Search

The computation of total flow in a flooded river is very crucial work in designing economical flood defense schemes and drainage systems. Further, under non-uniform flow conditions like in converging and diverging compound channel, the traditional methods provide poor results with high errors. The analytical methods require the system of nonlinear equations to be solved, which is very complex. So, mathematical models that prompt in taking care of a complex system of problems are solved here through an artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS). By utilizing ANN and ANFIS, an attempt is made to predict the discharge in converging and diverging compound channels. In the analysis, the most influencing dimensionless parameters such as friction factor ratio, area ratio, hydraulic radius ratio, bed slope, width ratio, relative flow depth, angle of converging or diverging, relative longitudinal distance, and flow aspect ratio are taken into consideration for computation of discharge. Gamma test and M-test have been performed to achieve the best combinations of input parameters and training length respectively. The significant input parameters that influence the discharge are found to be friction factor ratio, hydraulic radius ratio, relative flow depth, and bed slope. A suitable performance is achieved by the ANFIS model as compared to ANN model with a high coefficient of determination of 0.86 and low root mean square error of 0.005 in predicting the discharge of non-prismatic compound channels taken under consideration.

A model for stage–discharge relationship in two-stage wide meandering channels, devised by statistical analysis of new experimental boundary shear data and some published shear data, is presented. ...

Most open channel flows are generally unsteady in nature. Very few studies have been carried out in the past to investigate the turbulence characteristics in unsteady open channel flows over a roug...

In compound channels, much of the hydraulic resistance may be assigned by channel and floodplain geometry and bed roughness. Understanding the distribution of flow in the subsections of a compound river channel is a tedious work due to complex momentum transfer at the junction. The zonal discharges are mostly dependent upon the hydraulic resistance of the corresponding subsections. Hence, different experimentations in laboratory channels are required to be investigated by analyzing the dependence of momentum transfer on individual flow capacities of the subsections. So, experiments are performed in non-homogeneous roughness beds of asymmetric compound channels to examine the flow behavior. Total 272 numbers of experimental data sets comprising wide ranges of width ratio, relative flow depth, aspect ratio and roughness ratio with the present experimental data series are used for both training and validation of the model. Previous models can provide good results only for specific ranges of independent parameters whereas the back propagation of artificial neural network (BPNN) model is capable of performing well for the global ranges of independent parameters. This is because BPNN is able to perform the nonlinear mapping between the dependent and independent variables during the training. The efficacy of the models is verified with the standard statistical error analysis for the data sets. The BPNN model is found to perform well as compared to other researcher’s models.

Due to the exchange of momentum at the junction between the main channel and floodplain, the prediction of stage discharge relationship in a compound channel is not an easy task as in simple channel. Despite the availability of 2D and 3D flow models, 1D flow models are rather preferred for its fewer data requirements, easy access and shorter processing time. As a substitute, a simple 1D methodology is proposed here which includes effects due to lateral momentum transfer at junction by introducing a momentum transfer coefficient between the adjacent compartments. The model estimates the individual flow carried by the two compartments of an asymmetric compound channel considering the percentage boundary shear force distribution as an input parameters. The boundary shear force carried by floodplain is parameterized in terms of the channel dimensions, flow depth and roughness characteristics. The resulting average flow velocities in sub-sections and momentum transfer coefficient at junction are determined from a set of physics based equations. Utilizing the outputs, the quantification of momentum exchange in terms of apparent shear force is achieved by the difference between main channel and floodplain flow velocities along with this momentum transfer coefficient. Experiments are undertaken to investigate the asymmetric geometry in flow distribution of a compound channel. The performance of the method in calculating overall discharges competes well with previous investigators models, seven traditional methods and Conveyance estimation system (CES). The new model and its corollary are tested for their validity against the experimental channels and also found to predict the discharge well in real world application.

Discharge estimation in rivers is the most important parameter in flood management. Predicting discharge in the converging and diverging compound open channel by analytical approach leads to solvin...

The study establishes different analytical model for velocity distribution, boundary shear stress, stage–discharge curves and their application to the trapezoidal compound channel. The analytical s...

