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The Journal contains scientific and technical material of broader interest in the areas of theoretical, experimental and computational hydraulics and fluid mechanics in various fields of application (rivers, coasts, environment, structures and industrial flows). This may also include results of field studies and interdisciplinary studies. Further included is publication of state-of-the-art papers, information which is suitable for the end-user (design and consultancy) and forum articles. Discussions to papers and technical notes are welcomed. The scope of the Journal covers the fields in which IAHR is active.
The Journal of Hydraulic Research has been published (currently six issues per year) since 1964 by IAHR and is distributed to all IAHR Members as part of the Membership Subscription, together with the IAHR HydroLink newsletter. JHR is published in print and electronic format. Abstracts are available on-line from 1996,and Full papers from 2001.

Abstract of Papers - JHR Volume 47 Issue 6

Drag coefficient of unsubmerged rigid vegetation stems in open channel flows  
by UMESH C. KOTHYARI, KENJIROU HAYASHI and HARUYUKI HASHIMOTO  

Vol: 47 / Issue: 6

  
Results of an experimental study on the drag force measurement involving a single stem kept in a channel flow stem array are presented. The data collected herein and those from literature indicate that the stem drag coefficient logarithmically increases with the areal stem density. The stem Reynolds number is noticed to have only a small effect on the stem drag coefficient which was however found to depend on the stem staggering pattern. The drag coefficient is less influenced by the Froude number in subcritical flows but it decreases with the Froude number in supercritical flows. New relationships are proposed for the stem drag coefficient which appears useful in partitioning the total flow resistance of vegetated bed streams into the stem and the bed particle resistances. The bed particle resistance applies to sediment transport through such vegetated flows for which the average flow velocity is available.  

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Effect of tall vegetation on sediment transport by channel flows  
by UMESH C. KOTHYARI, HARUYUKI HASHIMOTO and KENJIROU HAYASHI  

Vol: 47 / Issue: 6

  
Results of an experimental study on sediment transport by channel flows with tall rigid stems are presented. The experiments were conducted for various stem areal densities, channel slopes and sediment sizes with uniformly distributed unsubmerged cylindrical rigid stems forming a regular square staggering pattern in plan. The rates of sediment transport in the presence of simulated vegetated surfaces were observed to be significantly smaller than those without the vegetation. A method is proposed to determine the effective (grain) shear stress in presence of vegetation under the condition that the apparent shear stress is available from easily measurable flow parameters. The present data along with literature data are used for quantification of the reduction in the rate of sediment transport by the rigid tall stems. The grain shear stress rather than the apparent shear stress is observed to better describe the variations in the rate of sediment transport by vegetated flows.  

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Entrainment of floating granules behind a barrier  
by AZIN AMINI, JEAN-LOUIS BOILLAT and ANTON J. SCHLEISS  

Vol: 47 / Issue: 6

  
To simulate the retaining capacity of an oil barrier in an uniform flow field, experiments were carried out in a laboratory flume at Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Hydraulic Constructions (LCH) by using Light Expanded Clay Aggregates (LECA) and plastic particles. It was demonstrated that under appropriate assumptions for the effects of buoyancy and gravity forces, the Shields approach is suitable to predict both the entrainment of suspended granules behind a barrier and the start of leakage underneath. The phenomenon was also simulated numerically with a multiphase model using a CFD code, Fluent, and the results were compared to those of the physical experiments. The “Eulerian model” multiphase model of FLUENT was selected to simulate the phenomenon. The numerical model successfully predicts the evolution of the slick shape behind the barrier for various flow conditions. The amount of LECA that leaked from the barrier agreed well with the experimental observations.  

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Application of the Shiono and Knight Method in compound channels with non-prismatic floodplains  
by BAHRAM REZAEI and DONALDW. KNIGHT  

Vol: 47 / Issue: 6

  
The Shiono and Knight Method (SKM) is known as a capable tool to model flow in prismatic compound channels. This research explores whether SKM can be used to predict depth-averaged velocity and boundary shear stress in compound channels with non-prismatic floodplains. For this reason SKM was modified and used in combination with an extensive experimental data set of depth-averaged velocity and boundary shear stress measurement to investigate the issue over three various floodplain converging angles and relative depths. The modeling results indicate a good agreement between the experimental data and the modified SKM. Also, based on the momentum balance and using the experimental data on compound channel with non-prismatic floodplains lateral variations of the depth-averaged apparent shear stress, the Reynolds shear stress, and the secondary flow were investigated. The results reveal that the Reynolds shear stress is significant at the interface between the main channel and floodplains and secondary flow has linear variation.  

