River Migration Research Articles

Accelerated River Meander Migration on the Tibetan Plateau Caused by Permafrost Thaw

AbstractThe migration of rivers in permafrost landscapes has critical implications for riverine infrastructure, ecosystem stability, and carbon cycling, yet its magnitude and underlying mechanisms remain poorly understood. Here, we leverage four decadal satellite imagery, hydrological observations, and permafrost modeling to investigate meander migration dynamics on the Tibetan Plateau. Our data show that the migration rates of permafrost rivers have increased by 34.6% from 1987 to 2022, in response to the combined effects of increased discharge, riverbank destabilization driven by ground ice melt and extended thawing days (increased by 35 days). In contrast, rivers flowing across seasonally frozen ground exhibited a decline in migration rate by 11.1%, driven by vegetation greening and riverbank stabilization. In a future warming climate for the Tibetan Plateau, the migration rates of permafrost rivers are anticipated to further accelerate, potentially threatening riverine infrastructure safety and aquatic ecosystems, and intensifying the permafrost carbon cycle.

Numerical Analysis of the Influence of 2D Dispersion Parameters on the Spread of Pollutants in the Coastal Zone

The transport of pollutants with flowing waters is one of the most common processes in the natural environment. In general, this process is described by a system of differential equations, including the continuity equation, dynamic equations, pollutant transport equations and equations of state. For the analyzed problem of pollutant migration in wide rivers and the coastal zone, a two-dimensional model is particularly useful because the velocity and mass concentration profile is vertically averaged. In this model, taking into account the dispersion flux leads to appropriate equations, and the dispersion process is described by the dispersion tensor. Due to the transverse isotropy of the dispersion process, the coordinates of this tensor are expressed in terms of local dispersion coefficients along the direction of the velocity and in the direction perpendicular to it. Commonly used methods for determining mass dispersion coefficients refer to a gradient velocity profile, typical for rivers. However, in the coastal zone, the velocity profile changes from gradient to drift when shear stresses on the surface caused by the wind begin to dominate. The drift profile also occurs in estuaries, where there is a difference in the density of fresh and salt water. This paper analyzes the numerical solution of the two-dimensional dispersion equations in the coastal zone for the dispersion coefficients adopted for the gradient and drift velocity profiles and then assesses how this affects the final result. Four typical scenarios of pollutant migration in the coastal zone of the Bay of Puck are presented. The calculated dispersion coefficients differ significantly depending on the adopted velocity profile: for the gradient, DLG = 0.17 [m2/s], and for the drift, DLD = 89.94 [m2/s].

Holocene evolution of the buried tidal sand body in the North Jiangsu Plain of China revealed by luminescence dating

In the northern Jiangsu coastal zone of China, the buried tidal sand body (BTSB) is suggested to share a similar origin with the offshore radial sand ridge system in the southwestern Yellow Sea. However, its chronological framework remains inadequately understood. This study conducted optically stimulated luminescence (OSL) dating of both silt- and sand-sized quartz on core LDC from the southwestern end of the BTSB. Together with data from the previously studied core XYK closer to the current coastline, this study aims to clarify the chronology of the BTSB and refine its evolution history. The results indicate that in both cores, sand-sized quartz provides more reliable age estimates than silt-sized quartz for the sandy sediment layers. Additionally, the discrepancy between ages derived from the single-grain central age model and the minimum age model is smaller within the top 11 m of the core, which was deposited over the last 0.9 ka. This period corresponds well with the southern migration of the Yellow River and its sediment discharge into the Yellow Sea from 1128 to 1855 CE. It suggests that distinct sediment sources from the Yellow and Yangtze Rivers may account for the observed differences in OSL characteristics. The OSL ages reveal significant temporal variations in sedimentation rates during the Holocene, with the most rapid deposition occurring between 1.2–0.4 ka and 10–8 ka in core LDC, and between 2–1 ka in core XYK. Together with dating results from the central part of the BTSB, it reveals complex spatiotemporal variations in sediment accumulation and emphasizes the need for detailed sediment sampling and dating to fully elucidate the evolutionary history of the coastal plain.