This paper presents a new methodology to predict the depth-averaged velocity along the lateral direction in an open channel flow. The novelty of this work is to determine the point velocity and estimate the discharge capacity by knowing the geometrical parameters at a section of an open channel flow. Experimental investigations have been undertaken in trapezoidal and rectangular channels to observe the variation of local velocities along both the vertical and transverse directions at testing sections. For different geometry, hydraulic and roughness conditions, the measurements are taken for several flow conditions. Multi-variable regression analysis has been adopted to develop five models to predict the point velocities in terms of non-dimensional geometric and flow parameters at any desired location. The present method is favourably compared with the analytical method of Shiono and Knight with reasonable accuracy. The performance of mathematical model is also validated with two natural river data sets. Further, statistical error analysis is carried out to know the degree of accuracy of the present models.

In the present investigation, the roughness characteristics of the gravel bed is tested and modelled for the no-load condition. A straight trapezoidal channel having gravel bed surface of grain siz...

Gravel bed flow is so generic condition that its study becomes fascinating as well as critical to apprehend flow characteristic. In this particular study, no bed load movement was maintained using grains of 13.5 mm (D₅₀ value) characterised as no load condition. Depth Average Velocity (DAV) and the Boundary Shear Stress (BSS) has been experimentally estimated for five different depths for the prevailing no load condition. Furthermore, the distribution of streamwise depth-averaged velocity and boundary shear stress at different flow depths of gravel bed are also calculated using different hydraulic software packages such as CES & ANSYS FLUENT. These numerical simulation results have shown reasonably good agreement with experimental data over main channel in inbank flow. Finally, results obtained are corroborated through error analysis. The overall idea of this study was to understand flow characteristic and behaviour of gravel bed having inbank flow through experimental and numerical simulation techniques.

Prediction of boundary shear force distributions in open channel flow is crucial in many critical engineering problems such as channel design, calculation of losses and sedimentation. During floods, part of the discharge of a river is carried by the simple main channel and the rest is carried by the floodplains. For such compound channels, the flow structure becomes complicated due to the transfer of momentum between the deep main channel and the adjoining floodplains. The complexity further increases when dealing with a compound channel with non-prismatic floodplains. Knowledge of momentum transfer at the different interfaces originating from the junction between the main channel and floodplain can be acquired from the distribution of boundary shear in the subsections. The calculation of boundary shear and depth average velocity in non-prismatic compound channel flow is more complex and simple conventional approaches cannot predict the boundary shear and depth average velocity with sufficient accuracy. Hence, in this area, an easily implementable technique, the Artificial Neural Network can be used for predicting the boundary shear and depth average velocity at different sections of a converging compound channel for different geometry and flow conditions. The model’s performance has lead satisfactory results. Statistical error analysis is also carried out to know the degree of accuracy of the model.

Accurate prediction of Manning’s roughness coefficient is essential for the computation of conveyance capacity in open channels. There are various factors affecting the roughness coefficient in a meandering compound channel and not just the bed material. The factors, geometric as well as hydraulic, are investigated and incorporated in the prediction of Manning’s n. In this study, a new and accurate technique, gene expression programming (GEP) is used to estimate Manning’s n. The estimated value of Manning’s n is used in the evaluation of the conveyance capacity of meandering compound channels. Existing methods on conveyance estimation are assessed to carry out a comparison between them and the proposed GEP model. Results show that the discharge capacity computed by the new model provides far better results than the traditional models. The developed GEP model is validated with three individual sections of a natural river, signifying that the model can be applied to field study of rivers, within the stated range of parameters.

Water surface profile prediction is an important task in flood risk management in the urban area. In the present research, based on the principle of the momentum balance a numerical method is investigated to predict the water surface elevations in compound channels with converging floodplains. Experimental data series are collected from literature on converging compound channels for different geometry and flow conditions to test the present model. The developed method requires the percentage of flow in the main channel. To deal with it, various existing flow distributions model is used in the developed numerical method to estimate the water surface elevation. The flow distribution model which provides less error in water surface profile computation for converging part of the compound channel is selected. Finite difference method is used to solve the numerical model using MATLAB tool. The results obtained from the simulation show a good agreement with the experimental datasets. Statistical error analysis has been performed to verify the strength of the present model and the other prevailing water surface profile models. The present model found to provide the minimum error in terms of mean absolute error, mean absolute percentage error and root mean square error.

