Channel Morphology Research Articles

River channel dynamics and flooding: A case of motorable bridge collapse due to abrupt flood in Chhabdi Khola, Tanahun, Nepal

The monsoon season in Nepal brings calamitous events like riverbank erosion, toe cutting, and the structural failure of bridges due to floods. In July 2021, a motorable bridge in Bhadgaun, Tanahun district, Nepal, collapsed during a massive flood in Chhabdi Khola. The study aims to comprehensively document the aftermath, specifically focusing on the causal factors that led to the damage of the Chhabdi Khola Dovan Bridge. The study delves into an in-depth analysis of the stream's channel morphology, with the 5.85 kilometers Chhabdi Khola partitioned into 28 distinct segments, each spanning approximately 200 meters. These segments, sequentially labeled from Site 1 to Site 28, encompass the area extending from the upstream at Chhabdi Barah temple to the downstream at bridge’s location. Rigorous measurements of length, breadth, and depth at each site form the basis for volumetric assessments of the stream. The study revolves around contrasting paleo channel attributes with contemporary alterations within the Chhabdi Khola catchment. The analysis leverages precipitation data sourced from the Department of Hydrology and Meteorology (DHM) to discern precipitation trends within the Chhabdi Khola catchment area. The hydrographic data underwent trend analysis utilizing Mann-Kendall and Sen's slope method through R software (version 4.3.2). The collapse of the Chhabdi Khola Dovan Bridge resulted from intense water flow and debris due to heavy rainfall and a narrow outlet near the bridge, impacting the local population and land users facing the enduring aftermath of a catastrophic monsoon event. The study highlights the significance of understanding river dynamics in small streams and advocates for proactive disaster preparedness measures, even in seemingly small river channels.

Hydromorphological response of heavily modified rivers to flood releases from reservoirs: A case study of the Spöl River, Switzerland

AbstractReleasing 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.

Visioning channel evolution for river management: Toward a functional decision support framework

AbstractImprovements in simulating and communicating the evolutionary trajectory of river morphology in response to environmental forcing over multi‐decadal timeframes would foreshadow the development of “foresight competency” in river management, whereby resource managers could strategically plan toward the most preferred of several plausible futures. Of the six steps in foresight competency, visioning, which involves translating scientific forecasts into a format useable by resource managers via a user‐friendly and interactive decision support tool that supports transparent decision‐making, is the least well developed. The approach requires converting forecasting model outputs into metrics of channel evolution that highlight transitions either within or between channel morphology states. Here, seven process‐based state transition metrics are proposed covering channel planform, morphological stability, corridor belt width, floodplain connectivity, bank erosion rate, bedform habitat diversity, and ecohydraulic diversity. To aid decision support, the metrics are converted into graphical indicators that are intuitive for management use and assembled into several prototype dashboard‐style graphical user interfaces designed to facilitate interactivity. A proof‐of‐concept illustration is provided and priorities in development toward a fully operational decision support tool are discussed. Such developments are critical in ensuring the practical relevance of geomorphology.

Review on different shapes of spurs and their effects on channel morphology

Abstract In this paper, the significance of the shape of spurs on flow and bed morphology is understood, accompanied by an appeal to investigate alternative shapes like L-head, T-head spurs, and hockey-shaped spurs, which could offer considerable benefits for river management. The spurs with T-head shape are found to be more efficient in reducing the bed scouring of the channel relatively, although it depends on the orientation of the spur, location of installation, and shape of the channel. Furthermore, development of horseshoe vortex is found insignificant near the base of the T-head spur dike. T-head spurs could more effectively redirect flow and prevent erosion while L-head spurs may enhance riverbank stability. This highlights the need for more investigation into how different spur shapes collectively affect river morphology, flow velocity, and sediment transport patterns. Temporal variations in bed morphology, especially the scour depth and sediment transport dynamics near spur dikes, should also be investigated to understand their changing impact better. Finally, this study provides a complete summary of existing knowledge gaps and future research initiatives relevant to various shapes of spur dikes and their role in riverbank erosion management.

