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The distal reach of the Lower Jingjiang River (LJR) in the middle of the Yangtze River consists of five adjacent bends, among which the Qigongling Bend is a Ω-shaped meander with a mean sinuosity of 2.2 and the narrowest neck 525 m in width. This bend is slowly approaching neck cutoff owing to progressive bank erosion. An abnormal phenomenon has occurred in this bend since the Three Gorges Reservoir (TGR) began to operate in 2003 which is erosion in the inner bank zone and deposition in the outer bank zone. This problem has not been fully understood because of the interplay of changes in water-sediment, bank erosion, and artificial bank revetment. In this study, aerial and remote sensing images, hydrological data, channel topography, and an existing bank erosion model are used to reveal channel morphodynamics of this bend and the trend of the potential neck cutoff induced by bank erosion. The study results show that the clear water released from the TGR has provided by forcefully eroded the point bar of inner bank but failed to scour the outer bank due to the protection of bank revetment since the 1990s. Thus far, the outer bank zone near the bend apex has increasingly widened in conjunction with the formation of 2 emerging sand bars. Consequently, the thalweg of the main channel has laterally shifted toward the inner bank by roughly 800 m. More severely, the rate of bank retreat on the upstream side of the bend neck was about 4.5 m/yr in 2010–2019, but the downstream side of this neck was experienced slight deposition. Bank erosion could be accelerated by progressively increasing erosion and eventually trigger the occurrence of neck cutoff in the next few decades, thereby significantly altering the quasi-equilibrium regime of channel morphodynamics in the LJR.

A one-dimensional numerical model (HEC-RAS) was calibrated to simulate morphological changes in the study reach of the Nile River downstream of Esna barrages by using the available field data of the years 2010 and 2013. The presented research utilizes the synergies between GIS and HEC-RAS in studying the morphological changes in the study area that affects directly the navigation condition and Proposes the optimum navigation path in the selected study reach based on the numerical model results data. Using data measurements, the model was calibrated and verified. It gave a reasonable agreement between the calculated and measured values for the water level and the morphological changes in the selected cross-sections and along the River's thalweg with accuracy 99.63% and 96.66% for hydraulic and sediment calibration and verification. It can be concluded from several runs of the model that the best equation for predicting morphological changes within the study area is the Ackers-White equation. Finally, the results indicate that the HEC-RAS model presents a satisfying performance for sediment transport.

We describe a machine learning seismic classification workflow in which the thousands of class labels needed for training a deep graph are automatically generated from just a handful of manually picked seed positions. The class labels are generated by a Thalweg tracker. This special kind of connectivity filter grows a 3D body of user-defined size from a single seed position by adding only one point at a time. The user controls the size such that the tracker stays within one seismic class. The shape of the growing body is the main criterion for deciding when and where the tracker starts tracking another class. We present two examples. The first example is a 3D seismic facies classification of a setting with stacked meandering channels. We classify the target interval into eight seismic facies classes. In the second example, we extract turbidite channels from a two-pass gradient (i.e., second derivative) attribute volume.

Sediment deposition is a significant feature of a dynamic floodplain river. As the river's carrying capacity decreases, it is forced to deposit sediment on the river bed. However, due to the construction of some hydraulic structures over the river bed at different times (bridges, dams), the velocity of the river in the floodplain area decreases with accelerating sedimentation process, which hinders water transport. The sub-catchment basin (Nabadwip-Kalyani stretch) of the Bhagirathi–Hooghly river in West Bengal (Ghosh et al. 2020), India is frequently used as a means of water transport by local stakeholders. Because of sedimentation, the thalweg depth of the river is constantly decreasing in Nabadwip–Kalyani stretch and the water transport is being disrupted. Therefore, it is very important to know the function of hydraulic structures over the river bathymetry and resultant sediment flow, transportation, and sediment deposition in this region. Therefore, this article mainly assesses to develop a 1D hydro-dynamic sediment transport model on river morphological change through seasonal quasi-unsteady flow accumulation and sediment budget in a given year (2018). The hydro-dynamic model is calibrated by 1D HEC-RAS v 5.0.7 software (Gibson et al. 2017) based on seasonal quasi-unsteady flow using various empirical equations and Manning's roughness coefficient and validated with R2, NSE, and RSR. The model also examines the role of hydrodynamic structures in scouring and sedimentation due to the location of these structures above the river. This model output will help local stakeholders to understand the amount of sediment in the river and keep river transport viable in all seasons.

