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Longitudinal profile of experimental flow depth in the main channel for converging floodplains Cv6 (a) and Cv2 (b).
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This paper investigates energy losses in compound channel under non-uniform flow conditions. Using the first law of thermodynamics, the concepts of energy loss and head loss are first distinguished. They are found to be different within one sub-section (main channel or floodplain). Experimental measurements of the head within the main channel and t...
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... is available at http://www.sciencedirect.com/, doi:10.1016/j.advwatres. 2009.10.003 The last configuration investigated is flow in symmetrically converging floodplains, Cv6 (δ = 3.8°) and Cv2 (δ = 11.2°), studied by Bousmar et al. [10,17], and presented in Fig. 2f. The streamwise profiles of flow depth in the main channel are presented in Fig. 7. The relative depth h* is measured here at mid length of the converging reach. The experimental sub-section-averaged heads in these converging geometries are presented in Fig. 8. The main results are listed ...
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Citations
... This enables to explicitly model the depth-averaged lateral exchanges of mass and momentum at the MC/FP interface, and to take into account the upstream flow partition between MC and FP. Prior to the present study, the ISM was validated against experimental measurements in various CC flumes for steady flows, either uniform or non-uniform in the streamwise direction [1,40], but has never been validated for unsteady river flood events that are more realistic hydrological situations for overflowing rivers. As a result, the present numerical study aims at validating the ISM under unsteady flow conditions in (as a first step) an idealized prismatic compound geometry, and using classical 1D simulations as benchmark. ...
... This can actually be explained by the relationship between the interfacial depth-averaged streamwise velocity U xd and streamwise sub-section velocities, U m and U f , in the presence of an interfacial lateral mass exchange by the mean flow. According to Proust et al. [1,40], the U xd -value is partly controlled by the direction of the lateral discharge, i.e. U xd ≈ U i when mass transfer occurs from sub-section i to j. ...
... U xd ≈ U i when mass transfer occurs from sub-section i to j. This hypothesis is based on experimental mean velocity profiles with mass transfers from narrowing FPs to MC [20,22] or with mass transfers from MC to enlarging FPs [20,40]. As a result, in the present experiments, as the flow occurs from FP to MC during the falling limb ( ⟨U y ⟩ d < 0 in Figs. ...
Unsteady flows are investigated in a compound open-channel flume, consisting of a Main Channel (MC) and an adjacent Flood Plain (FP). Two types of inflow hydrographs are studied, i.e., a discharge hydrograph with, at any time: a slightly unbalanced inflow partition between MC and FP (Case I); and a noticeably unbalanced inflow partition (Case II). Ensemble averages of the time-varying discharges, water depths and velocities are estimated based on 100 successive runs. The main focus of the experimental study is on assessing (i) the time-varying lateral discharge and depth-averaged Reynolds stress at the MC/FP interface, and (ii) the influence of the inflow partition on the downstream flow parameters. The experimental flows are then simulated using a 1D (one-dimensional) code that was adapted to implement the 1D+ Independent Sub-sections Model (ISM) (Proust et al. in Water Resour Res 45:1–16, 2009). The numerical study aims at validating the ISM under unsteady flow conditions, using classical 1D simulations as benchmark. It is experimentally found that 90 successive runs are required to get convergence of the ensemble averages of sub-section discharges and flow depth, while interfacial velocity is not fully converged after 100 runs. The influence of the inflow partition on the downstream parameters is felt along the whole flume. The ISM simulations are closer to the measurements than the classical 1D simulations. The ISM can accurately predict the time-varying flow depths and interfacial lateral discharge, and can approximate the interfacial Reynolds stresses.
... Guo and Julien (2005), Yang et al. (2005) and Yang (2005) continued their investigation into the boundary shear stresses, velocity distribution, and their interaction with secondary currents for 3-D channel flows. Proust et al. (2010) investigated the energy loss of a non-uniform flow by using the first law of thermodynamics. Derakhti and Kirby (2014) evaluated the wave dissipation per unit length of breaking crest based on the governing equations of flow and simulation results. ...
