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Understanding the relationship between a dam's size and its ecological effects is important for prioritization of river restoration efforts based on dam removal. Although much is known about the effects of large storage dams, this information may not be applicable to small dams, which represent the vast majority of dams being considered for removal. To better understand how dam effects vary with size, we conducted a multidisciplinary study of the downstream effect of dams on a range of ecological characteristics including geomorphology, water chemistry, periphyton, riparian vegetation, benthic macroinvertebrates, and fish. We related dam size variables to the downstream–upstream fractional difference in measured ecological characteristics for 16 dams in the mid‐Atlantic region ranging from 0.9 to 57 m high, with hydraulic residence times (HRTs) ranging from 30 min to 1.5 years. For a range of physical attributes, larger dams had larger effects. For example, the water surface width below dams was greater below large dams. By contrast, there was no effect of dam size on sediment grain size, though the fraction of fine‐grained bed material was lower below dams independently of dam size. Larger dams tended to reduce water quality more, with decreased downstream dissolved oxygen and increased temperature. Larger dams decreased inorganic nutrients (N, P, Si), but increased particulate nutrients (N, P) in downstream reaches. Aquatic organisms tended to have greater dissimilarity in species composition below larger dams (for fish and periphyton), lower taxonomic diversity (for macroinvertebrates), and greater pollution tolerance (for periphyton and macroinvertebrates). Plants responded differently below large and small dams, with fewer invasive species below large dams, but more below small dams. Overall, these results demonstrate that larger dams have much greater impact on the ecosystem components we measured, and hence their removal has the greatest potential for restoring river ecosystems. [ABSTRACT FROM AUTHOR]

As a prerequisite and foundation for studying the evolution mechanism of river channels, an in-depth understanding of the cross-sectional morphology adjustment is required. As a starting point, it is crucial to systematically summarize and generalize the research findings on channel morphological adjustment obtained to date, particularly in the context of the significant changes in the water and sediment conditions of large rivers that have occurred worldwide. This paper provides a comprehensive review of the research findings on the three following aspects of the Lower Yellow River: the transverse distribution of overbank flow velocity, the transverse distribution of suspended sediment concentration, and the morphological adjustment of the river cross-section. There are various equations available to predict the lateral depth–average flow velocity distribution. These equations are classified into the two following categories: empirical and theoretical formulas. Theoretical formulas are obtained through consideration of the cross-sectional morphology, accounting for inertial force terms caused by secondary flow, and momentum transfer between the main channel and its floodplain. Similarly, empirical equations and theoretical formulas for sediment concentration transverse distribution are also summarized, given the different influencing factors and assumptions. We also discuss the morphological adjustment of river cross-sections based on the analysis of measured data, mathematical model calculation, and the physical model test. In particular, we propose the idea of revealing channel cross-section morphology evolution mechanisms from the theoretical level of water and sediment movement and distribution. This review aims to enhance understanding of overbank flow, sediment transport, and channel morphology in the Lower Yellow River and may also serve to some extent as a reference for the evolution and management of channels in other rivers. [ABSTRACT FROM AUTHOR]

Accurate and precise measures of channel morphology are important when monitoring a stream post-restoration to determine changes in stability, water quality, and aquatic habitat availability. Practitioners often rely on traditional surveying methods such as a total station for measuring channel metrics (e.g., cross-sectional area, width, depth, and slope). However, these methods have limitations in terms of coarse sampling densities and time-intensive field efforts. Drone-based lidar or drone laser scanning (DLS) provides much higher resolution point clouds and has the potential to improve post-restoration monitoring efforts. For this study, a 1.3-km reach of Stroubles Creek (Blacksburg, VA, USA), which underwent a restoration in 2010, was surveyed twice with a total station (2010 and 2021) and twice with DLS (2017 and 2021). The initial restoration was divided into three treatment reaches: T1 (livestock exclusion), T2 (livestock exclusion and bank treatment), and T3 (livestock exclusion, bank treatment, and inset floodplain). Cross-sectional channel morphology metrics were extracted from the 2021 DLS scan and compared to metrics calculated from the 2021 total station survey. DLS produced 6.5 times the number of cross sections over the study reach and 8.8 times the number of points per cross section compared to the total station. There was good agreement between the metrics derived from both surveying methods, such as channel width (R2 = 0.672) and cross-sectional area (R2 = 0.597). As a proof of concept to demonstrate the advantage of DLS over traditional surveying, 0.1 m digital terrain models (DTMs) were generated from the DLS data. Based on the drone lidar data, from 2017 to 2021, treatment reach T3 showed the most stability, in terms of the least change and variability in cross-sectional metrics as well as the least erosion area and volume per length of reach. [ABSTRACT FROM AUTHOR]

Releasing experimental floods as part of environmental flow programs aims to restore river beds by moving and restoring sediments to improve hydromorphological conditions of the river. However, it remains a challenge to understand how flood release characteristics affect channel morphology, sediment transport, and hydrodynamics. In this study, field surveys and a 2D hydro‐morphodynamic and sediment transport numerical model were used to determine how differences in flood magnitude and falling limb alter hydrogeomorphic conditions within a 4 km reach of the lower Spöl River. The model was constrained by drone flight‐derived high‐resolution digital elevation models and two field‐measured flood releases. The highest flood magnitude of 40 m3/s resulted in 2,700 m3 of total sediment transport, 2,000 m3 of net total volumetric change and 16 900 m2 more wetted area after the flood. The same flood, simulated with an increase in falling limb slope, resulted in a decrease in the duration of full sediment mobility and a corresponding reduction of 8% in net total volumetric change and 5.3% in the total wetted area. Contrastingly, the lowest flood magnitude of 25 m3/s produced 130% lower total sediment transport, 105% lower net total volumetric changes and 10% less wetted area after the flood. Overall, we show that hydro‐morphodynamic modelling of river erosion and deposition combined with spatially rich topographic datasets are extremely useful in forming designed environmental flood scenarios to optimise sediment transport and thus hydrogeomorphic changes to set environmental flows. We contend that scenario modelling is necessary to help water managers optimise the amount of water allocated to environmental flows and to simultaneously restore and maintain riverine dynamics in heavily modified rivers. [ABSTRACT FROM AUTHOR]

Lightning channel morphology depends on the thunderstorm cloud charge structure, which in turn is influenced by the thunderstorm dynamics. In this paper, based on three‐dimensional radiation source localization data from the Lightning Mapping Array and radar‐based data, our analysis shows that the overall morphology and detailed morphology of the lightning channel correspond to different eddy dissipation rate (EDR) characteristics. Lightning with complex channel morphology occurs in regions with large EDRs. In single lightning events, channels that extend directly within a certain height range without significant bifurcation and turning tend to propagate in the direction of decreasing EDRs, while channel bifurcations and turns usually occur in regions with large radial velocity gradients and large EDRs. This study shows the relationship between channel morphology and thunderstorm dynamics and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics. Plain Language Summary: Turbulence in thunderstorms affects the charge distribution, which in turn affects the lightning channel morphology. Thus, the lightning channel morphology can reflect the characteristics of turbulence. The current understanding of the correlation between the two is still limited to the relationship between macroscopic thunderstorm dynamic characteristics and lightning activity. In this paper, the relationship between the morphology of the lightning channel and turbulence characteristics is investigated based on the Lightning Mapping Array (LMA) localization data and the cube root of the eddy dissipation rate (EDR) estimated from KABX radar‐based data. The turbulence strength affects the overall morphology of lightning, and lightning with complex morphology tends to occur in regions with large EDRs. In single lightning events, channels extending directly within a certain altitude range tend to propagate in the direction of decreasing EDRs, and lightning channel bifurcation or turning tends to occur in regions with large EDRs. This paper establishes the relationship between thunderstorm electricity and thunderstorm dynamics by using lightning channel morphology as a bridge and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics. Key Points: The morphology of lightning channels can reflect the distribution of turbulence intensity, and a certain correlation between the two existDirectly extended lightning channels tend to propagate in the direction of decreasing eddy dissipation ratesThe location of the channel bifurcations or turns often corresponds to regions with high eddy dissipation rates [ABSTRACT FROM AUTHOR]

While large dams provide society with many benefits, there are many environmental trade‐offs. One trade‐off of dam installation is the morphologic changes that ensue in the downstream channel. Channel widening due to streambank erosion is a common response to flow regulation (FR), but dominant erosion processes and rates have rarely been evaluated downstream of dams. This case study investigates how a 75‐year‐old flood control dam has affected downstream bank erosion on the Lower Smoky Hill River, located in central Kansas, USA. A one‐dimensional hydraulic, sediment transport, and bank erosion model was used to assess changes in erosion processes and rates with and without FR up to 86 river km downstream of the dam. The model showed that toe erosion was the dominant bank erosion process for both with and without FR scenarios. While toe erosion rates were significantly higher (α < 0.05) under the without FR scenario, more days of toe erosion occurred under the with FR scenario. More days of toe erosion are attributed to the change in the flow regime, with moderate flows (between 5% and 40% daily exceedance probability) increasing and hydrograph rise and fall rates decreasing since dam installation. Furthermore, it was observed that pioneer riparian vegetation may drown out during long duration, high‐flow events brought on by FR, amplifying erosion rates. These results provide broader insight into morphological responses to flood control dams, highlighting the effect changes in flow regime can have on downstream channel morphology and identifying major challenges in managing streambank erosion downstream of dams. [ABSTRACT FROM AUTHOR]