High‐resolution multibeam bathymetric and multichannel seismic data are used to investigate the morphology of a submarine canyon (Taiwan Canyon), and its surrounding strata, in the north‐east South China Sea. This submarine canyon shows two main branches at its head, and changes its orientation from north‐west/south‐east to east–west due to the effect of a tectonically active seamount. The asymmetry of the submarine canyon’s banks in its middle reach is due to the combined action of recurrent slope instability and turbidity currents. In addition, two fields of sediment waves were identified in the study area. Field 1 is located on the south‐west levée of the canyon and is fed by turbidity currents from one of its branches, being also associated with marked hydraulic jumps. Field 2 is observed in the southern bank of the lower canyon reach and was formed by the overspill of turbidity currents within the Taiwan Canyon due to the effect of inertial centrifugal forces. Turbidity currents sourced from Dongsha Channel also contributed to forming Field 2. Importantly, trains of plunge pools have been identified along the thalweg of the lower canyon reach, generated by turbidity currents deriving from the submarine canyons in the north of the Taiwan Canyon. These results not only provide a very detailed account of submarine bedforms within and around a large submarine canyon, but also contribute to a better understanding of their origin and development. The high‐resolution bathymetric and seismic data in this work reveal how gravity flows can drive erosion and deposition in submarine canyons.

The Amvrosiivka Upper Palaeolithic complex, composed of a camp site and nearby bison bone bed is located in the Donetsk oblast’, at the top of the Kazenna ravine, a right tributary of the Krynka river, which drains into the Mius river. The site is dated by an average of 19000—18000 uncal BP and belong to Epigravettian tradition. The results of the long-term research the Amvrosiivka bison bone bed was analyzed in the article. The features of topography (a gully-terrace on board of a ravine), planigraphy, stratigraphy of a bone bed (the ledges-thresholds and some sterile layers in cultural remains distribution), and also the seasons of the kill of animals (alternative, with prevalence of cold) was summarized. Data about the bison bones (Bison priscus, MNI = 650 and bones with cultural modifications) is presented. The prevalence of the hunter projectile weapon details (27 bone points and about 90 flint micropoints-inserts), and also flint tools for butchering animals among the archaeological finds is determined. The interpretation of the bone bed at the same times was controversial: as a refuse dump near dwelling (Evseev), as a resulted from a one-time (Pidoplichko) or repeated (Efimenko) mass drive of bison, or as a ritual locale (Boriskovskij). At present the site is interpreted as a place of numerous mass drive of bison and, mainly, primary butchering of hunting bag, and also, probably, storages of meat products in the form of the frozen carcasses of bison in a cold season (Krotova, Snizhko, Julien). The ethnoarchaeological data about methods of collective kills by Paleoindian and Indian pedestrian hunters on bison of the North America (Frison 2004) for the reconstruction of possible variants of the mass drive of bison in Amvrosiivka is used. The conclusion is made that for the purpose organization of the series of mass drive of bison at different seasons the hunters in Amvrosiivka used a natural trap — the gully-terrace on a board of ravine — the right tributary of a Kazenna ravine. This terrace with one abrupt and rather high (4—5 m) board, obviously, used for a drive of bison from above, a plateau (method of «jump») that the hunters, obviously, at a certain stage having added with the restraining structure (pens) which should keep the escaped and wounded animals. The variant of a possible shelter from below, a thalweg of the Kazenna ravine (an «arroyo trap» method) also is not excluded.

