Groyne Fields Research Articles

Experimental and numerical investigations of the mixing processes of pollutants at notched weirs in rivers

This study experimentally and numerically investigated the mixing processes at a notched weir to examine the relationship between the mass exchange coefficient and geo-hydraulic factors of notched weirs. Laboratory experiments on idealized notched weirs with variable notch spaces, notch heights, and hydraulic factors were performed to measure the flow field dynamics and depth-averaged concentration fields of the solute tracer. The experiment results demonstrated that flow separations occurred upstream of the notched weir. These flow structures controlled the horizontal storage zone and tracer mixing between the main flow and storage zone. The tracer cloud exhibited a longer retention time as the storage zone area increased. The normalized value of measured mass exchange coefficients by mean flow velocity, ke /Umean ranged from of 0.11 to 0.25, approximately one order larger than the values obtained in previous studies on lateral transient storage zones, such as lateral groin fields, and cavities, which implied that the notched weir in this study generated a storage zone with a fast exchange process and relatively weak storage effect. Numerical simulations with expanded geometric and hydraulic conditions revealed that the mass exchange coefficient was strongly correlated with the geometric factors, such as the notch space and height, and hydraulic factors, such as the Froude and Reynolds numbers. An empirical relationship applicable to rivers with notched weir structures under low-flow conditions (Fr < 0.1) was proposed based on the experiment and numerical results. The performance of the proposed empirical relationship showed a satisfactory level of R2 of 0.87. This relationship can be applied as a tool for estimating the mass exchange coefficient of notched weirs using easily measurable field data in rivers.

Evaluating the potential for re-using timber from deconstructed sea defence groynes from the Bournemouth groyne field

Groynes have been part of the coastal appearance for centuries, helping prevent coastal erosion resulting from the littoral drift of material with prevailing sea currents. Whilst the use of rock groynes increased during the late 20th Century, the use of timber still remains the material of choice. Their performance depends upon the timber species used, and often sections are suitable for re-use. Assessment of the replacement of groyne fields in Bournemouth, United Kingdom appears to show the suitability of certain species to be re-used. Results indicated that ekki was the most suitable species for re-use, closely followed by greenheart.

The effect of groyne field on trapping macroplastic. Preliminary results from laboratory experiments

Macroplastic, a precursor of microplastic pollution, has become a new scope of research interest. However, the physical processes of macroplastic transport and deposition in rivers are poorly understood, which makes the decisions of where to locate macroplastic trapping infrastructure difficult. In this research, we conducted a series of experiments in a laboratory channel, exploring the impact of groynes and flexible artificial vegetation on the floating macroplastic litter. The goal was to investigate the litter paths with different obstruction arrangements, which was done by implementing a particle tracking technique on video recordings from each experimental run. We found that increasing discharge correlated with the number of plastic litter floating into the recirculation zone within the groyne fields, especially if the upstream groyne had an extended length. This produced a strong mixing interface between the main flow and the groyne field, while a vegetation patch added in the same groyne field changed the paths of plastic litter by deflecting the flow. We noticed that during a moderate discharge rate, the litter pieces flowing into the groyne field with the vegetation circulated there for the longest period, and some of them got entangled between floating stems when discharge was at its lowest. This phenomenon points to the conclusion that low flow velocity paired with the presence of vegetation can be a primer for plastic deposition and consequently, its degradation. The insights from the experiment allowed us to recommend a place downstream of an extended groyne as the desirable (efficient) area for installing a plastic trapping infrastructure or conducting plastic cleaning actions.

Macrolitter budget and spatial distribution in a groyne field along the Waal river

Current research on riverine macrolitter does not yet provide a theoretic framework on the dynamics behind its accumulation and distribution along riverbanks. In an attempt to better understand these dynamics a detailed field survey of three months was conducted in which location of macrolitter items within a single groyne field along the Waal riverbanks was tracked. The data provided insight into the daily changing patterns of spatial item distribution with respect to the waterline. Furthermore, the rates of item uptake and deposition were monitored and related to hydrologic fluctuations. Uptake was initiated by rising water levels and was generally higher when the water level increased faster. Deposition occurred continuously, despite hydrologic fluctuations. This caused the riverbank macrolitter budget to be positive during stable or dropping water levels and negative during rising water levels. Although the results show clear patterns an extended monitoring duration is required to fully understand the fate of plastic objects.

