Abstract
The main aims and contributions of the present paper are to use new soft computing methods for the simulation of scour geometry (depth/height and locations) in a comparative framework. Five models were used for the prediction of the dimension and location of the scour pit. The five developed models in this study are multilayer perceptron (MLP) neural network, radial basis functions (RBF) neural network, adaptive neuro fuzzy inference systems (ANFIS), multiple linear regression (MLR), and multiple non-linear regression (MNLR) in comparison with empirical equations. Four non-dimensional geometry parameters of scour hole shape are predicted by these models including the maximum scour depth (S), the distance of S from the weir (XS), the maximum height of downstream deposited sediments (hd), and distance of hd from the weir (XD). The best results over train data derived for XS/Z and hd/Z by the MLP model with R2 are 0.95 and 0.96 respectively; the best predictions for S/Z and XD/Z are from the ANFIS model with R2 0.91 and 0.96 respectively. The results indicate that the application of MLP and ANFIS results in the accurate prediction of scour geometry for the designing of stable grade control structures in alluvial irrigation channels.
Highlights
Grade control structures are commonly used in irrigation channels for regulating water level, supplying required head upstream of weirs, measuring flow rate, enhancing water quality by reducing erosion, and preventing degradation in a bed channel of alluvial materials (Najafzadeh, 2015)
The results indicated that the application of multilayer perceptron (MLP) and adaptive neuro fuzzy inference systems (ANFIS) results in the accurate prediction of scour geometry for the designing of stable grade control structures in alluvial irrigation channels
The ability to accurately estimate the whole geometry of scour holes downstream of grade control structures is important for developing irrigation regulation structures
Summary
Grade control structures are commonly used in irrigation channels for regulating water level, supplying required head upstream of weirs, measuring flow rate, enhancing water quality by reducing erosion, and preventing degradation in a bed channel of alluvial materials (Najafzadeh, 2015). Water flowing from the top crest of the weir (as one of the grade control structures) creates a vortex and increases flow velocity downstream of hydraulic structures that result in local scour (Mohammadpour, 2017; Sarkar & Dey, 2004). Local scour creates holes downstream of a weir and its dimensions increase gradually and become unbalanced, which causes the failure of the hydraulic structures or weir (Goel & Pal, 2009). There are various hydraulic and geotechnical factors that have an effect on the local scour downstream of water level adjusting structures in erodible beds.
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