Julian Leyland

Despite significant advances in the study of meandering rivers, the precise mechanisms by which erosion and sedimentation interact to drive meander migration remain poorly understood. Two long-standing competing theories attempt to explain this interaction: one suggests that inner-bank sediment deposition precedes outer-bank erosion (bar push), while the other posits that outer-bank erosion initiates inner-bank sedimentation (bank pull). To date, empirical research addressing which of these mechanisms dominates in real-world environments has predominantly focused on a small number of bends and at limited temporal scales. In this paper, we identify analyse the occurrence of bank pull versus bar push across 4,923 river bends worldwide. We estimated outer-bank erosion and inner-bank sedimentation rates using a 38-year time series of Landsat data, from which classifications of bank pull and bar push were derived through Dynamic Cross-Correlation analysis. Of the 4,923 bends analyzed, 20 % were classified as bank pull dominated, 16 % as bar push dominated, whilst the remaining 63 % showed no clear migration signal. We also identified river characteristics that control the relative frequency of push versus pull migrating bends. Our findings indicate that vegetated bends, with higher soil compactness surrounded by sandy substrates and situated in rivers with slower flow velocities, are more likely to exhibit bend migration via bar push, where sediment deposition along the inner bank plays a dominant role. In contrast, less densely vegetated rivers with higher flow velocities and lower soil compactness show a higher occurrence of bends migrating via bank pull. This means that most bar-push migrating bends are located in densely vegetated tropical environments, with bar pull tending to dominate in other regions. This study represents the first quasi-global empirical framework capable of distinguishing the temporal sequencing of erosion and sedimentation across thousands of river bends using long-term satellite observations, providing valuable insights that could be used to improve river dynamics modelling and inform more effective river management strategies.

Despite significant advances in the study of meandering rivers, the precise mechanisms by which erosion and sedimentation interact to drive meander migration remain poorly understood. Two long-standing competing theories attempt to explain this interaction: one suggests that inner-bank sediment deposition precedes outer-bank erosion (bar push), while the other posits that outer-bank erosion initiates inner-bank sedimentation (bank pull). To date, empirical research addressing which of these mechanisms dominates in real-world environments has predominantly focused on a small number of bends and at limited temporal scales. In this paper, we identify analyse the occurrence of bank pull versus bar push across 4,923 river bends worldwide. We estimated outer-bank erosion and inner-bank sedimentation rates using a 38-year time series of Landsat data, from which classifications of bank pull and bar push were derived through Dynamic Cross-Correlation analysis. Of the 4,923 bends analyzed, 20 % were classified as bank pull dominated, 16 % as bar push dominated, whilst the remaining 63 % showed no clear migration signal. We also identified river characteristics that control the relative frequency of push versus pull migrating bends. Our findings indicate that vegetated bends, with higher soil compactness surrounded by sandy substrates and situated in rivers with slower flow velocities, are more likely to exhibit bend migration via bar push, where sediment deposition along the inner bank plays a dominant role. In contrast, less densely vegetated rivers with higher flow velocities and lower soil compactness show a higher occurrence of bends migrating via bank pull. This means that most bar-push migrating bends are located in densely vegetated tropical environments, with bar pull tending to dominate in other regions. This study represents the first quasi-global empirical framework capable of distinguishing the temporal sequencing of erosion and sedimentation across thousands of river bends using long-term satellite observations, providing valuable insights that could be used to improve river dynamics modelling and inform more effective river management strategies.

Despite significant advances in the study of meandering rivers, the precise mechanisms by which erosion and sedimentation interact to drive meander migration remain poorly understood. Two long-standing competing theories attempt to explain this interaction: one suggests that inner-bank sediment deposition precedes outer-bank erosion (bar push), while the other posits that outer-bank erosion initiates inner-bank sedimentation (bank pull). To date, empirical research addressing which of these mechanisms dominates in real-world environments has predominantly focused on a small number of bends and at limited temporal scales. In this paper, we identify analyse the occurrence of bank pull versus bar push across 4,923 river bends worldwide. We estimated outer-bank erosion and inner-bank sedimentation rates using a 38-year time series of Landsat data, from which classifications of bank pull and bar push were derived through Dynamic Cross-Correlation analysis. Of the 4,923 bends analyzed, 20 % were classified as bank pull dominated, 16 % as bar push dominated, whilst the remaining 63 % showed no clear migration signal. We also identified river characteristics that control the relative frequency of push versus pull migrating bends. Our findings indicate that vegetated bends, with higher soil compactness surrounded by sandy substrates and situated in rivers with slower flow velocities, are more likely to exhibit bend migration via bar push, where sediment deposition along the inner bank plays a dominant role. In contrast, less densely vegetated rivers with higher flow velocities and lower soil compactness show a higher occurrence of bends migrating via bank pull. This means that most bar-push migrating bends are located in densely vegetated tropical environments, with bar pull tending to dominate in other regions. This study represents the first quasi-global empirical framework capable of distinguishing the temporal sequencing of erosion and sedimentation across thousands of river bends using long-term satellite observations, providing valuable insights that could be used to improve river dynamics modelling and inform more effective river management strategies.