Impacts of coastal protection measures along the coast of Kerala, India (through remote sensing techniques)

ABSTRACT The maritime state, Kerala, is located along the southwest coast of the Indian peninsula, which extends from Trivandrum district (8° 17´ 41.03´´ N, 77° 5´ 37.29´´ E) in the South to Kasaragod district (12° 45´ 20.76´´ N, 74° 51´ 58.92´´ E) in the North, exposed to the waves from the Arabian Sea. The shoreline is extremely dynamic due to the impact of waves, tides, currents, coastal orientation and other associated occasional coastal hazards. The annual climatic calendar for the Kerala coast can be broadly classified as South-West monsoon (June to September), North-East Monsoon (October to December), and Pre-monsoon or Non-Monsoon (January to May). Prior to the 2004 Indian Ocean tsunami, a standardised seawall section had been preferred for highly eroding coastal stretches. The coastal hazards in addition to the tsunami impact paved the way for considering several other structures for coastal protection, of which groyne fields have been predominantly implemented. As it is essential to quantify the performance assessment of these protection measures, an exercise using the DSAS (Digital Shoreline Analysis System) tool was carried out, the results of which are presented and discussed in this paper.

Coastal erosion in Argentina: The retreating rates of southern South America

Tall cliffs are characteristic of the Patagonian and Tierra del Fuego coastline. They are receding at rates below 1 m/yr. Gravel-dominated beaches and spits are protecting the foot of these cliffs. At the Buenos Aires coastline, erosion also dominates. Sandy barriers constructed during the Holocene sea-level fluctuation are today under severe erosion, either natural or induced by human interventions. The Eastern Barrier is more threatened to sea level rise while the Southern barrier is located on top of former cliffs. Groyne fields were implemented but led to drift obstructions. Argentine coastal retreat is more extended and intense compared to other retreating rates of Brazil, Uruguay and Chile.

Dike fields as drivers and witnesses of twentieth-century hydrosedimentary changes in a highly engineered river (Rhône River, France)

Hydraulic structures, such as groyne fields, were commonly used to channelize European and North American rivers, thus forming engineered margins on the edges of the active channel. On the Rhône River (France), which was corrected with dike fields (classical groyne fields and specific ones closed with a longitudinal submersible dike; i.e., closed fields) and equipped with numerous dams (mid-twentieth century), the engineered margins have mostly been filled with fine sediments and become terrestrial. On the 11 km bypassed studied reach (middle Rhône), 55.6 ha in 167 dike fields (i.e., 75 % of the cumulated surface) have been subject to terrestrialization (i.e., the transformation of aquatic areas into terrestrial ones). Our study aimed to understand the trajectory of dike fields that serve as both drivers (e.g., inducing in-dike fine sediment trapping) and witnesses (e.g., informing the diversion impact) of hydrosedimentary changes. We combined geohistorical analyses (aerial photographs, riverbed elevations, and water levels) and GIS modeling, as well as topographic and ground-penetrating radar surveys (GPR), to emphasize the terrestrialization patterns and hierarchize the drivers and processes involved. We obtained a classification of diachronic patterns (five types) that highlight local recurrences and specificities (inherited forms) in the terrestrialization trajectory. Topographic and GPR surveys complemented our data, shedding light on the main characteristics of sediment deposits (volumes, thicknesses) and structural units. We also determined that the contribution to terrestrialization of phase 1 (channelized state; 1900s–1970s) is lower than that of phase 2 (channelized and bypassed state; 1970s–2000s), at 42 % (23.4 ha) and 58 % (32.2 ha), respectively. In phase 1, fine sediment deposition leads to deposit construction, triggered by the dike field setting, which shapes spaces with reduced shear stresses. The riverbed incision (induced by channelization) is shallow on this reach, so its contribution (by lowering the water level) is considered negligible. In phase 2, terrestrialization is mainly provoked by the diversion-induced drop in water level that has caused the retraction of the active channel and promoted its abandoned edges as new terrestrial margins. Understanding the evolution of these ecotones made it possible to adjust our recommendations in terms of management and restoration. It also highlights the relevance of strategic dike field reconnections to support the river by recreating gradients of hydrological connectivity (which are favorable to habitat diversity).

