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This study introduces a new application of GMDH in the prediction of scour depth around a vertical pier. Two models of the GMDH network were developed using genetic programming and a back propagation algorithm. Genetic programming was performed in each neuron of the GMDH instead of performing the quadratic polynomial. In the second model of the GMDH, the quadratic polynomial was used in each neuron of the network as a transfer function, and a back propagation algorithm was used for training of the network. Six effective parameters including pier diameter, flow velocity, flow depth, medium diameter of bed material, standard deviation of bed grain size and fluid dynamic viscosity were considered for prediction of the scour depth. Results of two GMDH networks were compared with results of several traditional equations. From result performances, it was found that although GMDH-GP is very time-consuming and more complicated, this proposed method has provided a better prediction of scour depth than GMDH-BP in training and testing stages. A sensitivity analysis was performed for the GMDH-GP model and the results indicated that the ratio of pier diameter to flow depth is the most significant parameter regarding scour depth. In particular, the GMDH network proved very effective in comparison with traditional equations.

This article presents, for the first time, an investigation into the presence of rip currents along the southern coast of the Caspian Sea. The study site is selected at the Anzali port where 3 people were drowned in one day of summer 2007. Bathymetric surveys were obtained twice during the summers of 2008 and 2009 and rip currents were measured for two days in the summer of 2008 and the summer of 2009 with different wave conditions, using five GPS drifters. An RCM 9 current meter was installed in the rip channel for credibility of the drifter velocity. The cross-shore location of their velocity maxima and the distance they extend offshore are just two important unknowns. These questions were investigated using drifter trajectories. An oblique and a classic rip current were observed in two experiments. A field validation of the drifters shows that correspondence between the drifters and RCM 9 measurements is good.