Showing papers on "Groyne published in 2011"

Flow Details near River Groynes: Experimental Investigation

Abstract: Experiments have been carried out in a fixed-bed flume for a schematized straight river reach with groynes on one side to study the dynamics of the flow near groynes. The flume had a geometrical scale of 1:40, based on typical dimensions of the Dutch River Waal. Both emergent and submerged groynes were studied. The measurements demonstrate the differences in the nature of the turbulence between submerged and emerged groynes stages; and provide insight into the flow pattern in the vicinity of groynes, the shape and the extent of the mixing layer at different flow stages, and the dynamic behavior of the velocity along the mixing layer between the main channel and the groyne fields. A parameterization of the turbulence characteristics of the flow near groynes is presented. Large-scale velocity fluctuations are found in all test cases, with timescales that vary with the flow stage. The large-scale u and v velocity fluctuations are in phase in the center of the mixing layer and out of phase for the points on the boundaries of the mixing layer.

Water-surface oscillations in channels with axi-symmetric cavities

Abstract: Transverse or longitudinal movements of a water body are observed for flows along cavities, river embayments, groyne fields or harbours. They are significant for certain flow conditions and geometrical properties. To study the effect of large-scale roughness on banks, 36 geometries of axi-symmetric, rectangular cavities were investigated in a laboratory flume under subcritical, turbulent free surface flow conditions. Significant movements of the water body were detected. The frequency of these periodic movements, identified by level and velocity observations, is in agreement with the natural frequency of the water body in a rectangular basin assuming the first-order mode of sloshing. Major movements of the water body, which lead to significant and periodic oscillations of the water surface, are avoided by excluding Strouhal numbers near 0.42 and 0.84. For low aspect cavity ratios, the periodic water-surface oscillations are insignificant if the flow reattaches to the sidewalls of the widened channel reach.

Distributions of sediments of the tidal flats in response to dynamic actions, Yangtze (Changjiang) Estuary

Abstract: Sediment samples with high spatial resolution (432 samples in total) and flow data were collected on the tidal flats in the mouth-bar region of the Yangtze Estuary. The data was collected in July 2005, July 2006 and May 2007. The samples were analyzed with a particle sizer, resulting in the sediment distribution. The grain sizes and related parameters were analyzed. The results were presented in a ternary diagram. The sediment mainly consisted of sand, silty sand, sandy silt, sand-silt-clay, silt and clayey silt. And sand skeletons and clay matrices were found. At Nanhui Shoal, silt skeletons could be identified as well. Furthermore, the results were discussed per shoal. Although some depth dependencies were found per shoal, no general relation was found. The results are as follows: sediment located at these tidal flats of the Yangtze Estuary was mainly composed of sand, silty sand and silt. The median grain size in sediment was relatively complex with a range from 2.5 φ to 8 φ. The distributions of sorting coefficients ranging from 1 to 2 were in agreement with median sizes. It was suggested that sediment of the tidal flats was coarser and better sorted or finer and worse sorted. The skewness in sediment distribution varied from 0.1 to 0.8. In addition, the distributions of sorting coefficient and skewness in sediment at Chongming Eastern Shoal, Hengsha Eastern Shoal and Jiuduan Shoal were of similar characteristics because there were closely positive correlated relationships among these parameters. However, due to the location difference between Nanhui Southern Shoal and Eastern Shoal, the values of sorting coefficient and skewness had relatively large distinctions. The tracks of sediment transport could be described based on the distributions of sediment, which might reveal sediment transport controlled by two dominant hydrodynamic factors of current and wave. It was appreciable that coarser sediment with lower sorted coefficient was affected by dominant ebb current action and intense wave action resulted from rapidly dissipated wave energy. Moreover, due to the effects of obstructed branches, guided current and broken wave actions of the Deep Water Channel Project, grain-size in sediment located at two sides of the groyne was of uneven distribution characteristics.