Satellite observations of surface water dynamics and channel migration in the Yellow River since the 1980s

Study regionthe Yellow River (YR) in China. Study focusDue to climate change and human activities, YR channel morphology has undergone significant spatiotemporal variations. Yet, a comprehensive understanding of channel migration in YR and its driving factors remains unclear. Here, we developed a multi-index water extraction method to track the changes in surface water and river channel migration of YR based on Landsat imagery since the 1980s. New hydrological insights for the regionWe find that the average surface water area of YR over the past four decades is 4013 km2, with 73.5 % of permanent surface water. Notably, the surface water extent has experienced a 9 % increase since the 1980s, while the river channel has undergone a 12.2 % decrease. The YR channel’s centerline exhibits diverse change patterns across the entire basin, which can be broadly categorized into six types ranging from unchanged to reverse migration. We identify that climate, particularly temperature and precipitation, contributed 71 % of channel changes in the upper reaches, while 65 % of changes in the lower reaches are from human activities, including reservoir operations and water management policies. Our results unveil the variations in water extent and channel migration of the YR, offering new insights into the interactions between channel migration and climate change and human activities in the YR over the past four decades.

Unraveling meandering river morphodynamics: A geospatial investigation of the Madhumati river in Bangladesh

The Madhumati River, located on the lower course of the Gorai River, experiences significant erosion and accretion, leading to annual changes in its morphological characteristics within the surrounding catchment area. Our study utilized Landsat satellite data and the ArcGIS platform to investigate the morpho-dynamic alterations and meander-bend formation mechanisms of the Madhumati River. Over a period of 43 years, from 1980 to 2023, we collected cloud-free images from Landsat 3, Landsat 5, Landsat 8, and Landsat 9 using the USGS Earth Explorer. River masks were then generated using the Water Ratio Index (WRI) and Sinuosity Index (SI) methods. In addition, each bend of the river was individually digitized to understand the bend development process, rate of movement, erosion and accretion, changes in river width, and sinuosity. Our findings reveal a gradual increase in river migration over the study period, attributed to significant erosion and accretion occurring at each bend. This research indicates a greater amount of erosion and accretion in river bends, with total sediment deposition exceeding net erosion throughout the study period. Most meandering bends have experienced considerable narrowing, indicating progressive river constriction over time. The construction of the Farakka Barrage contributed to higher sediment deposition from 1980 to 1990, whereas the Kamarkhali Bridge construction provoked an increasing amount of erosion from 1990 to 2010. Sediment deposition increased between 2010 and 2020. The erosion around the downstream bends grew once again when the investigation was carried up until 2023, proving beyond a doubt that the Kalna Bridge construction had an effect on this erosion rise. The increased sinuosity index of bends suggests heightened meandering. These findings have significant implications for engineering and geological practices, including infrastructure maintenance, expansion planning, riverbank protection measures, and agricultural and land management strategies concerning the Madhumati River.

Downstream Migration Success of Atlantic Salmon Smolts in a River Catchment Highly Fragmented by Hydroelectric Impoundments

ABSTRACTRiverine habitat fragmentation by barriers, including impoundments, is common and their effects on obligate aquatic organisms are manifold. Organisms, such as Atlantic salmon (Salmo salar), that make extensive river migrations are particularly vulnerable to the effects of impoundments. In this study, we use acoustic telemetry to examine the migratory behaviour of Atlantic salmon, as they migrate to sea for the first time as juvenile ‘smolts’, in a river with a series of dams that form a complex hydropower scheme. We demonstrate that overall migration success in the River Dee catchment and particularly through standing waters was remarkably high. We speculate that high migration success in standing waters could be due to relative current speeds providing good quality directional cues to migrants. Migration success past the two dams in this study, was relatively high, although the number of unsuccessful passage attempts before a successful passage was also very high. The vast majority of smolts passed the dams when the turbines were operational. At one dam, smolts did not use an available fish pass but migrated through the generating turbines. These findings provide several routes through which generation could be managed to enhance the success of downstream smolt migration in rivers where there are similar patterns of hydrogeneration in place.

Permafrost slows Arctic riverbank erosion.

