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The Nure and Trebbia catchments were affected by an extreme flood event on 13-14th September 2015. This study investigates the morphological responses to the flood of the Nure and Trebbia rivers and 18 tributaries with the aims to: i) quantify channel changes in width and pattern; (ii) identify the morphological and hydrological factors which might have driven channel response; (iii) quantify channel changes which have occurred after the flood event. Channel changes were characterized by field surveys and geomorphological analysis of multi-temporal orthophotos acquired before (2011), immediately after the flood (2015) and in 2020. In the tributaries, reach-scale channel widths after the flood reached up to 15 times their pre-flood values, whereas in the main channels the post/pre-flood width ratio attained a maximum value of 4. Augmented channel width in the main rivers was mostly associated with banks and islands erosion, whereas in the tributaries it was also due to deposition of coarse sediments onto the former floodplains. Islands were swept away in the main channels while both island erosion and formation occurred in the tributaries. In terms of channel pattern, pre-flood single-thread reaches displayed mainly multi-thread morphologies after the flood, mostly in response to a sudden input of coarse sediment supply. In the 5 yr following the flood, channels slightly narrowed but still remained wider than in 2011. The narrower reaches before the flood resulted to be the most sensitive to changes even some years after the flood. Statistical analyses between the channel width changes and a series of variables showed significant positive correlations with confinement index, channel slope, and the local storm rainfall depth. This study confirms how channel widening during large floods – usually neglected in flood hazard mapping and river basin management – is a very important process which must be considered in flood hazard assessment in mountain rivers. [Display omitted] • Flood-induced channel widening greatly differed within the study channels • Multi-thread patterns increased due to the flood in partly confined and unconfined reaches • Local rainfall intensity played a key role in the spatial distribution of channel changes • Narrower reaches were the most sensitive to changes 5 years after the flood [ABSTRACT FROM AUTHOR]

Unconsolidated regolith from fluvial and hillslope origin occurring along the eastern seaboard of the Northeastern Brazil passive margin has long been overlooked as viable proxy for Quaternary environmental changes, or simply dismissed and interpreted as sediments of older planation cycles, for example, Neogene sediments. This study applies geochemical and geochronological techniques to assess the degree of weathering, sediment provenance and time of residence in the landscape. The results shed light on the upper Quaternary geomorphological history of the Borborema Piedmont, with depositional units spanning the last 50,000 years, as a response to climatic inputs in sync with major Pleistocene events (e.g., Heinrich Event 1, 2, 3 and 5, Last Glacial Maximum) and Holocene events in the Northern Hemisphere (e.g., Holocene Climatic Optimum), and the morphotectonic rearrangement of stream channels base level along reactivated fault-line subordinated to the underlying Proterozoic structural framework. [Display omitted] • OSL data show sedimentation in tropical area is driven by abrupt climate changes. • Sedimentation in the study area dates to at least since the Heinrich 5 Event. • The Piemonte of Borborema Plateau has two main sedimentation phases: ∼25 and ∼9 Ka. • Neotectonic was responsible for the creation of hollows and changes in base level. [ABSTRACT FROM AUTHOR]

Salt marshes, serving as crucial ecosystems and carbon repositories, are currently under threat from climate change and anthropogenic activities. The formation and retreat of marsh-edge cliffs represent a major mechanism of marshland degradation and subsequent release of sequestered organic carbon. The volume of coastal erosion is determined by the product of cliff height and retreat rate; however, the factors governing cliff height remain elusive. In this study, we introduce an idealized process-based model to investigate the initial formation of marsh-edge cliffs and examine how cliff height responds to tidal range, sediment supply, and marsh bed erodibility. The results suggest that cliff height is primarily controlled by the tidal range, showing a strong positive correlation. An increase of 1 m in the tidal range corresponds to a rise of 0.2–0.3 m in cliff height. This is because, in macro-tidal flats, the elevation range suitable for marsh growth is broader, trapping muddy sediments within the marshes, which eventually leads to the formation of taller marsh-edge cliffs. The mud concentration at the open boundary (i.e., sediment supply) has limited impact. Additionally, an increase in marsh bed erodibility can modestly reduce cliff height. This model offers a basis for predicting marsh-edge cliff heights in the face of future environmental changes. Contrary to previous studies suggesting larger tidal ranges support salt marsh sustainability by fostering sediment deposition on the marshes to balance sea level rise, they could, in fact, elevate cliff heights, thus may accelerating erosion and increasing erosion volume. Consequently, the formation and retreat of marsh-edge cliffs demand significant focus for the conservation of meso- and macro-tidal coastal marshes. • Tidal range primarily governs marsh-edge cliff height with a strong correlation. • An increase of 1 m in tidal range raises cliff height by approximately 0.2–0.3 m. • Sediment supply has limited impacts on cliff height. • Higher marsh bed erodibility modestly reduces marsh-edge cliff height. • Marsh-edge cliffs require attention in meso- and macro-tidal marsh conservation. [ABSTRACT FROM AUTHOR]

The accuracy of sea-level rise predictions is highly dependent on reliably understanding the subglacial environment beneath ice streams. Bedforms result from the interaction between ice and its substrate, and therefore have the potential to shed light on poorly understood basal conditions influencing ice dynamics. However, theoretical models of bedform formation are often based on observations from deglaciated areas or from sparsely-sampled geophysical surveys over glaciated regions. Here, we use high-resolution three- and two-dimensional radar and seismic data to reveal details of the initiation and evolution of a subglacial bedform beneath Rutford Ice Stream, West Antarctica. Radar surveys at 20 m and 50 m line spacing allow detailed imaging of bed topography, including a moat up to 55 m deep, surrounding the upstream end of a 50-m high and >18-km long bedform. Many models rely on either a topographical or a locally resistant seed point to initiate bedform formation. The bedform described here is mostly composed of soft sediment (porosity >0.3) and lacks a boulder or outcrop, suggesting the bedform initiated without a topographic seed point. Sediment at the upstream end of bedforms appears stiffer over a distance of 2.3 km. We suggest sediment inhomogeneities in the initially flat bed cause the deposition of sediment, which, assuming resistant enough, acts as a seed point for bedform extension and moat erosion. The moat's geometry and its truncation of other bedforms suggest that it was eroded after the deposition of surrounding bedforms. These observations from a modern ice stream deliver information of subglacial processes involved in the initiation as well as in situ high-resolution topography and properties of bedforms and moats. Using these observations numerical models can be tested and developed accordingly. • Evidence for a bedform initiating without pre-existing topographic perturbations. • A moat around an elongated bedform revealed from high-resolution radar data. • Constraints of bedform formation mechanism from a modern ice stream. [ABSTRACT FROM AUTHOR]

The Upper Verde River in northern Arizona, USA is a vital resource for the wildlife and humans that rely on its waters. We characterize the riparian corridor topography using terrestrial laser scanner (TLS) data from 2021 to 2022. We also quantify geomorphic changes associated with human and climate-driven alterations in river flow and vegetation changes by combining the contemporary lidar surveys with legacy measurements from single line geomorphology transects measured by the United States Forest Service (USFS) in 2009. Seventeen plots along the Upper Verde River were surveyed with the TLS and the data were coregistered within individual plots with a Root Mean Square Error of <0.03 m among scan positions. Digital Elevation Models (DEM) were derived for each plot from the TLS data at 10 cm resolution and compared to the 2009 USFS cross-section data to quantify elevation changes. In areas with statistically significant change, we detected maximum changes in elevation due to erosion and deposition of −0.37 m and + 0.97 m, respectively. Topographic changes over the 13-year period were predominately aggradation and associated with sediment deposition, which we hypothesize might have resulted from altered river flow and vegetation encroachment. This study also demonstrates a quantitative and statistical methodology to fuse traditional single line cross-section data with contemporary lidar data to quantify geomorphic change. The novel approach demonstrated here is broadly applicable to natural resource managers for integrating and contextualizing legacy topographic data for understanding past, present, and future landscape and habitat changes. [ABSTRACT FROM AUTHOR]

The Bohai Sea is the receiving basin of the Yellow River (Huanghe), one of the largest contributors of global terrestrial materials to the sea. An area of fine-grained sediment deposition extends northeast of the Yellow River and its formation mechanism is still unclear. A calibrated, high-resolution coupled model of the Bohai and Yellow Seas was used to investigate sediment transport pathways in the region under the influence of strong and varying winds in winter. Numerical results highlight the importance of storm events in modifying the regional sediment resuspension and transport. During winter, the prevailing winds are typically from the northeast and northwest, interspersed by relaxation periods with weak winds. Winds influenced the currents and sediment movement in the Bohai Sea through several processes: local wind waves and resuspension, coastal-trapped waves in the Bohai Sea, and remotely forced coastal-trapped waves in the Yellow Sea. During northwesterly winds, sediment off the Yellow River Delta was mainly transported eastward along the south coast of Bohai Sea and escaped the Bohai Sea through the southern Bohai Strait. When northeasterly winds prevailed, sediment transport split into three branches: westward into the Bohai Bay, northeastward to the central Bohai Sea, and eastward along the south coast of Bohai Sea. Modeling results driven by synoptic winds indicate a more complex sediment transport pattern than previously understood with monthly average wind forcing. These findings challenge the traditional view of predominantly eastward sediment transport during winter and help to explain the observed grain size distribution in the Bohai Sea, in particular the accumulation of fine-grained sediments northeast of the Yellow River. • Storms are important in modifying the regional sediment resuspension and transport. • Sediment movement in BS depends on local winds, its related CTWs and CTWs in YS. • The formation of muddy areas northeast of the YRD is related to the varied winds. [ABSTRACT FROM AUTHOR]

The reconstruction of the human impacts on the morphodynamics of river deltas in the long term is challenging. The ternary diagram of Galloway (1975) used to classify morphodynamics of deltas does not include direct human influence which is now affecting most of the deltas of the world. The study of human-dominated deltas requires specific approaches and consideration of human processes and morphologies in interaction with more commonly studied natural processes and morphologies. This study demonstrates how to combine different datasets from natural and social sciences to reconstruct long term temporal trajectories of hybrid urban deltas. The Francolí delta, associated with the UNESCO city of Tarragona, offers a perfect case study to identify the different steps of a wave-dominated delta leading to a human-dominated delta over a long-term perspective. Tarragona emerged in the 1st millennium BCE and became a significant port city in the Roman period. This study identifies the evidence of a semi-protected harbour built 2000 years ago that initiates the evolution of a hybrid urban delta towards a human-dominated delta. Until the end 19th c. CE, cyclical changes at the river mouth are observed due to natural fluvial and coastal dynamics while progradation stages are partly affected by anthropogenic structures over time. The 19th c. CE is a major turning point. Morphodynamics controlled by anthropogenic factors strongly increase while fluvial and coastal sedimentation is partly erased by dredgings. The systematic approach proposed for the Francolí delta can be standardised and applied to other hybrid urban deltas allowing better comparison between urbanised deltas. [Display omitted] • Development of interdisciplinary concepts and tools to study hybrid urban deltas; • Identification of the different factors leading to a human-dominated delta over 2 millennia; • Discovery of a Roman built harbour initiating hybrid coastal morphodynamics in the Francolí delta; • Modification of the Galloway diagram to integrate human impacts more systematically in deltaic studies. [ABSTRACT FROM AUTHOR]

