Local scour at bridge foundations, particularly complex pier-abutment combinations, remains a leading cause of bridge failure worldwide, driven by intricate three-dimensional flow patterns and vortex interactions. This study employs an integrated numerical-experimental approach to investigate the turbulent flow field and scour mechanisms around a rectangular abutment with adjacent piers, assessing the influence of key geometric and hydraulic parameters. A three-dimensional CFD model using the RNG k-ε turbulence model was developed in FLOW-3D and rigorously validated against fixed-bed flume experiments, demonstrating high predictive accuracy for hydraulic parameters (R2 = 0.98, MAE = 0.003, and RMSE = 0.0057). The validated model analyzed six pier-abutment configurations, varying the pier-abutment gap \(\left( {{\text{}} 7.5{\text{ and }}30{\text{ cm}}} \right)\) and inter-pier spacing ( \(\left( {{\text{}} 10{\text{ and }}20{\text{ cm}}} \right)\) , to identify high-scour potential zones through detailed velocity analysis. Physical scour tests for the two most critical configurations under varying clear-water conditions \(\left( {{\text{u}}_{0} /{\text{u}}_{{{\text{cr}}}} = { }0.42 - 0.95} \right)\) confirmed the numerical predictions, showing a strong correlation between simulated hydrodynamic parameters and measured scour depths. Results establish that both geometric parameters and flow intensity significantly control scour severity. Increasing the flow intensity ratio from 0.42 to 0.95 amplified scour depth by 250–278% at the smallest pier-abutment gap \(\left( {{\text{}} 7.5{\text{ cm}}} \right)\) , demonstrating the compounding effect of close proximity and high flow intensity. Close proximity caused significant hydrodynamic interference, amplifying vortex strength regardless of flow intensity. Critically, scour is governed by the synergy between lateral flow deflection \(\left( {\text{v}} \right)\) and downflow \(\left( {\text{w}} \right)\) , rather than downflow magnitude alone. Increasing the distance to x = 30 cm reduced scour depth by approximately 30% by enabling flow separation and independent vortex development. This study conclusively demonstrates that maintaining a pier-abutment clearance exceeding 5–6 pier diameters is an effective scour countermeasure, particularly under high flow conditions, and provides a validated CFD framework for predictive scour assessment and optimized hydraulic design.
