Channel Cutoff Research Articles

Analysis of factors affecting the water regeneration capacity in Tarim River Basin

The formation, evolution and regeneration of water resources follow the general laws of nature. However, in recent years, with the increasing social and economic activities of human beings, the hydrological cycle of nature has undergone significant changes, which has led to a prominent contradiction in the water supply-demand. It has also led to a series of serious environmental and ecological problems, which have caused certain areas, such as the Tarim River Basin (TRB) to face severe conditions of water shortage, downstream river channel cutoff, vegetation degradation and ecological environment deterioration. The lack of water is the main problem to solve these problems, and the water resource reproducible ability, now and in the future, is the key to solving the core problem of water shortage. Through collecting data of precipitation, runoff and temperature of representative hydrographic stations of the Tarim River, as well as the data of geographical location and human activities, this paper studies the factors affecting the water resource reproducible ability in the TRB. The paper draws the following conclusions: (1) The water resource reproducible ability in the source flow area of TRB is increasingwhen the temperature and precipitation is increasing. (2) The water resource reproducible ability in the west of TRB is greater than that in the east. (3) With the elevation of the topography, the water resource reproducible ability in the TRB is stronger. (4) Human activities weaken the water resource reproducible ability.

High-resolution modeling of meander neck cutoffs: laboratory and field scales

Meandering rivers are distinguished by their characteristic sinuosity, which is subject to modulation through channel cutoff, resulting in the formation of oxbow lakes within the abandoned meander loops. Throughout the evolutionary course of a river, these cutoffs establish a connection between the channel and floodplain systems, both crucial to maintaining the dynamic equilibrium of the river system. Nonetheless, the interactive dynamic between the channel and floodplain and its influence on the transient behavior of the channel’s morphodynamics during a cutoff event are frequently reduced to simplistic representations in computational models. This study introduces a comprehensive numerical model that elucidates the adaptive processes of bed and planform during and subsequent to the inception of cutoff and oxbow lakes. The model is assessed through its application to a laboratory scale cutoff, before being employed to a real-world meandering river, specifically the Ucayali River in Peru, in order to gain understanding into channel development and the intricate patterns of planform dynamics following cutoff events. The model is able to capture the main modes of planform migration, translation and expansion for the case of the bend in the Ucayali River. During the neck cutoff, the model simulates the progression of erosional and depositional waves traveling in upstream and downstream directions respectively, underscoring the importance of incorporating both hydrodynamic and morphodynamic factors in characterizing the river dynamics associated with meander cutoffs.

Relativistic analytical R -matrix theory for strong-field ionization

The analytical R-matrix (ARM) theory has been known for an efficient description of the Coulomb effects of the atomic core in strong-field ionization in the nonrelativistic regime. We generalize the ARM theory into the relativistic domain aiming at the application to strong-field ionization of highly charged ions in ultrastrong laser fields. Comparison with the relativistic Coulomb-corrected strong-field approximations (SFA) is provided, highlighting the advantages and disadvantages. The weakly relativistic asymptotics and its accordance with the nondipole Coulomb-corrected SFA are examined. As an example of a physical application of the relativistic ARM, the Coulomb enhancement of tunneling ionization probability for highly charged ions at the cutoff of the direct channel is discussed.

How Is Time Distributed in a River Meander Belt?

AbstractRiver meandering controls the age of floodplains through its characteristic paces of growth and eventual cutoff of channel bends, forming oxbows. Hence, floodplain‐age distributions should reflect a river's characteristic size and migration rate. This hypothesis has been previously tested in numerical simulations, yet without systematic comparisons with natural systems. Here we analyze oxbow spacing and timescales of bend evolution and abandonment in natural and numerically simulated meander belts. In both cases, a saturated state is achieved whereby oxbows are spaced ∼1 meander radius apart. At saturation, the distribution of floodplain ages and probability of sediment‐storage time can be constrained from characteristic timescales of bend evolution and abandonment. Owing to the similar relationships between floodplain width and characteristic timescales in natural and simulated rivers, we postulate that this approach should apply to unconfined meandering rivers elsewhere—a hypothesis to be tested with independent geo‐ or dendrochronological data.