Numerical Investigation on Flow Characteristics in a Mildly Meandering Channel with a Series of Groynes

In single-bend channels or meandering channels, groynes are widely used as a river-training structure. Geometric factor is an important principle of groyne design. In this paper, the numerical method based on the Renormalization Group (RNG) k-ε turbulence model is used to study the effects of groynes with different lengths and orientations on the mean flow pattern and turbulence characteristics in a mildly meandering channel. The analysis shows that compared with equal-length groynes, the groynes arranged in descending order perform well in improving the flow velocity of the main channel, and the maximum longitudinal velocity at the channel center can be increased by 1.57 times the average velocity. However, at the same time, they bring higher Normalized Turbulent Kinetic Energy (NTKE) and Normalized Bed Shear Stress (NBSS) values. The attracting groynes arranged in descending order help to reduce scouring. The groynes arranged in ascending order reduce the velocity of the riverbank in some downstream areas and are suitable for bank protection. It effectively decreases the NTKE and NBSS around the groyne fields and can reduce the inner bank scouring of the mildly meandering channel. The findings are helpful for the management of meandering rivers.

Topo-bathymetric behaviour of a beach controlled by a groyne field and a dune-seawall backshore

The advances in morphodynamics numerical modelling and the free availability of such updated models have made XBeach a powerful tool to predict the hydrodynamic and morphologic processes on sandy coasts. This paper addresses the impact of the sea-structure-sediments interactions in the morphological evolution of a coastal stretch which undergoes erosion and overtopping despite having a combined groyne field-dune-seawall defence scheme. Preliminary tests, tailored to conclude on the model mode-version to be applied in the case study, evidence the importance of considering the NH mode. After calibrated and validated, the model was applied for a set of cases to compute and discuss the effect of the individual defence scheme structural elements and the hydrodynamic driving factors, namely the wave energy and obliquity and the tidal range, on the morphodynamics. The results revealed that the seawall aggravates the erosion of the beach, despite being essential in the protection against overtopping and coastline retreat, and that the present configuration of the groyne field does not provide enough protection at the downdrift part of the stretch. The knowledge acquired can support the interpretation of the topo-bathymetric behaviour in similar coastal defence schemes existent worldwide.

Temporal patterns and drivers of CO2 emission from dry sediments in a groyne field of a large river

Abstract. River sediments falling dry at low water levels are sources of CO2 to the atmosphere. While the general relevance of CO2 emissions from dry sediments has been acknowledged and some regulatory mechanisms have been identified, knowledge on mechanisms and temporal dynamics is still sparse. Using a combination of high-frequency measurements and two field campaigns we thus aimed to identify processes responsible for CO2 emissions and to assess temporal dynamics of CO2 emissions from dry sediments at a large German river. CO2 emissions were largely driven by microbial respiration in the sediment. Observed CO2 fluxes could be explained by patterns and responses of sediment respiration rates measured in laboratory incubations. We exclude groundwater as a significant source of CO2 because the CO2 concentration in the groundwater was too low to explain CO2 fluxes. Furthermore, CO2 fluxes were not related to radon fluxes, which we used to trace groundwater-derived degassing of CO2. CO2 emissions were strongly regulated by temperature resulting in large diurnal fluctuations of CO2 emissions with emissions peaking during the day. The diurnal temperature–CO2 flux relation exhibited a hysteresis which highlights the effect of transport processes in the sediment and makes it difficult to identify temperature dependence from simple linear regressions. The temperature response of CO2 flux and sediment respiration rates in laboratory incubations was identical. Also deeper sediment layers apparently contributed to CO2 emissions because the CO2 flux was correlated with the thickness of the unsaturated zone, resulting in CO2 fluxes increasing with distance to the local groundwater level and with distance to the river. Rain events lowered CO2 emissions from dry river sediments probably by blocking CO2 transport from deeper sediment layers to the atmosphere. Terrestrial vegetation growing on exposed sediments greatly increased respiratory sediment CO2 emissions. We conclude that the regulation of CO2 emissions from dry river sediments is complex. Diurnal measurements are mandatory and even CO2 uptake in the dark by phototrophic micro-organisms has to be considered when assessing the impact of dry sediments on CO2 emissions from rivers.

Laboratory investigation of flow and turbulent characteristics around permeable and impermeable groynes in a strongly curved meandering channel

ABSTRACT The study investigates the role of cocolog, an eco-friendly material, as groyne, in protecting the river banks in meandering channels. Laboratory experiments were conducted to compare the flow pattern and sediment dynamics in a mobile-bed meandering channel for cocolog (permeable) and impermeable groynes. It is observed that as the permeability increases, the vertical and transverse velocities are seen to be reduced in the groyne fields. The results also indicate that places of maximum scour depth display amplified velocity, turbulent intensity and turbulent kinetic energy. However, considerable reduction in these characteristics is being observed in the case of permeable groynes that have densities varying between 140 and 160 kg/m3. The eroded volume is seen to be reduced by 60% for permeable groynes of medium density compared to the tests done without groynes. Also impermeable groynes exhibit a wider distribution of the maximum values for scour depth, turbulence intensity and turbulent kinetic energy than that of permeable groynes. It is found that the cocolog groynes with suitable density (or permeability) can perform best in meandering channels by dampening the velocity and turbulence of the groyne fields.

