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• A strong signal of reduced winter conditions i.e. duration, snow accumulation and frost days. • Hydroclimatic regime shift alters the sediment flux seasonality in near future. • Thaw-seasons have important role controlling the annual sediment flux. Climate change alters high latitude hydrological cycle by diminishing the snow accumulation and spring flood magnitude, and by altering temperature and rainfall finally leading to hydroclimatic regime shift from snow-dominated to rain-dominated. These changes in temperature, precipitation patterns, and discharge strongly influence geomorphological processes in fluvial environments, leading to alterations in sediment transport, erosion, accumulation, and landscape changes. We conducted comprehensive analysis of hydroclimatic trends and shifts on boreal Oulanka River system, spanning over the past five decades. A strong signal of warming temperatures (+0.61 Celsius/decade), reduced winter conditions and warmer summers (+0.41 Celsius/decade) was detected. The spring flood magnitude diminished 7 %, but high discharge peaks (Q > annual p90m3/s) during other seasons increased 22 % together with 28 % increase of annual minimum discharge. Simultaneously, precipitation intensity increased during summer. The meander migration rate (mean 0.89 or 2.55 m/year) and bank erosion volume were interconnected to ground frost, high snow sum, high discharge, and high-water level during spring flood, but no significant long-term trends were observed. Our findings underscore that climate is the first-order control on fluvial geomorphology and emphasizes the complex interplay between various hydrological and climatic factors that shape the dynamics of river systems. Based on the results, we expect to see changes in the spatial–temporal distribution of high latitude rivers sediment flux in future. In addition, more attention should be addressed to the thaw seasons controlling the sediment transport, as majority of the observed shifts took place in these months. [ABSTRACT FROM AUTHOR]

Uranium (U) isotopes can be used to estimate the comminution age of sediments , i.e. the time elapsed from sediment production on continents, via weathering and physical erosion, to deposition in the sedimentary record. The calculation of this comminution age is based on measured (234U/238U) activity ratios in river sediments, and inferred time-dependent recoil effect, which leads to the preferential release of 234U from mineral lattices during erosion processes. In this study, we report on a large-scale (234U/238U) investigation of modern river sediments worldwide, with the aim to determine the extent to which parameters such as grain size, lithology, weathering, climate and geomorphology may influence the distribution of U isotopes in fine-grained sediments. Our extensive dataset (N = 64) includes U isotopic measurements for many of the world's largest rivers, but also rivers draining particular climatic and geological settings. Our results indicate that sediments collected from river basins draining mostly igneous, metamorphic or volcanic rocks often display (234U/238U) ratios > 1, with clay-size fractions (<4 µm) being less depleted in 234U (higher 234U/238U) than corresponding silt-size fractions (4–63 µm). In contrast, sediments derived from multi-lithological basins or draining sedimentary rocks are typically characterized by (234U/238U) ratios <1, with clays generally exhibiting more depleted 234U signatures than silts. Taken together, these observations suggest that the formation of secondary clay minerals in soils from basins draining mostly igneous, metamorphic is accompanied by partial incorporation by recoil injection of 234U initially released during weathering processes, possibly from U-rich minerals, such as sphene or apatite. Instead, in multi-lithological catchments draining sedimentary rocks, we propose that the erosion of recycled sediments having experienced several cycles of weathering, possibly over glacial-interglacial timescales, could explain the much lower (234U/238U) ratios observed in clay-size fractions. While no direct relationships can be identified between sediment (234U/238U) ratios and lithology, weathering intensity, climatic or geomorphic parameters in corresponding river basins, we show that the catchment size probably plays an important role in controlling the distribution of (234U/238U) in river sediments, through its direct influence on the sediment residence time. Finally, a multiple regression analysis of our data, combining various environmental parameters for the lithology, climate and geomorphology of studied river basins, indicates predicted (234U/238U) values that are very similar to measured values (with R2 ∼ 0.8). This finding provides further support for the usefulness of (234U/238U) ratios in the sedimentary record for reconstructing past landscape changes and their effect on sediment transport and residence time in river basins. [ABSTRACT FROM AUTHOR]

