Showing papers on "Groyne published in 2019"

Investigation of Flow, Erosion, and Sedimentation Pattern around Varied Groynes under Different Hydraulic and Geometric Conditions: A Numerical Study

Abstract: Groynes are popular hydraulic structures often used to control the erosion of banks by altering flow and sediment transport. In this paper, the effects of altering groyne orientation and spatial setup (from large to small and vice versa) on flow patterns, bed erosion, and sedimentation are numerically investigated. Studied groynes were parallel to each other, non-submerged, and impermeable. Numerical simulations were conducted in FLOW-3D. A nested mesh configuration combined with Van-Rijn formula on sediment transport yielded more accurate results when comparing numerical results to experiments. Groynes arranged from large to small at an angle of 45° decreased the scour depth by up to 55%, and an arrangement from small to large at an angle of 135° reduced the scour depth by up to 72%. Additionally, it was observed that simulations with an orientation closer to 90 degrees needed more equilibrium time when compared to other simulations.

Groyne spacing role on the effective control of wall shear stress in open-channel flow

Abstract: The objective of an effective configuration for a series of groynes in an open channel is the attainment of large bed shear stress in the main channel for channel deepening and small sidewall shear...

Impact of groyne on channel morphology and sedimentology in an ephemeral alluvial river of Bengal Basin

Abstract: Numerous groynes had been constructed on the Dwarkeswar River to improve bank protection. Among them, groynes adjacent to the village Rautara of Khandaghosh Block, West Bengal have been studied which were constructed in the year of 2009. This study investigates the alteration of channel morphology, sedimentology and flow characteristics influenced by emerged groynes through micro-level field study. An extensive field survey has been made with a dumpy level and fifty-nine sediment samples were collected from the field. Different channel parameters such as degradation aggradation ratio, braided index, channel instability and bar occupied area indices have been used from 2003 to 2018. The simulation of channel flow has been done using HEC RAS. It has been found that width/depth (w/d) ratio, bankfull channel width, channel area and sand-bed length of the river decrease due to groyne construction. On the other hand, channel maximum bankfull channel depth, depositional rate, the difference between average depth, maximum depth and braided index drastically increased. Increasing flow velocity, flow deflection with coarse and poorly sorted multimodal sediments near the tip of the groynes as well as decreasing flow velocity, curve flow path, accelerated sedimentation with elevating river bed have been observed. Altogether result indicates that the emerged groynes are effective in protecting the river banks at the cost of channel degradation.

Effect of Different Compositions in Unsubmerged L-head Groynes to Mean and Turbulent Flow Characteristics

Abstract: L-head groynes are extensively used for river bank protection, therefore encouraging the present study for the comparison of the near-bed turbulent flow characteristics among different compositions of L-head groynes. The turbulence characteristics near to the bed are needed to explore the turbulent structures fluctuations to achieve structure’s safety assurance for bank protection work; and their comparison can be used to utilize the efficiency of groynes according to the practical field requirement. In the present study, the mean and turbulent flow characteristics such as three-dimensional velocity distribution, turbulent Reynolds stresses, turbulent kinetic energy, and bed shear stress have been compared by conducting 36 experiments with varying compositions of groyne. With the increase in the groyne’s configuration and constriction ratio; the magnitude of the vertical Reynolds stress, turbulent kinetic energy and the bed shear stress decrease accordingly within the wake zone. Application of higher constriction to the flow creates comparative increased transverse and the vertical velocity region at the upstream of the groyne, leading to a state of maximum risk to the groyne’s foundation. The dominancy of horizontal turbulent mixing compared to vertical turbulent mixing; and the amplification of bed shear stress around the groyne are explored.

Roughness Effect of Submerged Groyne Fields with Varying Length, Groyne Distance, and Groyne Types

Abstract: Design guidelines were developed for a number of in-stream structures; however, the knowledge about their morphological and hydraulic function is still incomplete. A variant is submerged groynes, which aim to be applicable for bank protection especially in areas with restricted flood water levels due to their shallow height. Laboratory experiments were conducted to investigate the backwater effect and the flow resistance of submerged groyne fields with varying and constant field length and groyne distance. The effect of the shape of a groyne model was investigated using two types of groynes. The validity of different flow types, from “isolated roughness” to “quasi smooth”, was analyzed in relation to the roughness density of the groyne fields. The results show a higher backwater effect for simplified groynes made of multiplex plates, compared to groynes made of gravel. The relative increase of the upstream water level was lower at high initial water levels, for short length of the groyne field, and for larger distance between the single groynes. The highest roughness of the groyne fields was found at roughness densities, which indicated wake interference flow. Considering a mobile bed, the flow resistance was reduced significantly.

