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We explore the existence of a single width–discharge regime relation for alluvial rivers of braided and meandering patterns. The study relies on the field measurement of a channel's cross section geometry (width, depth), discharge, and grain size of 98 individual threads of braided and meandering rivers from the Ganga–Brahmaputra plains of the Himalayan Foreland. Using this data set, we show that, irrespective of the diverse climatic and geologic setting along the strike, the braided and meandering threads share statistically indistinguishable regime relations and scale according to Lacey's law. To explain the observed trend in this empirical relationship, we use the threshold theory introduced by Glover and Florey (1951) . Using this theory we detrend our data with respect to discharge to produce a statistically homogeneous ensemble of width measurements. The statistical distribution of the detrended width is similar for braided and meandering threads of the entire plains of the Foreland. This suggests that when we decompose a braided river into individual threads, each of these resemble single-thread meandering rivers. Based on this study, we conclude that the individual threads of braided and meandering rivers of the Himalayan Foreland are geometrically comparable and share a common width–discharge regime relation. [ABSTRACT FROM AUTHOR]

Abstract: Near-future climate change will affect the discharge and base level of rivers and thus cause channel changes. The nature and pace of such changes can be simulated using morphodynamic models. As part of an investigation of how the changing hydrology of the St-Lawrence River, Quebec, Canada, will affect its tributaries we have made additions and modifications to a one-dimensional morphodynamic model developed for gravel-bed rivers (SEDROUT). The changes allow simulation of sand-bed rivers, variable discharge, downstream water level fluctuations, and flow and sediment routing in channels with islands. A revised formulation for calculating the grain size distributions of the surface and subsurface material is presented to allow for alternating sedimentation and erosion. We test the enhanced model using small-scale simulations and present-day conditions in four tributaries of the St-Lawrence River. The model is calibrated and validated for the tributaries and the capability to simulate river morphology over a 100-year period is tested. Good validation agreement on water level, cross-sectional mean velocity, and sediment transport rate is obtained for the four tributaries of the St-Lawrence River. With these modifications, modelling a very wide range of river morphodynamic problems is now possible. [Copyright &y& Elsevier]

This work investigates the channel changes of Alpine rivers from the end of the Little Ice Age (1850s) to the 1950s, with the aim to determine the possible role of climatic variations occurred in this period before the onset of anthropic pressures (i.e., dams, check-dams, bank protections, and gravel mining). The research was conducted on 17 river catchments of South Tyrol (northern Italy), glaciated and unglaciated. A multitemporal GIS analysis approach was adopted to assess the morphological changes (in terms of channel width and pattern) from three different sources: (i) Austrian cadastral map (1858), (ii) maps from the Italian Institute of Military Geography (1917–1925), and (iii) two aerial photo sets taken in 1945 and 1954. The analysed river network (a total of 480 km) was subdivided into 162 morphologically homogeneous reaches (76 confined, 81 partly confined, and 5 unconfined), with lengths ranging from 630 to 5500 m, slope from 0.3 to 24%, and drained area from 20 to ~ 4000 km 2 . The statistical relationships among morphological changes and reach- and basin-scale factors were analysed by univariate and multivariate methods, and the relationships between width changes and 36 controlling factors were explored using Principal Component Analysis. The variability in width and morphological pattern changes were very pronounced between and within single rivers, highlighting the value of such a large data set. Overall, the analysed rivers varied their morphological pattern, mostly exhibiting a shift from multithread/transitional to single-thread patterns, but unchanged planform types were also common. Variations in channel width varied substantially among the analysed rivers, which featured narrowing (slightly prevailing) and widening (the least common) as well as many cases of very limited changes. Channel width variations appear statistically, although weakly, related to some morphometric variables; and significant differences emerge comparing glaciated vs. unglaciated basins. Climate-related variations (glacier dynamics and channel disturbance frequency) are argued to be the dominant factors that affected channel variations. [ABSTRACT FROM AUTHOR]

Anabranching rivers are defined as a system of multiple channels separated by stable alluvial islands. While substantial progress has been made in developing a physics-based understanding of what drives the differences between meandering and braided river channels, anabranching rivers have not been well-integrated into these models. Here, we propose that alluvial bar growth on the floodplain may be a precursor for the formation of anabranching rivers. Alluvial bar growth strongly depends on the aspect ratio of the flow (width divided by depth) and rivers with wide floodplains have flows with a large aspect ratio. Consistent with this idea, remotely sensed measurements of floodplain width of four rivers from different climatic and tectonic settings show that anabranching river patterns are often associated with relatively wide floodplains. To explore the physics behind that empirical relationship we carried out two sets of morphodynamic numerical simulations using boundary conditions from field-scale modern anabranching rivers spanning different climatic and geologic settings as well as hypothetical floodplain widths. Results from the simulations show that, for a given flood discharge, widening the floodplain changes the river pattern from single channel to multi-threaded with mobile bars to multi-channeled with immobile islands. Multi-channeled patterns arise because the emergence of bars causes flow bifurcation. Subsequent bifurcation instability leads to the emergence of multiple stable channels. As the channels increase their cross-sectional area, shields stresses on intervening bars are reduced until the bars stabilize into islands. We suggest that the presence of stable islands allows vegetation to grow or cohesive sediment to accumulate leading to enhanced channel bank strength and a stable anabranching pattern. Our results suggest that alluvial bar growth can be a precursor to formation of anabranching rivers. Compared with field measurements our simulations accurately predict the number of active channels to within ~ 20% which seems to support the idea that some anabranching rivers may originate from alluvial bar growth. [ABSTRACT FROM AUTHOR]

The freedom space concept applies hydrogeomorphic principles to delineate zones that are either frequently flooded or actively eroding, or that include riparian wetlands. Freedom space limits mapped for three rivers in southern Quebec (Canada) were assessed to determine whether they would still be valid under a future climate using a sensitivity analysis approach with numerical models predicting mobility of meanders (RVRMeander) and flood stage (HEC-RAS). The freedom space limits were also used in a cost–benefit analysis over a 50-year period where costs consist of loss or limitations to the right of farming and construction in this zone, whereas benefits are avoided costs for existing or future bank stabilization structures and avoided costs of flooding in agricultural areas. The economic value of ecosystem services provided by riparian wetlands and increased buffer zones within the freedom space were also included in the analysis. Results show that freedom space limits would be robust in future climate, and show net present values ranging from CDN$0.7 to $3.7 million for the three rivers, with ratios of benefits over costs ranging between 1.5:1 and 4.8:1. River management based on freedom space is thus beneficial for society over a 50-year period. [ABSTRACT FROM AUTHOR]

Tropical river systems, wherein much of the drainage basin experiences tropical climate are strongly influenced by the annual and inter-annual variations of the Inter-tropical Convergence Zone (ITCZ) and its derivative monsoonal winds. Rivers draining rainforests and those subjected to tropical monsoons typically demonstrate high runoff, but with notable exceptions. High rainfall intensities from burst weather events are common in the tropics. The release of rain-forming aerosols also appears to uniquely increase regional rainfall, but its geomorphic manifestation is hard to detect. Compared to other more temperate river systems, climate-driven tropical rivers do not appear to transport a disproportionate amount of particulate load to the world's oceans, and their warmer, less viscous waters are less competent. Tropical biogeochemical environments do appear to influence the sedimentary environment. Multiple-year hydrographs reveal that seasonality is a dominant feature of most tropical rivers, but the rivers of Papua New Guinea are somewhat unique being less seasonally modulated. Modeled riverine suspended sediment flux through global catchments is used in conjunction with observational data for 35 tropical basins to highlight key basin scaling relationships. A 50 year, daily model simulation illuminates how precipitation, relief, lithology and drainage basin area affect sediment load, yield and concentration. Local sediment yield within the Amazon is highest near the Andes, but decreases towards the ocean as the river's discharge is diluted by water influxes from sediment-deprived rainforest tributaries. Bedload is strongly affected by the hydraulic gradient and discharge, and the interplay of these two parameters predicts foci of net bedload deposition or erosion. Rivers of the tropics have comparatively low inter-annual variation in sediment yield. [ABSTRACT FROM AUTHOR]

Abstract: During uplift of the Tibetan plateau and surrounding ranges, tectonic processes have interacted with climatic change and with local random effects (such as landslides) to determine the development of the major river systems of Asia. Rivers draining northward from the Pamir syntaxis have three distinctive patterns that are controlled by different tectonic and climatic regimes. West of the Pamir, the rivers have moderate but irregular gradients and drain northwards to disappear into arid depressions. Relatively steady uplift of the Hindu Kush in northern Afghanistan allowed rivers to cut across the rising ranges, modified by the shear along the Harirud fault zone, local faulting, and by increasing rain-shadow effects from the rising Makran. In the transition to the Pamir the rivers have steeper but more even gradients suggesting more even flow and downcutting during uplift, possibly related to larger glacial sources. In the central Pamir, only one antecedent river, the Pyandzh appears to have kept its northward course with compression and uplift of the indenter, and its course strangely corresponds with a major geophysical boundary (a distorted subducted slab) but not a geological boundary: the other rivers are subsequent rivers developed along deformation fronts during development and northward displacements of the Pamir structural units. The above areas have sources north of the Cretaceous Karakorum–South Pamir Andean margin. On the eastern flank of the Pamir, in the Kunlun and northern Tibetan plateau, the rivers rise similarly north of the Cretaceous Andean margin of southern Tibet, but then flow with low gradients across the plateau, before cutting and plunging steeply down across the Kunlun to disappear into the arid Tarim. These steep profiles are the result of late Neogene uplift of the northern Tibetan plateau and Kunlun possibly modified by glacial diversion and river capture. The drainage history of the Pamir indenter can be reconstructed by restoring the gross movements of the plates and the tectonic displacements, uplift, and erosion of individual tectonic units. Most important changes in drainage took place in the last 10 million years, late Miocene to Quaternary times, as the Pamir syntaxis developed. [Copyright &y& Elsevier]