Thermophysical properties are an important characteristic of the general condition of soils, which determine the peculiarities of the distribution of heat flow in them. Today studies of thermophysical properties of soils, including the steppe zone of Ukraine, are practically not performed. This determines the relevance of the work, which is devoted to establishing the characteristics of the thermal properties of various soils. As a result of the study of thermal diffusivity, heat capacity and thermal conductivity of soils of northern and southern exposures, as well as the thalweg of the Voyskovoy Bayrak (located near the village of Voyskovoe Solonyansky district of Dnipropetrovsk region), it was found that the most important soil factors particles of physical clay and organic matter content. It was found that the eluvial horizons of the chernozem of the forest of the northern exposure differ in the reduced values ​​of heat capacity and thermal conductivity in comparison with the illuvial horizons. Eluvial horizons of forest-meadow soil of thalweg are characterized by increased values ​​of thermal diffusivity and thermal conductivity, as well as reduced values ​​of heat capacity compared to illuvial horizons. Eluvial horizons of forest chernozem of southern exposure are characterized by lower values ​​of thermal diffusivity, heat capacity and thermal conductivity compared to illuvial horizons. The most significant boundary between eluvial and illuvial horizons in terms of thermophysical properties is characteristic of the chernozem of forest southern exposure, which is manifested in a sharp increase in the values ​​of thermophysical properties in the first illuvial horizon. Cluster analysis revealed that the most similar in terms of thermal diffusivity are forest chernozems of southern and northern exposures, and in terms of heat capacity and thermal conductivity – forest chernozems of northern exposure and forest-meadow soil of thalweg ravine.

Intermittently open/closed estuaries (IOCE) are wave-dominated estuaries with entrances that temporarily close to the ocean. Wave–current interactions play a major role in estuary entrance morphodynamics and influence the degree of energy transfer from the ocean into the lagoon. This study utilizes artificial entrance openings of multiple ICOE in Victoria, Australia, to capture continuous hydrodynamic and geomorphic data throughout the opening cycle. We illustrate that water level oscillations in the infragravity (IG) band) are present in the basin during open entrance conditions. IG waves were observed to propagate up to 1.8 km upstream of the mouth while the entrance was open. Our work identifies that changes in cross-sectional area, bed depth at the berm position, and offshore wave height control the magnitude of IG waves within the estuary basin. IG wave magnitude is also tidally modulated and increases with high tides when the nearshore water level is higher. Late during the drainage phase, waves were observed to track the margins of the channel, away from the thalweg, and reach the basin. IG wave energy was highest immediately after the basin had ceased draining and while channel dimensions at the mouth were within 10% of their maximum value. As the entrance aggrades, IG wave magnitude decreases in the absence of energetic offshore wave conditions. We relate the changes in IG wave magnitude and frequency to a six-stage conceptual model of the opening–closure sequence. Within the basin, IG wave energy, height and frequency were also consistently highest closer to the mouth and decreased with distance upstream. Our findings indicate that water level oscillations in the IG band are a persistent feature in IOCE and may be the norm rather than the exception in these systems. As IG waves were captured serendipitously as part of a larger field campaign, future work will focus on instrumenting IOCE to gain high-resolution data to quantify IG wave processes during entrance openings. © 2020 John Wiley & Sons, Ltd.

Shatt al-Arab is the only navigational artery in Iraq, extending from the city of Qurna to its mouth in the Arabian Gulf at the city of Al-Fao within the governorate of Basrah for a length of approximately 204 km. Its width ranges from 400 m to 2000 m, and its depth ranges from 8 m to 20 m. The southern part of it, 93 km long from Umm al-Rassas Island to Ras al-Bisha, represents the international border between Iraq and Iran, where the Thalweg line represents the border between the two countries, which is the deepest point in the riverbed (according to the 1975 Algiers Agreement). The western bank (the Iraqi side) within the common border of Shatt al-Arab is subject to continuous erosion, which leads to the shifting of the Thalweg line towards Iraqi territory and thus leads to loss of Iraqi land to Iran. Reducing flow velocity along the Iraqi side can lead to reducing or preventing erosion in the river. Increasing the riverbed roughness will reduce the velocity of flow and then reducing the erosion. This principle was adopted in this study to investigate the effect of increasing roughness in a strip along a reach of the riverbed on the distribution of longitudinal velocity in cross-sections at the rest of the selected reach. A reach of Shatt al-Arab with a length of 2500 m, located 34 km north of Fao City, was selected to represent the study area. This reach was simulated by using numerical modeling CFD solver (fluent) with three different roughnesses for an upstream part of the river bed and the velocities compared with the natural (original) roughness of Shatt al-Arab. The results showed an appreciable effect of the increased bed roughness on the velocity distribution and the maximum velocity location by shifting it to the other side.

