Meander Geometry Research Articles

Mega-meander paleochannels of the southeastern Atlantic Coastal Plain, USA

Paleodischarge estimates based on the slope-area method and channel boundaries determined from stratigraphic cross-sections indicate that large, terminal Pleistocene meandering paleochannels (“mega-meanders”) in river valleys of the southeastern Atlantic Coastal Plain of the United States represent bankfull flows that were at least double the magnitude of those on modern rivers. Correlation of radiocarbon- and luminescence-dated paleomeanders with previously reported pollen and eolian sedimentary records suggests that greater discharge was driven by seasonally wetter conditions resulting from dynamic changes to regional precipitation and runoff that occurred in association with global warming at the end of the Pleistocene. While reflecting larger channel-forming flows, the exceptionally large widths and radii of curvature of mega-meanders were nonetheless maintained by a relatively modest discharge magnitude that was between two and four times larger than modern bankfull flow and within the size range of the present two- to five-year flood. Despite their large planform, the paleochannels conveyed relatively modest bankfull discharges because a wide, shallow shape limited their cross-sectional area and hydraulic radius. Within the late Quaternary evolution of fluvial systems in the region, scrolled mega-meanders constitute a transitional meandering planform that remained influenced by large volumes of sandy bedload following the sand-bed braided channels of the late Wisconsin interval, circa 30–17 ka. In addition to greater discharge, the large planimetric dimensions of paleochannels reflect a lack of cohesive vertical accretion facies on paleomeander floodplains, a sediment regime that transported large quantities of bedload sand, and the influence of these factors on channel boundary composition, bank stability, and channel shape. Findings underscore the importance of reconstructing channel cross-sectional dimensions and slope when estimating discharge for infilled paleomeanders. This approach reduces uncertainties surrounding channel cross-sectional area, gradient, and boundary composition inherent to studies lacking subsurface data that rely upon meander geometry to retrodict discharge.

Impacts of small-scale faults on continental to coastal plain deposition: Evidence from the Realgrunnen Subgroup in the Goliat field, southwest Barents Sea, Norway

Abstract In this study we synthesise sedimentological, fault, and Amplitude Versus Angle (AVA) analysis and propose that the Fruholmen and Tubaen formations (Realgrunnen Subgroup) are syn-kinematic deposits that record a previously undocumented early phase of Mesozoic rifting on the Troms-Finnmark fault Complex and within the Hammerfest Basin. The Realgrunnen Subgroup hosts one of two Triassic reservoirs currently being produced in the Goliat field. Here, the subgroup sits unconformably on top of the Storfjorden Subgroup (Carnian Snadd Formation). Away from the Goliat field, which is characterised by a periclinal anticline, the Realgrunnen Subgroup also comprises the Lower–Middle Jurassic Nordmela and Sto formations. Sedimentological analysis of six exploration wells reveals that the Fruholmen Formation was deposited in a prodelta to delta plain environment where tide-influenced and fluvial-dominated distributary channels are represented by clay/siltstones and very fine grained sandstones. The overlying Tubaen Formation is characterised by medium to very coarse-grained deposits (locally conglomeratic) and represents a widespread braid plain with localised alluvial fans. Displacement profiles of faults and along-fault thickness variations demonstrate that an immature fault system was active during deposition of the Realgrunnen Subgroup. A series of unconnected fault segments hosted isolated sub-basins and erosional catchment areas in their hanging and footwalls, respectively. An AVA attribute map generated from a 10 ms interval of the uppermost part of the subgroup reveals gross sand-prone depositional bodies, i.e., individual and amalgamated channels, (some of which show meandering geometries), ox-bow lakes and alluvial fans. Sand bodies frequently show elongate geometries parallel to faults indicative of syn-depositional fault-related subsidence. Driving mechanisms responsible for the Norian to Rhaetian event may relate to contemporaneous rejuvenation of the Fennoscandian hinterland, development of the Novaya Zemlya fold-and-thrust belt and/or the early Cimmerian tectonic phase in northern Europe.