River processes and patterns are affected by changes in the watershed driven by natural and human‐induced causes. A sudden pattern alteration from a "white river" (bare soils) to a "green river" (vegetated) influences riverine biodiversity and can increase flood risk. Despite these significant impacts, knowledge on the triggers that kickstart feedback exacerbating changes in bio‐geomorphic patterns is insufficient. In this study, we collected and analyzed detailed monitoring data on a sandy, hydro‐morphologically active, and monsoon‐driven river in Korea. The surface area covered by vegetation has been increasing; this increase intensified after the 2014–2015 drought, which provided a window of opportunity for vegetation establishment. During the drought, pioneer vegetation densely colonized bare sandbars and temporarily exposed riverbed. Despite partial rejuvenation by several subsequent floods, succession to woody vegetation occurred, resulting in a stable vegetation cover. Narrowing and incision of a low‐water channel occurred, and secondary channels formed inside the floodplain. The results of this study show a rapid bio‐geomorphic alteration triggered by the shifts in flow regime in a river primed by human‐induced changes. Furthermore, modified monsoon‐driven rivers might be on the brink of similar bio‐physical alterations triggered through shifting flow regime following climate change, leading to increased flood risk and impacts on endemic biodiversity. [ABSTRACT FROM AUTHOR]

Abstract Lightning channel morphology depends on the thunderstorm cloud charge structure, which in turn is influenced by the thunderstorm dynamics. In this paper, based on three‐dimensional radiation source localization data from the Lightning Mapping Array and radar‐based data, our analysis shows that the overall morphology and detailed morphology of the lightning channel correspond to different eddy dissipation rate (EDR) characteristics. Lightning with complex channel morphology occurs in regions with large EDRs. In single lightning events, channels that extend directly within a certain height range without significant bifurcation and turning tend to propagate in the direction of decreasing EDRs, while channel bifurcations and turns usually occur in regions with large radial velocity gradients and large EDRs. This study shows the relationship between channel morphology and thunderstorm dynamics and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics.

As a prerequisite and foundation for studying the evolution mechanism of river channels, an in-depth understanding of the cross-sectional morphology adjustment is required. As a starting point, it is crucial to systematically summarize and generalize the research findings on channel morphological adjustment obtained to date, particularly in the context of the significant changes in the water and sediment conditions of large rivers that have occurred worldwide. This paper provides a comprehensive review of the research findings on the three following aspects of the Lower Yellow River: the transverse distribution of overbank flow velocity, the transverse distribution of suspended sediment concentration, and the morphological adjustment of the river cross-section. There are various equations available to predict the lateral depth–average flow velocity distribution. These equations are classified into the two following categories: empirical and theoretical formulas. Theoretical formulas are obtained through consideration of the cross-sectional morphology, accounting for inertial force terms caused by secondary flow, and momentum transfer between the main channel and its floodplain. Similarly, empirical equations and theoretical formulas for sediment concentration transverse distribution are also summarized, given the different influencing factors and assumptions. We also discuss the morphological adjustment of river cross-sections based on the analysis of measured data, mathematical model calculation, and the physical model test. In particular, we propose the idea of revealing channel cross-section morphology evolution mechanisms from the theoretical level of water and sediment movement and distribution. This review aims to enhance understanding of overbank flow, sediment transport, and channel morphology in the Lower Yellow River and may also serve to some extent as a reference for the evolution and management of channels in other rivers.

Accurate and precise measures of channel morphology are important when monitoring a stream post-restoration to determine changes in stability, water quality, and aquatic habitat availability. Practitioners often rely on traditional surveying methods such as a total station for measuring channel metrics (e.g., cross-sectional area, width, depth, and slope). However, these methods have limitations in terms of coarse sampling densities and time-intensive field efforts. Drone-based lidar or drone laser scanning (DLS) provides much higher resolution point clouds and has the potential to improve post-restoration monitoring efforts. For this study, a 1.3-km reach of Stroubles Creek (Blacksburg, VA, USA), which underwent a restoration in 2010, was surveyed twice with a total station (2010 and 2021) and twice with DLS (2017 and 2021). The initial restoration was divided into three treatment reaches: T1 (livestock exclusion), T2 (livestock exclusion and bank treatment), and T3 (livestock exclusion, bank treatment, and inset floodplain). Cross-sectional channel morphology metrics were extracted from the 2021 DLS scan and compared to metrics calculated from the 2021 total station survey. DLS produced 6.5 times the number of cross sections over the study reach and 8.8 times the number of points per cross section compared to the total station. There was good agreement between the metrics derived from both surveying methods, such as channel width (R2 = 0.672) and cross-sectional area (R2 = 0.597). As a proof of concept to demonstrate the advantage of DLS over traditional surveying, 0.1 m digital terrain models (DTMs) were generated from the DLS data. Based on the drone lidar data, from 2017 to 2021, treatment reach T3 showed the most stability, in terms of the least change and variability in cross-sectional metrics as well as the least erosion area and volume per length of reach.

In-channel storage of both fine sediment and sediment-bound phosphorus has been recognized as potentially large contributors to respective watershed loads, yet they are rarely quantified in the field. In this field-based study, we quantified and characterized in-channel fine sediment and total phosphorus (TP) storage within a third-order stream. We hypothesized storage to be significant within the context of watershed-scale sediment and TP loads and that storage trends are influenced by channel characteristics and hydraulics. In May 2015, the volume of stored in-channel sediment was estimated within a 13.5 km stretch of Walnut Creek, an alluvial stream draining an agriculturally dominated watershed in Jasper County, Iowa, USA. Storage volume was estimated in-field through a series of 240 transects which were stratified across reaches of the varying channel and hydraulic conditions (e.g., sinuosity, stream power). Overall storage volume was broken down into feature classes (e.g., point bars) based on in-channel depositional processes. Following in-field quantification, feature class sediment samples were collected and analyzed for physical properties (e.g., bulk density) and TP concentration. Physical and chemical analyses, coupled with in-field volume estimation, allowed for watershed-scale masses of in-channel sediment and TP to be calculated and then placed within the context of respective annual loads. Sediment and TP were estimated to be stored at ~2.7 Mg m-1 and 0.7 kg m-1, respectively. Sinuous reaches exhibited significantly greater sediment storage volume (p < 0.001) and depth (p < 0.001) versus straight reaches. Reach sinuosity exhibited a significant positive correlation (p = 0.03) with storage mass and represented the most effective storage predictor. The majority of storage mass (72%) was represented by colluvial material accumulations at the streambank toe. Loose bed sediment was the second greatest contributor to storage mass (18%), with the remaining feature classes (e.g., bars) representing a combined ~10%. Sediment storage mass was ~3.25 times greater than the watershed suspended sediment load for 2015. The TP mass was found to be nearly equal to the respective watershed load for 2015. In-channel sediment and TP storage masses within Walnut Creek were found to be significant in comparison to respective annual loads, and thus storage is expected to play a significant role in respective watershed routing, loading, and the overall budgets of these parameters. Though challenging, quantification of in-channel fine sediment and TP storage is necessary to relate source contributions (e.g., streambank erosion) to watershed loads and is critical to account for interannual sediment and TP export. [ABSTRACT FROM AUTHOR]

Our research introduces the river regulation effects on three sections of the upper and middle Odra River (south-western Poland), with differently channelized parts. In the upper and lower reaches, the river was straightened, narrowed, and trained with groins, whereas in the middle section, it was also impounded by numerous barrages. The discharge duration (DD) and water stage duration (WSD) curves for water-gauge stations from these river sections were analyzed to recognize changes in river flows and channel morphology since the mid-20th century. This analysis is supplemented by an examination of repeated surveys of the gauge cross sections of the river, annual precipitation totals in its catchment, and their relationship to the variation of the North Atlantic Oscillation (NAO) index. Our findings provide new hydrological insights for the region. The three river sections exhibited different patterns of the adjustment of the channel morphology to the river channelization: upper section was typified by channel incision, middle section by channel stability, and lower section by channel incision in its upper part and vertical stability of the channel bed in the lower part. Barrages in the middle section stabilized water stages in a wide range of hydrological conditions. Annual precipitation totals and river run-off did not change systematically over the study period. The variation in precipitation totals was inversely related to annual values of the NAO index. The study confirms the usefulness of DD/WSD curves to analyze changes in river run-off and the vertical position of the channel bed. [ABSTRACT FROM AUTHOR]

