Spur Dykes Research Articles

Effects of Locations of Spur Dyke on Bed and Scour around Bridge Piers in Meandering Channel

Spur dykes are the structures which are used to protect the eroding bank of rivers. They are sometimes also used to safeguard the life of many structures such as bridge piers, abutments etc. The efficiency of spur dykes has been checked in straight channels by conducting model tests in laboratories by many investigators. Very few studies were done in curved channels. In present work an attempt has been made to study the effect of location of spur dyke on bed and scour around bridge pier in curved open channel (bend angle = 80o ) with time. Experiment has been carried out in 80o channel bend at constant discharge (3.5×10–3 m3 /s) and bridge pier is located at angular displacement ϴ = 60o . Here ϴ is the angle the line drawn at the inlet of any bend to the line joining the centre of curvature and any point on the outer portion of the bend. It is found that maximum scouring occurs at ϴ = 0o and 20o along inner wall and at ϴ = 60o and 80o along outer wall. It is also found that scouring around bridge pier is more in the vicinity of pier and decreases with increase in distance from pier. The most suitable location for spur dyke to protect bridge pier is at angular displacement ϴ = 20o . Scour developed rapidly during initial time and then rate of scouring decreases with elapse of time.

Effects of Spur Dyke’s Orientation on Bed Variation in Channel Bend

Spur dykes also known as Groynes are often used to either divert or attract the flow from the main structure to safeguard their life. Those structures may be bridge piers, abutments or any similar hydraulics structures. Spur dykes are also used to save the cutting of banks on concave side of stream. Lots of work have been done in recent past on spur dykes by many investigators in which various hydraulic and geometrical parameters of spur dykes such as discharge, sediment size, flow velocity, shear stress, spur dykes shape, size and submergence etc. are studied in detail. But mostly all the studies were pointed out in straight open channels. Very few studies were done in curved channel and only their similar effects were studied. In present thesis main emphasis is given to study the effect of orientation and location of spur dykes in meandering channel on the bed of downstream side. In the present study experimental work has been carried out in 80° bend and constant discharge (Q = 4.5 l/s) is allowed to pass in channel without spur dyke. It is found that maximum scouring occurs at angular displacement θ = 60° to 80° in the vicinity of outer bank. To minimize this scouring, spur dyke has been installed at angular displacement θ = 20°, 40° & 60° by changing the dyke angle α = 60°, 90° & 120° respectively. It is found that scouring at θ = 60° is reduced by installing spur dyke at angular displacement θ = 40° which is oriented at α = 60° and scouring at θ = 80° is reduced by installing spur dyke at angular displacement θ = 60° which is oriented at α = 60°.

Numerical investigation of flow field around T-shaped spur dyke in a reverse-meandering channel

Abstract In this paper, the flow characteristics around T-shape spur dyke situated in the reverse meandering channel with a rigid bed is simulated using renormalization group (RNG) turbulence model with ANSYS 2018 Fluent software. To solve the model in 3D ways we used Navier-Stroke's equation based on the principle of conservation of mass and momentum within a moving fluid. For studying the flow characteristics, computational fluid dynamics were applied with all geometric parameters and the turbulence was simulated using (RNG) equations of model. In this simulation, the structured meshes were used with different diameters and diameters of meshes are high at the exit channel for obtaining accuracy in the result. In this study, we mainly focus on the effect of Froude number on flow pattern and several other characteristics like velocity distribution, flow separation, bed-shear-stress distribution. The final result of this research work is compared with the condition when no structure is present in the channel.

Experimental Study Effect of the Flexible Collar on Bridge Pier Scouring Depth

Bridge pier's local scouring is known to be a destructive factor in river engineering science. This phenomenon is widespread in river intersecting structures such as bridge piers, spur dykes, and downstream river structures. Extensive research has been conducted to reduce and control destructive phenomena, and many solutions have been proposed. These solutions are divided into two parts, namely, direct and indirect protection. In this study, the direct method was studied by defining scenarios. Since many bridges are affected by scouring during the operation, in the present study, the collar method, which is known as a direct protection method, in the case of flexible and permeable, is suggested. The technique is presented an adjustable chain collar, three times bigger than the pier's width (w/d=3), and its effect is investigated in clear water conditions. In the defined scenarios, three different diameters of the chain as CI=5 mm, CII=10 mm, and CIII=15 mm were used to control chain shapes' effect, and three dimensionless flow parameters (U/Uc 0.73, 0.85, and 0.96) were selected to investigate the effect of flow conditions. According to the results, the scour depth is related to changes in the diameter of the collar chain, as the final scour depth decreases by increasing the diameter of the chain from CI to CIII. Therefore, in the best conditions, for CIII, the dimensionless ratio of scouring reduction ( ) is equal to 71% near to inception motion parameter (U/Uc=0.96).

