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With rising air temperature and precipitation, water and sediment fluxes in the Source Region of the Yangtze River (SRYR) have increased since 2000s. Nonetheless, the response of braided river morphology to climate‐driven water and sediment flux change is still unknown. Water bodies of 9 large braided rivers from 1990 to 2020 were extracted based on Google Earth Engine platform, and impacts of climate change on morphological indices and morphodynamic processes were quantified. A new segmentation method is presented to more precisely extract braided river water body when the branch width is less than an image pixel size. The warming and wetting trend led to vegetation cover increase. With the increase of water flux, the water area of each braided reach has increased in both flood and non‐flood season. The 3–5 years mean annual erosion and accretion intensity (newly proposed in this study) of the channel shows three different trends of increasing, weakening, and unchanged over time. These three trends can be classified into three patterns in response to climate‐change driven water and sediment flux change in the SRYR as follows: sediment increase constrained pattern (weakening or unchanged), sediment increase dominated pattern (increasing), and water increase dominated pattern (increasing or unchanged). In summary, the braided rivers in the SRYR showing consistent increasing of water area, general expansion of active channel, and increasing of erosion and accretion intensity for some of the rivers, with the climate‐driven increasing water and sediment flux. Key Points A new method of braided water body extraction improves accuracy of recognition The warming and wetting trend has led to the more durative inundation of braided rivers since 2000s and consistent expansion of the channel Mean annual channel erosion and accretion intensity differently responds to the increase of water and sediment flux in nine braided rivers

Braided rivers are a significant contributor to groundwater flow in braidplain aquifer (BPA) systems, yet the spatiotemporal variations in flow exchange remain poorly understood. This study presents an extensive active‐distributed temperature sensing data set collected over a 3‐year period from two 100‐m long fiber optic cables installed up to ∼5 m depth below a braided river channel in New Zealand to quantify specific discharge (i.e., parafluvial flow) within the BPA at high spatial resolution. Despite river flow fluctuating by two orders of magnitude, specific discharge within the BPA showed moderate variation, with values ranging from 3.5 to 5.9 m d−1 on HDD1 (20.4% variance relative to the median) and from 2.4 to 4.5 m d−1 on HDD2 (13.3% variance relative to the median) over the study period. Geomorphology influences hydraulic conductivity, thereby affecting the hydraulic gradient. Following a flood event, specific discharge increased beneath the river margins over time, with the largest increase corresponding with areas of greatest geomorphic change, and changes to the subsurface flow dynamics. Surveys conducted after the flood event, where river flow peaked at 225 m3 s−1 (compared to a median of 2.51 m3 s−1), showed a marked increase in specific discharge. These subsurface changes occurred gradually, with no obvious seasonal influence, compared to rapid geomorphic surface alterations. This translates to variable specific discharge within the BPA in both space and time caused by changing bedform and connectivity to preferential flowpaths. Geomorphic changes following a flood event had the largest impact on specific discharge. Key Points 28 active‐distributed temperature sensing surveys were conducted over a 3‐year period on two cables installed up to ∼5 m below a braided river River flow changed considerably, yet there was a negligible relationship between river flow and specific discharge estimates Following a flood event, significant geomorphological changes led to an increase in specific discharge beneath the river margins

Estimating morphological change in braided gravel bed rivers is important to determine the geometry of the active part of the braidplain, that is the width of the area where bed material is transported and the number of active branches during a certain time interval. Repeated surveys and photogrammetry have been used to measure morphological change with different spatial and temporal resolution but characterizing the geometry of braided rivers remains a problem. Increased satellite coverage and frequency of revisiting times motivated satellite‐based studies of river dynamics. Here we present a procedure to estimate morphological change in ephemeral, braided, gravel bed rivers from Differential Interferometry of Synthetic Aperture Radar (DInSAR) data conducted on Sentinel‐1 SAR images, that is information on areas where ground displacement larger than 5–6 cm occurred. We hypothesize that such displacement is representative of bedload transport and can be used to describe the morphologically active braidplain. The procedure is applied to the Trionto River in Southern Italy. Results indicate that the proposed approach has the potential to capture different channel dynamics related to lateral confinement and flood hydrographs. In agreement with field and laboratory observations reported in the literature, narrower morphological active width and fewer active branches are estimated where the valley is most confined. In response to a relatively frequent flood, active width remains independent of lateral confinement and one or two active branches are predicted. Conversely, a large, less frequent flood results in the reorganization of the channel network with comparatively larger active width and more active branches in the widest portion of the braidplain.

