Showing papers on "Groyne published in 2018"

Hydrodynamic and morphodynamic sensitivity of a river’s main channel to groyne geometry

Abstract: As is widely known, the groyne layout affects the three-dimensional flow situation and sediment budget in groyne fields. Lack of knowledge exists concerning the evolution of hydrodynamics and morph...

Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of caddisflies (Trichoptera)

Abstract: The influence of groynes in large rivers on caddisflies has been poorly studied in the literature. Therefore, we carried out an investigation on the 420-km stretch of the River Oder equipped with groynes. At 29 stations, we caught caddisflies in four habitats: current sites, groyne fields, riverine control sites without groynes and in the river’s oxbows. We found that groyne construction increased species richness, diversity, evenness, and altered the structure of functional groups into more diversified and sustainable ones compared to the control sites. The groyne field fauna is similar to that of natural lentic habitats, but its composition is largely governed by the presence of potential colonists in the nearby oxbows. We distinguished three of the river’s caddisfly assemblages. The distribution of Trichoptera was governed inter alia by the plant cover and the amount of detritus, and consequently, the food resources. Oxygen, nitrates, phosphates and electrolytic conductivity were important as well. Groynes have had positive effects for caddisflies—not only those in the river itself, but also those in its valley. They can therefore be of significance in river restoration (although originally they served other purposes), especially with respect to the radically transformed ecosystems of large rivers.

Validation of indigenous knowledge for disaster resilience against river flooding and bank erosion

Abstract: This chapter reveals the working principle of an indigenous technical knowledge, Bandalling, for disaster resilience against river flooding and bank erosion with scientific evidences. The hydraulic and morphological implications of this tradition wisdom are compared with those of typical modern engineering technologies: the revetment and the groyne. By characterizing the local flow structure and bed deposition properties around a group of revetments, groynes, and Bandal structures under suspended sediment transport conditions with experimental methods, unique characteristics of Bandalling are distinguished. The advantages and deficiencies of original Bandalling are clarified and recommendations are made to integrate indigenous knowledge with recent advances in science and engineering in pursuit of a sustainable and disaster resilient society.

Development of Design Guidelines for Shallow Groynes

Abstract: The need for river bank protection in an ecologically appropriate manner has led to the investigation of shallow groynes as a nature-oriented countermeasure against bank erosion. Shallow groynes are in-stream structures which have a horizontal crest and are submerged even during low flow conditions in order to minimize the effect on the flood level. Rather than enhancing the resisting forces like traditional bank protection measures, e.g. riprap, shallow groynes are used to redirect the attacking flow away from the river bank. In this way, the bank itself becomes available as habitat and the water-land interface is rehabilitated or preserved. Moreover, the shallow groynes increase the heterogeneity of the flow field, bed topography, and bed material, which is one of the key elements requested by the EU Water Framework Directive to improve the ecological condition of rivers. However, guidelines are necessary for a successful and sustainable design of shallow groynes. The objective of the study was to develop design guidelines for shallow groynes in river bends by experimentally investigating the design parameters, namely groyne inclination, length, width, location and spacing in a river bend. The experiments were carried out in a curved flume in the laboratory of Leichtweis-Institut fur Wasserbau (LWI). The three-dimensional flow field was measured with an Acoustic Doppler Velocimeter. The hydraulic boundary conditions were kept constant throughout the experiments. A reference run was carried out without a groyne providing the basis for quantification of the hydraulic effects due to the shallow groynes. The optimum groyne parameters were defined based on the highest reduction of stream-wise velocity close to the outer bank. The manipulation of the flow field throughout the bend was investigated with a single groyne as well as with a group of groynes varying the number of groynes as well as the spacing. Further experiments with a fixed bed and a mobile outer bank confirmed the effectiveness of shallow groynes for bank protection. The results of the different sets of experiments were combined to develop a design method for bank protection with shallow groynes throughout a river bend. The method incorporates geometric parameters of the bend as well as the hydraulic boundary conditions.