Abstract: Natural rivers are subjected to continuous adjustments in response to any change in the environment. These environmental changes may occur naturally, as in the case of climatic variation or changes in vegetative cover, or may be related to human activities including channelization, damming, bank protection, and bridge construction. Identifying the value of that discharge (‘dominant’ or ‘effective’ discharge, Q D ) considered responsible for the main changes operated by a river has been a subject of great challenge to scientists and engineers during the last decades. In fact, this threshold value is largely adopted for stream-management decisions, for predicting the stable slope upstream of grade-control structures, and for designing moderate- to large-sized hydraulic structures. In this paper, a simple concept of dominant discharge, corresponding to that value of Q D that accounts for at least 50% of the total suspended sediment load transported by the river, is introduced and discussed. The work is based on a long-term data set that includes measurements of monthly discharge and suspended sediment load in 27 stream gauge stations located in three different regions of southern Italy. The analysis showed that Q D corresponds to values of the return time, T, ranging from 1 to 5years, confirming previous findings by other authors in similar analyses. Also, as the values of Q D were well correlated with the 1.5-year peak discharges of the same investigated rivers, an empirical approach is suggested in order to estimate Q D in rivers with no sediment load measurements. [Copyright &y& Elsevier]

Small mountainous rivers can deliver considerable freshwater discharge and suspended sediment discharge (SSD) to the ocean during tropical cyclones (TCs), and this has received special attention worldwide. However, little information is available on how TCs impact variations in water discharge and SSD delivered by mountainous rivers into the ocean. Here, based on the daily water discharge and SSD at the gauging stations of the tidal limit in July and August from 1965 to 2017, the Qin River (QR) and Nanliu River (NR), 2 small mountainous rivers located in the north of the Beibu Gulf, South China, were selected to quantify variations in water discharge and SSD into the Beibu Gulf during the TC period. The main results show that the net TC-induced water discharges in the QR and NR during July and August are larger than those of non-TC days, respectively. The net SSD increases in the QR and NR induced by TCs are far larger than those of normal days, respectively. Meanwhile, the water discharge and SSD in the flood season can be dominated by TC-associated rainfall, but the impacts on water discharge and SSD are influenced by the TC characteristics and basin environment. Moreover, it is found that in these 2 mountainous rivers, high water discharge delivers high SSD, but extremely high water discharge caused by TCs fails to produce extremely high SSD. It is expected that TCs will produce great impacts on SSD and water discharge of the mountainous rivers in South China behind global climatic change with increasing TCs events. • Tropical cyclone-induced precipitation dominates the water discharge in the Qin and Nanliu River. • The SSDs in the Qin and Nanliu River caused by tropical cyclones contribute to 21% and 12% of the annual SSD, respectively. • Extremely high water discharge of the mountainous rivers induced by tropical cyclones fails to transport extremely high SSD. [ABSTRACT FROM AUTHOR]

Abstract: This paper assesses river channel management activities in the context of the interaction between coarse sediment delivery, climate change, river channel response and flood risk. It uses two main sources of evidence: (1) an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods; and (2) a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network. The field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself. Extreme events, that could occur at any time in the year (i.e. they are not dependent on wet antecedent conditions), were crucial for sediment delivery. However, sustained high river flows were responsible for the majority of transfer within the river itself. Application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s, regardless of the climate downscaling scenario used. First approximations suggested that this would translate into annual bed level aggradation rates of between 0.10 and 0.20 m per year in the downstream main channel reaches. Second, the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in-channel simulation with river flows scaled for climate change to the 2050s and 2080s. Short-term sedimentation could result in similar magnitude increases in inundated area for 1 in 0.5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude. Finally, we were able to develop an alternative approach to river management in relation to coarse sediment delivery, based upon reducing the rates of coarse sediment delivery through highly localised woodland planting, under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem. Thus, the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process, with a much more explicit focus on the catchment scale, if our river systems are to become more insulated from the impacts of future climate changes. [Copyright &y& Elsevier]

Palaeo–hydrological and sedimentary investigations were carried out in the Longmenxia Gorge of the middle Yihe River. Five bedsets of flood slackwater deposits (SWD) were found interbedded into Holocene aeolian loess–soil profiles in the river bank at the Longmenxia site. They were identified as the deposits of the suspended sediment load during the extreme flood events of the Holocene. The minimum flood peak discharges were estimated to be 12, 300–15, 300 m 3 /s using the slope–area method. These are about twice the largest gauged record (7180 m 3 /s) that has occurred since 1937. These flood events occurred at 3100–3000 a B.P., 1800–1700 a B.P., 700–550 a B.P. and 350–250 a B.P., as dated by optically stimulated luminescence (OSL) in combination with stratigraphic correlation, to which may be added the recorded events of the 223 and 1761 CE floods. These were associated with Holocene monsoonal shifts and abrupt climatic events. This research not only provides palaeoflood discharge estimates on the middle Yihe River, but also provides important data for understanding interactions between regional hydro–climatic systems and global climate change in humid and semi–humid monsoonal regions, such as China. [ABSTRACT FROM AUTHOR]

Abstract: The upper 20–30m of the Pleistocene alluvial sequence on the Tisza River, Hungary is investigated by 200km of VHR single-channel seismic sections. Frequent internal configurations, such as (1) bundles of inclined reflections, (2) trough-shaped converging, and (3) horizontal, parallel reflections are interpreted, respectively, as lateral accretion of point bars, abandoned channel fills and floodplain deposits. The series of 5–8m-thick inclined strata sets occurring at the same depth throughout the area suggest the presence of a meandering river dated to about 43–47ka in the Late Pleistocene according to OSL data. Newly recorded quasi-3D seismic profiles reveal that each 1–3km-long inclined series correlates with an individual point bar continuously migrating in the same direction. Small deviations in the direction of migration are caused by natural wandering of the meander bend. Morphometric parameters of point bars are used to calculate ancient channel parameters (width and depth of 200–500m and 5–8m, respectively). Values imply a channel-forming discharge of Q=400–900m3/s. These results imply a greater amount of runoff and supply in the basin during MIS3 compared to the present day. Long-lasting meandering indicates the role of local factors and a different fluvial environment compared to the commonly anastomosing systems in NW Europe. Our data support the thesis of the three-axis drainage system for the basin. New evidence is provided for the antecedent existence of a temporally active third trunk river in addition to the ancestors of Danube and Tisza Rivers, contrary to the present-day two-axis drainage pattern. [Copyright &y& Elsevier]

Abstract: To reconstruct the geomorphic imprint of the anthropogenic and natural environmental changes in the Late Holocene, we studied the alluvial record of the Bečva River floodplain (Outer Western Carpathians, Czech Republic). Coring, geophysical sounding and lithological analysis of floodplain deposits supported by AMS (accelerator mass spectrometry) dating enabled the establishment of the primary evolutionary stages of Late Holocene floodplain evolution. During the Late Atlantic and Early Subboreal periods, gravel aggradation and braided environments occurred in the studied floodplain. The Late Subboreal and Early Subatlantic are characterised by overbank sedimentation, and the Middle Subatlantic is marked by the recurrence of gravel aggradation. A major incision phase took place during the Mediaeval Warm Period. The onset of overbank sedimentation in the 15th century correlated with ongoing deforestation of the lower parts of catchment, and colonisation of the mountain ridges during the 16th–17th centuries further accelerated this process. During the 20th century, reforestation of mountains and river-channel training resulted in a significant incision phase. Our data suggest that climate fluctuations were major driving factors for the morpho-sedimentary evolution of the floodplain approximately up to the 12th century, whereas in the latter evolution period, anthropogenic activity superseded natural factors. This transition occurred more than one millennium later than in other Central and Western European catchments. [Copyright &y& Elsevier]

A revision of the data used to build the Caspian Sea level curve over the last 2200 years BP has been made based on a combination of geological and archaeo-historical data, using only those for which sufficient metadata were available. This compilation is completed by new sedimentological and palynological data from the south-east corner of the Caspian Sea, especially close to the known termini of the Sasanian Gorgan and Tammisheh Walls. A new calibration of the radiocarbon dates was used, i.e. with a freshwater offset reservoir of 351 ± 33 years. A literature survey of the Derbent lowstand indicated that this term has different definitions, depending on authors; it is thus to be used with caution. Here we therefore prefer to distinguish the mid-Sasanian lowstand and the later Medieval moderate lowstand. The "2600 years BP highstand" has not been found, mostly due to the calibration or recalibration of the datapoints used; data are indeed lacking at that time. Instead, a younger Parthian highstand (around 50 BC–50 AD) is clearly defined. The maximal amplitude and speed of change of the Caspian Sea level were respectively of >15 m and 14 cm per year. Compared to last century, the latter rate is 25% higher, but the amplitude is more than five times larger. The climatic causes of the Caspian Sea level changes are discussed. It is far from a simple case of temperature forcing; temperature forcing may result in several effects, that may impact the Caspian Sea level variations in opposite ways. Moreover, human intervention on river diversion and natural hazards were likely, for several time periods. • Revision of Caspian Sea level datapoints over last 2200 years with new points • Geological and archaeo-historical dara with new calibration of radiocarbon dates • Derbent lowstand & 2600 yr BP highstand revised, and newly named Parthian highstand • Ambiguous forcing by temperature, re-inforced role of river diversions • Amplitude and rate of changes both larger than in the last century [ABSTRACT FROM AUTHOR]