The Andaman Sea Basin, a well-known back-arc spreading centre and a mature petroliferous basin, presents a unique and complex scenario for understanding the interplay of sedimentary processes and fault tectonics on seafloor geomorphology evolution, particularly in the eastern shelf region. This study, using high-resolution 3D seismic data and published exploratory well-seismic interpretation results, aims to establish a comprehensive stratigraphic framework for the Tanintharyi region, spanning the Lower Miocene, Middle Miocene, Upper Miocene, Pliocene, and Quaternary. A submarine canyon system was identified and investigated along the Tanintharyi continental slope within the East Andaman Basin, comprising thirteen slope-confined canyons arranged predominantly in an east-west vertical slope orientation. By analysing seismic reflection features, five distinct seismic facies have been identified, including basal lag (BL), slump and debris-flow deposits (SDFDs), canyon confined sheets (CCSs), laterally inclined packages (LIPs), and channel-levees (CLs). The evolution of this canyon system, a vital focus of this study, can be categorised into three phases based on the morphology and sedimentary structures observed: canyon initiation, canyon extension, and erosion-sedimentation. The findings of this study highlight the critical controlling role of faults in canyon evolution, with the intensity of fault activity displaying a negative correlation with canyon size, indicating the direct impact of faults on geomorphological changes. In addition, the geomorphological changes induced by fault activity have resulted in changes in sediment supply, dispersal, and sedimentation rates, thus significantly impacting the spatial distribution and dimensions of slope-confined canyons within the East Andaman Basin, with far-reaching implications. [Display omitted] • A matured canyon system exists in the Tanintharyi region of the East Andaman Basin. • Thirteen slope-confined canyons show nearly an east-west vertical slope alignment. • The sedimentary characteristics of these canyons display three stages of evolution. • Geomorphological changes induced by fault activity impacted the canyon's evolution. • Intensity of fault activities displays a negative correlation with canyon extent. [ABSTRACT FROM AUTHOR]

Blue carbon stored in coastal wetlands can be highly impacted by extreme events, such as typhoons. However, the sediment carbon accumulation capacity in this circumstance, remains unclear. In this study, a field site crossing the bare mudflat-saltmarsh interface was established in Southern Hangzhou Bay, to investigate the geomorphological and subsequent sediment carbon accumulation changes during the typhoon season (2 months) and the succeeding calm weather period (10 months). Surface Elevation Tables (SETs) were used, together with GPS-RTK and UAV-LiDAR surveys, to observe surface elevation changes at different spatial scales. The elevation and sediment organic carbon density data were used to estimate the gain/loss of sediment carbon pool under the impact of two successive typhoons, "In-Fa" and "Chanthu". This revealed that during the typhoon season, 6.3 cm of surface erosion occurred on the bare mudflat whilst rapid depositions of 6.1 and 12.3 cm occurred in Scirpus mariqueter and Spartina alterniflora habitats, respectively. In the gap between the two typhoon events, the bare mudflat experienced deposition of 4.2 cm, signalling recovery from erosion, but deposition within the saltmarsh front slowed. During the calm weather period, sediment deposition increased landward, with magnitudes of 13.1 cm, 16.4 cm, and 18.2 cm. Sediment carbon budget estimates indicated that during the typhoon season, the bare mudflat lost ~3.4 Mg C ha−1 but saltmarshes gained ~4.9 Mg C ha−1 in their sediment organic carbon pools. These changes in sediment carbon accumulation rates over the typhoon season accounted for >30 % of annual change in the study area, and may be associated with tidal creek dynamics. This study suggests the important role of typhoons in mediating the sediment carbon pool across the mudflat-saltmarsh interface. With future climate change, increasingly frequent catastrophic events could cause considerable changes in coastal blue carbon sequestration capacity. • Sediment carbon accumulation rates were recorded at the mudflat-saltmarsh interface. • Differing patterns of carbon accumulation were found during typhoon and calm periods. • Typhoons caused a sediment carbon loss in mudflat but a gain in saltmarsh. • Typhoons accounted for >30 % of the annual change in the sediment carbon pool. • Tidal creeks could be crucial in mediating sediment carbon pools in typhoon season. [ABSTRACT FROM AUTHOR]

Large wood (LW) can exert strong influence on sediment storage patterns in fluvial systems. However its specific impact on sediment routing is largely dependent on the stability of individual LW pieces or LW jams. We used sediment (dis)connectivity principles to quantify the impact of LW on sediment erosion and storage along a meandering river reach. Decadal spatiotemporal changes of LW and fluvial landforms are appraised along a 3.65 km long reach of the Odra River (Czechia). Detailed orthophotos at two-year intervals from 2012 to 2022 are analysed alongside field inventories. During this study period, there was a single flood event with a 5–10-year recurrence interval, and three smaller flow events with a recurrence interval of up to 2 years. We assessed the sediment deposition, bank protection, and erosion effects of LW, finding that the impact of LW on decelerating sediment fluxes was more pronounced. Specifically, LW-related deposition varied between 13.6 m2 and 36.7 m2 per 100 m of channel length during the individual two-year periods. In contrast, we detected only 0.5 m2 to 7.8 m2 per 100 m of channel length of newly eroded material during the same periods. Additionally, 6.3 % to 7.8 % of the lengths of the outer meander bends were protected by persistent LW elements against erosion during these two-year periods. Finally, we developed a three-stage conceptual model depicting the impact of LW on sediment (dis)connectivity in a meandering river at different relative timescales. Our model accounts for the dependence of interactions between LW and fluvial sediments based on the LW stability and frequency-magnitude of the hydrogeomorphic processes. In general, our observations suggest that the presence of stable LW in meandering rivers primarily leads to the deceleration of the lateral and longitudinal dimensions of sediment (dis)connectivity. • Large wood (LW) influences sediment routing in fluvial systems. • We quantified LW impact on sediment (dis)connectivity in a meandering reach. • The effect of LW on decelerating sediment fluxes dominated. • Three-stage model depicts the impact of LW on morphodynamics. [ABSTRACT FROM AUTHOR]

This research aims to distinguish genetic sedimentary processes building canyon geomorphological patterns and the factors driving different sedimentary activities in two nearby Mediterranean shelf-incised submarine canyons (Carchuna and Motril) that exhibit different degrees of incision on the narrow margin of the northern Alboran Sea. The straight Carchuna Canyon incises the shelf up to 200 m off the coastline and exhibit steep canyon walls featuring narrow terraces, muddy sands with high contents of organic matter along the thalweg, and transported shelf benthic foraminifera in distal settings. The Motril Canyon head is wider and incises the shelf edge, ca. 2 km off the coastline. It exhibits a sinuous morphology and less steep walls, wider terraces, and higher sedimentation rates with muddy sediments along the thalweg. In both canyons, cross-section relief, width, incision, and area decrease downslope, although these parameters increase locally. The downslope variations of geomorphological parameters are attributed to enhanced erosional/depositional processes promoted by tectonically controlled abrupt changes of the axial channel orientation. The degree of shelf incision, the location of the canyon heads in relation with the local sediment sources, and the seasonally variable hydrodynamic regimes determine the different degrees of recent canyon activity. The Motril Canyon is interpreted as a mature system that reflects episodic activity, collecting fine-grained sediments from the nearby Guadalfeo River. The Carchuna Canyon exhibits a youthful developmental stage whose activity is more continuous and involves sediment trapping of littoral cells and continuous downslope sand transport. • Sedimentary processes in canyons are imprinted in their submarine morphology. • The degree of canyon shelf incision determines the amount of sediment capture. • The passive Motril Canyon accumulates sediments supplied by the Guadalfeo River. • Carchuna Canyon is an active system whose canyon head traps littoral cell sediments. • Oceanographic conditions influence the canyon heads as sediment traps or conduits. [ABSTRACT FROM AUTHOR]

Large-scale landforms originated from jökulhlaups or glacial lake-outburst floods (GLOFs), and their small-scale components help in recognising the sedimentary environment of the flood. The GLOF fans that developed along the Pleistocene ice-sheet margin have not been investigated in detail, and north-eastern Poland, with its Megaflood Landform System and Bachanowo and Szeszupka fans, seems ideal for landform and sedimentary studies. This paper provides (1) an important opportunity to recognise the origins of glacier lake-outburst flood outlets and their evolution during two GLOFs and (2) a model of the origin of ice-marginal fans considering changes in sedimentary environment reflecting flood stages. During the first GLOF (GLOF1), the rising stage of meltwater burst triggered the formation of a supraglacial outlet and the development of the Szeszupka outburst fan. During the pulsed peak discharge, subglacial multi-channelised meltwater outburst caused the formation of the Bachanowo Gate, which was finally transformed at the flood waning stage. Such processes were associated with the widening of the floodwater subglacial routeway, when floodwater outlets rapidly spread across the glacier snout. In contrast, GLOF2 was responsible only for the Szeszupka fan erosion and development of outburst terraces. The small-scale bedforms continuum, recognised on the outburst fan surface, is associated with the development of streamlined erosional residuals, scours and their trains during the rising stage and peak discharge, while the waning stage and very end of flood conditions were favourable to the formation of pendant bars, distributive channels with erosional bars and chute bars, regardless of the feeding systems of the outburst fans. The fan deposits were OSL-dated and revealed either, likely, overly old ages or an age of 13.2 ± 0.9 ka. The latter age would imply the 'normal' meltwater outflow having a correlation with the events in the region. Nevertheless, this age might be considered a minimum age of the flood. • Supraglacial outlet developed first due to hydrofracturing during the rising GLOF stage. • The second outlet started to form at the peak discharge due to subglacial multi-channelized drainage. • The dominant processes in outburst fan formation are riverbed scouring and subsequent sediment deposition. • The small-scale bedform continuum evolved on outburst fan surface in relation to GLOF stages. • Outburst fan deposits were OSL-dated and revealed too old ages or an age of 13.2 ± 0.9 ka. [ABSTRACT FROM AUTHOR]

Submarine fans play a crucial role in understanding deep-sea sedimentary processes, establishing source-to-sink linkages, and identifying deep-water hydrocarbon reservoirs. Various types of submarine fans have been documented. Here we present findings on the Guangya submarine fan in the Southwest subbasin (SWSB) of the South China Sea (SCS), by analyzing multibeam bathymetric and two-dimensional multichannel seismic data. Bathymetric data reveal that the Guangya fan, covering an area of ~22,500 km2, comprises seven leveed channels, leading to a large composite lobe off the channel mouths. Different from typical submarine fans, the Guangya fan exhibits an elongated shape, extending longitudinally from the shelf edge through the slope to the abyssal plain, while laterally confined within a trough-like morphology in the southwestern tip of the SWSB and beyond. Lacking a typical feeding canyon, the fan appears to be self-fed by the leveed channels that serve as the primary depositional element. In contrast to the radial channel pattern in typical fans, the channels within the Guangya fan form a unique braid to dendritic pattern, genetically linked to channel merging and intersecting effects. Long wavelength and low wave height cyclic steps are identified, highlighting the occurrence of energetic supercritical turbidity currents. Seismic stratigraphic analysis shows that the Guangya fan primarily consists of high-amplitude reflections, indicating its coarser-grained or sandy turbidite-dominated nature. The fan has been evolved since the Pliocene, and mainly comprises depositional elements including channel fills, levees, lobes, and mass transport deposits. The specific tectonic context at the convergence of the conjugate margins, bounding the funnel-shaped SWSB, significantly influences the development of the Guangya fan. The Guangya fan could be originated from a shelf-edge staging area predominantly fed by the Mekong River during sea-level lowstands. • We report a unique elongated channelized submarine fan in the South China Sea. • The fan extends from the shelf edge to the abyssal plain. • The fan appears to be self-fed by dendritic submarine channels. • Tectonics plays a key role in the development of the fan. [ABSTRACT FROM AUTHOR]