Design, fabrication, and testing of a low frequency MEMS piezoelectromagnetic energy harvester

This paper details a power solution for smart grid applications to replace batteries by harvesting the electromagnetic energy from a current-carrying wire. A MEMS piezoelectromagnetic energy harvester has been fabricated using PZT screen-printing technology with a centrally-supported meandering geometry. The energy harvesting device employs a symmetric geometry to increase its power output by reducing the effects of the torsional modes and the resultant overall strain nodes in the system subsequently reduce the complexities for the electrode fabrication. The unit is modelled using COMSOL to determine mode shapes and frequency response functions. A 12.7 mm by 14.7 mm unit is fabricated by screen-printing 75 μm-thick PZT on a stainless steel substrate and then experimentally tested to validate the FEA results. Experimentally, the harvester is shown to produce 9 μW from a wire carrying 7 A while operating at a distance of 6.5 mm from the wire. The design of the current work results in a greater normalized power density than other MEMS based piezoelectromagnetic devices and shows great potential relative to larger devices that use bulk or thin film piezoelectrics.

Towards the design of an intensified coagulator

This study compares the hydrodynamics in three millimeter-scale continuous reactor geometries that can be easily used in laboratories and industries – a straight tube, a coiled tube and a Dean-Hex reactor – via numerical simulations and analyses the data in a way that is specifically relevant to coagulation processes, thereby offering insights for engineers to develop new coagulation reactors. A numerical approach based on Lagrangian particle tracking is presented to better understand the impact of the geometry and flow on properties that influence coagulation. The results show that the Dean-Hex meandering geometry provides narrower residence time and shear rate distributions, as well as higher mean average shear rates and Camp number distribution than the other geometries. This is attributed to the generation of transverse flows and radial mixing in the Dean-Hex reactor and suggests that a faster and more homogenous coagulation can be expected.

A 3-D numerical model of the influence of meanders on groundwater discharge to a gaining stream in an unconfined sandy aquifer

Groundwater discharge to streams depends on stream morphology and groundwater flow direction, but are not always well understood. Here a 3-D groundwater flow model is employed to investigate the impact of meandering stream geometries on groundwater discharge to streams in an unconfined and homogenous sandy aquifer at the reach scale (10–200m). The effect of meander geometry was examined by considering three scenarios with varying stream sinuosity. The interaction with regional groundwater flow was examined for each scenario by considering three groundwater flow directions. The sensitivity of stream morphology and flow direction to other parameters was quantified by varying the stream width, the meander amplitude, the magnitude of the hydraulic gradient, the hydraulic conductivity, and the aquifer thickness. Implications for a real stream were then investigated by simulating groundwater flow to a stream at a field site located in Grindsted, Denmark. The simulation of multiple scenarios was made possible by the employment of a computationally efficient coordinate transform numerical method. Comparison of the scenarios showed that the geometry of meanders greatly affect the spatial distribution of groundwater flow to streams. The shallow part of the aquifer discharges to the outward pointing meanders, while deeper groundwater flows beneath the stream and enters from the opposite side. The balance between these two types of flow depends on the aquifer thickness and meander geometry. Regional groundwater flow can combine with the effect of stream meanders and can either enhance or smooth the effect of a meander bend, depending on the regional flow direction. Results from the Grindsted site model showed that real meander geometries had similar effects to those observed for the simpler sinuous streams, and showed that despite large temporal variations in stream discharge, the spatial pattern of flow is almost constant in time for a gaining stream.

Analysing the influence of Farakka Barrage Project on channel dynamics and meander geometry of Bhagirathi river of West Bengal, India

Farakka Barrage Project (FBP) constructed in 1975 on the river Ganga in West Bengal, India has largely altered hydro-geomorphic processes inducing a different kind of impetus in channel dynamics especially channel oscillation of the Bhagirathi river. Controlled hydro-geomorphological regime drastically altering natural regime has significantly influenced channel process with resultant change in channel geometry. Geospatial analysis using topographical maps of 1927, 1954 and 1974 along with satellite images of 1990, 2004, and 2014 clearly portrays rapidity in channel evolution in the post-Farakka period which is explicitly proved from four meander cut-offs after 1975. The meander geometry analysis of 66 loops of lower Bhagirathi river during 1927–2014 in terms of four basic parameters (radius of curvature, wavelength, amplitude, and channel length) and four indices (sinuosity index, radius–wavelength ratio, meander shape index and meander form index) depicts telltale pattern of channel straightening with increased number of wide and open loops after the construction of barrage. The average sinuosity of the loops has increased from 2.27 in 1927 to 2.35 in 1974 and dwindles to 1.80 in 2014. This distinct outcome induced by FBP is also found for other indices explained with special reference new hydraulic regime in post-Farakka period.