Experimental Study of Morphological Changes and Flow Structure around the Vegetated Groyne

Abstract: There are many steep rivers in Japan, one of them is Shigenobu river, and the water pressure at the time of flooding is severe. This study focuses on clarifying the vegetated groyne not only to prevent scouring and sedimentation problems but also to optimize for ecosystems and landscapes, which cuts the upper half of the existing groyne constructed and installs a permeable part at the top of it. In this research, investigation of the more efficient vegetated groyne was carried out. The vegetation has been represented as the wooden bar with setting various sizes (diameter of the wooden), changing the density of the vegetation part to be installed, with setting different conditions. The flow visualization and bed changes are the two components which analysed. The measurements in the laboratory flume were characterized by observation of flow structures with particle image velocimetry. The results show that the effect becomes vegetated groyne, the flow rate difference with the inner side of the river has been stabilized. Sediment accumulation and local scouring are reduced, and clearly, there is an effect of suppressing excessive scouring and sedimentation as compared with the existing groyne. With paying attention to the area ratio of the wood rod in the upper part of the groyne, the effect of suppressing riverbed fluctuation was more demonstrated when 1/5 than 1/10. Moreover, for the diameter of the wood stick, it was revealed that the vegetated groyne with the diameter of 8 mm and 5 mm exerts more effect than 10 mm.

Issues in Numerical Modelling and Assessing the Flow over Weirs and Groynes

Abstract: In this research two problem statements are defined, namely (1) the validity of the assumption that groynes and weirs are equivalent in hydraulic models, and (2) the difficulty of modelling groynes and weirs in the 3D numerical solver package OpenFOAM. Using the incompressible 3D Navier-Stokes equations solver for multiphase phase flows, the so-called interFoam solver un- der OpenFOAM framework, two different models are set up for tackling the two problem statements. The interFoam evaluation model addressed the issues of computational mesh types which affect the simulation results, and the methods for regulation of water level at the downstream boundary. The two types of the meshes which are used in the research are structured non-orthogonal mesh and unstructured more-orthogonal mesh. The benchmark test is the flow over the weir in the flume. The use of a non-orthogonal mesh could simulate the flow separation which is found downstream of the weir. However the unstructured meshes which are composed of more orthogonal parts and less non-orthogonal parts, could not reproduce the flow separation in 2D simulations correctly for high and small specific discharges. For the 3D simulations, the unstructured meshes apparently simulate the correct flow profile for low specific discharges. In this interFoam evaluation model the control structure or gate is used for maintaining the water level at the downstream boundary. In other words, it uses the physical method of water level boundary condition. The weir-groyne comparison model is developed with different settings from the former model for the assessment of the differences between weirs and groynes in open-channel flumes. The water level is regulated by a trial-and-error discharge adjustment method making use of inlet and outlet tanks. The mesh type used is the unstructured more-orthogonal mesh in 3D simulations since the severely non-orthogonal meshes introduce numerical artifacts. A variety of weirs and groynes with different slopes are simulated for the comparison of energy losses and streamlines patterns. From the simulation results, the streamlines of the flow over the weir and the groyne are found to be different and the energy head losses also differ between these two structures. For recommendations, to evaluate the skill of the interFoam solver the 3D simulations for unstructured meshes should be carried out to make sure that they can reproduce the flow sep- aration correctly. The use of a mathematical boundary condition for defining the water level is recommended to avoid the extra computational power for the control structure. To acquire the knowledge of flow around groynes and weirs, the experimental set-ups are recommended, and well-proved non-linear k − e and k − ω turbulence closure models should be applied in the numerical modellings.

Tracer advection in a pair of adjacent side-wall cavities, and in a rectangular channel containing two groynes in series

Abstract: A model is presented of particle advection near groynes in an open channel. Open channel hydrodynamics is modelled using the shallow water equations, obtained as the depth-averaged form of Reynolds-averaged continuity and Navier-Stokes momentum equations. A Lagrangian particle-tracking model is used to predict trajectories of tracer particles advected by the flow field, with bilinear interpolation representing the continuous flow field. The particle-tracking model is verified for chaotic advection in an alternating flow field of a pair of blinking vortices. The combined shallow flow and Lagrangian particle-tracking model is applied to the simulation of tracer advection in flow past a pair of side-wall cavities separated by a groyne, and in an open rectangular channel containing a pair of parallel groynes oriented normal to the channel wall. The study is potentially useful in understanding mixing processes in shallow flow fields near hydraulic structures in wide rivers.

