studies reporting near-complete scour suppression in optimized layouts. Recent eco-friendly and material-based innovations, including nano clay stabilization (up to 68% reduction), Cheng Kung Artificial Water Weeds (45.5% reduction), biocementation via MICP (>80% reduction in repeated treatments), roughening geometric elements, and ENRAN sheets offer lightweight and adaptable alternatives, though their field-scale applicability remains limited. The review further synthesizes recent findings on dual-pier interactions, showing that optimized collar configurations can effectively suppress vortex systems at both upstream and downstream piers, even under bed degradation. Overall, the study provides a critical comparative framework, identifies key limitations in existing research, and outlines future directions for developing resilient and practically deployable scour mitigation strategies.