Response of a small, forested stream to a large input of sediment

In small headwater channels coupled to hillslopes, episodic supplies of sediment from events like landslides can dominate local channel morphodynamics and impact ecosystem health. In this study we investigate the response of a small mountain stream in British Columbia to a sediment input event that was up to 150 times the volume of sediment transported in an average flood year caused by the upstream installation of a road bridge. Using four years of repeated UAV surveys, bedload tracers, and other field monitoring techniques, we examined the spatial and temporal changes in sediment storage along the reach, identified changes to channel morphology, and characterized the interaction between the channel bed and the supplied sediment. Historical monitoring of the reach allowed for a comparison of the response to nearly 20 years of information about bedload transport and morphologic change. We observed that most of the change within the reach occurred during the first flood after bridge installation. The supplied sediment mostly moved across the bed surface with little interaction, as tracers installed in the bed had lower than expected rates of mobility. A narrow, steep segment of the channel proximal to the bridge installation stored little sediment, whereas a wider, less steep segment further downstream absorbed much of the change. This effect was exacerbated by a logjam that formed during the first flood after bridge installation. Despite the relative magnitude of the sediment transport event, there was little change to the channel pattern, with the added sediment increasing the relief of the already existing morphologic units. This suggests river managers should focus their restoration attention on segments likely to respond to a disturbance and that the pool-riffle channel morphology can persist across a wide range of sediment-supply conditions.

River Damming Impacts on Fish Habitat and Associated Conservation Measures

AbstractRiver damming has brought great benefits to flood mitigation, energy and food production, and will continue to play a significant role in global energy supply, particularly in Asia, Africa, and South America. However, dams have extensively altered global river dynamics, including riverine connectivity, hydrological, thermal, sediment and solute regimes, and the channel morphology. These alterations have detrimental effects on the quality and quantity of fish habitat and associated impacts on aquatic life. Indeed, dams have been implicated in the decline of numerous fishes, emphasizing the need for effective conservation measures. Here, we present a global synthesis of critical issues concerning the impacts of river damming on physical fish habitats, with a particular focus on key fish species across continents. We also consider current fish conservation measures and their applicability in different contexts. Finally, we identify future research needs. The information presented herein will help support sustainable dam operation under the constraints of future climate change and human needs.

Influence of Sediment Supply Timing on Bedload Transport and Bed Surface Texture During a Single Experimental Hydrograph in Gravel Bed Rivers

AbstractChannel stability and sediment transport in gravel bed streams depend on temporally and spatially variable fluid forces, bed surface structures, armoring, and sediment supply/storage. Of particular interest here is the influence of sediment supply timing on bedload transport rate and grain size distribution, bed surface composition and channel morphology. We conducted flume experiments in a sediment feed flume with poorly sorted sediment. A symmetrical, identical stepped hydrograph was used with five different sediment feeding schemes: no feed, constant feed, rising‐limb only feed, falling‐limb only feed, and variable feed. The same sediment mass of 800 kg was fed during each experiment. Sediment transport rates ranged over five orders of magnitude regardless of feeding scheme. Clockwise hysteresis was observed for bedload transport rate and bedload grain size, that is, the transport rate was larger and coarser during the rising limb. Counterclockwise hysteresis was observed for the grain size distribution of the bed surface, that is, the bed surface was finest during the rising limb. In all experiments sediment yield during the rising was higher than during the falling limb, indicating that the rising limb is more capable to transport the supplied sediment. Our study provides insight on how timing of sediment supply influences sediment transport and bed surface during a single hydrograph, essential information for artificial sediment supply projects to restore and habilitate gravel bed streams.

Morphology and Transport Study of Acid-Base Blend Proton Exchange Membranes by Molecular Simulations: Case of Chitosan/Nafion.