River channels shape landscapes through gradual migration and abrupt avulsion. Measuring the motion of braided rivers, which have multiple channel threads, is particularly challenging, limiting predictions for landscape evolution and fluvial architecture. To address this challenge, we extended the capabilities of image‐based particle image velocimetry (PIV)—a technique for tracking channel threads in images of the surface—by adapting it to analyze topographic change. We applied this method in a laboratory experiment where a straight channel set in non‐cohesive sediment evolved into a braided channel under constant water and sediment fluxes. Topography‐based PIV successfully tracked the motion of channel threads if displacements between observations were less than the channel‐thread width, consistent with earlier results from image‐based PIV. We filtered spurious migration vectors with magnitudes less than the elevation grid spacing, or with high uncertainties in magnitude and/or direction. During braided channel initiation, migration rates varied with the channel planform development, showing an increase as incipient meanders developed, a decrease during the transitional braiding phase, and consistently low values during the established braiding phase. In this experimental setup, migration rates varied quasi‐periodically along stream at the half scale of initial meander bends. Lateral migration with respect to the mean flow direction was much more pronounced than streamwise migration, accounting for approximately 80% of all detected motion. Results demonstrate that topography‐based PIV has the potential to advance predictions for bank erosion and landscape evolution in natural braided rivers as well as bar preservation and stratigraphic architecture in geological records. Plain Language Summary Rivers naturally move across the landscape through gradual migration and abrupt shifts, with direct consequences for riparian ecosystems, fluvial sedimentology, and riverside communities. Current knowledge of river mobility is especially limited for braided rivers, which are composed of multiple interwoven sub‐channels (called channel threads) that can move independently. To address this knowledge gap, we expanded techniques that track channel thread motion from photos by applying them to elevation data. We find that for a laboratory experiment where a braided river is initiated from a straight channel, migration rates first accelerate and then slow down. These rates fluctuate regularly along the river, particularly around incipient meander bends. Channel banks and bars tend to migrate laterally rather than downstream, although this tendency diminishes over time. Findings from this study can help better understand past environments from sedimentary rocks and assess erosion and flood risk from shifting rivers. Key Points Topography‐based particle image velocimetry effectively tracks the migration of braided channel threads in a laboratory experiment During the initiation of a braided channel, channel threads migrate quickly as incipient meanders form and slow down as braiding develops Similar to channel belt growth, migration rates vary quasi‐periodically along stream, at the half scale of initial meander bends

Global warming exacerbates the magnitude and peak of flood discharge in braided rivers on the Qinghai-Tibet Plateau (QTP). The interaction between inter-annually increasing peak discharge and local-topographical constrained braided riverbeds remains unclear. Thereby, hydrodynamic processes and sediment transport under various flood magnitudes were simulated in a partially confined braided reach which is a bending-shape channel forced by confining valley in the Source Region of the Yangtze River on the QTP. We elaborate the influence of flood magnitude on local morphological changes in the topographically confined braided channel. These findings may also inform management and ecological considerations in other high-elevation braided river systems. The main results are summarized as follows: (i) The outer bank experienced predominant erosion under the flood process, with submerged and highly migrated sandbars, while the inner bank exhibits the opposite characteristics. (ii) Inactive channels on the inner bank reactivated under higher peak discharges, increasing braiding density. (iii) Owing to the sinuous boundary, flow velocity at the outer part of the mainstream (near outer bank) is significantly higher than of the inner part, causing intense erosion and incision. This study is of great importance on uncovering the morphodynamic processes of partly confined braided rivers on the QTP.