Experimental investigation on the local scour characteristics around groynes using a hydraulic model

Abstract: Scour holes resulting from the installation of a groyne are considered to perform the environmental function of providing a habitat and a haven for various aquatic organisms during floods, hence, the need for studies on the scour area and its volume near a groyne beyond the scope of past discussions on their stability In this study, hydraulic experiments were conducted in fixed and movable beds to examine the flow pattern, bed change and scour depth and hole around a groyne The results of the fixed-bed experiment indicated an effect on the flow change in the main channels and recirculation zones following the installation of a groyne Changes in tip velocity and flow angle as the scour factors around a groyne were quantitatively compared as well Through the movable-bed experiment, the scour-hole shape, scour area, scour depth and volume of bed change were examined and compared

Long term morphological modelling

Abstract: A morphological modelling concept for long term nearshore morphology is proposed and examples of its application are presented and discussed. The model concept combines parameterised representations of the cross-shore morphology, with a 2DH area model for waves, currents and sediment transport in the surf zone. Two parameterization schemes are tested for two different morphological phenomena: 1) Shoreline changes due to the presence of coastal structures and 2) alongshore migration of a nearshore nourishment and a bar by-passing a harbour. In the case of the shoreline evolution calculations, a concept often used in one-line modelling of cross-shore shifting of an otherwise constant shape cross-shore profile is applied for the case of a groyne and a detached breakwater. In the case of alongshore bar/nourishment migration an alternative parameterization is adopted. All examples are presented, analysed and discussed with respect to the question of realistic representation, time scale and general applicability of the model concept.

Block stone-reinforced concrete piling composite groyne bank protection structure

Abstract: The invention relates to a block stone-reinforced concrete piling composite groyne bank protection structure, which is used for bank protection in hydraulic engineering and ocean engineering. The block stone-reinforced concrete piling composite groyne bank protection structure consists of reinforced concrete pilings, connecting and tying beams and block stones. When the composite pile type groynestructure ensures the accretion promotion and pond protection effect of the pile type groyne, the goal of reducing the engineering manufacture cost is reached through enlarging the piling space and reducing the consumption of reinforced concrete.

Design of groynes modified with both alignment and permeability for lowland river problems

Abstract: A groyne is an important river restoration structure. Although its history is for long and widespread use, optimized design of new groynes is not attempted much, which is very important to treat the highly unstable lowland river channels. A completely blocked impermeable groyne suffers from instability of the structure itself; whereas, fully permeable structure can not divert the flow rightly. Considering the present demands, four different groyne structures including modified combined and bandal-structures are examined in the laboratory channel to recognize their fluvial responses, incorporation with some field information. The performance of a groyne is confirmed through three key features: scour near groynes (structure stability), deposition in the groyne field (bank stability) and erosion in channel bed (navigability). Analyses of data show that the combined groynes cause gradual deceleration of flow towards the land and minimize local scour compared with the conventional impermeable ones. Also two other important features: deposition near bank and channel erosion, are better responded from modified bandal-structures and modified combined groyne.

Impact of rubble mound groyne structural interventions in restoration of Koggala lagoon, Sri Lanka; numerical modelling approach

Abstract: Physical processes of the lagoon are influenced by structural interventions. Understanding the complex reality of physical processes sometimes difficult with field observations thus a model provides a simplified abstract view. Two dimensional hydrodynamic model is used to describe, restoration efforts to Koggala lagoon, a combined freshwater and estuarine complex of rich ecosystem on the southern coast of Sri Lanka. The lagoon mouth was naturally closed by a sand bar which controlled the seawater intrusion. Due to large-scale sand removal at lagoon mouth, formation of the sandbar shifted towards the lagoon. After the removal of natural sand barrier, rubble mound groyne structures were built to avoid sand deposition in the lagoon and to protect the highway bridge from the sea wave attack. Construction of the groyne resulted in the lagoon mouth being permanently open which in turn led to many environmental problems with saline intrusion. The aim of this study is to evaluate the current situation of the lagoon and propose alternative structural interventions for minimization of seawater intrusion and subsequently improve lagoon ecosystem. Hydrological parameters were investigated and mathematical models for hydrodynamic behavior of the lagoon were applied in order to describe the lagoon physical processes and flow characteristics. Existing rubble mound structures were redesigned in order to minimize the seawater intrusion. Numerical simulations were carried out for two different mouth widths (40 m and 20 m) with appropriate structural interventions. Existing salting factor for the lagoon is 0.68 and numerical simulation results showed salting factor for 40 m and 20 m openings are 0.61 and 0.54 respectively. This shows the mouth width can be reduced up to 20 m in order to obtain a slating factor close to 0.5, which indicates the predominant influence of fresh water which in turn leads lagoon to a fresh water ecosystem.

