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Estimation of streamwise depth-averaged velocity and boundary shear stress are important requisites for modelling of river flows associated with flood events. Recently, many methods have emerged to predict these flow variables with great accuracy, but they provide unsatisfactory results in shear layer regions. This paper presents an improved methodology to predict depth-averaged velocity and bed shear stress for a straight compound channel flow. An analytical solution to the depth-integrated turbulent form of the Navier–Stokes equation is obtained. The transverse shear stress in the mixing region is modelled using an effective eddy viscosity concept that contains horizontal coherent structures and three-dimensional bottom turbulence. The secondary flow term is modelled by considering the log-law profile for streamwise velocity and half cosine curve for the transverse velocity component. The analytical solution is successfully applied to a wide range of experimental compound channels and field cases. The efficacy of the present solution has been successfully tested by comparing with observed values.

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.

This paper demonstrates the influence of differential roughness on the boundary shear distribution for compound open channels. A mathematical relationship is derived between the percentage shear force carried by floodplains and five non-dimensional parameters (width ratio, relative flow depth, relative roughness, Reynolds number and Froude number). A procedure for assessing the flow distribution in terms of zonal boundary shear distribution and momentum transfer coefficients at the junction of a compound channel is presented. The efficiency of the model was tested by comparisons with published datasets and large experimental flood channel facility datasets. Compared with other standard approaches, the proposed method provided the least error in the predictions of both boundary shear and flow. The approach was also verified using actual river data and was found to provide good predictions in real-world applications.

In Kurnool district, due to the hot, arid climatic conditions, proper study of crop evapotranspiration and its effect on crop water demand for various crops is an extremely important issue. More focus will be given to the design and development of surface irrigation systems based mostly on furrow irrigation, as the rainfall pattern for this district was irregular in 2005. The crop water requirement and furrow irrigation design parameters for optimising the beneficial utilisation of available water resources and field performances are studied in this research. Some major crops, such as cotton, sugarcane, sorghum, maize, and sunflower, are considered when adopting a suitable furrow irrigation system for soil conditions of the types black clay, red loamy, and medium loam. The reference crop evapotranspiration was estimated for 2005 based on the Penman–Monteith equation as per FAO guidelines by the CROPWAT 8.0 model. Crop Water Requirement (CWR), Net Irrigation Requirement (NIR), and Gross Irrigation Requirement (GIR) were determined for available climatic and soil conditions. Soil surface characteristics were studied using AQUACROP 6.1 and compared with CROPWAT 8.0 for model accuracy. Various conservative and non-conservative crop characteristics were studied under limited set conditions, and correlation equations were developed between different parameters. Moreover, different furrow irrigation design parameters were considered by FURDEV (a module of the SURDEV model) for three modes of operation (i.e., fixed flow, cutback flow, and tailwater reuse method) under modified SCS (Soil Conservation Service) families of soil infiltration characteristics. NIR values were 200 mm, 1423.2 mm, 220 mm, 150 mm, and 150 mm for cotton, sugarcane, maize, sorghum, and sunflower, respectively. A maximum significant dry yield was observed for maize (13.586 tonnes/ha). Additionally, the maximum application efficiency and storage efficiency were obtained at 95.5% for sorghum and 99.3% for sunflower, which would be a beneficial outcome of this research. In general, the results of this research might be very effective for the irrigation authority of Kurnool District to plan suitable approaches for designing and developing proper water management systems.

Evaluation of flow resistance is necessary for the computation of conveyance capacity in open channels. For the case of channels with bedload conditions, the significance of the friction factor is of paramount importance. The gravel-bed channel response for a bedload transport condition in terms of flow resistance is distinct from that of a fixed bed and requires a different evaluation technique. The paper studies the different empirical approaches by various authors to determine the friction factor under bedload transport conditions and proposes an expression using genetic programming to derive the same. Flow resistance in the bedload transport condition is affected by various hydraulic as well as geometric parameters. In the present study, the factors proposed to be influencing friction factor for such a flow condition are undertaken as bed slope, relative submergence depth, aspect ratio, Reynolds number, and Froude number. A wide range of experimental datasets is used to determine the effect of these influencing parameters. The predictability of the proposed model is compared to the various empirical equations in literature. The proposed model is observed to effectively predict the friction factor for a wide range of datasets, unlike the existing models. The evaluated value of the friction factor from different models is used to validate the conveyance capacity of a river. The developed Multi-Gene Genetic Programming (MGGP) model is observed to reasonably predict discharge in the river, signifying that the model is competent to be applied to field study, within the specified range of parameters.