There is always an exchange of momentum between the deep main channel and its shallow floodplains of a compound channel section. When rivers have single side floodplains, they are known as asymmetr...

Gravel bed can be categorised into three bed load conditions, i.e. no load, moderate and intense. An experimental investigation was carried out in an open channel flow with gravel bed surface of gr...

In overbank flow due to the interaction mechanism between the main channel and floodplain, the flow property of the compound sections gets affected. The complexity is more when the compound channels have non-prismatic floodplains. Additional complexity occurs during the interaction between the subsections as well as due to non-uniformity of flow through converging parts of the compound channel. For prediction of flow, calculation of energy loss parameters from section to section is an important task for river engineers. In this paper, an experimental investigation for the energy losses of converging compound channels for different flow depths along the converging path is performed. The loss of energy due to contraction and compound geometry for a compound channel is evaluated, and the dependency of energy loss for such channels is analyzed. A generalized multivariable regression model has been developed to predict the energy slope with high accuracy. Using the expression of the energy loss concept, the discharge capacity in the converging compound is found to provide good results as compared to other standard model exists in the literature.

Factors affecting roughness coefficient in a meandering compound channel are investigated and used to predict Manning’s roughness by dimensional analysis. Factors affecting Manning’s roughness, are considered to be geometric as well as hydraulic, namely relative depth of flow, width ratio, bed slope and sinuosity for a meandering compound channel. An experimental investigation was carried out for the highly meandering channel of sinuosity 4.11. Observations of various researchers, on the laboratory study of meandering channels have also been used in the investigation. The proposed equation for predicting composite Manning’s roughness is used to estimate the conveyance of a channel with floodplain flow. The proposed dimensional analysis model is observed to predict the conveyance capacity better than other existing methods of Manning’s n prediction.

The faster flowing main channel water and the slower flowing flood plain water induce a strong shear layer at the junction of a compound channel. Due to intense interaction at the junction between main channel and flood plain, the prediction of the flow parameters become complex particularly in shear layer regions. So, the current analysis presents an improved method to Reynolds averaged Navier–Stokes equation for predicting depth averaged velocity for a compound open channel. The new approximation includes the dispersion and transverse convection components in the secondary flow term of the governing equation. Independent calibrating coefficients are chosen for main channel, side slope, and flood plain regions. Further, an attempt has been taken to quantify the Reynolds shear stress term by introducing a new factor for shear layer regions of the compound channel. The approach is examined through the experimental data sets. For both homogenous and non-homogenous compound channels, the new approach...

Flow modeling in rivers during flood is a complex matter as two-phase geometry occurs normally called as compound channels. Rivers with two equal adjoining flood plains are referred to as symmetric otherwise, they are known as unsymmetrical compound channels. The interaction technique at shear layer induces complex flow phenomenon, indeed due to the higher velocity in the main channel than the flood plain. Present work focuses on predicting the flow and its distribution in an unsymmetrical compound channel as it emulates a natural river. The hydraulic resistance of an unsymmetrical compound channel is attributed by sub-sectional geometry, boundary roughness and flow characteristics. As channel conveyance is influenced by boundary friction along the periphery of the compound channel which manifests the resistance to flow. So, two improved expressions are proposed depending on geometric, roughness and hydraulic parameters to predict boundary shear distribution in each sub-compartments. Further, the ...

When a river overflows, either side of its flood plain during flood is named as asymmetric compound channel; however, if two adjacent flood plains are inundated, it is called as symmetric compound channel. Due to the complex flow mechanism at the junction between main channel and flood plain, modeling of depth-averaged velocity and boundary shear stress in an asymmetric compound channels becomes an exigent task. The analytical solution of the Shiono and Knight Method accounts three governing parameters, i.e., lateral shear, bed friction and secondary flows for prediction of these flow variables. In order to investigate the influence of these governing coefficients on flow parameters, experiments were employed in asymmetric compound channels. Variation of boundary shear stress and depth-averaged velocity across the channel was investigated. Some experimental data sets from large flood channel facility and from measurements taken by other researchers have also been used in this study. The variation of three calibrating coefficients, i.e., eddy viscosity coefficient (\(\lambda \)), friction factor (f) and secondary flow coefficient (k) against the geometric and hydraulic parameters, has been studied. Expressions for secondary flow coefficients in terms of hydraulic and flow parameters have been procured for different panels which are required to get the distribution of boundary shear and depth-averaged velocity. The performance of the models has been successfully proved for experimental channels and natural river data sets.