This research provides geomorphological and sedimentary data on the Salado-Juramento fluvial megafan, the second largest megafan (204,747 km2) of the Chaco aggradational plain, generated by the Salado-Juramento River in NE Argentina. It comprises one of the most extensive depositional systems of the Central Andean foreland basin system in South America, also being among the largest megafans on Earth. Despite this, it has not been previously studied from the perspective of its geomorphology, stratigraphy and dynamic evolution. An integrated approach focusing on the analysis of morpho-sedimentary processes, the resulting landforms and the reconstruction of the Late Quaternary evolution is presented here. The applied methods combine geomorphological mapping from remote sensing images analysis, assessment of landforms and processes, and field data. Historical documents were also analysed. Insights into the near sub-surface stratigraphy were obtained from analysis of research boreholes (up to 30 m depth), integrated with groundwater borehole information. The Fluvial Megafan of the Salado-Juramento Geomophological System comprises four geomorphological units: 1) the middle-proximal area of the megafan, 2) the distal area of the megafan, 3) the complex fluvio-aeolian belt of the Golondrinas-Calchaquí, and 4) the present fluvial belt of the Salado. Thirteen geomorphological sub-units were defined and mapped, representing the complexity of sub-environment interactions. Amalgamated braided channel deposits and aggradation lobes with limited floodplain muds are common in the proximal area, while mixed-load, low-energy, narrow, shallow, and sinuous palaeochannels and associated floodplain marsh deposits characterize the distal area, with groundwater discharges and hydromorphic soils. The megafan construction was dominated by short-term sedimentation and channel avulsions to overbank areas. Fan-shaped depositional lobes of the proximal area and sandy channel deposits and sand sheets linked to terminal splays that are covering mud-flat deposits (floodplains, including palaeosols) in the middle area suggest a high-flow regime. Neotectonics favoured subsidence, avulsion, and prolonged flooding events, with high potential of preservation of an extensive Late Quaternary wetland unit, ponds, lakes, soils, and loessic deposits in the distal megafan. Aggradation and progradation patterns have been conditioned by tectonic control regulating the interaction between the megafan and its axial trunk river (Paraná). Furthermore, the Late Quaternary megafan sequences would also have responded to climatic changes, primarily related to strong hydroclimatic seasonality linked to changes in the South American monsoon system strength. Seasonal high sediment load of the formative river linked to the characteristics of the Andean basin (38,000 km2) and its climatic patterns are considered as the main control on megafan dynamics over at least the Upper Quaternary. Morpho-stratigraphical data of the megafan presented here and the first interpretation of its Quaternary evolution is the key to support socio-economic decisions on aquifer exploitation, land uses, and infrastructure planning. • Analysis of the Salado-Juramento megafan (204,747 km2), Central Andean foreland basin • Megafan geomorphology studied using satellite images, fieldwork, boreholes and dating • Megafan comprises regional to local fluvial, floodplain and aeolian landform units. • Foreland basin tectonics controls megafan aggradation and progradation. • Late Quaternary evolution linked to South American monsoon system climate change [ABSTRACT FROM AUTHOR]

The Mazeri Valley in the southern Caucasus Mountains, Georgia, is characterized by a highly dynamic landscape with several active mass-wasting processes. The spatial and temporal dynamics of these geomorphic processes have, over time, resulted in the formation of large cones and fans. In this context, the coupling between the hillslope and the channel plays a fundamental role in controlling the catchment sediment dynamics. The sediment produced at higher altitudes on hillslopes may occasionally reach the debris-flow channel network, and downstream propagation may have significant effects on the fluvial environment and create potential hazards for the population and infrastructure. In this regard, we report a tree-ring-based chronology of the debris-flow activity on a large cone to shed light on sediment connectivity and better understand the coupling between the main debris-flow channel and a bedload river in this remote area under global climate change and glacial retreat. The 161 sampled trees demonstrated the appearance of 12 significant events over the last 65 years, with all of the events involving possible sediment input into the stream system of the Dolra River. These successional events, with a return interval of 5.4 years, have partially destabilized the fluvial system and locally induced a switch in the channel style to a braided channel. Surficial sedimentary characteristics, such as morphometric indices, have enabled the discrimination between sediments from the debris-flow activity and river dynamics (alluvium inputs). Finally, most of the reconstructed event-years are characterized by at least one month of above-average rainfall. • The coupling between channelized debris flows and fluvial network was analyzed. • Tree-ring reconstruction of debris flows indicates a return period of 5.4 years. • Sediment inputs in the river induced a switch in channel style to a braided channel. • The roundness index of clasts enables discrimination of sediment sources. [ABSTRACT FROM AUTHOR]

Predictions of river channel adjustment to changes in streamflow regime based on relations between mean channel characteristics and mean flood magnitude can be useful to evaluate average channel response. However, because these relations assume equilibrium sediment transport, their applicability to cases where streamflow and sediment transport are decoupled may be limited. These general relations also lack the specificity that is required to connect specific characteristics of the streamflow and sediment regime with the dynamics of channel morphological change that create channel complexity, which is often of ecological interest. We integrate historical records of channel change, observations of scour and fill during a snowmelt flood, measurements of sediment transport, and predictions from a two-dimensional streamflow model to describe how annual peak flow magnitude and peak-flow duration interact with the upstream sediment supply to control channel form for a 15-km study reach on the regulated Green River in Canyonlands National Park, Utah. Two major decadal-scale episodes of channel narrowing have occurred within the study area. For each of these episodes, the reduction in average channel width was consistent with the change predicted by hydraulic geometry relations as a function of average flood magnitude. However, channel narrowing occurred during periods of exceptionally low annual floods. The most recent episode of channel narrowing occurred between 1988 and 2009, during low-flow cycles when the 5-yr mean peak flow was less than 60% of the long-term (1959–2016) mean peak flow. These findings, together with findings from previous studies, demonstrate that decreases in peak-flow magnitude caused by streamflow regulation, climate change, or a combination of those factors have driven episodes of channel narrowing on the Green River. Observations of streamflow, sediment-transport, and morphologic change coupled with predictions from a two-dimensional streamflow model indicate that peak flow magnitudes of at least 75% of the long-term mean peak flow are required to transport bed-material sand in suspension in all regions of the multi-thread channel and that the ~2-month duration of the snowmelt flood played an important role in creating conditions necessary to maintain channel conveyance. These results indicate that detailed characterizations of channel response such as these are needed to predict how river channels will respond to changes in streamflow regime that affect annual peak flow magnitude and duration. • Streamflow regulation by dams and drought has contributed to channel narrowing. • Magnitude of channel narrowing was consistent with magnitude of flood reduction. • Channel narrowing initiated by consecutive years of low flood magnitude • Maintenance of channel width depends on both flood magnitude and duration. • Floods ≥75% of the average flood needed to transport bed material in suspension [ABSTRACT FROM AUTHOR]

The study of drainage evolution in the Songnen Plain, Northeast China, is essential for understanding the interactions between tectonics-topography-climate-drainage evolution in the region. Despite this, it remains unclear whether the paleo-Songhua River (upper-middle reaches of the Songhua River) once flowed westward into the Songnen Plain and what forcings influenced the drainage development of the Songnen Plain. In this contribution, we provide insight into drainage development on the Songnen Plain using an integrated approach of magnetic susceptibility, geochemical (elemental and Sr Nd isotopic) and heavy mineral composition recovered from a 102-m sediment core sediments extracted from the eastern edge of the Songnen Plain with sedimentological and topographic archives. Our results show that a dramatic provenance shift occurred at the depth of 62.2 m (~0.94 Ma) in the core sediments. It is proposed that the Songhua River was separated by the Jia-Yi (Jiamushi-Yilan) divide into two segments before ~0.94 Ma, the west-flowing proto-Songhua River and the east-flowing proto-Sanjiang River (lower reach of the Songhua River). However, the proto-Songhua River reversed direction at ~0.94 Ma when the Jia-Yi divide was cut through by headward erosion of the proto-Sanjiang River, marking the birth of the Songhua River as a single, eastward-flowing river system. Tectonics is suggested as the first-order control on the evolution of the Songhua River before 1.20 Ma, whereas climate changes may be responsible after 1.20 Ma. • Integrated microscopic and macroscopic constraints on drainage evolution. • The paleo-Songhua River once flowed westward into the Songnen Basin until ~0.94 Ma. • Tectonics is main control on evolution of the Songhua River before 1.2 Ma, but climate change is responsible after 1.2 Ma. [ABSTRACT FROM AUTHOR]

Abstract: The paper investigates the morphodynamic reaction of a schematic river to a perturbation of the sediment input imposed at its upstream end. The consequent evolution of the initially equilibrium river can be studied by means of various models (0-dimensional; 1-D parabolic and 1-D hyperbolic with uniform sediments; 1-D hyperbolic with graded sediments), depending on the more or less simplified differential equations applied for describing the water and sediment motion. The paper discusses a number of analytical solutions obtained with two types of boundary conditions, namely: (i) stepwise change of the sediment input, very often connected to anthropogenic actions, and (ii) sinusoidal input variation with prescribed period, typically associated to the meteorological cycles (short period) or to the geological and climate change (long period). The solutions provide an explicit expression for the Response Time of the river for the condition (i) and the Attenuation Length of the river for the condition (ii). The two quantities as defined in this paper do have a specific physical meaning, strictly connected with the corresponding boundary conditions, which measures the reactivity of the river to external disturbances. A comparative application of the analytical solutions to various (prevalently large) rivers of the world is given, together with a final discussion. [Copyright &y& Elsevier]