Sediment Load Concentration and Resultant Channel Planform in the Lower Gandak Plain

Erosion, transportation and deposition by running water are closely related and these works are performed in association and not in isolation. One cannot be performed without others. These works are determined on other factors like topography, geology, structure and composition of rocks, slope, amount of water availability and its characteristics, climate etc. Huge catchment area of the Gandak River is lying in the Himalayan mountainous region. This region is receiving good amount of rainfall concentrated in four months of monsoonal period June to September (JJAS). This period has also high temperatures leading to large amount of glacial ice melt. Hence, enormous water is drained off the mountain steep slope. The Himalaya is very young and has fragile rocks and ecosystem. Anthropogenic activities in those areas are primary cause, apart from natural weathering, for generation of more and more shattered materials which are brought by running water downstream much easily. Therefore, highly sediment concentrated water brings large quantity of loads. It is deposited in suitable conditions along its paths in the plain and with flood water. It results the formation of flood plain. According to the erosion and deposition, different types of major and minor features are formed. In other words, water and sediment determine the layout of the plain appearance. In this background, it is attempted to (i) study sediment concentration in discharged water and (ii) illustrate the channel planform of the Gandak River in the plain. To achieve these aims, secondary data has been collected and analyzed. It is expected that this study will help in executing an integrated development plan for the flood affected area of Lower Gandak River Plain. Keywords: sediment load, channel bars, channel planform, meandering, braiding, slope/gradient and channel cutoff.

Morphology, sedimentology and origin of an anomalous cut-off along the Pravara river, deccan trap region, India

River meanders have always been an intriguing subject in fluvial geomorphology because of their ubiquity, dynamism, remarkable forms and practical consequences of their movement. Sometimes a relatively straight channel flowing over bedrock may develop a lone meander bend cut-off which is very out of the place from the surrounding area. The occurrence of a sudden bend along a river may not be a meandering bend but may be manifestation of sudden change in the river dynamism due to many reasons, such as, lithology, change in rainfall regime, tectonics etc. The formation of such features highlights the behavior of river in the past. One such striking feature has been observed along the River Pravara in the Deccan Trap Region, Maharashtra, India. Rivers in Deccan Trap Region do not meander and form cut-offs by rule. It is rocky country where rivers flow in deeply incised bedrock. Hence, the observed feature displays a striking anomaly in this region. Hence, an attempt has been made in the present paper to evaluate the mode of formation of this single cut-off along this channel. Morphological and sedimentological data were generated and analyzed for the channel loop and the link channel to understand the competence of the river in the past and present which were directly or indirectly responsible for the development of this channel anomaly in this reach. Based on the results of the analysis and intensive field observations, it has been inferred that this is a classic example of natural morphological adjustment of a river when a set of events occurred, first retardation of vertical erosion encountering bedrock followed by series of floods to induce the channel to divert from the original path to resume the present course. Presence of a tributary further aided to the process of the loop development. The study can provide additional knowledge to the studies involving anomalous channel cut-offs at any part of the world.

Responses of two dominant desert plant species to the changes in groundwater depth in hinterland natural oasis, Tarim Basin.

Groundwater is increasingly becoming a permanent and steady water source for the growth and reproduction of desert plant species due to the frequent channel cutoff events in arid inland river basins. Although it is widely acknowledged that the accessibility of groundwater has a significant impact on plant species maintaining their ecological function, little is known about the water use strategies of desert plant species to the groundwater availability in Daryaboyi Oasis, Central Tarim Basin. This study initially determined the desirable and stressing groundwater depths based on ecological and morphological parameters including UAV‐based fractional vegetation cover (FVC) images and plant growth status. Then, leaf δ13C values of small‐ and big‐sized plants were analyzed to reveal the water use strategies of two dominant woody species (Populus euphratica and Tamarix ramosissima) in response to the groundwater depth gradient. The changes in FVC and growth status of plants suggested that the actual groundwater depth should be kept at an appropriate range of about 2.1–4.3 m, and the minimum groundwater depth should be less than 7 m. This will ensure the protection of riparian woody plants at a normal growth state and guarantee the coexistence of both plant types. Under a desirable groundwater condition, water alternation (i.e., flooding and rising groundwater depth) was the main factor influencing the variation of plant water use efficiency. The obtained results indicated that big‐sized plants are more salt‐tolerant than small ones, and T. ramosissima has strong salt palatability than P. euphratica. With increasing groundwater depth, P. euphratica continuously decreases its growth status to maintain hydraulic efficiency in drought condition, while T. ramosissima mainly increases its water use efficiency first and decreases its growth status after then. Besides, in a drought condition, T. ramosissima has strong adaptability than P. euphratica. This study will be informative for ecological restoration and sustainable management of Daryaboyi Oasis and provides reference materials for future research programs.