Namurian (Carboniferous) eustatic fluctuations drove the incision and backfill of shelf‐crossing valley systems located in humid subequatorial regions, which are now preserved in successions of the United Kingdom and Ireland. The infills of these valleys archive the record of palaeoriver systems whose environmental, hydrological and palaeogeographic characteristics remain unclear. A synthesis of sedimentological data from fluvial strata of 18 Namurian incised‐valley fills in the United Kingdom and Ireland is undertaken to elucidate the nature of their formative river systems and to refine regional palaeogeographic reconstructions. Quantitative analyses are performed of facies proportions, of geometries of incised‐valley fills and related architectural elements, and of the thickness of dune‐scale sets of cross‐strata. Reconstruction of the size of the drainage areas that fed these valleys is attempted based on two integrative approaches: flow‐depth estimations from dune‐scale cross‐set thickness statistics and scaling relationships of incised‐valley fill dimensions derived from late‐Quaternary examples. The facies organization of these incised‐valley fills suggests that their formative palaeorivers were perennial and experienced generally low discharge variability, consistent with their climatic context; however, observations of characteristically low variability in cross‐set thickness might reflect rapid flood recession, perhaps in relation to sub‐catchments experiencing seasonal rainfall. Variations in facies characteristics, including inferences of flow regime and cross‐set thickness distributions, might reflect the control of catchment size on river hydrology, the degree to which is considered in light of data from modern rivers. Palaeohydrological reconstructions indicate that depth estimations from cross‐set thickness contrast with observations of barform and channel‐fill thickness, and projected thalweg depths exceed the depth of some valley fills. Limitations in data and interpretations and high bedform preservation are recognized as possible causes. With consideration of uncertainties in the inference of catchment size, the palaeogeography of the valley systems has been tentatively reconstructed by integrating existing provenance and sedimentological data. The approaches illustrated in this work can be replicated to the study of palaeohydrological characteristics and palaeogeographic reconstructions of incised‐valley fills globally and through geological time.

Ephemeral and perennial streams of mountainous catchments in Sabaragamuwa Province of Sri Lanka and Hong Kong of China were studied for two years on vegetation dynamics. Each year, sampling was conducted during a period when ephemeral streams had low surface flows. Sampling was realized contiguously using belt transects. The standing crop biomass (hereafter biomass) of herbaceous vegetation in ephemeral channels was comparatively lower than perennials and so was the herb diversity. Herb diversity showed a peak from 1.5 to 4.5 m from the centerline/thalweg of ephemeral and perennial streams. Out of 24 herbs, only three were common for both. A peak herb biomass zone was observed in perennials in the same region where diversity peaked. In ephemerals, herb biomass increased laterally up to ∼1.5 m, and was constant thereafter. Seedling experiment results tallied with the field diversity observations of both stream types, and suggested that seed dispersion was the main reason for herb colonization. Furthermore, it showed sapling emergence to be significantly higher in perennials than ephemerals. Return period of annual maximum monthly rainfall was a strong indicator of age of trees in ephemeral streams, and elucidated the possibility of hindcasting past flow episodes. Electrical conductivity was significantly high in ephemeral streams among all the water quality parameters. The contents of the water nutrients were approximately the same in both stream types. While recommending further studies on eco-hydrology of ephemerals, we recognize ephemeral streams to be valuable references in climate change studies due to their responsiveness and representativeness in long term hydrological changes.