Optimum design of groynes for stabilization of lowland rivers

Abstract: Alluvial rivers at low land as in Bangladesh are highly dynamic in nature; where huge landloss due to severe bank erosion at high flood as well as repeated interruptions of navigation system due to rapid sedimentation at low flow are very common. Groynes, revetments etc. are typically used to overcome these problems, but the goals are not achieved as expected. This study investigates the optimum design of a groyne for its effective functioning. A 2D model, RIC-Nays is utilized in this study upon confirmation. The channel and flow parameters are based on conformity to a typical river of Bangladesh. Four orientations and three configurations of groynes are considered here. The performance of groynes is evaluated through three key indices erosion in channel bed (thalweg), deposition in groyne field, and scour near groyne-tip. Computations reveal that a modified groyne functions better over the straight ones through protection of channel bank from erosion and maintenance of navigation channel as well.

Physical modelling of overbank flows with a groyne set on the floodplain

Abstract: If in natural or anthropized rivers, the river cross-section generally gradually and continuously varies, transversal and discontinuous obstacles either natural or artificial may partially or totally block off floodplains. The flow overbanking in the floodplain is therefore contracted by this obstacle which then promotes two recirculation zones of both sides of the obstacle, resulting in a reduction of the flow section and in the generation of strong mass exchange between channels that superimposes to the classical turbulent interactions. New experiments are conducted in two different compound channels: rapidly varied flows in compound channel with a groyne set on the floodplain. Flows with various groyne lengths and total discharges were investigated. Effects on the hydraulic parameters of the superimposition of the two problems that are (i) flow in compound geometry and (ii) rapidly varied flow in the vicinity of a thin obstacle were analysed. Finally, dominance of physical processes in such flow configuration is discussed

Sand and seagrass wrack modelling in Port Geographe, south-western Australia

Abstract: Port Geographe, a marina and residential canal estate development, was developed in the early nineties. The design incorporated a sand bypass system to transfer sand across the harbour entrance from the west (upstream) to nourish the beaches in Wonnerup in the east; however, the artificial bypassing became a challenging issue because of the presence of seagrass wrack, which was more efficiently trapped by the sand trap than the sand. The wrack accumulation caused severe environmental problems (e.g. odour, reduced beach use) on the western side of the development and erosion of beaches to the east at Wonnerup. In this paper, the results from a numerical model study of sand and seagrass wrack transport that was undertaken to alleviate these problems are presented. Models developed by the Danish Hydraulic Institute (DHI MIKE 2D) were used to predict the waves, currents, and changes in morphology and were linked to a particle-tracking model developed as part of the study to simulate wrack transport. The model runs included the existing coastal structures and other configurations designed to bypass naturally both sand and seagrass wrack. An optimum configuration for the coastal structures to promote the natural bypassing of sand and seagrass wrack included an angled groyne on the western side of Port Geographe to replace the existing breakwater and the removal of groynes associated with the pocket beaches by a foreshore seawall.