Coupled modeling of bed deformation and stability analysis on a typical vulnerable zone on the Ningxia reach of the Yellow River during flood season

AbstractThe Ningxia reach of the Yellow River (NRYR) is wide and shallow, and instability and damages are likely to occur at its vulnerable zone. In this study, based on the one‐dimensional hydro‐sediment dynamics, two‐dimensional hydro‐sediment dynamics and vulnerable zone stability analysis model, a coupled model was established to analyze the scouring risk of the vulnerable zones in the NRYR during flood season. Considering the morphological change of bank slope at the vulnerable zones caused by flow erosion, the seepage stability of a typical spur dyke and protection embankment under the water level fluctuation conditions was analyzed. To fully reflect the coupled scouring effect of flow and sediment, the water flow scouring intensity index α is proposed. A significant increase of water flow scouring intensity index α will result in bank toe scouring, while its significant decrease will lead to silting of the bank toe. The probability of instability failure of the bank for the spur dyke slope is greater during the flood recession period. Compared with the influence of the change of river water level in the flood season, the slip stability of the bank slope is more sensitive to the change of bank toe erosion.

Effect of bed roughness on flow field around spur dyke in a rigid bed meandering channel

ABSTRACT Effect of bed roughness on flow field and turbulence characteristics due to spur dyke in rigid bed meandering channel is presented in this study. This is an extension of authors’ earlier work. In the experiments, cement mortar, sand particles on cement mortar and small aggregates on the cement mortar surfaces are used to generate different bed roughness. 3-D velocity measurements are obtained with Acoustic Doppler Velocimeter (ADV). In a rigid bed meandering channel without spur dyke, flow concentrates near the convex bank up to inflection point in the downstream of Apex. Inflection point moves towards the upstream with increase in the roughness of the channel. The water surface slope along the center line increases with increase in bed roughness. In presence of spur dyke, the maximum velocity in the channel decreases with increase in bed roughness. When the spur dyke is located on the convex bank of Apex, the length and width of separation zone decrease with increase in bed roughness. The magnitude of turbulence intensities decreases with increase in roughness.

Flow behaviour around spur dyke founded in cohesive sediment mixtures

This paper presents the results of flow and turbulence characteristics measured by a down-looking 16 MHz micro acoustic Doppler velocimeter around partially submerged spur dyke founded in a clay–gravel sediment mixture. Velocity and turbulence data were collected at various cross-sections at the wake and upstream sides of the spur dyke within and outside of the scour hole. The longitudinal velocity, turbulence intensities and Reynolds stresses were measured and quantitative analysis was carried out. Very small values of the longitudinal velocity component (negative) were obtained within the scour hole whereas larger values were obtained beyond the scour hole region. Turbulence intensities and Reynolds stresses were larger within the scour hole in the wake zone of the spur dyke. Bursting events, including outward interaction, ejection, inward interaction and sweep, were also analysed around the spur dyke. Quadrant analysis of the velocimeter data showed that the values of outward and inward interaction were higher within the scour hole around the spur dyke compared with the values of ejection and sweep events, while outside of the scour hole, the values of ejection and sweep events were higher than the values of outward and inward interaction events.

The development and application of an autonomous working turbidity measurement network: Assessing the spatial and temporal distribution of suspended particulate matter on tidal flats in the North Frisian Wadden Sea

Measuring suspension load (i.e. turbidity) in tide-dominated shallow marine systems like the North-Frisian Wadden Sea forms a major challenge with respect to understanding and modelling sediment origin, transport and dispersal. Sediment transport and deposition in highly dynamic and vulnerable coastal regions becomes especially relevant in terms of the natural adaption capacity of intertidal and supratidal areas to global sea-level rise.We have developed a network of eight autonomously operating turbidity measuring stations in an island-like salt marsh area (Hallig Langeness) in the tidal flats of the North-Frisian Wadden Sea. Using this system we got first insights about the availability of suspended particulate matter (SPM). In order to obtain the best possible estimation of the SPM concentrations in our study area, each measuring station has been individually calibrated considering the local conditions by using sediment collected by self-built sediment accumulators which are installed next to the respective measuring station. With this method we have investigated the availability of SPM and its spatial and temporal distribution during several spring and winter months.The results indicate strong and systematic SPM variability between individual stations ranging on average from 0.04 to 0.56 g/l. Control factors include installation altitude, the proximity to tidal channels, the positive influence on SPM availability by adjacent land reclamation areas or the negative influence on SPM availability due to a shielded position between two spur dykes. Further results show a strong increase of the SPM concentration under harsh weather conditions and inundation events whereby strong winds alone are not sufficient for a significant SPM increase. Instead, the combination of suitable wind direction, its strength and duration play a major role. The increase in SPM concentrations under harsh weather conditions tends to be highest at stations with less protection against the open water. Our new extensive network of turbidity measurements also allows for detecting areas with predominantly low SPM availabilities, the so-called low spots.