Recently developed models of coastal barrier morphodynamics include marsh and lagoon processes that have been shown to impact barrier island evolution. To gain additional insights into the simulated barrier-backbarrier system dynamics, this study explores the parameter space of a barrier evolution model using global sensitivity analysis. Influential parameters, their interactions with one another, and regions of sensitivity within the parameter space were identified using Sobol indices and factor mapping techniques for model results through the end of the century. The results of this study highlight an important relationship between initial and critical barrier island geometries and suggest that narrow and low-relief barriers are most vulnerable to be eroded away (width drowning) or overtaken by sea level rise (height drowning), respectively. Width drowning was also strongly associated with other model input parameters such as toe depth, sea level rise rate, and backbarrier critical bed shear stress, which suggests that sub-centennial drowning is dependent on a unique combination of input parameter values and may be averted (or delayed) with a single input parameter change. Barrier dynamics were significantly influenced by the backbarrier marsh platform, which was more impacted by sediment transport parameters such as critical bed shear stress and ocean sediment concentration than maximum annual overwash flux. This suggests that inorganic sediment deposition through tidal inlet dispersion is much more significant to the backbarrier marsh and lagoon system than overwash over sub-centennial timescales and can help to reduce the risk of width drowning. • Initial and critical barrier geometries significantly influenced sub-centennial changes in barrier island evolution. • Narrow and low-relief barriers are most vulnerable to sub-centennial drowning. • Sub-centennial width drowning required a unique combination of multiple input parameters. • Inorganic sediment deposition influenced sub-centennial marsh and lagoon dynamics more than overwash. [ABSTRACT FROM AUTHOR]

Up to several meters thick fine-grained Holocene overbank deposits are ubiquitously found in most Western and Central European lowland floodplains. However, despite their large importance for the geomorphological and geoecological floodplain properties, the interplay of different possible causes for their formation are not well understood yet. Most authors suggest human-induced deforestation as the main precondition for sediment mobilization and transport from the slopes to the floodplain, whereas others suggest a stronger influence of climatic factors. This current research gap is caused by often missing well-resolved fluvial chronostratigraphies and spatio-temporal information about former human activity within the studied catchments. To fill this gap we exemplarily studied Holocene overbank sedimentation and possible human or natural drivers in the meso-scale Weiße Elster catchment in Central Germany. To do so, we applied numerical dating as well as sedimentological and micromorphological analyses to Holocene fluvial sediments along three floodplain transects. Furthermore, we built up an unprecedented systematic spatio-temporal database of former human activity within the catchment from the Neolithic until the Early Modern Ages. Together with published paleoclimatic data, this database allowed an unprecedented, systematic comparison of Holocene overbank sedimentation phases with possible external controls. Our data show that some overbank sedimentation phases were directly linked with human activities in the affected site sub-catchments, whereas others were not. Instead, all phases seemed to be linked with natural factors. This difference with most former studies could possibly be explained by previously often limited numerical dating of the fluvial sediments and by largely missing spatio-temporally well-resolved regional settlement records, hindering a precise temporal link of fluvial sedimentation with former human settlement. Furthermore, this difference could possibly also be explained by a relatively high natural sensitivity of the landscape dynamics in the Central German lowlands, showing a subcontinental climate, towards climatic external controls. [Display omitted] [ABSTRACT FROM AUTHOR]

Since the 1950s, Moenkopi Wash, in Arizona, United States, has been transformed from a relatively wide river with little riparian vegetation, to a narrow, heavily vegetated river that is less than half of its former width. We analyzed a ∼95-years-long instantaneous-discharge record, an extensive sediment-transport record, oblique and aerial photographs, historical channel surveys, and historical stage-discharge rating relations to determine the primary mechanisms responsible for this transformation. Frequent, large floods dominated the early part of the discharge record between 1926 and 1940. A dramatic ∼30 % decrease in annual mean discharge, and ∼27 % decrease in the mean of the partial-duration flood series occurred in 1941. This decline did not result in widespread channel change but provided an opportunity for vegetation to establish along the channel margins. Widespread channel narrowing began after a second decline in mean and peak discharge in 1956 at which time the channel banks became heavily vegetated. Between 1952 and 2019, the river channel narrowed by 57–59 %. Approximately 2–4 m of bed aggradation occurred at most study sites. As the channel narrowed and became more vegetated, large floods maintained the narrower channel width but did not cause rewidening. Suspended-sediment transport data illustrate the sediment trapping effects of vegetation that lead to channel narrowing; suspended-sand concentrations decline, thereby indicating sediment deposition, as vegetation becomes progressively inundated during floods. Furthermore, dense channel-margin and floodplain vegetation provide increased roughness, resulting in flood-peak attenuation and alteration of hydrograph shape. Vegetation expansion causes positive feedbacks whereby sediment deposition during floods is exacerbated by the roughness and sediment-trapping effects of vegetation leading to further narrowing. These positive feedbacks have reduced sediment delivery to the Little Colorado River downstream. Channel widening is not likely to occur unless there are very large floods that exceed the erosional threshold of the channel-margin vegetation, or unless large-scale vegetation removal efforts are undertaken. • Vegetation plays a stronger role than hydrology alone in causing channel change. • Channel change was caused by biogeomorphic feedbacks associated with vegetation. • Channel narrowing began as vegetation trapped sediment during a low flow period. • Biogeomorphic feedbacks caused flood attenuation and reduced flood-peak discharge. • Biogeomorphic feedbacks reduced sediment delivery to downstream rivers. [ABSTRACT FROM AUTHOR]

Documenting and interpreting channel responses to catastrophic floods help understanding how rapid fluvial metamorphosis can propagate in a catchment under sediment cascading effects. The recent example of the October 2020 Storm Alex in SE France (∼500 mm of rain in 24 h) provides a unique opportunity to investigate major geomorphic responses along 70 km of two confined alpine valleys (Vésubie and Roya) and to link them to sediment wave initiation and propagation. GIS-based analysis of remote sensing data (high-resolution ortho-imagery and airborne LiDAR data) acquired before and after the flood allowed combining channel changes with sediment erosion and deposition along a 35-km reach of the Vésubie, including the most impacted portions of the valley. In the Roya, the analysis was restricted to 2D morphological changes reconstructed with the sequence of ortho-imagery. Archives of aerial imagery were also used to integrate the storm impact in the historical trajectory of the rivers. The reconstruction of geomorphic responses shows a quasi-continuous fluvial metamorphosis along the investigated stream networks, with dramatic active channel widening and aggradation, having no antecedent analogs during the last 70 years in both valleys. The different glacial imprints between the two valleys are considered a key factor explaining the exacerbated channel response in the Vésubie, where a braided channel emerged along a 35-km river length. Many evidences strongly support that the fuelling effect of alluvial storage is a key element of the sediment cascade at the origin of the braided channel formation. This regional case study allows us to discuss the critical role of floodplain and terrace erosion in the formation of the post-flood braided channel, and to compare the geomorphic impact of the storm with similar reported cases in the literature. [ABSTRACT FROM AUTHOR]

Alluvial rivers in semi-arid and arid landscapes are prone to episodic geomorphic adjustments related to long-term sediment accumulation and occasional reworking by flash floods. However, few studies document the rates, patterns and processes leading to channel breakdown, particularly avulsion and floodout. These intrinsically driven adjustments may pose a risk to water resource availability through redistribution of water and sediment on the floodplain. To address this knowledge gap, channel change associated with avulsion and flooding in the last ∼30 years were quantified for Little Faulkenhagen Creek, a dryland river of the Murray-Darling Basin, Australia. The semi-arid, low gradient catchment promotes transmission losses, which with loss of valley confinement leads to channel adjustment and contraction to occur where water, sediment and energy are spread across the floodplain. Pronounced downstream changes occur in channel capacity (i.e., reductions in bankfull width, depth and area) and hydrology (i.e., reductions in bankfull discharge and stream power) as the river enters the floodout zone. Vegetation roughness increases in and around the floodout, where shrubs and river redgum trees line and encroach upon the channel. Mapping and analysis of hydro-geomorphological parameters using cross sections from 1991 to 2021 reveal recent changes in channel capacity, discharge and stream power. The upper reach has experienced substantial channel widening from erosion, while the lower reach leading into the floodout has contracted because of sediment deposition within the channel. Unchannelised floodwaters are deflected around a raised alluvial ridge and over the floodout eventually dropping into several migrating upstream knickpoints (head-cutting gullies) with retreat rates up to 32 m a−1. Therefore, both the existing channel slope (i.e., decline) and potential avulsion courses (i.e., increase) are affected by reduced energy and enhanced sedimentation. The net result of upstream in-channel sedimentation and aggradation on the floodout and downstream incision and gullying is that the floodout has migrated ∼1 km upstream and the river is at risk of a secondary avulsion as gullies retreat towards the main channel, potentially circumventing the floodout within ∼11 years. An erosion cell conceptual model is suitable for this system, where sediment from the local upstream production (erosion) zone is transferred downstream to a sink (deposition) zone. Erosion and deposition will fluctuate over the long-term, leading to periods with dominantly incisional or aggradational processes. Cycles of erosion and deposition will vary over time and external forces may influence a wholesale shift to a new fluvial state. Understanding the context and patterns of recent dryland river adjustments, as well as the dominant processes and their variability, can assist water and land management. [Display omitted] • Dryland river character and behaviour reflect a combination of external environmental controls and internal hydro-geomorphic processes. • Channel breakdown is a non-equilibrium river response to downstream declining discharge and stream power, where sediment deposition occurs. • Erosion and deposition cycles influence channel breakdown and reformation, as rivers adjust from channelised to unchannelised states. • Understanding the geomorphic complexity and variability of dryland rivers is critical for water, land, and ecosystem management. [ABSTRACT FROM AUTHOR]

Repeat multibeam bathymetric surveys conducted in 2004, 2005 and 2018 show that seven slope-confined canyons on the continental slope of the Pearl River Mouth Basin, South China Sea, were dominated by large volume, widespread erosion. Erosion volumes were up to 3.4 times greater than deposition volumes. Erosion-dominated areas of the canyons are up to 2.3 times greater than areas dominated by deposition. Average rates of erosion (ranging from 0.7 to 0.8 m/yr) were greater than average rates of deposition (ranging from 0.5 to 0.8 m/yr). In plan view, the erosion-dominated zones exhibit two characteristic shapes: (1) linear, found mainly in upper canyon reaches, distributed predominantly along canyon axes and at the base of eastern canyon walls, and; (2) blocky, found mainly in lower canyon reaches, widely distributed along the steep canyon walls and on lower-canyon interfluves. The deposition-dominated zones are scattered along canyon floors and walls. Seismic reflection data show lateral shifts of canyon fill deposits through time, indicative of longer-term eastward canyon migration. The linear erosion-dominated zones may be attributed to erosive turbidity currents triggered by energetic internal solitary waves shoaling on the shelf. The eastward canyon shifts were likely induced by rapid near-bed eastward currents generated mainly by westward propagating powerful internal solitary waves of depression. The widespread erosion in the deeper canyon areas and interfluves is likely a consequence of slope instabilities associated with the presence of gas hydrates. This study indicates that active sedimentary processes can occur in slope-confined canyons even during sea level highstands. Local, site-specific oceanographic and geological features (e.g., internal solitary waves, gas hydrates) can significantly increase sedimentary activity in and around submarine canyons. • Seven slope-confined canyons in the northern South China Sea were dominated by erosion, 2004–2018 • Ratios of erosion-dominated to deposition-dominated area in the canyons ranged from 1 to 2.3 • Ratios of eroded to deposited sediment volumes ranged from 1.2 to 3.4 • In the upper canyon reaches, internal solitary waves resulted in the triggering of turbidity currents. • In the lower reaches, gas hydrate activity likely caused submarine slope instabilities. [ABSTRACT FROM AUTHOR]