Etude expérimentale de refuges à poissons aménagés dans les berges de rivières soumises aux éclusées hydroélectriques

Abstract: Downstream of hydroelectric storage dams, the rivers suffer from rapid, frequent and intense flow variations linked to the power production constraints. Subjected to this hydropeaking phenomenon, the fish population suffers from a known decline. In the research of mitigation solutions, shelters in riverbanks are a protection measure against excessive flow velocities. This project gives the design basis for such shelters. The research process is based on experimentations with fish swimming in a canal built on purpose with a lateral embayment. The principle is to generate hydrodynamic conditions that are uncomfortable in the canal on one hand and attracts the fish to the shelter on the other hand. The significant parameter is the flow velocity distribution in the intersection between the main channel and the lateral fish shelter. The frequentation rate of fish in the shelter can be considered as the performance indicator. With a length of 12 m and a width of 1.2 m, the canal is supplied with freshwater from a river. At mid-length, the canal holds a one side enlargement of 1.2 m, shaped like a rectangular gap of 2 m long. For each test, after a steady flow of 10 l/s with a mean velocity of 0.1 m/s, 10 to 20 juvenile brown trout are suddenly exposed during 3 hours to a hydropeaking flow of 220 l/s. At that time, the mean velocity in the canal is of 1 m/s. The fish position is observed every 20 minutes and their movements are recorded continuously in the shelter sector. The first tests have been conducted with a basic rectangular shelter configuration. The frequentation rate was only of 35%. This rate has doubled by introducing a deviation groyne that enforced a water exchange between the canal and the shelter. Following this experiment, the position and the orientation angle of the groyne have been systematically varied with the purpose of maximising the frequentation rate. This way, 12 configurations have been tested 3 times each. The flows transiting in the shelter are calculated using a 2D numerical simulation. By analysing the fish positioning, the mean frequentation rate is determined for each configuration. The maximum rate is of 87%, the mean is of 75% and the standard deviation is of 8%. Using video pictures treatment, the preferential fish trajectories are updated and the fish entrance distribution is determined for each configuration at the interface between the shelter and the channel. On the same interface, ultrasonic velocity profiles (UVP) have been measured for the 12 configurations. By associating the fish entries distribution with the velocities distribution, the preferences are globally established. The entrances happen mostly from downstream of the derivation groyne, in a flow shear zone where the velocities are in a range of 0.0 to 0.2 m/s. Finally, the analysis of all the results confirmed the representativity of the configuration that gives the best frequentation rate, for the development of the experimental shelter's prototype to be realised in rivers. It is composed of a groyne shaped like an equilateral triangle. Finally, recommendations are given for the execution of an experimental prototype shelter to be realized in a river for validation tests.

Three-dimensional simulation of flow around a groyne with large-eddy turbulence model

Abstract: This article uses the Flow-3D software to provide a numerical model of groyne-surrounding flow by using the large-eddy turbulence model while studying the effects of these factors on separation length and width of separation region behind a groyne by applying various groyne lengths, installation angles and flow velocities. A comparison of results of the numerical model with the experimental results of other researchers indicates that increase in groyne length, the separation region is increased and between the installation angles of groyne, the maximum separation region length and width were related to installation angle on 105°. In addition, the results of the numerical model indicate that while the groyne length change, the ratio of separation region width to groyne length remains almost the same.

Morphodynamic responds of groyne fields to the lowering of crest level of the groynes in the Waal River, The Netherlands