Blending a basic polymer (e.g., chitosan) with Nafion can modify some membrane properties in direct methanol fuel cell applications, e.g., controlling methanol crossover, by regulating the morphology of hydrophilic channels. Unraveling the mechanisms by which the channel morphology is modified is essential to formulate design strategies for acid-base blend membrane development. Thus, we use molecular simulations to analyze the morphological features of a blend membrane (at 75/25 chitosan/Nafion wt %), i.e., (i) water/polymer phase organizations, (ii) number and size of water clusters, and (iii) quantitative morphological measures of hydrophilic channels, and compare them to the pure Nafion in a wide range of water contents. It is found that the affinity of water to different hydrophilic groups in the blend membrane can result in more distorted and dispersed hydrophilic phase and fewer bulk water-like features compared to pure Nafion. Also, the width of the hydrophilic network bottleneck, i.e., pore limiting diameter (PLD), is found to be almost five times smaller for the blend membrane compared to Nafion at their maximum water contents. Moreover, by changing the chitosan/Nafion weight ratio from 75/25 to 0/100, we show that as Nafion content increases, all channel morphological characteristics alter monotonically except PLD. This is mainly due to the strong acid-base interactions between Nafion and chitosan, which hinder the monotonic growth of PLD. Interestingly, water and methanol diffusion coefficients are strongly correlated with PLD, suggesting that PLD can be used as a single parameter for tailoring the blending ratio for achieving the desired diffusion properties of acid-base membranes.

The context dependency of fish-habitat associations in separated karst ecoregions.

Fish populations may be isolated via natural conditions in geographically separated ecoregions. Although reconnecting these populations is not a management goal, we need to understand how these populations persist across landscapes to develop meaningful conservation actions, particularly for species occupying sensitive karst ecosystems. Our study objective was to determine the physicochemical factors related to the occurrence of four spring-associated fishes. Arbuckle Uplift and Ozark Highlands ecoregions, USA. We used a hierarchical approach to identify habitat relationships at multiple spatial scales. We collected detection data using snorkeling and seining. We examined the physicochemical relationships related to the detection and occurrence of four spring-associated fishes using occupancy modeling in a Bayesian framework. We found physicochemical relationships that differed and were similar between ecoregions for several fishes. For three species, we found different water temperature relationships between ecoregions. Smallmouth bass were ubiquitous in their use of drainage areas in the Ozark Highlands but only associated with the lower network of the Arbuckle Uplift. There were several mirrored relationships between ecoregions, including an interaction between residual pool depth and water temperature, where sites with deeper pools were more likely to be occupied during warmer water temperatures. There were single-species occurrence relationships with percent vegetation and percent agriculture. Lastly, snorkeling was a more efficient sampling method compared to seining for all fishes. Our results indicate stream temperature mitigation may be possible via the maintenance of key channel morphologies, and we identify shared stressors between ecoregions. Channel mitigation to maintain reaches with deeper pools may be an important strategy for maintaining thermal refugia, particularly when considering climate change. Identifying the mechanistic underpinning of other multiscale ecological relationships would be helpful to discern if some of the different ecoregion relationships represent warning signals or interactions with unmeasured biotic or abiotic factors.

Extending morphometric scaling relationships: the role of bankfull width in unifying subaquatic channel morphologies

Subaquatic channels, situated in lakes, fjords, submarine canyons and on deep-sea fan systems, exhibit diverse morphometric characteristics controlled by sediment transport processes, particularly turbidity currents. These processes play a significant role in transporting sediment, organic carbon, nutrients, and pollutants and pose hazards to critical infrastructure. This study examines a balanced set of subaquatic channels across various settings, sizes, and locations, employing novel data harmonization techniques to address biases toward larger channels. The analysis reveals consistent scaling relationships, particularly the dominant role of bankfull width, influencing bankfull depth, cross-sectional area, wavelength, and amplitude. The aspect ratio (width-to-depth) emerges as a significant parameter, reflecting a necessary channel compactness to maintain turbidity currents. Meandering development reveals relations between width, wavelength, and amplitude, with a preference for specific ratios. Meandering is most pronounced at channel beginnings, transitioning to straighter forms downstream, potentially influenced by flow dynamics and flow confinement. The study broadens the understanding of subaquatic channel evolution, emphasizing the importance of bankfull width and providing insights applicable across settings and scales.