The geomorphological disposition of (para/peri) glacial landforms, elemental geochemistry, and optical chronology of the relict lake sediment in the Southern Zanskar ranges, northwest Himalaya are used to understand the relationship between glacial dynamics and the lake sedimentation during the mid-Holocene climate variability. Following the Last Glacial Maxima (LGM), pulsating deposition of outwash gravels until the early Holocene overwhelmed the Zanskar valley. The obstruction of Tsarap Chu (chu = river) by alluvial fans during the mid-Holocene led to the development of Padum Lake. In the present study, cirque glacier moraines representing three minor glacial advances were mapped along with sedimentological details and dated using Optically Stimulated Luminescence (OSL) dating technique. The oldest cirque glacier advance - Padum Cirque moraine-3 (PDCm-3) is dated to 11.4 ± 0.9 ka. The succeeding advance (PDCm-2) is dated to 5.3 ± 0.6 and 4.8 ± 0.8 ka whereas, the younger cirque glacier advance (PDCm-1) remains undated. The mid to late Holocene climate variability inferred using major and trace element geochemistry of the relict Padum lake sediments supported by optical chronology indicates six centennial to millennial-scale climatic phases. The prominent warmer phases are represented by decreased mineralogical fine grain flux (low K/Ti, Fe/Si, and Al/Si) with a corresponding increased coarse grain flux (higher Ti/Al and Sr/Al ratios). These phases are dated between 5.9 and 5.5 ka (phase-I), 3.8 and 3.4 ka (phase-IV), and 2.8 and 2.5 ka (phase-VI). The increased mineralogical finer fraction (higher K/Ti, Fe/Si, and Al/Si) between 5.5 and 5.1 ka (phase-II) and 3.4 and 2.8 ka (phase-V) indicate reduced meltwater flux during cooler phases. The intervening phase-III (5.1–3.8 ka) is characterized by increased mineralogical coarse grain flux (decreasing K/Ti, Fe/Si, Al/Si) suggesting gradual warming. The oscillatory climate at millennial scale was further used to understand glacier dynamics. The PDCm-2 advance in the lake record corresponds to the first major cooling (5.5 and 5.1 ka; phase-II) and continued until ∼3.8 ka. Using geochemical data of lake record, a major recession is inferred after 3.8 ka that persisted until around 3.4 ka (phase-IV). Similarly, the undated younger cirque glacier advance (PDCm-1) is assigned to the second cooling event (3.4 and 2.8 ka; phase-V). Thereafter, the cirque glaciers receded, most likely under increasing dryness and fluctuating climate (2.8–2.5 ka, phase-VI). After ∼2.6 ka, the development of ice-wedge pseudomorphs indicates the onset of permafrost conditions that degraded after ∼2.5 ka implying an increase in air temperature. The lake sedimentation terminates with the deposition of multiple younger alluvial fan facies. The climate variability shows a close correspondence with regional climate records suggesting that marginal glacier advancements were triggered by enhanced moisture via atmospheric rivers and cooler winter temperatures. The study highlights the potential of relict lake sediment in association with para- and peri-glacial landforms to reconstruct the pattern of minor glacier responses to climate variability during the Holocene. [Display omitted] • Mid-Holocene glacier fluctuations inferred from relict glacial lake and landforms. • Cirque glaciers responded to minor climatic perturbations ∼12, 6, and 4 ka. • Glacier advances triggered by westerlies and atmospheric rivers. • Deglaciation pulsating in nature with major aggradation in the early Holocene. • Permafrost conditions deteriorated after ∼2.5 ka due to increased temperature. [ABSTRACT FROM AUTHOR]

Climbing dunes are a form of topographic barrier dunes that feature in the aeolian landforms on the Qinghai-Tibetan Plateau. Topography fundamentally influences the spatial distribution and morphological characteristics of climbing dunes by modifying the near-surface airflow and creating space for sediment deposition. Previous studies have considered several aspects of the influence of topography on aeolian landforms. However, morphological differences between climbing dunes in different geomorphic contexts and dynamic changes in the area have received little attention. Therefore, topographic measurements, near-surface flow field measurements, dune morphology analysis, and remote sensing image analysis were combined to explore relationships between dune morphology and topography. Topographic obstacles can accelerate the near-surface airflow, particularly with a 25–35° slope gradient, which is beneficial for sand transport and deposition. Suitable accommodation space (concave slope morphology) and abundant sediment comprise the primary factors that control the scale and morphological diversity of climbing dunes, which are also influenced by a variable wind direction. In general, the morphology of the climbing dunes becomes progressively more complicated from the bottom to the middle of the windward slope, and the sand ridge lines of the dunes are perpendicular to the prevailing wind direction. Based on the influence of climate and human activities, the total area of climbing dunes in this region has decreased over the past 30 years. Despite general evidence of enhanced human-induced desertification in semi-arid and sub-humid regions, warming has not led to the rapid expansion of climbing dunes in these arid locations. This research offers new insights into the relationship between the terrain and dune morphology, enriching the theoretical basis for the plateau aeolian geomorphology. Furthermore, it allows us to consider the dynamic changes in climbing dunes area in the context of global warming. • Clarify the relationship between terrain, near-surface airflow and dune morphology • Sand sources and slope morphology are controlling the scale of climbing dune. • Analysis of the dynamic changes of climbing dune under climate warming [ABSTRACT FROM AUTHOR]

Despite studies showing that dams have significant effects on the sediment dynamics and evolution of a river upstream of a dam, the knowledge of relationships between river topography and sediment transport in a dam's backwater zone has hardly been applied in reservoir sedimentation management. This study investigated the potential of an alternating sequence of engineered topographic nozzles and oversized landforms, utilizing flow convergence routing theory, to redistribute sediment erosion foci in a dam's backwater zone for remote mountain reservoirs with a sediment storage capacity of ~105 m3. To test scientific ideas and engineering alternatives, the current topography of the backwater zone upstream from Our House Dam on the confined, mountainous Middle Yuba River, California, was virtually re-contoured into different scenarios for numerical experimentation. As most of the dam's backwater zone is filled with sediment (a common global problem) in a narrow, confined canyon, two-dimensional hydrodynamic modeling was useful for evaluating erosion patterns resulting from different manipulations. The results found that high velocity concentrates through nozzles and dissipates through oversized landforms, resulting in the latter exhibiting hydraulics indicative of functioning as sediment settling basins. These basins can be located away from the dam where key infrastructure needs clearance from sedimentation. As flow increases through the sequence of nozzles and oversized landforms, each nozzle's hydraulic jet will persist farther into the oversized area. Moderate in-channel flow (daily recurrence of ~5–30 %) was best for creating conditions to force deposition of sediment in oversized landforms. At high enough discharge (recurrence of <1–5 %) significant sediment erosion can occur throughout the constructed terrain in the backwater zone, so the whole topographic scheme can become overwhelmed and ineffective. Thus, the performance of re-contouring as an aid in reservoir sedimentation management is location and flow-dependent, necessitating careful design refinement for local conditions and assessment of financial benefits and costs. Overall, this study opens a new realm of sediment management for dam operators and regulators hard-pressed to know what to do when a moderate-sized mountain reservoir with poor accessibility has a sediment storage capacity of ~105 m3. [Display omitted] • Sediment in confined mountain reservoirs may be too remote, polluted, costly to excavate. • We propose to re-contour sediment in such reservoir for permanent in-situ storage. • Designing with flow convergence routing controls where future sediment deposits. [ABSTRACT FROM AUTHOR]

Anthropogeomorphic changes to channels and floodplains occurred in response to destructive agricultural practices following the arrival of European settlers into the Americas. The southeastern Piedmont physiographic region of the USA experienced severe erosion and sedimentation after settlement in the 1700s and farming up through the 1930s. In places, deep floodplain aggradation formed uninterrupted alluvial deposits that extend many kilometers. This research examines anthropogenic impacts of land-use change on valley bottom sedimentation in the Chicken Creek Watershed of South Carolina. Abrupt contacts between precolonial floodplain soils and a thick overburden of historical legacy sediment are common and well exposed throughout the two-km study reach and provide clear evidence of extensive postcolonial sedimentation. Soil stratigraphic and sedimentologic evidence are presented to identify and contrast pre- and postcolonial sediment characteristics and thicknesses. LiDAR-based spatial analysis is used to examine patterns of legacy sediment deposition and floodplain storage and—together with field observations of bank stratigraphy—examine the environments in which this occurred. Precolonial geomorphic stability is indicated by a buried soil epipedon (A b horizon) and other features on precolonial floodplain surfaces. Legacy sediment 2 to 4 m thick rests on top of exposed precolonial soils throughout the stream corridor, with the pre−/postcolonial contact ~1.5 m above the channel bed on average. Linear regression analysis shows that legacy sediment thickness varies statistically with changes in valley width and proximity to tributary sediment sources. Thin precolonial alluvium over bedrock suggests modest erosion and sedimentation rates prior to the arrival of EuroAmerican settlers. Mean grain-sizes are similar between the pre- and postcolonial alluvium, but substantial contrasts in the degree of stratification and bulk density document differences between the respective depositional environments and post-depositional changes to the two units. Channel adjustments since the time of maximum aggradation include bed incision to at least as low as the precolonial longitudinal profile and widening that is ongoing. Unlabelled Image • Precolonial environments inferred from floodplain stratigraphy and sedimentology. • Buried soil horizons indicate sedimentation history and fluvial stratigraphy. • Spatial patterns of historical alluvium are related to geomorphic variables. • Textures & bulk densities of pre-colonial and legacy sediment are compared. [ABSTRACT FROM AUTHOR]

Grassland ecosystems are some of the most modified ecosystems in the world, largely due to conversion to cropland, and the High Plains of the central United States is no exception. Playa wetlands are ubiquitous features of the High Plains and have experienced increased sediment accumulation, which is the primary cause of reduced playa ecosystem function. Seven playas on the High Plains of western Kansas, five with cropland-dominated watersheds and two with grassland-dominated watersheds, were examined to quantify the amount of recent (past ~100–175 yr) sediment accumulated within playas and to establish chronologies of playa filling. Thicknesses of recent sediment were determined in the field, and soil cores were extracted from study playas. Four playa cores were analyzed for 210Pb to establish the chronology of recent sediment accumulation and sedimentation rates. Chronologies of pre-agricultural sediments and sedimentation rates were calculated by 14C dating of buried soils preserved within playa cores. Radiocarbon ages indicate playa stratigraphic records span the Holocene and that these playas have persisted on the landscape since at least the Late Pleistocene. Long-term, natural sedimentation rates were highest during the Pleistocene-Holocene transition and early Holocene, at ~2–4 cm/century. During the middle and late Holocene, sedimentation rates averaged ~1 cm/century. Cropland playas accumulated ~10–15 cm of recent sediment at average rates of ~6.5–10 cm/century, while grassland playas accumulated only ~2 cm of recent sediment. Conversion of watersheds to cropland has greatly accelerated sediment accumulation within playas, which is generally resulting in a decline in critical playa ecosystem functions. • Long-term playa sedimentation rates ranged from ~1–4 cm/century throughout the Holocene. • Cropland playas accumulate sediment 2–10 times faster than long-term sedimentation rates. • Grassland playas accumulate sediment approximately equal to long-term sedimentation rates. • 210Pb chronologies indicate recent sediment thickness can reliably be determined visually. [ABSTRACT FROM AUTHOR]