In prismatic compound channels, the water level remains uniform throughout the length of the channel. But in case of non-prismatic compound channels, the flow becomes non-uniform and complex. This paper examines the use of Lateral Distribution Method (LDM) and its modifications in the computation of depth-averaged velocity and boundary shear stress distribution in a compound channel for both prismatic and non-prismatic floodplains. The modification of LDM has been done considering the friction slope and secondary current effect. Finite difference scheme has been used for discretizing the Modified LDM using MATLAB tool. For the present study, different prismatic and non-prismatic compound channels having converging flood plains have been considered to evaluate the strength of Modified LDM over other numerical approaches like LDM and Conveyance and Afflux Estimation system.

Study of interaction mechanism in compound channels consisting of main channel with adjoining floodplains is very important for environmental, ecological and design issues. The flow structures at junction between main channel and floodplain are rigorous due to the complex exchange of momentum. It leads to the imprecise quantification of the discharge in compound channel. Many investigators have proposed various discharge prediction methods among which divided channel method is widely acceptable. This current study approaches a simple way to predict discharge in a compound channel by incorporating an interacting length at the interface between the main channel and adjoining flood plains. From the experimental results of NITR channel data and Flood Channel Facility of UK data, the interacting lengths have been estimated for different combinations of flow depths and width ratios. The functional relationships of the interacting length with the non-dimensional hydraulic and geometric parameters have be...

Total resistance of a compound channel may be ascribed to channel roughness, geometry and flow characteristics and is exhibited in the form of tangential stress from point to point along the periphery, known as boundary shear stress. This paper reports the boundary shear stress distribution of compound channels with asymmetric flood plains. Due to the scarcity of data sets in asymmetric compound channel as evident from the previous literatures, wide ranges of data sets have been generated by application of SKM. New expression for predicting boundary shear distribution is found to give better results as compared to other models. Using the new expression, a modified flow prediction approach in a two-stage asymmetric compound channel has been presented. The approach has been tested with asymmetric flood channel facility experimental data, other investigators data and with natural river data sets. The efficacy of the model has been proved from the error analysis.

The complexity of transfer of momentum between the main channel and flood plain in a compound channel can be tackled through the analytical solution of Shiono and Knight Method. Solution of this approach counts on the calibration of three indispensable parameters i.e., secondary currents, eddy viscosity coefficient and bottom friction. Due to uniqueness of these parameters, the boundary friction factor changes unevenly throughout the lateral direction especially at the shear layer region. In this paper, the analytical solution eventuating in the Shiono Knight Method is solved considering a new panel of shear layer width at the junction. Reliable experimental measurements are employed for quantification of shear layer width and to procure the new calibrating coefficients for secondary flow and friction factor for the proposed panels. The model is found to provide satisfactory results when applied to experimental, FCF channels and natural river data sets.

A multivariable regression model has been developed to predict the water surface profile for different compound channels with the non-prismatic flood plain. The nonlinear regression models are developed using relevant experimental data obtained from laboratory experiments. Three sets of laboratory experiments were carried out to exhibit the overbank flow in converging flood plains. The water surface profiles flow measurement was then related to various dimensionless parameters such as converging angle, width ratio and relative distance to develop the model. The results of calculations of water surface profile from the present model show good agreement with the observed data and data of other researchers. Several statistically based analyses were performed to verify the reliability of the developed multivariable regression model.

The complexity of two-dimensional SKM model is to calibrate the three governing parameters (bed friction f, eddy viscosity coefficient λ or turbulent friction and secondary flow Г) before it can be applied to predict the depth-averaged velocity in an open channel flow. To quantify the secondary current, the factor k needs to be calibrated from reliable data-sets. The roughness parameter f is considered from the surface properties of the channel, whereas the eddy viscosity parameter λ is generally taken to be constant value. A computer program has been developed to solve the two-dimensional SKM model analytically so as to simulate the depth-averaged velocities from point to point along the lateral directions. The results reveal that the secondary flow factor k bears a specific relationship with flow depths over the constant depth domain and another relationship for variable depth domain. In this study, mathematical relationships have also been developed for accurate estimation of secondary flow coe...