Unravelling submarine channel morphology in the lower Bengal Fan through ultra-high-resolution autonomous underwater vehicle (AUV) survey

Unravelling submarine channel morphology in the lower Bengal Fan through ultra-high-resolution autonomous underwater vehicle (AUV) survey

Effects of sediment transport on flood hazards: Lessons learned and remaining challenges

Sediment transport (bedload and suspension) plays a relevant role in the morphological response of river channels to large floods. Sediment load controls erosion and aggradation patterns during high flows, drives the migration of macroforms and contributes to the definition of thresholds for bank erosion and channel instability. Given this influence on channel morphology, it is clear that sediment transport influences both the channel geometry and water stage reached during floods and should therefore be considered in flood hazard analysis. So far, however, legislation on flood hazard and flood management plans still continues to typically disregard sediment transport. This is due mainly to the paucity of available data on sediment transport and the lack of standardized approaches for its integration into flood hazard analysis. The present work, which aims to provide some guidance on how to advance in this issue, has undertaken a bibliometric study and thorough review of the published scientific literature that had previously addressed the implications of sediment transport on flood hazards assessment. This review showed that: i) most studies on the influence of sediment transport on flood risk have focused on mountain streams, as they are highly sensitive systems to changes in sediment supply; ii) research has also focused on explaining historical changes in channel-conveyance capacity and flood frequency based on long-term trends in sediment supply; and iii) recent developments in hydrodynamic and morphodynamic numerical models provide opportunities to explicitly incorporate sediment transport in flood hazard analysis. However, despite the recent advances, we have identified important challenges and discussed needs to better consider sediment transport in flood hazards at different spatial and temporal scales.

Steady-state forms of channel profiles shaped by debris flow and fluvial processes

Abstract. Debris flows regularly traverse bedrock channels that dissect steep landscapes, but our understanding of bedrock erosion by debris flows and their impact on steepland morphology is still rudimentary. Quantitative models of steep bedrock channel networks are based on geomorphic transport laws designed to represent erosion by water-dominated flows. To quantify the impact of debris flow erosion on steep channel network form, it is first necessary to develop methods to estimate spatial variations in bulk debris flow properties (e.g., flow depth, velocity) throughout the channel network that can be integrated into landscape evolution models. Here, we propose and evaluate two methods to estimate spatial variations in bulk debris flow properties along the length of a channel profile. We incorporate both methods into a model designed to simulate the evolution of longitudinal channel profiles that evolve in response to debris flow and fluvial processes. To explore this model framework, we propose a general family of debris flow erosion laws where erosion rate is a function of debris flow depth and channel slope. Model results indicate that erosion by debris flows can explain the occurrence of a scaling break in the slope–area curve at low-drainage areas and that upper-network channel morphology may be useful for inferring catchment-averaged erosion rates in quasi-steady landscapes. Validating specific forms of a debris flow incision law, however, would require more detailed model–data comparisons in specific landscapes where input parameters and channel morphometry can be better constrained. Results improve our ability to interpret topographic signals within steep channel networks and identify observational targets critical for constraining a debris flow incision law.

Drainage area is not enough: multivariate hydraulic geometry in the Southern Blue Ridge Mountains, U.S.A.

ABSTRACT Regional hydraulic geometry curves, which relate drainage area to channel morphology, are powerful tools for river restoration and watershed management. While there is a strong correlation between channel morphology and drainage area, the importance of watershed slope and relief on channel-forming flow, especially in mountainous regions, cannot be ignored. This research used single variable power functions along with multiple regression to determine which network- and or local-scale variables are influencing channel morphology in the Southern Blue Ridge Mountains. Within this region, watershed topography (i.e. relief and slope) and or local-scale characteristics (e.g. channel slope and sinuosity) are better predictors of channel morphology than drainage area. Additionally, the importance of local-scale characteristics in the multiple regression models provide strong evidence that site-specific conditions can be just as important as watershed characteristics in determining channel morphology. While multiple regression has been used to create hydraulic geometry equations in other regions, this is the first study that determined whether non-drainage area multiple regression models perform better than models that include drainage area. With the increasing ease with which network- and local-scale characteristics can be calculated, this research shows a clear need to incorporate additional network- and or site-specific characteristics into hydraulic geometry equations.

