S. Porbakhshian; M.R. Majdzadeh Tabatabaei; S.S. Mousavi; Sh. Mansouri
Abstract
Abstract
Morphological river models are designed to provide physical insight into the morphological response and to assist river engineers and managers in the design, operation and maintenance of river systems. Here deterministic modeling weak for a dynamic and stochastic of nature river environment. ...
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Abstract
Morphological river models are designed to provide physical insight into the morphological response and to assist river engineers and managers in the design, operation and maintenance of river systems. Here deterministic modeling weak for a dynamic and stochastic of nature river environment. Specially, these could not predict the exact shape of the river bed, Specially e.g. for braided river because the bed level variability and variations in cross-sectional. Since a stochastic model approach copes with the variability of system behavior of the time, therefore need for Stochastic modeling on the location of morphological changes in rivers and variations in river bed seems necessary. Many large rivers in the world have recently undergone through a great deal of morphological changes, Which has led to the development of local scouring, therefore, it has become an important problem for the river engineering. The change of river morphology is evaluated by braid parameter in braided rivers. A decrease in braid parameter results in a braided channel changes to meandering. As a result, local scouring process is accelerated. Since Process of the changes in river cross section are usually caused by change in water and sediment discharges or by river works. Moreover, river gradient plays a key role in channel morphological changes therefore In this research, local scouring relationship with river morphologic changes are investigated by stochastic modeling in braided rivers based upon for parameters such as maximum water, sediment discharges, river bed gradient river and bed elevation. The model was then tested by data obtained from Yahagi river in Japan. That the month Maximum Stream flow data is predicted by time series models (ARIMA) and three sediment transport equation were used to calculate the bedload such as Bagnold, Meyer-peter and Einstien Brown. predicted results show If calculate the bedload with the Bagnold equation, this model could predict significantly in cross-sectional and local scour depth, predict river morphological changes.
Keywords: Braided river, Local scouring, Stochastic modeling, ARIMA, Non linear variant regression
A. Danandehmehr; M.R. Majdzadeh Tabatabaei
Abstract
Abstract
Accurate prediction of river flow is one of the most important factors in surface water recourses management especially during floods and drought periods. In fact deriving a proper method for flow forecasting is an important challenge in water resources management and engineering. Although, ...
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Abstract
Accurate prediction of river flow is one of the most important factors in surface water recourses management especially during floods and drought periods. In fact deriving a proper method for flow forecasting is an important challenge in water resources management and engineering. Although, during recent decades, some black box models based on artificial neural networks (ANN), have been developed to overcome this problem and the accuracy privilege to common statistical methods (such as auto regression and moving average time series method) have been shown. However these types of models are implicit and complex in proper network design and can not be simply used by other investigators. In this research the genetic programming (GP) model has been developed as an explicit method for river flow prediction and has been used for investigation the effect of daily discharge trend in Absardeh river flow forecasting. The results have been compared with artificial neural network technique. The results indicated that the proposed GP method performed quite well compared to artificial neural network method and is applicable for river flow prediction.
Keywords: Daily discharge, Flow prediction, Genetic programming
M. Khezriyan; M.R. Majdzadeh Tabatabaei; S.S. Mousavi
Abstract
Abstract
The concept of armouring is used to discuss the coarse surface layer in rivers. Selective erosion in an alluvial channel reach for which there is no upstream sediment supply can lead to formation of a layer coarser than the under laying material. This phenomenon inhibits sediment transport ...
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Abstract
The concept of armouring is used to discuss the coarse surface layer in rivers. Selective erosion in an alluvial channel reach for which there is no upstream sediment supply can lead to formation of a layer coarser than the under laying material. This phenomenon inhibits sediment transport from the reach.Numerical modeling of armouring river bed, provides an approach to simulation of this phenomenon, however, these models are complicated in application. In addition, discretisation errors, affect the solution. Herein this paper, an analytical-based model has been developed; it is a simple one layer, 1-D, model to analysis different parameters in development of an armour layer, to predict depth of erosion and bed gradation curve of an armour bed. Differential equations describing armouring process, have been solved analytically, for each time step. The time steps are selected small enough to solve the equations analytically, for uniform flow, by avoiding discretisation errors.Predicted results are then compared by experimental data and numerical model results. This has shown reasonable validation of the model.
Keywords: Analytical model, Sediment transport, Armouring, Depth of erosion, Grain sizes
M.R. Pirestani; M.R. Tabatabai; N. Barkhordari
Abstract
Abstract
The diversion flow pattern is quite 3-D and nonuniform. In general, diversion flow occurs either naturally like streams or artificially like lateral intakes. According to the performed investigations the intake location affects the rate of diversion discharge and entry of sediments to the diversion ...
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Abstract
The diversion flow pattern is quite 3-D and nonuniform. In general, diversion flow occurs either naturally like streams or artificially like lateral intakes. According to the performed investigations the intake location affects the rate of diversion discharge and entry of sediments to the diversion channel. Since the main purpose of lateral intakes is to facilitate water transfer without sediments, and most rivers are zigzagged through their path, therefore, more research on the location of the lateral intake and its angle in the bending channels seems necessary. For this purpose, to determine the velocity and secondary flow fluctuations caused by hydraulic parameters changes in domain of lateral intakes with no diversion dam in winding channels a U-shaped flume with rectangular cross section was built. A straight channel with rectangular cross-section was used as a diversion channel. Based on the past researches, water intake was performed from the outer bend with 60˚ diversion angle at different locations (40˚, 75˚, 115˚) and with Froude numbers 0.27, 0.41, and 0.55, respectively. The obtained results of velocity distribution, secondary flow strength and radial flow momentum in a bend channel with diversion channel showed that the maximum variation of the above hydraulic parameters occur in the intake entrance.
Key words: Bend channel, lateral intake, Velocity distribution, Secondary flow