Abstract: The lowering of the crest of the groynes in the River Waal is one of the measures being applied in the Netherlands to reduce the water levels at high water conditions. A total of 750 groynes will be lowered lengthwise by 1 to 2 meters. An expected side-effect is sedimentation in the main channel, due to redistribution of the discharge in the cross-section. Also, the flow through the groyne fields will increase, so erosion in the groyne field is to be expected. In order to get insight in the morphological developments after lowering the groynes, a pilot project has been conducted. It consisted of the lowering of the 70 groynes from April 2009 till September 2009. A monitoring program was implemented, including multi beam measurements of the groyne fields and the main channel. The measured groyne fields included river sections with and without lowered groynes. The measurements were carried out during a high water event, with a return period of once per year, in March 2010. Measurements of the bed levels for this high water event, were conducted at three moments: before the high water event, during the peak and after. The patterns of erosion and sedimentation in the groyne fields were analyzed and the effect of the lowering of the groynes on the morphology of the groyne field was quantified. This paper addresses the morphological developments of the groyne fields and near the head of the groynes. The measurements show that between the initial situation and the discharge peak, erosion occurred in the groyne field in the first 40 m from the normal line towards the banks for both types of groyne fields. However, the amount of erosion in the groyne fields between lowered groynes, is twice as much as the erosion in the groyne field without lowering. In the period after the peak discharge, in the first 25 m from the normal line towards the banks, sedimentation occurred in the groyne fields without lowering, and erosion in the groyne field with lowered groynes. Between 25 m and 50 m towards the banks, sedimentation occurred in both types of groyne fields, but the sedimentation in the groyne fields between lowered groynes was twice as much as in the groyne field between groynes without lowering. Furthermore, the measurements show that the measured scour-holes near the groyne head, caused by local flow contraction and turbulence, are less deep for the lowered groynes. This is probably due to the

The Impacts of a Groyne Field on Secondary Flow Phenomena in a High Curvature Bend

Abstract: Groyne fields can be used to protect river banks against sediment erosion in regions of high curvature. While the low flow velocity within the embayments protects the outer bank, the main channel mean velocity is increased. Little is known about how groynes affect the structure and strength of the streamwise and cross-stream flow in sharp channels and their impact on erosion. This Large Eddy Simulation (LES) study compares flow with and without submerged groynes (channel depth/groyne height=1.8) in a sharp 135 bend under initial scour conditions. Both simulations show that besides the main channel recirculation cell, strongly coherent streamwise oriented vortices (SOVs) form close to the inner bank. The LES results quantify the streamwise variation of the crossstream circulation induced by the main eddies in the cross flow. Results show the groynes significantly increase friction velocity over part of the inner bank close to the SOVs. The larger potential for inner bank erosion should be considered in groyne design for sharp channels with banks close to vertical.

Stream barb performance in a semi-alluvial meandering channel

Abstract: A series of seven stream barbs were installed at two consecutive channel bends in Sawmill Creek, a semi-alluvial stream located in Ottawa, Canada. Stream barbs (also known as submerged groynes) are low-profile linear rock structures that extend from the outside bank regions of channel bends in an upstream direction, to redirect the attacking currents and prevent erosion of the bank. As well as providing bank protection, these structures promote vegetated stream banks, create resting pools and scour holes for fish habitat, and increase biodiversity for aquatic species. Despite these benefits, because of their relative novelty as river training structures, stream barbs are not a common means of stream bank protection in Canada and are possibly non-existent for semi-alluvial or clay channels. Three years of monitoring and measurement of flow conditions (discharge, water velocity and depth) and bathymetry, before (2 years) and after (1 year) the construction of the barbs, have been collected at the Sawmill Creek study site, providing valuable data for understanding their performance in a semi-alluvial channel. Sawmill Creek has a predominately clay bed and banks, presenting a rare opportunity to study the unique dynamics between flow and sediment transport within a clay channel. This paper reports on (i) the unique site conditions and monitoring methodology; (ii) preliminary results of the 3 year monitoring program; and (iii) recommendations for future design and implementation of these structures.