In this study, a modified form of the total mechanical energy budget equation is developed for 3-D turbulent flows with different hydraulic regimes in open-channel transitions, from which the effect of all turbulence parameters can be evaluated by applying some equalizations and RANS numerical simulations. The total energy equation is also used to extract an explicit relationship for energy loss based on turbulence parameters. The findings are presented in the form of the application of the relationship to calculate the energy loss based on simulation results for subcritical turbulent flow and hydraulic jump in open-channel transitions, which leads to identifying the effect of non-homogeneity and anisotropy of turbulence on flow energy balance. The results show that the work done by viscous shear stresses, the viscous diffusion of turbulence, and the turbulent diffusion have little to no effect on the total mechanical energy budget of open-channel turbulent flows; instead, the effect of the variations of turbulent kinetic energy and the work done by turbulence stresses is more significant. The benefit of using the modified energy equation is demonstrated by the potential for evaluating the details that were not previously considered.
... The three contributing factors of transverse momentum flux are estimated here: depth-averaged lateral Reynolds shear stress, a dispersive term of transverse velocity over different depths, and velocity components. Eddy viscosity approach over the vertical interface between the main channel and floodplain(s) was given since it is critical in one-, two-, pseudo-two-, and three-dimensional numerical modelling [43][44][45][46]. The experiments conducted for the different configurations were compared, and the effect of the depth ratio on the mass and momentum exchange in uniform flow was investigated and presented for the present novel test cases. ...
In high-flow events, inland surface flow cross sections are defined as compound staged channels with irregular and asymmetric nature of floodplains. Understanding the transverse exchange processes of mass and momentum in compound channel sections with different floodplain widths is essential as these effects are linked directly to the riverbank stability, sedimentation and nutrient transport. Three configurations were tested to study time-averaged lateral flow, advection transport of momentum, and their interaction with the shear layer turbulence over different-sized floodplains in compound open channels. Three factors, viz. depth-averaged flow, shear layer turbulence, and dispersive term of transverse velocity, are assessed to investigate this interaction. The 3D flow structures over the different-sized floodplains in the compound channels were studied using the power density spectral and the quadrant analysis of Reynolds shear stresses to reveal the coherent structure effect over the transverse exchange of momentum in these new test cases. The results showed that the transverse exchange and eddy viscosity for the asymmetric compound channels with two floodplains have a higher magnitude than the symmetric compound channel due to higher momentum redistribution over distinct floodplain widths. The shear layer tends to shift towards a stronger transverse current side for the new asymmetric compound channels with different floodplain widths. Irrespective of roughness, more significant mixing layers are commonly viable on the smaller floodplain. The floodplains' size and roughness strongly influence the main channel shear layer width dynamics.
... The study of energy losses in compound open channels based on the 1-D energy equation (Proust et al. 2010), the analysis of turbulent energy dissipation (Førde 2012), the investigation of turbulent flow components (Pumir et al. 2014), and the evaluation of wave dissipation per unit length of breaking crest based on the governing equations of flow and simulation results (Derakhti & Kirby 2014) have all been done previously regarding the energy of flow, but only a few studies have concentrated on the details of total mechanical energy equation in 3-D turbulent flows. Liu et al. (2014) used the Navier-Stokes equations for steady turbulent flows to examine an energy equation. ...
The issue of mechanical energy budget has received a lot of attention in open-channel flows which are frequently turbulent. Turbulent motions play a major role in the total mechanical energy of the flow field. It is difficult to evaluate total mechanical energy balance and energy loss for 3-D turbulent flows in irregular open channels due to the formation of vortices and the presence of secondary currents. In 3-D turbulent flows, the effect of these phenomena has often been considered as the empirical coefficient of energy loss. In this study, these details in the total mechanical energy budget are investigated through theoretical analysis and numerical simulation, a new form of the total mechanical energy equation and a relationship for the energy loss in 3-D turbulent flows are derived, and their applications are examined in open-channel transitions. For this purpose, the Navier-Stokes equations are solved numerically, and the results are used to obtain the various terms in the total mechanical energy balance equation and analyze the details. The relationships derived in this study generally support the concept of the total mechanical energy budget to comprehend the turbulence parameters affecting the mechanical energy balance in various open-channel flows.