Tropical fluvio-lacustrine depositional processes along the toe of the Paraguay fluvial megafan were investigated with a focus on Lake Uberaba (LU), the largest lake in the Pantanal wetlands. A limnogeological analysis of LU was conducted using remote sensing imagery, lake water chemistry, sedimentological and radiochemical data from lake floor samples and short cores. Echo-sounding revealed that LU is deepest (Z max = ~3.5 m) near its southern shoreline and outlet; the lake is hydrologically open throughout the year and is characterized by a dilute Ca+2-Na+-HCO 3 − chemistry. Key environmental controls on sedimentation in LU include inflowing transverse and axial rivers and water level changes, which influence the composition, mixing, accumulation, and the organization of facies. Structureless brown sandy silts with relatively low organic carbon (TOC mean = ~1.7 wt%) and low to moderate biogenic silica (BiSi mean = ~1.9 wt%) comprise most offshore lake floor sediments, whereas northern lake margin sediments consist of peaty silts and sandy silts whose origins are linked to inflowing Paraguay megafan distributary channels. Sediment core stratigraphy revealed that extant lacustrine deposits are underlain by oxidized clayey silts and sands, suggesting recent subaerial exposure of the basin floor. Sedimentary datasets conclusively suggest that LU is a shallow overfilled lake basin that is strongly influenced as a depositional system by its persistently open hydrology, shoreline channel density, and absence of margin coincident topography. This study provides new insights on lacustrine landform development in distal megafan settings, which is important for improving our understanding of fluvial landscapes. Unlabelled Image [ABSTRACT FROM AUTHOR]

Foredunes are defined as the first shore-parallel dune ridges adjacent to stable and prograding beaches, formed on the backshore by aeolian sand deposition influenced by vegetation. Foredunes have the important functions for mitigating impacts caused by extreme events, providing sediment to the beaches during storm and accumulating sediment again under fair weather wave conditions. Mainly for this reason, there is currently great interest in preserving, building or recovering foredunes. On a long-term timescale (decades), foredunes are recognized as exhibiting possible equilibrium conditions. The identification of this condition is of interest to projects involving the recovery and creation of foredune/beach systems. Therefore, the main objective of this work is to identify the morphometric characteristics of equilibrium foredunes and the interrelations between the morphometric parameters of height, width, volume and maximum slope (allometric relationships). To reach this objective, 193 foredune/subaerial beach profiles from along the northern coast of Spain that have characteristics close to equilibrium conditions were evaluated. The results indicate that foredune size can vary significantly; however, strong correlations between morphometric parameters have been verified and allometric relationships between foredune volume, height, width and maximum slope are proposed. • Foredunes along the northern Spain coast exhibit important variability in size. • Foredunes represent approximately 50% of the volume and width of the entire backshore. • Strong correlations between foredune morphometric parameters were verified. [ABSTRACT FROM AUTHOR]

Sediment transport pathways and resulting erosion-deposition patterns across beach-foredune systems can be complex. Although a great deal is known about the effects of wind fetch, surface moisture, topographic forcing, and vegetation cover, the role of large woody debris (LWD) as a control on sediment redistribution across beaches is relatively understudied. Pieces of LWD act as non-porous roughness elements that induce secondary flow circulation, thereby creating unique sedimentation patterns that differ markedly from those over a flat beach. Large accumulations of LWD collectively have a bulk porosity that provides substantial sand trapping volume, yet, no studies to date have quantified the effect of LWD on aeolian sand transport. Results from a field study on a macrotidal beach on Calvert Island, British Columbia, Canada, show that the LWD matrix alters the character of the turbulent boundary layer in a way that reduces sediment flux by 99%. Sand is trapped within the LWD matrix, thereby interrupting sediment delivery from the nearshore to the foredune. As such, LWD has the potential to modulate rates of foredune recovery, growth, and evolution. The relative importance of this effect depends on the density and arrangement of LWD as a fundamental control on aeolian sediment transport, as well as on the magnitude and frequency of events that erode the beach periodically and re-organize the LWD matrix. • Large woody debris can modulate sand transport and deposition on a beach-dune system. • A large woody debris matrix stopped 99% of sand from reaching the foredune. • Large woody debris matrix density affects how far sand can travel into the matrix. • The large woody debris traps sand in the backshore to be eroded before the foredune. [ABSTRACT FROM AUTHOR]

The flow dynamics within and immediately above an artificial plastic vegetation canopy are measured in the field and wind tunnel. Artificial plants created from wooden dowels and cable (zip) ties were arranged in a variety of arrays on pegboards where plant cover (or lateral cover) could be accurately controlled. Plant covers examined ranged from ~12% to 60%. Wind velocity profiles and the bedforms (incipient dunes) that developed within and beyond the vegetation in a few hours were measured. The results indicate that flow deceleration and drag increases within the canopy as plant density increases. In general, there is a marked reduction and inflection in velocity at the canopy top, and a second major inflection in the velocity profiles occurs immediately below the base of the four arrays equal or >23% density. Tall vegetation allows flow to sweep under the canopy and local high speed maxima flows may develop leading to minimal sedimentation in those canopies, but deposition downwind beyond the canopies. Short vegetation, where the leaves fill the canopy close to the ground, display significantly greater drag and rapid rates of sand deposition. Flow velocities above the canopy increase as plant cover or density increases due to flow compression and acceleration. Bedform development is strongly correlated with plant cover, density or lateral cover and short plants such that shorter length, higher bedforms develop in higher density and/or shorter plants. The relationship between plant cover, density or lateral cover and within canopy velocity is non-linear, and a new tentative flow regime is proposed, canopy flow, which may occur between wake interference flow and skimming flow. This study further confirms that plant density plays a defining role in determining bedform and dune morphology. The results also apply to flow in semi-arid grasslands. Development of velocity profiles downwind in high (50%) and low (12%) density plants. The profiles are shown for the upwind edge of vegetation (right side), and at 50 cm and 100 cm downwind. Unlabelled Image [ABSTRACT FROM AUTHOR]

The morphology and present-day sediment distribution of the Zambezi turbidite system was investigated using new bathymetric and sub-bottom profiler data as part of the PAMELA research project. The Zambezi turbidite system is composed of two depositional systems: a channelized fan (the Zambezi Fan) and a semi-confined fan (in the lntermediate Basin). The Zambezi Fan includes the Zambezi Valley, which is deeply incised in the Mozambique Channel and is more than three times as large and deep as the great Tanzanian and North Atlantic Mid-Ocean channels. The erosion in the Zambezi Valley is evidenced by its V-shaped morphology and the existence of a U-shaped thalweg affected by several generations of incisions. Based on echo facies and cores from literature, sediments of the Zambezi Fan are dominantly coarse-grained and fine-grained overbank deposits are infrequent. The distal portion of the Zambezi Fan is a main depositional area where typical transparent wedged-shape seismic bodies are interpreted as terminal lobes. Seismic facies in the Intermediate Basin are thought to represent mostly fine-grained turbidites intercalated with infrequent coarse-grained sheet-like turbidites. Hydrodynamic circulation (from surface eddies to the deep circulation of NADW) appears to have a great impact on the Mozambique Channel sedimentation and is suggested (1) to be involved in the delivery of the Zambezi River sediments along the Mozambique margin, (2) to entrain the upper suspended load of turbidity currents, contributing to the absence of fine-grained sedimentation and (3) to contribute to the erosion of the valley flanks leading to the exceptionally great dimensions of the valley. • The Zambezi turbidite system comprises a channelized fan and a semi-confined fan. • The Zambezi Valley has an atypical morphology compared to other turbidite systems. • Erosional processes dominate in the valley. • From echo facies, deposition appears mainly fine-grained in the semi-confined fan. • Oceanic and turbidity currents control sediment distribution and erosion. [ABSTRACT FROM AUTHOR]

Abstract As rivers approach base level, their water and sediment dynamics are affected by a transitional reach known as the backwater zone. At low flows, backwater zones cause flow deceleration and in-channel sedimentation, but at high flows, they cause flow acceleration and erosion. Over many floods, the dynamics of deposition and erosion in the backwater zone are thought to control the locations of avulsions on some large deltaic channels. However, in various studies, the role of the backwater is often inferred or modeled, and directly observed evidence of how backwater affects channel dynamics at avulsion sites remains scarce. In this study, we show how the backwater zone impacts the evolution and avulsion of the Qingshuigou channel, a recent lobe on the Yellow River Delta, using four decades (1976–2015) of data from systematic surveys of water discharge, sediment load, cross-sectional profiles and water surface elevation. The results show that the channel was commonly eroded during flood seasons and aggraded during nonflood seasons. Erosion rates generally decreased in the downstream direction along the lower channel reach during flood seasons, primarily due to downstream channel widening and the subsequent decrease in sediment transport capacity. The erosion rate reached zero at the cross-sections farthest downstream, which is contrary to expectations under hydrodynamic backwater effects, where drawdown causes erosion to increase downstream during high flows. During nonflood seasons, maximum sedimentation occurred upstream of the backwater zone, possibly due to impacts of local topography of meandering bends or constriction from dikes. Morphodynamic backwater accompanied by the deposition and gradual progradation of a mouth bar resulted in downstream increasing sedimentation, superelevation, and lateral migration rates along the lower channel reach from 1985 to 1996. The predicted avulsion location was near cross-sections Q6 or Q7 with an avulsion length of ~20–30 km upstream of the shoreline, which was consistent with those for historical avulsions. We emphasize the close interplay between backwater effects and channel geometry and argue that morphodynamic backwater may play a more important role than hydrodynamic backwater in setting up and triggering avulsions on the Yellow River Delta. Highlights • Backwater effects are strongly influenced by the downstream changes in channel geometry. • Erosion rate decreased downstream along the widening lower reach during high flows. • Sedimentation under morphodynamic backwater effects rendered the channel unstable. • The channel may be more impacted by morphodynamic than hydrodynamic backwater. [ABSTRACT FROM AUTHOR]

Abstract Oxbow lakes represent important geomorphic and depositional units of meandering river systems, whose rates of sediment accumulation may significantly exceed those of surrounding floodplains. Natural and artificial oxbow lakes may differ considerably, although both can offer unique sedimentary records of recent past events in river catchments. We provide an insight into the initial stages of oxbow lake evolution in terms of morphology, dynamics, sediment accumulation rates, sediment architecture and switching between sediment source areas. The study is based on a combination of geomorphic observations, multi-proxy stratigraphic analysis and geochemistry of sediment cores in four abandoned meanders of the Odra River, in the northeastern part of the Czech Republic. Two of the meanders were formed in non-regulated parts of the floodplain following a flood in 2010. In addition, two abandoned meanders formed by the artificial shortening of an upstream section of the Odra River were studied in order to compare processes in both sections. Several site-specific factors controlled the sedimentation patterns. In the naturally abandoned meanders, the initial stages of oxbow lake succession were characterised by extremely high sediment accumulation rates (up to 32 cm/yr), which caused the Stará Bělá abandoned meander to completely fill up over the course of several years. Relative to natural oxbow lakes, artificial lake successions revealed much slower sedimentation rates and higher levels of organic sedimentation and eutrophic conditions. The accumulation rates were influenced by both local (oxbow lake size, position and geometry) and catchment-wide factors (sediment yield). The annual occurrence of low-magnitude floods was an important factor in the natural reaches of the Odra River. The geochemical composition of sediments in naturally and anthropogenically formed abandoned meanders also differed due to the fact that the river tributaries drain two geologically contrasting areas, the Variscan Bohemian Massif and the Cretaceous-Cenozoic Outer Western Carpathians, respectively. Highlights • The initial stages of oxbow lake succession were characterised by extremely high sediment accumulation rates. • The initial stage was completed within four to seven years following cutoff. • The oxbow lakes evolution were influenced by both local site-specific and catchment-wide factors. [ABSTRACT FROM AUTHOR]