Flow over and around submerged groynes: Numerical modelling and analysis of a groyne flume experiment

Abstract: In submerged conditions groynes add resistance to a river, thereby increasing the water levels for a particular discharge. Groynes are modelled in two ways, either they are included in the bed topography when the grid resolution is sufficiently high or with a sub-grid parametrisation when the grid cell-size is larger than the geometry of the groyne. To investigate the flow patterns over and around groynes, data from a groyne flume experiment, as carried out by the BAW, is analysed. This to investigate to what extent a groyne behaves as a weir. The experiment is modelled in 2DH and in 3D to compare the performance of the sub-grid parametrisation with full 3D non-hydrostatic simulations.

Predicting the scour around open groyne using different models of turbulence & vortices flow in variety of open & close groyne

Abstract: Predicting the scour around different structures built in the rivers using numerical models is always of high significance for researchers and designers. Since the groyne was one of these structures for accounting the rivers in this study, it has been attempted to anticipate the scour around the open groyne using the numerical simulation. Because the turbulence models in software is of high concern, therefore, in this study, different turbulence models have been used in Flow-3D software and compared with experimental results. Then, the best turbulence model which is successful in accounting the amount of maximum scour and location of this amount acted. was introduced. In the following, by changing the opening of groyne, vortices caused by numerical simulation, in section of groyne installed was shown. Then changes in cross-flow power and vortices caused by cross-flow power, in different cross section examined for open and close groyne with different percentage of opening.

3D flow simulation of straight groynes using hybrid DE-based artificial intelligence methods

Abstract: In this study, hybrid differential evolution algorithms were run to study the three-dimensional mean flow field around straight groynes. The three-dimensional velocity components in a refined mesh around a groyne were measured using an acoustic Doppler velocimeter. Two novel hybrid methods, namely differential evolution-based multilayer perceptron (DE-MLP) and differential evolution-based radial basis function (DE-RBF), were used to simulate the most significant flow features. It was found that the DE-MLP method modeled well the separation of the bottom boundary layer, downward deflection of the upper layers’ streamlines and horseshoe vortex (HSV) development at the upstream groyne face. However, the DE-RBF model was unable to predict the main flow features correctly, especially the HSV system. Both DE-MLP and DE-RBF models predicted the overall flow structure of the separation zone downstream of the groyne well. However, the RBF model could not predict the inflection points in the transverse velocity profiles, which are indicative of a mixing layer bounding the separation zone. The DE-RBF model underestimated the velocity amplification at the groyne head. The DE-MLP model perfectly simulated the distribution of the streamwise cross-stream Reynolds shear stress around the groyne head and also along the turbulent mixing layer.

Near-bed turbulence around an unsubmerged L-head groyne

Abstract: L-head groynes are widely used in river training, thereby motivating the present study of the near-bed turbulence around an unsubmerged L-head groyne. Near-bed turbulence characteristics are requir...

Performance Test of Parabolic Equilibrium Shoreline Formula by Using Wave Data Observed in East Sea of Korea

Abstract: Lim, C.B.; Lee, J.L., and Kim, I.H., 2019. Performance test of parabolic equilibrium shoreline formula by using wave data observed in East Sea of Korea. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 101-105. Coconut Creek (Florida), ISSN 0749-0208.This study is the validity examination of an equilibrium shoreline formula of parabolic type, which was introduced by Hsu in 1987, for real phenomena. Hsu's formula of parabolic type is practical for estimation of shoreline change after coastal or harbor structure construction. The wave data observed at Maengbang beach of East Sea of Korea and the CERC formula on longshore sediment transport were used in the present study. Performance test was conducted for the case of a shoreline change after the construction of a groyne. It was reasonable between the observed wave data and the data obtained under a wave spreading parameter, S = 3.5. However, when S increased, significant changes were observed. Thus, it is required to apply an equilibrium shoreline formula of parabolic type carefully.

Determination of best groyne combination for mitigating bank erosion

Abstract: This paper presents a novel approach for determining the best combination of groynes in terms of their number, lengths and positions for controlling bank erosion. The vulnerable bank is considered to be protected if a very small value of water flow speed is achieved on the near bank area. A linked simulation–optimization model is developed in this regard which minimizes the total construction cost of the groyne project. At the same time, a constraint in terms of low flow speed in a predefined zone is incorporated, which helps in bank erosion prevention. In the simulation model, the depth-averaged shallow water equations are solved using a finite difference scheme. The optimization problem is formulated in three different approaches to tackle different types of in situ field problems. Genetic algorithm (GA) is used to solve the optimization problem. The proposed optimization model is used in two hypothetical test cases including one straight channel and one meandering channel. The results obtained with all the three formulations are found to be logical and establish the potential of the present model for application in real cases.

