Predicting temporal clear water scour depth around bridge piers with XGBoost and SVM–PSO approaches

ABSTRACT Scouring around a bridge pier involves removing sediment from the riverbed and banks due to water flow. This paper employs eXtreme Gradient Boosting (XGBoost) and support vector machine with particle swarm optimization (SVM-PSO) machine learning (ML) approaches to model the temporal local scour depth around bridge piers under clear water scouring (CWS) conditions. CWS datasets, incorporating bridge pier geometry, flow characteristics, and sediment properties, are collected from existing literature. Five non-dimensional influencing parameters, such as ratio of pier width to flow depth (b/y), ratio of approach mean velocity to critical velocity (V/Vc), ratio of mean sediment size to pier width (d50/b), Froude number (Fr), and standard deviation of sediment (σg), are chosen as input parameters. XGBoost and SVM-PSO ML models demonstrate superior predictive capabilities, achieving coefficient of determination (R2) values exceeding 0.90 and mean absolute percentage error (MAPE) and root mean square error (RMSE) values less than 17.07% and 0.0341, respectively. Comparison with the previous four empirical models based on statistical indices reveals that the proposed XGBoost model outperforms SVM-PSO and empirical models in predicting scour depth, so it is recommended for estimating clear water scour depth under varying temporal conditions within the specified dataset range.