The rate of river migration affects the stability of Arctic infrastructure and communities1,2 and regulates the fluxes of carbon3,4, nutrients5 and sediment6,7 to the oceans. However, predicting how the pace of river migration will change in a warming Arctic8 has so far been stymied by conflicting observations about whether permafrost9 primarily acts to slow10,11 or accelerate12,13 river migration. Here we develop new computational methods that enable the detection of riverbank erosion at length scales 5-10times smaller than the pixel size in satellite imagery, an innovation that unlocks the ability to quantify erosion at the sub-monthly timescales when rivers undergo their largest variations in water temperature and flow. We use these high-frequency observations to constrain the extent to which erosion is limited by the thermal condition of melting the pore ice that cements bank sediment14, a requirement that will disappear when permafrost thaws, versus the mechanical condition of having sufficient flow to transport the sediment comprising the riverbanks, a condition experienced by all rivers15. Analysis of high-resolution data from the Koyukuk River, Alaska, shows that the presence of permafrost reduces erosion rates by 47%. Using our observations, we calibrate and validate a numerical model that can be applied to diverse Arctic rivers. The model predicts that full permafrost thaw may lead to a 30-100% increase in the migration rates of Arctic rivers.

Geomorphic evolution of Sutlej valley catchment in Western Himalayas: Imprint of surface processes in modulating fluvial erosion

The Sutlej River catchment in the tectonically active western Himalayas has several geomorphic signatures of river piracy and drainage reorganization across the Upper Sutlej-Zhada basin upstream. The accelerated growth of the Leo-Pargil Horst across the Kaurik Chango-fault (KC-fault) Zone and affected regional tectonics triggered enormous incisions, causing southward migration of the present Sutlej River, which is highly infested by bedrock landslides and debris flows and evolves as a very steep valley catchment. In order to understand the changing regional landscape and identify the tectonic perturbation over the channels, we evaluate the slope-break knickpoints in the Sutlej River profile. Furthermore, we model the presence of an elevated low-relief relict landscape in the Upper Sutlej-Zhada basin and the rapid incising lower Sutlej valley catchment using the Celerity model. The observation suggests that major knickpoints at ~2000–3000 m elevation comprise the fluvial erosion process, while higher elevation knickpoints recommend the hillslope process. In order to understand how fluvial erosion and surface process imprints have changed the landscape over time, we spatially correlate terrestrial datasets, such as rates of denudation and exhumation ages, with topographic metrics and climate variables. We observe a strong correlation between the pattern of denudation rates and the conditioning factors that modulate the surface processes. Increased channel erosion, high stream power, topographic metrics, and the occurrence of bedrock landslides over a regional structural disruption exhibit a positive spatial relationship, but their role in regional drainage capture, tectonic uplift, and the gradation process remains poorly understood.

Determinants of riverine migration success by Atlantic salmon (Salmo salar) smolts from rivers across the UK and Ireland.

There is some evidence that the river migration success of Atlantic salmon smolts, on their first migration to sea, varies both spatially and temporally. However, we have only a poor understanding of what may be driving this variation. In this study, we used acoustic telemetry to quantify the spatial and temporal variations in river migration success in Atlantic salmon smolts on their first migration to sea. In total 4120 Atlantic salmon smolts migrating through 22 rivers in Scotland, England, Ireland, and Northern Ireland over multiple years were included in the study. Individuals were defined as successful migrants if detected leaving the river to enter marine waters. The results show significant temporal (up to 4 years) and spatial (river) variations in migration success, with overall between-river migration success varying from 3.4% to 97.0% and between years from 3.4% and 61.0%. Temporal variation in migration success was river specific, with some rivers being more temporally stable (exhibiting little variation between years) than others. Across all rivers and years, individual migration success was predicted positively by body condition and negatively by tag burden. The rate of migration success for a population (migration success standardized to a common river distance [proportion km-1]) was predicted by a number of environmental factors. The proportion of river catchment that comprised wetland and woodland positively predicted migration success, whereas the proportion of grassland and peatland in a catchment negatively predicted the rate of migration success. Although the mechanisms through which these effects may be operating were not directly examined in this study, we discuss some potential routes through which they may occur.