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Shallow turbulent wakes behind bed-mounted cylinders in open channels  
by M.A. FAHEEM SADEQUE, NALLAMUTHU RAJARATNAM and MARK R. LOEWEN  

Vol: 47 / Issue: 6

  
Flow patterns in the shallow turbulent near-wakes behind bed-mounted cylinders are investigated on smooth and rough beds. A wall wake analysis revealed that the flows in the region away from the bed are similar and well described by the plane wake equation. Wall wake similarity was also observed for turbulent kinetic energy and primary Reynolds stress for moderate to deeply submerged cylinders.Wake analyses in the horizontal plane revealed that similarity of mean velocity profiles across the flow exist in the near-wake region at all elevations for slightly submerged and surface piercing cylinders; and at all elevations below the object height close to moderate and deeply submerged cylinders. For slightly submerged and surface piercing cylinders similarity was observed in the near-wake region between the non-dimensional velocity profiles across the wake and the plane wake equation. However, the similarity of the velocity profiles improves if a modified transverse length scale is used for shallow near-wake flows.  

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Classical hydraulic jump: Basic flow features  
by OSCAR CASTRO-ORGAZ and WILLI H. HAGER  

Vol: 47 / Issue: 6

  
The dynamics of free surface flow is characterised by the so-called Froude number F, whose value F = 1 separates subcritical (F < 1) and supercritical (F > 1) flows. The transition from F < 1 to F > 1 is smooth and continuous, as observed in weir flow. However, the reverse transition from F > 1 to F < 1 is abrupt and discontinuous. In the present research the simplest approximation is proposed to describe hydraulic jump flow. The 2D flow features of the classical hydraulic jump are properly described and favorably compared with experimental data. Based on one-dimensional results, the hydraulic jump flow is rationally related to the critical flow condition and it is proved that the specific energy of the main flow reaches a minimum value at F = 1, whereas the total energy head decreases due to energy dissipation. Further results relate to the effects of air, and the non-uniform pressure and velocity distributions.  

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Flow resistance due to a single spur dike in an open channel  
by HOSSEIN AZINFAR and JAMES A. KELLS  

Vol: 47 / Issue: 6

  
A method for quantifying the flow resistance exerted due to a single spur dike located in an open channel is presented. The work was carried out in a rigid bed flume, with the model spur dike being simulated using various sizes of a rectangular plate. The drag force exerted by the spur dike plate for both submerged and un-submerged flow conditions was directly measured using a specially-designed apparatus and also by applying the momentum equation to a control volume that included the plate. The results indicate that an increase in the blockage due to the spur dike plate is the main parameter responsible for an increase in the spur dike drag coefficient, hence the associated flow resistance. Based on the present experimental results, relationships are given to estimate the backwater effect due to a single spur dike.  

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Verification of Q-QUICK scheme for convective flux in incompressible flow on unstructured grids  
by ZULIN HUA, LINGHANG XING, KEJIAN CHU and LI GU  

Vol: 47 / Issue: 6

  
Accuracy of convective flux approximation is important for numerical computation of incompressible flow on unstructured grids. The Quasi-QUICK scheme by Davidson is proposed to improve the accuracy of convective flux approximation. The numerical performances of the Q-QUICK scheme on unstructured grids are explored, including numerical accuracy, convergence stability, CPU time consumption and solution sensitivity to high grid deformation. Several test cases such as 90◦ and 30◦ 2D lid-driven cavity flows, diverging channel and 3D lid-driven cavity flow are considered. The results show that the Q-QUICK scheme performs well in terms of numerical accuracy, convergence stability or adaptability to high grid deformation if compared with other schemes. Moreover, the convergence speed of momentum equation and CPU time consumptions are also compared for each type of grid and scheme.  

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Numerical aspects of the simulation of discontinuous saline underflows: The lock-exchange problem  
by FABIAN A. BOMBARDELLI, MARIANO I. CANTERO, MARCELO H. GARCIA and GUSTAVO C. BUSCAGLIA  

Vol: 47 / Issue: 6

  
Issues associated with the adequate representation of flow instabilities of saline, discontinuous density currents in two and three dimensions are discussed. First, simulations of the experiments by Alahyari and Longmire (1996) developed with an advanced commercial code are presented, and they are compared with results obtained through Direct Numerical Simulation of the problem. Various meshes and turbulence models are then tested with the commercial code, including a Large Eddy Simulation. The features of the density current that are not reproduced well by the simulations with the commercial code are further analyzed. Then, two-dimensional numerical simulations of an unpublished set of experiments are presented. The response of commercial and open-source codes to different grids is addressed. Important conclusions on the risks of using inadequate resolution with codes in which not all the variables are controlled are obtained, and the nature of these two-dimensional, “mathematical” numerical solutions is discussed.  

