Spur Dike Research Articles

Flow near a model spur dike with a fixed scoured bed

Three-dimensional flow velocities were measured using an acoustic Doppler velocimeter at a closely spaced grid over a fixed scoured bed with a submerged spur dike. Three-dimensional flow velocities were measured at 3,484 positions around the trapezoidal shaped submerged model spur dike. General velocity distributions and detailed near field flow structures were revealed by the measurement. Clear differences were revealed between flow over fixed flat and scoured beds. Strong lateral flows were the dominant cause of the observed local scour. Shear stresses were higher for the scoured bed than in the flat bed case. Decreasing rates of scour as the scour hole developed were attributed to increases in critical shear stress in the scour holes caused by the increase in the length and magnitude of adverse slopes associated with the two main scour holes.

Macroinvertebrate assemblages in relation to environments in the West River, with implications for management of rivers affected by channel regulation projects

Rivers have many service functions, and play an important role in people's living and agricultural production. During the last decades, intensive human activities have been threatening river ecosystem. For shipping, hydraulic engineering facilities (e.g. spur dikes) have been built along river bank to increase water depth. However, natural habitat conditions (i.e. substrate, flow regime, water physico-chemical properties) are accordingly altered. Therefore, it is necessary to select representative organisms as indicators to assess the aquatic ecological status of different habitat conditions, furthermore, management strategies are to be put forward. Macroinvertebrates are often considered as good indicators of long-term changes in environments due to their confinement to the bottom, long life cycles and limited abilities of movement. In this study, field investigations of macroinvertebrates in the West River were conducted in November 2009 (at low water level) and May 2010 (at high water level). Altogether 70 taxa of macroinvertebrates belonging to 30 families and 59 genera were identified. Among them were 16 annelids, 21 mollusks, 32 arthropods and 1 miscellaneous animal. The average density and biomass of total macroinvertebrates were 140 ind m−2 and 0.23 g dry weight m−2, respectively. Canonical Correspondence Analysis (CCA) revealed that major factors structuring macroinvertebrate assemblages were flow velocity (U), water depth (Z), conductivity (Cond), total nitrogen (TN) and substrates (clay, silt, cobbles and bedrock). Density and diversity of macroinvertebrates peaked in the cobbles, while biomass reached the maximum in the bedrock. It is indicated that stable and heterogeneous habitats were beneficial to development of benthic assemblages. To conserve these habitats, type and construction position of spur dikes should receive enough attentions. Thus, it is suggested that as few spur dikes as possible can be constructed in the riverbed covered with cobbles and bedrocks. Otherwise, the angle between spur dike and river bank need be analyzed to generate the appropriate flow regime which can prevent the stable substrates from being buried by sands. Some advice about length and separation distance of spur dikes is also presented.

Two-Dimensional Numerical Investigation for Short- and Long-Term Effects of Spur Dikes on Weighted Usable Area of Rhinogobius candidianus (Goby)

AbstractThe weighted usable area (WUA) is one of the popular metrics to quantify the stream physical habitat and the effects of instream structures. However, most habitat studies only considered existing or proposed channel geometries in their WUA computations and not how the channel will evolve over time. This study reports a numerical investigation for the effects of spur dikes on WUA along the Juanchiao levee, Touchien River, Taiwan. Seven virtual dikes were placed along the outer bend in the study reach and the Rhinogobius candidianus was selected for target species. The horizontal two-dimensional (2D) flow fields at various flows and the corresponding WUAs for R. candidianus were computed under four channel bathymetry configurations, including: (1) existing; (2) immediately after dikes are implemented; (3) after 10-year channel migration without dikes; and (4) 10 years after dikes are implemented. The WUA obtained from the first two bathymetry configurations aimed to investigate the short-term spur d...

영천강 만곡부의 저수수제군이 생태계 및 하상변동에 미치는 효과

In order to assess the effects of ecosystem and landscape in around spur dikes, this study had carried out monitoring on the changes of ecosystem and morphologic characteristics in around spur dikes that had been settled in bend of Youngcheon River. The study site was a short reach with length 190m, spur dikes were installed in March, 2008. Monitoring of the site had been started in May 2008 and had been completed September 2011. The results are as follow ; 1) Spur dikes that were installed for channel stabilization are performing effectively hydraulic functions at flooding time. 2) Spur dikes that were installed in water colliding front of river bend brought about sediment deposition between those and formed pools around front of those. Therefore, it was verified to create various physical characteristics in the aspect of channel topography and flow consequently. 3) The survey results that was carried out in October 2008 showed to emerge 25 species of plant, 9 species of fish and 17 species of benthic macroinvertebrates, but the survey results in October 2010 showed to emerge 74 species of plant, 12 species of fish and 19 species of benthic macroinvertebrates. In particular, plant species that emerged in 2011 increased about three times more than those in 2008.