Abstract: This paper describes 20th century climate and human impacts on terrestrial and fluvial systems in the Dabie Mountains, Anhui Province, China, based on analyses of four types of information. Analyses of particle size, mineral magnetism, organic carbon, nitrogen and phosphorus in a sediment core taken from the Longhekou reservoir, built in 1958 AD in the upper reaches of Hangbu River, provide an ∼45 year record of fluvial responses, while monitored meteorological and hydrological data provide records of climate and river discharge. Census data compiled for the local Shucheng County provide records of population and land use, complemented with analyses of satellite images. The Xiaotian river delivers over 65% of the total water and silt to the reservoir. Analyses indicate that the fluvial regime tracks the monsoon climate over seasonal timescales, but human activities have a strongly mediating effect on sediment supply, sediment delivery and, to a lesser extent, runoff over longer timescales. Notable periods of human impact on erosion include the Great Leap Forward (1958–1960) and Great Cultural Revolution (1966–1976). A rising trend in precipitation and new land use changes at the present time may be leading to an enhanced flood risk. [Copyright &y& Elsevier]

Multiple continental-scale large rivers originate from the Qinghai–Tibetan Plateau (QTP), known as the "Asia Water Tower", because of glacial melting. However, the timing of fluvial processes in the headwaters of these large rivers and their correlation with global climate changes remain uncertain. Among these rivers, the Mekong River, the third-longest in Asia, flows through the southeastern QTP. In this study, we investigated fluvial terraces, buried paleochannels, hillslope-derived colluvium, and remnants of dammed lake in the Nangqian Basin, which is in the headwaters of the Mekong. We reconstructed the fluvial aggradation and incision history employing optically stimulated luminescence (OSL) dating. Our results suggest that orbital-scale climate changes have significantly influenced fluvial processes in the Nangqian Basin since the Late Pleistocene. During marine isotope stage (MIS) 3 (57–29 ka), a relatively warm period within the last glacial epoch, the Nangqian Basin experienced aggradation of fluvial sediment. Subsequently, during the later part of the Last Glacial Maximum (LGM) (21–17 ka), episodic landslides and debris flows caused valley infilling, resulting in river blockage and the formation of a dammed lake. At around 16 ka, the Mekong in the Nangqian Basin shifted from aggradation to fluvial incision. Since the late Holocene, the basin returned to aggradation, forming a new terrace at around 1.1 ka. This may be due to the combination of decreased stream power and increased sediment supply, potentially linked to intensified human activities and its associated vegetation degradation. Overall, our study highlights the close links between glaciation and fluvial processes in the region. Specifically, we propose that the observed aggradation pattern during the last glacial period on the plateau primarily resulted from substantial detrital input from glacier activities. The transition from aggradation to incision during the last deglacial period is likely influenced by increased discharge from glacier meltwater. The presence of colluvium interbedded within the late LGM fluvial sediment sequences highlights the significant impact of climate changes on fluvial processes in the headwater areas of the QTP, especially those events stemming from hillslope activity, such as landslides and debris flows. • Glacial/interglacial climate change drove fluvial process of headwaters in Tibet. • Aggradation occurred in the Upper Mekong at 40 ka due to glacial induced sediments. • Landslides and debris flows were frequent and caused a dammed lake during 21–17 ka. • River transition from aggradation to incision at 16 ka by rising glacial melting • A concept model for high plateau fluvial process by glacial activity was proposed. [ABSTRACT FROM AUTHOR]

The sensitivity of fluvial sediment load to climate change and predictions of future sediment load in cold basins remain poorly investigated, although changes in river sediment transport have important geomorphological, ecological, and societal implications. Here, we adapt a sediment elasticity approach to examine the sensitivity of fluvial suspended sediment load to changes in air temperature and precipitation in the headwater of the Yangtze River (HYR) on the inner Tibetan Plateau. Results show that every 1 °C increase in air temperature can increase the suspended sediment load by 14–27 % by intensifying thermally-driven glacial and permafrost erosional processes, and every 10 % increase in precipitation can increase the suspended sediment load by 16–24 % through enhancing pluvial-driven erosional processes. We predict an increase of 60–85 % in the suspended sediment loads in HYR by 2050 relative to the present-day period under the Representative Concentration Pathway 4.5, as both air temperature and precipitation are projected to increase. Our analysis highlights that smaller upland rivers appear to respond to modern climate change more rapidly and intensively than larger downstream rivers due to the larger glacier and permafrost coverages, poorer vegetation, as well as steeper fluvial relief, and higher sediment connectivity. This study provides a framework and a data-driven sediment elasticity approach to predict climate change and cryosphere degradation-driven changes in future fluvial suspended sediment load in cold basins, highlights the importance of the spatial scale effects in modulating fluvial responses, and has implications for assessing the impacts of climate change on channel morphology and aquatic ecosystems. • A sediment elasticity approach is introduced to estimate sediment load sensitivity to climate change in cold basins • One degree increase in temperature can increase sediment load by 14-27%, and every 10% increase in precipitation can lead to a 16-24% increase in sediment load in HYR • Sediment loads will increase in a warmer and wetter climate, with negative impacts on hydropower and aquatic ecosystems • Sediment loads tend to respond more rapidly and intensively to climate change in upland smaller basins than larger downstream basins [ABSTRACT FROM AUTHOR]

Understanding the processes of fluvial geomorphic evolution is based on thorough evaluation of how rivers respond to tectonic activity and climatic change, with river terraces representing a key archive of alternating deposition and incision in response to such forcing, enabling an excellent means for correlation with tectonic and climatic records. An example presented here points to a difference in fluvial response to climate fluctuations along a trunk river and its tributary: the Yellow River and its tributary the Xike River, which has incised the Lajia Gorge to pirate the Zoige Basin, in the eastern Tibetan Plateau. Based on Accelerator Mass Spectrometry 14C dating, the chronological sequence of basin fill top and fluvial terraces below has been established, defining the drainage reorganization of the Yellow River excavation through the Zoige Basin since the Last Glacial Maximum. Spatial and stratigraphic comparison between the two fluvial sequences, combined with correlation with high-resolution climatic records, indicates that the tributary Xike River formed more terraces in response to trunk incision (base-level variation), climatic fluctuations, and underlying weak bedrock than the Yellow River. Thus, our results not only demonstrate a combined archive of climatic fluctuation and tectonic uplift recorded in the fluvial terrace sequences, but also suggest that the generation of fluvial terraces may be influenced by the underlying bedrock within the same tectonic and climatic settings. • The Yellow River excavating through the Zoige Basin is constrained before 19 ka. • Fast uplift drives a sensitive fluvial response to sub-orbital climatic cycles. • Drainage scale affects the sensitivity of fluvial response to climate change. • Fluvial terrace is archive of the coupling between uplift and climate change. [ABSTRACT FROM AUTHOR]

In the south Central Andes, a complex relationship between climate, tectonics, erosion and topography is well documented. Building on recent advances in the mechanical modelling of subduction zones, we isolate the contribution of fault motion to topography and observe how rock uplift has been recorded in river valley morphology. Rivers on the wetter, western Chilean-side of the Andean cordillera have steep and narrow valleys, in stark contrast to those draining east across the arid Argentinian cordillera, whose valleys are variably wider and less steep. The Chilean rivers have responded to fault slip along the western mountain front by incising vertically and propagating a steepening zone upstream. In Argentina, there is little evidence of channel steepening despite predictions for higher vertical rock uplift rates. We hypothesise that the aridity of the Argentinian region has limited the transport capacity of the rivers to export their sediment fill and as a result, vertical incision has been inhibited and lateral incision and valley widening favoured. The long-term climate gradient appears to have been important in modulating the morphological response of these rivers to fault slip. These factors precondition future landscape sensitivity to both tectonic and climatic change. [Display omitted] • Investigation of how climate modulates river incision responses to Andean uplift • Rock uplift contribution to topography isolated by modelling plate subduction • In arid Argentina, areas of high uplift have low local relief and shallow, wide valleys. • Contrasts with wetter Chile, where incision propagates upstream from frontal fault • Persistent climate patterns modulate bedrock rivers by limiting sediment mobility. [ABSTRACT FROM AUTHOR]

Abstract: The Jamuna River is the downstream continuation of the Brahmaputra in Bangladesh. It is one of the largest sand-bed braided rivers in the world and every year it erodes thousand hectares of mainland floodplain, rendering tens of thousands of people landless and/or homeless. Understanding the morpho-dynamics of this river and its responses to the various drivers of morphological change that act on it is essential to improving the livelihoods of millions of floodplain dwellers in Bangladesh, especially given the threats posed by climate change. Reliable data, information and knowledge of river process are sparse and so progress in linking the impacts of multiple drivers (including neo-tectonics, earthquakes, large-scale avulsions and engineering interventions) to complex morphological responses depends on making best use of historical maps, time-series satellite images, hydro-morphological data, expert judgment and local knowledge. This paper draws on all these sources to chronicle the morphological evolution of the Jamuna River since the avulsion that created it about 200years ago, and to establish temporal trends and spatial patterns in the changes that have characterized process–response mechanisms in this fluvial system since then. The understanding gained from these investigations then supports deeper analyses to: explain how historical migration of the river westward has produced significant contrasts between left and right (west) bank material properties; elucidate the relationships between discharge, fluvial processes, anabranch instability and floodplain erosion rates, and; identify causal links between drivers and morphological responses at a variety of time and space scales. Finally, the new knowledge generated by the analyses developed herein are combined with existing, conceptual and empirical process–response models for the Jamuna to predict possible future morphological adjustments in ways helpful in identifying appropriate strategies for climate change adaptation in Bangladesh. The enhanced knowledge gained from these historical and contemporary investigations may also be useful in assessing the impacts of natural and anthropogenic drivers on other large, braided rivers. [Copyright &y& Elsevier]

