Development of a Semiempirical Model for Transient Scour Depth Prediction around Bridge Piers in Clear Water Conditions

Building on previous research that underscored the influence of the bridge pier shape and angle of attack on scour depth, this study further investigates their effects on both time-dependent transient scour and equilibrium scour depth. The findings reveal that adding a nose element to square piers significantly reduces scour depth. Specifically, a triangular nose on a rectangular pier with an aspect ratio (L/D=9, where L is length and D is width of pier) resulted in the most substantial reduction, reducing the maximum scour depth by up to 80% relative to the benchmark model in clear-water conditions with uniform sediment (d50=1.2 mm) and a flow intensity ratio of V/Vc=0.96. Using extensive experimental data obtained in clear-water conditions, a semiempirical model was developed to predict time-dependent scour depth. Sensitivity analysis revealed that among all considered parameters, the Froude number, Fr, had the greatest influence on scour depth prediction, followed by the pier shape correction factor, KSh, and the angle of attack correction factor, Kθ, which exhibited nearly similar levels of sensitivity, highlighting their critical importance in accurately representing the effects of pier geometry and flow alignment. Compared to the existing models evaluated, the proposed model demonstrated improved performance in predicting scour depth, with NSE=0.86 and RMSE=0.033.