The June 2013 disaster in Kedarnath hit the Mandakini–Alaknanda river valley, resulting in devastating floods. This study deals with the pre- and post-flood event changes in the channel morphology and aims to investigate the geomorphological processes under river management in the Alaknanda valley, NW Himalaya and how the hydroelectric reservoir may have impeded the natural impact of the disaster and created geomorphic discontinuity. This work analyses the spatio-temporal variations in channel morphology over the last decade 2010–2020, discussing the impact of 2013 extreme event; the role of gradient in morphological patterns in river basin system. It highlights how the channel parameters like the thalweg shifts, active channel width, and area under sedimentation responded, from headwaters to lower gradient Lesser Himalayan zones to the 2013 event and suggests that any positive changes in these parameters diminish soon after the reservoir. The study implies that the capability of the reservoir to adjust the sediment load of the event in its upstream is an immediate short-term effect, but brings out the fact that it creates a geomorphic disconnect in the channel between upstream and downstream channel reaches of the reservoir. This disconnect may have a negative impact on sediment storage and sediment–water routing of the river and should be factored into the dam design ensuring natural continuum of geomorphic processes. Further, the study argues that the terrain north of the Main Central Thrust (Higher Himalaya) should be kept free from major human interventions to reduce flood hazards. [ABSTRACT FROM AUTHOR]

The Trinity River in northern California was adjusting to unregulated flood and mining impacts when it was dammed and flow regulation began in 1960. We examine the subsequent evolution of the river's alluvial channel through 60 years of increases in regulated mainstem flow regimes in an unconfined and confined valley where Rush and Indian creeks respectively join the river 6.9 and 26.7 river kilometres from Lewiston Dam. The resulting capacity of the tributary junctions for rearing Chinook salmon fry in the current flow regime is evaluated with an empirical model developed for the Trinity River. Results indicate that morphologic changes at Indian Creek were relatively minor after damming because mainstem flows were restricted to a narrow channel in comparison to the channel at Rush Creek. Conversely, active channel and bar areas significantly declined at Rush Creek because the mainstem sediment supply was more severely reduced by flow regulation that enabled riparian vegetation to colonize the expansive alluvial surfaces that were present. These changes reduced instream habitat, suggesting salmon populations in large valleys may be at higher risk below dams than in smaller valleys where the reduced flow is confined to an already narrow channel. However, the relatively wide and unconfined valley responded more positively to increases in flow and sediment through the regulatory periods to yield significantly higher capacities for rearing Chinook fry. Therefore, while unconfined reaches may be particularly susceptible to change when a river is dammed, they may also provide the greatest opportunity for restoration of salmon populations. [ABSTRACT FROM AUTHOR]

The present study aims to study the morphological changes resulting from the extraction of sediment from the Mahananda riverbed, located on Himalaya foothill, very close to the Siliguri town, West Bengal, India. Temporal morphological changes in Mahananda River have been detected from satellite images and topographical sheets. Sediment sampling of some quarrying sites has been done through field investigation. Sediment sampling of some quarrying sites has been done through field investigation. The average bank full depth difference in different sediment quarrying section ranges between 0.1 m and -2.1 m and width-depth ratio varies from -0.22 to -66.56 in pre-monsoon and post-monsoon period. The correlation between the amount of sediment quarried and the width of the quarried area suggests that when the amount of bed material quarried increases, the width of the river also increases. Similarly, a correlation between width and depth also indicates that human activities have altered the natural process of the river. [ABSTRACT FROM AUTHOR]

The Three Outlets Channel (TOC) consisting of three anabranching rivers formed due to natural avulsion by extremely high floods, is the primary water–sediment channel connecting the Jingjiang in the middle Yangtze River and Dongting Lake (the second largest freshwater lake in China). Since the impoundment of the Three Gorges Reservoir (TGR) in 2003, the decreasing diversion of runoff and sediment load of the TOC has an impact on the hydrological connectivity of the river–lake relation. Nonetheless, it lacks complete understanding on the diversion of runoff and sediment load, erosion and deposition amount, and the calculation method of diversion runoff in the TOC. We used remote sensing images, hydrological data, and channel topography to analyze the change in runoff and sediment load, channel morphology, local erosion and deposition amounts. The main results show that: (i) Meander cutoffs of the Lower Jingjiang accelerated the reduction process of the Ouchi River's runoff and sediment load and the increase in the number of dry days. After the impoundment of the TGR, the diversion of sediment load of the TOC was greatly affected, but the decreasing trend of the runoff diversion slowed down. (ii) The morphological change of the inlet zone of Ouchi River is larger than that of Songzi River and Hudu River. The morphological evolution of the inlet area led to the change in the diversion of runoff and sediment load of the TOC. (iii) In the dry season, the water level drop in the inlet zone of the TOC leads to a decrease in the diversion discharge. Therefore, considering the water level drop and channel width adjustment in the inlet zone, five empirical formulae for the diversion discharge of the five hydrological stations in the TOC are proposed. These empirical formulae can be used as a short-term forecast for future changes in the hydrologic regime and the dynamics of the Jingjiang–Dongting Lake relation. [ABSTRACT FROM AUTHOR]

This paper presents a numerical model study on the ice cover effect on bank stability in non-cohesive alluvial channels. The model consists of a coupled two-dimensional finite element unsteady hydrodynamic model with bank erosion and mass failure processes for open water and ice-covered conditions. The associated morphological change is modeled with non-equilibrium sediment transport, including the side slope effect on bed load transport. The model adopts two sets of repose angles for emerged and submerged bank materials in analyzing non-cohesive bank mass collapses and redistributions. The model is validated with published laboratory experiments on bank retreat caused by dam-break flow and equilibrium cross-section evolution and showed improvements over existing numerical models. Simulated results showed that the ice cover caused larger bank retreats and bed depositions and slower channel cross-sectional change due to the reduced bed shear stress and the increased flow depth. Article Highlights: A bank stability model is developed by coupling the unsteady hydrodynamics, non-equilibrium sediment transport, and bank erosion and mass failure processes. The model is validated with published laboratory experiments and other models. The ice-covered flow causes larger riverbank retreats and slower cross-sectional changes than that of the open channel flow. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms controlling downstream water‐level variations after the operation of the Three Gorges Dam is important for riverine flood and drought management. However, our quantitative understanding of the multiple controls of river morphology, vegetation, and floodplain resistance on water levels in the Middle Yangtze River (MYR) remains limited. Here, we analyze changes in river channels and floodplain resistance in the MYR using 450 cross‐sectional profiles as well as data on discharge, water levels, sediment, and satellite images from 2003 to 2015. Results show an overall decline in low‐flow water‐levels (at a given small discharge) due to severe incisions of low‐flow channels caused by a sharp reduction of ∼90% in sediment loads from 1950–2002 to 2003–2020. In contrast, high‐flow water‐levels (at a given large discharge) display minor changes. Our analysis shows that the notably increased floodplain resistance due to vegetation growth is likely the dominant factor elevating flood water‐levels, followed by riverbed coarsening and greater fluctuations in the river longitudinal profiles. Our findings further the understanding of downstream geomorphic response to dam operation and their impacts on water levels and have important implications for riverine flood management in dammed river systems. Key Points: Hungry‐water‐driven channel erosion causes the sharp reduction in low‐flow water‐levelsFloodplain resistance increase dominates the minor change in high‐flow water‐levels, followed by riverbed coarsening and greater fluctuations in the river longitudinal profileFloodplain resistance increase mainly caused by vegetation expansion in floodplain and channel bars due to the reduced floodplain submerged frequency [ABSTRACT FROM AUTHOR]

Submarine channels are the most extensive sediment transport systems on Earth. They transport sediment over hundreds of kilometers and form sediment deposits in the deep-sea, which can act as hydrocarbon reservoirs. During the Late Miocene, a sinuous submarine channel with sediment processes was discovered in the Yinggehai Basin, northwestern South China Sea. However, process interpretations of the factors that influence the stacking patterns, distribution, and morphology of these sinuous channel deposits in this region are not well understood. Based on the interpretation of high-resolution 3D seismic data and exploration well data, and insights from flow dynamics, we analyzed the factors influencing channel morphology, the architecture of the channel, and its associated geomorphic evolution. The channel can be divided into three sections (Sections Ⅰ, Ⅱ, and Ⅲ) in terms of its planform, and into two seismic units (Unit 1 and Unit 2) in terms of its vertical structure. The sinuous submarine channel originated from a combination of inherent structural features from secondary faults and strong erosion from turbidity currents, which occurred due to a sharp decline in sea level during the Late Miocene. Changes in the channel's orientation led to erosion and channel-margin failures, causing an increase in channel width and a decrease in margin gradient. The distribution and stacking patterns of the deposits are greatly influenced by the provenance, sea level changes, and the morphology of the channel. In Sections Ⅰ and Ⅲ, a river-like secondary flow with a limited lateral density gradient leads to vertical deposits. In Section Ⅱ, changes in the channel's orientation altered its morphology and induced topographic forcing, producing a strong river-like secondary flow. This flow consistently caused sediment to accumulate on the inner bank and erode on the outer bank, leading to lateral stacking of deposits in Unit 2. During the filling of Unit 2, diapiric activity uplifted the strata, resulting in thinner deposition in Section Ⅲ, while deposition thickness increased in Section Ⅱ with sufficient provenance. Unit 1 of Section Ⅲ displays desirable properties for a hydrocarbon reservoir, including thick sandstone with good sorting and roundness. This study provides valuable insights into the diverse architectures of spatially and temporally linked submarine channels, and establishes a correlation between the evolutionary process of the channel and the stacking patterns of its constituent elements. • Five depositional elements and three stacking patterns of the channel are identified from a 3D seismic perspective. • The geomorphology of the channel is affected by faults, provenance, sea level changes, and diapir. • Channel morphology controls the evolutionary process of the channel and the stacking patterns of its constituent elements. [ABSTRACT FROM AUTHOR]

