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Erosion and scouring caused by the outflow jets of hydraulic structures is one of the most important topics in hydraulic engineering. In free overfall spillways, a water jet impacts the erodible downstream bed almost vertically and creates a scour hole. The scour hole can affect the safety and stability of the dam. In the present paper, the multivariate adaptive regression splines (MARS) approach has been adopted as a new soft computing tool for estimating the equilibrium scour depth below free overfall spillways. Using experimental data and dimensionless parameters, the MARS model has been developed to predict scour depth. Results obtained from the MARS approach were compared with those from the artificial neural network (ANN) and decision-tree algorithm. Statistical indicators demonstrated that the MARS approach had a good performance and presented competitive results, slightly better than ANN, for the prediction of this phenomenon.

ABSTRACT:In the present work, a numerical study was performed to analyze the flow behavior in a reservoir in the presence of strong vortices. A challenging subject in this study was the flow field in the reservoir and the mechanism of vortex formation. The numerical model was verified with the available theories and experimental data. Experiments were conducted in a reservoir in which strong vortices were formed over an intake. Measurements of the flow field were carried out with an Acoustic Doppler Velocimeter (ADV) for a constant intake submerged depth and two different intake Froude numbers. The agreement between numerical and experimental results for 3D velocity field was good. Finally, using the validated numerical results, the flow behavior in the reservoir was analyzed. A funnel shape flow pattern was recognized in the reservoir toward the intake and its boundaries were identified. Another flow pattern observed was a spiral vortex motion from the water surface towards the intake. The present paper intends to make a deep understanding of flow field in a reservoir due to water withdrawal.

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The velocity field in a reservoir in the presence of surface vortices was experimentally studied. Experiments were performed with a horizontal intake and with a constant submerged depth and two different intake Froude numbers.The spline smoothing method was used to improve the graphical presentation of the measured data. Results are presented and compared in different horizontal sections in the reservoir. A downward conical flow over the intake axis and an upward one below the intake axis were observed in the reservoir. Finally, the prevailing domains of vertical and horizontal velocities were determined.

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