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Numerical modeling of flow over a chute spillway  
by MEHMET SALIH KIRKGOZ, MEVLUT SAMI AKOZ and AHMET ALPER ONER  

Vol: 47 / Issue: 6

  
The simulation performance of two-dimensional flow over a round-crested chute spillway is examined using the finite element method along with the standard k-ε and the standard k-ω turbulence models. The volume of fluid method is used to determine the free surface of the flow.A mesh dependence study is conducted using the results obtained from three meshes of different densities. Grid convergence analyses indicate that the discretization error in the predicted velocities on the fine-mesh solution is within 2%. A two-layer model for the near-wall treatment was adopted involving a sufficiently fine mesh to model the viscosity-affected region. The numerical results are compared with experimental data for validation of turbulence models. Mean square errors of measured and predicted free surface and velocity profiles indicate that although both closure models predict the chute flow properties with a reasonable accuracy, the agreement using the k-εmodel is slightly better.  

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Turbulence structure and “Monami” phenomena in flexible vegetated open-channel flows  
by TAKA-AKI OKAMOTO and IEHISA NEZU  

Vol: 47 / Issue: 6

  
Aquatic plants in natural rivers are essentially important components of ecosystems. In vegetated canopy open-channel flow, velocity profiles are changed largely in the vertical direction resulting in the Kelvin-Helmholtz instability. Consequently, large-scale organized vortices are induced, which dominate the momentum transfer and scalar concentration among canopies. The downstream advection of coherent vortices causes the coherent waving of aquatic vegetation, referred to as Monami. However, the flow-visualization techniques such as PIV have not been sufficiently applied to these complicated flows in previous studies, such that no detailed information on the interaction between the flow field and the plant motion exists. Simultaneous measurements of turbulence and vegetation motion were conducted herein for open-channel flows with flexible vegetation by using a combination of PIV and PTV techniques. The former part of this study focuses on the effects of Monami phenomena on mean-flow and turbulence structures. The latter part examines an interaction between the coherent structure and the vegetation motion.  

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Finite-volume solution of one-dimensional shallow-water sensitivity equations  
by VINCENT GUINOT, BERNARD CAPPELAERE and CAROLE DELENNE  

Vol: 47 / Issue: 6

  
Solving the Shallow-Water-Sensitivity Equations for discontinuous flows involves the discretization of a Dirac source term accounting for discontinuities. Failing to account for this source term usually results in solution instability, with empirical sensitivity solutions exhibiting artificial peaks in the neighbourhood of shocks. An extension of the Harten-Lax-van Leer approximate Riemann solver is presented that allows the one-dimensional shallow-water-sensitivity equations to be discretized more accurately than in previously published versions. A discretization of boundary conditions and source terms is also provided. The proposed discretization allows for discontinuities in both the hydraulic and sensitivity boundary conditions. Numerical experiments indicate the superiority of the proposed approach for sensitivity analysis over the classical, empirical approach if the flow solution is discontinuous. A numerical convergence analysis demonstrates that the numerical and analytical solutions converge.  

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Discharge coefficient of sharp-crested weirs using potential flow  
by HOSSEIN AFZALIMEHR and SARA BAGHERI  

Vol: 47 / Issue: 6

  
Sharp-crested weirs are used in hydraulic structures for accurate discharge measurement. Using a plane vertical plate perpendicular to the flowdirection and applying the theory of complex variables, an equation is developed for estimating the discharge coefficient of rectangular sharp-crested weirs by the potential flow theory. The results reveal that the ratio of overflow head to the weir height can be presented by a power equation to obtain a correction factor to determine the discharge coefficient. Experimental data indicate that the suggested equation for the discharge coefficient gives reasonable results for a large range of relative overflow depths.  

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DISCUSSIONS
A turbulent approach to unsteady friction 		 
by IVO POTHOF, Journal of Hydraulic Research, IAHR, 2008, 46(5), 679–690.  

Vol: 47 / Issue: 6

  
Discussers : a) HUAN-FENG DUAN b) UNO LIIV c) BRUNO BRUNONE, SILVIA MENICONI, MARCO FERRANTE Reply by the author: IVO POTHOF  

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Flow patterns in nappe flow regime down low-gradient stepped chutes  
by L. TOOMBES and H. CHANSON, Journal of Hydraulic Research, IAHR, 2008, 46(1), 4–14.  

Vol: 47 / Issue: 6

  
Discussers: J. THORWARTH, A. SCHLEISS, J. KÖNGETER and H. SCHÜTTRUMPF Reply by the authors: L. TOOMBES and H. CHANSON  

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