Marsh-induced backwater: the influence of non-fluvial sedimentation on a delta's channel morphology and kinematics

Abstract. We investigate the interaction of fluvial and non-fluvial sedimentation on the channel morphology and kinematics of an experimental river delta. We compare two deltas: one that evolved with a proxy for non-fluvial (“marsh”) sedimentation (treatment experiment) and one that evolved without the proxy (control). We show that the addition of the non-fluvial sediment proxy alters the delta's channel morphology and kinematics. Notably, the flow outside the channels is significantly reduced in the treatment experiment, and the channels are deeper (as a function of radial distance from the source) and longer. We also find that both the control and treatment channels narrow as they approach the shoreline, though the narrowing is more pronounced in the control compared to the treatment. Interestingly, the channel beds in the treatment experiment often exist below sea level in the terrestrial portion of the delta top, creating a ∼ 0.7 m reach of steady, non-uniform backwater flow. However, in the control experiment, the channel beds generally exist at or above relative sea level, creating channel movement resembling morphodynamic backwater kinematics and topographic flow expansions. Differences between channel and far-field aggradation produce a longer channel in-filling timescale for the treatment compared to the control, suggesting that the channel avulsions triggered by a peak in channel sedimentation occur less frequently in the treatment experiment. Despite this difference, the basin-wide timescale of lateral channel mobility remains similar. Ultimately, non-fluvial sedimentation on the delta top plays a key role in the channel morphology and kinematics of an experimental river delta, producing channels which are more analogous to channels in global river deltas and which cannot be produced solely by increasing cohesion in an experimental river delta.

The impact of sediment flux and calibre on flood risk in the Kathmandu Valley, Nepal

AbstractThis paper investigates how variations in sediment supply, grain size distribution and climate change affect channel morphology and flood inundation in the Nakkhu River, Kathmandu, Nepal. Climate change‐induced extreme rainfall is expected to increase flood intensity and frequency, causing severe flooding in the Kathmandu basin. The upper reaches of the Nakkhu River are susceptible to landslides and have been impacted by large‐scale sand mining. We simulate potential erosion and deposition scenarios along a 14 km reach of the Nakkhu River using the landscape evolution model CAESAR‐Lisflood with a 10 m digital elevation model, field‐derived sediment grain size data, daily discharge records and flood forecast models. In a series of numerical experiments, we compare riverbed profiles, cross‐sections, flood extent and flow depths for three scenarios (1.2‐, 85‐ and 1000‐year return period floods). For each scenario, the model is first run without sediment transport and then with sediment transport for three grain size distributions (GSDs) (observed average, finer and coarser). In all cases, the inclusion of sediment led to predicted floods of a larger extent than estimated without sediment. The sediment grain size distribution was found to have a significant influence on predicted river morphology and flood inundation, especially for lower magnitude, higher probability flood events. The results emphasise the importance of including sediment transport in hydrological models when predicting flood inundation in sediment‐rich rivers such as those in and around the Himalaya.

Deconstructing dams and disease: predictions for salmon disease risk following Klamath River dam removals

The health of fish populations and the river systems they inhabit have broad ecological, cultural, recreational, and economic relevance. This is exemplified by the iconic anadromous salmonid fishes native to the West Coast of North America. Salmon populations have been constrained since the mid nineteenth century by dam construction and water reallocation. In the Klamath River (Oregon and California, USA), a series of dams built in the early-mid 20th century cut the basin in two and blocked anadromous fish access to more than 600 river kilometers. This dramatic loss of habitat, coupled with infectious diseases and resulting epizootics, have impacted the wellbeing of these salmonid populations. In 2023-2024, the Klamath River will undergo the largest river restoration project in US history. Removal of the four lowermost dams will cause profound physical changes to the river, including flow, water temperature, and channel geomorphology. The dam removals will reconnect the lower and upper portions of the basin, and provide fish passage after a century of segregation. Reestablishment of upstream and downstream fish movements will also alter the occupancy and abundance of the salmonid hosts and their pathogens. The increased habitat availability and longer migration routes will increase duration of pathogen exposure and potential impacts on juvenile survival and adult pre-spawn mortality. However, restoration of more natural flow and sediment regimes will decrease overall fish disease risk by disrupting complex parasite life cycles. To better understand these multifarious, competing factors, we review the salmonid species in the Klamath River, and provide an overview of their historical pathogen challenges and associated diseases and use this as a framework to predict the effects of dam removals on disease dynamics. Our review and predictions are a synthesis of expertise from tribal biologists, fish health specialists and fish biologists, many of whom have lived and worked on the Klamath River for decades. We conclude with recommendations for expansion of current pathogen monitoring and research efforts to measure changes in host-pathogen dynamics basin-wide.