Design of a Microwave Lowpass – Bandpass Filter using Deep Learning and Artificial Intelligence

In this paper, a lowpass – bandpass dual band microwave filter is designed by using deep learning and artificial intelligence. The designed filter has compact size and desirable pass bands. In the proposed filter, the resonators with Z-shaped and T-shaped lines are used to design the low pass channel, while coupling lines, stepped impedance resonators and open ended stubs are utilized to design the bandpass channel. Artificial neural network (ANN) and deep learning (DL) technique has been utilized to extract the proposed filter transfer function, so the values of the transmission zeros can be located in the desired frequency. This technique can also be used for the other electrical devices. The lowpass channel cut off frequency is 1 GHz, with better than 0.2 dB insertion loss. Also, the bandpass channel main frequency is designed at 2.4 GHz with 0.5 dB insertion loss in the passband.

Hydrological and landscape dynamics of floodplain wetlands of the Diara region, Eastern India

Wetland dynamics research primarily concentrates on individual wetland’s loss or gain of area where landscape specific approach is majorly ignored. While the fate of floodplain wetlands depends largely on the actions of the parent rivers such as increased flow, channel migration path, flooding events, channel cut-offs and others that are rather episodic in nature, so the overall situation may not be defined by the loss or gain of any specific wetland. Therefore, instead of using individual wetland-specific strategies if landscape-specific approaches are adopted, it might be possible to better interpret the wetland scenario. From this perspective, the floodplain wetland dynamics of the Diara region which is an active floodplain region of River Ganga has been assessed in three key dimensions like spatial, hydrological, and landscape ecological. Centroid method, hydro-period analysis, water presence, threshold dependent NDWI-NDVI are the key methods used for spatial and hydrological dynamics. A new method of Mean NDWI-NDVI Depth (MNND) has been introduced to measure the hydrological change in the wetlands. Few major landscape ecological metrics have been calculated using FRAGSTATS and lastly, the forest fragmentation rules are adopted to divide the wetland landscape into patch, edge, perforated and core areas. The result shows that wetland dynamics are very much unpredictable and strongly influenced by the behaviour of River Ganga. The wetland area has significantly gone up to 12095.37 ha in 2011 from 6795.9 ha in 1991 due to massive flood of 2010 and again it has gone down to 5725.35 ha in 2019. In 2019 the wetland centroid location has moved 2.14 km away from 1991′s centroid location in the opposite direction where River Ganga exists. Most of the wetlands are here heavily fragmented into smaller patches that results into the presence of only 10% core wetlands. Thus the vast portion of the floodplain wetlands can be degraded at any time due to hydrological instability, severe fragmentation and over-dependence on episodic events like floods.

Experimental study of a low-pressure hybrid RF discharge

Experimental study of the low-pressure hybrid RF discharge with both inductive and capacitive channels was carried out. The RF power unit consists of inductor (antenna) and capacitor plates connected in parallel to the same RF power source. A separating capacitor Csep is included into the circuit between the antenna ends and the lead connected to the discharge capacitor plate in order to prevent the closing of the capacitive circuit through direct current by inductor and to control the contribution of capacitive channel to discharge sustaining. It is shown that at low power of the RF power source, power coupling to the discharge mainly occurs through the capacitive channel. Increasing the power of the RF power source increases the power coupled in the inductive channel, electron density, and current flowing through the capacitive channel. This leads to increasing voltage drop on the separating capacitor and partial cutoff of the capacitive channel. At separating capacitance values below certain value (below 50 pF in the present experiments), the self-bias of the loaded plate of the discharge capacitor becomes positive indicating that the thickness of the electrode sheath of the loaded electrode decreases compared to thickness of the sheath of the grounded electrode. The thickness of the space-charge sheath of the grounded electrode decreases with increasing power coupled to the plasma. At separating capacitance below 50 pF, higher harmonics of the RF voltage and current are actively generated in the capacitive discharge channel. Increasing the separating capacitance leads to decreasing electron density, increasing effective electron temperature and more effective RF energy coupling to plasma due to increasing relative importance of the capacitive discharge channel.