• Overlapping crater populations constrain the total era of martian valley formation. • Martian valleys may have formed intermittently over hundreds of millions of years. • Long-term erosion rates would have been similar to the modern Atacama Desert. A number of studies have constrained the cessation of martian valley network activity to around the Noachian-Hesperian boundary, but the total time period over which these features formed remains poorly constrained. Most attempts to ascertain valley network formative timescales rely on an intermittency factor that varies widely for terrestrial rivers and is unknown for Mars. In this contribution, superposition relationships are used to identify crater populations that pre- and postdate valley network incision, resulting in maximum cumulative valley formation times of ∼108 years. These timescales correspond with long-term erosion rates of ∼0.25 m/Myr, similar to those calculated for the Middle to Late Noachian as well as the central Atacama Desert since the Late Miocene. Assuming sediment transport rates previously calculated for other martian valley networks, this implies a minimum fluvial intermittency of ∼10−5, several orders of magnitude lower than modern day Earth rivers but similar to values independently calculated for some martian fluvial deposits. This low intermittency suggests that martian valley incision may have been significantly hindered by erosion into existing bedrock or by boulder armoring of the valley floor. Alternatively, unlike river valleys on Earth, runoff events driving martian valley network activity may have been non-seasonal, Milankovitch-like cycles, with long eras of quiescence between periods of intensified fluvial activity. [ABSTRACT FROM AUTHOR]

Topographic relief and bedrock fractures caused by fault activity can accelerate surface erosion, suggesting that erosion rates increase with decreasing distance to the fault core. To test this hypothesis, we used 10Be cosmogenic nuclides to quantify catchment-wide erosion rates at various distances from a fault in the footwall of the Daqing Shan fault system, a 200-km-long active normal fault in Inner Mongolia, northern China. In addition, in order to examine the influence of topography and bedrock fractures on the surface erosion processes in the fault-weakened zone, their relationships with hillslope erosion, fluvial sediment grain size and transport efficiency, erosion rates, and erosion coefficients were studied. The resulting catchment-wide erosion rates ranged from 0.01 ± 0.00–0.13 ± 0.01 mm yr−1. These erosion rates and coefficients were unaffected by distance from the fault. The analysis of topography, bedrock fractures, and hillslope erosion yielded distinct hillslope erosion processes at different distances from the fault. Rapid mass wasting events, such as landslides, occurred at <15 km from the fault in steep, rocky hillslopes with abundant bedrock fractures. In contrast, at >15 km from the fault, hillslopes gradually become more gentle and soil-mantled. These spatial-slope configuration differences result in a decrease in sediment grain size delivered to river channels with increasing distance from the fault. Once sediments enter river channels, they impact fluvial transport capacity by influencing the initial motion threshold of sediment. Correlation analyses revealed that sediment transport efficiency in channels directly controls the catchment-averaged erosion rate and coefficient. This mechanism explains why the erosion rate remains insensitive to variations in topography and bedrock fractures in fault-weakened zones. • Study of patterns and controls on erosion rate across Daqing Shan fault zone. • Cosmogenic nuclide 10Be used to derive catchment-averaged erosion rate. • Erosion rates do not vary with distance from the fault. • Erosion rate remains insensitive to variations in topography and bedrock fractures. • Sediment transport efficiency in channels controls erosion rate. [ABSTRACT FROM AUTHOR]

Lateral inputs from hillslopes and tributaries exert a variable impact upon the longitudinal connectivity of sediment transfer in river systems with differing drainage network configurations. Network topology influences channel slope and confinement at confluence zones, thereby affecting patterns of sediment storage and the conveyance of sediments through catchments. Rates of disturbance response, patterns of sediment propagation, and the implications for connectivity and recovery were assessed in two neighbouring catchments with differing network configurations on the East Cape of New Zealand. Both catchments were subject to forest clearing in the late 1940s and a major cyclonic storm in 1988. However, reconstruction of landslide runout pathways, and characterization of connectivity using a Tokunaga framework, demonstrates different patterns and rates of sediment transfer and storage in a dendritic network relative to a more elongate, herringbone drainage network. The dendritic network has a higher rate of sediment transfer between storage sites in successive Strahler orders, whereas longitudinal connectivity along the fourth-order mainstem is disrupted by lateral sediment inputs from multiple low-order tributaries in the more elongate, herringbone network. In both cases the most dynamic (‘hotspot’) reaches are associated with a high degree of network side-branching. [ABSTRACT FROM AUTHOR]