Fabrication process induced changes in scattering parameters of meander type RFMEMS shunt switch

This paper reports about the effect of fabrication process induced changes on scattering parameters of RF MEMS switch structure with meander geometry for 18–40 GHz (Ka-band) application. The designed structure showed a return loss better than 15 dB with a maximum isolation of 43 dB at 35 GHz. From the parametric analysis, both the return loss and isolation parameters are found to be more dependent on the meander width and dielectric thickness compared to the other dimensions. The switch structure is fabricated by surface micromachining technique. The effect of variation of fabricated device dimensions, due to the various processing steps, on the isolation characteristic is also studied. The fabricated structure exhibited an on–off capacitance ratio of ~200:1. The pull-down voltage is found to be 12.5 V. The return loss of the fabricated switch structure is found to be better than 13.5 dB; whereas, the maximum isolation (32 dB) is observed at 33 GHz. The shift in the resonance is due to the reduction of silicon nitride layer thickness during sacrificial layer removal (to release the switch structure) in diluted HF solution. The measured scattering parameters are found to be matching well with the corresponding simulation data of the fabricated switch dimensions.

Bio-Inspired Algorithms Applied on Microstrip Patch Antennas: a Review

Design of small broadband, multiband and high-directivity microstrip patch antennas (MPAs) is a challenging task for the antenna research community since the classical MPAs do not perform well enough to be used in the real world applications. In this sense, various performance improvement techniques such as stacked patches, air gaps, compact meandering geometries, fractal-shapes and shorting pins are applied to design improved MPAs. Use of bio-inspired algorithms along with these techniques is trending due to their capability of manipulating antenna parameters to achieve optimized performance. Literature presents use of bio-inspired algorithms such as Genetic algorithms (GA), Particle swarm optimization (PSO), Differential evolution (DE), Invasive weed optimization (IWO), Wind driven optimization (WDO) and Ant colony optimization (ACO) on MPAs for performance enhancement. This paper begins with an introduction to MPAs followed by an analysis of the performance improvement techniques. Evolution of bio-inspired algorithms and their applications in the field of MPAs are also presented. Based on the compilation of studies, importance of applying multi-objective bio-inspired algorithms for simultaneous optimization of multiple antenna parameters is emphasized. Further, research voids in the field are revealed and direction is shown to design compact multifunctional MPAs.

Channel dynamics associated with land use/cover change in Ganges river, India, 1989–2010

Shifting river courses and braiding in large rivers are part and parcel in fluvial morphology. The study aims at probing the changes of the Ganges river courses with accompanying land use/land cover characteristics. Here the changes that took place over a period ranging a couple of decades were recorded using multi-temporal Landsat 4–5 Thematic Mapper data. Meander geometry was precisely estimated. River course change pattern along with the changes in land use/land cover were studied over the period of 21 years (1989–2010). Results showed 0.14 km bank erosion and 0.85 km valley area was prone to erosion during the entire study period. The study exhibited the active channel area decreased by 22.88 km2 (0.33 % of the original river course) from 1989 to 2010. Land use characteristics showed settlement and plantation with settlement and crop lands were increased, whereas agricultural land was decreased in the study area. The overall kappa statistics were recorded as more than 0.84 during the study period. Rivers tend to maintain its high volume flow by eschewing additional silt load through bank overflow, called flash flooding; which is a natural process for any river to maintain the health of its thalweg.