HIGHLIGHTS
Efforts are made to determine the various parameters affecting the total mechanical energy budget in open-channel transitions with turbulent flows.;
The contribution of the turbulence parameters to the total mechanical energy budget is investigated.;
A deeper understanding of the details of the mechanical energy transformation process and the energy loss mechanism in the irregular open channels are achieved.;
... Any methods of dealing with the problem are based on theoretical and experimental studies. Some flow aspects are studied under several shapes of channels: energy losses (Proust et al. 2010), (Saghebian 2019), momentum transfer (Wang et al. 2007), estimation of discharge (Yang et al. 2012;Kavousizadeh et al. 2019), flow resistance ), shear stress (Liu et al. 2013;Sheikh Khozani et al. 2019) and rapidly varied flow (Peltier et al. 2013). The flow hydraulics in compound channels with the different experimental setup is also coupled with: stochastic modeling (Al-Khatib and Gogus 2014), artificial intelligence methods (Sahu et al. 2011) and so on. ...
The difficulty of the problem of the flow hydraulics in compound channels is due to the implicit interaction between the floodplains and the main channel, characterizing every particular shape of the compound channel. The problem is much more complicated when it comes to an energy dissipator like a hydraulic jump as is the case in the present study. In this paper, the general regression neural network (GRNN) was applied to predict the basic characteristics of hydraulic jumps in a straight rectangular compound channel: (i) the sequent depths ratios, (ii) the relative energy losses, and (iii) the relative lengths. Experiments were carried out with three different values of the ratio between the main channel width and the flood plain one (Wy). The Wy values were: (1/4, 1/3, and 1/2). For each Wy ratio, several values of inflow Froude number were considered according to the five inflow ratio depths’ (Wz) values (0.167, 0.200, 0.253, 0.287, and 0.333) between the first sequent depth and of the main channel one. The predicted values in the testing stages using GRNN followed the experimental ones with a correlation coefficient (R) of 0.990 for the sequent depth’s ratios, 0.982 for relative energy losses, and 0.873 for the relative lengths of hydraulic jumps. The best models have been selected among several input configurations for each of three considered characteristics of the jump.
... Based on this fact, one goal of this study is to examine how flow and sediment motions change in the longitudinal direction from a single channel to a compound channel. Previous studies have investigated the flow and discharge patterns in compound channels with varying widths (e.g., [1,3,4,21]), in compound channels with non-prismatic floodplains (e.g., [22,24,25]), and in compound channels shaped like a lotus root (e.g., Fig. 1 Tongluoxia navigation channel in the upper Yangtze River (China), which is located at N 29.57, E 106.67 [7,31]). ...
Experiments were conducted on a straight channel that widens from a single channel to a compound channel based on a real navigation channel with a similar shape in a mountainous region of China. Flow entered the single channel and then the compound channel with vegetated floodplains. The channel widened at the interface between the single and compound channels, resulting in different flow depths between the single and compound channels. An equation was proposed to estimate the percentage that the flow depth decreased from the single channel to the compound channel. Vegetation increased the floodplain resistance, causing more water to flow in the main channel and yielding a greater mean velocity in the main channel relative to the nonvegetated case. The velocity reached a maximum and gradually decreased until reaching a constant in the compound channel. Sediment motion (bedload vs. deposition) was determined by the local bed shear and the critical bed shear. Sediment was deposited in the compound channel at the position where the local bed shear was smaller than the critical bed shear. When the floodplains were vegetated, the increase in the main channel velocity enhanced the local bed shear, which surpassed the critical bed shear; thus, deposited sediment was reinitiated and moved downstream, and no deposition was observed.
... Usually, model simulations are carried out by a combined one dimensional/two dimensional approach in which river flow is assumed one dimensional while twodimensional flow is considered in the surrounding floodplain (Leandro, Chen, Djordjevi c, & Savi c, 2009;Mazzoleni et al., 2014). The two-dimensional approach integrates shallow water motion equations, (Costabile & Macchione, 2012;Proust, Bousmar, Riviere, Paquier, & Zech, 2010). Threedimensional or quasi-three-dimensional ones (Orton et al. 2012) methods have also been used. ...