The geometric parameters of plants on the spur dykes in a selected section of the Odra River

Spur dykes are structures for regulating rivers. They are designed for medium water levels, when spur dyke tops are above the water surface. In the central section of the Odra River the water level is changeable, and the spur dykes work in different hydrological conditions: as non-submerged and submerged. Correct recognition of the plant structure growing on the spur dykes is of great importance in the context of the subsequent allocation of its measure related to the hydraulic action, among others coefficients of resistance of plant zones and refers mainly to grasses. In hydraulic calculations, it is required to determine the value of flow resistance coefficients. In such a departure, the flow is omitted in the area occupied by vegetation. Therefore, it is necessary to know the quantitative characteristics of overgrowth. Vegetation should be presented in the form of a model reflecting the impact of plants growing on the spur dykes and their impact on the water flow conditions in the river. Literature data are not very numerous and are still awake unsatisfied. The paper presents the results of research on the density of vegetation on the Odra River in the Nowa Sól region.

Quantification of spatial lag effect on sediment transport around a hydraulic structure using Eulerian–Lagrangian model

The spatial lag effect on sediment transport around a hydraulic structure is quantified through numerical simulation using a Eulerian–Lagrangian model. The Eulerian–Lagrangian model uses a deterministic approach of bed load motion and stochastic approach of Einstein's concept, which allows for a reasonable quantification of both non-equilibrium and equilibrium bed load transport rates. Numerical simulations are conducted for local scour around a spur dyke and a weir-type structure. As pointed out in previous experimental studies on the one-dimensional problem, Eulerian–Lagrangian simulation reveals an unsaturated bed load in a scour hole around a hydraulic structure. Furthermore, an oversaturated bed load is also found in the deposition region, particularly behind the structure. The validity of the linear adaptation equation is discussed using numerical results, revealing the possibility that the linear adaptation equation does not appropriately represent the existence of the strong spatial lag effect. The present study finds there are two modes in the response of the adaptation length to the unsaturated bed load, which depend on the clear-water scour condition or the live-bed scour condition. Findings of this study will contribute to multi-dimensional sediment transport simulations that consider the spatial lag effect.

How effective is river restoration in re-establishing groundwater–surface water interactions? – A case study

Abstract. In this study, we investigated whether river restoration was successful in re-establishing groundwater–surface water interactions in a degraded urban stream. Restoration measures included morphological changes to the river bed, such as the installation of gravel islands and spur dykes, as well as the planting of site-specific riparian vegetation. Standard distributed temperature sensing (DTS) and novel active and passive DTS approaches were employed to study groundwater–surface water interactions in two reference streams and an experimental reach of an urban stream before and after its restoration. Radon-222 analyses were utilized to validate the losing stream conditions of the urban stream in the experimental reach. Our results indicated that river restoration at the study site was indeed successful in increasing groundwater–surface water interactions. Increased surface water downwelling occurred locally at the tip of a gravel island created during river restoration. Hence, the installation of in-stream structures increased the vertical connectivity and thus groundwater–surface water interactions. With the methods presented in this publication, it would be possible to routinely investigate the success of river restorations in re-establishing vertical connectivity, thereby gaining insight into the effectiveness of specific restoration measures. This, in turn, would enable the optimization of future river restoration projects, rendering them more cost-effective and successful.

Euler–Lagrange model for local scour and grain size variation around a spur dyke

This paper presents a three-dimensional Euler–Lagrange two-phase flow model. The fluid phase is simulated by solving the unsteady Reynolds-averaged Navier–Stokes equations with a k–ε turbulence closure on an unstructured Eulerian grid, and a Lagrangian model integrating the grain trajectory and momentum equations is employed to predict the granular phase in motion. Considering the deterministic nature of the movement of individual grains and the stochastic nature of the behavior of grain groups, the grain–bed exchanges in terms of the grain entrainment and deposition are modeled with a stochastic approach. The vertical bed sorting and armouring processes are simulated by introducing a layering scheme for static grains in the bed. The numerical model is applied to predict the bed deformation around a spur dyke in a uniform and a non-uniform sediment beds. It is found that both the predicted local scour geometry and the grain size distribution are reasonably consistent with those of the experiments. According to the results, local scour in a non-uniform bed is smaller than that in a uniform one. The non-uniform bed around the spur dyke is coarsened, but sand ribbons occur in the upper part of the scour hole and at the downstream of the spur dyke.