Microwave dynamics of high aspect ratio superconducting nanowires studied using self-resonance

We study the microwave impedance of extremely high aspect ratio (length/width ≈ 5000) superconducting niobium nitride nanowires. The nanowires are fabricated in a compact meander geometry that is in series with the center conductor of a 50 Ω coplanar waveguide transmission line. The transmission coefficient of the sample is measured up to 20 GHz. At high frequency, a peak in the transmission coefficient is seen. Numerical simulations show that this is a half-wave resonance along the length of the nanowire, where the nanowire acts as a high impedance, slow wave transmission line. This resonance sets the upper frequency limit for these nanowires as inductive elements. Fitting simulations to the measured resonance enables a precise determination of the nanowire's complex sheet impedance at the resonance frequency. The real part is a measure of dissipation, while the imaginary part is dominated by kinetic inductance. We characterize the dependence of the sheet resistance and sheet inductance on both temperature and current and compare the results to recent theoretical predictions for disordered superconductors. These results can aid in the understanding of high frequency devices based on superconducting nanowires. They may also lead to the development of novel superconducting devices such as ultra-compact resonators and slow-wave structures.

Role of the geomorphic setting in controlling groundwater–surface water exchanges in riverine wetlands: A case study from two southern Québec rivers (Canada)

There is great interest worldwide to reconnect floodplain wetlands to their rivers. Whilst the surface water connection between rivers and wetlands is fairly well understood, the linkages via groundwater are not well known. In this study, it is hypothesized that the significance of the groundwater pathways between rivers and wetlands is largely determined by the geomorphic setting of the riverine corridor. This was tested by measuring the response of water levels and temperatures in floodplain groundwater and in wetlands to river pulses in two geomorphologically distinct riverine corridors in Southern Québec. In the De la Roche River (DLR; 145 km2), the floodplain is narrow and the alluvial sediments consist of sandy silt (wetland A; abandoned meander) or clayey silt (wetland B; stable floodplain), depending on the location. During within-channel floods, exchanges of water between the river and the floodplain are limited to some bank recharge where the alluvial sediments are permeable, and over-bank storage where the sediments are finer. Water levels in the DLR floodplain wetlands were controlled by a combination of over-bank flow and groundwater discharge from adjacent uplands. In the Matane River (1678 km2), the floodplain substrate is coarser, and the floodplain is wider and has a meandering planform geometry. The response of the Matane River wetland during floods shows storage of water due to a groundwater flood wave. This response of the wetland to within-channel flood pulses could play a role in downstream flood attenuation. In this river, the presence of river infiltration in this floodplain was also illustrated by the warming of floodplain groundwater during flood pulses. This study has shown with three distinct examples how riverine wetlands can be connected to their rivers via either a surface or subsurface pathway depending on the geomorphic setting of the riverine corridor.

The influence of meander bend evolution on the formation of multiple cutoffs: findings inferred from floodplain architecture and bend geometry

AbstractThe evolution of meander bends and formation of cutoffs, including a series of cutoffs developed simultaneously in a number of bends, have been investigated by many researchers. However, relatively little is known about factors that lead to the development of multiple cutoffs that are formed subsequently at one location. The present study aims to determine the influence of meander bend development on multiple chute cutoff formation in a single bend. The research is based on the sedimentary record of meander migration and cutoffs preserved in a lowland river floodplain (the lower Obra River, Poland). Analysis of changes in meander geometry was conducted to describe the influence of their migration on cutoff formation and in other rivers where multiple cutoffs occurred. The results showed that multiple cutoffs in the lower Obra River have occurred during the last 3000 years, owing to the interaction of upstream and downstream controls: migration of meander bends in opposing directions accompanied by an increase of flood frequency and sediment supply. The flow and sediment supply has been further altered since the nineteenth century due to anthropogenic impacts: an artificial cutoff of the downstream bend and elevation of channel levées. Similar mechanisms driving the formation of multiple cutoff have been found in other river courses, despite significantly higher energy of the compared rivers. Moreover, development of a confined‐shape bend (caused by artificial barrier or autogenic bend behaviour) may also favour the formation of multiple cutoffs. However, counter migration of meanders enhanced by increased flood frequency and sediment supply are primary triggers for such events. Copyright © 2015 John Wiley & Sons, Ltd.