Mercury stocks in discontinuous permafrost and their mobilization by river migration in the Yukon River Basin

Abstract Rapid warming in the Arctic threatens to destabilize mercury (Hg) deposits contained within soils in permafrost regions. Yet current estimates of the amount of Hg in permafrost vary by ~4 times. Moreover, how Hg will be released to the environment as permafrost thaws remains poorly known, despite threats to water quality, human health, and the environment. Here we present new measurements of total mercury (THg) contents in discontinuous permafrost in the Yukon River Basin in Alaska. We collected riverbank and floodplain sediments from exposed banks and bars near the villages of Huslia and Beaver. Median THg contents were 49+13/-21 ng THg g sediment−1 and 39 +16 /-18 ng THg g sediment−1 for Huslia and Beaver, respectively (uncertainties as 15th and 85th percentiles). Corresponding THg:organic carbon ratios were 5.4+2 /-2.4 Gg THg Pg C-1 and 4.2+2.4 /-2.9 Gg THg Pg C-1. To constrain floodplain THg stocks, we combined measured THg contents with floodplain stratigraphy. Trends of THg increasing with smaller sediment size and calculated stocks in the upper 1 m and 3 m are similar to those suggested for this region by prior pan-Arctic studies. We combined THg stocks and river migration rates derived from remote sensing to estimate particulate THg erosional and depositional fluxes as river channels migrate across the floodplain. Results show similar fluxes within uncertainty into the river from erosion at both sites (95 +12 /-47 kg THg yr-1 and 26 +154/-13 kg THg yr-1 at Huslia and Beaver, respectively), but very different fluxes out of the river via deposition in aggrading bars (60 +40/-29 kg THg yr-1 and 10+5.3/-1.7 kg THg yr-1). Thus, a significant amount of THg is liberated from permafrost during bank erosion, while a variable but generally lesser portion is subsequently redeposited by migrating rivers.

Prediction of Dynamics of Riverbank Erosion: A Tale of the Riverine Town Chandpur Sadar

River channel migration often occurs inside the floodplain areas of the river. The structural changes occurring in rivers within floodplain zones serve as a significant ecological signal of their tremendous impact on both ecological and human survival. The aim of the research is to assess the spatial and temporal fluctuations of the Meghna River's bankline from 1990 to 2020 (for 30 years), and to predict the future bankline position. The Landsat imageries from USGS were used for this study. The bankline was extracted from satellite imageries (Landsat) using Modified Normalized Difference Water Index (MNDWI) indices. The variations in bankline dynamics were assessed through the application of Net Shoreline Movement (NSM) and End Point Rate (EPR) analyses using the Digital Shoreline Analysis System (DSAS). Predictive modeling was conducted utilizing the Modified EPR Model, with validation performed via the Root Mean Square Error (RMSE) technique. Adjustment of errors was achieved by employing error coefficients tailored to each individual transect. Over the past three decades, the cumulative river erosion in Chandpur Sadar amounted to 18.03 square kilometers, with the highest Net Shoreline Movement (NSM) recorded at −1979.62 m during the study period. The forecasted maximum Net Shoreline Movement (NSM) is anticipated to be −495.79 m, signifying that the transect is associated with erosion, resulting in landward movement. Conversely, the minimum NSM is projected to be −1.01 m. The most significant movement is expected to occur in Puran Bazar, while the least movement is foreseen in Bakharpur. On average, the NSM across all transects is predicted to be −76.25 m. This study presents a cost-effective approach for evaluating the changes in river erosion over time. This technique may be valuable for policymakers in developing effective plans to reduce the negative impacts of erosion-related risks.

Findings from a National Survey of Canadian perspectives on predicting river channel migration and river bank erosion

AbstractRiver bank erosion and river channel migration are geomorphic processes that can result in significant hazards when there are impacts to humans or infrastructure. Unlike flooding, there are limited national guidelines in Canada that provide recommendations on how to best assess riverine erosion hazards. Instead regional and local jurisdictions rely on techniques based on varying levels of policy maturity. The current study presents findings of a nationwide survey on Canadian perspectives on predicting river channel migration and river bank erosion which received more than 40 responses from across Canada. Results showed that predictions were used for a variety of purposes, but that confidence intervals were rarely reported. Aerial imagery and survey‐based methods were the well‐known and widely‐used techniques for predicting river channel migration and river bank erosion. A majority of respondents identified both technical and financial challenges to improving accuracy including client willingness to pay, data quality/cost issues, and hydrologic changes due to land use and climate change. Several recommendations for improving best‐practices are provided, with a focus on the development of erosion datasets, improving data access, and providing additional training opportunities.