Effect of the Conductive Channel Cut-Off on Operation of n+–n–n+ GaN NW-Based Gunn Diode

Nowadays modern science and technology require development of efficient electromagnetic emitters covering far GHz and THz ranges. Semiconductor elements with negative differential resistance (NDR) such as Gunn diodes based on GaAs and InP are well-established powerful microwave emitters. In this work the Gunn diode structure based on single GaN nanowire with the potential of THz device development was proposed and investigated both theoretically and experimentally. According to the results of the numerical modeling, the Gunn generation can be obtained in the proposed geometry. Dependence of the doping concentration on the NW length necessary for the electrons domain formation was obtained. The nanostructures were grown via molecular beam epitaxy technique. Contacts to single nanowires were fabricated with the combination of e-beam lithography and thermal evaporation. It was shown experimentally that the volt-ampere characteristics of the GaN nanowire structure possess current saturation region. Experimental results correspond well to proposed numerical model.

Late Holocene channel pattern change from laterally stable to meandering – a palaeohydrological reconstruction

Abstract. River channel patterns may alter due to changes in hydrological regime related to changes in climate and/or land cover. Such changes are well documented for transitions between meandering and braiding rivers, whereas channel pattern changes between laterally stable and meandering rivers are poorly documented and understood. We hypothesize that many low-energy meandering rivers had relatively low peak discharges and were laterally stable during most of the Holocene, when climate was relatively stable and human impact was limited. Our objectives in this work are to identify a Late Holocene channel pattern change for the low-energy Overijsselse Vecht river, to develop and apply a novel methodology to reconstruct discharge as a function of time following a stochastic approach, and to relate this channel pattern change to reconstructed hydrological changes. We established that the Overijsselse Vecht was laterally virtually stable throughout the Holocene until the Late Middle Ages, after which large meanders formed at lateral migration rates of about 2 m yr−1. The lateral stability before the Late Middle Ages was constrained using a combination of coring information, ground-penetrating radar (GPR), radiocarbon (14C) dating, and optically stimulated luminescence (OSL) dating. We quantified bankfull palaeodischarge as a function of time based on channel dimensions that were reconstructed from the scroll bar sequence and channel cut-offs using coring information and GPR data, combined with chronological constraints from historical maps and OSL dating. We found that the bankfull discharge was significantly greater during the meandering phase compared to the laterally stable phase. Empirical channel and bar pattern models showed that this increase can explain the channel pattern change. The bankfull discharge increase likely reflects climate changes related to the Little Ice Age and/or land use changes in the catchment, in particular as a result of peat reclamation and exploitation.

Construction of avulsion potential zone model for Kulik River of Barind Tract, India and Bangladesh.

Avulsion is a natural fluvial process but considered it as a hazard in the populated region due to the chance of immense failure of lives and properties. So, early warning indicates that the zone of avulsion can facilitate the people living there. About 317 numbers of local and regional historical imprints of channel cutoff along river Kulik claim the need of this work. The present study tried to identify avulsion potential zone (APZ) of Kulik river of Indo-Bangladesh using multi-parametric weighted combination approach. Analytic hierarchy approach (AHP) is applied for weighting the used parameters. Avulsion potential model clearly exhibits that 9.51-km stream segment of middle and lower catchment is highly susceptible for avulsion especially during sudden high discharge and earthquake incidents. There is also high chance of channel avulsion following the existing Paleo-avulsion courses and left channels. Hard points can also be erected alongside the main channel for resisting channel avulsion propensity.