Sea defences design in the vicinity of a river mouth: the case study of Lignano Riviera and Pineta

Abstract: To guarantee the proper functioning of sea defences over a medium-long period, the knowledge of the complex interaction between tidal currents and nearshore wave field is fundamental in order to estimate the longshore sediment transport. In particular, the morphological evolution of coastal environments close to river mouths is deeply affected also by the riverine sediment transport, which can contribute to the overall coastal balance of erosion and deposition processes. Groynes are commonly used to intercept the longshore sediment transport and to stabilize the littorals, as the case of Lignano beach near the Tagliamento river mouth. In particular, the groyne closest to the river has been shortened in the recent years, influencing in this manner the coastline balance. In this study, a numerical model coupling a morphodynamic model and a wave generation spectral model has been used to study the effects of the variation of the groyne length on the beach. Results are presented and discussed, showing that the numerical modelling can be used for the sea defences design to improve the integrated coastal zone planning and management.

Analysis of Spur Dikes Spatial Layout to River Bed Degradation Under Reversing Tidal Flow

Abstract: Spur dikes (also known as groynes) are not only used to protect river banks from erosion but also a good approach to maintain maritime transport way. A single groyne makes only change in the local flow regime while groynes in series can be used as an effective measure to train the river. This paper aims to study the spatial arrangement of groynes to maintain maritime transport way in tidal rivers which are affected by reversing tidal flow. A series of 10 groynes have been set up on both sides of a small scale numerical reversing tidal flow flume using Flow-3D software. This numerical flume can simulate the time process of tidal level and flow velocity as well as the river bed changes with good reliability. The flow fields around the groynes, which vary with the installation of the groyne under reversing tidal flow at different times in a period, are simulated. In this paper, the impacts of different groyne length in groups of symmetrical groynes with extending and shortening arrangement into the middle (with varying at 25%, 50%, 75% of groyne length) are investigated. Analyses of data show that performance of symmetrical groynes with varying length is explored including the flow dynamics and morphological changes compared with classic groyne having the same length by the reversing tidal flow and to find the most effective arrangement of groynes for maximizing the scour depth in main channel to maintain martime transport way.

An investigation on mechanisms of equilibrium-stage scour and deposition process around a submerged L-head groyne

Abstract: A numerical model based on large eddy simulation code supported with a laboratory experiment was used to explore the mechanism of scour and deposition process around a submerged L-head groyne at eq...

Efektivitas Krib Untuk Mengurangi Gerusan Di Tikungan Luar Sungai Bengawan Solo

Abstract: Bengawan Solo River considered as a meander river. This condition has potentially triggered local scouring due to high flow velocity at the outer bend of the river. The scouring phenomenon occur in the segment of of Bengawan Solo river in junction with Kali Pepe river where the river bank has shifted ± 2 meter. This condition indicates that the erosion and scouring have occurred and need immediate scenarios because the river banks was eroded and the nearby residential areas wa threaten. To protect the critical river banks, groyne structure was implemented. This study aims to investigate the effectiveness of the placing of groyne structure along the outer river bend using 3 dimensional physical model test at the Hydraulics Laboratory. The obtained resutls will be verified by 2 dimensional numerical modeling. Based on the physical hydraulic model testing, groyne and riprap setup with optimum distance can be effective to reduce the energy and flow velocity of the river flow to secure the dikes and river embankments.

Modeling Procedure of Coastal Protection Shaped Blocks with High Wave Suppressing and Interlocking Capacity

Abstract: A groyne is a shore protection structure built perpendicular to the shoreline of the coast (or river), over the beach and into the shoreface (the area between the nearshore region and the inner continental shelf), to reduce longshore drift and trap sediments. A groyne field or system is a series of groynes acting together to protect a beach. Concret is often used as construction material.On the basis of analysis of wave suppression efficiency and stability on the slope of more than one hundred existing shaped massives the new type of coast protecting reinforced concrete blocks – so called “Hexablock” (“Hexablock” was called because of its 6 facets) characterized with higher wave suppression properties, interlocking capacity, stability on the slope and longer life time is proposed.