This study systematically investigates the lithofacies, sedimentary microfacies, vertical evolution, and spatial distribution of the braided river delta–shallow lacustrine carbonate mixed sedimentary rocks of the Upper Ganchaigou Formation in the Huatugou Oilfield of the Qaidam Basin, China. This study integrates data from field outcrops, core observations, thin section petrography, laboratory analyses, and well-logging interpretations. Based on these datasets, the sedimentary characteristics are identified, and a comprehensive sedimentary model is constructed. The results reveal that the study area contains five clastic facies, three types of mixed sedimentary facies, and ten sedimentary microfacies. Two distinct modes of mixed sedimentation are recognized: component mixing and stratigraphic mixing. A full lacustrine transgression–regression cycle is formed by the two types of mixed sedimentation characteristics, which exhibit noticeable differences in vertical evolution. Component mixing, which occurs in a mixed environment of continuous clastic supply and carbonate precipitation during the transgression, is the primary characteristic of the VIII–X oil formation. The mixed strata that make up the VI–VII oil formation show rhythmic interbedding of carbonate and clastic rocks. During the lacustrine regression, it shows the alternating sedimentary environment regulated by frequent variations in lacustrine levels. The planar distribution is affected by both intensity of sediment from the west and the changes in lacustrine level. During the lacustrine transgression, it is dominated by littoral-shallow lacustrine mixed beach bar and mixed sedimentary delta. On the other hand, during the lacustrine regression, it is dominated by laterally amalgamated sand bodies in the braided-river delta front. Based on this, a mixed sedimentary evolution model controlled by the coupling of “source–lacustrine level” is established. It offers a guide for reconstructing the sedimentary environment in basins that are similar to it and reveals the evolution path of mixed sedimentation in the short-axis source area of arid saline lacustrine basins.

The present study aims to investigate the dynamics of channel bar morphology of river Raidak-II within the Himalayan foreland basin on multi-decadal timescales (1980–2020). Multi-temporal Landsat satellite images have been used for identifying and monitoring different types of channel bars and their morphological changes. Here, several indices (braiding index, total sinuosity and mode of bar development) are used to measure the braiding intensity. Additionally, fluvio-hydrological and field investigation methods have been adopted to assess the channel form and behaviour affecting the evolution of channel bars. Further, sediment grain size distribution has been analysed to understand the reach-scale variation of instream sediment characteristics. The results show that higher value of all the braiding indices in reach-1 indicates its high braiding intensity compared to other reaches of the river. Numerical investigation shows spatiotemporal dynamics of bar morphology (bar length, bar width, bar area and bar perimeter) of nine stable bars during the period 2000–2020. This study shows the reach-scale variation of different fluvio-hydraulic parameters, which are highly associated with the bar dynamics. Grain size analysis reveals that most of the materials are coarser in the upper and middle reach of the river. Consequently, coarser sediments are being deposited in high energy flow environment of upper and middle reach while finer sediments are deposited by low energy flow regime in the lower reach. However, morphological changes of different types of channel bars indicate their dynamic nature. These changes have occurred due to the collective effects of different factors, including variable discharge, frequent floods, physiographic control, active tectonics, huge sediment supply and channelisation in the study area. Research Highlights The present study shows higher value of braiding Index, total sinuosity and bar mode in reach-1 indicating its higher braiding intensity compared to another two reaches of the river. The study indicates spatiotemporal dynamics of bar length, bar width, bar area and bar perimeter during the period of 2000–2020. This scientific study exhibits reach scale variation of different fluvio-hydraulic parameters which are highly associated with the spatiotemporal dynamics of bar morphology. The scientific analysis revealed that different types of bars have been developed and modified in the study area due to different natural and anthropogenic factors during recent past time.

Sandy braided river deposits are widely preserved in ancient stratigraphic records and act as a significant type of hydrocarbon reservoir. Due to the frequent and rapid migration of channels within the riverbed, the sedimentary architecture is highly complex. In this paper, a flume experiment was conducted to reveal the detailed depositional process and establish a fine sedimentary architecture model for sandy braided rivers. The result showed that (1) Three types of braid channels, including the lateral migration channel, the confluence channel, and the deep incised channel, were recognized based on geometry, scale, distribution, and spatial patterns; they are interconnected, forming a complex channel network. (2) Braid channels were characterized by lateral migration, abandonment, filling, and chute cutoff. Lateral migration of channels shaped the braid bars and dominated the formation, growth, and reworking of braid bars. (3) Controlled by the fast and frequent variations of the braid channel network, braid bars were continuously formed, reworked, reshaped, and composited of multiple accretions with different types, orientations, scales, and preservation degrees. Symmetrical and asymmetrical braid bars presented significantly different composition patterns. (4) Dominated by the continuous reworking of braid channels, temporary deposits were limited preserved, braid channel deposits account for 54.3 percent of the eventually preserved braided river deposits, and four types of amalgamate patterns were recognized. Braid bars were cut and limited preserved, only accounting for 45.7 percent of the eventually preserved braided river deposits. (5) During the experiment, only 28 percent of near-surface temporary deposits were eventually preserved in fragmented forms with the final experimental braided river; the shape, spatial patterns, and most of the deposits observed during the depositional process were largely reworked and poorly preserved. (6) The scale of eventually preserved braid bars and braid channels is significantly smaller than the temporary deposits from geomorphic observations. The aspect ratio of the eventually preserved braid bars and the width-to-depth ratio of the eventually preserved braid channel are also significantly different from that of the temporary ones measured from topography data.