Despite significant advances in the study of meandering rivers, the precise mechanisms by which erosion and sedimentation interact to drive meander migration remain poorly understood. Two long-standing competing theories attempt to explain this interaction: one suggests that inner-bank sediment deposition precedes outer-bank erosion (bar push), while the other posits that outer-bank erosion initiates inner-bank sedimentation (bank pull). To date, empirical research addressing which of these mechanisms dominates in real-world environments has predominantly focused on a small number of bends and at limited temporal scales. In this paper, we identify analyse the occurrence of bank pull versus bar push across 4,923 river bends worldwide. We estimated outer-bank erosion and inner-bank sedimentation rates using a 38-year time series of Landsat data, from which classifications of bank pull and bar push were derived through Dynamic Cross-Correlation analysis. Of the 4,923 bends analyzed, 20 % were classified as bank pull dominated, 16 % as bar push dominated, whilst the remaining 63 % showed no clear migration signal. We also identified river characteristics that control the relative frequency of push versus pull migrating bends. Our findings indicate that vegetated bends, with higher soil compactness surrounded by sandy substrates and situated in rivers with slower flow velocities, are more likely to exhibit bend migration via bar push, where sediment deposition along the inner bank plays a dominant role. In contrast, less densely vegetated rivers with higher flow velocities and lower soil compactness show a higher occurrence of bends migrating via bank pull. This means that most bar-push migrating bends are located in densely vegetated tropical environments, with bar pull tending to dominate in other regions. This study represents the first quasi-global empirical framework capable of distinguishing the temporal sequencing of erosion and sedimentation across thousands of river bends using long-term satellite observations, providing valuable insights that could be used to improve river dynamics modelling and inform more effective river management strategies.

Study RegionThe Vietnamese Mekong Delta (VMD).Study focusThis study quantifies bedload transport and its hydro-morphodynamic controls in the Tien and Hau rivers of the VMD using repeated MBES surveys and dune tracking. Statistical analysis and regional calibration of empirical equations were applied to identify controls and improve bedload prediction under tide-influenced, sediment-deficient conditions.New hydrological insightsThis study presents the first delta-wide, field-based quantification of bedload transport across the main rivers of the Vietnamese Mekong Delta, utilising sequential multibeam bathymetric surveys and dune tracking. A pronounced episodic characteristic marks bedload transport, with upwards of 80% of annual sediment flux occurring during the seasonal flood pulse. The bed material exhibits progressive fining downstream, transitioning from medium sand to fine silt. This is consistent with observed decreases in dune volume, diminished migration rates, and reduced transport potential, coinciding with intensifying tidal effects near the estuary. Dune migration velocity stands out as the principal factor controlling bedload transport, while the Shields parameter and dune morphology contribute additional controls on transport variability. Bedload transport equations overestimate under low-gradient, tidal conditions found in the Vietnamese Mekong Delta, though regional recalibration leads to marked improvements in predictive capabilities. This research introduces new parameters that restrict morphodynamic modeling, thereby furnishing a more robust framework for sediment budget evaluations and responsible sand extraction management in deltaic rivers with limited sediment supply.

Bankfull discharge, the maximum flow a river can convey before spilling over its banks, is central to modelling flood risk and understanding river-channel evolution. Global flood inundation models assume a 2-year return period for bankfull conditions, but this assumption remains untested globally. Here we use observations and machine learning to estimate bankfull discharge at ~1-km resolution along a recently developed global river network. We show that the widely used 2-year discharge reasonably approximates bankfull-flow magnitude, but bankfull return periods vary substantially within and across climate zones. Bankfull conditions occur more frequently in tropical and temperate regions (median return periods of 1.5 and 1.8 years; interquartile ranges of 2.5 and 3.2 years, respectively) and less frequently in cold and arid regions (2.8 and 4.3 years; interquartile ranges of 4.8 and 6.0 years). This variation across climate zones provides a basis for improving the representation of channel capacity in global flood models.