Reservoirs behind dams act as deposition sites for much of the sediment being transported by rivers. As a result, the downstream river flow can be well below the transport capacity for bed-material. This promotes bed erosion and other geomorphic changes over some length of river located immediately downstream from a dam. These adjustments have been characterized for the Trinity River, TX, downstream of Livingston Dam. Field measurements and results from a 1D numerical model define a 50–60 river kilometer segment of river undergoing bed erosion as the transport capacity for bed material is reestablished. Consequences of this erosion include lowering of the channel bed, reduction in the sediment volume of channel bars, coarsening of sediment on bar tops, steepening of channel banks, and reduction in lateral migration rates of river bends. Repeat surveys of the river long profile reveals that 40 yr of dam closure has produced up to seven meters of channel-bottom incision downstream of the dam, transforming an initially linear profile into a convex-up long profile. The model output matches this observed change, providing confidence that calculated estimates for spatial and temporal changes in bed-material sediment flux can be used to explore the long-term signature of dam influence on the geomorphology of a sand-bed channel. Measurements of channel geometry, profile, lateral migration, and grain size of the lower Trinity River with distance downstream define both the trend and expected variability about the trend associated with the disruption to the bed-material load. [ABSTRACT FROM AUTHOR]

Subaqueous slopes of many actively prograding deltas are heavily modified by widespread submarine sediment failures, forming highly complex geomorphic features that undergo continuous evolution even over short time scales. However, the effects of wave-seabed interactions (especially liquefaction) on the evolution of seabed sediment failures are rarely studied. Here, we use side-scan sonar, sub-bottom profilers, multibeam bathymetry, and in situ and laboratory geotechnical tests to map the bottom morphology and sediment structure of the Yellow River subaqueous delta. Our results indicate that: 1) The morphology along the Yellow River subaqueous delta is highly complex and can be categorized as a moderately disturbed area and heavily disturbed area; 2) Heavily disturbed area shows notable lines of evidences of liquefication-related sediment failure and four separate morphological zones (Zones 1–4). Zone 1 consists of differently sized sediment highs, which considered to be scarp or monadnock features. Zone 2 undulates with widely distributed tabular sediment blocks, gullies, and small-scale seafloor irregularities. Zone 3 is characterized by irregular, elongate sediment ridges. Finally, Zone 4 is characterized by relatively flat terrain with some localized highs; 3) Sub-bottom profiles used to visualize failure features in Zone 1 show acoustically continuous high-amplitude parallel or subparallel reflection, and the geomorphic features in this area are mainly caused by erosion. In comparison, Zones 2, 3 and 4 lack internal structures and display chaotic/disturbed signatures in corresponding sub-bottom data, which might be an indication of liquefaction; and 4) A combination of preconditioning and triggering factors lead to sediment failures and the complex morphological features in this area; however, silt liquefaction under storm conditions is the most important controlling factor. Based on this evidence, we propose formation mechanism for the liquefaction-related sediment failure features in this area. Sediment liquefaction forms an initial depression and gully when fine particles are resuspended along the arc-shaped liquefaction boundary as sediment vents and re-solidification of the liquefied sediment leads to a stiffer bed. Gullies are then widened and deepened by the predominant currents, and the disturbed depressions develop into elongated highs because of the denser structure and higher strength following liquefaction. While disturbed by engineering activities, the sediment highs become fragmented due to intense localized erosion, having the potential for downslope transport and the formation of sediment ridges. The geometries and distributions of the sediment failure features on the Yellow River subaqueous delta provide insights into process mechanisms and causative factors, especially when compared with other, similar phenomena reported elsewhere. • The geomorphology of the Yellow River subaqueous delta was characterised. • Distinct morphological zones are identified and associated processes explored. • Silt liquefaction under storm conditions dominates. • An evolutionary model for liquefaction-related sediment failure is proposed. [ABSTRACT FROM AUTHOR]

This study examines the role of topography as a dynamic boundary condition that limits the efficiency of fluvial erosion in the post-glacial Teton Range landscape. The volume of sediment currently stored in two major catchments was estimated using high-resolution LiDAR and geometric reconstructions of depth to bedrock. Seismic reflection data in Moran Bay reveals post-glacial sediment preserved behind a submerged moraine, which isolates the bay from the larger Jackson Lake depocenter. The volume of post-glacial sediment stored in the canyons and bay totals 173.82 ± 19.5336.0 (×10−3 km3), which translates to a catchment-wide sediment production rate of 0.17 ± 0.02 mm/yr. The rock-equivalent sediment volume in Moran Bay is 4.4 ± 0.9 (×10−3 km3), only ∼2.6% of the total post-glacial volume. While the estimated sediment production rate in the canyons is similar to the uplift rate, the denudation rate derived from Moran Bay sediment is 0.004 ± 0.001 mm/yr, implying highly inefficient post-glacial sediment transport. The fluvial system has been disequilibrated by glacial erosion such that interglacial valley profiles lack the steepness needed to transport sediment, delaying sediment evacuation until the next glacial advance, or until uplift sufficiently steepens the fluvial system so that it regains efficiency. Furthermore, colluvial production rates in the deglaciated valleys are close to long-term denudation and uplift rates, suggesting that once topography has been equilibrated to glacial erosion processes, subsequent glaciers do not need to produce much bedrock erosion, but mainly sweep out accumulated sediment to maintain equilibrium. • Sediment budget quantified for two catchments in the Teton Range, Wyoming. • Flattened post-glacial topography limits efficient fluvial erosion. • Sediment transport delayed until next glacial advance or uplift steepens system. • Colluvial production rates are close to long-term denudation and uplift rates. • Subsequent glaciers may not need to produce much bedrock erosion. [ABSTRACT FROM AUTHOR]