Effects of Ecological Spur Dikes on Spring Phytoplankton in Wangyu River

In order to study the effects of the newly-built ecological spur dikes on spring phytoplankton in Wangyu River, a riverway of water diversion project from Yangtze River to Taihu Lake, triple samplings were carried out in eleven sites from the near and upper water around the ecological spur dikes in April and May, 2011. The samples were collected to investigate the species and density of phytoplankton. Meanwhile, some environmental factors, such as temperature, pH, total nitrogen (TN), total phosphorus (TP) were determined. Indices of Simpson (D), Shannon-Wiener (H), Pielou (J) and Margalef (Dm) were used to analyze the change regulations of phytoplankton diversity. H, J, Dm were also used to evaluated the water quality, and they were 2.873, 0.532, 3.037. The results indicated that the composition of phytoplankton species was similar to the typical character of large or medium rivers. Based on the diversity indices, higher biological plankton diversity and better water quality emerged near the dikes. Results of this research supplied a theory for building ecological spur dikes to improve water quality of large or medium rivers and also provided a basis of using phytoplankton to monitor changes of water quality.

3D Flow and Sediment Dynamics in a Laboratory Channel Bend with and without Stream Barbs

AbstractA series of laboratory flume experiments were performed to study the effect of stream barbs on flow field dynamics and sediment erosion in a 135° mobile-bed channel bend. Stream barbs (also known as spur dikes or submerged groynes) are low-profile linear rock features that redirect high velocity flow away from the outer bank of channel bends. Unlike emergent groynes, the submerged nature of these structures creates a unique combination of horizontal shear (plunging type flow) and vertical shear (at the groyne tip). Spatially dense, high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three-dimensional (3D) velocity throughout the bend and in the vicinity of the stream barbs. This paper demonstrates that the outer bank region (particularly between barbs) may still be at risk of erosion (or even increased erosion greater than the same case without barbs) if stream barbs generate excessive secondary velocities (because of their size and layout) that are op...

Study on Spacing Threshold of Nonsubmerged Spur Dikes with Alternate Layout

This paper investigated the spacing threshold of nonsubmerged spur dikes with alternate layout to classify the impact scale of spur dikes. A mathematical model was built based on standardk-εmodel, finite volume method (FVM), and rigid lid assumption and was verified by experimental data. According to dimensional analysis, three indices, that is,Fr(Froude number),B/b(channel width to dike length), andB/h(channel width to water depth), were identified as the influencing factors on the spacing threshold, based on which fifteen sets of conditions were simulated. The calculation results indicate thatB/his the most influencing parameter onSc/b(spacing threshold to dike length), followed byB/bandFr. A dimensionless empirical formula of spacing threshold is fitted by multivariate regression. The results of four sets of additional conditions illustrate that the generalization of empirical formula is satisfactory and the precision of interpolation is higher than that of extrapolation. Furthermore, the spacing threshold of alternate spur dikes is generally smaller than ipsilateral spur dikes.

連続水制を伴う開水路乱流における自由水面のガス輸送に関する基礎的研究

In this study, gas transfer velocity through free surface is investigated in open channel flow with a series of spur dikes. Spur dikes formed closed dead-water zones between the neighboring members. The slow-speed circulation observed in such cavity zones is quite different from high-speed mainstream. Therefore, the cavity zones and the mainstream are assumed to have different reaeration coefficient. The reaeration coefficients are evaluated by means of laboratory measurements. The measurement theory is also specially developed together with consideration of gas transfer through the junction between main-channel / side-cavity. It is found out from present results that reaeration coefficient depends strongly on the aspect ratio (width/length) of dead water zones under same hydraulic condition.

Verification of numerical study of scour around spur dikes using experimental data

AbstractScour phenomenon around a series of impermeable, nonsubmerged spur dikes has been investigated with both experimental and numerical methods. The experiments were conducted under different states of flow intensity (U/Ucr). The scour geometry was measured with a high‐resolution laser bed‐profiler (LBP). For the numerical simulation phase, a three‐dimensional computational fluid dynamics (CFD) model, namely SSIIM 2.0, was used to compute the sediment transport around the spur dikes. The numerical model was based on the finite‐volume method. Two turbulence models, namely k‐ε standard and k‐ε with re‐normalization group (RNG) extensions, were used to predict turbulence, and the k‐ε model with some RNG extensions was selected because of its best agreement with the measurements. Furthermore, a variety of grids and empirical sediment transport equations were used to find the best state for simulation of scour around a series of spur dikes. Finally, a comparison between experimental and numerical results was carried out to verify the CFD model.