Abstract The late Quaternary deposits of the lakeshore plain and western edge of Lake Chalco in the southeastern Basin of Mexico were explored in order to understand the influence of alluvial sedimentation on archeological visibility and preservation, as well as to seek out records that would permit direct comparison of erosion and sedimentation with the demographic record derived from the archeological survey. The Chalco lakeshore plain is traversed by two of the largest rivers in the region, and the pattern of human settlement recorded here by archeological survey is partly an artifact of alluvial sedimentation, where the most prominent settlements were observed in areas with little or very slow sedimentation. Detailed radiocarbon dating of the alluvial deposits indicates that prior to the establishment of a sedentary lifestyle, alluvial sedimentation was slow. Catastrophic soil erosion is inferred from a period of widespread rapid alluviation and mass movements during late Preceramic, Early and Middle Formative periods, which were periods of rapid population growth. Mass movements appear to coincide also with periods of wetter climate. No evidence of sedimentation was noted during the population collapse that occurred at the end of the Formative. The next phase of alluvial sedimentation occurred during the Early Classic to Late Toltec periods, which were also periods of population expansion during a gradually drying climate. The Postclassic period, which was the largest Pre-Columbian demographic expansion, was paradoxically accompanied by minor evidence of alluvial activity. The last and most widespread period of alluvial activity occurs in the post-Conquest period and is difficult to date with precision but appears to occur primarily during the seventeenth and eighteenth centuries. Graphical abstract Unlabelled Image Highlights • Alluvial sedimentation obscures archeological site visibility in the Basin of Mexico Survey • Episodic river sedimentation was common during the Late Holocene • River sedimentation may provide exceptionally well preserved archeological sites and landscapes • This study reveals that the relationship between intensified erosion-sedimentation periods and demographic change is complex. [ABSTRACT FROM AUTHOR]

Abstract We examine medieval urban expansion of Moissac, a town located at the outlet of the Tarn River basin draining 15,400 km2 in southern France, in order to understand the association of Moissac's expansion to river position and sedimentation patterns in the river valley. A chronostratigraphic framework was derived from three auger holes and an archaeological excavation using radiocarbon dating and standard field and laboratory characterization of sediments. Five radiocarbon dates were obtained from one auger hole, along with particle size, magnetic susceptibility, organic matter, and quantitative soil color analyses to augment field descriptions. Results indicate Moissac spawned from the Abbey of Saint-Pierre on the apex of a small alluvial fan surrounded by backswamps ca. 850 CE, and urban growth radiated down the fan toward the river bottomlands throughout the following several centuries. At ca. 1000–1200 CE, human-induced soil erosion in the watershed caused very rapid aggradation of surrounding alluvial backswamps (at long-term average sedimentation rates of 20–30 mm/y). Such rapid bottomland accretion probably was driven by rampant agricultural soil erosion linked with wet climatic periods and enhanced flooding. This bottomland accretion enabled urban expansion and agricultural activities to cover the former backswamp and wetlands by the late Middle Ages (ca. 1300–1500 CE). Although we normally associate human-induced soil erosion with negative consequences of ecosystem services, the rapid bottomland accretion and resulting habitable and arable land can be viewed as a positive ecosystem service outcome resulting from human-induced soil erosion. [ABSTRACT FROM AUTHOR]

Abstract Spatial models are an effective tool for determining potential rockfall source, transit and deposit areas. The reliability of the final rockfall modelling results depends on the quality of the input data, which is mostly based on the digital elevation model (DEM). The spatial resolution of the DEM holds key information about the main morphological properties of the surface, which is crucially important when modelling this kind of geomorphological phenomenon. Therefore, this article studies the influence of DEM spatial resolution on the modelling of rockfall source, transit and deposit areas. Modelling was carried out at five different DEM spatial resolutions available for Slovenia (1 m, 5 m, 12.5 m, 25 m and 100 m). Rockfall source areas were identified using a geomorphometric approach based on a high resolution DEM and a geographical information system. Rockfall transit and deposit areas were modelled using the Conefall computer program, which is designed to estimate potential rockfall risk areas. The area of study was the municipality of Vipava (107.4 km2) in Slovenia, EU. A spatial resolution of 1 m was chosen as a reference layer to which all modelling results of the other spatial resolutions were compared. Validation of modelling included rockfall source area comparison with orthorectified aerial images and location collection of silent witnesses (rock deposits) in the field for estimating maximum runout zones. The modelling results indicate that a spatial resolution of 1 m is the most suitable for modelling on a local scale; resolutions of 5, 12.5 and 25 m can be used for modelling on a regional scale (depending on the purpose of the modelling results); and a resolution of 100 m should not be used for rockfall modelling. Major differences between spatial resolutions can be observed when modelling rockfall source areas, i.e. in areas with the most diverse topography, while in deposit areas the observed differences are smaller due to the less rugged surface. Highlights • The influence of the spatial resolution of the digital elevation model was observed at five different spatial resolutions. • Deviations between modelling results are greater for rockfall source areas than for rockfall runout zones. • High spatial resolutions (1 m) should be used for modelling on a local scale. • Lower spatial resolutions (5 m, 12.5 m and 25 m) can be used for modelling on a regional scale. • Spatial resolution 100 m should not be used for modelling rockfalls. [ABSTRACT FROM AUTHOR]

Abstract Research on karst in the Calabria region recognized three different hypogenic cave systems, all related to sulfidic thermal springs. Cave morphology, the depositional setting and isotopic characteristics of gypsum deposits reveal that the main process for cave formation was the oxidation of H 2 S to sulfuric acid. This process, known as sulfuric acid speleogenesis, was induced by thermal water rising towards the oxidizing zone in tectonic windows where dolomitic or limestone rocks outcrop. The δ34S values of most gypsum deposits prove they originated from sulfuric acid produced by H 2 S oxidation in the cave atmospheres. Most gypsum deposits in the Calabrian caves, in fact, exhibit δ34S values very similar to those of H 2 S, not to those of sulfate in the groundwater. On the contrary, the barite and part of the gypsum in the Terme Luigiane have δ34S values similar to those for sulfate in the water, implying that the sulfate minerals precipitated in a subaqueous environment. A large-scale deposition of replacement gypsum occurred only in the water table caves of Cassano, where subaerial corrosion greatly influenced cave morphology and the typical passage cross-sections. In the Terme Luigiane and Mount Sellaro cave systems, these subaerial processes caused only minor changes in inclined passages that had evolved mainly in subaqueous conditions. Highlights • Hypogene cave systems produced by sulfuric acid speleogenesis • Depositional setting and geochemical characteristics of sulfate deposits • Co-existence of subaerial and subaqueous gypsum inside the same cave • Relationship between thermal water hydrodynamic and morphology of the caves [ABSTRACT FROM AUTHOR]

Abstract The relief evolution of several areas of northeastern Brazil has been increasingly related to tectonic events. This is the case for the Paraíba Basin, where an abundance of faults and folds were recorded in Neogene and even Late Pleistocene-Holocene deposits. We tested whether dome-like morphologies in the northern sector of this basin, where geological exposures are scarce, were also formed by tectonic deformation. The work combined limited geological data with qualitative and quantitative analyses of the relief applying the 1 arc-second digital elevation model provided by the Shuttle Radar Topography Mission. The geomorphic indices of basin asymmetry factor (AF), swath topographic profiles, enhanced transverse hypsometry index (THi*) and normalized river long-profiles were used for validating a neotectonic origin for the dome-like morphologies. This interpretation was also supported by other morphological evidence of the dome relief, including: recurving channels featured in radial to recurved trellis patterns; tectonically-controlled drainage sub-basins; high relative relief values related to increased fluvial incision; and anomalous river long-profiles indicative of ungraded rivers. The domic structures were attributed to fault- and fold-related strike-slip deformation during the late Quaternary. This record supports the proposal that the South American passive margin remained under tectonic stress long after the main rifting in the late Jurassic-early Cretaceous. Highlights • DEM-based geomorphic indices suggest tectonically-molded landforms. • Dome-like reliefs of northern Paraíba Basin evidence compressive deformation. • Tectonic deformation is related to reactivation of late Quaternary strike slip faults. • Our data support late stage active neotectonics of South American passive margin. [ABSTRACT FROM AUTHOR]

Abstract Reservoir siltation surveys facilitate the quantification of the mean area-specific sediment yield (SSY) of catchments for decadal and longer time spans. This requires information on the volume (V S) and dry bulk density (dBD) of reservoir deposits, the period of time (T R) during which they were accumulated, the reservoir sediment trap efficiency (TE) and the catchment area (A). For the calculation of the catchment-wide average rate of erosion by water (E), the sediment delivery ratio (SDR) of the catchment needs to be estimated. Each step in this workflow represents a potential source of uncertainty. Here, we explore the extent to which individual error sources contribute to uncertainties in SSY and E values. Mean SSY and E values are inferred for small to medium-sized catchments (≤100 km2) of 15 small (≤350 × 103 m3) intermittently dry reservoirs located in the southern Kruger National Park and observation periods of 30 to 65 yr. Mean relative uncertainties of resulting SSY and E values amount to ±21% and ±46% at the 95% confidence level, respectively. Uncertainties in SSY values arise mainly from the TE estimation (mean fractional uncertainty contribution of 64%), while the SDR estimation is the major cause (79%) for uncertain E values. Uncertainties in the determination of V S and dBD values are rather unimportant, contributing together <30% and <6% to the uncertainty of SSY and E values on average, respectively. Conclusions are drawn regarding reasonable surveying and sampling strategies. Highlights • Reservoir siltation surveys (N = 15) are carried out in the Kruger National Park. • Mean sediment yield and erosion rates are quantified for the reservoir catchments. • The importance of various sources of uncertainty is analyzed. • Conclusions are drawn concerning opportune surveying and sampling strategies. [ABSTRACT FROM AUTHOR]

Abstract The extent to which deposition within river systems is driven by climate over glacial-interglacial timescales, and the nature of such linkages, is much debated. Answering such questions from the geological record is often limited by a lack of geochronological precision. Numerical modelling allows us to scale up what we know of climate response on short timescales to these longer timescales. To generate a robust reconstruction, relevant parameters need to be included in the model setup, and model output needs to be evaluated against the geological record. Here we introduce the model C leopatra (CybErosion-based Landscape Evolution On Periglacially Altered TeRrAin), the first reduced complexity model to include periglacial processes explicitly within a river catchment. We also use a pattern-oriented sampling approach to model evaluation and introduce innovative methods, particularly the quantification of the comparison of synthetic borehole data with geological sequences using Spearman rank correlation. Sediment starvation is observed within the model compared with the geological data, suggesting either the importance of sediment reworking within the catchment or that we have yet to specify the full complexity of periglacial processes in the model. In this sediment-starved situation, gelifluxion drives sediment supply but climate is less important in dictating the timing of aggradation and incision than intrinsic controls and elapsed time. [ABSTRACT FROM AUTHOR]