The boundary shear force distribution in open channel flow is needed for various purposes such as the flow resistance relationship, for designing stable channels. During floods, river overtops the main channel and flows over the flood plain located to its sides. For such compound channels the flow structure becomes complicated due to the transfer of momentum between the deep main channel and the adjoining flood plains that magnificently affects the shear stress distribution in flood plain and main channel subsections. Due to the rapidly growing population and the consequent demand for food and accommodation, more and more land on floodplain regions of a river system has been used for agriculture and settlement. This also causes flood plain geometry to vary along the length of the flow called converging compound channel. In this paper an experimental investigation concerning the distribution of shear stress in the main channel and flood plain of the converging compound channels are presented. Based...

Experiments were performed in the symmetric compound channel with diverging and converging floodplains for different relative flow depths to investigate the resistance characteristics of ov...

Boundary shear stress distribution of a compound channel is generally influenced by the geometric, roughness, and hydraulic parameters. Experiments are performed on both homogeneous and non...

50 free eprints here: http://www.tandfonline.com/eprint/xAuhsRyd5hpzRMfgdcxX/full The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. his paper presents numerical analysis for prediction of depth-averaged velocity distribution of compound channels with converging flood plains. Firstly, a 3D Computational Fluid Dynamics model is used to establish the basic database under various working conditions. Numerical simulation in two phases is performed using the ANSYS-Fluent software. k-ω turbulence model is executed to solve the basic governing equations. The results have been compared with high-quality flume measurements obtained from different converging compound channels in order to investigate the numerical accuracy. Then Artificial Neural Network are trained based on the Back Propagation Neural Network technique for depth-averaged velocity prediction in different converging sections and these test results are compared with each other and with actual data. The study has focused on the ability of the software to correctly predict the complex flow phenomena that occur in channel flows.

Very few studies have been carried out in the past in estimating depth-averaged velocity and bed shear stress in unsteady flow over rough beds. An experiment is thus conducted to investigate the vertical and lateral velocity profiles under unsteady flow conditions in a rough open channel for various flow depths. One hydrogram is repeatedly passed through the rectangular flume with a fixed rigid grass bed. Using micro Pitot tube and Acoustic Doppler Velocimeter (ADV), the flow patterns are investigated at both lateral and longitudinal positions over different cross-sections. For two typical flow depths, the velocities in both the rising limb and falling limb are observed. Hysteresis effect between stage-discharge (h ~ Q) rating curve between rising and falling limbs is illustrated. Lateral distribution of depth-averaged velocity and bed shear stress are plotted at three different cross sections and compared with the steady flow conditions. In falling limb of an unsteady flow case, both depth-averaged velocity and bed shear stress distribution in the central region is higher than that of steady flow case. However, in the rising limb, the bed shear stress of unsteady flow is less than that of steady flow case. Further, in an unsteady flow, the magnitude of depth-averaged velocity is found to increase towards the downstream sections. Along the downstream positions, bed shear stress values increase for lower flow depths and decrease for higher flow depth cases.

The present work investigates the analysis of depth-averaged velocity and boundary shear stress distribution in compound channels with non-uniform flow condition. A quasi two-dimensional model is proposed to assess the flow variables by accounting the physical processes that are specific to non-uniform flow. For analyzing the flow behavior, experimental data sets concerning compound channels with narrowing and enlarging floodplains of previous investigators are considered. The model accounts the influence of momentum transfer on the flow variables through additional shear stresses that are developed in non-uniform flow. Three types of effective stresses produced by molecular viscosity, turbulent and dispersion on the vertical planes are discussed. An analytical solution to the model is presented. Terms associated with the effective stresses are investigated relating them to the geometric and hydraulic parameters. The significance of lateral variation of energy slope is further investigated. For both homogenous and heterogeneous non-prismatic channels, the approach is examined to predict the flow variables with reasonable accuracy.