Building a bimodal landscape: bedrock lithology and bed thickness controls on the morphology of Last Chance Canyon, New Mexico, USA

Abstract. We explore how rock properties and channel morphology vary with rock type in Last Chance Canyon, Guadalupe Mountains, New Mexico, USA. The rocks here are composed of horizontally to near-horizontally interbedded carbonate and sandstone. This study focuses on first- and second-order channel sections, where the streams have a lower channel steepness index (ksn) upstream and transition to higher ksn values downstream. We hypothesize that differences in bed thickness and rock strength influence ksn values, both locally by influencing bulk bedrock strength and also nonlocally through the production of coarse sediment. We collected discontinuity intensity data (the length of bedding planes and fractures per unit area), Schmidt hammer rebound measurements, and measured the largest boulder at every 12.2 m elevation contour to test this hypothesis. Bedrock and boulder mineralogy were determined using a lab-based carbonate dissolution method. High-resolution orthomosaics and digital surface models (DSMs) were generated from drone and ground-based photogrammetry. The orthomosaics were used to map channel sections with exposed bedrock. The United States Geological Survey (USGS) 10 m digital elevation models (DEMs) were used to measure channel slope and hillslope relief. We find that discontinuity intensity is negatively correlated with Schmidt hammer rebound values in sandstone bedrock. Channel steepness tends to be higher where reaches are primarily incising through more thickly bedded carbonate bedrock and lower where more thinly bedded sandstone is exposed. Bedrock properties also influence channel morphology indirectly, through coarse sediment input from adjacent hillslopes. Thickly bedded rock layers on hillslopes erode to contribute larger colluvial sediment to adjacent channels, and these reaches have higher ksn values. Larger and more competent carbonate sediment armors both the carbonate and the more erodible sandstone and reduces steepness contrasts across rock types. We interpret that in the relatively steep, high-level ksn downstream channel sections, the slope is primarily controlled by the coarse alluvial cover. We further posit that the upstream low-level ksn reaches have a base level that is fixed by the steep downstream reaches, resulting in a stable configuration, where channel slopes have adjusted to lithologic differences and/or sediment armor.

The study of channeled vacuum GaAs photocathodes for enhanced electron emission properties

In this paper, we design and analyze the channeled vacuum photocathodes with novel structures towards low operating temperature, high current density, and miniaturized cathode electron sources. We simulate the characteristics of the electron emission of the channeled vacuum GaAs photocathodes in detail with the commercial CST software. Simulation results indicate that the emission current of the photocathode can increase with the optimal gate and anode voltage choices, and the emission efficiency can reach up to 63.4 %. Using this optimized structure as the benchmark, the quantum efficiency and emission efficiency are also investigated. Furthermore, we have altered the channel morphology, i.e., with the curved vacuum channel structures, to enhance the current density. We have found that the emission current density can increase significantly and reach up to 2.68 times of the regular rectangular channel. The simulation results can lay the foundation for the development of new type of micro-structured GaAs photocathodes.

Sub-20 nm ultrathin perfluorosulfonic acid-grafted graphene oxide composite membranes for vanadium redox flow batteries

Perfluorosulfonic acid (PFSA) membranes, such as Nafion, are widely used in vanadium redox flow batteries (VRFBs) because of their high proton conduction through the ion channels and excellent chemical stability. However, the high vanadium permeability of PFSA membranes induced by the randomly interconnected channels limits efficient cell operation. In this work, we demonstrate a sub-20 nm ultrathin PFSA-grafted graphene oxide/PFSA (PFSA-g-GO/PFSA) composite membrane with highly aligned ion channel morphology, which results in a 100-fold improvement in proton/vanadium ion selectivity compared to 25 μm-thick Nafion 211. In addition, the PFSA-g-GO nanosheets physically reinforce the ultrathin membrane while enabling the proton transport through the grafted PFSA ionomers, leading to stable cell operation at overall current densities from 40 to 200 mA cm−2. Especially, at a high current density of 200 mA cm−2, the PFSA-g-GO/PFSA composite membrane shows an energy efficiency (EE) of 78%, which is higher than that of Nafion 211, indicating its potential as an ion-selective membrane for VRFB.