The natural forests of the southern variant of the steppe zone of Ukraine (according to the classification of O. L. Belgard) are located on the territory of the former porous part of the Dnieper. The properties of edaphotopes of these forests were studied in detail by the staff of the Comprehensive expedition of the Oles Honchar Dnipro National University for the study of forests in the steppe zone of Ukraine (A. P. Travleev, N. A. Bilova, A. A. Dubina, K. M. Bozhko). However, there are no data on the structural and aggregate composition of the genetic horizons of edaphotopes of natural forests of the southern variant of the steppe zone of Ukraine, established by classical methods of determination. This work is devoted to the coverage of these features. As a result of research it is established that the best conditions for the formation of structural aggregates are characteristic of the upper horizons of all studied soils and especially for the forest chernozem in the conditions of northern exposure. The highest content of agronomically valuable structural aggregates is characterized by forest chernozem in the conditions of northern exposure of the ravine, the lowest – meadow-forest soil of thalweg, and forest chernozem in the conditions of southern exposure occupies an intermediate value. The eluvial horizons of ravine edaphotopes differ most contrastingly from the illuvial horizons in the conditions of northern and southern exposures. Eluvial horizons are characterized by a reduced fraction content of > 10 mm and increased values ​​of the structural coefficient compared to illuvial horizons. In the thalweg, these differences are not so clear. The upper horizons have an increased content of water-resistant fraction size > 5 mm compared to the horizons below. With depth in all studied edaphotopes there is an increase in the content of the fraction size < 0.25 mm with depth. Among the upper horizons, the highest content of water-resistant fraction size > 5 mm and the lowest content of fraction < 0.25 mm differs meadow-forest soil in thalweg conditions. Very close to the meadow-forest soil in terms of the values ​​of the respective fractions is forest chernozem in the conditions of northern exposure. Forest chernozem in the conditions of southern exposure differs by the lowest content of water-resistant fraction size > 5 mm and the highest content of fraction size < 0.25 mm among all studied soils. Eluvial horizons of forest chernozems of northern and southern exposures differ from illuvial horizons by reduced content of water-resistant fractions of > 5 and 5–3 mm. The eluvial horizons of the meadow-forest soil of the thalweg differ from the illuvial horizon by a sharp decrease in the content of the water-resistant fraction of 1–0.5 mm. A comparative analysis of the structural and aggregate composition of the studied edaphotopes revealed that the best conditions for the formation of agronomically valuable fractions are characteristic of the forest chernozem of the northern exposure. As a result of comparing the characteristics of eluvial and illuvial horizons, it was found that the change of eluvial process to illuvial is accompanied by a sharp decrease in forest chernozems content of agronomically valuable fractions during dry sieving, as well as an increase in water resistance. In meadow-forest soils, this transition is characterized by a sharp decrease in the content of agronomically valuable fractions in the illuvial horizon during wet sieving compared to the eluvial horizon.

A comparative analysis of bedform fields along the submarine flanks of insular volcanoes, characterized by different morpho-structural settings, volcanic and meteo-marine regimes (Vanuatu, Kermadec, Bismark, Madeira and Aeolian archipelagos), is presented here to provide insights on the size distribution, morpho-dynamic and genesis of such bedforms. Two main types of bedforms are recognized according to their size, location and preconditioning/triggering processes. Small-scale bedforms have wavelengths of tens to hundreds of metres and wave heights of metres. Because of their small-size, they are typically not recognizable at water depths greater than 400 m from vessel-mounted bathymetric surveys. Few examples of small-scale bedforms are reported from upper volcanic flanks, where steep gradients commonly hinder their formation. Their recognition is mostly limited to the thalweg of shallow and flat-bottomed channels that carve the insular shelf on slope gradients