Effects of Groin Type and Bed Properties on Flow in Groin Fields: Comparison of Fixed- and Mobile-Bed Experiments

Groin type and vegetation in groin fields directly affect flow field, bank protection, and river evolution. Many studies focus on fixed-bed contexts, but there are few studies on the influence of riverbed changes on hydrodynamic characteristics around groins. In this study, three types of groins are investigated experimentally in fixed and mobile beds in terms of time-averaged flow characteristics, turbulence characteristics, and bed changes. In both fixed- and mobile-bed experiments, vegetation reduced erosion of the groin field and main stream. Compared with the fixed-bed experiment, the velocity in the main stream was decreased in the mobile-bed experiment, and the longitudinal turbulence intensity and lateral momentum exchange were increased. In this study, an improved three-dimensional groin group (upstream wing submerged T-shaped groin group) produced a lower sediment scouring capacity, average scour depth, and entrainment coefficient k than I-shaped and T-shaped groin groups.

Geomorphological development of aquatic mesohabitats in shore channels along longitudinal training dams

AbstractLongitudinal training dams (LTDs) are novel hydraulic engineering structures in the river Waal intended to facilitate intensive navigation and safe discharges in the main channel while providing sheltered habitats for aquatic biota in shore channels. Monitoring data collected using light detection and ranging, multibeam echosounder and aerial photography for the years during and after the construction of the LTDs were analysed in order to determine patterns of erosion and deposition, the retreat rate of steep eroding banks and shoreline length change through time. The LTD shore channels and two traditional groyne fields (references) were divided into nine mesohabitats based on physical attributes. Net erosion was estimated for eight out of the nine mesohabitats for the 2015–2020 period. Generally, there was a pattern of riverbed aggradation towards the LTDs and degradation or bank erosion towards the littoral zones of the LTD shore channels. This kind of continuous behaviour could be indicative of current or eminent channel and thus habitat stability. The bankline erosion in shore channels had mean retreat rates of 1.4–1.6 m/year. The shorelines were longer in sand‐dominated mesohabitats, which could be key for habitat heterogeneity. The LTD shore channels offered more complex relatively natural continuous littoral zones than the traditional groyne fields while maintaining the multifunctionality of the river. Thus, the development of sandy shorelines in the LTD shore channels should be encouraged through management in order to enhance biodiversity. Geomorphological monitoring of the shore channels should continue in the future in order to detect any long‐term changes in the sedimentary processes and ecological functions.

Simulation of scour and deposition in the flow field and adaptability of fishes around eco-friendly notched groins

Over the past few decades, eco-friendly channel construction has gained wide attention around the world including China, as it considers both navigational and ecological functions. The Groin system is a hydraulic structure that can effectively increase the area of fish habitats. Groin shape has an influence on the local flow field and the scour and deposition pattern near the structure, thereby affecting the adaptability of fishes to the groin fields. In this study, a new groin structure with a notch in its middle part was proposed. A lab experiment was conducted on a physical model to investigate the characteristics of the flow field including patterns of water level distribution, flow velocity distribution, and scour and deposition on different submergence levels and incoming flows. This experiment used four notch depths: 0 (unnotched), 1/3 of groin height, 2/3 of groin height, and full groin height. Then the distribution of habitat suitability index (HSI) was calculated based on the assessment index system of the indicator fish species (Cyprinidae). The results showed that the notches created in the middle of localized overflow groins had a significant effect on the surrounding flow pattern. Due to localized overflow, both the flow velocity and the velocity gradient behind each groin increased. The flow velocity behind each groin was positively correlated with notch depth, while the flow velocity in the main channel was negatively correlated with notch depth. Under the complex flow conditions, depositional features did not occur along the edges of the groin fields, ensuring connectivity between groin fields and the main channel. An analysis of water depth and flow velocity suitability indexes of Cyprinidae suggests when notch depth is 2/3 of groin height, the notched groins have good ecological effects, especially in the groin fields.