Despite significant advances in the study of meandering rivers, the precise mechanisms by which erosion and sedimentation interact to drive meander migration remain poorly understood. Two long-standing competing theories attempt to explain this interaction: one suggests that inner-bank sediment deposition precedes outer-bank erosion (bar push), while the other posits that outer-bank erosion initiates inner-bank sedimentation (bank pull). To date, empirical research addressing which of these mechanisms dominates in real-world environments has predominantly focused on a small number of bends and at limited temporal scales. In this paper, we identify analyse the occurrence of bank pull versus bar push across 4,923 river bends worldwide. We estimated outer-bank erosion and inner-bank sedimentation rates using a 38-year time series of Landsat data, from which classifications of bank pull and bar push were derived through Dynamic Cross-Correlation analysis. Of the 4,923 bends analyzed, 20 % were classified as bank pull dominated, 16 % as bar push dominated, whilst the remaining 63 % showed no clear migration signal. We also identified river characteristics that control the relative frequency of push versus pull migrating bends. Our findings indicate that vegetated bends, with higher soil compactness surrounded by sandy substrates and situated in rivers with slower flow velocities, are more likely to exhibit bend migration via bar push, where sediment deposition along the inner bank plays a dominant role. In contrast, less densely vegetated rivers with higher flow velocities and lower soil compactness show a higher occurrence of bends migrating via bank pull. This means that most bar-push migrating bends are located in densely vegetated tropical environments, with bar pull tending to dominate in other regions. This study represents the first quasi-global empirical framework capable of distinguishing the temporal sequencing of erosion and sedimentation across thousands of river bends using long-term satellite observations, providing valuable insights that could be used to improve river dynamics modelling and inform more effective river management strategies.

More than one billion people are exposed to flood risk globally, with this number projected to double by 2050. Global flood models underpin risk assessment and adaptation planning, yet typically assume that river bankfull capacity corresponds to a fixed two-year return period, neglecting spatial and temporal variability in channel characteristics. Here, we evaluate how inundated areas and population exposures respond when forced with empirically-derived bankfull capacities in the Mississippi basin using the Fathom Global Flood Model. We find that present-day bankfull flows generally correspond to return periods of less than one year, leading to systematic underestimation of flood extent (9–152%) and exposure (15–472%) across 5-, 20- and 100-year flood events, with the largest discrepancies for more frequent floods. We further show that historical changes in channel morphology can influence flood impacts at magnitudes comparable to projected climate change over multi-decadal timescales, depending on emission scenarios. Our work highlights a key structural limitation in current global flood modelling frameworks with implications for risk assessments.

Despite significant advances in the study of meandering rivers, the precise mechanisms by which erosion and sedimentation interact to drive meander migration remain poorly understood. Two longstanding competing theories attempt to explain this interaction: one suggests that inner-bank sediment deposition precedes outer-bank erosion (bar push), while the other posits that outer-bank erosion initiates inner-bank sedimentation (bank pull). To date, research addressing which of these mechanisms dominates in real environments has predominantly focused on a small number of bends and at limited temporal scales, leading to inconclusive results. In this paper, we analyse the occurrence of bank pull versus bar push across 4,923 river bends worldwide. This was done by estimating outerbank erosion and inner-bank sedimentation rates using a 38-year time series of Landsat data, from which classifications of bank pull and bar push were derived through Dynamic Cross-Correlation analysis. We found that both bank pull and bar push occur frequently in a wide range of natural environments, but with a slight dominance (55.7% of bends) of bank pull over bar push (47.3%). Nevertheless, we also identify subtle patterns in the relative frequency of push versus pull migrating bends based on river characteristics. Vegetated rivers with slower, less variable, flow and finer boundary materials are more likely to exhibit migration via bar push, where sediment deposition along the inner bank plays a dominant role. In contrast, less densely vegetated rivers with faster, more variable flows and with coarser boundary materials, show a higher occurrence of bends migrating via bank pull. This means that most bar-push migrating bends are located in densely-vegetated tropical environments, with bar pull tending to dominate in other regions. This study represents the first largescale analysis of bank pull and bar push in real rivers, providing valuable insights that could be used to improve river dynamics modelling and inform more effective river management strategies.