The concept of resilience acknowledges the ability of societies to live and develop with dynamic environments. Given the recognition of the need to prepare for anticipated and unanticipated shocks, applications of resilience are increasing as the guiding principle of public policy and programs in areas such as disaster management, urban planning, natural resource management, and climate change adaptation. River science is an area in which the adoption of resilience is increasing, leading to the proposition that resilience may become a guiding principle of river policy and programs. Debate about the role of resilience in rivers is part of the scientific method, but disciplinary disunity about the ways to approach resilience application in policy and programs may leave river science out of the policy process. We propose six elements that need to be considered in the design and implementation of resilience-based river policy and programs: rivers as social-ecological systems; the science-policy interface; principles, capacities, and characteristics of resilience; cogeneration of knowledge; adaptive management; and the state of the science of resilience. [ABSTRACT FROM AUTHOR]

The modern Amazonian ecosystem outcomes from the complex interplay of different factors performed over the geological history, with tectonics being long speculated as perhaps a fundamental one. Nevertheless, areas where tectonic activity can be fully characterized are still scarce in view of the large dimension of this region. In this work, we investigate the signature of neotectonics in one megafan paleolandform that typifies a large sector of the Negro-Branco basin in northern Amazonia. The approach joined regional morphostructural descriptions of the Viruá megafan surface and the acquisition of topographic, sedimentological, and chronological data focusing on the central sector of the megafan. The results revealed an abundance of rivers that form dendritic, subdendritic, and trellis patterns. These rivers also have numerous straight segments, orthogonal junctions, and orthogonal shifts in courses. Structural lineaments, defined by straight channels and also straight lake margins, are aligned along the NW-SE and NE-SW directions that are coincidental with the main regional structural pattern in Amazonia. This study also led to recognize two large areas of lower topography in the south-central part of the megafan that consist of rectangular depressions parallel to the morphostructural lineaments. A sedimentological survey indicated that cores extracted external to the largest depression have only distributary channel and overbank sand sheet megafan deposits. Optically stimulated luminescence (OSL) ages ranged from 17.5 ± 2.0 to 46.9 ± 3.4 ky and radiocarbon ages ranged from 5.9–5.7 to 20.1–19.6 cal ky BP. In contrast, cores extracted within the depression consisted of fluvial deposits younger than 2.1–1.9 cal ky BP that increased in thickness toward the central part of the depression. We propose that the studied megafan was affected by tectonic reactivation until at least a couple thousand years ago. Tectonics would have produced subsiding areas more prone to flooding than adjacent terrains, which constituted sites for renewed deposition of fluvial sediments reworked from the megafan surface following its abandonment. A comparison of our data with those from other Amazonian areas with similar records of late Holocene tectonics suggests a landscape imprinted by faulting, probably of strike-slip motion. This finding increases the record of neotectonic activity in the Amazonian wetlands and may be useful in studies aiming at discussing the origin and extension of late Holocene deformation in the South American intraplate. In addition, we present a megafan with an unusual development in a cratonic region under the combined effect of climate and tectonics. [ABSTRACT FROM AUTHOR]

Floodplain inundation regime defines hydrological connectivity between river channel and floodplain and thus strongly controls structure and function of these highly diverse and productive ecosystems. We combined an extensive LiDAR data set on topography and vegetation, long-term hydrological records, as well as the outputs of hydrological and two-dimensional hydraulic models to examine how floodplain inundation regimes in a dynamic, regulated, gravel-cobble river in a Mediterranean-climate region are controlled by reach-scale valley morphology, hydroclimatic conditions, and flow regulation. Estimated relative differences in the extent, duration, and cumulative duration of inundation events were often as large as an order of magnitude and generally greatest for large and long duration events. The relative impact of flow regulation was greatest under dry hydroclimatic conditions. Although the effects of hydroclimate and flow impairment are larger than that of valley floor topography, the latter controls sensitivity of floodplain hydroperiod to flow regime changes and should not be ignored. These quantitative estimates of the relative importance of factors that control floodplain processes in Mediterranean, semiarid rivers contributes to better understanding of hydrology and geomorphology of this important class of channels. We also discuss implications of our findings for processes that shape floodplain habitat for riparian vegetation and salmonid fish, especially in the context of ecological restoration. [ABSTRACT FROM AUTHOR]

Channel width is an important parameter of the hydraulic geometry of a river and can be linked to the tectonic, topographic, lithologic, and climatic controls in a particular reach. As such, variations in channel width can be the result of one or many factors acting at a specific location. For the rivers flowing in the intermontane valleys along the frontal Himalaya, active tectonics plays a major role in controlling their geometry by providing the space, energy, and sediment. Dehra Dun is an intermontane valley in the northwestern Himalaya where the rivers have their source in the Lesser Himalaya and Sub-Himalaya; they show remarkable variability in the channel width along their course. In this work, we have attempted to identify and evaluate the relative importance of various controlling factors on the channel width of these drainage systems. We selected 20 streams (six North Flank rivers - NFRs; two Main Axial rivers - MARs; twelve South Flank rivers - SFRs) flowing in the valley. In the hilly stretches, the NFRs flow over the Lesser Himalaya and the SFRs flow over the poorly consolidated upper Siwalik gravelly sediments. Channel width in the mountainous region varies generally from 5 to 30 m. The SFRs that have smaller catchments are relatively wider than the NFRs in the mountainous areas. In the Dun, the width variation is mostly between 50 and 400 m. The NFRs show widening in their middle stretches except for the Tons River, which is wide in its lower stretch. Channels widen as they cross the structural zones (i.e., the Main Boundary Thrust (MBT), the Santaurgarh Thrust (ST), and the Bhauwala Thrust (BT)) as a result of the change in the gradient across the structures. Large sediment supply generated by mass wasting processes from the weak zones (i.e., fault-related zones) and uplifted surfaces make the river transport limited, resulting in the deposition of the sediments. Consequently, channel bed armoring in these gravel-bed rivers protects the channel floor causing the erosive actions to be intensified on the banks. In the Dun, where the channel banks consist of cohesive materials, the bank erosion is found to be limited. Apart from these controls, anthropogenic interventions and activities also impact the channel width in the valley. The NFRs and MARs are embanked at many places. On the other hand, most of the SFRs become indistinct before the confluence with the larger rivers because of farming-related activities. This study suggests that in the mountainous stretches, the lithology and geologic structures exercise a primary control over the channel width; whereas within the Dun, the sediment concentration, channel bed armoring, and the properties of bank materials act as the main controls. [ABSTRACT FROM AUTHOR]

Changes in the morphological pattern of the gravel-bed Belá River, Slovak Carpathians, were investigated to infer about the impact of flood events and environmental changes on the evolutionary trend of the river since the mid-twentieth century. The post-flood period serial geomorphic analysis (POPSEGA) approach coupled with GIS analysis was used to identify morphological changes that occurred during particular flood periods. The study focused on assessing how six flood periods (FP) with differing flood characteristics have influenced the evolutionary trend of the river. Several sets of aerial photos (1949, 1961, 1973, 1986, 1992, 2003, 2009) taken after the periods with the occurrence or lack of major floods provided data about channel landform changes in 227 river segments of 100-m length. A decreasing trend of the area of the river's active zone (from 2.5 km 2 in 1949 to 1.4 km 2 in 2009) was identified. The first FP (1949–1961), with a very high-magnitude flood in 1958 (RI 50 ), was characterized by increasing total channel length, island number/area, and the number/density of confluence–diffluence pairs (nodes), and by decreasing bar area. During this FP the frequency of cores of channel dynamics as well as the Shannon's index of landforms diversity reached the highest values. The following FP (1962–1973) with four 5- to 10-year floods exhibited the inverse pattern of changes in channel form parameters, although the core frequency of channel dynamics and Shannon's diversity index were still high. The river system seems to have been relatively stable between 1974 and 1986 (third FP) with some decrease in the area of channel forms and in pattern metrics values. During the fourth FP (1987–1992) several 1.5- to 3-year floods occurred and were associated with a decrease in some channel forms and a further decrease of the pattern metrics values. An increase in all analysed channel parameters, especially bar area and pattern metrics values, occurred in the years 1993–2002 (fifth FP) as a consequence of two floods of moderate magnitude in 1997 (RI 7 ) and 2001 (RI 3.5 ). The lowest values of bar area and pattern metrics during the whole study period were recorded during the last FP (2002–2008), whereas island area increased at that time. The study shows that the occurrence of floods during the last six decades has not returned the Belá to its former state because of the overall decrease in flood magnitudes, changes in catchment sediment supply induced by the increasing forest cover in the catchment (from 22.7% in 1957 to 34.8% in 2008), and changes in channel boundary conditions (channelization, channel incision, small hydropower plant constructions). [ABSTRACT FROM AUTHOR]