Evolution and controlling factors of natural levees during the past 4500 years derived from lowland archaeological ruins in central Kanto Plain, Japan

Lowland archaeological ruins are frequently used in conjunction with sediment cores to reconstruct geomorphological evolution on alluvial plains. Lowland ruins are, as a rule, heterogeneously distributed across alluvial plains and retain short chronological records when compared to sediment cores. Along the historic banks of the Tone River, in the central Kanto Plain, thorough surveying prior to major construction projects in the Tokyo metropolitan area uncovered a dense swath of lowland archaeological ruins. This study demonstrates the evolution of natural levees during the past 4.5 kyr by compiling data from uniformly distributed lowland archaeological ruins in the central Kanto Plain. The location and age of 774 lowland archaeological ruins and 101 radiocarbon dates from surficial fluvial sediments in 42 sediment cores were compiled and arranged chronologically. As a result, levees and river terraces aged < 4.5 ka were found to be contiguous with modern sedimentology in the Arakawa Lowland, while relatively young natural levees aged < 2.8 ka are contiguous with the present Nakagwa Lowland. The Tone River migrated from the Arakawa Lowland to the Nakagawa Lowland at ∼5 ka. Subsequently, sea levels lowered between 4 ka and 3 ka. Due to sea level lowering, a minor tributary of the Tone River partially eroded the alluvial plain, and relatively old geomorphology persisted in the Arakawa Lowland. In contrast, in the Nakagawa Lowland, the major tributary of the Tone River eroded the entire alluvial plain. Following sea-level rises up to 2 ka, natural levees aggraded and formed new surface sediments in the Nakagawa Lowland due to large sediment discharge from the major tributary of the Tone River. Natural levee evolution in the central Kanto Plain is influenced by both river migration and sea-level fluctuation.

Geomorphic risk maps for river migration using probabilistic modeling – a framework

Abstract. Lateral migration of meandering rivers poses erosional risks to human settlements, roads, and infrastructure in alluvial floodplains. While there is a large body of scientific literature on the dominant mechanisms driving river migration, it is still not possible to accurately predict river meander evolution over multiple years. This is in part because we do not fully understand the relative contribution of each mechanism and because deterministic mathematical models are not equipped to account for stochasticity in the system. Besides, uncertainty due to model structure deficits and unknown parameter values remains. For a more reliable assessment of risks, we therefore need probabilistic forecasts. Here, we present a workflow to generate geomorphic risk maps for river migration using probabilistic modeling. We start with a simple geometric model for river migration, where nominal migration rates increase with local and upstream curvature. We then account for model structure deficits using smooth random functions. Probabilistic forecasts for river channel position over time are generated by Monte Carlo runs using a distribution of model parameter values inferred from satellite data. We provide a recipe for parameter inference within the Bayesian framework. We demonstrate that such risk maps are relatively more informative in avoiding false negatives, which can be both detrimental and costly, in the context of assessing erosional hazards due to river migration. Our results show that with longer prediction time horizons, the spatial uncertainty of erosional hazard within the entire channel belt increases – with more geographical area falling within 25 % &lt; probability &lt; 75 %. However, forecasts also become more confident about erosion for regions immediately in the vicinity of the river, especially on its cut-bank side. Probabilistic modeling thus allows us to quantify our degree of confidence – which is spatially and temporally variable – in river migration forecasts. We also note that to increase the reliability of these risk maps, we need to describe the first-order dynamics in our model to a reasonable degree of accuracy, and simple geometric models do not always possess such accuracy.

Analysis of land use change and its impact on channel morphology of Ginzo River Basin, Nigeria

ABSTRACT The study examined land use change and its impact on channel morphology of Ginzo basin. Multi-decadal (1980, 1990, 2000, 2010, 2020) Landsat imageries were rectified for radiometric and geometric errors, classified, and analyzed to assess land use change, river channel area, length, channel width, centerline migration area, and distance using the ArcGIS software. The results show an increase in the built-up area, bare land, and water bodies by 21.9%, 27.7%, and 1.1% respectively between 1980 and 2020. Farmland and forest, however, decreased by 11.1% and 38.2%. River channel area, length, and width increased and decreased over the study period. The center line migrated eastward in the upstream and midstream while shifting westward in the downstream sections. Variations in channel area were attributed to the forest and bare land, constituting 86% and 14%, respectively. Changes in channel length were influenced by farmland, bare land, built-up area, and water bodies contributing 32.8%, 30.8%, 8.6%, and 27.8%, respectively. Channel width adjustments were explained by farmland and the built-up area contributing 70.9% and 29.1%, respectively. Forest and farmland constitute 52.8% and 48.2% of variations in river migration area. Conclusively, Land use impact models aid in predicting channel adjustments, offering insights for river basin management.