Insect flight along river corridors is a fundamental process that facilitates sustainable succession and diversity of aquatic and terrestrial insect communities in highly dynamic fluvial environments. This study examines variations in the thickness of the insect boundary layer (i.e., the pre-surface atmosphere layer in which air velocity does not exceed the sustained speed of flying insects) caused by interactions between diurnal winds and the heterogenous habitat mosaics in the floodplain of a braided river. Based on advective–diffusive theory, we develop and test a semi-empirical model that relates vertical flux of flying insects to vertical profiles of diurnal winds. Our model suggests that, in the logarithmic layer of wind, the density of insect fluxes decreases exponentially with the altitude due to the strong physical forcing. Inside the insect boundary layer, the insect fluxes can increase with the altitude while the winds speed remains nearly constant. We suggest a hypothesis that there is a close correspondence between the height of discontinuity points in the insect profiles (e.g. points with abrupt changes of the insect flux) and the displacement heights of the wind profiles (e.g. points above which the wind profile is logarithmic). Vertical profiles were sampled during three time-intervals at three different habitat locations in the river corridor: a bare gravel bar, a gravel bar with shrubs, and an island with trees and shrubs. Insects and wind speed were sampled and measured simultaneously over each location at 1.5-m intervals up to approximately 17 m elevation. The results support our working hypothesis on close correspondence between discontinuity and displacement points. The thickness of the insect boundary layer matches the height of the discontinuity points and was about 5 m above the bare gravel bar and the gravel bar with shrubs. Above the island, the structure of the insect boundary layer was more complex and consisted of two discontinuity points, one at the mean height of the trees’ crowns (ca. 15 m), and a second, internal boundary layer at the top of the shrubs (ca. 5 m). Our findings improve the understanding of how vegetation can influence longitudinal and lateral dispersal patterns of flying insects in river corridors and floodplain systems. It also highlights the importance of preserving terrestrial habitat diversity in river floodplains as an important driver of both biotic and abiotic (i.e., morphology and airscape) heterogeneity.

Strong aggradational tendencies during the late Pleni-Weichselian have been noted in river valleys in central Europe. Thick series of mineral deposits were laid down, but also organic or mineral-organic horizons were formed under favourable conditions. The study area is located in the central section of the valley of the River Warta within an extraglacial area of the last glaciation. At the Warenka site alluvia, that attain thicknesses of 16 m, were analysed. Lithofacies analysis, OSL dating of mineral sediments and radiocarbon dating of organic and mineral-organic strata were performed. Organic and mineral-organic deposits were also subjected to pollen and Cladocera analyses. Together this set of analyses was used to determine fluvial processes and environmental conditions during the late Pleni-Weichselian. The results obtained allow the conclusion that these levels were deposited in the sedimentary environment of a low-energy, sand-bed braided river, which operated in the period from approximately 30 to 24 cal kBP – the late Pleni-Weichselian. During this time, there were periods when shallow water bodies were formed on the valley bottom, where deposition of organic material was possible. The presence of this type of sediment made it possible to reconstruct the vegetation cover; this had the character of a steppe-tundra, periodically shrubby steppe-tundra. Short-lived reservoirs were characterised by shallow-water settings with weakly developed vegetation and temporary influence of floodwaters as indicated by changes in cladoceran assemblages. Pollen spectra, low concentration of cladocerans, as well as the presence of the cold-tolerant Cladocera taxa are indicative of cold climatic conditions.