Geomorphic assessments are crucial to understanding stream processes, defining ecological stream conditions, and improving management and restoration recommendations. This project presents the first systematic geomorphic assessment of a perennial stream in Israel. The Morphological Quality Index (MQI) protocol was applied in 2017–2018 to test its applicability for Eastern-Mediterranean ecosystems, where heavily regulated streams are common, hydrologic variability is high, and no natural reference streams exist due to long-term anthropogenic pressures. Stream segments were analyzed according to the 25 defined MQI metrics and the protocol was customized for local conditions, characterized by a lack of woody species cover. Results showed that the upstream and downstream segments were in very poor and poor condition, respectively. However, most of the stream was in moderate to good condition, and two segments were rated in very good condition. Reduced functionality was found, especially in longitudinal connectivity of sediment and stream flow, with artificiality found in the most upstream and downstream segments. Riparian vegetation was highly degraded along the entire stream, lacking continuity and providing little functionality or ecological services. Bed substrate analyses indicated a lack of typical downstream fining. Previous flood-management efforts modified channel morphology, and ongoing agricultural pressures prevent lateral stream movement. In addition, water extraction in downstream segments and stream-regulation efforts have greatly reduced water flow and natural depositional processes. Combining all the considered elements, the MQI was found to be a highly suitable tool for evaluating Eastern-Mediterranean perennial streams, with modifications recommended based on local management needs.

In-channel storage of both fine sediment and sediment-bound phosphorus has been recognized as potentially large contributors to respective watershed loads, yet they are rarely quantified in the field. In this field-based study, we quantified and characterized in-channel fine sediment and total phosphorus (TP) storage within a third-order stream. We hypothesized storage to be significant within the context of watershed-scale sediment and TP loads and that storage trends are influenced by channel characteristics and hydraulics. In May 2015, the volume of stored in-channel sediment was estimated within a 13.5 km stretch of Walnut Creek, an alluvial stream draining an agriculturally dominated watershed in Jasper County, Iowa, USA. Storage volume was estimated in-field through a series of240 transects which were stratified across reaches of the varying channel and hydraulic conditions (e.g., sinuosity, stream power). Overall storage volume was broken down into feature classes (e.g., point bars) based on in-channel depositional processes. Following in-field quantification, feature class sediment samples were collected and analyzed for physical properties (e.g., bulk density) and TP concentration. Physical and chemical analyses, coupled with in-field volume estimation, allowed for watershed-scale masses of in-channel sediment and TP to be calculated and then placed within the context of respective annual loads. Sediment and TP were estimated to be stored at ~2.7 Mg m-1 and 0.7 kg m-1, respectively. Sinuous reaches exhibited significantly greater sediment storage volume (p < 0.001) and depth (p < 0.001) versus straight reaches. Reach sinuosity exhibited a significant positive correlation (p = 0.03) with storage mass and represented the most effective storage predictor. The majority of storage mass (72%) was represented by colluvial material accumulations at the streambank toe. Loose bed sediment was the second greatest contributor to storage mass (18%), with the remaining feature classes (e.g., bars) representing a combined ~10%. Sediment storage mass was ~3.25 times greater than the watershed suspended sediment load for 2015. The TP mass was found to be nearly equal to the respective watershed load for 2015. In-channel sediment and TP storage masses within Walnut Creek were found to be significant in comparison to respective annual loads, and thus storage is expected to play a significant role in respective watershed routing, loading, and the overall budgets of these parameters. Though challenging, quantification of in-channel fine sediment and TP storage is necessary to relate source contributions (e.g., stream- bank erosion) to watershed loads and is critical to account for interannual sediment and TP export. [ABSTRACT FROM AUTHOR]

The lightning channel morphology is closely related to developmental processes, which depends on the charge structure. There is currently a lack of understanding of how lightning channel morphology reveals developmental characteristics and charge structure. Based on the Lightning mapping array radiation source localization data of six lightning flashes, we studied the lightning channel morphology characterization method and obtained the spatial distribution of the fractal dimension (FD). We found that the fractal distribution had a consistent spatial and temporal correspondence with the channel development characteristics. Compared to regions with unidirectional extended channels, regions with more channel branches or direction change of channel development have a larger FD and a higher power density, where horizontal channel development is accelerated. These correspondence features reflect the inhomogeneous presence of pocket charge, which provides a new method to use lightning morphology information to reveal the characteristics of charge level distribution within thunderstorm clouds. Plain Language Summary: The charge distribution within the horizontal charge region may have a more significant effect on the extension of the lightning channel. At present, it is still difficult to directly observe the charge structure of thunderstorm clouds, especially the horizontal charge structure. Also, the morphological study of the channel is not perfect due to the limitations of observation and data acquisition. Therefore, there is currently a lack of understanding of how lightning channel morphology reveals developmental characteristics and charge structure. In the paper, the relationship between the lightning channel morphology, developmental characteristics, and charge structure was investigated for the first time based on Lightning mapping array localization data, and the spatial distribution of the lightning fractal dimension (FD) was obtained. It is found that, compared to regions with unidirectional extended channels, regions with more channel branches or direction change of channel development have a larger FD and a higher power density, where horizontal channel development is accelerated. These correspondence features reflect the inhomogeneous presence of pocket charge, which provides a new method to use lightning morphology information to reveal the characteristics of charge level distribution within thunderstorm clouds. Key Points: The spatial distribution of fractal dimension (FD) is obtained, and uesd to describe lightning channel morphologyThe channel morphology characterized by the FD is closely related to channel development velocity and radiation power densityThe channel morphology can be used to reflect the inhomogeneous state of charge level distribution [ABSTRACT FROM AUTHOR]

Modeled stream discharge is often used to drive sediment transport models across channel networks. Because sediment transport varies non‐linearly with flow rates, discharge modeled from daily total precipitation distributed evenly over 24‐hr may significantly underestimate actual bedload transport capacity. In this study, we assume bedload transport capacity determined from a hydrograph resulting from the use of hourly (1‐hr) precipitation is a close approximation of actual transport capacity and quantify the error introduced into a network‐scale bedload transport model driven by daily precipitation at channel network locations varying from lowland pool‐riffle channels to upland colluvial channels in a watershed where snow accumulation and melt can affect runoff processes. Transport capacity is determined using effective stresses and the Wilcock and Crowe (2003) equations and expressed in terms of transport capacity normalized by the bankfull value. We find that, depending on channel network location, cumulative error can range from 10% to more than two orders of magnitude. Surprisingly, variation in flow rates due to differences in hillslope and channel runoff do not seem to dictate the network locations where the largest errors in predicted bedload transport capacity occur. Rather, spatial variability of the magnitude of the effective‐bankfull‐excess shear stress and changes in runoff due to snow accumulation and melt exert the greatest influence. These findings have implications for flood‐hazard and aquatic habitat models that rely on modeled sediment transport driven by coarse‐temporal‐resolution climate data. Key Points: Modeled bedload transport capacity error caused by using daily precipitation to model flow tends to be highest in headwater channelsError is mediated by storm hydrometeorologic conditions including snow dynamics, baseflow and event magnitudeError diminishes as erosion thresholds decrease (bed mobility increases) and/or runoff increases [ABSTRACT FROM AUTHOR]