Abstract The movement of sediment from source to sink in a watershed is a complex process with multiple interactions and feedbacks across scales. At small scales, the size characteristics of a sediment mixture affect the transport of that sediment through hiding and through the nonlinear effect of sand content on gravel transport. At large scales, the channel network itself, through network geometry and the spatial pattern of transport capacity, adds additional complexity in organizing sediment moving through the system such that aggradational hotspots can emerge. The purpose of this paper is to present a Lagrangian framework for exploring complexities of mixed-size sediment transport in gravel-bedded river networks. The present model builds off of previous network-based, bed-material sediment transport models; but key advancements presented herein (i) allow for a mixture of sediment sizes in the river network, (ii) incorporate a mixed-size sediment transport equation, and (iii) utilize a daily flow hydrograph to drive intermittent transport. The model is applied to the roughly 4700 km2 Methow River Basin in Washington State, USA, using simplified model inputs with the goal of illustrating the utility of the model for motivating future work. Highlights • Model for mixed-size sediment transport in gravel-bedded river networks. • Illuminates complexities arising from sediment mixtures and river networks. • Illustrates the utility of the model to motivate future work. [ABSTRACT FROM AUTHOR]

Intertidal ecosystems are threatened by sea level rise and anthropogenic pressures. Understanding the processes controlling the morphodynamic developments of tidal flats is crucial for sustainable management of these systems. Analysis of three extensive fieldwork campaigns carried out on two adjacent mudflats fringing the Dutch Western Wadden Sea (from 2016 to 2018) provides important new insights into the conditions controlling a permanent increase of tidal flat elevation ('accretion'), in which the wind and consolidation processes play a pivotal role. Sediment temporarily settles ('deposition') on the flats during a period of high suspended sediment availability and water level setup (often following a storm). A tidal flat accretes when a new layer of sediment over-consolidates: a state in which the bed strength is much larger than it would attain during inundated conditions, due to high stresses experienced during prolonged drying. This happens when a phase of sediment deposition is followed by a sufficiently long period with a low ambient water table (phreatic level) and aerial exposure. The chronological order of sediment deposition and over-consolidation provides a window of opportunity for tidal flat accretion. Such a window of opportunity depends on the hydrodynamic forcing (tides, waves, wind), on the consolidation state of the bed, and on sediment availability. Wind plays a crucial role in creating the conditions for tidal flat accretion because the wind direction influences the duration of a low water table and aerial exposure and therefore (over-)consolidation rates, which we refer to as the 'winds of opportunity'. An abundance of sediment may even limit tidal flat accretion, because large deposition rates substantially increase consolidation timescales. [Display omitted] • The bed of intertidal areas becomes stronger through aerial exposure and low deposition rates. • Large sediment deposition rates do not always lead to net accretion because the deposited sediment remains easily erodible. • The wind-controlled chronology of sediment deposition and consolidation provides a window of opportunity for net accretion. [ABSTRACT FROM AUTHOR]

The integrated interpretation of high-resolution multibeam bathymetry, seismic profiles and backscatter data in the S. Eufemia Gulf (SEG; Calabro-Tyrrhenian continental margin, south-eastern Tyrrhenian Sea) documents the relationship between postglacial fault activity and morpho-sedimentary processes. Three systems of active normal faults that affect the seafloor or the shallow subsurface, have been identified: 1) the S. Eufemia fault system located on the continental shelf with fault planes mainly oriented N26E-N40E; 2) the offshore fault system that lies on the continental slope off Capo Suvero with fault planes mainly oriented N28E-N60E; 3) the Angitola Canyon fault system located on the seafloor adjacent to the canyon having fault planes oriented N60E-N85E. The faults produce a belt of linear escarpments with vertical displacement varying from a few decimeters to about 12 m. One of the most prominent active structures is the fault F1 with the highest fault length (about 9.5 km). Two main segments of this fault are identified: a segment characterised by seafloor deformation with metric slip affecting Holocene deposits; a segment characterised by folding of the seafloor. A combined tectono-stratigraphic model of an extensional fault propagation fold is proposed here to explain such different deformation. In addition to the seabed escarpments produced by fault deformation, in the SEG, a strong control of fault activity on recent sedimentary processes is clearly observed. For example, canyons and channels frequently change their course in response to their interaction with main tectonic structures. Moreover, the upper branch of the Angitola Canyon shows straight flanks determined by fault scarps. Tectonics also determined different sediment accumulation rates and types of sedimentation (e.g., the accumulation of hanging wall turbidite deposits and the development of contourite deposits around the Maida Ridge). Furthermore, the distribution of landslides is often connected to main fault scarps and fluids are locally confined in the hanging wall side of faults and can escape at the seabed, generating pockmarks aligned along their footwall. • Active faults are imaged by multibeam bathymetry and seismic profiles. • Three main systems of faults affect the continental shelf and slope sectors. • A tectono-stratigraphic model of an extensional fault propagation fold is proposed. • Tectonic activity exerts a strong control on seabed morphology and recent processes. • Margin shaping results from the interplay between tectonic and non-tectonic factors. [ABSTRACT FROM AUTHOR]

The western Peruvian region is prone to erosion and geomorphic change. Extreme precipitation events lead to rapid change in river channel and floodplain morphology due to bank erosion and debris flows delivering detrital material to the fluvial system. Monitoring geomorphic events and their associated topographic changes at high spatial and temporal resolutions remains a challenge. Here, we used an Uncrewed Aerial Vehicle - Post-Processing Kinematic - Structure from Motion (UAV-PPK-SfM) approach that includes co-registration of point clouds by using relative Ground Control Points (GCPs). This workflow adjusts each elevation model to a reference model using invariant features that did not change their position or form over time. We applied this technique to monitor landscape change (2019–2021) in an area of 0.3 km2 located in the Cañete River basin. Our results showed that a minimum observable elevation change of 0.56 m (95 % confidence interval) can be achieved using this workflow, beyond which an actual elevation change can be separated from systematic error. Using object-based classification techniques on the aerial images, we separated geomorphic dynamics from land cover changes. This allowed us to isolate the effect of geomorphic processes, and quantify rates related to gully erosion, river scouring, bank erosion, and sediment deposition. Within the study area, a hotspot of geomorphic change corresponded to an ephemeral tributary channel. The gully channel incising an alluvial fan is highly dynamic, showing bank erosion of 0.75 to 3.2 m and net export of 37 m3 of sediment in the 25-month study period. Given that the monitoring period did not include high intensity rainfall events, the study illustrates how geomorphic activity in ungauged Andean river basins, such as the Cañete valley, may be considerably underestimated in literature. [Display omitted] • Western Peruvian Andes is prone to rapid geomorphic change in ephemeral channels. • Hotspots of surface elevation change are detectable using UAV-PPK-SfM workflow. • Object-based classification techniques separate geomorphic dynamics from land cover changes. • Co-registration outperforms image co-alignment techniques in dynamic environments. • Specific sediment yields of about 9500 t km−2 yr−1 due to river undercutting and bank erosion in ephemeral channels. [ABSTRACT FROM AUTHOR]

Considerable interest has been directed toward the recognition and documentation of legacy sediment (i.e., anthropogenic sediment) in fluvial systems. Little has been written, however, to identify implicit or explicit theories about how these deposits form and evolve over decennial to centennial time scales. This review attempts to redress this void by examining conceptual models of the physical behavior and characteristics of catchment-scale anthropic fluvial sedimentation events. These concepts, which are not unique to anthropogenic sediment, include cascades, sediment delivery ratios, waves, aggradation-degradation episodes, residence times, budgets, connectivity, stream power, nonlinear dynamical systems, and geohistorical, geoarchaeological, and chronostratigraphic principles. A broad definition of legacy sediment as episodically produced anthropogenic sediment is adopted that includes early episodes of large-scale, human-induced sedimentation throughout the world. The models apply to a variety of environments, so the examples from North America following the introduction of European settlement can be related to other post-settlement sedimentation episodes elsewhere. During aggradation episodes, rates of erosion and sedimentation often increased an order of magnitude in response to land clearance for agriculture, timbering, or mining. These sediments may remain as a lasting geomorphic legacy that provides evidence of anthropogenic change and governs modern rates of sediment production and nonpoint source pollution. [ABSTRACT FROM AUTHOR]

Debris flows with long reaches are one of the major natural hazards to human life and property on alluvial fans, as shown by the debris flow that occurred in the Dongyuege (DYG) Gully in August 18, 2010, and caused 96 deaths. The travel distance and the runout distance of the DYG large-scale tragic debris flow were 11 km and 9 km, respectively. In particular, the runout distance over the low gradient channel (channel slope < 5°) upstream of the depositional fan apex reached up to 3.3 km. The build-up and maintenance of excess pore pressure in the debris-flow mass might have played a crucial role in the persistence and long runout of the bouldery viscous debris flow. Experiments to measure pore pressure and pore water escape have been carried out by reconstituting the debris flow bodies with the DYG debris flow deposit. The slurrying of the debris is governed by solid volumetric concentration (SVC), and the difference between the lower SVC limit and the upper SVC limit can be defined as debris flow index ( I d ). Peak value ( K p ) and rate of dissipation ( R ) of relative excess pore pressure are dependent on SVC. Further, the SVC that gives the lowest rate of dissipation is regarded as the optimum SVC ( C v o ). The dissipation response of excess pore pressure can be characterized by the R value under C v o at a given moment (i.e., 0.5 h, 1 h or 2 h later after peak time). The results reveal that a relatively high level of excess pore pressure developed within the DYG debris-flow mass and had a strong persistence capability. Further research shows that the development, peak value and dissipation of excess pore pressure in a mixture of sediment and water are related to the maximum grain size (MGS), gradation and mineralogy of clay-size particles of the sediment. The layer-lattice silicates in clay particles can be the typical clay minerals, including kaolinite, montmorillonite and illite, and also the unrepresentative clay minerals such as muscovite and chlorite. Moreover, small woody debris can also contribute to the slurrying of sediments and maintenance of debris flows in well vegetated mountainous areas and the boulders suspended in debris flows can elevate excess pore pressure and extend debris-flow mobility. The parameters, including I d , K p , R and etc., are affected by the intrinsic properties of debris. They, therefore, can reflect the slurrying susceptibility of sediments, and can also be applied to the research on the occurrence mechanisms and risk assessment of other debris flows. [ABSTRACT FROM AUTHOR]

Sediment deposition and storage are important functions of batture lands (the land between the channel's low-water elevation and the flood mitigation levee). However, sedimentation processes within these areas are not fully understood. In this paper, we explore the spatiotemporal patterns, rates, and volume of sedimentation within the batture lands along the middle Mississippi River (MMR; between the confluence of the Missouri and Ohio rivers) using three approaches: (1) comparison of historical to modern elevation data in order to estimate long-term (>100 yr) sedimentation rates; (2) estimation of medium- to short-term (<50 yr) sedimentation rates using dendrogeomorphological methods; and (3) geomorphic change detection (GCD) software to estimate short-term sedimentation rates (~12 yr), spatial patterns of deposition, and volumes of geomorphic change within the batture lands. Comparison of long- to short-term sedimentation rates suggests up to a 300% increase in batture land sedimentation rates (from 6.2 to 25.4 mm yr −1 ) despite a substantial decrease in the MMR's suspended-sediment load (>70%) attributed largely to sediment trapping by dams during the second half of the twentieth century. The increase in MMR batture land sedimentation rates are attributed to at least two potential mechanisms: (1) the above average frequency and duration of low-magnitude floods (>2-yr and ≤5-yr flood) during the short-term assessment periods which allowed for more suspended sediment to be deposited within the batture lands; and (2) the construction of levees that substantially reduced the floodplain area (~75%) available for storage of overbank deposits increasing the vertical accumulation and consequently the detectability of a given volume of sediment. The GCD estimated batture land sediment volumes were ~9.0% of the suspended load at St. Louis. This substantial storage of sediment (~8.5 Mt yr −1 ) along the MMR suggests batture lands are an important sink for suspended sediments. [ABSTRACT FROM AUTHOR]