Investigation of hydrodynamics on local scour by shape of single spur dike in river bend

A series of experiments were conducted in which the the scour hole associated with model spur dike was measured in a 180 degree laboratory flume bend under clear-water overtopping flows. In this study, the local scour were conducted for three different shapes of oblong, rectangulat chamfered of straight spur dikes at the bend with various Froude number. The main goals of the experiments were to evaluate the effect of the three different shapes of straight spur dikes on the volume of scour and potential aquatic habitat and on minimizing erosion adjacent to the streambanks. The experiments showed that of the three different shapes of straight spur dikes tested, the least erosion of the around in the near bank region was associated with the spur dikes with oblong shape, while the greatest volume of the scour hole was associated with the rectangular shape. So it was observed that, as Froude number increases, the scour increases.

New Type of Spur Dike at the Exit of Diversion Channel: Courter-Arc Vertical Ladder Spur Dike

Arranging spur dike at the exit of diversion channel significantly influences the safety of the downstream cofferdam and the scour of the downstream bed by changing the water velocity and turbulence. In order to compare the advantages of different arrangement of spur dike, detailed profiles of velocity and scouring are measured in laboratory flume. And water depths, surface velocity and the condition of downstream bed scouring are investigated at the exit of diversion channel at different arrangement. A new type of spur dike is designed, which is named as courter-arc vertical ladder spur dike. Through experiments on physical model, the new type of spur dike alters the direction of the outflow, decreases water speed and reduces downstream bed scouring and ensure high slope safety.

Evaluation of bendway weir bank stabilization techniques for stream restoration

In this study, velocity distribution patterns in a stream in the presence of bendway weirs were assessed for their effectiveness in bank stabilization in a demonstration site in the Las Vegas Wash, Nevada, USA. Streambanks of the target stream had been stabilized previously by longitudinal stone toe protection (LSTP) and stone spur dikes. Stone toes are meant to protect the toe of streambanks. Similarly, stone spur dikes consist of a series of dikes (of a crest relatively higher than that of the bendway weirs) protruding at right angles from the convex side of the streambanks. Velocity measurements were taken to evaluate the velocity field in the channel in the following three different cases: Case 1, channel with LSTP and the pre-existing spur dikes; Case 2, channel with LSTP with no deflecting structures (spur dikes removed); and Case 3, channel with LSTP and bendway weirs. The results suggested that bendway weirs caused a reduction in the uncontrolled high-velocity flow near the outer bank (right bank), allowing only controlled flow. Thus, bendway weirs were found to be more effective than spur dikes in reducing the velocity of flow at the vulnerable weir zones near the outer banks, thus providing a means to stabilize the streambanks.

New 3‐D flow interpolation method on moving ADCP data

A simple but accurate interpolation procedure for obtaining the three‐dimensional distribution of three‐component velocity data, from moving acoustic doppler current profiler (ADCP) observation data, is proposed. For understanding actual flow structure within a river with complex bathymetry, the three‐dimensional mean velocity field provides a basic picture of the flow. For obtaining the three‐dimensional distribution of three‐component velocity data, in this work, anisotropic gridding was introduced in order to remove the random component of measured velocity data caused by the turbulence of the flow and measurement error. A continuity correction based on the pressure equation was used to reduce both random and systematic errors. The accuracy of the developed method was evaluated using three‐dimensional flow simulation data from a detached‐eddy simulation (DES). By using the procedure developed, the complex flow structure surrounding the spur dikes section in the Uji River was successfully visualized and explored. The proposed method shows superiorities in both accuracy and consistency for the interpolated velocity field, as compared to the kriging and inverse‐distance weighted (IDW) methods.

Experimental Study on Scour around a T-Shaped Spur Dike in a Channel Bend

This paper deals with the study of the geometry of the scour hole and topography of the bed around a T-shaped unsubmerged spur dike located in a 90° bend. The experiments were carried out in a channel with a 90° bend. Uniform sediments having an average diameter of 1.28 mm were used under clear-water scour conditions. The effects of parameters like the length of a spur dike, the wing length of a spur dike, the location of a spur dike in the bend, the radius of bend, and flow intensity on the scour around a T-shaped spur dike were investigated. A new equation for scour parameters at a T-shaped spur dike is developed. DOI: 10.1061/(ASCE)HY.1943-7900.0000536. © 2012 American Society of Civil Engineers.

Experimental Study on Flow Turbulence Distribution around a Spur Dike with Different Structure

The spur dike is an important building in river guiding and bank protection. In the present paper, the turbulence intensity distribution around spur dikes with different structures under the same flow condition is studied through model experiment and it gives the turbulence contours. Combining with theoretical analysis, it can be calculated that the turbulence intensity in the arc-like spur dike and fan-like are relatively weaker than that of the hook-like spur dike, and the strongest turbulence intensity occurs around the trapezoidal spur dike. The conclusion will provide a scientific basis for a reasonable choice of the structure of a spur dike, which provides the references for a better structure of a spur dike.