Spatial Variability and Hotspots of Methane Concentrations in a Large Temperate River

Rivers are significant sources of greenhouse gases (GHGs; e.g., CH4 and CO2); however, our understanding of the large-scale longitudinal patterns of GHG emissions from rivers remains incomplete, representing a major challenge in upscaling. Local hotspots and moderate heterogeneities may be overlooked by conventional sampling schemes. In August 2020 and for the first time, we performed continuous (once per minute) CH4 measurements of surface water during a 584-km-long river cruise along the German Elbe to explore heterogeneities in CH4 concentration at different spatial scales and identify CH4 hotspots along the river. The median concentration of dissolved CH4 in the Elbe was 112 nmol L−1, ranging from 40 to 1,456 nmol L−1 The highest CH4 concentrations were recorded at known potential hotspots, such as weirs and harbors. These hotspots were also notable in terms of atmospheric CH4 concentrations, indicating that measurements in the atmosphere above the water are useful for hotspot detection. The median atmospheric CH4 concentration was 2,033 ppb, ranging from 1,821 to 2,796 ppb. We observed only moderate changes and fluctuations in values along the river. Tributaries did not obviously affect CH4 concentrations in the main river. The median CH4 emission was 251 μmol m−2 d−1, resulting in a total of 28,640 mol d−1 from the entire German Elbe. Similar numbers were obtained using a conventional sampling approach, indicating that continuous measurements are not essential for a large-scale budget. However, we observed considerable lateral heterogeneity, with significantly higher concentrations near the shore only in reaches with groins. Sedimentation and organic matter mineralization in groin fields evidently increase CH4 concentrations in the river, leading to considerable lateral heterogeneity. Thus, river morphology and structures determine the variability of dissolved CH4 in large rivers, resulting in smooth concentrations at the beginning of the Elbe versus a strong variability in its lower parts. In conclusion, groin construction is an additional anthropogenic modification following dam building that can significantly increase GHG emissions from rivers.

Initial biological development of a newly established side channel at the Lower Rhine

AbstractWithin the EU LIFE‐Nature project ‘River and floodplain revitalisation Emmericher Ward’, three small temporary waters and a former gravel pit were connected by a side channel running parallel to the river Rhine through former groyne fields. The initial status of macrozoobenthos, fish, avifauna, flora, vegetation, and habitats before and their development after implementation of the project's measures were recorded and compared. The monitoring years 2018 and 2019 were exceptionally dry and accompanied by an extremely low runoff in the Rhine and the side channel. These conditions likely affected the development of habitats and species populations in the new side channel. The new side channel showed intensive morphodynamic development and differentiation of its structures. While the more complex vegetation and habitat types appeared as mostly species‐poor initial stages, short‐lived species‐rich pioneer habitats such as annual mud banks in the water exchange area were already established. Two years after the implementation, the benthic invertebrate fauna was still predominantly species‐poor and dominated by neozoans. Occasionally, representatives of the more sensitive EPT fauna (Ephemeroptera, Plecoptera, Trichoptera) were already detected but were, in general, strongly underrepresented in the main stream. Low colonisation potential, nonpermanent flow, and lack of river wood limit the development of the macrozoobenthos community. The relative abundance of rheophilic fish species increased in the project area and high juvenile fish densities proved the function as a nursery habitat. As pioneer species of riverine landscapes, sand martins and little ringed plovers colonised the new structures already in the first year. The initial state of the side channel represented a typical dynamic pioneer habitat pattern of a sandy lowland river, which was almost absent in the Lower Rhine area. The new habitats were quickly colonised by pioneer flora and fauna, but the potential for more demanding and complex communities was restricted by the poor structural and biological states of the Lower Rhine.

Shoreline changes due to construction of groyne field in north of Chennai Port, India.

Chennai Port (13.099872° N, 80.297407° E), located along the southeast coast of India, has been a hub for maritime trade since the fifteenth century. An artificial harbour was initially constructed in 1881 which underwent numerous expansions in the following years. The breakwaters of the harbour intercepted the heavy sediment-laden littoral drift along the coast, resulting in the formation of the world's second-longest urban beach south of the port, i.e. on its up-drift side. Meanwhile, the coast north of the port, i.e. the down-drift side, experienced intense erosion due to a lack of sediment supply and forces induced on the coast due to waves and currents. The shoreline change study in this paper investigates a shoreline stretch of about 6km (protected by transitional groynes), north of Chennai Port by dividing it into three segments. The rate of shoreline changes over a period of about 12years across three different segments was assessed using statistical parameters by employing remote sensing techniques complemented with geographical information system (GIS) and digital shoreline analysis system (DSAS) tool. It is inferred that the coast has witnessed accretion and sizable growth in beach width has been observed post the construction of groyne field.