水制の頭部形状がわんど内の水理に与える影響

水制の頭部形状がわんど内の水理に与える影響

Hydraulic characteristics of typical bank‐protection works along the Brahmaputra/Jamuna River, Bangladesh

AbstractSevere bank erosion is one of the most challenging problems in the management of large rivers in Bangladesh. This paper describes the detailed flow patterns around typical bank‐protection works on the Brahmaputra/Jamuna River as well as their morphological implications. Based on field surveys at several locations along this large alluvial river that are highly susceptible to erosion, attempts are made to clarify the flow fields and mechanisms of bank erosion. The performance of existing measures such as revetments and spur dykes are evaluated, and possible solutions for further enhancements are proposed. It is found that existing conventional works are generally huge in both size and cost, potentially exerting great disturbances on the river's dynamism and ecosystem. That said, the Bandal – a historied and indigenous structure – is cost‐effective and environmentally friendly. This study suggests the recurrent use of Bandal‐like structures for channel stabilisation and flood management of the braided Brahmaputra/Jamuna River.

Experiment Study on Channel Bed Characteristics around Spur Dykes of Different Shapes

This manuscript describes an experiment study on the local flow and bed variation around different types of spur dykes in sediment mixtures. The permeable spur dyke, impermeable spur dyke and three kinds of hybrid spur dykes are investigated under non-submerged clear-water scour conditions. The local scour and wake deposition properties and the characteristics of the sediment size distribution due to the differences in the type of the spur dykes are focused on. In general, both the flow structure and the bed properties around a hybrid spur dyke are a combined one of that of a permeable and an impermeable spur dykes. Sand ribbons are observed in the downstream of spur dykes, mainly caused by the sediment sorting in the transverse direction. Desirable flow patterns and bed properties may be achieved by taking full advantages of those of a permeable and an impermeable spur dykes.

Three-dimensional modeling of pollutants transportation in the flow field around a spur dyke

Pollutants are carried by sediment-laden flow dissolved in water or adsorbed on sediment particles. A transient three-dimensional model based on a compressible VOF (volume of fluid) method was developed to simulate the transport of dissolved and particulate pollutants. VOF is a numerical technique for acquiring and tracking the free surface of water flow. Local scouring, deposition and re-suspension were simulated and the processes of adsorption and desorption of pollutants on suspended sediment were analyzed. A series of experiments and numerical simulations were performed to study the transportation and dispersion of pollutants in the flow around a non-submerged spur dyke in a straight flume of rectangular shape. The simulation results agreed well with the experimental results. A certain volume of pollutants solution was released into the flow at upstream of the spur dyke. The concentration reduced with time. The concentration reduction was slower in the circumfluence zone than in the main flow. The ratio of adsorption to desorption coefficients was different for pollutants on suspended sediment with different diameter. The peak concentration of dissolved pollutants increased with the ratio of the adsorption to the desorption coefficients. The angle of the spur dyke affected the peak concentration around the dyke. The effect of the angle on dissolved pollutants decreased with the ratio of adsorption to desorption coefficients. The adsorption and desorption coefficients, as well as the saturated adsorption capacity had no effect on the concentration of particulate pollutants.

Bed morphology and grain size characteristics around a spur dyke

This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke. A series of experiments are conducted with different types of sediment beds. It is found that the heterogeneity of the sediment exerts an influence on detailed bed topographies around the spur dyke, but does not influence the typical features of scour-deposition morphologies. The mean grain size and the geometric standard deviation of the bed sediment are two important and practical parameters in characterizing the changes of the bed morphologies and the bed compositions around the spur dyke. The sediment sorting process plays a crucial role in the grain size distribution, and the process occurs longitudinally, laterally and vertically. In the proximity of the spur dyke, the bed is generally coarsened from upstream to downstream and sand ribbons consisting of fine particles are observed. Within the scour hole, the bottom sediment is coarser than that at the top.

Separation Zone in Flow past a Spur Dyke on Rigid Bed Meandering Channel

AbstractFlow past a spur dyke on a rigid bed meandering channel with a trapezoidal cross section has been studied experimentally. An acoustic Doppler velocimeter (ADV) was used to measure the velocities. The results show that length of the downstream separation zone changes according to the location of the spur dyke. It varies from 4.0 to 22.8 times the spur dyke length. In addition, the separation zone at higher elevations is wider compared to that near the bed for most of the locations of the spur dyke. The effect of contraction ratio and inflow Froude number on separation zone is also presented.

相対水制高が水制周辺の局所洗掘と粒度変化に与える影響

相対水制高が水制周辺の局所洗掘と粒度変化に与える影響

側壁に千鳥状に配置した遮蔽物がカワムツの休憩特性に及ぼす影響

側壁に千鳥状に配置した遮蔽物がカワムツの休憩特性に及ぼす影響