Flow Bifurcation at a Longitudinal Training Dam: Effects on Local Morphology

Abstract: Longitudinal training dams (LTDs) have been built over a length of 10 km in the Dutch River Waal as an alternative to groyne fields, splitting the river in a fairway and a bank-connected side channel in the inner bend. Here, we study the physical mechanisms governing the three-dimensional flow and its effect on local morphology at the flow divide using a mobile bed physical model of an LTD, centred around a side channel intake. In line with previous experiments, polystyrene granules are used as a lightweight sediment that allows to achieve dynamic similarity between the model and the prototype. An Acoustic Doppler Velocimetry (ADV) profiler is used to monitor the flow characteristics, whereas a line laser scanner set-up is used to measure the morphological imprint of the flow near the bifurcation point. To study the dependence of the results on the sill height at the side channel intake, different forms and heights of the sill are used. First results show striking similarities with measurements from the field pilot in the Waal River, as well as larger sedimentation in the side channel for a uniform low sill compared to a downstream increasing sill height.

Morphodynamic effects of stone and wooden groynes in a restored river reach

Abstract: Restoration works on an 11 km long reach of the Spree River near Cottbus in Germany were accomplished in 2014. The overall objective was to improve the biodiversity, changing the morphological structure from a straight single-thread river to a braiding one with reshaped thalweg, and creating zones with varying flow velocities required for fish spawning. Several interventions were made, among which also two types of groynes were constructed along the reach: impermeable stone groynes, with an inclined crest so that only the tip is typically submerged during normal flow conditions, and wooden groynes made of several large trunks, which are mainly submerged at normal flow conditions. To compare local morphodynamic effects caused by the different types, flow velocities and bed topography were measured at distances of 12 m upstream and 16 m downstream of two selected groynes. The vertical profile was captured by measuring at five levels above the bed. Bed material was sampled at several locations around the groynes. The analysis of the measurements showed the effect of each groyne type on the flow velocity, bed topography and bed material. Furthermore, the differences in the effects of each groyne type on the flow, bed topography and bed material were highlighted.

Turbulence Flow Modeling of One-Sharp-Groyne Field

Abstract: Groyne arrangements had been subject of numerous studies, which demonstrate that the first groyne plays a crucial role on the hydraulic behavior of the whole arrangement This contribution presents the application of two 3D numerical techniques (RNG and LES) to compute one single sharp-groyne field in a rectangular channel In the laboratory, flow velocities and water levels were measured in order to calibrate and verify the accuracy of the numerical models Two turbulence parameters, namely the Reynolds Shear Stresses in the XY-plane and the Turbulent Kinetic Energy, were estimated and compared Both numerical techniques present good agreement with the time average velocity components recorded in the laboratory Nonetheless, as expected, the Large Eddy Simulation (LES) is more appropriate for the computation of turbulence characteristics, but more expensive in terms of computational costs

Novel method for groyne erosion stability evaluation

Abstract: This paper concentrates on the simulating methodology for the reliability analyses of the groyne erosion stability with the randomness, including the probabilistic turbulences of the mean value, the variation, and the correlation of the pertinent parameters. On the basis of the interpretation for the mechanism of the groyne erosion, the backslope gradient of the local eroded pit is adopted as the major factor for the establishment of the reliability function. Created for the reliability analyses in this paper is the systematic algorithm that can solve the complicated reliability function of the groyne erosion stability and compute the corresponding failure probability. The reliability function here incorporates the random parameters that are non-Gaussian and statistically correlated. These complicated parameters exist in most coastal engineering cases. The comprehensive sensitivity of the groyne erosion stability is investigated based on the measured data of the random parameters and their designe...

Power generation groyne

Abstract: The invention relates to a power generation groyne. The groyne comprises a groyne body, a purified water extraction unit and a seawater salt drying unit which are arranged in sequence, the groyne is characterized in that the groyne body comprises a first-level groyne and a second-level groyne which is arranged above the first-level groyne, the first-level groyne and the second-level groyne are provided with water inlets, and a water storage pond is arranged at the back side of the second-level groyne; a first gate and a second gate which are driven by motors to ascend or descend are arranged in the first-level groyne and the second-level groyne, the working mode of the first gate is that the first motor drives a first gear to ascend or descend on a first rack, and the working mode of the second gate is that the second motor drives a second gear to ascend or descend on a second rack. The power generation groyne has the advantages that through the reasonable and ingenious design, a powergeneration device is arranged in the groyne, the groyne has the functions of seawater desalination and salt drying and has multiple functions, effective utilization of natural resources is achieved,and the groyne is suitable for popularization and application.