A better understanding of how vegetation influences alluvial channels could improve (a) assessments of channel stability and flood risks, (b) applications of vegetation as a river management tool, and (c) predictions of channel responses to climate change and other human impacts. We take advantage of a natural field experiment in the semi‐arid to arid Henry Mountains, Utah, USA: large spatial differences in bed and bank vegetation are found along some alluvial channels due to localized perennial springs caused by aquicludes in the underlying bedrock. Airborne LiDAR topography and flood modeling are used to constrain channel morphology, vegetation density, and flow velocity at different flood discharges for three spring‐fed reaches along intermittently flowing streams. The spatial distribution of vegetation quantitatively influences both the magnitude and direction of channel adjustment. Reaches with abundant bed vegetation are significantly wider (by an average of ≈50%), with shallower flows and lower velocities, than reaches with little bed vegetation. Reaches with dense channel bank vegetation are ≈25% narrower and ≈25% deeper than sparsely vegetated reaches. We interpret that sediment grain size influences the spatial distribution of vegetation within spring reaches, but that bank vegetation may be more important than grain size for "threshold" width adjustments. Widths, depths, and velocities are fairly insensitive to whether local hydraulic roughness is parameterized in terms of local vegetation density or is assumed spatially constant, suggesting that the underlying "bare earth" topography of the channel bed and banks exerts more control on local flow than does local vegetation density in this landscape. Plain Language Summary: Vegetation is found almost everywhere on Earth's surface and varies with regional climate rather than over short distances. It is therefore difficult to isolate vegetation influences on river channel dimensions from other controls such as flood discharge or sediment grain size, or to predict how climate change may drive river change. We isolate vegetation controls by studying river channels with large natural variations in vegetation due to localized groundwater springs. We use high‐resolution topographic data (collected using lasers shot from airplanes) to measure how much vegetation is found along and in channels, and we use computer models to calculate the width, depth, and velocity of flow at different flood discharges. We find that vegetation can cause channels to either be narrower or wider, depending on whether more vegetation is located on channel beds or banks, and we quantify the magnitude of these effects. Key Points: Groundwater‐fed springs in dryland landscapes provide an opportunity to isolate effects of vegetation on channel morphodynamicsVegetation can drive channel widening or narrowing, depending on whether the vegetation is focused on the channel bed or banksAt‐a‐station hydraulic geometry exponents are relatively insensitive to vegetation density in our data [ABSTRACT FROM AUTHOR]

Among braided rivers developed on the Qinghai-Tibet Plateau of China at very high elevations (>3,500 m), the middle and lower reaches of the Lhasa River have been affected by comprehensive human activities mainly involving dam construction, urbanization, farming, afforestation, and mining. In the current study, the impacts of these human activities on hydrology and morphology of the four braided reaches downstream of a cascaded of two dams are investigated. The study period was divided into 1985–2006 (P1), 2006–2013 (P2), and 2013–2019 (P3), representing the natural and changed flow regimes by dams. Using available daily discharge data at two stations within the four braided reaches, dam-induced hydrological alteration was analyzed based on the indicators of hydrologic alteration and range of variability approach and key discharge proxies were calculated. Remotely sensed images also were selected in the three periods and morphological metrics extracted from them were compared for the four reaches among these periods. Attenuated hydrological regimes were found for only two reaches. The total channel width (W c) and braiding intensity (BI t) followed different temporal trends among the four reaches. Annual average shift rates of the main channel in the four reaches were higher in the short (P2–P3) than in the long (P1–P2 and P1–P3) periods. The longitudinal changes of W c and the number of channels did not have any identifiable trend among the four reaches. By linking the morphological changes to quantified spatial and temporal patterns of various human activities, it was found that (1) the two dams had insignificant impact on channel morphology, suggesting that the studied braided river might have a short relaxation time and (2) the evolutional trajectories of morphological changes in most of the four reaches were similar, suggesting that temporal trends of morphological changes due to complex human activities are not affected by the different physiographic settings of the reaches. Continuous exploitation of the valley area requires comprehensive river management strategies for coordinating various human activities. [Display omitted] • A cascaded of two dams only changed the flow regime of the immediately downstream braided reach. • Channel morphology of the near-dam reach likely had a short relaxation time to recover from less intense disturbances. • Urbanization and farming constrain the space available for allow the braided river to change. • Historical trajectories of channel adjustment in response to human activities are similar among different braided reaches. [ABSTRACT FROM AUTHOR]

We describe the development of a high‐resolution, two‐dimensional hydrodynamic model for a multi‐inlet rapidly eroding tidal wetland on the western shore of Delaware Bay, using the finite‐volume, primitive equation community ocean model (FVCOM). Topo‐bathymetric surveys, together with water surface and current velocity measurements during calm and stormy conditions, have been conducted to support model validation. The tested model is then used to quantify the tide‐induced residual transport and asymmetry at major inlet entrances to determine the governing hydrodynamics. We chose a skewness method to calculate the tidal asymmetry and serve as a proxy for sediment transport estimates. The effects of the dredging of an artificial entrance channel and progressive channel deepening in shifting wetland hydrodynamics are shown by developing a scenario analysis. Model results show that the artificially dredged channel has altered the volume exchange at other inlet entrances and increased the net seaward export. The changes in the characteristic frequency of the frictional dissipation in the channel and the system's natural frequency are investigated using a simple ocean–inlet–bay analytical model. Subsequently, we have compared the channel friction scale to the inertia scale and observed that the new connection and gradual channel deepening reduce the overall frictional dominance. Ultimately, the study has shown how the short‐ and long‐term channel bathymetry changes, mainly the artificially dredged channel and progressive channel deepening, can affect the connected system's net circulation and trigger internal marsh erosion. [ABSTRACT FROM AUTHOR]

The dynamic nature of meandering poses several challenges in a river. The river Ganga shows severe bank erosion in many of its stretches which creates insecurity to the habitats. In the present study, channel morphology and lateral mid-line migration for 1975 to 2020 in 5 years intervals have been studied. The prediction of lateral mid-line migration from 2020 to 2050 by using multi-temporal Landsat satellite images was made by using the ARIMA model. The river reach was divided into 8 bends and 48 cross-sections were identified. The channel length was observed as 224.35 km in 1975 which reduces to 199.96 km in 2020. A decreasing trend was observed for the mean of channel length and meander ratio, and an increasing trend was noted in the mean of sinuosity ratio and tortuosity ratio. A total of 11 cross-sections showed the rightward shifting and 36 cross-sections showed the leftward shifting. Observed and predicted values showed a good R2 value of 0.90 and 0.89 at CS-24 and CS-25, respectively. The results may be used for planning and management of various river training work and understanding the river system dynamics. HIGHLIGHTS To investigate the variations in river morphometric parameters of the river Ganga.; Prediction of centerline channel shifting in the middle part of river Ganga from 1975 to 2050.; Outcome of the proposed research will definitely help the government in decision making, management and implementation of future projects.;

Twenty-four years (1999–2022) of channel change is assessed using specific-gage analysis based on the United States Geological Survey (USGS) rating curve calibration data from thirteen sites (drainage area < 500 km2) to understand the sensitivity of discharge-specific stage (DSS) or its inverse, stage-specific channel capacity (SSCC) to streamflow regimes, hydroclimatological history, and land use in small Piedmont watersheds of North Carolina, USA. We compare observed channel changes to common streamflow and flood metrics, Atlantic Multi-decadal Oscillation Index (AMOI), and land use/land cover data using regression and correlation techniques to suggest drivers of change and infer sensitivity. In addition to interannual variability, our results at most sites reveal three coherent periods of DSS/SSCC variation at the sub-decadal scale as well as multidecadal trend variation. The magnitudes and frequencies of these changes indicative of potential sensitivity vary substantially amongst sites. The trendlines from the DSS plots for the full length of record indicate that six sites showed increased specific stage while the remaining seven sites showed either reduced or a near-zero change in specific stage. Coefficients of determination relating specific stage and the index of AMO are low (R2 = 0.14—0.38) with both positive and negative relationships exhibited. Multiple regression, coefficients of determination relating specific stage and average monthly discharge are more variable, ranging from 0.18 to 0.94. Both positive and negative correlations (r ≤ 0.7) are found between specific stage and basin land use/land cover intensity indices, although few are significant at 95 % confidence interval. Both qualitative observations and correlation analyses support inferences that drought and persistent low mean discharge conditions tend to increase discharge-specific stage values (decreasing SSCC), by aggradation of the bed and/or lower banks. At our sites, this may be responsible for a sub-decadal trend of increasing specific stage between roughly 2013 and 2018, followed by ongoing reductions over the subsequent period. • Changes in discharge-specific stage were analyzed for 13 small stream channels. • Several channels exhibited similar coherent patterns of change over 24 years. • Correlations with annual and monthly streamflow were low to moderate. • Correlations with the Atlantic Multidecadal Oscillation were also low to moderate. • Watershed land use/land cover influences were apparent at some sites. [ABSTRACT FROM AUTHOR]

Our research introduces the river regulation effects on three sections of the upper and middle Odra River (south-western Poland), with differently channelized parts. In the upper and lower reaches, the river was straightened, narrowed, and trained with groins, whereas in the middle section, it was also impounded by numerous barrages. The discharge duration (DD) and water stage duration (WSD) curves for water-gauge stations from these river sections were analyzed to recognize changes in river flows and channel morphology since the mid-20th century. This analysis is supplemented by an examination of repeated surveys of the gauge cross sections of the river, annual precipitation totals in its catchment, and their relationship to the variation of the North Atlantic Oscillation (NAO) index. Our findings provide new hydrological insights for the region. The three river sections exhibited different patterns of the adjustment of the channel morphology to the river channelization: upper section was typified by channel incision, middle section by channel stability, and lower section by channel incision in its upper part and vertical stability of the channel bed in the lower part. Barrages in the middle section stabilized water stages in a wide range of hydrological conditions. Annual precipitation totals and river run-off did not change systematically over the study period. The variation in precipitation totals was inversely related to annual values of the NAO index. The study confirms the usefulness of DD/WSD curves to analyze changes in river run-off and the vertical position of the channel bed.