The floodplains in the interfluve between the Ganga and Sai rivers in the Central Ganga Plains exhibit a broad suite of geomorphic features such as a linear array of meander cut-offs and oxbows representing abandoned sinuous channels. Here we integrate regional and local scale geomorphic analysis using satellite imageries with detailed chronostratigraphic and paleoclimatic reconstruction from a large oxbow lake (Baraila Tal) in the paleochannel belt to infer landscape evolution in this region. The stratigraphic succession at Baraila Tal supported by sedimentology and stable isotope composition of organic matter and micro-gastropod shells suggests that the lake was previously a part of an active fluvial system, and the depositional environment transformed from a fluvial to a lacustrine system in response to geomorphic and climatic changes during the post-LGM period. Integrating geomorphic and paleoclimatic data, we identify four stages (I-IV) of landscape evolution in the Ganga-Sai interfluve region during the Late Pleistocene-Holocene interval: (I) active channel phase of paleo-Sai river before 12 kyr, (II) development of paleochannel belt and meander cut-offs during 12–8 kyr, (III) development of 'misfit' Sai river and gullied landscape during 8–7 kyr, and (IV) expansion of ephemeral lakes (wetlands) and subsequent filling post 7 kyr. We have demonstrated the use of paleoclimate and paleovegetation data retrieved from a meander cut-off lake for deciphering landscape evolution. • Integration of geomorphic and paleoclimatic data to decipher landscape evolution in Central Ganga plains. • A spectacular linear array of meander cut-offs and oxbows mapped from satellite images • Paleoclimate and paleovegetation data retrieved from a meander cut-off lake. • Depositional environment interpreted from sedimentology, and stable isotope data. • Four stages of landscape evolution in response to post-LGM geomorphic and climatic changes. [ABSTRACT FROM AUTHOR]

The Someș fluvial fan is located in the NW extremity of the Great Hungarian Plain (Pannonian Basin). It was formed by the left-side tributaries of the Tisa River (a tributary of the Danube) as they developed westward, following the avulsion of the main Tisa channel. Drainage reorganisation after the avulsion has occurred via a complex interplay between tectonic, climatic and autogenic controls over the past ~50–30 ka. In this study, we discuss the role of these factors in the spatial and temporal dynamics of the fluvial system that constructed the Someș fluvial fan during the second half of the last glacial cycle, using a combination of cartographic, sedimentary, and chronological tools. Our data suggests that, within a general setting of subsidence, spatial and temporal variation in the rate of this subsidence between different tectonic blocks created four local base levels, while autogenic factors play only a secondary role. The modern drainage configuration results from spatial channel adjustments during the last ca. 3000 cal BP, related to the current subsidence centre located in the NW extremity of the Someș fluvial fan. Over the entire period analysed, the rivers draining across the fluvial fan predominantly meandered, except when the river switched to a braided pattern. This braided phase likely occurred before ~30–32 ka ago, apparently coeval with a similar short, braided phase that has been documented along the middle Tisa River. The braiding phase is coincident with intense deglaciation in the Someș catchment area and development of open forest vegetation at lower elevations. Climatic changes during and after the Last Glacial Maximum had a reduced impact on the style of fluvial flow, which returned to a meandering pattern. Ca. 5000 cal BP these changes impacted suspended sediment delivery to drainage networks resulting in the present-day channel dimensions, at least along their lower reaches (our study area). Our results highlight the lower sensitivity of rivers draining the Great Hungarian Plain to the Late Quaternary climate changes compared to the far more responsive rivers of Western European. This behaviour is, in our opinion, most likely due to the presence of glacial forest refugia in the catchment areas, which modulated the response of discharge and fluvial dynamics to climatic changes. • Reconstruction of Somes fluvial fan (Pannonian Basin, Europe) during Late Quaternary. • Uses remote sensing, sedimentology, mineral magnetics, OSL and 14C dating. • Fluvial fan built by Somes-Crasna-Tur Rivers, after Tisa River abandonment >30 ka. • Fan building via base-level changes linked to differential tectonic block movements. • Climate and autogenic factors modified styles and patterns of individual fan lobes. [ABSTRACT FROM AUTHOR]

Understanding how the environmental factors that determine erosion operate is essential to know the past and future evolution of the Earth and adequately manage natural resources. In this work, the main controlling factors of the current sediment export in the western side of the extratropical Andes (20°-55°S) are investigated using multidecadal series of specific suspended sediment yields from 42 rivers, as well as land cover, climatic, cryospheric, topographic, seismological and geological data. Through an automatic selection of Generalized Additive Models based on predictability and complexity, it was found that the combined effects of extreme runoff, glacier cover and channel steepness explain ~90 % of the spatial variability of sediment export. The runoff effect varies from positive for hyper-arid and semi-arid settings to slightly negative for moderate and wet settings, probably because of an associated increase in vegetation coupled with a recurrence and magnitude of floods that becomes greater than the time it takes for the basins to generate sediment. Cryosphere and channel steepness influences were also observed on the average suspended sediment concentration, which is less associated with water availability and more associated with erodibility and sediment availability. • Extreme runoff, glacier cover and channel steepness explain ~90 % of sediment export. • Runoff effect would depend on ratio between floods' frequency and sediment production. • Vegetation would have a negative resulting effect on mechanical denudation in the area. • Sediment concentration helps to understand land properties' effect on sediment export. [ABSTRACT FROM AUTHOR]

The Baodun archaeological site, which is representative of Baodun Culture (4.5–3.6 cal. ka BP), is a well-known walled site covering large areas of the Chengdu Plain (CDP), which is located in the upper reaches of the Yangtze River. The CDP is a low-lying sedimentary basin that is one of the cradles of Chinese civilization and was formed by many rivers originating from the northeastern part of the Qinghai–Tibetan Plateau. Geological and hydrological characteristics have strongly influenced the development of ancient cultures on the CDP. However, their relationship has not been validated. Based on field investigations, ground surveys, microgeomorphological discrimination, grain-size measurements, tree species identification, and the analysis of fluvial deposits, including age dating, height measurement, and observations of gravel layers, we investigated the effects of geomorphology and river channel migration on the evolution of the Baodun site. The results showed that three grades of terraces developed at the Baodun site region during the past ~50 ka BP, which had important impacts on the regional evolution of geomorphology and river systems. The chronology constrains the ages of terraces T1, T2, and T3 to ~7, ~22, and ~48 ka, respectively; T2 and T3 were closely related to tectonic activity, whereas T1 was related to climate variation. Similar to the modern river system, ancient waterflow primarily originated from the northwest; however, it mixed with water from other directions in the past. We attribute the construction of the Baodun site to the persistently outcropped terraces and the attraction of more stable rivers, which provided space and resources for the Baodun people. The evolution of the river system influenced the safety of the Baodun site, and flooding was the main factor leading to its decline and abandonment. The stability of the terrace and sedimentary environments and the decreased precipitation were important factors influencing the large-scale habitation of archaeological sites on the CDP during the middle and late Holocene. • Field observations were combined with laboratory experiments to interpret human settlement pattern variations. • Three terraces had been developed in the Baodun site region over the past 50 ka. • T3 and T2 were driven by tectonic activity whereas T1 was controlled by the climate. • River channel migration was common, the best-preserved waterflow direction was NW, and flooding threatened the Baodun site. • The stability of terraces and sedimentary environment promoted the development of sites on the Chengdu Plain. [ABSTRACT FROM AUTHOR]

Abstract: The Ouarzazate basin is a Cenozoic foreland basin located to the south of the High Atlas Mountains. The basin has been externally drained during the Quaternary, with fluvial dynamics dominated by erosive processes from a progressive base level drop. The current drainage network is composed of rivers draining the mountain and carrying large amounts of coarse sediments and by piedmont streams with smaller catchments eroding the soft Cenozoic rocks of the Ouarzazate basin. The coarse-grained sediments covering the channel beds of main rivers cause the steepening of the channel gradient and act as a shield inhibiting bedrock incision. Under such circumstances, piedmont streams that incise to lower gradients evolve to large, depressed pediments at lower elevations and threaten to capture rivers originating in the mountain. Much of the current surface of the Ouarzazate basin is covered by coarse sediments forming large systems of stepped fan pediments that developed by the filling of low elevation pediments after a capture event. We identified 14 capture events, and previously published geochronology support an~100ka frequency for fan pediment formation. Our study indicates that the reorganization of the fluvial network in the Ouarzazate basin during the late Pleistocene and Holocene has been controlled by the piedmont-stream piracy process, a process ultimately controlled by the cover effect. The stream capture is influenced by erosion, sediment supply and transport, and therefore may not be entirely decoupled from tectonic and climatic forcing. Indeed, we show that at least two capture events may have occurred during climate changes, and local tectonic structures control at most the spatial localization of capture events. [Copyright &y& Elsevier]

Abstract: The River Ognon in eastern France is the principal drainage of the southwestern Vosges Mountains. Its lowermost valley reach is oriented parallel to the northwestern front of the Alpine collision zone and is characterized by a well-developed terrace system. Geomorphological, sedimentological, and geochronological analyses were performed on this terrace system and associated deposits. The results allow for reconstructing the Pleistocene evolution of the river valley and for concluding on the processes that led to the formation of the terrace system. The lithological characterization of the terrace deposits by means of heavy mineral analyses indicates pronounced modifications of the river''s drainage area. Optically stimulated luminescence dating suggests that the last significant catchment modification and associated sediment accumulation correlates with the last glacial advance in the Vosges Mountains. Despite the apparently strong impact of climatic processes on the evolution of the River Ognon, our investigation also indicates a mild tectonic influence on presently observed terrace distribution. [Copyright &y& Elsevier]