Calculation method for interaction of waves and arc-shaped plate type groyne

Abstract: The invention provides a calculation method for interaction of waves and an arc-shaped plate type groyne. According to the method, pressure-implicit with splitting of operators (PISO algorithm) is implemented, a prediction step and two modification steps are carried out, pressure is adjusted through iteration, then an internal fluid unit meets continuous equations, a free surface unit meets free surface power boundary conditions, and meanwhile a speed field is adjusted; compared with a conventional calculation method for interaction of the waves and the arc-shaped plate type groyne, the calculation method has the advantages that the calculation efficiency is high and value results are relatively approximate to physical practice since a speed field is modified by using the PISO algorithm, variable information is arranged based on alternative grids, and interaction of the waves and the arc-shaped plate type groyne is simulated by using a virtual boundary force method through central difference method discrete control equations.

Experimental Study on the Performance of Slope-crested Groynes in Erodible Meandering Channels of Different Sinuosity

Abstract: Riverbank erosion is a vital issue in the management and restoration of rivers, especially in alluvial meandering channels because of their unique channel morpho-dynamics. Various countermeasures are thus implemented to minimize riverbank erosion and maintain stable channel sections of meandering channels. This study analyzes the performance of modified impermeable groynes with sloped crests as a countermeasure for bank erosion. Experiments were conducted in erodible meandering channels of two different sinuosities to evaluate the performance of the proposed countermeasures under varying sinuosity as well as analyze the overall morphological evolution of the channel. The results show that the low sinuosity (LS) channel was more prone to erosion compared to the higher sinuosity (HS) channel. Channel sinuosity also affected the overall channel morphological evolution with the LS channel showing more distinct characteristics of a meandering channel forming point bar and pool and riffle sequences. The proposed countermeasure showed slightly better performance in the case of the LS channel. Although the presence of the proposed groynes did not significantly deflect the high-velocity core towards the channel center, the velocity near the bank region was significantly reduced.

Performance of a groyne in controlling flow, sediment and morphology around a tributary confluence

Abstract: In a middle stream reach, irreversible morphological changes are observed such as growth of a huge sandbar in front of the confluence, thalweg migration from the left to right bank, erosion of the main channel and sedimentary deposit on the floodplain As a countermeasure against such degradation of river morphology, a groyne was constructed beneath the tributary confluence Performance of a groyne in controlling flood flow, sediment transport and river morphology was investigated by a twodimensional hydrodynamic model The analysis on twenty years of morphological change indicates that the groyne has an excellent performance in improving quality of river morphology such as reduction of the sandbar development and migration of the thalweg to the original position

Numerical groyne layout optimisation for restoration projects in large rivers: An adaptive approach towards a desired morphodynamic equilibrium

Abstract: Integrative restoration measures at large rivers target the improvement of morphological and ecological conditions, under consideration of economic demands, specifically navigational ones. Alternative groyne layouts with e.g. reduced groyne spacing and lowered crest elevation reduce ecological deficits and have the potential to cease frequently encountered river bed incision of heavily modified rivers. On the other hand, the induced change in the morphodynamic equilibrium may interfere with navigation by reducing the water depth in the fairway. In 2009, a pilot project was realised on the Austrian Danube, including an alternative groyne layout. As a consequence the desired aggradations in the fairway became too large, leading to an increased dredging effort. In 2014, a numerical groyne optimisation, specifically a 3D numerical model in combination with a sediment transport model, was applied. In 2015, after implementing the optimised groyne layout in the field, morphodynamic equilibrium was reached reducing the need of extensive dredging. This equilibrium could be shown by analysing subsequently observed bathymetries until 2017. Moreover, the morphodynamic changes due to the groyne optimisation in 2015 were reproduced successfully with the numerical models. Thus they represent a cost effective tool for planning and optimising future restoration measures in large and heavily modified rivers.

