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This paper comparatively investigates the capability of 10 solo and hybrid Data Driven Models (DDMs) in predicting the pier scour depth. These models include Support Vector Machine (SVM), Adaptive Neuro Fuzzy Inference System (ANFIS), Artificial Neural Network (ANN), Gene-Expression Programming (GEP), improved Group Method of Data Handling (GMDH1 and GMDH2) and two hybrid forms of GMDH in combination with Harmony Search (HS) and Shuffled Complex Evolutionary (SCE) algorithms (GMDH1-HS, GMDH1-SCE, GMDH2-HS, GMDH2-SCE), respectively. A large set of experimental data collected from the literature were used to evaluate the capability of applied models in prediction of bridge pier scour depth. The results of the developed DDMs were compared with two mathematical formulas of HEC-18 and HEC-I8- K4Mo. The performance of all utilized models was evaluated by statistical criteria of RMSE, MSRE, CE and R2. The results indicated that ANFIS was the superior model in terms of all statistical criteria in both training (CE = 0.969, RMSE = 0.038, MSRE = 0.049 and R2 = 0.971) and testing phases (CE = 0.986, RMSE = 0.036, MSRE = 0.011 and R2 = 0.985). GMDH2-SCE, ANN, GMDH2-HS, SVM and GEP were placed in the next ranks, respectively. This study recommends using DDMs, as powerful tools, for accurate prediction of pier scour depth. [ABSTRACT FROM AUTHOR]

This is the first attempt to study the effect of debris on the scour at side by side pier and abutment. A large set of experimental tests was carried out at the hydraulic laboratory of Shahid Bahonar University of Kerman, in a tilting flume with 10 m length, 0.8 m width and 0.5 m depth. Effect of debris shape, thickness, position, length, and the distance between abutment and pier was investigated. Results revealed that the main factor in deepening and developing of scour hole is the distance between pier and abutment, lp, by increasing the distance, the scour depth primarily increases and then decreases to eventually reach the scour depth at single pier. The observations indicated the significant effect of debris on dimensions of scour hole, for example, increasing the debris thickness and length increased the maximum scour depth up to 30 and 8%, respectively. Based on the measured data, some improvements were made on the existing equations and a set of new relations was presented to estimate the side by side pier and abutment scour depth. Flow and scour pattern at side by side pier and abutment were investigated. Effect of debris accumulation on the scour processes was studied. Based on the measured data, improvements were made on the previous equations. New relations were proposed to predict side by side pier-abutment scour depth. [ABSTRACT FROM AUTHOR]