Average Error Rates and Achievable Capacity in Large Office Indoor Wireless Environments

Performance of common digital modulation techniques is analyzed over indoor wireless environments modeled through the recently proposed joint fading and two-path shadowing (JFTS) channel model. Mathematically tractable expressions for the instantaneous signal-to-noise ratio statistics, average bit error rates, and achievable channel cutoff rates are derived. Analytical results are used to: 1) investigate the impact of different JFTS model parameters and different modulation techniques on bit error rates and cutoff rates and 2) demonstrate how the JFTS channel model affects system performance in comparison with conventional empirical channel models. Finally simulation results are used to corroborate this analysis and evaluate the usefulness of such an analysis.

Achievable Channel Cutoff Rate and Bandwidth Efficiency in Indoor Wireless Environments

In this paper, analytical expressions for the channel capacity, channel cutoff rate, and achievable bandwidth efficiency associated with M-ary signaling and Joint Fading Two-path Shadowing (JFTS) fading/shadowing channel model that characterize mobility-constrained indoor propagation scenarios are derived. Expressions for the bandwidth efficiency of a JFTS fading channel involve infinite-series summation since the probability density function of the JFTS signal-to-noise ratio (SNR) contains infinite series. We derive lower and upper bounds on the errors resulting from truncating the infinite series in the bandwidth efficiency expression. The cutoff rate and bandwidth efficiency analysis can be used to demonstrate how much throughput can be practically achieved when M-ary signaling techniques are implemented over indoor composite fading/shadowing channel conditions. Simulation results show that in order to achieve 3 bits/symbol, the average SNR for a 16-quadrature-amplitude-modulation (16-QAM) system requires almost 10 dB more for a JFTS channel model compared with a traditional Rayleigh channel model, thus reinforcing the necessity of using proper channel models for indoor communication systems.

Climate variability over the last 2000 years inferred from glycerol dialkyl glycerol tetraethers (GDGTs) in alkaline Nalin Lake of Inner Mongolia, China

Nalin Lake from western Inner Mongolia of China is a shallow oxbow lake with a laminated sedimentary record. The distributions of glycerol dialkyl glycerol tetraethers in lacustrine sediment core collected in Nalin Lake in June 2011 were examined in combination with other paleoclimate proxies. The cyclization index of branched tetraethers (CBTs)-inferred pH values changed primarily between 7.67 and 8.63. These changes were synchronous with those from the actual measurement and previous studies. The newly proposed CBT/methylation index of branched tetraethers (MBTs) palaeothermometer was also applied to produce a mean annual air temperature record for Nalin Lake spanning circa the last 2000 years. Over much of the record temperature fluctuated from ~2.76 to 7.61 °C, with a mean value of ~4.76 °C. The proposed CBT/MBT-based temperatures revealed a strong similarity to the local records, both documenting the moderate Medieval Warm Period from 600 to 1200 A.D. (1400–800 cal year BP) and a cooling anomaly Little Ice Age around 16th century. The CBT/MBT temperature patterns seemed to follow variations in the historical and Northern Hemisphere records of the mean annual air temperature. These suggested that the signals were produced during this period. Identification of high alkalinity in association with the decreased fluvial input by multiple indices was consistent with the previous observations due to the cutoff of Yellow River channel. Therefore, CBT/MBT temperature records of lake sediment core can potentially be a useful tool in reconstructing past variations of alkaline lacustrine climate.

Environment-friendly reduction of flood risk and infrastructure damage in a mountain river: Case study of the Czarny Dunajec

Migration of a mountain river channel may cause erosional risk to infrastructure or settlements on the valley floor. Following a flood of 2010, a cutbank in one of the bends of the main channel of the Czarny Dunajec, Polish Carpathians, approached a local road by 50m. To arrest the erosion of the laterally migrating channel, water authorities planned construction of a ditch cutting the forested neck of the bend, reinforcement of the ditch banks, and damming the main channel with a boulder groyne. In order to avoid channelization of the highly valued, multithread river reach that would deteriorate its ecological status and cause increased flood risk to downstream reaches, an alternative approach to prevent bank erosion was proposed. The new scheme, applied in 2011, included opening of the inlets to inactive side braids located by the neck of the bend of the main channel. This solution reestablished the flow in the steeper low-flow channels, allowing us to expect a cutoff and abandonment of the main channel during subsequent floods. Gravelly deflectors were constructed directly below the inlets to the reactivated side channels to divert the flow into the channels and prevent the water from entering the main channel. Hydraulic measurements performed before and after the implementation of the scheme confirmed that it enabled shifting the main water current, with the highest average velocity and bed shear stress, from the braid closest to the road to the most distant braid. Similar surveys of fish and benthic macroinvertebrate communities indicated that flow reactivation in the side channels was beneficial for these groups of river biota, increasing their abundance and taxonomic richness in the reach. Not only was the implemented solution significantly less expensive, but it also enhanced ecological functions of the multithread channel and the variability of physical habitat conditions and maintained the role of the reach as a wood debris trap. However, avulsion of the main channel in the river bend immediately upstream during the flood in May 2014 again caused erosional risk to the road, although at another location. This indicates that with the highly unstable, multithread channel pattern of the Czarny Dunajec, the best practice of river maintenance in a relatively unmanaged valley reach would be allowing free channel migration within the floodplain area and reinforcing, where necessary, the boundary between the erodible river corridor and the managed terrace.