Post event flooding maps are currently extracted from synthetic‐aperture radar (SAR) and/or optical satellite images or developing using hydraulic model simulations. Several sources of uncertainties impact the accuracy of such flood maps constructed from each method, especially in urban areas. An integrated approach that combines satellite imagines of flooded areas, hydraulic models, and markers from social media that should reduce these uncertainties and allow a more accurate reconstruction of flooded urban areas, is presented in this paper. The flooding associated with Hurricane Harvey in Houston, TX was chosen as a case study. Model validations demonstrate the effectiveness of our integrated approach in reconstructing an accurate flooding map, as well as the temporal and spatial patterns of flooding. Using the experience from this case study we discuss the possibility to use satellite data, instead of ground‐based rainfall gauge measurements as precipitation inputs to the hydraulic model; and possible error sources in simulating flooding in urban areas using the hydraulic model.
... Khatua (2019a, 2019b) presented an improved solution for solving the Reynolds-averaged Navier-Stokes equation for the prediction of the depth-averaged velocity for a uniform open-channel flow. Proust et al. (2010) distinguished the concepts of energy loss and head loss for non-uniform flow conditions. Furthermore, the non-uniformity of flow in compound channels was emphasised by Das and Khatua (2018) and Devi et al. (2018). ...
... Furthermore, the non-uniformity of flow in compound channels was emphasised by Das and Khatua (2018) and Devi et al. (2018). Flow modelling of non-uniform flow has been carried out by Rezaei (2006), Proust et al. (2010), Naik et al. (2017), Das and Khatua (2018) and Devi et al. (2018), who analysed longitudinal variations in the roughness coefficient and depth-averaged velocity and noted the importance of lateral variations of the energy slope. ...
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.
... The FP flow is accelerated by the KHCSs but also by the time-averaged flow as highmomentum fluid from the MC is entering the FP (see the values of −ρU xd U yd in figure 5f). Both the mean flow and the KHCSs therefore contribute to the increase in δ f , as also observed in diverging FPs (e.g., Proust et al. 2010). The difference in the relaxation towards flow uniformity (depending on the direction of transverse currents) visible in figure 8 partly originates from noted trends in KHCSs developments and the effect of the depth-averaged transverse mean flow ( §7.2). ...
The structure of free-surface flows in a straight compound channel was investigated in a laboratory flume, consisting of a central smooth-bed main channel (MC) and two adjacent rough-surface floodplains (FPs). The experiments covered both uniform and non-uniform flow conditions, with the latter generated by imposing an imbalance in the discharge distribution between MC and FPs at the flume entrance. The non-uniform cases involved transverse currents directed from MC to
FPs and vice versa. The focus of the study was on assessing the effects of transverse currents on: (i) transverse shear layer and horizontal Kelvin–Helmholtz-type coherent structures (KHCSs) forming at the interfaces between MC and FPs; (ii) helical secondary currents (SCs) developing across the channel due to topography-induced flow heterogeneity; and (iii) turbulent large- and very-large-scale motions (VLSMs). Transverse currents can entirely displace the shear layer over FP or in MC, but they do not alter the KHCSs to the same degree, resulting in a mismatch between shear layer extent and KHCS length scales. KHCSs emerge once dimensionless velocity shear exceeds a critical value above which KHCS length scales increase with the shear. Three well-established SC cells, which are induced by turbulence anisotropy, are observed in uniform flow and non-uniform flow with transverse currents towards FP. They are replaced by a single cell in the presence of a transverse mean flow
towards MC. The spectral signatures of VLSMs are visible at the upstream section of the flume but they quickly disappear along the flow, being suppressed by simultaneous development of KHCSs and SCs.
... An analytical model for computing water surface profile was developed by Rezaei (2006) based on the experiment in converging compound channel (Fig. 1a). Utilizing the first law of thermodynamics, a one-dimensional energy loss model was developed by Proust et al. (2010). Though this model predicts the energy loss in each subsection (i.e., left floodplain, main channel, and right floodplain), the method is complex and contains calibrating coefficients and also does not show good results for all the relative flow depths. ...
The analytical methods require the system of non-linear equations to be solved which are very complex. So, mathematical models that prompt in taking care of complex system of problem are solved here through an artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS). By utilizing ANN and ANFIS, an attempt is taken to predict the discharge in converging and diverging compound channel. 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.