Delamination phenomena in aluminum/polyimide deformable interconnects: In-situ micro-tensile testing

The deformation and failure mechanisms of metal/polymer electrical interconnects with S-shaped planar meanders are investigated. Samples consist of 1μm thick aluminum conductive coating evaporated on a 10μm thick polyimide substrate. Uniaxial tensile tests up to 40% stretch with in-situ optical and scanning electron microscopy (SEM) were performed to assess the effects of different meander geometries on the local mechanics. As a consequence of the large strain experienced by the underlying polymeric substrate, two different delamination modes were observed at the metal/polymer interface, namely, (a) shear-based and (b) buckling-based delamination. Mechanisms (a) and (b) are activated depending on the specific meander geometry: interestingly, a crucial role was played by the length of rectilinear arms, which was shown to influence the extent of transverse contraction experienced by the interconnect. Upon increasing stretch, in-situ SEM observations revealed detrimental effects related to the interfacial failure, as metal fracture localizes in the delaminated areas. Experimental results suggest that, in addition to the need of surface treatments aimed at improving the metal/polymer interface adhesion, it is also crucial to conceive optimal geometrical designs to achieve mechanical reliability of stretchable interconnects.

Geophysical evidence for a major palaeochannel within the Obosum Group of the Volta Basin, Northern Region, Ghana

We have identified a 230km long palaeochannel cutting through the sediments of the Obosum Group within the Volta Basin, Ghana. The channel is visible in regional airborne magnetic data as a pair of parallel magnetic anomalies which we interpret to be lateral terrace placer deposits of magnetite or maghemite and show both meandering and braided geometries. The palaeochannel is also visible in the airborne radiometric data for part of its length, as well as in airborne electromagnetic data, where it is marked by a zone of low conductivity. The meanders have a wavelength of around 20km and together with the 2km spacing between magnetic anomalies, suggest a major palaeo-river system, of as yet unknown age, although based on published detrital zircon ages for the host sediments and geomorphological arguments it is probably between 509±68and 45Ma, and is comparable in size to the modern-day Niger River. Given the known occurrences of alluvial gold and diamonds in Ghana, and the general prospectivity of meandering and braided rivers systems, we believe the region has exploration potential for a range of economically valuable minerals, and could also potentially host a shallow aquifer.

Design and Implementation of an RF Coupler Based on YBCO Superconducting Films

A radio-frequency coupler was designed and implemented using high-temperature superconductor (HTSC) YBCO films. A circuit for a single superconducting coupling channel was implemented and serves as the primary component in the multichannel coupling system geometry, allowing a high-power broadcast due to low losses of superconductors below the critical temperature (T c ). In this paper, a solution for the multiple antennas' isolation problem is proposed by reducing the number of antennas to a single antenna. Multichannel transmission systems require high-power broadcasts in order to transmit signals over long distances. A coupling system with low losses was used to improve the system's active performance. In this paper, the system is implemented in a very high-frequency range using a microstrip in meander geometry.

Direct transfer of magnetic sensor devices to elastomeric supports for stretchable electronics.

A novel fabrication method for stretchable magnetoresistive sensors is introduced, which allows the transfer of a complex microsensor systems prepared on common rigid donor substrates to prestretched elastomeric membranes in a single step. This direct transfer printing method boosts the fabrication potential of stretchable magnetoelectronics in terms of miniaturization and level of complexity, and provides strain-invariant sensors up to 30% tensile deformation.

Optimized Monolithic 2-D Spin-Valve Sensor for High-Sensitivity Compass Applications

We have designed and fabricated 2-D giant magnetoresistance spin-valve sensors on the basis of exchange-biased NiFe-CoFe/Cu/CoFe/IrMn nanolayers in monolithic integration for high-sensitivity compass applications. For a maximum signal-to-noise ratio, we have realized a focused double full-bridge layout with an antiparallel alignment of the pinned layer magnetization for neighboring meanders. This precise alignment is achieved with microscopic resolution by laser heating and subsequent in-field cooling. Striving for high-signal sensitivity and low hysteresis, we study in detail how the geometry of the constituent single meanders influences their magnetic structure and the resulting electronic transport properties. The investigated geometrical parameters include stripe width, stripe length, U-turn material, and total meander length. Moreover, the influence of the relative alignment between reference magnetization and shape anisotropy is studied. We compare our experimental results to the predictions of tailored micromagnetic simulations. Applying the best-suited meander geometry, we demonstrate how the developed 2-D sensor may be readily employed to determine the direction of small magnetic fields, such as that of the Earth, as a 2-D vector with high spatial (~1mm) and temporal (~1ms) resolution.