Theoretical Accuracy Analysis of Indoor Visible Light Communication Positioning System Based on Received Signal Strength Indicator

This paper analyzes an indoor positioning system using white lighting LEDs. The performance of the positioning system is determined by the layout of LEDs, the receiver circuit, incidence angle of light, LED light source, and the photodiode. The Cramer-Rao bound as the theoretical accuracy limitation of received signal strength indicator algorithm is derived. The influences to positioning accuracy of multipath reflections and unparallel optical axis of LEDs and receivers are analyzed in certain scenarios. It is concluded that if the diffuse channel gain is measured previously in a certain environment and the modulation speed is far less than the channel cutoff frequency, the theoretical accuracy limit is not affected by multipath link. Multiple noises of system are analyzed in detail. The influence to positioning accuracy of indoor uniform illumination is also discussed. The result proves that the theoretical estimated accuracy of triangular LEDs array is higher than square LEDs array. With typical parameter values, the simulated theoretical accuracy of system is up to the level of centimeter.

Model describes river meandering

Understanding and predicting the evolution of meandering rivers could be useful to geoscientists as well as to engineers who may be dealing with practical problems related to river movement. Asahi et al. created a computational model for predicting the evolution of complex meandering rivers that captures short‐term processes, such as flooding, and ­longer‐term processes. The model considers bank erosion, land accretion along meander bends, and the formation of channel cutoffs and describes how river width and sinuosity evolve together. In general, the authors found that discharge variation plays an important role in the shape and behavior of river meanders. They note that their model produces a rich pattern of meander evolution that appears to be consistent with that observed in natural rivers.

Numerical simulation of river meandering with self-evolving banks

[1] In this study, the natural process of river meandering is captured in a computational model that considers the effects of bank erosion, the process of land accretion along the inner banks of meander bends, and the formation of channel cutoffs. The methodology for predicting bank erosion explicitly includes a submodel treating the formation and eventual removal of slump blocks. The accretion of bank material on the inner bank is modeled by defining the time scale over which areas that are originally channel become land. Channel cutoff formation is treated relatively simply by recomputing the channel alignment at a single model time step when migrating banks meet. The model is used to compute meandering processes in both steady and unsteady flows. The key features of this new model are the ability (a) to describe bank depositional and bank erosional responses separately, (b) to couple them to bed morphodynamics, and thus (c) to describe coevolving river width and sinuosity. Two cases of steady flow are considered, one with a larger discharge (i.e., “bankfull”) and one with a smaller discharge (i.e., “low flow”). In the former case, the shear stress is well above the critical shear stress, but in the latter case, it is initially below it. In at least one case of constant discharge, the planform pattern can develop some sinuosity, but the pattern appears to deviate somewhat from that observed in natural meandering channels. For the case of unsteady flow, discharge variation is modeled in the simplest possible manner by cyclically alternating the two discharges used in the steady flow computations. This model produces a rich pattern of meander planform evolution that is consistent with that observed in natural rivers. Also, the relationship between the meandering evolution and the return time scale of floods is investigated by the model under the several unsteady flow patterns. The results indicate that meandering planforms have different shapes depending on the values of these two scales. In predicting meander evolution, it is important to consider the ratio of these two time scales in addition to such factors as bank erosion, slump block formation and decay, bar accretion, and cutoff formation, which are also included in the model.