Historical Shoreline Analysis and Field Monitoring at Ennore Coastal Stretch along the Southeast Coast of India

A shoreline change analysis has been carried out for the coastal stretch from Ennore creek to Karungali village located along the southeast coast of India. This 15 km-long coastal stretch had undergone significant changes such as erosion and accretion concerning infrastructure developments and leading to large impact on the livelihood of the community. To assess the shoreline changes, the analysis of multi-temporal satellite images has been carried out. A historical trend is established for the study period from 1991 to 2019. The analysis has been made in three timelines considering various developing activities. There was no significant coastal infrastructure development during 1991 to 1999; however, between 1999 and 2009, a major port, pier, and a groyne field were constructed. Additionally, a port was established between 2009 and 2019. Erosion was observed on the coast from Kattupalli to Karungali at a rate of −16.85 m/yr since 2009, while the coast on the south of Ennore port is accreting at the rate of +12.43 m/yr during the same period. The near-future projection using a linear regression model shows further erosion in the coast under similar conditions. The results of this study provide a baseline data for future anthropogenic activities along this coast.

UAS-SfM approach to evaluate the performance of notched groins within a groin field and their impact on the morphological evolution of a beach nourishment

Beaches are dynamic systems characterized by frequent morphological changes due to storm events, gradients in longshore sediment transport, seasonal variations in wave climate and more. The complexity of variations in beach morphology can increase significantly after a beach nourishment, particularly when coastal structures are involved. This study investigates the impacts of a groin field, consisting of both notched and traditional groins, on the morphological evolution of a beach in Deal, New Jersey, USA. More specifically, an evaluation of the performance and specifications of the notched groins is undertaken. In 2016, the beach in Deal was nourished and three of the eight groins comprising the groin field were concurrently notched in order to promote increased movement of longshore sediment transport while maintaining a stable shoreline. The study site was monitored nine times over a period of two years (2018–2019) using Unmanned Aerial Systems Structure from Motion (UAS-SfM) photogrammetry. The near-term morphological response of the study site was evaluated by analyzing high-resolution digital elevation models (DEMs) and longshore sediment transport estimates based on measured wave data.The elevation change maps established that in general, the groin notching was partially successful in reducing shoreline asymmetry in consequence of sediment transport bypassing through the notches. Differences in behavior and patterns of elevation change adjacent to each individual notched groin was observed even though they were all notched according to the same specifications. While all three notched groins were effective in stabilizing the adjacent shoreline, they varied in their effectiveness at promoting longshore sediment transport through the notch. This is likely attributable to the relative location of the notched groins within the groin field and the characteristics of the post-nourishment morphological evolution; the direction of net annual longshore sediment transport at Deal beach is northward, which caused the southern areas of the study site to narrow and the northern areas of the study site to widen. Consequently, the notched groins in the wider sections of beach did not function as intended, as the notches filled in with sediment causing them to mimic the behavior of a traditional groin, including restricted longshore sediment transport and significant erosion/accretion offsets. In the narrower section of beach, the notched groin functioned as designed, such that the notch was located in the swash zone and therefore allowed bi-directional sediment transport and maintained a stable and relatively symmetrical shoreline. Thus, the notched groins performed most effectively when the notch was consistently located toward the seaward end of the swash zone.

Numerical Simulation of Flow Pattern in Series of Impermeable Groynes in Fixed Bed

This paper presents a numerical simulation of recirculating flow patterns in groyne fields. Moreover, it entails the concept determination of proper spacing of vertical unsubmerged and impermeable groynesin seriesto control the bank erosion. Flow pattern between the groynes varies along their space. The flow in groyne field may significantly affect the flow change, bed change, bank erosion and condition of habitat. In this regard, an assessment of flow along the space of groynes will yield important data needed to diversify the object of groyne installation. So, knowledge about determination of the proper spacing of groynes in groyne field is important. Space of vertical groynes was set from 1.5 to 10 times the length of groynes. The velocity field between groynes was simulated by using Computational Fluid Dynamics (CFD) model Nays 2D. Simulated velocity field was compared with existing experimentaldata for the same parameter, which agreed satisfactorily. Based on simulated results,the optimal spacing of vertical groynes to control the bank erosion was recommended.