Abstract: This paper uses a multifaceted remote sensing and morphometric approach to investigate if the surface of subcatchments in the Parana Valles area of Mars (20–30°S, 0–20°W) is reflective of hydrology and sediment transport by water. Using digital elevation model (DEM) data obtained from the Mars Orbiter Laser Altimeter (MOLA), three nested subcatchments were examined using a suite of terrestrial geomorphic and hydrologic statistics to determine if their shape and form lies within the known range of fluvial catchment properties on Earth. Further, an examination of statistical accuracy via an innovative pixel-by-pixel solution of two statistics established that despite mineralogical homogeneity confirmed by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral survey, erosion processes were likely to be variable across the study site. The DEM-based methods outlined here can be employed at other sites to investigate geomorphic properties and attributes of the Martian surface. [Copyright &y& Elsevier]

• An efficient 2D shallow water hydro-sediment-morphodynamic model is presented. • Morphodynamic processes under the impact of cascade movable weirs are studied. • Disparate morphological changes may result under different operation schemes. • An alternating operation scheme is proposed to constrain morphological changes. Cascade movable weirs have been increasingly widely used for river landscaping, water storage and ecological wellbeing. The weirs disturb the prior equilibrium in line with fluvial hydrology, sediment transport and geomorphology, and may lead to profound changes in the river, of which, however, the understanding has so far remained poor. Here, the first of its kind, a computational modelling study is presented on the morphodynamic processes under the impact of cascade hydraulic lifting dams, a type of movable weirs, as to the middle Fen River, China. A two-dimensional shallow water hydro-sediment-morphodynamic model is applied to resolve the fluvial processes, which is physically coupled and computationally efficient based on Finite Volume Method, unstructured mesh, local time stepping and parallel computing. Computational results show that the cascade dams alter the flow and sediment transport locally and on the reach scale in a distinct manner under different operation schemes, which in turn incur disparate morphological changes. Collapse of all the dams all year round would lead to net degradation in the study reach, with the floodplains aggrading and the main channel degrading. Operation of all the dams all year round may induce an overall aggradation both on the floodplains and in the main channel. If all the dams collapse in flood seasons and operate in dry seasons (CF), degradation occurs in the main channel whereas the floodplains experience aggradation, with a net degradation. When only the dams in the main channel operate all year round (OM), the floodplains degrade while the main channel aggrades, resulting in a net aggradation in the study reach. Either aggradation or degradation may prevail locally on floodplains, in main channel and individual subreaches. The present findings lead us to propose a complex operation scheme of annually alternating CF and OM to constrain significant morphological changes. [ABSTRACT FROM AUTHOR]

Abstract: The present study investigated the use of computational fluid dynamics (CFD) in predicting the formation, development, and migration of free-forming meander bends. The three-dimensional CFD model computed water flow and sediment transport in alluvial channels and predicted vertical and horizontal bed changes. Different algorithms and parameters were tested to provide an insight into the application range of CFD when modelling free-forming meander formation. The computational domain was discretized by an unstructured grid. A control volume method was used for the discretization of the Navier–Stokes equations for the flow calculation and of the convection–diffusion equation for the sediment transport calculation. Turbulence was modelled by the k–ε turbulence model. The simulation was started from an initially straight grid, with neither sediment feed nor any perturbation at the inflow boundary. The model computed the river bed evolution over a real time period of 3 d. Results were compared with laboratory experiments and showed that the CFD model can predict many of the characteristics of the alluvial meander formation and migration. However, some limitations and uncertainties exist that have to be clarified in future investigations. [Copyright &y& Elsevier]