固定床上に設置した水制周りの流れと流砂・河床変動特性

Spur dikes were expected to create new aquatic habitats according to produce local scour and sediment deposition area around them on the movable bed. However, when the spur dikes were set on the rigid bed for creating new aquatic habitats, it was not known the potential ability to accumulate sediment deposition behind spur dikes. In this study, we conducted experimental flume tests and numerical analysis to confirm the characteristics of flow, sediment transport and bed deformation around the spur dikes on the rigid bed. These results showed that the sediment was not deposited behind the spur dikes, because the sheer stress is smaller than the critical sheer stress in the upstream area of the spur dikes, so that all bed materials were transported to the opposite bank side. However, when the flow is under unsteady condition, it is confirmed that the no sediment transport area is reduced because the large transverse water surface gradient is formed in the downstream area of the spur dikes during the increase process of water discharge and would change the direction of sediment transport material.

Experimental Study on the Effect of Froude Number on Temporal Variation of Scour around a T Shaped Spur Dike in a 90 Degree Bend

In the past few decades, the use of spur dikes for stability of the outer banks of rivers has attracted the attention of hydraulic engineers. Setting spur dikes in the flow’s direction leads to local scour around the spur dike and changes the topography of the bed. This paper deals with the study of the temporal variation of the scour hole and topography of the bed around a T shaped spur dike located in a 90 degree bend. The experiments were carried out in a channel with a 90 degrees bend. Uniform sediments having an average diameter of 1.28mm were used under clear water condition. The effects of Froude number on the amount and the geometry of scour hole around a T shaped spur dike and the time variation of scour were investigated.

Flow and turbulence structure around a spur dike in a channel with a large scour hole

The flow and turbulence structure around a vertical‐wall spur dike that extends over the whole depth of a straight channel are investigated using detached eddy simulation (DES). The channel Reynolds number in DES and the corresponding experiment is ReD = 2.4 × 105, which is typical of applications in small rivers and outside the range where well‐resolved large eddy simulation (LES) can be conducted. The bathymetry at equilibrium scour conditions is obtained from a loose bed experiment. This paper discusses the main mechanisms which drive the growth of the scour hole upstream and downstream from the spur dike during the later stages of the scour process, and how these mechanisms change between the initial (flat bed conditions) and later stages of the scour process. Scale effects are investigated by comparing simulation results at ReD = 2.4 × 105 with those from simulations performed at a much lower Reynolds number, ReD = 18,000. Results show that while the structure of the horseshoe vortex (HV) system changes with respect to the case in which the bed is flat, the main necklace vortex of the HV system is still subject to large‐scale aperiodic oscillations, similar to the ones observed in flows past in‐stream bluff‐body obstacles mounted on a flat surface. Present results show that the amplification of the horizontal vorticity within the lower part of the separated shear layer (SSL) and the associated formation of streaks of high‐bed shear stress below the region where the SSL eddies are convected in the near‐bed region is a general feature of high‐Reynolds‐number flow past a vertical‐wall spur dike placed in a loose‐bed channel at all stages of the scour process.

Turbulent burst around experimental spur dike

Three-dimensional turbulent flow field was measured around an experimental spur dike by using a micro-acoustic Doppler velocimeter. Time fractions of turbulent burst events including outward interaction, ejection, inward interaction, and sweep were analyzed in each quadrant at the neighbor of the dike before and after the formation of scour hole. Over 80% of burst events near the bed have lower-order of magnitudes for both flat and scoured bed surfaces. Ejections and sweeps are prevalent before the local scour was initiated, and then outward interactions are dominant after the scour hole was formed. Conditional Reynolds stresses and high-order moments of turbulent velocities were analyzed along the thalweg. The magnitudes of u′– w′ pair were much larger than those of v′– w′ pair in the scour zone. Among four burst events, ejections and sweeps are the higher order events contributing to the Reynolds stresses. Since sediment entrainment and transport are closely associated with turbulent bursts near bed, the development of scour hole greatly depends on the higher order event near the bed.

Coherent structures around isolated spur dikes at various approach flow angles

The turbulent flow structures around an isolated spur dike located at three different approach flow angles are investigated. Detached eddy simulation is used at a channel Reynolds number of 45,000. Experimental velocity measurements were also conducted using acoustic Doppler velocimetry for validating the simulations. It is found that the size and orientation of the horseshoe vortex system change considerably with the approach flow angle. The main necklace vortex is largest in size and most coherent for 90°. Within this orientation it has larger amplitude bimodal oscillations compared to the 60° and 120° cases. A new scour mechanism is defined for the 60° case which is expected to generate more scour upstream of the spur dike. The possible scour area around the spur dike is found to be the maximum in the 90° case which is roughly by 15% larger than that of the 120° case.