In West Africa, most palaeoenvironmental studies have focused on the role of climatic change on the environment. Because of the richness of its deposits, the Yamé River (Mali), a tributary of the Niger River, offers an opportunity to reconstruct the evolution of this fluvial system in comparison with both climatic and anthropogenic changes during the Late Holocene. To investigate more closely the spatio-temporal response of the fluvial system, sedimentary analyses were conducted on seven reaches distributed along the 137 km length of the Yamé valley. This approach testifies of the possibility for each time slice and river reach (1) to reconstruct the fluvial style and processes and (2) to estimate the sediment storage volume reflecting sediment distribution patterns. Results reveal a wide variability of the sedimentary cascade suggesting contrasting responses to external and local controls. Humid (4200–2900 cal. BP; 450–24 cal. BP) or arid (2350–1700 cal. BP) phases have been recorded in fluvial archives while an intensification in erosion and sediment supplies, even during the arid period (2900–2350 cal. BP and the 20th century), may be associated with an increase in human pressure. Two other periods are related to both climate and anthropogenic factors. During 1700–1400 cal. BP phase huge sediment supplies can be explained mainly by the reactivation of both hydrological processes and human occupation after an intense and long arid event. Dispersed sediment sinks recorded during the 450–24 cal. BP period originate from the combination of intensification of colluvial processes and a wet phase context originating from global climatic change. Thus, this study provides evidence that climate is the strongest driver for the fluvial response of these semi-arid and tropical rivers while human disturbance appear as a secondary factor due to the high sensitivity of the environment to climate variability in such areas. • First reconstruction of the Holocene sedimentary cascade within a fluvial system in West Africa • Study of the hydro-sedimentary records for six reaches along the valley (137 km) • Results attest of seven phases with different sedimentary cascade patterns. • Different responses to climatic and/or anthropogenic forcing factors [ABSTRACT FROM AUTHOR]

Abstract River channel dynamics are natural autogenic occurrences for fluvial rivers with influences from human modifications and climatic factors. Remote sensing and geographic information system tools and techniques, aerial photographs, and satellite imagery have been used to determine epochal channel erosion, accretion, and unchanged locations along Tana River, Kenya's longest river. Six reaches within a 142-km Saka-Mnazini stretch were studied by comparing sequential changes in the position of the channel in 1975–1986, 1986–2000, 2000–2017, and 1975–2017 epochs. Manual and automatic digital processing procedures and GIS tools were applied to visualize and quantify the reach-wise spatial and temporal morphological changes. The erosion and accretion channel changes over the study period were observed and quantified at all reaches. Meandering and switching off or abandoning the main active channel was also illustrated. The potential driving forces of morphological changes included varying hydrological regime, upstream land use practices, nature of channel gradient, and riparian vegetation occurrence changes. We found no clear evidence to link river regulation with the river channel dynamics. Results deliver the latest evidence on the dynamics of Tana River. This information is crucial for understanding river evolution characteristics and aid in planning and management at the lower reaches which has remained poorly understood. Use of remote sensing data in concert with GIS provides efficient and economical quantitative spatial and temporal analysis of river channel changes. Highlights • River channel dynamics at a floodplain reach using remote sensing and GIS tools • Erosion/accretion vulnerability of Tana River is higher at lower reaches. • The Tana River exhibits dynamic channel behaviour, both, before and after regulation. • Reach-wise historical morphological dynamics guide river engineering and planning. [ABSTRACT FROM AUTHOR]

Abstract: Over a historical timescale, landscapes have been strongly affected by fluctuations in climate and by the impact of human societies. This study examines the historical evolution of mid-altitude fluvial systems in the Western Alps and Cévennes (SE Massif Central) in the context of marked climate and anthropogenic change at the end of the Little Ice Age (late 19th century). This work contributes to the reconstruction of river paleodynamics by investigating the nature and chronology of geomorphological changes in upper river basins. In order to produce a detailed reconstruction of hydromorphological changes, we combined two approaches: the study of historical archives and the use of bioindicators (the dating of terraces using dendrochronology and of silt benches using lichenometry in order to reconstruct the evolution of the river channels). The 19th century is a particularly propitious period for the study of surface dynamics because archives have preserved a wealth of qualitative and quantitative data concerning rivers (economic statistics, meteorological and hydrological observations, illustrative documents, descriptions by contemporary observers). It is also a period for which reliable dating methods are available for detrital deposits in rivers. The period provides new information on how the transition between the Little Ice Age and current climate conditions affected the evolution of drainage basins and stream channels by highlighting a succession of phases in the erosive process (e.g., the preparatory role of the drought of 1830–1838 in the erosion crisis of 1855–1870) and refining the chronology of events (very early onset of riverbed incision). The results highlight the effect of climate (small hydroclimatic fluctuations), amplified by strong anthropization, on the rhythm of landscape change and on the relative stabilization of the landscape at the end of the 19th century. In addition, the synchronization of phenomena on the two sides of the Rhone Valley shows that these changes took place on a regional scale. [Copyright &y& Elsevier]

Abstract Geomorphic studies on the Taiwan orogen have long focused on the rapid erosion and efficient sediment transport in response to active tectonic uplift and frequent earthquakes/heavy rains. Little attention has been paid to the common low-relief surfaces in high mountains that appear to have been geomorphically stable for a long period of time. We undertook a study on a group of such gentle surfaces in Alishan, which consist of poorly drained hummocky slopes averaging 15° and as wide as 2 km. These gentle slopes are underlain by mass-wasting gravels 60–100 m thick, from which 22 radiocarbon dates >50 to 40 ka BP in age were obtained. Below these thick colluvial deposits are ~20° bedrock bedding planes apparently exposed by dip-slope failures. Combining these data reveals alternating hillslope erosion and deposition, along with episodic river downcutting, at a time scale of several 104 yr. We relate this temporal change in geomorphic processes to glacial-interglacial climate change. During the wet inter-/post-glacial periods characterized by frequent heavy rains, landslides/debris flows prevailed and rivers were capable of conveying most sediment eroded from hillslopes. Frequent debris flows combined with sufficient bedload sediments serving as tools for fluvial erosion caused rapid river downcutting. In contrast, the low river erosion/transport capacity during the dry last-glacial period allowed progressive deposition of thick colluvium on the preexisting, gentle bedding surfaces probably eroded during the last interglacial period. This study shows how glacial-interglacial climate change influenced the river/hillslope processes and landscape evolution of the Taiwan orogen. Highlights • Low-relief surfaces in the 2000-m high Alishan mountain are studied. • The surfaces are underlain by thick mass-wasting gravels dated >50 to 40 ka BP. • The coupling between river incision and mass movements are demonstrated. • The controls of glacial climate on geomorphic processes in Taiwan are shown. [ABSTRACT FROM AUTHOR]

Abstract: During the last few decades, many case studies focused on the dynamics of fluvial systems in response to hillslope erosion, land-use impact, and climate changes. This paper will review the current state of knowledge of the dynamics of past soil erosion and gullying in small catchments (< 1 km2), the effects to adjacent fluvial systems and possible feedback mechanisms to land-use changes for the last 7000 years in central Europe. The discussed studies were made on hillslopes and gully systems in low mountain range areas. They are characterised by coupled slope–channel systems as well as uncoupled systems like closed depressions in Pleistocene lowlands, maars, lakes, and sunken areas. The studies show that sediment fluxes in small catchments are highly sensitive to local land-use changes while river sediments show regional trends in land-use and climate changes. Peaks of soil erosion and gullying took place during phases of rapid climate change. Particularly, extreme precipitation events caused intensive runoff on slopes used for agriculture. The most remarkable phases occurred in the first half of 14th and in the mid-18th to the early 19th century. Most of the gully systems in Europe today are a result of these catastrophic occurrences. These punctuated events triggered land abandonment and influenced the ecosystem and the socio-economic situation. The results imply that a future increase in land-use intensity and extreme precipitation events during climatic change might have severe consequences regarding soil erosion, flood risk, and ecological aspects. [Copyright &y& Elsevier]

Abstract: The understanding of climate impacts on tropical rivers and catchments has developed, in part, from models developed for temperate landscapes, and a common rhythm is often apparent when millennial-scale studies are compared. At this level issues arising from the complex response of rivers to internal and external factors appear less important than the climate-driven signal. Understanding the fluvial record, however, depends on the availability and interpretation of other sources of proxy data such as pollen spectra, lake levels and ocean cores. In many rainforest areas few pollen records exist and many of these reveal a hiatus at the time of the Last Glacial Maximum. Examples of fluvial archives from Africa, Indonesia and tropical Queensland, Australia are discussed in relation to independent records of vegetation change and inferences are made concerning critical episodes in fluvial history, focusing on the transitions from Oxygen Isotope Stage (OIS)3 towards ‘glacial’ conditions in OIS2 and the Pleistocene–Holocene transition to modern climates. Links between climate, vegetation change and fluvial activity are presented as descriptive models. [Copyright &y& Elsevier]

Abstract: A previously established non-linear theory of river cyclicity as a response to climate change states that short phases of fluvial instability occur both at the transition from relatively warm (temperate) to cold (periglacial) and from relatively cold to warm periods. Such instability typically starts with vertical erosion, successively followed by sedimentary fill of the erosive scar. In spite of frequent confirmation of this theory by geomorphological reconstructions, a few problems arise. First, there are fewer incision phases than climatic transitions. Secondly, remnants of erosion at ‘cold–warm’ transitions are scarce, in contrast to obvious erosion relics at ‘warm–cold’ transitions. Furthermore, it appears that the incision style is strikingly different at both kinds of climatic transitions. Similarly, the long stable phases are also expressed in terms of different floodplain development in cold and warm periods. These arguments require a modification of the general non-linear theory. At the transition from relatively temperate to colder conditions, rivers transformed gradually from a regular, low-energy, single-channel course to a periodically high-energy, multi-channel type. The latter (braided) type is characterized by intense lateral movement, rather than by deep vertical erosion. This results in a well-expressed morphology of wide, extensive floodplains and terraces. In contrast, the linear and constrained, meandering channels incise with small width–depth ratio and build floodplains of limited lateral extent. Consequences are twofold: 1) the spatial limitation of the deeply incised, meandering valleys at the beginning of warm periods counts against their recognition; 2) relatively strong, lateral migration of the braided rivers removes most traces of previous (meandering) systems, which contrasts with the limited lateral activity of confined meandering channels. It means that in a ‘warm–cold–warm’ alternation generally only one phase of vertical erosion is preserved, the one that is caused by the high-energy, braided river at the start of the cold period. [Copyright &y& Elsevier]