Riparian areas provide many ecosystems services to humans that have been utilized for thousands of years and are the main reason why these areas are degraded. Their importance for maintaining biodiversity and stream channel health is even more important in semi-arid and arid region, such as the south-western United States. A common practice to protect riparian areas and streams in the region is the exclusion of human activities with a prime example the Gila Box Riparian National Conservation Area. In this study, we examine if the exclusion of human activities has benefited the Bonita Creek that flows through this conservation area. Cross sections at five locations along Bonita Creek were taken in 1994 and 2013. Based on the comparison of the thalweg depth, the width-depth ratio, the channel erosion/deposition and the floodplain erosion/deposition the stream channel of the two surveys, Bonita Creek appears, in general, to be benefiting from the current exclusion of human activities. Still recovery rates are not very fast indicating landscape and ecosystem-based approaches should be adopted for more effective and sustainable conservation of the area.

Drifting post yolk-sac (PYS) lake sturgeon Acipenser fulvescens larvae were believed to seek refuge in substrate during daytime although there were no data to support this theory. There is growing scientific literature on important habitat, such as for adults and where eggs are spawned and hatch, however a gap remains in understanding duration of drift for PYS larvae, especially during daytime. This study was undertaken to find drifting PYS lake sturgeon larvae during the day in the Sturgeon River, Michigan, a clear yet tannin-rich river with a well-studied self-sustaining population. River substrates were mapped, and light, velocity, and depth data gathered to describe ‘believed’ refuge for larvae during daylight. From 2013 through 2016 nighttime drift samples (n = 463) for PYS lake sturgeon larvae were complemented with 143 daytime kick net samples and 43 daytime drift sets. No drifting larvae were collected in the daytime kick nets covering a variety of substrate types while over 1,600 PYS larvae were captured in drift nets at night, and 34 were captured in daytime drift sets. These 34 PYS larvae were in the previously unsampled thalweg in ~5% of surface light and at velocities of 0.24 to 0.57 m/s. Data suggest that drifting PYS lake sturgeon larvae do not stop and seek refuge during daylight but rather drift quickly and continuously downstream until suitable habitat is encountered. Measures of light, depth, velocity and thalweg presence combined with LiDar and Sonar mapping will be critical to understanding river suitability and restoration success for this species.

The aim of this study is to investigate the flood management and mitigation measures in ungauged NATURA protected watersheds. The examined watersheds are located in one the most European significant NATURA areas (Prespa Natural Park North Greece). SCS-CN model was applied to perform the hydrological modeling for extreme rainfalls of 50, 100 and 1000 return periods. Extensive field research was conducted to record all the hydrotechnical works of the study area, to evaluate their current condition and measure the respective hydraulic characteristics. The results of the hydrological modeling showed that the flood danger in the study area is generally low. However, almost the half of the hydrotechnical works could not discharge the high and medium probability (50 and 100 years) peak flows. The main causes are the extremely dense riparian vegetation that has been developed on the banks and the thalweg of the riverbeds and in some cases the inappropriate dimensioning of the technical works. The intense development of the riparian vegetation, has increased the roughness coefficient and reduced the dimensions and discharge capability of the technical works, while NATURA restrictions and regulations may be limiting any logging and trimming activities within the streams, especially in priority habitat types. Special Ecological Evaluation studies and educating the public about the necessity of the flood control measures and impact, could provide a framework for a thorough discussion about the flood management in NATURA areas.

This study aims to describe how the construction process of a reservoir dam affects and changes in river morphology such as cross-section changes and total sediment movement in different annual and seasonal scales. Cross-sectional and profile changes, and spatial distribution of differences (degradation and aggradation areas) between topographic measurements and bend variations are also discussed. For this purpose, a field measurement campaign was carried out on Buyukkumla stream, where Buyukkumla dam is built, from the spillway of the dam to the Marmara Sea. Topographic measurements were taken every six months from the beginning of the dam’s construction until the body is completed. Precise measurements were made across the entire stream, including the thalweg of the mainstream bed, up to 25 m on the right and left bank at 20-m intervals, and at the intermediate points where the required cross-sectional changes were found. The aggradation and degradation volumes were determined as much as the number of cross-sections available for each region at different time periods. Besides, the reasons for these aggradations and degradation were investigated considering the construction activities and meteorological conditions. Finally, our results show that there is a correlation between dam construction activities and downstream geomorphology changes. It is also observed that excavation activities in dam construction have a significant impact and regulate downstream and the changes in annual and semi-annual periods differ.