Impact of Benthic Species on River Morphology

Abstract: The invasion of benthic exotic species in aquatic systems has increased in the last couple of decades due to the increase of human activities in waterways (e.g. ballast water transport, attachment to boat hulls). Many studies have been done on the interaction between benthic organisms, sediment dynamics and thus morphology of aquatic systems. Nevertheless, these studies have been mainly conducted in marine and estuarine systems, involving different sediment and hydrodynamic conditions. Until now no studies are known on the impact benthic species on river morphology. The main objective of this Master Thesis is to investigate, by using the Delft 3D model, the influence of benthic species on sediment dynamics, and the possible changes on river bed morphology due to the presence of benthic species. Delft 3D is a numerical modelling system developed by Delft Hydraulics, fully applicable for 3-dimensional computations of hydrodynamics and morphodynamic simulations of coastal, river and estuarine areas. The study considers three exotic bivalve species in the River Waal: the Corbicula fluminea, Dreissena polymorpha and the Dreissena bugensis, where through the alteration of the erosion threshold, the C. fluminea living in the groyne field are the only species exerting a direct impact on sediment. Literature shows that the effect of the benthic activity on sediment dynamics may result in an increase/decrease of the erosion threshold, merely depending on two mechanisms: the bioturbation caused by benthic communities and the formation of biofilms (EPS) that “sticks” the sediment together. In order to model the possible benthic effects, three scenarios were investigated: One scenario subjected to sediment biostabilization (high erosion threshold), another one to biodestabilization (low erosion threshold) and finally a scenario that accounts for the anticipated maximum possible biostabilization in rivers. When using the transport formulation developed by Van Rijn (84), the erosion threshold is proportional to the median grain size D50, and therefore, in this study this value is locally increased/decreased inside the groyne fields in order to introduce the benthic effects into the Delft 3D model. The results show that under steady hydrodynamic conditions, the benthic effects do not exert significant changes in morphology. Contrary to this, the impact of changing hydrodynamic conditions and navigation are expected to alter the sediment processes within the groyne fields and therefore the benthic impact. These were not quantitatively considered in this study, however, are highly recommended for future research due to the importance of groyne fields for the sediment exchange in a river.

Experimental Study on the Flow Characteristics of ㄱ-Type Groyne

Abstract: A hydraulic model test for ㄱ-type groynes (with “ㄱ” shape) was conducted to analyze the flow characteristics around these groynes. The results of the model tests are expected to be used as fundamental information in designing the ㄱ-type groyne constructed in the field. Main hydraulic factors such as velocity and thalweg line changes in the main channel and separation area were analyzed in this study. The thalweg line is a stream line where the maximum velocity occurs, whereas the separation area is the boundary between the main flow and the recirculation zone. Model tests with 5 different arm lengths of the ㄱ-type groynes were conducted by changing the velocity. The LSPIV (Large-Scale Particle Image Velocimetry) technique was used to measure and analyze flow variation around the ㄱ-type groynes. The velocity in the main channel measured to be increased by 1.5 times. The velocity variation on groyne arm length is little. The width of the thalweg lines (TCL) was changed to 55% - 57% of the channel width. The Froude number did not affect the thalweg line (TCL) and separation line (Sh) changes, however.

Impact of Grain Size Distribution on Bed Topography around a Groyne

Abstract: This paper presented an experimental study on the impact of grain size distribution on the bed topography around an impermeable groyne. The importance of two governing parameters, i.e. the mean grain size D and the geometric standard deviation σg, was emphasized with quantitative evidences. It was found in the current experiments that with the increase of D, the maximum local scour depth decreased and the slope of the scour hole increased for a sediment bed with a uniform grain size distribution. The maximum local scour depth in a non-uniform sediment bed was smaller compared with that in a uniform one and generally decreased with the increase of σg.

Development of Large Scale Vortex around T-type and L-type Groynes

Abstract: There are several types of groyne, such as T-type and L-type groynes, that have been constructed worldwide in accordance with different river environments. However, little information has been obtained on the structures of large-scale vortex-development around differently shaped groynes. Because these flow structures are expected to significantly affect the formation of sand waves further downstream, this phenomenon should be considered systematically and in detail. To reveal such flow effects, flow is visualized around several types of groyne by means of particle tracking velocimetry, which was developed especially for estimating large-velocity difference. To discuss the flow pattern around the groynes, Analyses of conditional sampling and spectral distribution and Weiss function are applied to reveal the coherent structures. The results show strong and large vortex development from the tips of groynes toward downstream. The differences in flows around several types of groyne are the distributions of large areas of coherent vortex downstream.