Abstract: Global climate change may have a noticeable impact on the northern environment, leading to changes in permafrost, vegetation and fluvial morphology. In this paper we compare the results from three geomorphological models and study the potential effects of changing climatic factors on the river channel types in North-European Russia. Two of the selected models by Romashin [Romashin, V.V., 1968. Variations of the river channel types under governing factors, Annals of the Hydrological Institute, vol. 155. Hydrometeoizdat, Leningrad, pp. 56–63.] and Leopold and Wolman [Leopold, L.B., Wolman, M.G., 1957. River channel pattern: braided, meandering and straight, Physiographic and hydraulic studies of rivers. USA Geological Survey Professional Paper 252, pp. 85–98.] are conventional QS-type models, which predict the existence of either multi-thread or single-tread channel types using data on discharge and channel slope. The more advanced model by Van den Berg [Van den Berg, J.H., 1995. Prediction of alluvial channel pattern of perennial rivers. Geomorphology 12, 259–270.] takes into account the size of the sediment material. We used data from 16 runoff gauges to validate the models and predict the channel types at selected locations under modern and predicted for the future climatic conditions. Two of the three models successfully replicated the currently existing channel types in all but one of the studied sites. Predictive calculations under the hypothetical scenarios of 10%, 15%, 20% and 35% runoff increase gave different results. Van den Berg''s model predicted potential transformation of the channel types, from single- to multi-thread, at 4 of 16 selected locations in the next few decades, and at 5 locations by the middle of the 21st century. Each of the QS-type models predicted such transformation at one site only. Results of the study indicate that climatic warming in combination with other environmental changes may lead to transformation of the river channel types at selected locations in north-western Russia. Further efforts are needed to improve the performance of the fluvial geomorphological models and their ability to predict such changes. [Copyright &y& Elsevier]

Abstract: Much of the drainage of Africa is relatively youthful. Many of its major rivers have shown substantial changes in their courses since the break up of Gondwanaland in the Cretaceous. In addition, many of the rivers have distinctive morphological characteristics such as inland deltas, cataracts and elbows of capture. Tectonic and climatic changes, including the development of the East African Rift System and the aridification of the Quaternary, help to explain the nature of these rivers. The history of the Saharan rivers, the Niger, the Nile, the Congo, the Cunene, the Zambezi, the Limpopo and the Orange, is reviewed. [Copyright &y& Elsevier]

Since the last decades of nineteenth century, Italian rivers experienced remarkable morphological changes. Most of the previously investigated river channels were affected by intense human disturbances, which were frequently indicated as the main control factor. In contrast, the Tammaro River (southern Italy) underwent less complex human interventions than other Italian rivers, at least since the recent closure of the Campolattaro Dam in the median zone of the catchment. Thus, it represents a good example to analyze the effects of changes in climate and land use on short-term channel adjustments. In this paper, the channel adjustments experienced by the Tammaro River over a period of ~140 yr (1870–2011) were investigated. The study integrated results from GIS-based geomorphological and land-use analysis, field surveys, and analysis of hydrological data (rainfall, flow discharges, extreme floods). From the last decades of nineteenth century to the mid 1930s, the river experienced widening and a slight increase in transitional channel morphologies (Phase-1). From the 1930s to the late 1990s, the river underwent a marked narrowing and limited to moderate incision (Phase-2). The geomorphological effects of the 1949 extreme flood were superimposed on the Phase-2 response. Finally, from 1990s onwards (Phase-3), the river experienced substantial stability with respect to the changes during the previous phases and different behaviors at the reach scale. During Phase-3, changes in channel morphology were observed a few years after the closure of the Campolattaro Dam. The morpho-evolutionary phases observed for the Tammaro River were very similar, even if slightly diachronous, to those reported in the literature for more anthropized rivers of southern Italy. • The Tammaro R. (Southern Italy) underwent negligible in-channel human disturbances, at least since 2006. • In 141 years, it experienced three phases of remarkable channel changes. • These changes were fully comparable with those of more anthropized rivers. • Main control factors were extreme floods, decadal rainfall changes, land-use changes. [ABSTRACT FROM AUTHOR]

Rivers are dynamic landscape features which are often altered by human activity, making it difficult to disentangle human impact on geomorphic change from natural river dynamics. This study evaluated the human impact on river planform change within the context of short- and long-term river channel dynamics in the Himalayan Sutlej and Beas Rivers, by (i) systematically assessing river planform change over centennial, annual, seasonal and episodic timescales; (ii) connecting observed changes to human-environment drivers; and (iii) conceptualising these geomorphic changes in terms of timescale-dependent evolutionary trajectories (press, ramp, pulse). Landsat imagery was used to extract components of the post-monsoon active river channel (1989–2018), using the modified Normalized Differences Water Index to identify the wet river area, and visible red to determine active gravel bars. Findings were compared with a historical map to represent the pre-dam period (1847–1850) and with data on potential driving factors of change (discharge, climate and land cover). River planform characteristics changed significantly over all timescales, exhibiting strong spatiotemporal variation between and within both rivers. Dam construction likely caused channel narrowing and straightening at the centennial scale (press trajectory). In the Sutlej, this process has continued over the last 30 years, likely enforced by the cumulative effect of water abstraction and climatic changes (ramp trajectory). In the Beas, the pattern of change in river planform metrics was less pronounced over the same period and more variable along the length of the river, possibly linked to different dam operations that maintain a higher degree of flow variability and peak flows (press trajectory). High local erosion rates caused by aggregate mining (episodic) in the Sutlej were also observed (pulse trajectory). Expressed as evolutionary trajectories, the observed responses to human activity confirm the importance of legacy effects of human impact on river systems, and stress the dependency on spatial and temporal scales to determine trajectories of change. The multi-timescale assessment and conceptualisation provide insights into different dimensions of human impact on river planform change, which is pivotal to developing holistic management strategies. • Human impact on river planform change in the Himalayan Beas and Sutlej Rivers was evaluated. • Historical maps and remote sensing were combined in a multi-timescale analysis. • Evolutionary trajectories of planform change are strongly dependent on the considered spatial and temporal scale. • Differences in trajectories between two neighbouring rivers appear to be pre-dominantly linked to different dam operations. [ABSTRACT FROM AUTHOR]

Whether or not climatic variations play a major role in setting the erosion rate of continental landscapes is a key factor in demonstrating the influence of climate on the tectonic evolution of mountain belts and understanding how clastic deposits preserved in sedimentary basins may record climatic variations. Here, we investigate how a change in precipitation influences the erosional dynamics of laboratory-scale landscapes that evolved under a combination of uplift and rainfall forcings. We consider here the impact of a decrease in the precipitation rate of finite duration on the erosive response of a landscape forced by a constant uplift and initially at a steady state (SS1). We performed several experiments with the same amplitude but different durations of precipitation decrease ( Tp ). We observe that the decrease in precipitation induces a phase of surface uplift of landscapes to a new steady state condition (SS2); however, the details of the uplift histories (timing, rate) differ between the experiments according to Tp . We also observe a decrease in the erosion rate induced by the precipitation change; however, the timing and amplitude of this decrease vary according to Tp , defining a delayed and damped erosion signal. Our data show that the landscape response to precipitation change is dictated by a critical water-to-rock ratio (ratio of precipitation over uplift) that likely corresponds to a geomorphic threshold. Our study suggests that variations in precipitation that occur at a geological time scale (> 10 6 years) may have a weak impact on the erosion of landscapes and on the delivery of siliciclastic material to large rivers and sedimentary basins. [ABSTRACT FROM AUTHOR]

Chile is an elongated country, running in a north-south direction for more than 30° along a subduction zone. Its climate is progressively wetter and colder from north to south. This particular geography has been used positively by a growing number of studies to better understand the relationships between erosion processes and climate, land use, slope, tectonics, volcanism, etc. Here we review the erosion rates, factors, and dynamics over millennial to daily periods reported in the literature. In addition, 21 new catchment mean erosion rates (suspended sediment and 10 Be) are provided, and previous suspended sediment-derived erosion rates are updated. A total of 485 local and catchment mean erosion rates are reported. Erosion rates vary between some of the smallest values on earth (10 −5 mm/a) to moderate values ≤0.5 mm/a compared to other active ranges. This review highlights strong limitations concerning the quantification of local erosion factors because of uncertainties in sampling point location, slope and rainfall data. For the mean erosion rates E for the millennial and decennial catchments, a model of the form E ∝ S / [1 − ( S /0.6) 2 ] R α with α = [0.3,0.8] accounts for 40 to 70 % of the erosion variance, confirming a primary role of slope S compared to precipitation rate R over this time scale. Over the long-term, this review points to the long (5 to >10 Ma) response time of rivers to surface uplift in north-central arid Chile. Over millennia, data provide evidence for the progressive contribution of extreme erosion events to millennial averages for drier climates, as well as the link between glacier erosion and glacier sliding velocity. In this period of time, a discrepancy exists between the long-term offshore sedimentological record and continental decennial or millennial erosion data, for which no single explanation appears. Still, little information is available concerning the magnitude of variation of millennial erosion rates. Over centuries, data show the variable role of groundwater in the dynamics of suspended load and document a decrease in erosion over hundreds of years, probably associated with historical harvesting. [ABSTRACT FROM AUTHOR]