Abstract: The Guil River Valley (Queyras, Southern French Alps) is prone to catastrophic floods, as the long historical archives and Holocene sedimentary records demonstrate. In June 2000, the upper part of this valley was affected by a “30-year” recurrence interval (R.I.) flood. Although of lower magnitude and somewhat different nature from that of 1957 (>100-year R.I. flood), the 2000 event induced serious damage to infrastructure and buildings on the valley floor. Use of methods including high-resolution aerial photography, multi-date mapping, hydraulic calculations and field observations made possible the characterisation of the geomorphic impacts on the Guil River and its tributaries. The total rainfall (260 mm in four days) and maximum hourly intensity (17.3 mm h−1), aggravated by pre-existing saturated soils, explain the immediate response of the fluvial system and the subsequent destabilisation of slopes. Abundant water and sediment supply (landsliding, bank erosion), particularly from small catchment basins cut into slaty, schist bedrock, resulted in destructive pulses of debris flow and hyperconcentrated flows. The specific stream power of the Guil and its tributaries was greater than the critical stream power, thus explaining the abundant sediment transport. The Guil discharge was estimated as 180 m3 s−1 at Aiguilles, compared to the annual mean discharge of 6 m3 s−1 and a June mean discharge of 18 m3 s−1. The impacts on the Guil valley floor (flooding, aggradation, generalised bank erosion and changes in the river pattern) were widespread and locally influenced by variations in the floodplain slope and/or channel geometry. The stream partially reoccupied former channels abandoned or modified in their geometry by various structures built during the last four decades, as exemplified by the Aiguilles case study, where the worst damage took place. A comparative study of the geomorphic consequences of both the 1957 and 2000 floods shows that, despite their poor maintenance, the flood control structures built after the 1957 event were relatively efficient, in contrast to unprotected places. The comparison also demonstrates the role of land-use changes (conversion from traditional agro-pastoral life to a ski/hiking-based economy, construction of various structures) in reducing the Guil channel capacity and, more generally, in increasing the vulnerability of the human installations. The efficiency of the measures taken after the 2000 flood (narrowing and digging out of the channel) is also assessed. Final evaluation suggests that, in such high mountainous environments, there is a need to keep most of the 1957 flooded zone clear of buildings and other structures (aside from the existing villages and structures of particular economic interest), in order to enable the river to migrate freely and to adjust to exceptional hydro-geomorphic conditions without causing major damage. [Copyright &y& Elsevier]

Many world's large rivers have experienced significant sediment reduction in the past century. However, channel aggradation near the mouth of these rivers may be still occurring or even accelerating, as evidenced by a recent study on the Lowermost Mississippi River. This study aims to investigate whether such a trend exists near the mouth of another large lowland alluvial river, the Atchafalaya River, which enters the Gulf of Mexico via two outlets — the natural mainstem and a man-made straight channel that is shorter and has a much greater slope. The overarching hypothesis is that, despite the reduction in riverine sediment delivery, lowland alluvial rivers such as the Lower Atchafalaya River in their backwater zone aggrade. We collected bathymetric survey records in 1977 and 2006 to analyze riverbed deformation. We utilized stage records at several gauging stations to determine the change in the hydraulic head over time. Geospatial techniques were used to develop channel bed Digital Elevation Models which were used to identify deformation of the 174-km channel bed of the Lower Atchafalaya River. We found a cumulative erosion of 6.34 × 107 m3 and a cumulative deposition of 8.79 × 107 m3, resulting in a net deposition of 2.45 × 107 m3 during the study period. While much of the river including the man-made channel was in a degrading state, the last 35 km of the river's natural mainstem experienced substantial aggradation. On average, riverbed elevation of the Lower Atchafalaya decreased by 1.47 m in the upper 98 km, but increased by 0.96 m in the final 35 km of the river's mainstem to the Gulf of Mexico. The channel erosion in the upstream reach will likely continue with the river discharge projected to increase, and the channel deposition in the downstream mainstem may accelerate because of sea-level rise. • Assessment of channel bed dynamics of a large lowland alluvial river on the Mississippi River Delta • Changes in volume and mass of the channel beds are quantified, and factors affecting them are analyzed. • Channel degradation occurs in the upper reach of the Lower Atchafalaya, mainly affected by flood frequency. • Channel aggradation mainly occurs in the river's final 35 km despite of reduced sediment delivery. [ABSTRACT FROM AUTHOR]