Seismic reflection data were used to investigate the multiple stages of headward erosion, incision, and sedimentation on the initiation and evolution of the Central Canyon, a Late Miocene-Pliocene continental slope-parallel canyon on the northwestern margin of the South China Sea. Secondary channels of the early stage generally display deep, V-shaped cross-sectional morphologies, indicating that vertical erosion was dominant in the early stage of canyon formation, while later-phase secondary channels have shallow, U-shaped cross sections, indicating that sedimentation dominated in the late stage. Influenced by gradual sea-level rise, headward erosion shifted the Central Canyon head from the Qiongdongnan Basin to the southeastern margin of the Yinggehai Basin. The length of headward erosion is up to 140 km, equivalent to one-fourth of the total length of the Central Canyon (525 km). The thalweg depth, height, and width of the Central Canyon increases down canyon from 2723 m, 164 m, and 2 km to 5318 m, 1023 m, and 16 km, respectively. This increase is gradual on gently-sloping palaeoseafloor, and more abrupt on steep-gradient palaeoseafloor. Canyon segments on gently-sloping palaeoseafloor are also characterised by a good correlation between canyon height and width. The sediments fill in the Central Canyon differ across the canyon’s segments. Turbidites and debrites infill the upstream segment of the Central Canyon. Turbidites and Mass-transport deposits are widespread in the middle reaches of the Central Canyon. The typical feature of the Central Canyon’s downstream segment is under-compensation, and canyon wall collapse are common in the upper fill of the downstream segment. We reconstruct the multistage evolution of the Central Canyon as comprising primary erosion, burial, renewed erosion, infilling, and abandonment stages. This multistage evolution was mainly controlled by relative sea-level fluctuations of the Qiongdongnan Basin.

Deposits in dam areas of large reservoirs, which are commonly composed of fine-grained sediment, are important for reservoir operation. Since the impoundment of the Three Gorges Reservoir (TGR), the sedimentation pattern in the dam area has been unexpected. An integrated dynamic model for fine-grained sediment, which consists of both sediment transport with water flow and gravity-driven fluid mud at the bottom, was proposed. The incipient motion driven by gravity in the form of fluid mud was determined by the critical slope. Shallow flow equations were simplified to simulate the gravity-driven mass transport. The gravity-driven flow model was combined with a 3D Reynolds-averaged water flow and sediment transport model. Solution routines were developed for both models, which were then used to simulate the integral movement of the fine-grained sediment. The simulated sedimentation pattern agreed well with observations in the dam area of the TGR. Most of the deposits were found at the bottom of the main channel, whereas only a few deposits remained on the bank slopes. Due to the gravity-driven flow of fluid mud, the deposits that gathered in the deep channel formed a nearly horizontal surface. By considering the gravity-driven flow, the averaged error of deposition thickness along the thalweg decreased from −13.9 to 2.2 m. This study improved our understanding of the mechanisms of fine-grained sediment transport in large reservoirs and can be used to optimize dam operations.