Physical Modelling Study on Sediment Removal of Sungai Habu and Sungai Ringlet, Cameron Highlands

Abstract: Numbers of reservoir in Malaysia has experienced excessive sedimentation problem due to soil erosion caused by rapid urbanization, infrastructure development and uncontrolled agricultural activities. With an increased in sediment deposition rate, the approximated useful life of the reservoir is significantly shorten. This also reduces the reservoir power generation capacity and dangerously affects dam stability and flood control storage. The aim of this study is to simulate alternative method for efficient sediment removal in Ringlet reservoir. The construction of physical sediment removal model of Ringlet Reservoir took place in the Hydraulic and Instrumentation Laboratory, National Hydraulic Research Institute of Malaysia (NAHRIM), with geometric scale effect of 1:30. Sungai Habu and Ringlet were tested up to three different ARI of 1, 5 and 100. Groyne was identified as control mitigation structure for sediment removal and total of 23 groynes were constructed. The finding showed that the gross deposition and erosion areas increased as the return period rose. It was also noticed that bed sediment in 100 year ARI was eroded more and further than 1 and 5 year ARI due to local scour resulted from the flow transition from fixed bed to mobile bed. The morphological changes occurred at Habu is due to the local flow. The movement of bed sediment at Habu end were deposited before the check dam and was not travel further downstream. The results of Ringlet showed that the sediment was deposited mostly before the first check dam for 1 year ARI. Sediments may further be transported for 5 ARI and 100 years ARI which then deposited before the second check dam.

A fending groyne for protecting important coastal facilities or areas

Abstract: A fending groyne for protecting important coastal facilities or areas (22), involving the field of natural disaster prevention and control in coastal areas. The fending groyne includes a base (18), a pillar assembly, a baffle (01) and a power device (08). There are several pillar holes (13) arranged on the base (18). The pillar assembly is mounted in the above-mentioned pillar holes (13) of corresponding shape. A conical pillar (14), several convex pillars (02) and above-mentioned baffle (01) installed between the protrusions of every two convex pillars (02) as mentioned together form an inverted V-shaped pillar assembly. The terminal pillar (17) is arranged at the end of the above-mentioned inverted V-shaped pillar assembly. The fending groyne can change the direction of high winds and large waves and gradually reduce the height or intensity of the wave from the upper layer to the lower layer, so as to protect important facilities or areas (22) along and near the coast. The fending groyne is strong in stability and the base (18) can reduce damage to the fending groyne caused by earthquakes.

Assessment of Channel Stability with Groynes

Abstract: This study investigates channel stabilities with groynes by developing the assessment of it and applying a 2-dimensional numerical model, which simulates flow and sediment transport with various flows in the channel. Evaluation inventories are composed of five items, which are width to depth ratio, sinuosity, bed slopes, velocities in the flow flied, Shields number with discharges and geomorphic characteristics in the study reach. The channel stability is evaluated by applying the evaluation indicators to the channel with and without groynes in the study reach between Dalseong-weir and Gangjeonggoryeong-weir in the Nakdong river. Width to depth ratio, sinuosity, and bed slopes, which are index of river characteristics, little affect the channel stability. However, velocities in the flow flied, and Shields number, which is dimensionless tractive, near the banks of the channel strongly affect the stability. The evaluation values of the stability in the channel on the left and right banks decrease as the number of groynes increase in both the left and right banks, which means that the bank stability increases with the groynes.

Design of a Groyne Field to Counteract Beach Erosion at Wenduine, Belgium

Abstract: The Belgian coastal town of Wenduine is situated at a change in coastline orientation and experiences beach erosion. A few kilometres to the northeast, the access channel to the Blankenberge marina experiences sedimentation due to littoral drift. On behalf of the Coastal Division of the Flemish Government, an integrated study on the mitigating measures for these morphodynamic issues at both Wenduine and Blankenberge is performed. This paper focuses on the design studies of the measures at Wenduine. A feasibility study is performed to investigate different solutions considering soft and hard measures. A conceptual design of the measures is carried out as a basis for a cost-benefit analysis. The solutions are also evaluated for morphodynamic effectiveness, currents and swimming safety, ecology and architectural aspects. The morphodynamic response and the hydrodynamic conditions are simulated using the numerical model XBeach and exported to a web application to visualize the effects of the different scenarios during stakeholder workshops. The construction of a rock groyne field in front of the dike of Wenduine is identified as the most effective and economic solution. During the design phase, the layout of the groyne field is optimized and this solution is further detailed.