Experimental Study of Local Scour Around Elliptic and Semi-parabolic Groynes in Straight Channels

Abstract: This study was carried out to investigate local scour around curved groynes under different conditions including flow condition, average values of radius of curvature, spacing between groynes, width of groynes, number of groynes, and shapes of groynes. Laboratory works were achieved with 300 runs for elliptic and semi-parabolic groynes models. Three different widths of groynes were adopted as (7, 10, and 13 cm), as well as, using three different number of groyne, single, double and triple. Four different spacing between groynes of (1, 1.5, 2, and 2.5) times of width of groyne were used in the study. The average values of radius of curvature for all adopted shapes used was computed as an additional significant parameters. Dimensional analysis techniques and (MATLAB V.13) program were used to detect the two dimensionless formulas of maximum scour depth for elliptic and semiparabolic groynes. The results gave good determination coefficient of (99) % for both formulas. Generally, the elliptic groyne is the best case of all groynes because gives minimum scour depth, minimum volume of scour and transition of sediments.

Applying of depth-averaged hydrodynamic modeling with different methods of turbulence closure for flow near channel groyne. Part I – hydrodynamic background

Abstract: Training structures in flow stream play an important role in shaping flow and bed properties. Planning to introduce such training elements like groins or dikes into the river stream one need to know consequences they may introduce into flow field and bed shear stresses. These consequences can be investigated by laboratory experiments on hydraulic models or by numerical modelling using hydrodynamic simulation models. In the paper the second possibility is exploited by applying two-dimensional depth-averaged model for straight rectangular channel with a groyne. This paper contains the first part of the research results and it describes hydrodynamic background of the flow phenomenon, concentrating on hydrodynamic equations for depth-averaged flow, types of eddy viscosity method used and kind of boundary conditions applied. Based on the hydrodynamic descriptions, different simulation experiments have been conducted for the flow problem and the whole analysis of simulation results for flow in channel near groyne is contained in the second part of the research activity (Part II = Analysis of simulation).

Applying of depth-averaged hydrodynamic modeling with different methods of turbulence closure for flow near channel groyne. Part II – Analysis of simulation

Abstract: Training structures in flow stream play an important role in shaping flow and bed properties. To investigate consequences of introducing training elements like groins or dikes into the river stream one can successfully use numerical modelling. This paper is the second part of the research concentrated on utilizing some hydrodynamic models for resolving the problem. In the first part some hydrodynamic background has been described and here the analysis of applying two-dimensional depth-averaged model for straight rectangular channel with a groyne is discussed. Three models of eddy viscosity were applied to investigate their influence on results of simulation and to attempt choosing the most suitable method of modelling the flow phenomena around the groin. Results of simulation in steady flow conditions show that from the hydrodynamic point of view the more profitable method of turbulence description is the mixed-length or even the parabolic method instead of the broadly suggested k-e model. They allow producing the most reliable vortexes in the shear layer of flow behind the training structure end well preserve the mass balance contrary to the results obtained with k-e model of eddy viscosity.

Flow Near Groynes: Experimental or Computational Approaches

Abstract: The research of Mohamed F.M. Yossef and Huid J. de Vriend published in the Journal of Hydraulic Engineering (2011) presented in detail the dynamics of the flow near groynes. By physical experiment, in a fixed bed flume, the authors found out the differences in nature of turbulence between submerged and emerged groyne stage. They provided insight into the flow pattern in vicinity of groynes, the shape and extent of the mixing layer at different flow stages, and the dynamic behavior of velocity along the mixing layer the main channel and the groyne fields. With the aim of modeling with a numerical tool the observed results, this paper presents the work developed with the TELEMAC-3D modeling system and the hypothesis used by Yossef and De Vriend. The simulated results are quite similar with the experiment in many aspects. The performance of the simulation demonstrates the strong capacity of computational modeling systems like TELEMAC-3D in representing the flow stage in different cases. The result also confirms preeminence of computational program about flexibility, simulated time and result expression in comparison with experiment. The paper is expected to provide an insight view about using computational model for hydraulic research and to be useful for studying the dynamics of flow near groynes by hydrodynamics simulation.