Hydrochemical and geophysical data collected during a hydrological survey in September 2017, reveal patterns of small-scale hydrological connectivity in a small water track catchment in the north-European Arctic. The stable isotopic composition of water in different compartments was used as a tracer of hydrological processes and connectivity at the water track catchment scale. Elevated tundra patches underlain by sandy loams were disconnected from the stream and stored precipitation water from previous months in saturated soil horizons with low hydraulic conductivity. At the catchment surface and in the water track thalweg, some circular hollows, from 0.2 to 0.4 m in diameter, acted as evaporative basins with low deuterium excess (d-excess) values, from 2‰ to 4‰. Observed evaporative loss suggests that these hollows were disconnected from the surface and shallow subsurface runoff. Other hollows were connected to shallow subsurface runoff, yielding d-excess values between 12‰ and 14‰, close to summer precipitation. ‘Connected’ hollows yielded a 50% higher dissolved organic carbon (DOC) content, 17.5 ± 5.3 mg/L, than the ‘disconnected’ hollows, 11.8 ± 1.7 mg/L. Permafrost distribution across the landscape is continuous but highly variable. Open taliks exist under fens and hummocky depressions, as revealed by electric resistivity tomography surveys. Isotopic evidence supports upward subpermafrost groundwater migration through open taliks under water tracks and fens/bogs/depressions and its supply to streams via shallow subsurface compartment. Temporal variability of isotopic composition and DOC in water track and a major river system, the Vorkuta River, evidence the widespread occurrence of the described processes in the large river basin. Water tracks effectively drain the tundra terrain and maintain xeric vegetation over the elevated intertrack tundra patches.

Concern has been expressed regarding the impacts of climate change on river ice and ice jam formation in cold regions. Ice jams are easily initiated in bends and narrow channels and cause disasters. In this study, observations and remote sensing monitoring are used to study the freeze-up ice jam formation of bends. Sediment transport and freezing process of the river interact, influencing bed changes profile and sedimentary budget. River ice processes, channel evolution, ice hydro-thermodynamics, and ice jam accumulation are explored. The results show that the channel topography determines the river thalweg, and that the channel elevation interacts with the river ice through sediment transport. The channel shrinkage increases the probability of ice jam, and the sharp bend is prone to ice jam formation. Under the effect of secondary circulation flow in the bend and in the outer bank, the juxtaposed freeze-up and the hummocky ice cover occur in the same location, and frazil ice accumulates under the junction of the main channel and the shoals. Affected by the increase of the hydraulic slope and the velocity downstream, open water reaches develops downstream of the ice accumulation. An open water section is emerged upstream of the bend, due to the ice deposition, and partly cut-off supply of the frazil.

The progressive and sequential shifting of the banklines and centerlines (thalweg) due to bank erosion and channel bar formation, as well as channel planform changes and avulsion of the Dwarkeswar river of West Bengal during the last 100 years, have been studied. For this purpose, police station maps, Survey of India topographical maps, and satellite images were used along with extensive field surveys. The channel was divided into reaches and segments for measuring the amount of migration and quantifying planform indices. Four types of changes have been observed: (1) channel planform change due to meander development and migration, (2) avulsion and consequent alteration in the flow direction, (3) thalweg shifting as a consequence of mid-channel bar formation, and (4) widening of the channel due to bank erosion. The study reveals that the alluvial plain upper (APU) is the most dynamic reach due to the meandering nature of the river. The thalweg shifted up to 1.71 km in this reach. An avulsion occurred in the lower course of the river during a large flood in 1978. The Jhumjhumi Nala became the main course of the river, and the earlier channel had become completely abandoned due to this avulsion. The sinuosity index of the entire study reach has been increasing since 1920, whereas the braiding index has decreased at most of the segments. Therefore, the channel planform is transforming into the meandering pattern from the braided pattern.

Channel junctions and lateral intakes are always caused turbulence in the passing flow. In this research, an experimental study was carried out to explore a possible method for sediment control for a series of skimming walls and a single spur dike, simultaneously. In order to direct the flow into the diversion channel and increase the skimming wall function, a single spur dike was utilized at the opposite side of the intake channel. The flow patterns for three conditions, including (1) without structures, (2) with skimming wall and (3) skimming wall and spur dike, are considered. The results showed that the use of skimming wall and a combination of skimming wall and spur dike makes it possible to direct the thalweg toward the intake port. In addition, by using the skimming wall, a trench is made toward the intake, which in turn increases the impoundment efficiency by 81% in the skimming wall combined with spur dike and up to about 66% for using the skimming wall.