The present study has been a pioneering effort examining the role of an annual flood as a potent stimulus inducing changes in channel geomorphology of the Mayurakshi River, India. Twenty cross sections have been considered for the measurement of various hydro-geomorphic attributes of the river in both the pre- and post-flood conditions in 2018. The study sensed an escalating trend for channel width, width/depth ratio, and wetted perimeter while the reverse was also detected for average depth, maximum depth, cross-sectional area, and hydraulic radius. For example, the width/depth ratio recorded an increase of ~ 11%, and the hydraulic radius depicted a decrease of ~ 8%. Furthermore, channel asymmetry, bed asymmetry and bed relief index experienced a decrease after the flood. The sudden hydraulic impulse during monsoon flood as manifested in velocity, discharge, specific stream power, Reynolds number, Froude number increases the erosivity of the fluid. Besides the hydraulic factors, bank material (massive sandbank susceptible to hydraulic action and mixed bank constituted by alternate bands of sand and silt, and vulnerable to failure by piping action) brings substantial changes in channel morphology. Moreover, anthropogenic interventions such as sand mining are found to play a significant role in channel behaviour. The role of the multiple factors driving the morphological changes of the cross sections has been unpacked using canonical component analysis. [ABSTRACT FROM AUTHOR]

An artificial chute cutoff was implemented to eliminate the danger caused by the lateral migration of meandering river in the upper Yellow River in 2018. However, the earlier studies on chute cutoff have not provided a clear understanding of the hydrodynamic and morphodynamic characteristics of this artificial chute cutoff. In this study, three field measurements have been conducted to reveal the channel morphology and flow structure of the artificial chute channel. The results show that, compared with the natural chute cutoff, a 20-m-deep scour hole and a 2.26-km-long scour belt formed in the diversion channel are the significant features of this artificial cutoff. Further, a dual counter-rotating helical cell separated by a distinct shear layer is observed at the scour hole. Therefore, the formation of scour hole is likely related to the helical cells. However, flow stagnation was not observed in the chute channel, but the flow recirculation and separation zones were observed. Among them, the flow separation zone observed on the right bank of the diversion channel promoted the formation of bar. The observed counterclockwise single helical cells aggravated the erosion of the left bank. These findings provide useful insights on the artificial chute cutoff with complex flow structure and channel morphology characteristics, which can be used to improve the conceptual models of chute cutoff. [ABSTRACT FROM AUTHOR]

Given the complex array of processes influencing river networks, conceptual frameworks of rivers are critical to our understanding of channel processes and response potential, as well as restoration efforts. Yet despite their wide usage, many classifications are based on limited observations over homogenous landscapes, raising questions about their general applicability and quantitative thresholds. Leveraging a large, transect‐based morphological field dataset across California, USA, we use data‐driven methods to evaluate multivariate patterns in channel morphology and linkages with landscape properties considering a diversity of physio‐climatic settings. Emergent patterns highlight the variability in channel form observed across an extensive dataset over heterogeneous but spatially linked watersheds. In general, identified dominant channel attributes and landscape properties align with established channel types defined through expert judgement, but key differences also emerge. Similar to past studies, bed sediment composition and sub‐reach depth variability were discriminating channel attributes. The dominance of landscape properties associated with sediment supply or transport capacity suggests that morphological diversity largely reflects these differences as posited by prior classifications. Results also show some channel forms to be largely independent of valley confinement, with several channel bedforms and dominant grain sizes occurring across valley settings. This data analysis study demonstrates the utility of considering channel reaches and landscapes as multi‐dimensional features to elucidate and test established geomorphic understanding over large field datasets. [ABSTRACT FROM AUTHOR]

Summary: Changes in bed topography that build and maintain channel morphology are driven by the displacements of individual particles, either though their entrainment or deposition. However, the linkages between these topographic changes and individual grain displacements have not been comprehensively addressed, as many historical tracer studies have not included coincident topographic data. In this study, we compare the movements of bedload tracers to the differences in repeat topographic surveys across four gravel‐bed river reaches. To do this, we apply a 1‐D Bayesian survival process model to the starting and ending locations of tracers. This model estimates downstream trapping probabilities, which represent the likelihood that a given segment of channel will "trap" an entrained particle. We then adapt this model to estimate downstream trapping probabilities using digital elevation models of difference and compare the results. The estimates from the tracer and topographic trapping models showed general alignment, meaning that tracers were preferentially trapped in segments that experienced deposition along the channel. Thus, tracers in this study were able to identify downstream differences in bedload transport. The comparison also highlighted that tracer‐estimated trapping probabilities were larger than topographically estimated ones. This supports previous observations that sediment travel distances estimated using tracers are shorter than those estimated using morphological methods. We find that the differences between these two estimates vary systematically across study environments. These variations are attributable to either study design (i.e., tracers being larger than the median size of the sediment that deforms the bed) or differences in compensating scour and fill. We explore potential causes for differences in compensating scour and fill, including hydrograph shape, sediment delivery regime, channel deformation style, and channel width, highlighting that morphodynamics needs to be considered in designing bedload tracer studies. [ABSTRACT FROM AUTHOR]

Managers need to know how to mitigate rising stream water temperature (WT) due to climate change. This requires identifying the environmental drivers that influence thermal regime and determining the spatial area where interventions are most effective. We hypothesized that (i) extreme thermal events can be influenced by a set of environmental factors that reduce thermal sensitivity and (ii) the role played by those factors varies spatially. To test these hypotheses, we (i) determined which of the environmental variables reported to be the most influential affected WT and (ii) identified the spatial scales over which those environmental variables influenced WT. To this end, the influence of multi-scale environmental variables, namely land cover, topography (channel slope, elevation), hydromorphology (channel sinuosity, water level, watershed area, baseflow index) and shade conditions, was analyzed on the three model variables (day thermal sensitivity, night thermal sensitivity, and non-convective thermal flux) in the model developed by Georges et al. (2021) of the temporal thermal dynamics of daily maximum WT during extreme events. Values were calculated on six spatial scales (the entire upstream catchment and the associated 1 km and 2 km circular buffer, and 50 m wide corridors on each side of the stream with the associated 1 km and 2 km circular buffer). The period considered was 17 extreme days during the summer identified by Georges et al. (2021) based on WT data measured every 10 min for 7 years (2012–2018) at 92 measurement sites. Sites were located evenly throughout the Wallonia (southern Belgium) hydrological network. Results showed that shade, baseflow index (a proxy of the influence of groundwater), water level and watershed area were the most significant variables influencing thermal sensitivity. Since managers with finite financial and human resources can act on only a few environmental variables, we advocate restoring and preserving the vegetation cover that limits solar radiation on the watercourse as a cost-effective solution to reduce thermal sensitivity. Moreover, management at small spatial scale (50 m riparian buffer) should be strategically promoted (for finance and staffing) as our results show that a larger management scale is not more effective in reducing thermal sensitivity to extreme events. [ABSTRACT FROM AUTHOR]

Managers need to know how to mitigate rising stream water temperature (WT) due to climate change. This requires identifying the environmental drivers that influence thermal regime and determining the spatial area where interventions are most effective. We hypothesized that (i) extreme thermal events can be influenced by a set of environmental factors that reduce thermal sensitivity and (ii) the role played by those factors varies spatially. To test these hypotheses, we (i) determined which of the environmental variables reported to be the most influential affected WT and (ii)identified the spatial scales over which those environmental variables influenced WT. To this end, the influence of multi-scale environmental variables, namely land cover, topography (channel slope, elevation), hydromorphology (channel sinuosity, water level, watershed area, baseflow index) and shade conditions, was analyzed on the three model variables (day thermal sensitivity, night thermal sensitivity, and non-convective thermal flux) in the model developed by Georges et al. (2021) of the temporal thermal dynamics of daily maximum WT during extreme events. Values were calculated on six spatial scales (the entire upstream catchment and the associated 1 km and 2 km circular buffer, and 50 m wide corridors on each side of the stream with the associated 1 km and 2 km circular buffer). The period considered was 17 extreme days during the summer identified by Georges et al. (2021) based on WT data measured every 10 min for 7 years (2012–2018) at 92 measurement sites. Sites were located evenly throughout the Wallonia (southern Belgium) hydrological network. Results showed that shade, baseflow index (a proxy of the influence of groundwater), water level and watershed area were the most significant variables influencing thermal sensitivity. Since managers with finite financial and human resources can act on only a few environmental variables, we advocate restoring and preserving the vegetation cover that limits solar radiation on the watercourse as a cost-effective solution to reduce thermal sensitivity. Moreover, management at small spatial scale (50 m riparian buffer) should be strategically promoted (for finance and staffing) as our results show that a larger management scale is not more effective in reducing thermal sensitivity to extreme events.