Effects of slope-changed bed in a groyne field on its flow structures and mass-exchangeing

Abstract: PIV and LIF techniques were conducted to reveal relationship between sedimentation and mass exchange property in a groyne field. It was found from the PIV measurements that different bed-form conditions, that is to say, with and without bed slope, yielded corresponding gyre formations. The other experiment, the LIF results allowed us reasonably to evaluate transfer velocity of dye through boundary between mainstream and dead water zone, They suggest that mass exchange properties have significant relations with horizontal gyres, thereby, with the conditions of bed slope. The results normalized by turbulence intensity and length scale of gyre were in good agreement with a large-eddy model.

The Study on Stability Channel Technology by Using Groyne in Alluvial Stream - Riverside Protection Techniques by Using Groyne -

Abstract: As demonstrated in study for non-submerged groynes, the flow field is predominantly two-dimensional, with mainly horizontal eddies. The eddies shed form the tips of the groynes and migrate in the flow direction. These eddies have horizontal dimensions in the order of tens of meters and time-scales in the order of minutes. In the standard flow simulations, these motions are usually not resolved, due to a too coarse grid, too large time steps and, more importantly, the use of inadequate turbulence modelling. using for example a k- model, it is necessary to introduce substantial modifications. Therefore simulation resolved in this study, were carried out using the DELFT-3D-MOR programme, which is part of the DELFT3D software package of WL/Delft Hydraulics and In this study, apply a two-dimensional depth-averaged model, taking an horizontal large eddy simulation(HLES). The bed morphology computed when using HLES, as well as the associated time-scale, is similar to what has been obseved in a field case. When using a mean-flow model with-out HELS, the bed morphology is less realistic and the morphological time-scale is much larger. This slow development is the result of neglecting(or averaging). the strong velocity fluctuations associated with the time-varying eddy formation.

Hydrodynamic Effects of Sedimentation on Mass Transport Properties in Dead Water Zone of Natural Rivers

Abstract: We can often see dead water zones composed of consecutive groynes in natural rivers. The groynes are generally constructed in the bank of actual rivers in order to navigate stream direction and to prevent bank erosion. Dead water zones such as side cavities are also observed in harbors of rivers, and it is well known that there are significant differences between streamwise velocities of the mainstream and the cavity zone. Of particular significance is that shear instability related to the velocity difference induces coherent horizontal vortex along the boundary of the mainstream and the cavity. Further, large-scale gyres are formed in the dead water zone which conveys suspended sediment from the main-channel, and local sedimentations are promoted in the cavity as shown in photo 1. So, it is necessary to reveal the hydrodynamic properties included with turbulence phenomena in order to control sedimentation reasonably. Akkerman et al.(2004) conducted the sensitivity analysis with a 1-dimensional morphodynamic model, and they discussed the several effects on sedimentation and flood water depth after the occurrence of groyne damage. Recently, permeable groynes are proposed to realize stable bed condition. For example, Kadota & Suzuki (2010) discussed experimentally effects of the permeability and the scales of the groynes and stone gabion in submerged and emerged flow conditions. Tominaga & Sakaki (2010) conducted ADV measurements around the permeable groynes in a natural river, and they evaluated distributions of bed shear stress accurately. In these cavities, not only sedimentation but also congestion of pollutants is often highlighted. It is thus very important to investigate mass & momentum exchanges between the main-channel and the side-cavity in river environment and hydraulic engineering. The above-mentioned horizontal gyres and coherent turbulent structures play significant roles on mass and momentum exchanges. Uijttewaal et al.(2001) measured distribution of dye concentration and pointed out that aspect ratio of side cavity has significant effects on exchange rate of mass between the mainstream and the dead water zone. Weitbrecht et al.(2007) have also conducted laboratory measurements, in which distribution of velocity components and dye were obtained. They examined the relation between the exchange rate and the bed configuration of the cavity.