Post-glacial small delta process uncovered by luminescence and radiocarbon chronology of core sediments from coastal South China Sea

Reliable chronology is crucial for reconstructing delta processes. The past decades witnessed a boost of dating works on the most economically influential large deltas (i.e., subaerial area >1000 km2), but chronology remains lacking on many small deltas (i.e., subaerial area <1000 km2) that are also densely populated and economically active. Luohe River Delta (LRD) in the coastal South China Sea is such a small delta, whose evolution concerns hundreds of thousands of people, and literally no reliable dating results have been reported to support research of its processes. Herein, dating work combining radiocarbon (14C) on mollusk shells and quartz Optically Stimulated Luminescence (OSL) methods were performed on core LFZK06 from LRD, to test applicability of both methods by age comparison and to establish a chronological framework, using Bayesian age-depth models, of LRD for the first time. 14C ages are systematically c. 0.5–1 ka younger than OSL ages from the same depths. Such young bias of 14C ages in LRD contrasts with previously observed overestimated 14C results in the nearby Pearl River Delta (PRD), likely due to the distinction in bedrock types between Luohe River (granites and sandstones only) and Pearl River (limestone prevalence causing hardwater effect) drainages. Ages of core LFZK06 span from 57 ± 7 ka to 3.42 ± 0.05 cal ka BP and contain a hiatus between 57±7–11.9 ± 1.7 ka. Holocene deltaic sequence of the core shows three-stage sedimentary processes: (1) rapid deposition of prodelta/delta front sediments at 10.2‐0.4+0.5 ka–7.7‐0.3+0.4 ka related to rapid sea level rise, (2) hiatus during 7.7‐0.3+0.4 ka–5.7‐0.8+0.5 ka likely due to reduced sediments input or river channel migration, (3) rapid accumulation of delta plain sediments during 5.7‐0.8+0.5 ka–3.42‐0.85+0.42 ka reflecting depocenter shift toward core location. Moreover, changes of quartz OSL sensitivity were detected, indicative of sediment provenance transition. A change in sediment source from nearby granite weathering towards fluvial long-transported materials occurred at a depth of 24.7 m, with low quartz OSL sensitivity in the gravelly layer below (11.9 ± 1.7 ka) and one magnitude higher quartz OSL sensitivity in prodelta deposits above (10.2‐0.4+0.5 ka).

A global dataset of carbon pumping by the world’s largest tropical rivers

The eco-morphodynamic activity of large tropical rivers interacts with riparian vegetation causing implications for the carbon cycle within inland waters. Through a multi-temporal analysis of satellite data spanning the years 2000–2019, we analyzed rivers exceeding 200 m in width across the tropical regions, revealing a Carbon Pump mechanism driving an annual mobilization of 12.45 million tons of organic carbon. The study identifies fluvial eco-morphological signatures as proxies for carbon mobilization, emphasizing the link between river migration and carbon dynamics. To enhance accessibility, our results are encapsulated in a visually compelling WebGIS application, offering a comprehensive understanding of the eco-geomorphological influences on the global carbon cycle within large tropical rivers. Our findings are instrumental in determining the carbon intensity of future hydropower dams, thereby contributing to informed decision-making in the realm of sustainable energy infrastructure. This study elucidates the intricate relationships that govern the nexus of tropical river dynamics, riparian ecosystems, and the global carbon cycle.