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.

A new method is proposed to calculate flow in a compound meandering channel by considering the momentum transfer between different zones. Vertical momentum transfer, at the horizontal interface of the lower main channel and the meander belt; and the horizontal momentum transfer, at the vertical interfaces between the meander belt and the adjoining outer floodplains. Modelling of this analytical method for the bend apex section is carried out, for a control volume of unit length. Calibration has been carried out for different laboratory channels and a natural river, demonstrating that the present model is capable of providing an adequate prediction of discharge in experimental as well as in field study. A constant value of 0.01 as the momentum transfer coefficient is verified to act at the interacting interfaces for the meandering channels. The zonal velocity for each subsection is determined, which facilitates prediction of discharge distribution.

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.

Estimating flow resistance is essential for the hydraulic analysis of a river and the evaluation of conveyance in a specific flow condition. Under bed-load transport conditions, the resista...

Experiments have been performed in compound channels with three different diverging angles (5.93°, 9.83°, and 14.57°) to study the behaviour of flow in the diverging compound section. In this research, depth-averaged velocity, water surface profile and discharge distribution have been studied for six different relative flow depths (0.15, 0.20, 0.25, 0.30, 0.40 and 0.50) cases. The new experiment shows that, in this diverging geometry: (1) for low relative flow depth cases, water surface profile decreases from upstream to downstream with small gradient and for high relative flow depth cases it increases significantly; (2) depth-averaged velocity distribution in the main channel region is found to be of similar magnitude for low relative flow depths from upstream to downstream, but for high relative flow depth cases it decreases. An empirical model has also been suggested to compute percentage discharge distribution in main channel region by considering four non-dimensional geometric parameters such as width ratio, relative flow depth, flow aspect ratio, and relative longitudinal distance. Along with the present experimental dataset, other published data have been used to develop the model. The new model found to give satisfactory results when compared with experimental values. Different statistical error analysis has been performed to check the strength of the present model in predicting the percentage floodplain discharge distribution.

International audience; We report here a laboratory study on the effects of bed roughness and emergent rigid veg-etation on the unsteady flows associated with flash floods and extreme flood events. The flow structure of unsteady open-channel flows over rough bed with and without emergent rigid vegetation has been investigated in an 18m long and 3m wide laboratory flume. Steady uniform flows were also studied and served as reference flows. For both steady and unsteady flows, two geometries are tested: (1) uniform bed roughness (uniform dense synthetic grass modelling meadow) along the flume and (2) a uniform staggered distribu-tion of emergent wooden circular cylinders (model of rigid vegetation) set on the bed roughness. Transient flow depths are simultaneously measured at six longitudinal positions using ultra-sonic sensors. Transient velocities are measured at one longitudinal position over the water column using a side looking ADV probe to estimate depth-averaged veloci-ty. In order to compute ensemble averages of the flow parameters, 109 runs of the same hydrograph are carried out repeatedly at the flume entrance. Two consecutive runs are separated by a base flow. The ensemble averages of the measured discharge, flow depths and velocity are found to be converged after 72 runs. For the two geometries: at the peak flow of the hydrograph, the vertical profiles of mean streamwise velocity and horizontal Reynolds shear stress are comparable to the profiles obtained for steady uniform cases of same flow depth; and accelerated and decelerated velocity profiles are obtained during the rising limb and falling limb of the hydrograph, respectively. Reynolds shear stresses are also found to be higher during the rising limb than during the falling limb for a fixed flow depth. The hysteresis in the depth-averaged velocity / flow depth relationships is compa-rable in shape and size for the two geometries highlighting the weak effect of the rigid vegetation compared to the effects of un-stationarity.

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...

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...

Water level determination during a flood is always a challenging task for river engineers. Because the flow inundates the surrounding area where it gets the least resistance. The floodplain thus in...

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.

This paper studies the effect of different independent variables related to the characteristics of the compound channels on the kinetic energy and momentum correction coefficients (termed as α and β, respectively) of non-prismatic compound channels. A series of experiments were carried out in a converging compound channel with three converging angles, six width ratios, six relative depths and three relative distances. Meanwhile, flow data sets from three different authors were used for diverging compound channels, which include simple rectangular and trapezoidal cross sections. In the present study, conventional multivariable regression technique and gene expression programming were used for developing different models for calculating kinetic energy and momentum correction coefficients for converging and diverging compound channels, respectively. The independent variables used in the curve fitting process were also tested for their accountability and influence on the proposed models. The developed models were finally established with the validation data set and a natural river system.

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.