The Three Outlets Channel (TOC) consisting of three anabranching rivers formed due to natural avulsion by extremely high floods, is the primary water–sediment channel connecting the Jingjiang in the middle Yangtze River and Dongting Lake (the second largest freshwater lake in China). Since the impoundment of the Three Gorges Reservoir (TGR) in 2003, the decreasing diversion of runoff and sediment load of the TOC has an impact on the hydrological connectivity of the river–lake relation. Nonetheless, it lacks complete understanding on the diversion of runoff and sediment load, erosion and deposition amount, and the calculation method of diversion runoff in the TOC. We used remote sensing images, hydrological data, and channel topography to analyze the change in runoff and sediment load, channel morphology, local erosion and deposition amounts. The main results show that: (i) Meander cutoffs of the Lower Jingjiang accelerated the reduction process of the Ouchi River’s runoff and sediment load and the increase in the number of dry days. After the impoundment of the TGR, the diversion of sediment load of the TOC was greatly affected, but the decreasing trend of the runoff diversion slowed down. (ii) The morphological change of the inlet zone of Ouchi River is larger than that of Songzi River and Hudu River. The morphological evolution of the inlet area led to the change in the diversion of runoff and sediment load of the TOC. (iii) In the dry season, the water level drop in the inlet zone of the TOC leads to a decrease in the diversion discharge. Therefore, considering the water level drop and channel width adjustment in the inlet zone, five empirical formulae for the diversion discharge of the five hydrological stations in the TOC are proposed. These empirical formulae can be used as a short-term forecast for future changes in the hydrologic regime and the dynamics of the Jingjiang–Dongting Lake relation.

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. • Differentiated artificial revetments lead to inner bank erosion and two sand bars formation in outer bank zone. • Cross-section hydraulic geometry at the apex adjusted by lateral shift of the thalweg and progressive retreat of inner bank. • Neck cutoff of this bend may occur in the next 30–50 years without bank revetments. [ABSTRACT FROM AUTHOR]

Strong wind events frequently result in creating large areas of windthrow, which causes abrupt environmental changes. Bare soil surfaces within pits and root plates potentially expose soil to erosion. Absence of forest may alter the dynamics of water circulation. In this study we attempt to answer the question of whether extensive windthrows influence the magnitude of geomorphic processes in 6 small second- to third-order catchments with area ranging from 0.09 km2 to 0.8 km2. Three of the catchments were significantly affected by a windthrow which occurred in December 2013 in the Polish part of the Tatra Mountains, and the other three catchments were mostly forested and served as control catchments. We mapped the pits created by the windthrow and the linear scars created by salvage logging operations in search of any signs of erosion within them. We also mapped all post-windthrow landslides created in the windthrow-affected catchments. The impact of the windthrow on the fluvial system was investigated by measuring a set of channel characteristics and determining bedload transport intensity using painted tracers in all the windthrow-affected and control catchments. Both pits and linear scars created by harvesting tend to become overgrown by vegetation in the first several years after the windthrow. The only signs of erosion were observed in 10% of the pits located on convergent slopes. During the period from the windthrow event in 2013 until 2019, 5 very small (total area <100 m2) shallow landslides were created. The mean distance of bedload transport was similar (t-test, p=0.05) in most of the windthrow-affected and control catchments. The mapping of channels revealed many cases of root plates fallen into a channel and pits created near a channel. A significant amount of woody debris delivered into the channels influenced the activity of fluvial processes by creating alternating zones of erosion and accumulation. [ABSTRACT FROM AUTHOR]

The formation of wetland channel networks on coastal river floodplains is affected by spatial transitions in tidal‐fluvial processes. This study evaluated sedimentation patterns in tidal marshes on the 147‐km tidal Columbia River and its 87‐km estuary and characterized the cross‐sectional geometry and planform morphometry of tidal wetlands along the estuarine to riverine gradient. Tidal marshes were predominantly depositional (median 0.7 cm yr−1, primarily silt), consistent with late‐Holocene rates. Marsh sediment accretion rate increased with annual maximum 7‐day average daily maximum water depth. Elevation was negatively correlated with accretion rate in the tidal river and positively correlated with total organic carbon (TOC%) in the tidal river and estuary. TOC% was greater in the estuary and, like percent fines, greater farther from the main‐channel Columbia River. For four single‐channel and six channel‐network planforms of tidal marsh, shrub‐dominated, and forested wetlands: (1) Spatial patterns of cross‐sectional morphology conformed to typical coastal wetland morphology in estuarine reaches up to the tidal river. (2) Reach‐based and common slope linear models for channel perimeter on wetland area were predictive in the estuary (R2 > 0.81) and differed between island (n = 144) and mainland (n = 164) wetlands. No planform linear models were predictive for the entire study area or the tidal river. No models for channel outlets were acceptable. (3) Channel perimeter, surface area, and outlets were all highly variable within and among estuarine–riverine reaches. Analyses of sediment, cross‐section, and planform support the use of a "natural network paradigm" for wetland‐restoration design on tidal river floodplains. Key Points: A new metric, the annual maximum of the 7‐day average daily maximum water depth, explains much variability of tidal river floodplain sedimentation rateIn the estuary, up to the tidal river, cross‐sectional morphology and planform channel network perimeter tend to conform to coastal processesOrganic carbon is positively correlated with elevation and with distance from the main river channel. It is highest in the estuary [ABSTRACT FROM AUTHOR]

Transverse drainages are prominent landscape features in active foreland thrust-and-fold belts. Understanding their response to folding processes is pivotal for comprehending landscape evolution and erosion-deformation interactions within the foreland. Here, we focus on the extensively developed transverse drainages across the Tugerming anticline in the southern Tian Shan foreland. Based on fold topography, drainage patterns, and various morphometric indices, we conducted a detailed geomorphological analysis of the Tugerming anticline. Our results suggest that the Tugerming fold laterally grows towards both ends, exhibiting notable segmentation along its strike. The westward lateral fold growth is characterized by interactions between the Tugerming anticline and two adjacent anticlines (Yiqikelike and Tuziluoke). At its eastern termination, lacking nearby folds, the Tugerming anticline laterally propagates without other adjacent folds, resulting in an elongated, gentle termination. Additionally, the hinterland catchment controls sediment and water flux of foreland transverse rivers, and its size has a significant influence on both channel morphology and river-fold interactions of the Tugerming anticline. Among the transverse rivers studied, those with large hinterland catchments (>80 km2) were dominated by braided river channels. In these cases, rivers respond to changes in channel gradient due to fold growth primarily through aggradation and degradation processes. Conversely, rivers with limited hinterland catchments (<80 km2) or originating within the fold, show a prevalence of incised meander channels. Moreover, channels accommodate gradient changes induced by the growing fold, primarily altering channel morphology, including channel sinuosity, slope, and width-to-height ratio. Our study reveals the significance of considering the hinterland catchment size in interpreting river-fold interactions and associated channel morphology within foreland transverse drainages. • We study transverse drainages in the Tugerming anticline in South Tian Shan foreland. • Geomorphic indices suggest lateral growth of the Tugerming fold towards both ends. • The lateral fold growth exhibits significant along-strike segmentation characters. • Hinterland catchment sizes affect channel morphology and river-fold interaction. [ABSTRACT FROM AUTHOR]

Barak River is highly meandering rivers flowing through the alluvial plains of Assam in India. However, due to dynamic system, it is found that channel being subjected to regular shifting which creates uncertainty to the habitants residing nearby the river. Therefore, it is anticipated to carry out a study regarding changes in channel morphology and prediction of centerline channel migration during 1984–2030, using multiperiod Landsat remote sensing images along with autoregressive integrated moving average model (ARIMA). From morphometric analysis, it was found that the mean value of meander length (ML), meander width (MB), and meander ratio (MR) indicates an increasing trend, while sinuosity (C), wavelength (λ), and radius of curvature (RC) show a decreasing trend. The outcome of ARIMA model specifies that channel shifting of mid-line is going to change suddenly either to rightward or leftward directions. Throughout the whole alluvial part of the Barak River, rightward side is recognized as major concern. Observed and predicted values have shown a good R2 value (R2 = 0.89 and R2 = 0.88) at CS-30 and CS-18 respectively. Also, lowest RMSE is observed at CS-12 and highest RMSE is observed at CS-21. Finally predicted values were generated for the estimation of centerline channel shifting between two time intervals (2017–2023 and 2023–2030), which shows that the channel shifting of the river basin will occur at many regions particularly at critical sections. Overall, the findings of this study could be used further in river training works and in understanding the future dynamics of channel. [ABSTRACT FROM AUTHOR]