Bank strength variability and its impact on the system-scale morphodynamics of the upper Amazon River in Brazil

Large anabranching rivers form channels in sediments of varying strength, resulting from erosional and depositional processes that act over geological time scales. Although bank strength variability is known to affect channel morphodynamics, its impact on the migration of large sand-bed rivers remains poorly understood. We report the first in situ measurements of bank strength from an ∼100-km-long reach of the Solimões River, the Brazilian Amazon River upstream of Manaus. These show that cohesive muds in Pleistocene terraces along the river’s right margin have bank strengths as much as three times greater than Holocene floodplain deposits composing the left bank. Image analysis suggests these resistant outcrops determine channel-bar dynamics: channel widening and bar deposition are inhibited, which lowers planform curvature and reduces erosion of the opposing bank. Planform analysis of the 1600-km-long Solimões River between 1984 and 2021 shows that where the channel is associated with Pleistocene terraces, lower rates of bank erosion and bar deposition are evident. Heterogeneity in bank strength is thus a first-order control on the large-scale morphodynamics of the world’s largest lowland river.

A physics-based model for fluvial valley width

Abstract. The width of fluvial valley floors is a key parameter to quantifying the morphology of mountain regions. Valley floor width is relevant to diverse fields including sedimentology, fluvial geomorphology, and archaeology. The width of valleys has been argued to depend on climatic and tectonic conditions, on the hydraulics and hydrology of the river channel that forms the valley, and on sediment supply from valley walls. Here, we derive a physically based model that can be used to predict valley width and test it against three different datasets. The model applies to valleys that are carved by a river migrating laterally across the valley floor. We conceptualize river migration as a Poisson process, in which the river changes its direction stochastically at a mean rate determined by hydraulic boundary conditions. This approach yields a characteristic timescale for the river to cross the valley floor from one wall to the other. The valley width can then be determined by integrating the speed of migration over this timescale. For a laterally unconfined river that is not uplifting, the model predicts that the channel-belt width scales with river flow depth. Channel-belt width corresponds to the maximum width of a fluvial valley. We expand the model to include the effects of uplift and lateral sediment supply from valley walls. Both of these effects lead to a decrease in valley width in comparison to the maximum width. We identify a dimensionless number, termed the mobility–uplift number, which is the ratio between the lateral mobility of the river channel and uplift rate. The model predicts two limits: at high values of the mobility–uplift number, the valley evolves to the channel-belt width, whereas it corresponds to the channel width at low values. Between these limits, valley width is linked to the mobility–uplift number by a logarithmic function. As a consequence of the model, valley width increases with increasing drainage area, with a scaling exponent that typically has a value between 0.4 and 0.5, but can also be lower or higher. We compare the model to three independent datasets of valleys in experimental and natural uplifting landscapes and show that it closely predicts the first-order relationship between valley width and the mobility–uplift number.

Late‐Holocene counterpoint deposition in the Lower Rhine River

ABSTRACTChannel deposits from meandering rivers have proven to be far more complex than the well‐known lithofacies model consisting of coarse‐grained channel, gravelly channel‐lag and fine‐grained overbank deposits. Sharp bends in rivers are subject to different hydraulic processes than bends with lower curvatures, enabling erosion of inner banks and deposition of fine‐grained sediments in the outer bend, resulting in downstream migration of river bends. This phenomenon is known as counterpoint deposition, forming counterpoint bars. This research investigates whether scroll bars associated with a sharp bend in the Lower Rhine River, The Netherlands, are such a counterpoint‐bar deposit. A counterpoint bar is expected based on: (i) the surface morphology of the scroll bar; (ii) the confinement of the river course by an ice‐pushed ridge resulting in a sharp bend; and (iii) the archaeological context of successive Roman settlements atop the ice‐pushed ridge, potentially moving downstream with the migrating river bend. This hypothesis is tested through detailed borehole descriptions combined with optically stimulated luminescence dating, the latter being a novel approach to identifying counterpoint deposits. The deposits consist of clays and sandy clays with fine sand laminations, and sporadic larger sand bodies. Further upstream these deposits grade into channel deposits dominated by coarser sands with gravels. These lithologies are explained using earlier proposed mechanisms for counterpoint formation; substrata match those described in previously studied counterpoint deposits and their point bar counterparts. Optically stimulated luminescence dates indicate that the Lower Rhine River bend migrated downstream, confirming counterpoint deposition. A migration rate of 1.93 m/year was established through weighted linear regression. This study demonstrates the potential of optically stimulated luminescence dating to investigate counterpoint bar presence. The identified counterpoint bars and associated bend migration provide insight into meandering river dynamics that is crucial for river management and in aiding river restoration and rewilding initiatives.