Influential parameters on submerged discharge capacity of converging ogee spillways based on experimental study and machine learning-based modeling Kiyoumars Roushangar, Ali Foroudi and Mojtaba Saneie ABSTRACT Ogee spillways with converging training walls are applied to lower the hazard of accidental flooding in locations with limited construction operations due to their unique structure. Hence, this type of structure is proposed as an emergency spillway. The present study aimed at experimental and machine learning-based modeling of the submerged discharge capacity of the converging ogee spillway. Two experimental models of Germi-Chay dam spillway were utilized: one model having a curve axis which was made in 1:50 scale and the other with a straight axis in 1:75 scale. Using visual observation, it was found that the total upstream head, the submergence degree, the ogee-crest geometries and the convergence angle of training walls are the crucial factors which alter the submerged discharge capacity of the converging ogee spillway. Furthermore, two machine-learning techniques (e.g. artificial neural networks and gene expression programming) were applied for modeling the submerged discharge capacity applying experimental data. These models were compared with four well-known traditional relationships with respect to their basic theoretical concept. The obtained results indicated that the length ratio (L2=(L 0 :Lch)) had the most effective role in estimating the submerged discharge capacity. Kiyoumars Roushangar (corresponding author) Ali Foroudi Department of Civil Engineering, University of Tabriz, Tabriz, Iran E-mail: kroshangar@yahoo.com Mojtaba Saneie Hydraulic Structures, Soil Conservation and Watershed Management Research Institute (SCWMRI), Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran Key words | ANN, artificial neural network, converging ogee spillway, gene expression programing, GEP, submerged discharge capacity INTRODUCTION Accidental flooding of an overflow control structure during large discharge incidents is a common concern. A spillway is a hydraulic structure and a major part of a dam for dispos- ing of flood flows. Dissipation of energy over the spillway usually happens by: (i) a standard stilling basin downstream of the spillway to dissipate energy of flow by forming a hydraulic jump (large amount); (ii) a high velocity water jet taking off from a flip bucket and entering into a down- stream plunge pool; and (iii) the construction of steps on the spillway to assist in energy dissipation (Li et al. ; Roushangar et al. ). One of the most common and effective spillways which can pass significant flow with considerably moderate/low construction cost is an ogee spillway. The ogee spillway has a control weir that is ogee shaped (‘S’ shaped) in profile. The upper curve of the ogee spillway ordinarily conforms closely to the profile of the lower nappe of a ventilated sheet falling from a sharp-crested weir. Flow over the crest adheres to the face of the profile by preventing access of air to the underside of the sheet. For discharges at designed head, the flow glides over the crest with no interference from the boundary surface and attains near maximum 474 © IWA Publishing 2019 Journal of Hydroinformatics | 21.3 | 2019 doi: 10.2166/hydro.2019.120 Downloaded from https://iwaponline.com/jh/article-pdf/21/3/474/566407/jh0210474.pdf by guest on 04 June 2020