Distribution of flow and velocity in a meandering river is important in river hydraulics to be investigated from a practical point of view in relation to the bank protection, navigation, water intakes, and sediment transport-depositional patterns. When flow enters a bend, the centrifugal force arising from the channel curvature leads to a transversal slope in the water surface. The interaction between the centrifugal force and transversal pressure gradient causes secondary flows in cross-sections, and the secondary flows spread further by moving along the bend. Hence, at the bends, these processes lead to longitudinal velocity increase in the inner wall and decrease at the outer wall. In this paper, experimentation is carried out for two different bed roughness on a 4.11 sinuosity meandering channel with 110° crossover. Longitudinal velocity distribution is analysed with the graphical illustrations for the detailed experimental study. Study of flow profile across the crossover is also particularly important as the inner bank of the bend changes to the outer bank and vice versa which has a significant effect on the water surface profile and hence on the velocity distribution along the full meander path. The objective of the analysis is to determine the effect of curvature and roughness on the velocity profiles, throughout the meander path. It is determined that the resistance of flow, on the smoother bed channel, is higher than that of the channel with higher Manning’s n above a certain depth at the apex and transition sections. A reciprocal study of the experimental investigation is attempted with a numerical hydrodynamic tool, namely, CCHE (Centre for Computational Hydroscience and Engineering) developed by NCCHE, University of Mississippi, US. The model is applied to simulate the inbank flow velocity distribution and validate the experimental observation for the meandering channel with rough bed.

Movement of water during flood creates a compound channel appearance which consists of a main channel and its adjoining floodplains are very important for environmental, ecological and design issues. The structures of the flow in such channels are rigorous. The principal reason of this flow structure is due to the momentum transfer mechanism between the main channel and the floodplain. Flow mechanism in an asymmetric compound channel is different than that of a symmetric compound channel. There is a stronger interaction exists between the main channel and floodplain in asymmetric compound channel as compared to symmetric compound channel where the interaction is distributed to the both sides of the floodplain. Analysis of depth-averaged velocity distribution in both compound channels is strongly influenced by width ratio, aspect ratio and relative flow depth. The variation of depth-averaged velocity distribution in such channels for different geometry and flow conditions has been analysed. Proper prediction of depth-averaged velocity distribution in a compound channel is depending upon the magnitude of shear layer for which the advanced software CES is not providing accurate prediction especially for asymmetric compound channel. Suggestions and improvements to predict depth-averaged velocity distribution in both symmetric and asymmetric compound channels have been made.

Momentum transfer between a main channel and side floodplains tends to increase the floodplain shear and decrease the main channel shear. The increase and decrease in shear are greatly infl...

Objectives: This present paper investigated experimentally on the variation of local friction factor over the cross section in channels of different geometries. The dependency of the variation of friction factor with aspect ratio has been well compared with the results of other researchers and natural river data. Methods/Analysis: Experiments have been conducted on trapezoidal and rectangular open channel for different geometry, hydraulic and roughness conditions. The local friction factors along every vertical interface have been carried out. The actual prediction of boundary shear stress and depth averaged velocity distribution have been calculated by finding the changes of these indispensible parameters, from wide range of data collected from previous literatures. Also the experimental depth averaged velocity and boundary shear stress have been carried out for assessing the friction factor. Findings: The global friction factor f g and local friction factors f l were calculated based on the measured depth-averaged velocity and boundary shear stress. The local friction factor does not remain constant across the channel as it depends upon the geometry and roughness parameter. The paper describes the variation of friction factor for both smooth and rough channels under different flow condition. Local boundary shear stress around the wetted perimeter τ b , and depth averaged velocity, U d , data are used to evaluate local friction factor, f l . Applications/Improvement: Local friction factor variation analysis is a very rare factor that few researchers are taken into consideration. But it has a more importance for flow characteristics which is studied in this paper.

Five different sinuosities of trapezoidal meandering channels were tested to investigate the effects of the geometry and flow parameters on the resistance to flow in meandering channels. The Manning’s roughness coefficient is considered to depend on the aspect ratio, Reynolds number, Froude number, bed slope, and sinuosity. An empirical equation to predict the Manning’s roughness coefficient of a meandering channel is obtained by using laboratory experimental data. The empirical equation used takes care of these geometric and hydraulic nondimensional parameters. The equation gives satisfactory stage-discharge results as compared to other approaches for large-scale channels, small-scale channels, and natural river data.