This paper uses flume experiments to investigate the influence of lateral width confinement on channel morphology, sediment sorting, and bedload transport. Three runs of about 60 hr were carried out under constant feeding rate equal to 0.6 l/s and 8 g/s, with a bimodal mixture of natural sediments, a fixed flume slope of 3%, and width imposed by lateral walls from 0.12 to 0.50 m in order to model three different flow confinement configurations. Despite the three runs transporting at the same rate on average, they presented different gravel‐bed river morphologies and different degrees of bed complexity. The three runs also presented differences in bedload transport rate fluctuations associated with different magnitude and mechanisms of bed storage and release of sediments. The intermediate width configuration (Run 2) was found to have a minimum storage and release of sediments compared with both the wider configuration (Run 1) and the narrower configuration (Run 3). Runs 1 and 3 were characterized by a significant storage and release of sediments resulting in a highly fluctuating bedload transport rate; however, while Run 1 (braiding morphology) stored and released sediments through lateral deposits and bed variations with planimetric sorting, Run 3 (single‐thread channel) stored and released sediments through variations in bed elevation accompanied by vertical sorting. We extrapolated this concept to the full set of gravel‐bed river morphologies, thus speculating about the channel morphology for optimal sediment transfer. Key Points: We perform flume experiments to represent poorly‐sorted gravel‐bed rivers with the same active channel width but different extents of lateral confinementChannel morphologies, geometries, sorting patterns, and bedload transport rates are strongly influenced by lateral width constraintsAmong the three configurations tested, the one with intermediate width confinement promotes a single‐thread to braided pattern and presents less variation in sediment transport rate [ABSTRACT FROM AUTHOR]

Wood accumulations are important morphological agents forming the character of high-gradient streams in the Moravskoslezské Beskydy Mts. The aim of the research is to define both the extent and character of the impact of wood accumulations on the streams. A total of 126 accumulations have been identified of the total wood volume of 503 m3 that is unevenly distributed within the studied streambeds. The wood volume in the studied streambeds is particularly dependent on the age and species composition of vegetation, channel morphology, and the geological bedrock resistance to the action of the stream, especially in forced alluvial reaches. The research revealed the deposition of fine-grained material immediately upstream of the wood accumulations, creating gravel bars and capturing fine organic debris. On the other hand, immediately downstream of the accumulations fine-grained fractions are carried away and coarser material is deposited, creating pools and plunge pools, evorsion potholes and bank scours. The research further showed a low intensity of the transport of woody material through the streambeds. The accumulations usually occur in the place where the stream has been dammed by a fallen tree member or in structurally predisposed streambed segments. As a result, discontinuities in energy and material flow occur that help to increase the streambed heterogeneity.

Summary: Tracer studies are a commonly used tool to develop and test Einstein‐type stochastic bedload transport models. The movements of these tracers are controlled by many factors including grain characteristics, hydrologic forcing, and channel morphology. Although the influence of these sediment storage zones related to morphological features (e.g., bars, pools, riffles) have long been observed to "trap" bedload particles in transport, this influence has not been adequately quantified. In this paper we explore the influence of channel morphology on particle travel distances through the development of a Bayesian survival process model. This model simulates particle path length distributions using a location‐specific "trapping probability" parameter (pi), which is estimated using the starting and ending locations of bedload tracers. We test this model using a field tracer study from Halfmoon Creek, Colorado. We find that (1) the model is able to adequately recreate the observed multi‐modal path length distributions, (2) particles tend to accumulate in trapping zones, especially during large floods, and (3) particles entrained near a trapping zone will travel a shorter distance than one that is further away. Particle starting positions can affect path lengths by as much as a factor of two, which we confirm by modelling "starting‐location‐specific" path length probability distributions. This study highlights the importance of considering both tracer locations and channel topography in examinations of field tracer studies. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Patch‐burn grazing (PBG) can promote terrestrial heterogeneity and biodiversity, but can temporarily increase stream nutrients and ecosystem metabolism, and alter macroinvertebrate assemblages. The impacts of grazing on stream channel morphology and post‐PBG recovery patterns are unclear.We assessed the influence of grazing in PBG managed grassland streams in Missouri, USA, and subsequent recovery when grazing ceased for 2 years. We hypothesized that grazing would degrade water quality, stream biotic integrity and channel morphology, but that riparian fencing would mitigate these effects. We predicted that biological and chemical variables in unfenced streams would return to pre‐PBG levels within 2 years after grazing ceased, but channel morphology would not.Six small headwater streams (two in ungrazed control watersheds, two in PBG watersheds with 10 m fenced riparian zones and two in PBG unfenced) were sampled over 7 years; 2 years before PBG, 3 years during PBG and 2 years post‐PBG. We sampled macroinvertebrates and water chemistry monthly when water was present and surveyed channel morphology at least once each study period.During grazing, unfenced watersheds showed the greatest changes in channel width, depth and area. During the post‐PBG period, one of the two unfenced watersheds showed partial recovery of channel morphology. Although grazing increased concentrations of nutrients and chlorophyll‐a, concentrations returned to pre‐PBG conditions after grazing ceased, indicating recovery. Very fine organic sediments increased in the unfenced watersheds compared to the control during grazing but recovered afterwards. Contributions of Chironomidae to total invertebrate abundance increased in the unfenced watersheds during grazing, and then decreased during the post‐PBG period.Riparian fencing mostly mitigated effects of grazing on the streams. Unfenced streams were resilient to effects of grazing in a PBG managed grassland, with most metrics recovering within 2 years after grazing ceased, except for channel morphology.Synthesis and applications. Grazing in a patch‐burn grazed managed grassland coupled with riparian fencing could be an effective conservation tool for land managers of prairies, with relatively modest influences on stream water quality and biotic integrity. Persistent changes in stream channel morphology and effects of longer periods of grazing deserve further research. [ABSTRACT FROM AUTHOR]

We describe the joint dynamics of bedload transport and bed elevation changes with a stochastic population model, and we analyze (1) the dependence of bedload flux statistics on local bed elevations and (2) resting time distributions for sediment undergoing burial in the fluctuating sedimentary bed. The model involves entrainment and deposition in a control volume characterized by elevation‐dependent rates, and it exhibits a statistical regulation effect, whereby bed aggradation suppresses the variance of the bedload flux while degradation enhances it. This variance regulation effect is contingent on collective entrainment, whereby moving grains destabilize stationary grains in a positive feedback. When collective entrainment is turned off,bedload transport fluctuations become independent of the bed elevation. Return times from above in the bed elevation time series provide heavy‐tailed power law distributions of resting times with tail behavior characterized by the mean erosion rate and the active layer depth. These results imply bedload statistics measurements on relatively short timescales can be strongly biased by bed elevation changes when collective entrainment occurs, and they support the growing consensus that sediment burial generates heavy‐tailed sediment resting times that ultimately generate anomalous bedload diffusion. Key Points: Two‐species stochastic population model describes fluvial bedload particle activity and local bed elevationsModel predicts elevation‐dependent transport statistics and power law distributed resting times for sediment undergoing burialBed elevation changes modify particle activity fluctuations by up to 90%, and sediment burial generates anomalous bedload diffusion [ABSTRACT FROM AUTHOR]

Neck cutoffs and their resultant oxbow lakes are important and prominent features of riverine landscapes. Detailed field‐based research focusing on the morphologic evolution of neck cutoffs is currently insufficient to fully characterize cutoff evolution. High‐resolution bathymetric data were collected over 3 years for the purpose of determining channel morphology and morphologic change on three actively evolving neck cutoffs. Results indicate the following general trends in morphologic adjustment: (1) a longitudinal bar in the upstream meander limb that develops near the entrance to the abandoned bend; (2) a deep scour hole in the downstream meander limb immediately downstream of the cutoff channel; (3) erosion of the bank opposite the cutoff in the downstream meander limb; (4) a cutoff bar in the downstream meander limb at the junction corner of the cutoff channel and the downstream meander limb; and (5) perching of the exit of the abandoned bend above the cutoff channel due to channel bed incision. The results presented herein were used to develop a conceptual model that depicts the morphologic evolution of highly curving neck cutoffs. The findings of this research are combined with recent analyses of the three‐dimensional flow structure through neck cutoffs to provide a mechanistic explanation for the morphodynamics of neck cutoffs. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The area between the river and its surrounding vegetation constitutes the riparian zone which produces woody debris (WD) that modifies the fluvial dynamics. The WD is constituted by branches and trunks deposited in the river channel. One of the ways that WD can modify the geomorphology of the river is to form steps and pools (step-pool system). In this way, the objective of the present study was to perform a literature review on woody debris in rivers and, to identify the main focus used in research on the occurrence and monitoring of these materials. It was observed that the WD can be found as individual pieces or forming accumulations, and that there is a tendency among the researchers to analyze the diameter and length of the pieces, obtaining the total volume in length of river. There is a gap regarding the woody debris management in Brazil, because only one biome (Atlantic Forest) was included in the few researches carried out. The knowledge of WD dynamics can be surely used in the future in the watersheds management and for rivers renaturalization. [ABSTRACT FROM AUTHOR]