Using a combination of airborne LiDAR (2005) and terrestrial laser scanning (2007, 2008, 2010, 2011), sediment delivery processes and sediment connectivity in an ~ 20-ha gully complex, which significantly contributes to the Waipaoa sediment cascade, are quantified over a 6-year period. The acquisition of terrain data from high-resolution surveys of the whole gully-fan system provides new insights into slope processes and slope-channel linkages operating in the complex. Raw terrain data from the airborne and ground-based laser scans were converted into raster DEMs with a vertical accuracy between surveys of <±0.1 m. Grid elevations in each successive DEM were subtracted from the previous DEM to provide models of change across the gully and fan complex. In these models deposition equates to positive and erosion to negative vertical change. Debris flows, slumping, and erosion by surface runoff (gullying in the conventional sense) generated on average 95,232 m 3 of sediment annually, with a standard deviation of ± 20,806 m 3 . The volumes of debris eroded from those areas dominated by surface erosion processes were higher than in areas dominated by landslide processes. Over the six-year study period, sediment delivery from the source zones to the fan was a factor of 1.4 times larger than the volume of debris exported from the fan into Te Weraroa Stream. The average annual volume of sediment exported to Te Weraroa Stream varies widely from 23,195 to 102,796 m 3 . Fluctuations in the volume of stored sediment within the fan, rather than external forcing by rainstorms or earthquakes, account for this annual variation. No large rainfall events occurred during the monitoring period; therefore, sediment volumes and transfer processes captured by this study are representative of the background conditions that operate in this geomorphic system. [ABSTRACT FROM AUTHOR]

The dramatic changes that occurred to the post-glacial landscape in the headwaters of the Waipaoa River basin are a consequence of perturbations about the equilibrium that exists between the rate of tectonic uplift and fluvial incision. At times when the amount of coarse sediment delivered to channels exceeds the capacity of streams to remove it, the channel bed rises at the rate of tectonic uplift. Once bedload overcapacity is replaced by undercapacity and the alluvial cover is depleted, streams reestablish contact with bedrock and recuperate the time lost to fluvial incision. The first major perturbation occurred during the final phase of the last glaciation (ca. 33–17.5 cal. ka), when aggradation was driven by a climate-forced variation in the relative supplies of sediment and water. We suggest that the subsequent transformation of channels in the headwaters of the Waipaoa River basin, from alluvial to bedrock, occurred as the atmospheric and oceanic circulation converged on their contemporary patterns ca. 12 cal. ka. A second major perturbation that continues to the present began ca. 1910–1912 CE, when a massive increase in sediment load was accompanied by a modest increase in water discharge after the native vegetation cover in the headwaters was replaced by pasture. The processes of terrace creation and incision are inherently unsteady, and in five interim cases incision was arrested by a transient increase in the thickness of the alluvial cover that was a response to climatic forcing. Events that disrupted the native vegetation cover in the headwaters also modulated patterns of sediment dispersal and accumulation in other parts of the fluvial system and caused rapid, storm-driven infilling of the Poverty Bay Flats. Tectonic subsidence dictates the course of the Waipaoa River across Poverty Bay Flats which, because the modern rate of floodplain construction by vertical accretion is rapid relative to the amount of destruction by lateral channel migration, has remained virtually unchanged for the past 100 years. During this time the channel assumed a narrower, deeper form that is in equilibrium with the contemporary supply of sediment and hydraulic regime. [ABSTRACT FROM AUTHOR]

Long-term fluvial incision processes and corresponding geomorphic evolution are difficult to quantify, especially in complex systems affected by lithological and tectonic factors. Volcanic landscapes offer the most appropriate environment for the study of landscape evolution, as there is a clear starting time of formation and the lithology is homogenous. In the present study we aim to: (1) analyse the interplay of construction and incision processes throughout eruptive activity; (2) study fluvial erosion processes; (3) analyse sedimentary and volcanic lithological responses to channel erosion; and (4) calculate the incision rates in young basaltic bedrock. We have integrated existing and new 40 Ar/ 39 Ar ages of lava flows with estimates of channel geometry and tectonic activity, and considered process geomorphology concepts, to fully understand evolution of a bedrock channel incised at the boundary between basalts and sedimentary rocks with coeval active volcanic processes forcing drainage evolution. Our findings indicate that the Sa'ar basin evolution is controlled by: (1) rock strength of the mixed lithology; (2) alternating cycles of volcanic activity followed by erosion and incision; and (3) the Plio-Pleistocene uplift of Mt. Hermon. The carbonate slopes composing the southern flank of Mt. Hermon are moderate (18–26%) while the basalt slopes deriving from the Golan Heights are much steeper (26–51%). The highly erodible sedimentary rocks at Mt. Hermon's piedmont accelerated river incision, shaping a 650 m wide by 100 m deep canyon. Inside the canyon, the steep channel slope (8.6%) enables downstream movement of large boulders, including autochthonous mega-blocks (D 90 size > 2.5 m); 24 knickpoints were identified using DS plots, developed within a knick zone over a distance of 6 km. The brittle and porous structure of the rubbly and blocky interflow layers (clinkers), interbedded between two massive basalt flows, enhances erosion and accelerates scouring of the plunge-pool bottom and walls. Three volcanic phases shaped the Sa'ar basin: (1) The 3.25 Ma Cover Basalt flowed over large areas of the Levant and reached up to the northern Golan; (2) Dalwe Basalt was emplaced between ~ 1.2 Ma and ~ 750 ka, from vents including Mt. Qatzaa and Mt. Odem, and extended to Mt. Hermon covering sedimentary cuestas; (3) Ein Zivan Basalt (including the Sa'ar Lava Flow – the youngest basalt flow known in Israel) erupted before ~ 110–120 ka and quickly accumulated at least three distinct flows into the deeply incised Paleo-Sa'ar canyon, refilling the canyon to a height of ~ 50 m. Rates of incision are consistent with other rivers draining the Golan Heights. The total incision rate of the Sa'ar channel during the last 760 ka is at least 19.7 cm/ka. Over the past 100 ka, the incision rate was 22–30 cm/ka and the back-erosion of the Sa'ar highest knickpoint occurred at 68 cm/ka. Our findings reflect the latest evolution history of a special, mixed lithology channel, developed at the border of a large basaltic province, in an active tectonic environment. The results suggest that fluvial adjustment of basalt-limestone rivers is determined first by the interplay of construction and incision processes throughout alternating cycles of volcanic activity and quiescence. The lithology is an extremely important factor determining the type and rate of erosion. While the tectonic factor might determine the basin relief and slope, the lithological factor accelerates erosion and river incision. [ABSTRACT FROM AUTHOR]

There is a notable discrepancy between detailed sediment budget studies in small headwater catchments (< 10 2 km 2 ) focusing on the identification of sedimentary landforms in the field (e.g. talus cones, moraine deposits, fans) and large scale studies (> 10 3 km 2 ) in higher order catchments applying modeling and/or remote sensing based approaches for major sediment storage delineation. To bridge the gap between these scales, we compiled an inventory of sediment and bedrock coverage from field mapping, remote sensing analysis and published data for five key sites in the Upper Rhone Basin (Val d'Illiez, Val de la Liène, Turtmanntal, Lötschental, Goms; 360.3 km 2 , equivalent to 6.7% of the Upper Rhone Basin). This inventory was used as training and testing data for the classification of sediment and bedrock cover. From a digital elevation model (2 × 2 m ground resolution) and Landsat imagery we derived 22 parameters characterizing local morphometry, topography and position, contributing area, and climatic and biotic factors on different spatial scales, which were used as inputs for different statistical models (logistic regression, principal component logistic regression, generalized additive model). Best prediction results with an excellent performance (mean AUROC: 0.8721 ± 0.0012) and both a high spatial and non-spatial transferability were achieved applying a generalized additive model. Since the model has a high thematic consistency, the independent input variables chosen based on their geomorphic relevance are suitable to model the spatial distribution of sediment. Our high-resolution classification shows that 53.5 ± 21.7% of the Upper Rhone Basin are covered with sediment. These are by no means evenly distributed: small headwaters (< 5 km 2 ) feature a very strong variability in sediment coverage, with watersheds drowning in sediments juxtaposed to watersheds devoid of sediment cover. In contrast, larger watersheds predominantly show a bimodal distribution, with highest densities for bedrock (30–40%) being consistently lower than for sediment cover (60–65%). Earlier studies quantifying sedimentary cover and volume focus on the broad glacially overdeepened Rhone Valley that accounts for c. 9% of our study area. While our data support its importance, we conservatively estimate that the remaining 90% of sediment cover, mainly located outside trunk valleys, account for a volume of 2.6–13 km 3 , i.e. 2–16% of the estimated sediment volume stored in the Rhone Valley between Brig and Lake Geneva. Furthermore, our data reveal increased relative sediment cover in areas deglaciated since the Little Ice Age, as compared to headwater regions without this recent glacial imprint. We therefore conclude that sediment storage in low-order valleys, often neglected in large scale studies, constitutes a significant component of large scale sediment budgets that needs to be better included into future analysis. [ABSTRACT FROM AUTHOR]

The Manawatu incised-valley estuary was rapidly infilled between 12,000–4700 cal. yr BP. A combination of empirical measurements of sedimentation rates, a reconstruction of relative sea-level (RSL) change, and digital elevation models of key surfaces within the Holocene sedimentary fill of the valley were integrated to produce a numerical model to investigate the influence of the system controls of sea-level change, sediment flux, and accommodation space on the rapid infilling history of the palaeo-estuary. The numerical model indicates that sediment flux into the palaeo-estuary was greatest during the Holocene marine transgression between 12,000–8000 years BP. The average rate of sediment deposition in the estuary during this period was ~ 1.0 M m 3 yr − 1 . This rapid rate of sedimentation was controlled by the rate of accommodation space creation, as regulated by the rate of sea-level rise and the antecedent configuration of the valley. By the time sea levels stabilised c. 7500 cal. yr BP, the palaeo-estuary had been substantively infilled. Limited accommodation space resulted in rapid infilling of the central basin, though sediment flux into the estuary between 7100 and 4500 cal. yr BP was at a lower rate of 234,000 m 3 yr − 1 . The limited accommodation space also influenced hydrodynamic conditions in the estuarine central basin, driving export of fine-grained sediment from the estuary. Once the accommodation space of the estuarine basin was infilled sediment bypassed the system, with a consequent reduction in the sedimentation rate in the valley. More accurate partitioning of the sources of sediment driving the infilling is necessary to quantify sediment bypassing. Post-depositional lowering of RSL index points from the valley is driven by neotectonics and sediment compaction. [ABSTRACT FROM AUTHOR]