An assessment on the nature of channel migration of River Diana of the sub-Himalayan West Bengal using field and GIS techniques

Lateral movement of river channel within its valley with time is a universal phenomenon. Various processes of fluvio-geomorphological environment such as rapid valley fill deposition due to very low channel gradient and resultant migration of active channel, bank failure and bankline migration, frequent occurrence of floods, capturing of lower courses of the tributaries by the trunk streams, and abandonment of tracks and avulsion are the most prominent factors behind channel dynamics in the sub-Himalayan part of West Bengal. Additionally, human interventions in the form of engineering constructions (bridges, flood embankments, etc.), tea plantation, mining and quarrying, and agricultural encroachment have emerged as another dominant issue which is pulverizing the ways of natural channel adjustment as well as also the channel behaviors. Both these processes are carrying significant messages of immense vulnerability for the study area known for its geomorphological instabilities. The dynamics of channel adjustment in terms of lateral migration can be lucidly illustrated through the application of modern tools of geoinformatics, i.e., the techniques of remote sensing and geographic information system (GIS) which is widely capable of detecting as well as representing the changes that took place over space and time. A meticulous endeavor has been made to assess the channel dynamics of the Diana River of this concerned region for an 85-year spanning period to unveil the nature of channel migration in terms of changes in historical bankline and centerline positions and alterations in meander geometries through numeric and graphical methods coupled with field observations to define the overall zone of channel migration for three subsequent reaches of the Diana River.

Preliminary data on the Jiu River meanders in the lower course (South-West Romania)

The aim of this study is the complex monitoring of the Jiu river bed in terms of geometry and complexity of meanders in its lower sector (on a length of 77 km). The detailed analysis of the lower Jiu sector meanders completes the geomorphologic knowledge of rivers in Romania, starting from the identification and determination of the type of meanders: the results that were achieved are represented by the indexes concerning their age and migration rate (wavelength, 1977 4721 m; meanders amplitude, 511 2862 m; the mean radius of curvature, 270 997 m and the sinuosity index, from 0.87 to 2.17). Another aim of this study is the identification of the evolution features of the Jiu river, the relationships between some hydrological factors of control (liquid flow and suspended sediments annual average values) and the generations of meanders (actual or open meanders, and incised meanders or paleomeanders) distributed in two sectors: Podari Padea sector and the sector stretching from Padea up to the Danube confluence. In addition, our concern is motivated by the fact that in the last years there were analyzed the landslides and subsidence on the right slope of the Jiu river (next to Bâzdâna and Dranic settlements), strongly eroded and in close connection with the meandering of the watercourse.

Meandered TWAs array for near‐field UHF RFID applications

An array of 2 × 2 travelling wave antennas (TWAs) is proposed for near-field RFID applications in the UHF band (865-928 MHz). Each array element is characterised by a meandered line based on coplanar waveguide technology. All the TWAs end on a matched load, which allows for non-stationary current and field distributions as well as a low far-field gain. Thus, strong and uniform fields within a confined volume above the antenna surface have been obtained, with a field maximisation in the antenna central area, where tagged items are supposed to lie on. The meander geometry allows exciting all-field components, making the tag detection almost independent of tag location and orientation when it lies on the antenna surface. Since TWAs are not resonating structures, the proposed antenna results are scalable, allowing for an easy integration in commercial readers with arbitrary sizes. In particular, a 275 × 135 × 10 mm 3 antenna has been designed to fit a particular commercial desktop reader size. Measured tests on the antenna read range were carried out, showing a field distribution maximised in the broadside direction within 10 cm from the antenna surface.